EP0885980A2 - Process for forming a superficial layer having a high hardness by plasma-free thermochemical treatment - Google Patents

Process for forming a superficial layer having a high hardness by plasma-free thermochemical treatment Download PDF

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Publication number
EP0885980A2
EP0885980A2 EP98401235A EP98401235A EP0885980A2 EP 0885980 A2 EP0885980 A2 EP 0885980A2 EP 98401235 A EP98401235 A EP 98401235A EP 98401235 A EP98401235 A EP 98401235A EP 0885980 A2 EP0885980 A2 EP 0885980A2
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EP
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Prior art keywords
treatment
parts
gas
nitrogen
temperature
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EP98401235A
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German (de)
French (fr)
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EP0885980A3 (en
EP0885980B1 (en
Inventor
Patrick Jacquot
Sylvain Foissey
Gérard Veyssiere
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Bodycote SAS
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Innovatique SA
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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/20—Carburising
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C8/00—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals
    • C23C8/06—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases
    • C23C8/08—Solid state diffusion of only non-metal elements into metallic material surfaces; Chemical surface treatment of metallic material by reaction of the surface with a reactive gas, leaving reaction products of surface material in the coating, e.g. conversion coatings, passivation of metals using gases only one element being applied
    • C23C8/24—Nitriding

Definitions

  • the present invention relates to a method for forming, by processing thermochemical without plasma, a surface layer having a hardness high and with tribological properties, on alloy parts sensitive or reactive towards nitrogen, carbon and / or oxygen.
  • a titanium-based alloy or zirconium in an atmosphere which may include ammonia, a hydrocarbon and / or an oxidizing gas or even a gaseous composition including one or more of these compounds.
  • thermochemical treatments of this kind In general, we know that there are currently various techniques thermochemical treatments of this kind.
  • the oldest, namely the salt bath tends to disappear from the fact that it is particularly polluting and dangerous due to the release of toxic gases and rinsing water it generates.
  • ion bombardment treatments involve a relative vacuum heat treatment installation specially equipped with so as to generate a luminescent discharge on the parts to be treated in a process gas atmosphere.
  • This technique has the disadvantage of being relatively expensive and not suitable for complex shaped parts and, in particular, tubular in shape due to the hollow cathode.
  • thermochemical treatments carried out under a gaseous atmosphere at atmospheric pressure such as gaseous nitriding, consist of carrying the parts at a temperature of the order of 500 ° C to 600 ° C and to sweep them with a gas nitriding such as ammonia.
  • This treatment has the disadvantage of being long, to consume large amounts of process gas and therefore to be relatively polluting.
  • This process which provides excellent results for the treatment of steel and steel alloys has the disadvantage of using a relatively expensive process gas composition and installation sophisticated to ensure uniform scanning of the parts to be treated by gases treatment.
  • Another disadvantage of this process lies in the fact that in temperature and pressure conditions suitable for processing steel it does not work on titanium or zirconium alloys.
  • the catalyst used is incompatible with the treatment of titanium and zirconium alloys because it would form a diffusion barrier to nitrogen (layer of Ti or Zr oxide)
  • the object of the invention is a method for treating this type of alloy.
  • a treatment method consisting in bringing the pieces to treat at a temperature above 500 ° C inside an enclosure whose the atmosphere is maintained at a pressure less than or equal to 0.1 mbar, at inject a treatment gas comprising ammonia and / or a hydrocarbon and / or an oxidizing gas, the pressure inside the enclosure then establishing itself at a value below atmospheric pressure, but greater than 100 bar for a period which can range from a few tens minutes to more than 24 hours, depending on the depth of treatment desired.
  • This treatment makes it possible both to improve the mechanical characteristics of the parts treated, in particular as regards resistance to friction and surface hardness, and to give them a pale yellow more or less shiny appearance, particularly aesthetic.
  • This aspect is a function of the initial surface state and the stoichiometry of the Ti x N y layer.
  • this processing is a diffusion processing: it therefore does not generate significant modification of the initial roughness of the parts and it eliminates any risk of separation of the titanium nitride layer.
  • Another advantage of this process is that the fact that it operates at low pressure (always lower than atmospheric pressure) it consumes only very little treatment gas and is therefore not polluting in relation to the processes high pressure which require the use of specific ovens and constraints of safety due to high pressure.
  • the process according to the invention may also include a post-processing phase intended to dehydrogenate the treated alloy.
  • This dehydrogenation treatment can be carried out by bringing the parts to a temperature of the order of 700 to 900 ° C. for a period which can range from 1 to 5 hours, in a vacuum of 10 -3 to 10 -4 mbar.
  • a titanium alloy of the TH6V type, dehydrogenated at 790 ° C. for 2 hours, under vacuum of 5 10 -4 mbar will see its hydrogen content drop from 256 to 11 ppm.
  • the treatment installation used involved a vacuum treatment of conventional structure equipped with a turbine circulation of process gases.
  • This oven includes a sealed enclosure containing a muffle made of a material (metal or graphite) which cannot retain polluting elements (in particular oxygen or water vapor) likely to affect the quality of treatment.
  • a muffle made of a material (metal or graphite) which cannot retain polluting elements (in particular oxygen or water vapor) likely to affect the quality of treatment.
  • electrical heating resistors mainly by radiation and convection
  • This enclosure is connected on the one hand to pumping equipment capable of achieve a primary vacuum P ⁇ 0.1 mbar and, on the other hand, two gas sources (one nitrogen source and ammonia source) through a distribution.
  • the parts to be treated (here prostheses made of alloy titanium TA6V) were placed in the muffle, preferably on a mounting titanium alloy having previously undergone the same treatment.
  • the rooms On this assembly the rooms have been arranged so as to be spaced from each other by a few millimeters so that the diffusion is the most homogeneous possible on their surface.
  • the temperature of the nitrogen convection oven (injected from the nitrogen source) and / or by radiation (resistances) until a temperature level between 500 ° C and 900 ° C, here of the order of 900 ° C.
  • Temperature maintenance at this level was continued for a sufficient period of time to ensure the homogeneity of the room temperature.
  • a primary vacuum was then applied to the enclosure to ensure elimination of the nitrogen previously injected and then at the start of the diffusion thanks to an ammonia injection at a pressure P between 100 and 900 mbar, here 300 mbar, the temperature being above 500 ° C.
  • This dissemination phase was continued for approximately 7 hours so as to obtain a diffusion layer of approximately 0.040 mm in average thickness.
  • the treated parts exhibited on the extreme surface a compact and homogeneous yellow layer of titanium nitride Ti x N y with a thickness of the order of 4 ⁇ m and very high hardness (> 1000 HV), and therefore very good resistance to friction. and excellent wear resistance.
  • the diffusion layer (a few hundredths of a millimeter thick and hardness> 400 HV) was then likely to improve the resistance to fatigue (the hardness at the core being 339 HV)
  • An important advantage of this process is that it provides a very good homogeneity of the treatment even in the case of shaped parts and complex geometries including hollow shapes.
  • the treatment extends to the contact areas of the parts on their support.
  • the treatment gas could be other than ammonia and could for example consist of a hydrocarbon-based atmosphere (C 2 H 2 , C 3 H 8 , CH 4 ....) in order to cement superficially these alloys.
  • a surface layer of metallic gray color of great hardness and having increased tribological properties, is obtained.
  • the treatment atmosphere could include an oxidizing gas such as oxygen so as to obtain a surface layer (Ti0, Ti0 2 , Ti 2 0 3 , Zr0 2 ..) having various colors (blue, green, purple ) and great hardness.
  • an oxidizing gas such as oxygen so as to obtain a surface layer (Ti0, Ti0 2 , Ti 2 0 3 , Zr0 2 ..) having various colors (blue, green, purple ) and great hardness.
  • This layer of Ti x O y oxide is compact and homogeneous over the entire surface of the part.
  • the colors that we obtain are brilliant and very varied. It considerably improves the friction resistance of the parts.
  • the appearance of the parts is a function of the initial surface condition and the stoichiometry of the layer of Ti x O y .
  • the treatment atmosphere could also consist of a combination of NH 3 + CH 4 so as to obtain a surface layer of carbonitrides TiC x N y or Zr CN of pink or butter color.

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Mechanical Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Solid-Phase Diffusion Into Metallic Material Surfaces (AREA)
  • Carbon And Carbon Compounds (AREA)

Abstract

A hard surface layer is formed on a piece of alloy which is reactive with nitrogen, oxygen or carbon, such as titanium or zirconium, by heating the piece to over 650 degrees C in an enclosure where the pressure is no more than 0.1 mbar, then injecting a suitable reactive gas but still maintaining a pressure below atmospheric for a period between a few tens of minutes and 24 hours or more, depending on the layer thickness required.

Description

La présente invention concerne un procédé pour la formation, par un traitement thermochimique sans plasma, d'une couche superficielle présentant une dureté élevée et possédant des propriétés tribologiques, sur des pièces en alliages sensibles ou réactifs vis à vis de l'azote, du carbone et/ou de l'oxygène.The present invention relates to a method for forming, by processing thermochemical without plasma, a surface layer having a hardness high and with tribological properties, on alloy parts sensitive or reactive towards nitrogen, carbon and / or oxygen.

Elle s'applique notamment mais non exclusivement à un traitement sous atmosphère contrôlée à haute température, d'un alliage à base de titane ou de zirconium dans une atmosphère pouvant inclure de l'ammoniaque, un hydrocarbure et/ou un gaz oxydant voire même une composition gazeuse incluant un ou plusieurs de ces composés.It applies in particular but not exclusively to treatment under controlled atmosphere at high temperature, of a titanium-based alloy or zirconium in an atmosphere which may include ammonia, a hydrocarbon and / or an oxidizing gas or even a gaseous composition including one or more of these compounds.

D'une manière générale on sait qu'il existe à l'heure actuelle diverses techniques de traitements thermochimiques de ce genre.In general, we know that there are currently various techniques thermochemical treatments of this kind.

La plus ancienne, à savoir le bain de sel tend à disparaítre du fait qu'elle est particulièrement polluante et dangereuse en raison des rejets de gaz toxiques et des eaux de rinçage qu'elle engendre. The oldest, namely the salt bath tends to disappear from the fact that it is particularly polluting and dangerous due to the release of toxic gases and rinsing water it generates.

Plus récents, les traitements par bombardement ionique font intervenir une installation de traitement thermique sous vide relatif spécialement équipée de manière à engendrer sur les pièces à traiter une décharge luminescente dans une atmosphère de gaz de traitement. Cette technique présente l'inconvénient d'être relativement coûteuse et de ne pas convenir pour des pièces de forme complexe et, en particulier, de forme tubulaire et ce, en raison de cathode creuse.More recent, ion bombardment treatments involve a relative vacuum heat treatment installation specially equipped with so as to generate a luminescent discharge on the parts to be treated in a process gas atmosphere. This technique has the disadvantage of being relatively expensive and not suitable for complex shaped parts and, in particular, tubular in shape due to the hollow cathode.

Par ailleurs les traitements thermochimiques effectués sous atmosphère gazeuse à pression atmosphérique tels que les nitrurations gazeuses, consistent à porter les pièces à une température de l'ordre de 500°C à 600°C et à les balayer avec un gaz de nitrurations tel que de l'ammoniac. Ce traitement présente l'inconvénient d'être long, de consommer de grandes quantités de gaz de traitement et donc d'être relativement polluant.In addition, the thermochemical treatments carried out under a gaseous atmosphere at atmospheric pressure such as gaseous nitriding, consist of carrying the parts at a temperature of the order of 500 ° C to 600 ° C and to sweep them with a gas nitriding such as ammonia. This treatment has the disadvantage of being long, to consume large amounts of process gas and therefore to be relatively polluting.

Pour tenter de résoudre ces problèmes, la demanderesse a déjà proposé (brevet fiançais n° 94 05062) un procédé de nitruration à basse pression réalisée à une température du même ordre que précédemment et faisant intervenir un gaz de traitement comprenant de l'ammoniac ainsi qu'un catalyseur. Ce catalyseur a pour but de favoriser la dissociation de l'ammoniac au contact des pièces à traiter et de s'opposer à la recombinaison de l'azote actif provenant de cette dissociation en azote moléculaire.In an attempt to resolve these problems, the applicant has already proposed (patent n ° 94 05062) a nitriding process at low pressure carried out at a temperature of the same order as before and involving a gas of treatment comprising ammonia and a catalyst. This catalyst has to promote the dissociation of ammonia on contact with the parts to be treated and oppose the recombination of active nitrogen from this dissociation in molecular nitrogen.

Ce procédé qui permet d'obtenir d'excellents résultats pour le traitement de l'acier et des alliages d'acier présente cependant l'inconvénient d'utiliser une composition de gaz de traitement relativement coûteuse et une installation sophistiquée pour assurer un balayage homogène des pièces à traiter par les gaz de traitement. Un autre inconvénient de ce procédé réside dans le fait que dans des conditions de température et de pression appropriées au traitement de l'acier il est inopérant sur des alliages de titane ou de zirconium. De plus le catalyseur utilisé est incompatible avec le traitement des alliages de titane et de zirconium car il formerait une barrière de diffusion à l'azote (couche d'oxyde de Ti ou de Zr)This process which provides excellent results for the treatment of steel and steel alloys has the disadvantage of using a relatively expensive process gas composition and installation sophisticated to ensure uniform scanning of the parts to be treated by gases treatment. Another disadvantage of this process lies in the fact that in temperature and pressure conditions suitable for processing steel it does not work on titanium or zirconium alloys. In addition, the catalyst used is incompatible with the treatment of titanium and zirconium alloys because it would form a diffusion barrier to nitrogen (layer of Ti or Zr oxide)

Or justement l'invention a pour but un procédé de traitement de ce type d'alliages.Now precisely the object of the invention is a method for treating this type of alloy.

A cet effet elle propose un procédé de traitement consistant à porter les pièces à traiter à une température supérieure à 500°C à l'intérieur d'une enceinte dont l'atmosphère est maintenue à une pression inférieure ou égale à 0,1 mbar, à injecter sur les pièces un gaz de traitement comprenant de l'ammoniaque et/ou un hydrocarbure et/ou un gaz oxydant, la pression à l'intérieur de l'enceinte s'établissant alors à une valeur inférieure à la pression atmosphérique, mais supérieure à 100 bar pendant une durée pouvant aller de quelques dizaines de minutes à plus de 24 heures, en fonction de la profondeur de traitement désiré.To this end, it proposes a treatment method consisting in bringing the pieces to treat at a temperature above 500 ° C inside an enclosure whose the atmosphere is maintained at a pressure less than or equal to 0.1 mbar, at inject a treatment gas comprising ammonia and / or a hydrocarbon and / or an oxidizing gas, the pressure inside the enclosure then establishing itself at a value below atmospheric pressure, but greater than 100 bar for a period which can range from a few tens minutes to more than 24 hours, depending on the depth of treatment desired.

Dans le cas d'un traitement de nitruration, ce procédé n'utilise en tant que gaz de traitement que de l'ammoniaque, c'est-à-dire un gaz relativement courant et bon marché. L'installation de traitement s'en trouve également considérablement simplifiée. Le substrat traité en alliage de titane ou de zirconium joue le rôle de catalyseur de dissociation des molécules d'ammoniaque qui se rajoute à l'effet de dissociation thermique.In the case of a nitriding treatment, this process does not use as treatment only ammonia, that is to say a relatively common and good gas market. The treatment facility is also found considerably simplified. The treated substrate made of titanium or zirconium alloy plays the role of catalyst for dissociation of ammonia molecules which adds to the effect of thermal dissociation.

Par ailleurs aux températures élevées où s'effectue le traitement, le problème de dissociation et de recombinaison précédemment évoqué ne se pose plus et il devient possible d'obtenir une bonne homogénéité du traitement sans avoir à utiliser de dispositions particulières ni de gaz catalyseur. Seul un brassage de l'atmosphère intérieure du four, par exemple à l'aide de turbines usuelles, pourra être éventuellement mais non nécessairement effectué pour accroítre l'homogénéité.Furthermore, at the high temperatures where the treatment takes place, the problem of dissociation and recombination previously mentioned no longer arises and it becomes possible to obtain a good homogeneity of the treatment without having to use special provisions or catalyst gas. Only a brewing of the interior atmosphere of the furnace, for example using conventional turbines, may possibly but not necessarily done to increase homogeneity.

Dans ce cas le traitement thermochimique selon l'invention conduit à l'obtention d'une diffusion d'azote sans plasma sur des pièces en alliage de titane, et plus particulièrement :

  • en extrême surface d'une couche de combinaison de type Tix Ny présentant une épaisseur de quelques microns
  • d'une sous-couche de diffusion de dureté plus élevée que celle du substrat.
In this case, the thermochemical treatment according to the invention results in obtaining a diffusion of nitrogen without plasma on parts made of titanium alloy, and more particularly:
  • at the extreme surface of a Ti x N y type combination layer having a thickness of a few microns
  • of a diffusion sub-layer of higher hardness than that of the substrate.

Ce traitement permet à la fois d'améliorer les caractéristiques mécaniques des pièces traitées notamment en matière de résistance au frottement et de dureté superficielles et de leur donner un aspect jaune pâle plus ou moins brillant, particulièrement esthétique. Cet aspect est fonction de l'état de surface initial et de la stoechiométrie de la couche Tix Ny This treatment makes it possible both to improve the mechanical characteristics of the parts treated, in particular as regards resistance to friction and surface hardness, and to give them a pale yellow more or less shiny appearance, particularly aesthetic. This aspect is a function of the initial surface state and the stoichiometry of the Ti x N y layer.

En outre ce traitement est un traitement de diffusion : il n'engendre donc pas de modification importante de la rugosité initiale des pièces et il écarte tout risque de décollement de la couche de nitrure de titane.In addition, this processing is a diffusion processing: it therefore does not generate significant modification of the initial roughness of the parts and it eliminates any risk of separation of the titanium nitride layer.

Grâce à ces particularités le procédé selon l'invention s'applique au traitement de pièces utilisées dans de nombreux domaines d'applications, à savoir, notamment

  • le domaine biomédical : instruments et prothèses
  • les sports et loisirs
  • le domaine automobile et aérodynamique
  • l'armement
  • le domaine des arts décoratifs
  • la chimie et la pétrochimie
Thanks to these features, the method according to the invention applies to the treatment of parts used in numerous fields of applications, namely, in particular
  • the biomedical field: instruments and prostheses
  • sports and leisure
  • automotive and aerodynamics
  • armament
  • the field of decorative arts
  • chemistry and petrochemistry

Un autre avantage de ce procédé consiste en ce que du fait qu'il s'opère à basse pression (toujours inférieure à la pression atmosphérique) il ne consomme que très peu de gaz de traitement et n'est donc pas polluant relativement aux procédés haute pression qui exigent l'emploi de fours spécifiques et des contraintes de sécurité dues à la haute pression.Another advantage of this process is that the fact that it operates at low pressure (always lower than atmospheric pressure) it consumes only very little treatment gas and is therefore not polluting in relation to the processes high pressure which require the use of specific ovens and constraints of safety due to high pressure.

Avantageusement, dans le cas où le traitement est un traitement de nitruration, le procédé selon l'invention pourra en outre comprendre une phase de posttraitement destinée à déshydrogéner l'alliage traité.Advantageously, in the case where the treatment is a nitriding treatment, the process according to the invention may also include a post-processing phase intended to dehydrogenate the treated alloy.

On constate en effet que l'apport d'azote atomique en surface d'une pièce au moyen de la dissociation thermique et catalitique de molécules d'ammoniac peut conduire, aux températures de nitruration utilisées, à un enrichissement en hydrogène et à la formation d'hydrures, par exemple d'hydrures de titane de type TiH jusqu'à TiH2.It is found in fact that the supply of atomic nitrogen to the surface of a part by means of the thermal and catalitic dissociation of ammonia molecules can lead, at the nitriding temperatures used, to a hydrogen enrichment and to the formation of hydrides, for example titanium hydrides of TiH type up to TiH 2 .

En conséquence, il s'avère judicieux, dans certains cas, de procéder à une phase de traitement supplémentaire, après le traitement de nitruration basse pression de l'alliage (par exemple de l'alliage de titane) en vue d'extraire cet hydrogène qui pourrait être défavorable à la tenue à la fatigue de la pièce avec notamment une résistance amoindrie à la propagation de fissures. Consequently, it is advisable, in certain cases, to carry out a phase additional treatment, after the low pressure nitriding treatment of the alloy (for example titanium alloy) in order to extract this hydrogen which could be unfavorable to the fatigue resistance of the part with in particular a reduced resistance to crack propagation.

Ce traitement de déshydrogénation pourra être réalisé en portant les pièces à une température de l'ordre de 700 à 900°C pendant une période pouvant aller de 1 à 5 heures, dans un vide de 10-3 à 10-4 mbar.This dehydrogenation treatment can be carried out by bringing the parts to a temperature of the order of 700 to 900 ° C. for a period which can range from 1 to 5 hours, in a vacuum of 10 -3 to 10 -4 mbar.

A titre d'exemple, un alliage de titane de type TH6V, déshydrogéné à 790°C durant 2 heures, sous vide de 5 10-4 mbar verra sa teneur de hydrogène chuter de 256 à 11 ppm.By way of example, a titanium alloy of the TH6V type, dehydrogenated at 790 ° C. for 2 hours, under vacuum of 5 10 -4 mbar will see its hydrogen content drop from 256 to 11 ppm.

Un exemple de mise en oeuvre du procédé selon l'invention sera décrit ci-après à titre d'exemple non limitatif.An example of implementation of the method according to the invention will be described below in by way of nonlimiting example.

Dans cet exemple l'installation de traitement utilisée faisait intervenir un four de traitement thermique sous vide de structure classique équipé d'une turbine de circulation des gaz de traitement. Ce four comprend une enceinte étanche renfermant un moufle réalisé en une matière (métal ou graphite) ne pouvant pas retenir d'éléments polluants (en particulier l'oxygène ou la vapeur d'eau) susceptible de nuire à la qualité du traitement. A l'intérieur du moufle sont installées des résistances électriques de chauffage (essentiellement par rayonnement et par convection) capables de porter la température des pièces à plus de 1000°C.In this example, the treatment installation used involved a vacuum treatment of conventional structure equipped with a turbine circulation of process gases. This oven includes a sealed enclosure containing a muffle made of a material (metal or graphite) which cannot retain polluting elements (in particular oxygen or water vapor) likely to affect the quality of treatment. Inside the muffle are installed electrical heating resistors (mainly by radiation and convection) capable of bringing the temperature of the rooms to over 1000 ° C.

Cette enceinte est raccordée d'une part à un équipement de pompage apte à réaliser un vide primaire P<0,1 mbar et, d'autre part, à deux sources de gaz (une source d'azote et une source d'ammoniaque) par l'intermédiaire d'un circuit de distribution.This enclosure is connected on the one hand to pumping equipment capable of achieve a primary vacuum P <0.1 mbar and, on the other hand, two gas sources (one nitrogen source and ammonia source) through a distribution.

Après un dégraissage soigné, les pièces à traiter (ici des prothèses en alliage de titane TA6V) ont été disposées dans le moufle, sur un montage de préférence en alliage de titane ayant subi préalablement le même traitement. Sur ce montage les pièces ont été disposées de manière à être distantes les unes des autres de quelques millimètres de façon à ce que la diffusion soit la plus homogène possible à leur surface.After careful degreasing, the parts to be treated (here prostheses made of alloy titanium TA6V) were placed in the muffle, preferably on a mounting titanium alloy having previously undergone the same treatment. On this assembly the rooms have been arranged so as to be spaced from each other by a few millimeters so that the diffusion is the most homogeneous possible on their surface.

Une fois la charge préparée et l'enceinte refermée hermétiquement, un vide poussé à été établi (P < 0,1 mbar) puis maintenu une dizaine de minutes de manière à éliminer le plus d'éléments polluants possible. L'atmosphère est alors une atmosphère neutre composée d'azote, exempte d'oxygène et de vapeur d'eau. Once the load has been prepared and the enclosure hermetically sealed, a vacuum pushed to be established (P <0.1 mbar) and then maintained for ten minutes so as to remove as many pollutants as possible. The atmosphere is then a neutral atmosphere composed of nitrogen, free of oxygen and water vapor.

A l'issue de cette phase préparatoire on a procédé à une montée en température du four par convection à l'azote (injecté à partir de la source d'azote) et/ou par rayonnement (résistances) jusqu'à obtenir un niveau de température compris entre 500°C et 900°C, ici de l'ordre de 900°C.At the end of this preparatory phase, the temperature of the nitrogen convection oven (injected from the nitrogen source) and / or by radiation (resistances) until a temperature level between 500 ° C and 900 ° C, here of the order of 900 ° C.

Un maintien en température à ce niveau (palier de température) a été poursuivi pendant une période de temps suffisante pour s'assurer de l'homogénéité de la température des pièces.Temperature maintenance at this level (temperature level) was continued for a sufficient period of time to ensure the homogeneity of the room temperature.

Il a été ensuite procédé à une mise sous vide primaire de l'enceinte pour assurer une élimination de l'azote précédemment injecté puis au démarrage de la phase de diffusion grâce à une injection d'ammoniaque à une pression P comprise entre 100 et 900 mbars, ici de 300 mbars, la température étant supérieure à 500°C.A primary vacuum was then applied to the enclosure to ensure elimination of the nitrogen previously injected and then at the start of the diffusion thanks to an ammonia injection at a pressure P between 100 and 900 mbar, here 300 mbar, the temperature being above 500 ° C.

Cette phase de diffusion a été poursuivie pendant environ 7 heures de manière à obtenir une couche de diffusion d'environ 0,040 mm d'épaisseur moyenne.This dissemination phase was continued for approximately 7 hours so as to obtain a diffusion layer of approximately 0.040 mm in average thickness.

A la fin de la phase de diffusion on a effectué une nouvelle mise sous vide primaire de l'enceinte pour éliminer l'ammoniaque puis on a procédé à un reffoidissement du four jusqu'à la température ambiante. On a ensuite ouvert le four et défourné la charge.At the end of the diffusion phase, a new vacuum was carried out primary enclosure to remove ammonia and then we proceeded to a re-cooling the oven to room temperature. We then opened the oven and charge the load.

Les pièces traitées présentaient en extrême surface une couche jaune compacte et homogène de nitrure de titane Tix Ny d'épaisseur de l'ordre de 4µm et de dureté très élevée (>1000 HV), et par conséquent une très bonne résistance aux frottements et une excellente tenue à l'usure. La couche de diffusion (épaisse de quelques centièmes de mm et de dureté >400 HV) était alors de nature à améliorer la résistance à la fatigue (la dureté à coeur étant de 339 HV)The treated parts exhibited on the extreme surface a compact and homogeneous yellow layer of titanium nitride Ti x N y with a thickness of the order of 4 μm and very high hardness (> 1000 HV), and therefore very good resistance to friction. and excellent wear resistance. The diffusion layer (a few hundredths of a millimeter thick and hardness> 400 HV) was then likely to improve the resistance to fatigue (the hardness at the core being 339 HV)

Un avantage important de ce procédé consiste en ce qu'il permet d'obtenir une très bonne homogénité du traitement même dans le cas de pièces de formes et de géométries complexes y compris de formes creuses. En outre le traitement s'étend aux zones de contact des pièces sur leur support.An important advantage of this process is that it provides a very good homogeneity of the treatment even in the case of shaped parts and complex geometries including hollow shapes. In addition the treatment extends to the contact areas of the parts on their support.

Bien entendu l'invention ne se limite pas au mode d'exécution précédemment décrit. En effet, le gaz de traitement pourrait être autre que de l'ammoniaque et pourrait par exemple consister en une atmosphère à base d'hydrocarbure (C2H2, C3H8, CH4....) en vue de cémenter superficiellement ces alliages. Dans ce cas on obtient une couche superficielle de couleur gris métallique, de grande dureté et possédant des propriétés tribologiques accrues.Of course, the invention is not limited to the embodiment described above. Indeed, the treatment gas could be other than ammonia and could for example consist of a hydrocarbon-based atmosphere (C 2 H 2 , C 3 H 8 , CH 4 ....) in order to cement superficially these alloys. In this case, a surface layer of metallic gray color, of great hardness and having increased tribological properties, is obtained.

De même l'atmosphère de traitement pourrait comprendre un gaz oxydant tel que l'oxygène de manière à obtenir une couche superficielle (Ti0, Ti02, Ti203, Zr02..) présentant des colorations diverses (bleu, vert, violet) et une grande dureté.Similarly, the treatment atmosphere could include an oxidizing gas such as oxygen so as to obtain a surface layer (Ti0, Ti0 2 , Ti 2 0 3 , Zr0 2 ..) having various colors (blue, green, purple ) and great hardness.

Cette couche d'oxyde Tix Oy, d'une épaisseur de quelques microns et de dureté supérieure à 1000 HV est compacte et homogène sur toute la surface de la pièce. Les couleurs que l'on obtient sont brillantes et très variées. Elle permet d'améliorer considérablement la résistance au frottement des pièces. Bien entendu l'aspect des pièces est fonction de l'état de surface initial et de la stoechiométrie de la couche de Tix Oy.This layer of Ti x O y oxide, a few microns thick and with a hardness greater than 1000 HV, is compact and homogeneous over the entire surface of the part. The colors that we obtain are brilliant and very varied. It considerably improves the friction resistance of the parts. Of course the appearance of the parts is a function of the initial surface condition and the stoichiometry of the layer of Ti x O y .

L'atmosphère de traitement pourrait également consister en une combinaison de NH3 + CH4 de manière à obtenir une couche superficielle en carbonitrures TiCx Ny ou Zr CN de couleur rosée ou beurre.The treatment atmosphere could also consist of a combination of NH 3 + CH 4 so as to obtain a surface layer of carbonitrides TiC x N y or Zr CN of pink or butter color.

Elle pourrait en outre consister en un mélange d'oxygène et d'azote O2 + N2 ou N20 + N2 de manière à obtenir des couches d'oxynitrures : Ti Ox Ny ; Zr Ox Ny de colorations diverses.It could also consist of a mixture of oxygen and nitrogen O 2 + N 2 or N 2 0 + N 2 so as to obtain layers of oxynitrides: Ti O x N y ; Zr O x N y of various colors.

Claims (12)

Procédé pour la formation par un traitement thermochimique d'une couche superficielle présentant une dureté élevée et possédant des propriétés tribologiques, sur des pièces en alliages de métaux tels que du titane ou du zirconium, sensibles ou réactifs vis à vis de l'azote, du carbone et/ou de l'oxygène,
caractérisé en ce qu'il consiste à porter lesdites pièces à une température supérieure à 500°C à l'intérieur d'une enceinte dont l'atmosphère est maintenue à une pression inférieure ou égale à 0,1 mbar, puis à injecter sur les pièces un gaz de traitement comprenant de l'ammoniaque et/ou un hydrocarbure et/ou un gaz oxydant, la pression s'établissant alors à une valeur inférieure à la pression atmosphérique mais supérieure à 100 mbars pendant une durée comprise entre quelques dizaines de minutes à 24 heures ou plus, en fonction de la profondeur de traitement désirée.Process for the formation by a thermochemical treatment of a surface layer having a high hardness and having tribological properties, on parts made of metal alloys such as titanium or zirconium, sensitive or reactive with respect to nitrogen, carbon and / or oxygen,
characterized in that it consists in bringing said parts to a temperature above 500 ° C inside an enclosure whose atmosphere is maintained at a pressure less than or equal to 0.1 mbar, then to inject on the parts a treatment gas comprising ammonia and / or a hydrocarbon and / or an oxidizing gas, the pressure then being established at a value lower than atmospheric pressure but greater than 100 mbar for a period of between a few tens of minutes 24 hours or more, depending on the desired treatment depth. Procédé selon la revendication 1,
caractérisé en ce que les pièces sont en titane et en ce que le susdit traitement est un traitement thermochimique de diffusion d'azote sans plasma, ce traitement utilisant de l'ammoniaque en tant que gaz de traitement de manière à obtenir : en extrême surface, une couche de combinaison de type Tix Ny présentant une épaisseur de quelques microns une sous-couche de diffusion de dureté plus élevée que celle du substrat. Method according to claim 1,
characterized in that the parts are made of titanium and in that the above treatment is a thermochemical treatment of diffusion of nitrogen without plasma, this treatment using ammonia as the treatment gas so as to obtain: on the extreme surface, a combination layer of Ti x N y type having a thickness of a few microns a diffusion sub-layer of higher hardness than that of the substrate. Procédé selon la revendication 2,
caractérisé en ce que la susdite atmosphère est une atmosphère neutre et exempte d'oxgène et de vapeur d'eau.Method according to claim 2,
characterized in that the above atmosphere is a neutral atmosphere free from oxygen and water vapor. Procédé selon la revendication 3,
caractérisé en ce que la susdite atmosphère est composée d'azote.Method according to claim 3,
characterized in that the above atmosphere is composed of nitrogen. Procédé selon l'une des revendications précédentes,
caractérisé en ce qu'il comprend un brassage du gaz de traitement.Method according to one of the preceding claims,
characterized in that it comprises a mixing of the treatment gas. Procédé selon l'une des revendications précédentes,
caractérisé en ce qu'il comprend les phases successives suivantes : un dégraissage préalable des pièces à traiter l'enfournement des pièces à l'intérieur de l'enceinte une première mise sous vide de l'enceinte de manière à éliminer les éléments polluants une montée en température du four par convection à l'azote et/ou par rayonnement jusqu'à l'obtention d'une température de 500°C à 900°C le maintien de cette température pendant une durée déterminée de manière à obtenir une température homogène des pièces une deuxième mise sous vide éventuelle de l'enceinte pour assurer l'élimination de l'azote injecté à l'occasion de la montée en température du four l'injection de gaz de traitement à une pression comprise entre 100 et 900 mbars de préférence 300 mbars pendant une période pouvant atteindre 24 heures une troisième mise sous vide de l'enceinte pour éliminer le gaz de traitement et le refroidissement du four le défournement des pièces. Method according to one of the preceding claims,
characterized in that it comprises the following successive phases: prior degreasing of the parts to be treated the furnace of the parts inside the enclosure a first evacuation of the enclosure so as to eliminate the polluting elements a rise in temperature of the oven by convection with nitrogen and / or by radiation until a temperature of 500 ° C. to 900 ° C. is obtained maintaining this temperature for a determined period so as to obtain a uniform temperature of the parts a second possible vacuuming of the enclosure to ensure the elimination of the nitrogen injected during the rise in temperature of the oven injection of process gas at a pressure between 100 and 900 mbar, preferably 300 mbar for a period of up to 24 hours a third evacuation of the enclosure to eliminate the treatment gas and the cooling of the oven the furnishing of the parts. Procédé selon l'une des revendications 2 à 6,
caractérisé en ce qu'il comprend en outre un traitement supplémentaire de déshydrogénation destiné à extraire l'hydrogène engendré lors du traitement thermochimique.Method according to one of claims 2 to 6,
characterized in that it further comprises an additional dehydrogenation treatment intended to extract the hydrogen generated during the thermochemical treatment. Procédé selon la revendication 7,
caractérisé en ce que le traitement de déshydrogénation s'effectue en portant les pièces à une température de l'ordre de 700 à 900°C pendant une période comprise entre 1 et 5 heures, dans un vide de 10-3 10-4 à mbar.Method according to claim 7,
characterized in that the dehydrogenation treatment is carried out by bringing the parts to a temperature of the order of 700 to 900 ° C for a period of between 1 and 5 hours, in a vacuum of 10 -3 10 -4 at mbar . Procédé selon la revendication 1,
caractérisé en ce que le susdit traitement est un traitement de cémentation et en ce que, dans ce cas le gaz de traitement comprend des hydrocarbures.Method according to claim 1,
characterized in that the above treatment is a case hardening treatment and in that, in this case, the treatment gas comprises hydrocarbons. Procédé selon la revendication 1,
caractérisé en ce que le susdit traitement est un traitement d'oxydation et en ce que, dans ce cas, le gaz de traitement comprend un gaz oxydant tel que de l'oxygène.Method according to claim 1,
characterized in that the above treatment is an oxidation treatment and in that, in this case, the treatment gas comprises an oxidizing gas such as oxygen. Procédé selon la revendication 1,
caractérisé en ce que le susdit traitement est un traitement de carbonitruration et en ce que, dans ce cas le gaz de traitement est une combinaison NH3 + CH4.Method according to claim 1,
characterized in that the above treatment is a carbonitriding treatment and in that in this case the treatment gas is a combination of NH 3 + CH 4 . Procédé selon la revendication 1,
caractérisé en ce que le susdit traitement est un traitement d'oxynitruration et en ce que dans ce cas le gaz de traitement consiste en un mélange d'oxgène et d'azote.Method according to claim 1,
characterized in that the above treatment is an oxynitriding treatment and in that in this case the treatment gas consists of a mixture of oxgene and nitrogen.
EP19980401235 1997-05-23 1998-05-22 Process for forming a superficial layer having a high hardness by plasma-free thermochemical treatment Expired - Lifetime EP0885980B1 (en)

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FR9706518A FR2763604B1 (en) 1997-05-23 1997-05-23 PROCESS FOR THE FORMATION, BY A THERMOCHEMICAL TREATMENT WITHOUT PLASMA, OF A SURFACE LAYER HAVING A HIGH HARDNESS
FR9706518 1997-05-23

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DE102010028165A1 (en) * 2010-04-23 2011-10-27 Robert Bosch Gmbh Process for the carbonitriding of metallic components

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WO2022184812A1 (en) 2021-03-03 2022-09-09 Elos Medtech Pinol A/S Surface hardening of group iv metals

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DE69831530T2 (en) 2006-06-14
FR2763604A1 (en) 1998-11-27
EP0885980B1 (en) 2005-09-14

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