EP0885980B1 - 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
EP0885980B1
EP0885980B1 EP19980401235 EP98401235A EP0885980B1 EP 0885980 B1 EP0885980 B1 EP 0885980B1 EP 19980401235 EP19980401235 EP 19980401235 EP 98401235 A EP98401235 A EP 98401235A EP 0885980 B1 EP0885980 B1 EP 0885980B1
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Prior art keywords
treatment
parts
temperature
nitrogen
furnace
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EP19980401235
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German (de)
French (fr)
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EP0885980A2 (en
EP0885980A3 (en
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Patrick Jacquot
Sylvain Foissey
Gérard Veyssiere
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Bodycote SAS
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Bodycote SAS
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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 process for the formation, by a treatment Thermochemical without plasma, a superficial layer with hardness high and possessing tribological properties, on parts made of alloys sensitive or reactive towards nitrogen, carbon and / or oxygen.
  • a titanium-based alloy or zirconium in an atmosphere that may include ammonia, a hydrocarbon and / or an oxidizing gas or even a gaseous composition including one or more of these compounds.
  • thermochemical treatments In general, we know that there are at present various techniques such thermochemical treatments.
  • the oldest, namely the salt bath tends to disappear because it is particularly polluting and dangerous because of the release of toxic gases and rinsing water it generates.
  • ion bombardment treatments involve relative vacuum heat treatment plant specially equipped with to generate on the parts to be treated a glow discharge in a treatment gas atmosphere.
  • This technique has the disadvantage of being relatively expensive and not suitable for complex shaped parts and, in particular, of tubular shape and this, because of hollow cathode.
  • thermochemical treatments carried out under a gaseous atmosphere atmospheric pressure consist in wearing 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. It is the same with regard to treatments carried out under high pressure, “Hochdrucknitrieren von Titantechnikstoffen “HTM Harterei - Technische Mitteilungen, 46 (1991) Nov./Dez, No. 6 and in patent JP 0709541. This treatment presents the disadvantage of being long, consuming large quantities of gas from treatment and therefore to be relatively polluting.
  • This process makes it possible to obtain excellent results for the treatment of steel and steel alloys, however, has the disadvantage of using a relatively expensive treatment gas composition and an installation Sophisticated to ensure a homogeneous sweep of the parts to be treated by the gases treatment.
  • Another disadvantage of this method lies in the fact that in temperature and pressure conditions suitable for the treatment of steel it is inoperative on titanium or zirconium alloys.
  • the catalyst used is incompatible with the processing of titanium and zirconium alloys because it would form a diffusion barrier to nitrogen (Ti oxide layer or Zr).
  • the aim of the invention is to provide a treatment method of this type alloys.
  • this process does not use as a gas only ammonia, that is to say a relatively common gas and cheap.
  • the treatment facility is also located greatly simplified.
  • the substrate treated with titanium alloy or zirconium acts as a catalyst for dissociation of molecules of ammonia which adds to the thermal dissociation effect.
  • This treatment makes it possible at the same time to improve the mechanical characteristics of the treated parts, in particular as regards resistance to friction and surface hardness, and to give them a pale yellow appearance that is more or less shiny and particularly aesthetic.
  • This aspect is a function of the initial surface state and the stoichiometry of the Ti x N y layer.
  • this treatment is a diffusion treatment: it does not generate significant change in the initial roughness of the parts and it eliminates all risk detachment of the titanium nitride layer.
  • Another advantage of this process is that because it operates at low pressure (always lower than the atmospheric pressure) it only consumes very little treatment gas and is therefore not polluting with respect to the processes high pressure which require the use of specific furnaces and safety due to high pressure.
  • the method according to the invention may further comprise a post-processing phase intended to dehydrogenate the treated alloy.
  • the atomic nitrogen supply at the surface of a room 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 .
  • This dehydrogenation treatment can be carried out by bringing the pieces to a temperature of the order of 700 to 900 ° C for a period ranging from 1 to 5 hours, in a vacuum of 10 -3 to 10 -4 mbar.
  • a TH6V-type titanium alloy dehydrogenated at 790 ° C. for 2 hours, under a vacuum of 10 -4 mbar, will have its hydrogen content drop from 256 to 11 ppm.
  • the treatment plant used involved a furnace of vacuum heat treatment of conventional structure equipped with a turbine of flow of process gases.
  • This oven includes a sealed enclosure containing a muffle made of a material (metal or graphite) that can not be retain pollutants (especially oxygen or water vapor) likely to affect the quality of the treatment.
  • pollutants especially oxygen or water vapor
  • Inside the mitt are installed electrical heating resistors (essentially by radiation and convection) able to bring the temperature of the parts to more than 1000 ° C.
  • This chamber is connected on the one hand to pumping equipment suitable for realize a primary vacuum P ⁇ 0.1 mbar and, on the other hand, two gas sources (one source of nitrogen and a source of ammonia) via a distribution.
  • the parts to be treated (here alloy titanium TA6V) have been arranged in the muffle, on a mounting preferably in titanium alloy having previously undergone the same treatment.
  • the parts were arranged so as to be distant from each other a few millimeters so that the diffusion is the most homogeneous possible on their surface.
  • Temperature maintenance at this level was continued for a period of time sufficient to ensure the homogeneity of the room temperature.
  • This diffusion phase was continued for approximately 7 hours in order to obtain a diffusion layer of approximately 0.040 mm average thickness.
  • the treated parts had, at the extreme surface, a compact and homogeneous yellow layer of titanium nitride Ti x N y with a thickness of about 4 ⁇ m and a very high hardness (> 1000 HV), and consequently a very good resistance to friction. and excellent wear resistance.
  • the diffusion layer (a few hundredths of a millimeter thick and with a hardness of> 400 HV) was then likely to improve the fatigue resistance (the core hardness being 339 HV).
  • An important advantage of this method is that it makes it possible to obtain a very good homogenous treatment even in the case of pieces of shapes 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 .7) with a view to cementer superficially these alloys. In this case we obtain a surface layer of metallic gray color, of great hardness and having increased tribological properties.
  • a hydrocarbon-based atmosphere C 2 H 2 , C 3 H 8 , CH 4 .
  • the treatment atmosphere could comprise an oxidizing gas such as oxygen so as to obtain a surface layer (Ti0, Ti0 2 , Ti 2 O 3 , Zr0 2 ..) with various colors (blue, green, violet). ) and a great hardness.
  • an oxidizing gas such as oxygen so as to obtain a surface layer (Ti0, Ti0 2 , Ti 2 O 3 , Zr0 2 ..) with various colors (blue, green, violet). ) and a great hardness.
  • This Ti x O y oxide layer of a thickness of a few microns and a hardness greater than 1000 HV is compact and homogeneous over the entire surface of the workpiece.
  • 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 Ti x O y layer.
  • 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 pinkish color or butter.

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 process for the formation, by a treatment Thermochemical without plasma, a superficial layer with hardness high and possessing tribological properties, on parts made of alloys 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 processing under controlled atmosphere at a high temperature, a titanium-based alloy or zirconium in an atmosphere that 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 at present various techniques such thermochemical treatments.

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 because it is particularly polluting and dangerous because of 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 recently, ion bombardment treatments involve relative vacuum heat treatment plant specially equipped with to generate on the parts to be treated a glow discharge in a treatment gas atmosphere. This technique has the disadvantage of being relatively expensive and not suitable for complex shaped parts and, in particular, of tubular shape and this, because of 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. Il en est de même pour ce qui concerne des traitements effectués sous haute pression, "Hochdrucknitrieren von Titanwerkstoffen" HTM Harterei - Technische Mitteilungen, 46 (1991) Nov./Dez, N°6 et dans le brevet JP 0709541. Ce traitement présente l'inconvénient d'être long, de consommer de grandes quantités de gaz de traitement et donc d'être relativement polluant.Furthermore, the thermochemical treatments carried out under a gaseous atmosphere atmospheric pressure, such as gaseous nitriding, consist in wearing 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. It is the same with regard to treatments carried out under high pressure, "Hochdrucknitrieren von Titanwerkstoffen "HTM Harterei - Technische Mitteilungen, 46 (1991) Nov./Dez, No. 6 and in patent JP 0709541. This treatment presents the disadvantage of being long, consuming large quantities of gas from treatment and therefore to be relatively polluting.

De même il a été proposé, par le brevet EP-A-449793 un procédé consistant à injecter de l'azote pur sur des pièces à traiter portées à une température de 650° à 1000°C à une pression inférieure à la pression atmosphérique.Similarly, it has been proposed, by the patent EP-A-449793, a method consisting in inject pure nitrogen onto parts to be treated heated to a temperature of 650 ° 1000 ° C at a pressure below atmospheric pressure.

Pour tenter de résoudre les problèmes précedemment évoqués, 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 the problems mentioned above, the plaintiff already proposed (French Patent No. 94 05062) a low nitriding process pressure carried out at a temperature of the same order as before and making operating a process gas comprising ammonia and a catalyst. This catalyst is intended to promote the dissociation of ammonia on contact parts to be treated and to oppose the recombination of the active nitrogen from of 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 makes it possible to obtain excellent results for the treatment of steel and steel alloys, however, has the disadvantage of using a relatively expensive treatment gas composition and an installation Sophisticated to ensure a homogeneous sweep of the parts to be treated by the gases treatment. Another disadvantage of this method lies in the fact that in temperature and pressure conditions suitable for the treatment of steel it is inoperative on titanium or zirconium alloys. In addition, the catalyst used is incompatible with the processing of titanium and zirconium alloys because it would form a diffusion barrier to nitrogen (Ti oxide layer or Zr).

Or, justement, l'invention a pour but un procédé de traitement de ce type d'alliages.However, the aim of the invention is to provide a treatment method of this type alloys.

A cet effet, elle propose un procédé de traitement thermochimique sans plasma d'une couche superficielle présentant une dureté élevée et possédant des propriétés tribologiques, sur des pièces en alliages de métaux sensibles ou réactifs vis à vis de l'azote, tels que du titane ou du zirconium, 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 650°C à 900°C, la pression étant maintenu à une pression inférieure ou égale à 0,1mbar,
  • 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 d'un gaz de traitement comprenant de l'ammoniaque sur les pièces à traiter portées à une température supérieur à 500°C, et le maintien de la pression à l'intérieur du four à une valeur comprise entre 100 et 600 mbars, de préférence 300 mbars, pendant une durée comprise entre quelques minutes et 24 heures ou plus en fonction de la profondeur de traitement désirée 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,
  • une troisième mise sous vide de l'enceinte pour éliminer le gaz de traitement et le refroidissement du four,
  • le défoumement des pièces.
For this purpose, it proposes a method of thermochemical treatment without plasma of a superficial layer having a high hardness and having tribological properties, on parts made of alloys of sensitive or reactive metals with respect to nitrogen, such as titanium or zirconium, that it includes the following successive phases:
  • a preliminary degreasing of the parts to be treated,
  • the charging of parts inside the enclosure,
  • a first evacuation of the chamber so as to eliminate the polluting elements,
  • a temperature rise of the oven by convection with nitrogen and / or by radiation until a temperature of 650 ° C. to 900 ° C. is obtained, the pressure being maintained at a pressure less than or equal to 0.1mbar ,
  • maintaining this temperature for a predetermined period so as to obtain a uniform temperature of the parts,
  • a second possible evacuation of the chamber to ensure the elimination of the nitrogen injected during the rise in temperature of the oven,
  • injecting a process gas comprising ammonia onto the workpieces heated to a temperature greater than 500 ° C, and maintaining the pressure inside the oven at a value between 100 and 600 mbar , preferably 300 mbar, for a period of between a few minutes and 24 hours or more depending on the desired treatment depth to obtain:
    • in extreme area Ti type of combined x N y layer having a thickness of a few microns,
    • a diffusion sub-layer of higher hardness than that of the substrate,
  • a third evacuation of the chamber to eliminate the treatment gas and the cooling of the oven,
  • the defouement of the pieces.

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 a gas only ammonia, that is to say a relatively common gas and cheap. The treatment facility is also located greatly simplified. The substrate treated with titanium alloy or zirconium acts as a catalyst for dissociation of molecules of ammonia which adds to the thermal dissociation effect.

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.Moreover, at the high temperatures where the treatment is carried out, the problem previously mentioned dissociation and recombination is no longer becomes possible to obtain a good homogeneity of the treatment without having to use special provisions or catalyst gas. Only a brew of the interior atmosphere of the furnace, for example using conventional turbines, may be possibly but not necessarily carried out to increase uniformity.

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 at the same time to improve the mechanical characteristics of the treated parts, in particular as regards resistance to friction and surface hardness, and to give them a pale yellow appearance that is more or less shiny and 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 treatment is a diffusion treatment: it does not generate significant change in the initial roughness of the parts and it eliminates all risk detachment 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 many fields of applications, namely, in particular
  • the biomedical field: instruments and prostheses
  • sports and recreation
  • the automotive and aerodynamic field
  • 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 because it operates at low pressure (always lower than the atmospheric pressure) it only consumes very little treatment gas and is therefore not polluting with respect to the processes high pressure which require the use of specific furnaces and 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 post-traitement destinée à déshydrogéner l'alliage traité.Advantageously, in the case where the treatment is a nitriding treatment, the method according to the invention may further comprise 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.Indeed, it is found that the atomic nitrogen supply at the surface of a room 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 some cases, to proceed with 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 strength of the part, in particular with less resistance to the propagation of cracks.

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 pieces to a temperature of the order of 700 to 900 ° C for a period ranging 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 TH6V-type titanium alloy, dehydrogenated at 790 ° C. for 2 hours, under a vacuum of 10 -4 mbar, will have 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 as a non-limitative 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 plant used involved a furnace of vacuum heat treatment of conventional structure equipped with a turbine of flow of process gases. This oven includes a sealed enclosure containing a muffle made of a material (metal or graphite) that can not be retain pollutants (especially oxygen or water vapor) likely to affect the quality of the treatment. Inside the mitt are installed electrical heating resistors (essentially by radiation and convection) able to bring the temperature of the parts to more than 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 chamber is connected on the one hand to pumping equipment suitable for realize a primary vacuum P <0.1 mbar and, on the other hand, two gas sources (one source of nitrogen and a source of ammonia) via 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 a careful degreasing, the parts to be treated (here alloy titanium TA6V) have been arranged in the muffle, on a mounting preferably in titanium alloy having previously undergone the same treatment. On this montage the parts were arranged so as to be distant from each other 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 charge has been prepared and the enclosure is sealed, a vacuum pushed to be established (P <0.1 mbar) then maintained ten minutes of to eliminate 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, a temperature rise of convection oven with nitrogen (injected from the nitrogen source) and / or by radiation (resistors) 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 plateau) was continued for a period of time sufficient 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.It was then carried out a primary vacuum of the enclosure to ensure elimination of the previously injected nitrogen and then at the start of the diffusion by 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 diffusion phase was continued for approximately 7 hours in order to obtain a diffusion layer of approximately 0.040 mm 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 refroidissement 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 evacuation was performed primary chamber to remove ammonia and then proceeded to a cooling the oven to room temperature. We then opened the oven and unloaded 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 had, at the extreme surface, a compact and homogeneous yellow layer of titanium nitride Ti x N y with a thickness of about 4 μm and a very high hardness (> 1000 HV), and consequently a very good resistance to friction. and excellent wear resistance. The diffusion layer (a few hundredths of a millimeter thick and with a hardness of> 400 HV) was then likely to improve the fatigue resistance (the core hardness 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 method is that it makes it possible to obtain a very good homogenous treatment even in the case of pieces of shapes 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 ....) with a view to cementer superficially these alloys. In this case we obtain a surface layer of metallic gray color, of great hardness and having increased tribological properties.

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 comprise an oxidizing gas such as oxygen so as to obtain a surface layer (Ti0, Ti0 2 , Ti 2 O 3 , Zr0 2 ..) with various colors (blue, green, violet). ) and a 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 Ti x O y oxide layer, of a thickness of a few microns and a hardness greater than 1000 HV is compact and homogeneous over the entire surface of the workpiece. 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 Ti x O y layer.

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 pinkish color or butter.

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 oxynitride layers: Ti O x N y ; Zr O x N y of various colors.

Claims (6)

  1. Process for forming, by plasma-free thermochemical treatment, a superficial layer having high hardness and tribologic properties, on parts in metal alloys sensitive or reactive to nitrogen, such as titanium or zirconium, characterized in that it comprises the following successive phases:
    prior degreasing of the parts to be treated,
    furnacing the parts in the enclosure,
    producing a first vacuum in the enclosure to remove polluting elements,
    raising the furnace temperature by nitrogen convection and/or by radiation until a temperature of 650°C to 900°C is reached, the pressure being maintained at a pressure of 0.1mbar or less;
    maintaining this temperature for a determined period of time so as to obtain a homogeneous temperature of the parts,
    producing an optional second vacuum in the enclosure to ensure removal of the nitrogen injected when raising the furnace temperature,
    injecting a treatment gas containing ammonia onto the parts to be treated raised to a temperature greater than 500°C, and maintaining the pressure inside the furnace at a value of between 100 and 600 mbars, preferably 300 mbars, for a period of between a few minutes and 24 hours or more in relation to the depth of desired treatment, so as to obtain:
    on the top surface a combination layer of TixNy type having a thickness of a few microns,
    a diffusion sub-layer of greater hardness than the substrate hardness,
    producing a third vacuum in the enclosure to remove the treatment gas and cool the furnace,
    removing the parts from the furnace.
  2. Process as in claim 1 characterized in that said above atmosphere is a neutral atmosphere and free of oxygen and water vapour.
  3. Process as in claim 2 characterized in that said above atmosphere consists of nitrogen.
  4. Process as in any of the preceding claims characterized in that comprises mixing the treatment gas.
  5. Process as in claim 1, characterized in that said above treatment is a carbonitriding treatment and in that, in this case, the treatment gas is a combination of NH3+CH4.
  6. Process as in claim 1 characterized in that said above treatment is an oxynitriding treatment and in that, in this case, the treatment gas consists of a mixture of oxygen 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)

Applications Claiming Priority (2)

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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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DE19909694A1 (en) * 1999-03-05 2000-09-14 Stiftung Inst Fuer Werkstoffte Production of carbonitrided edge layers in a low pressure carburization process comprises enriching the edge layers with nitrogen at the end of the process using molecular nitrogen as donor gas
IT1316270B1 (en) * 2000-12-28 2003-04-03 Ct Sviluppo Materiali Spa PROCEDURE FOR SURFACE TREATMENT OF TITANIUM, PRODUCTS AND MANUFACTURED PRODUCTS MADE OR COATED IN TITANIUM AND TREATED ACCORDING TO SUCH
DE10221605A1 (en) * 2002-05-15 2003-12-04 Linde Ag Method and device for the heat treatment of metallic workpieces
DE102010028165A1 (en) 2010-04-23 2011-10-27 Robert Bosch Gmbh Process for the carbonitriding of metallic components
EP4301884A1 (en) 2021-03-03 2024-01-10 Elos Medtech Pinol A/S Surface hardening of group iv metals

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FR2136037A5 (en) * 1971-04-05 1972-12-22 Metaux Precieux Sa
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JPH0723527B2 (en) * 1986-12-22 1995-03-15 三菱重工業株式会社 Carburizing method for Ti-6Al-4V alloy
SE9001009L (en) * 1990-03-21 1991-09-22 Ytbolaget I Uppsala Ab PROCEDURE SHOULD CREATE A HAIR AND Wear-Resistant Layer With Good Adhesion To Titanium Or Titanium Regulations And Products, Manufactured According To The Procedure
FR2663953B1 (en) * 1990-07-02 1993-07-09 Aubert & Duval Acieries METHOD AND INSTALLATION FOR CEMENTING LOW PRESSURE METAL ALLOY PARTS.
DE4239392A1 (en) * 1991-11-29 1993-06-03 Volkswagen Ag Surface hardness increase of titanium material components - by deoxidising thermal treatment, and application of nitrogen diffusion coating
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FR2763604A1 (en) 1998-11-27
ES2247665T3 (en) 2006-03-01
EP0885980A2 (en) 1998-12-23
EP0885980A3 (en) 2000-10-11
FR2763604B1 (en) 1999-07-02
DE69831530T2 (en) 2006-06-14

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