CN115740449A - Multi-energy-field auxiliary sintering method and device for material difficult to deform - Google Patents

Abstract

The invention provides a multi-energy field auxiliary sintering device for a material difficult to deform, which comprises: the device comprises a sintering mold, a pressurizing system, a direct-current pulse power supply, an ultrasonic generating system, a temperature control system and a vacuum system. The invention utilizes the skin thermal effect and the Joule thermal effect of the pulse current, the softening effect of the ultrasonic vibration field, the external force action of the pressure field in the sintering process and the eddy heating action among powder particles, can effectively promote the densification process of the material in the sintering process and improve the mechanical property of the sintered material. Meanwhile, the heating and cooling time in the sintering process is shortened through the coupling effect of the multi-energy field, the coarsening of crystal grains in the sintering process can be effectively inhibited, and the material with uniform structure can be prepared in a short time.

Description

Multi-energy-field auxiliary sintering method and device for material difficult to deform

Technical Field

The invention belongs to the technical field of powder metallurgy, and particularly relates to a multi-energy field auxiliary sintering method and device for a material difficult to deform, which are used for the powder metallurgy and composite material preparation technology.

Background

With the continuous development of material synthesis technology, the application of some functional characteristic materials is more and more extensive, and new materials such as composite materials, high-temperature materials, gradient materials, nano materials, porous materials and the like are continuously developed and widely applied to the fields of aviation, aerospace, petroleum, chemical industry, ships and the like. The common characteristic of the novel materials is that the large-size block with good mechanical property is difficult to prepare by using the traditional preparation process. Taking a composite material as an example, the composite material refers to a novel material with high-performance fibers, nano reinforcement and the like introduced into a traditional material, and mainly comprises a metal matrix composite material, a ceramic matrix composite material, a resin matrix composite material and the like. The traditional method for preparing the composite material is smelting, but the sufficient mixing of the matrix and the reinforcement is not easy to ensure, and the performance of a bonding interface can be influenced by long-time overheating in the smelting process, so that the material is easy to generate cracks and accelerate crack propagation, and the mechanical property is seriously influenced.

Powder metallurgy is a solid-phase sintering method, which is a method of forming materials with operating temperatures below the melting point of the material. The novel material prepared by the powder metallurgy method has low interface reaction degree, can prevent material macrosegregation, and the bulk material prepared by sintering has uniform tissue composition, good hot processing performance and strong grain size controllability. The traditional solid phase sintering process comprises pressureless sintering, hot pressing sintering, hot isostatic pressing sintering and the like, and the sintering processes have the defects of slow temperature rise, long heat preservation and pressure maintaining time, high sintering temperature, energy waste and the like.

The pulse current is introduced into the material forming process, so that the plasticity of the material can be obviously improved. In addition, the material can be rapidly heated through the Joule heat effect of the low-voltage pulse current, so that the material is softened, the deformation resistance of the material is further reduced, and the forming quality is improved. The ultrasonic vibration field is introduced into the material forming process, so that the tissue component distribution of the material can be effectively homogenized, the forming force of the material is reduced, and the microstructure of the material can be improved.

For the solid phase sintering technology, chinese patent CN 110666175A, "a hot isostatic pressing method of nickel-based superalloy powder", proposes a powder metallurgy method for forming a disc superalloy component in a hot isostatic pressing manner under vacuum conditions, but since special energy fields such as pulse current and ultrasonic vibration are not introduced, the forming efficiency needs to be further improved. In addition, the current special energy field assisted sintering usually adopts a single physical field, mainly focuses on the forming size precision, and needs to be further improved in the aspects of controlling and improving the material deformation microstructure performance.

Disclosure of Invention

In order to solve the technical problems, the invention provides a multi-energy-field auxiliary sintering method and a device for a material difficult to deform by combining special energy fields such as pulse current and ultrasonic vibration with a powder metallurgy sintering technology. The invention utilizes the skin thermal effect and the Joule thermal effect of the pulse current, the softening effect of the ultrasonic vibration field, the external force action of the pressure field in the sintering process and the eddy heating action among powder particles to effectively promote the densification process of the material in the sintering process and improve the mechanical property of the sintered material. Meanwhile, the heating and cooling time in the sintering process is shortened through the coupling effect of the multi-energy field, the coarsening of crystal grains in the sintering process can be effectively inhibited, and the material with uniform structure can be prepared in a short time.

In order to achieve the above object, the present invention provides a multi-energy field assisted sintering apparatus for a material difficult to deform, comprising: the device comprises a sintering mold, a pressurizing system, a direct-current pulse power supply, an ultrasonic generating system, a temperature control system and a vacuum system.

The sintering mold includes: the cylindrical die cavity, the upper punch, the lower punch, the positioning circular truncated cone, the heat insulation gasket and the positioning gasket are all made of graphite because the graphite has the advantages of strong conductivity, high temperature resistance, easiness in processing and the like. The main body of the cylindrical die cavity is a cylinder, a temperature measuring hole with the depth of 8mm is formed in the surface of the outer circle of the cylinder, and a through cavity structure is arranged at the axis of the cylinder and used for positioning the upper graphite punch and the lower graphite punch and storing powder materials. The upper punch and the lower punch are cylinders with the same size and shape, the upper punch and the lower punch are sequentially placed on the upper side and the lower side of the cylindrical die cavity in the installation process, powder to be sintered is placed in the middle, and high-temperature lubricants such as graphite paper, boron nitride and the like are placed at the positions where the upper punch and the lower punch are in contact with the powder in the cylindrical die cavity and used for demoulding of materials after sintering. The main body of the positioning circular truncated cone is a circular truncated cone, and a circle of protruding structures are sequentially arranged on the upper surface and the lower surface of the circular truncated cone. The positioning circular truncated cone is arranged between the punch and the heat insulation gasket and used for limiting the movement between the upper punch and the lower punch and the heat insulation gasket and ensuring the concentricity of the sintering die system. The heat insulation gasket is a cylindrical gasket, is arranged between the positioning circular truncated cone and the table top with the larger diameter and the positioning gasket, and is used for isolating the cylindrical die cavity from heating. The positioning gasket is a cylindrical gasket, and the outer rings of the upper end face and the lower end face of the positioning gasket comprise a convex structure for ensuring the concentricity of the heat insulation gasket and the upper pressure head and the lower pressure head.

The pressurizing system consists of an upper pressure head capable of conducting electricity and a control system, the control system consists of a displacement control system and a pressure controller, the displacement control system detects the displacement of the upper pressure head through a grating ruler, and the detection result of a sensor is used as a feedback signal to control the motor to act; the pressure controller detects the pressure of the upper pressure head and the lower pressure head through the pressure sensor, so that the function of the pressurization system is realized. The upper pressure head can realize axial movement with the stroke of 25mm, and can provide 3t of pressure in the axial direction at most.

The power of the direct current pulse power supply is 30kW, and 0-3000A of pulse current can be instantaneously output to provide temperature for the sintering material.

The ultrasonic generating system consists of a ceramic ultrasonic transducer, an amplitude transformer, a bracket and an electric box, and is arranged on the outer side of the vacuum furnace through the bracket and used for fixing the ultrasonic transducer and the amplitude transformer; the transducer can convert current into ultrasonic vibration, and the ultrasonic vibration is amplified by the amplitude transformer and acts on a workpiece.

The temperature control system measures the temperature of the die through the thermal infrared imager and then controls the output power of the direct-current pulse power supply as a feedback signal.

The vacuum system comprises a vacuum furnace, a vacuum pump, a vacuum breaking valve and the like and is used for vacuumizing and ensuring a vacuum environment in the sintering process.

In some embodiments, the cylindrical cavity and the upper and lower dies may be made of electrically conductive materials such as hot-work die steel, high-temperature alloys, etc. when the sintering temperature is not high, and carbon-carbon composites, electrically conductive ceramics, etc. may be used as the die material when the sintering temperature is high.

In some embodiments, the thermometry is thermocouple thermometry. A large temperature measuring hole and a small temperature measuring hole are formed in the cylindrical die cavity, and the temperature of powder in the die cavity is measured by aligning the thermal infrared imager with the large temperature measuring hole or extending the thermocouple into the small temperature measuring hole.

In some embodiments, the mold may be a multi-cavity mold, i.e., one mold is provided with a plurality of cavities, and the compaction of the powder is performed by the integrated upper and lower punches, so that a plurality of sintered bodies can be simultaneously prepared.

The invention also provides a multi-energy field auxiliary sintering method for the difficult-to-deform material sintered body by using the device, which comprises the following steps:

step 1: preparing sintered powder, selecting a proper mould, coating a high-temperature lubricant on the contact part between the punch die and the powder inside the cylindrical mould cavity, then filling the powder inside the cylindrical mould cavity, and wrapping heat-insulating cotton outside the mould.

Step 2: sequentially loading the positioning gasket, the heat insulation gasket, the positioning circular truncated cone, the punching die and the cylindrical die cavity into a working position according to the installation sequence; the position and the height of the cylindrical die cavity are adjusted, so that the temperature measuring hole can be accurately aligned to the thermal infrared imager, and the temperature can be accurately measured.

And step 3: the positions of the upper pressure head and the die are adjusted to ensure that the upper pressure head and the die are coaxial. The upper pressure head is lowered to pre-compress the powder to eliminate the large volume voids in the powder.

And 4, step 4: and closing the furnace door of the vacuum furnace, opening a vacuum pump, and vacuumizing by using the vacuum pump to ensure that the powder in the cylindrical mold cavity reaches the required vacuum degree.

And 5: loading axial pressure on the powder by using a pressurizing system; opening the direct current pulse current, setting a given current parameter, and performing closed-loop control on the current parameter according to a temperature measurement result of the temperature control system; and opening the ultrasonic generating system, and adjusting the electric box to enable the vibration frequency to reach a target value. Controlling current parameters to complete the stages of temperature rise, heat preservation and temperature reduction according to a set loading route, keeping a pressurizing system, a pulse power supply, an ultrasonic generating system and a vacuum pump working in the whole sintering process, and completing powder solid phase sintering under the assistance of a multi-energy field.

And 6: and after sintering, closing the pressurizing system, the direct current pulse power supply and the ultrasonic generating system power supply, and opening the vacuum breaking valve to enable the pressure in the furnace to reach the atmospheric pressure state. And lifting the upper pressure head, opening the furnace door, taking out the sintered test piece, and cooling the test piece in the air to obtain a sintered blank.

In some embodiments, the high temperature lubricant may be selected from boron nitride, graphite spray, graphite paper, and the like; if the graphite paper is selected, the thickness of the graphite paper is selected according to the matching degree of the punch die and the hole, and the graphite paper with the thickness of 1-2mm and the punch are used for manufacturing a graphite paper gasket to be placed between the punch and the powder.

In some embodiments, after sintering, the test piece can be placed in a vacuum furnace to be cooled along with the furnace, and after cooling, vacuum breaking is performed to take out the test piece. The furnace cooling mode can prevent the surface of the sintered test piece from being oxidized, but the production efficiency is lower than that of air cooling.

In some embodiments, the vacuum is less than 10 degrees f ^-3 Pa, the pressure of a pressurizing system is 30-80MPa, the ultrasonic vibration frequency is 15-40kHz, the amplitude is 5-10 mu m, and the heat preservation time is 300-900s. In some embodiments, the powder is heated at a rate of 100 to 250 deg.C/min.

The invention has the beneficial effects that:

1) The invention fully utilizes the coupling effect of the multi-energy field, shortens the sintering pressure maintaining time to 5-15min, obviously improves the production efficiency, and shortens the sintering time by more than 90 percent compared with the existing hot isostatic pressing.

2) According to the invention, by introducing the pulse current, an energy field of the impressed current directly acts on the powder to be sintered, heating through a resistance wire is not required, the energy transmission process is simplified, and energy consumption can be remarkably saved.

3) The invention introduces the ultrasonic vibration energy field, and the external vibration energy field directly acts on the sintering powder, so that the formation of larger holes and pores among powder particles can be obviously avoided in the sintering process, and the sintering density can be improved.

4) The invention is coupled with the action of a multi-energy field, the grain size of the sintered material is controllable, the coarsening of the grains can be obviously inhibited, the prepared blank has high densification degree, uniform microstructure and good mechanical property, and the comprehensive performance of the material is obviously improved.

5) The invention provides a multi-energy field auxiliary sintering device for a material difficult to deform, which integrates a pulse current, ultrasonic vibration and other special energy field generating devices, and has the advantages of compact structure and high integration degree.

Drawings

FIG. 1 is a schematic diagram of a multi-energy field-assisted sintering forming process.

FIG. 2 is a schematic structural view of a multi-energy field-assisted sintering apparatus according to example 1 of the present invention.

FIG. 3 is a schematic view of a cylindrical sintering mold according to example 1 of the present invention.

FIG. 4 is a schematic view of a gear sintering die in embodiment 2 of the present invention.

FIG. 5a is a schematic drawing of a sintered cylinder according to the present invention.

FIG. 5b is a schematic illustration of a sintered gear blank in accordance with the present invention.

FIG. 6 is a schematic diagram of a microscopic secondary electron morphology phase of a sintered cylinder in accordance with the present invention.

The numbers in the figures illustrate the following:

the device comprises a sintering mould 1, a pressurizing system 2, a direct current pulse power supply 3, an ultrasonic generating system 4, a temperature control system 5 and a vacuum system 6;

a cylindrical die cavity 11, an upper punch 12 and a lower punch 13 of a gear die cavity 11', a positioning circular table 14, a heat-insulating gasket 15,

Positioning gaskets 16 and a wedge-shaped die 17;

an upper ram 21; a ceramic ultrasonic transducer 41, a horn 42, a holder 43; a vacuum furnace 61 and a vacuum breaking valve 63.

Detailed Description

In order to make the technical means, device characteristics, objectives and functions of the present invention easy to understand, the present invention will be further described with reference to the accompanying drawings and examples. It is to be understood that the disclosed embodiments are merely exemplary of the invention, and are not intended to limit the invention to the precise embodiments disclosed. The examples described below are intended to facilitate the understanding of the invention without having any limiting effect thereon.

The invention mainly combines the advantages of powder metallurgy and multi-energy field auxiliary manufacturing technology in the aspect of shape cooperative control, and provides a multi-energy field auxiliary sintering technical method for a material difficult to deform, which is shown in figure 1. The multi-energy field-assisted sintering method combines respective advantages of an electric field activation sintering process and ultrasonic vibration-assisted forming, utilizes heat generated by strong current when low-voltage pulse current passes through powder particles to melt particle interfaces to form a solid-liquid mixed state, and applies extrusion force to manufacture parts with compact tissues. During sintering, current tends to flow through the regions where the resistance is small. In the initial stage of sintering, the gaps between the alloy powders are large, the resistance is large, and only a small amount of current is discharged and conducted through the particle contact surface. Therefore, the graphite die has high current density and high heat productivity, and can heat the alloy powder. Under the assistance of the ultrasonic vibration effect, the powder is axially vibrated, so that the originally existing larger gap is gradually reduced until the larger gap disappears; under the action of the temperature field, the yield strength of the powder is reduced, and plastic deformation is facilitated to occur; under the action of pressure, the powder particles are subjected to plastic deformation, and the distance between the powder particles is closer and closer, so that the discharge effect among the powder particles is facilitated, and the current density at the powder position is further increased. In the later stage of sintering, through the coupling action of the ultrasonic vibration field, the pressure field, the temperature field and the pulse current, the powder is gradually sintered and compacted, and more discharge effects can also appear among powder particles. The discharge shock wave generated by pulse discharge, electrons and ions flow at high speed in an electric field, and an oxide layer on the surface of powder particles can be broken down to a certain extent, so that the powder is purified; on the other hand, the instantaneous high temperature of the discharge can generate a large amount of joule heat at the contact position of the powder particles, and promote the gasification and diffusion of the powder particle atoms. This diffusion phenomenon is further amplified by the ultrasonic vibration, causing sintering necks to grow from powder particle to particle. As the multi-energy field-assisted sintering proceeds, the sintering necks grow and eventually join together, during which the electrical resistance of the powder regions also gradually decreases and the current density of the powder regions increases. At the moment, the electric field intensity is high and covers the whole powder, the discharge effect is severe, the self-heating effect of the particles is obvious, the heating particles are uniformly distributed in the whole powder under the condition of the assistance of the ultrasonic vibration field, and the powder area becomes a main heating area. The sintering process is rapidly and uniformly densified by the assistance of the multi-energy field, and the multi-energy field-assisted sintering can obviously inhibit the generation of internal defects of a sintered body.

Fig. 2 is a schematic structural diagram of a multi-energy-field assisted sintering device for a material difficult to deform according to the present invention, including: the device comprises a sintering mould 1, a pressurizing system 2, a direct current pulse power supply 3, an ultrasonic generating system 4, a temperature control system 5 and a vacuum system 6. The sintering mold comprises: the device comprises a cylindrical die cavity 11, an upper punch 12, a lower punch 13, a positioning circular truncated cone 14, a heat insulation gasket 15 and a positioning gasket 16; the pressurization system comprises: an upper ram 21; the ultrasonic wave generation system includes: a ceramic ultrasonic transducer 41, a horn 42, a holder 43; the vacuum system includes: a vacuum furnace 61 and a vacuum breaking valve 63.

The input current of the direct current pulse power supply 3 is 220/380V alternating current which is used daily, and low-voltage pulse current of 0-3000A can be instantly output through rectification, filtering, voltage stabilization and the like. By controlling the frequency of the pulse current, different sintering effects are also produced on the sintered body (powder) heating. For the ultrasonic generation system 4, one end of the bracket 43 is fixed on the vacuum furnace through 8 evenly distributed bolts on the flange, and the other end is connected with the amplitude transformer 42 through 4 evenly distributed bolts on the flange. A thinner wave-insulating material is provided between the flange of the bracket and the horn 42 to avoid variations in the amplitude and mode of vibration of the horn. The lower end of the bracket is provided with a mounting hole for enabling the upper end of the amplitude transformer 42 to penetrate through the mounting hole to be connected with the lower pressure head to conduct ultrasonic vibration. The lower end of the amplitude transformer 42 is connected with the ceramic ultrasonic transducer 41, the daily used 220/380V alternating current is converted into an ultrasonic frequency oscillation electric signal of 15-40KHz by a special ultrasonic power supply, then the received ultrasonic frequency oscillation electric signal is converted into longitudinal ultrasonic frequency mechanical vibration by a lead zirconate titanate PZT-8 piezoelectric ceramic element, and the vibration amplitude is amplified by the amplitude transformer 42 so as to achieve ultrasonic vibration conditions with different amplitudes. The ultrasonic amplitude is calibrated by a mechanical vibration measuring device and can be adjusted in real time within the range of 5-10 mu m. In particular, the vibration generated by the ceramic ultrasonic transducer 41 is concentrated at the top end, i.e., the contact position with the lower pressure head, by the maximum amplitude after being applied by the horn 42. The powder is transmitted by the lower pressure head and then acts on the sintering die 1 and the powder (sintering body), so that a pressure field, a pulse current field and ultrasonic vibration can be coupled and act on a sintered test piece together, and the sintering process under the auxiliary action of a multi-energy field is completed.

The vacuum system comprises electromagnetic valves V1, V2, V3 and V4, a backing pump P1 and a molecular pump P2. The backing pump P1 has a relatively large displacement and is used to maintain the backing pressure of the vacuum pump below its critical backing pressure. The molecular pump P2 has high rotation speed and small exhaust amount and is placed at the next stage of P1. P2 is a vacuum pump which uses a rotor rotating at a high speed to transfer momentum to gas molecules, so that the gas molecules obtain a directional speed, are compressed and are driven to an exhaust port, and then are pumped away as a preceding stage. In the vacuum-pumping stage, firstly, locking a vacuum furnace door; then starting a backing pump P1 and an upper valve V1, and enabling the backing pump P1 to pump out most of gas in the vacuum furnace; opening a lower valve V2 every 3 minutes to allow P1 to pump out gas in the vacuum pipeline; and after the vacuum degree is pumped to 5pa, starting the molecular pump P2, closing the V1 and opening the V3 after the rotating speed is normally and completely started, so that the molecular pump continuously improves the vacuum degree of the vacuum furnace. In the vacuum breaking stage, the molecular pumps P2 and V3 are closed, and after the rotating speed of P2 is reduced, the molecular pumps V2 and P1 are closed; the vacuum breaking valve V4 is opened after the furnace door lock is unscrewed.

Implementing a cylindrical die:

fig. 3 is a schematic diagram of a cylindrical sintering die, which includes a cylindrical die cavity 11, an upper punch 12, a lower punch 13, a positioning circular truncated cone 14, a heat insulation gasket 15, and a positioning gasket 16. Wherein the outer diameter of the upper punch and the lower punch is equal to the inner bore diameter of the cylindrical die cavity 11 and the bore diameter of the positioning circular truncated cone 14, and clearance fit is adopted, so that the installation and demoulding are convenient. The powder is loaded inside the cylindrical die cavity 11 between the upper punch 12 and the lower punch 13, and the size of the cylindrical blank after sintering is equal to the outer diameter of the punches. The sum of the lengths of the upper punch and the lower punch is equal to the length of the cylindrical die cavity, the upper punch and the lower punch are preferably equal to the cylindrical die cavity, if the length is too short, the phenomenon of incompactness can be caused when a short cylinder is sintered, and if the length of the punches is too long, the rigidity is poor and the punches are easy to damage. The diameter of the heat insulation gasket 15 is equal to the diameter of the pressure head, and the heat insulation gasket is made of a conductive heat insulation material, so that the heat of the mold is insulated while the current conduction is ensured, and the phenomenon of overheating of the pressure head or the pulse power supply electrode is prevented. The positioning gasket 16 is made of graphite, the diameter of the positioning gasket is larger than that of the heat insulation gasket and the pressure head, and cylindrical pits are respectively sunken on two sides of the positioning gasket and used for positioning the pressure head and the sintering mold to ensure that the pressure head and the mold are concentric in the working process and the pressure is uniformly applied to the mold.

In this example, a GH4169 superalloy blank having a diameter of 10mm and a height of 10mm was prepared by sintering using the apparatus described above with reference to FIG. 3, wherein the cylindrical cavity 11 had an outer diameter of 40mm, a height of 50mm, and a central through hole diameter of 10mm. The upper punch 12 and the lower punch 13 have a diameter of 10mm and a length of 25mm, and are made of graphite. The specific preparation process of the blank comprises the following steps:

step 1: preparing GH4169 high-temperature alloy powder, and selecting a proper die

The GH4169 high-temperature alloy powder is mainly prepared by a ball milling method. Commercial grade GH4169 powder was placed in a teflon ball mill pot of 115mm diameter, zirconium balls of 20mm diameter were added, and the powder was sieved after ball milling to control the powder particle diameter. And selecting a cylindrical sintering mold for standby.

Step 2: pouring GH4169 high-temperature alloy powder, and installing a cylindrical sintering die

Spraying high-temperature lubricant graphite, spraying the graphite on the inner hole of the cylindrical die cavity and the surface of the punch, filling GH4169 high-temperature alloy powder prepared in the step 1 into the inner hole of the cylindrical die cavity after the surfaces are dried, and wrapping heat insulation cotton outside the die. The die is sequentially installed according to the installation sequence, the positions of the upper pressure head and the die are adjusted, and the coaxiality of the upper pressure head and the die is ensured.

And step 3: prepressing the sintering mould

The upper pressure head is lowered to pre-compress the powder to eliminate the large volume voids in the powder.

And 4, step 4: preparation of vacuum Environment

Closing the door of the vacuum furnace 61, opening the vacuum pump, and vacuumizing by using a vacuum system until the vacuum degree in the vacuum furnace 61 is 10 ^{- 3} Pa or less.

And 5: multi-energy field application and heat-preservation sintering

The upper pressure head is controlled to descend through a pressurizing system, and the powder is pre-pressurized for 0.1 t. The pulse current parameters are controlled to raise the temperature of GH4169 to 950 ℃. And (3) starting an ultrasonic generation system while heating, and increasing the pressure of a pressurization system to enable the powder to be pressurized to 35MPa, namely the pressure of the pressurization system is 0.2805t.

And measuring the temperature inside a temperature measuring hole of the die by using an infrared thermal imager in the temperature control system, inputting a measurement result serving as a feedback signal into the control system so as to adjust the pulse current parameter, controlling the temperature of the powder to 950 ℃, and simultaneously keeping the axial pressure of 35MPa and sintering for 5min.

And 6: the sintering system is closed and cooled along with the furnace

And after the sintering heat-preservation pressure-maintaining stage is finished, closing the pulse power supply, the ultrasonic vibration and the pressure of the pressure system to cool the GH4169 high-temperature alloy sintered product along with the furnace, breaking the vacuum after the blank is cooled, lifting the upper pressure head, and taking out the sintering mold.

The sintered GH4169 superalloy article in the example is shown in FIGS. 5a and 5b, and the SEM secondary morphology phase diagram of the microstructure is shown in FIG. 6, and it can be seen that the bonding condition among most powder particles is good, the number of generated voids is small, and the sintered density of the microstructure is good.

Implementing a gear mold:

fig. 4 is a schematic diagram of a gear sintering die, which comprises a gear die cavity 11', an upper punch 12, a lower punch 13, a positioning circular truncated cone 14, a heat insulation gasket 15, a positioning gasket 16 and a wedge-shaped die 17. A tapered hole is arranged in the gear die cavity 11', the taper of the tapered hole is the same as that of the wedge-shaped die, and the tapered hole is used for positioning and clamping the wedge-shaped die when an upper pressure head presses down and ensuring the concentricity. The powder is loaded between an upper punch 12 and a lower punch 13 inside a wedge die 17, the wedge die 17 is composed of two identical parts and is installed in a tapered hole on a gear die cavity 11', each die is provided with a half tooth-shaped groove, and the two parts are combined to form a complete tooth shape. The tooth profile is the same as the shapes of the upper punch and the lower punch and the shaped gear, a round hole is formed in the positioning round platform 14, and the aperture of the round hole is larger than the diameter of the addendum circle of the gear so as to facilitate installation and positioning.

In this example, a 5mm high-temperature GH4169 alloy blank was sintered and formed by the apparatus described above with reference to FIG. 4, wherein the height of the gear cavity 11' was 50mm. The upper punch 12 and the lower punch 13 are 25mm in length and made of graphite. The sintering condition is that the pressure is maintained for 10min under the conditions of the sintering temperature of 900 ℃ and the pressure of 40MPa by the assistance of a multi-energy field, the specific preparation process of the blank is the same as that of the cylindrical example, and the sintered product is shown in figures 5a and 5 b.

Claims (10)

1. A multi-energy field auxiliary sintering device for a material difficult to deform comprises: the device comprises a sintering mould, a pressurizing system, a direct-current pulse power supply, an ultrasonic generating system, a temperature control system and a vacuum system; the method is characterized in that:

the sintering mold includes: the device comprises a cylindrical die cavity, an upper punch, a lower punch, a positioning circular table, a heat insulation gasket and a positioning gasket; the main body of the cylindrical die cavity is a cylinder, the outer circle surface of the cylinder is provided with a temperature measuring hole, and the axis of the cylinder is provided with a through cavity structure for positioning the upper graphite punch and the lower graphite punch and storing powder materials; the upper punch and the lower punch are both cylinders with the same size and shape; the upper punch and the lower punch are sequentially arranged on the upper side and the lower side of the cylindrical die cavity, the powder to be sintered is arranged in the middle, and the high-temperature lubricant is arranged at the positions where the upper punch, the lower punch and the cylindrical die cavity are in contact with the powder and is used for demoulding the sintered material; the positioning circular truncated cones are arranged between the upper punch and the lower punch and the heat insulation gasket and used for limiting the movement between the upper punch and the lower punch and the heat insulation gasket and ensuring the concentricity of the sintering die system; the heat insulation gasket is a cylindrical gasket, is arranged between the table top with the larger diameter of the positioning circular truncated cone and the positioning gasket and is used for isolating the heating of the cylindrical die cavity;

the pressurizing system consists of an upper pressure head capable of conducting electricity and a control system, the control system consists of a displacement control system and a pressure controller, the displacement control system detects the displacement of the upper pressure head through a grating ruler, and the detection result of a sensor is used as a feedback signal to control the motor to act; the pressure controller detects the magnitude of the pressure of the upper pressure head and the lower pressure head through the pressure sensor to realize the function of a pressurization system;

the direct current pulse power supply provides temperature for the sintering material;

the ultrasonic generating system consists of a ceramic ultrasonic transducer, an amplitude transformer, a bracket and an electric box, and is arranged on the outer side of the vacuum furnace through the bracket and used for fixing the ultrasonic transducer and the amplitude transformer; the transducer converts current into ultrasonic vibration, and the ultrasonic vibration is amplified by the amplitude transformer and acts on a workpiece;

the temperature control system measures the temperature of the die through the thermal infrared imager and then controls the output power of the direct-current pulse power supply as a feedback signal;

the vacuum system consists of a vacuum furnace, a vacuum pump and a vacuum breaking valve and is used for vacuumizing and ensuring the vacuum environment in the sintering process.

2. The multi-energy field-assisted sintering device for the difficultly deformable material as claimed in claim 1, wherein: the main body of the positioning circular truncated cone is a circular truncated cone, and a circle of protruding structures are sequentially arranged on the upper surface and the lower surface of the circular truncated cone; the positioning gasket is a cylindrical gasket, and the outer rings of the upper end face and the lower end face of the positioning gasket comprise a convex structure for ensuring the concentricity of the heat insulation gasket and the upper pressure head and the lower pressure head.

3. The multi-energy field-assisted sintering device for the difficultly deformable material as claimed in claim 1, wherein: the upper pressure head realizes axial movement with the stroke of 25mm, and provides 3t of pressure at most along the axial direction; the power of the direct current pulse power supply is 30kW, and 0-3000A of pulse current is instantaneously output.

4. The multi-energy field-assisted sintering device for the difficultly deformable material as claimed in claim 1, wherein: when the sintering temperature is not high, hot-working die steel and high-temperature alloy conductive materials are adopted to prepare a cylindrical die cavity, an upper die and a lower die; when the sintering temperature is high, carbon-carbon composite materials and conductive ceramics are used as the die materials.

5. The multi-energy field-assisted sintering device for the difficultly deformable material as claimed in claim 1, wherein: the temperature measurement mode is thermocouple temperature measurement; a large temperature measuring hole and a small temperature measuring hole are formed in the cylindrical die cavity, and the temperature of powder in the die cavity is measured by aligning the large temperature measuring hole with a thermal infrared imager or extending a thermocouple into the small temperature measuring hole.

6. The multi-energy field-assisted sintering device for the difficultly deformable material as claimed in claim 1, wherein: the sintering mould is made of graphite; the sintering mold adopts a multi-cavity mold, namely, one mold is provided with a plurality of cavities, the powder is compacted by an integrated upper punch and an integrated lower punch, and a plurality of sintered bodies are prepared at the same time.

7. A multi-energy field auxiliary sintering method for a material difficult to deform comprises the following steps:

step 1: preparing sintering powder, selecting a proper mould, coating a high-temperature lubricant on the contact part of the punching die and the cylindrical mould cavity with the powder, filling the powder into the cylindrical mould cavity, and wrapping heat-insulating cotton outside the mould;

and 2, step: sequentially loading a positioning gasket, a heat insulation gasket, a positioning circular truncated cone, a punching die and a cylindrical die cavity into a working position; the position and the height of the cylindrical mold cavity are adjusted, so that the temperature measuring hole can be accurately aligned to the thermal infrared imager, and the temperature can be accurately measured;

and 3, step 3: adjusting the positions of the upper pressing head and the die to ensure that the upper pressing head and the die are coaxial; descending an upper pressure head, pre-pressing the powder, and removing large-volume gaps in the powder;

and 4, step 4: closing the furnace door of the vacuum furnace, opening a vacuum pump, and vacuumizing by using the vacuum pump to ensure that the powder in the cylindrical mold cavity reaches the required vacuum degree;

and 5: loading axial pressure on the powder by using a pressurizing system; opening the direct current pulse current, setting a given current parameter, and performing closed-loop control on the current parameter according to a temperature measurement result of the temperature control system; opening an ultrasonic generation system, and adjusting an electric box to enable the vibration frequency to reach a target value; controlling current parameters to complete heating, heat preservation and cooling stages according to a set loading route, keeping a pressurizing system, a pulse power supply, an ultrasonic generating system and a vacuum pump working in the whole sintering process, and completing powder solid phase sintering under the assistance of a multi-energy field;

step 6: after sintering is finished, closing a pressurizing system, a direct current pulse power supply and an ultrasonic generating system power supply, and opening a vacuum breaking valve to enable the pressure in the furnace to reach an atmospheric pressure state; and lifting the upper pressure head, opening the furnace door, taking out the sintered test piece, and cooling the test piece in the air to prepare a sintered blank.

8. The multi-energy field-assisted sintering method for the hard-to-deform material according to claim 7, characterized in that: the high-temperature lubricant is selected from boron nitride, graphite spray or graphite paper; if the graphite paper is selected, the thickness of the graphite paper is selected according to the matching degree of the punch die and the hole, and the graphite paper with the thickness of 1-2mm and the punch are used for manufacturing a graphite paper gasket to be placed between the punch and the powder.

9. The multi-energy field-assisted sintering method for the difficultly deformable material as claimed in claim 7, wherein the method comprises the following steps: after sintering, placing the test piece in a vacuum furnace to cool along with the furnace, breaking vacuum after cooling, and taking out the test piece; the furnace cooling mode is to prevent the surface of the sintered test piece from oxidation.

10. The multi-energy field-assisted sintering method for the hard-to-deform material according to claim 7, characterized in that: the vacuum degree is less than 10 ^-3 Pa, the pressure of a pressurizing system is 30-80MPa, the ultrasonic vibration frequency is 15-40kHz, the amplitude is 5-10 mu m, and the heat preservation time is 300-900s; the heating rate of the powder is 100-250 ℃/min.

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