CN109226954B - Diffusion connection method for Ti-Al alloy annular parts - Google Patents

Diffusion connection method for Ti-Al alloy annular parts Download PDF

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CN109226954B
CN109226954B CN201811223935.0A CN201811223935A CN109226954B CN 109226954 B CN109226954 B CN 109226954B CN 201811223935 A CN201811223935 A CN 201811223935A CN 109226954 B CN109226954 B CN 109226954B
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tial
alloy
alnb
furnace
diffusion
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CN109226954A (en
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李金山
张晓强
唐斌
朱雷
寇宏超
王军
王毅
孙智刚
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Northwestern Polytechnical University
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    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
    • B23K20/02—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating by means of a press ; Diffusion bonding
    • B23K20/023—Thermo-compression bonding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
    • B23K20/14—Preventing or minimising gas access, or using protective gases or vacuum during welding
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
    • B23K20/22—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating taking account of the properties of the materials to be welded
    • B23K20/233—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating taking account of the properties of the materials to be welded without ferrous layer
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
    • B23K—SOLDERING OR UNSOLDERING; WELDING; CLADDING OR PLATING BY SOLDERING OR WELDING; CUTTING BY APPLYING HEAT LOCALLY, e.g. FLAME CUTTING; WORKING BY LASER BEAM
    • B23K20/00—Non-electric welding by applying impact or other pressure, with or without the application of heat, e.g. cladding or plating
    • B23K20/24—Preliminary treatment

Abstract

A method for diffusion bonding of Ti-Al alloy ring-shaped parts is characterized in that the size of thermal stress is controlled by controlling the cooling rate in a high-temperature interval, so that a joint is prevented from being damaged at high temperature; the effect of eliminating partial residual stress can be achieved by ladder heat preservation in a high-temperature interval, and cracking of a connecting interface caused by overlarge final residual stress is avoided. The invention provides a method for preventing the diffusion bonding cracking completely comprising the whole process from processing to diffusion bonding, detects the flaw at the key node, and is beneficial to more accurately realizing process monitoring in the actual production process, more clearly judging the link of problem generation and realizing process adjustment. The invention also provides reference for welding other alloy annular structural members and preventing welding cracks from being generated by other welding methods of Ti-Al alloy.

Description

Diffusion connection method for Ti-Al alloy annular parts
Technical Field
The invention relates to diffusion bonding of intermetallic compounds, in particular to a method for preventing cracks from generating in the processes of processing and diffusion bonding of a Ti-Al alloy annular part.
Background
The Ti-Al intermetallic compound has the characteristics of low density, high specific strength, good oxidation resistance and the like, is an ideal light high-temperature metal structure material, and has wide application prospect in the fields of aeroengines, aerospace aircrafts and the like. Wherein the TiAl alloy can be used at a temperature of 700-900 ℃ and Ti2The service temperature of the AlNb alloy can reach 650 ℃. However, Ti-Al alloys have intrinsic brittleness and difficult workability, and are prone to induce residual stress during machining, which may cause cracks in subsequent processes, and limit the applications thereof. The base material does not need to be melted in the diffusion connection, and the diffusion connection can effectively reduceThe method is an effective method for realizing the connection of the dissimilar alloy complex structural members, but the influence of the thermal stress and the residual stress on the subsequent use of the connecting piece can not be completely eliminated. Thus avoiding TiAl/Ti2The generation of cracks in the AlNb alloy in the machining process and the control of the residual stress in the connection process of the annular structural member are the keys for preventing welding cracks. The size and distribution of the residual stress of the connecting piece with the annular structure are greatly different from those of the conventional structure due to the structural particularity of the connecting piece, and the control and the elimination of the residual stress are more difficult. Researchers have made relevant studies on the problem, analyzed the magnitude and distribution of residual stress during the processing and diffusion bonding processes, and proposed control and elimination methods.
The literature, "expansion differential pressure method diffusion bonding residual stress numerical simulation" researches the diffusion bonding of titanium alloy (Ti-6Al-4V) and copper alloy (QA110-3-1.5) cylindrical parts. Under the condition of 850-60 min-10 μm clearance fit process, the diffusion connection of the titanium alloy and the copper alloy cylindrical part is realized, but an obvious unwelded area exists on a contact interface close to the end face, and the residual stress is larger. The method utilizes the fact that the expansion coefficient of the outer layer metal Ti-6Al-4V alloy is small, and the expansion pressure difference with proper size can be obtained in the heating process through simple clearance assembly. However, in the diffusion bonding cooling stage, the method generates large residual tensile stress on the diffusion bonding interface, and the diffusion bonding interface is easy to crack after welding.
The invention patent of CN107745178A by shang and et al, northwest university of industry, proposes a method for diffusion bonding an outer layer TiAl alloy rim with a special fixture by using an expansion pressure difference generated during heating. The method utilizes a clamp to realize partial limitation on expansion of the TiAl alloy wheel rim, so that the TiAl alloy wheel rim is opposite to Ti2The AlNb has small expansion, and generates expansion pressure difference on an interface to realize diffusion connection. Although the method can realize diffusion connection of annular parts with larger expansion coefficient of outer layer metal, the overall stress ratio is larger, partial residual stress can be eliminated even if the annular parts are cooled to 800 ℃ and kept for 30min, and TiAl alloy rim final residual stressThe force is still close to 200MPa and may have detrimental effects on subsequent heat treatment and machining.
At present, for TiAl/Ti2The research on residual stress in the AlNb alloy processing and diffusion bonding process is not deep enough, and generally only the residual stress in the diffusion bonding process is considered, but the phenomenon that the residual stress possibly exists in the processing process to cause cracking is ignored. Therefore, it is necessary to consider the residual stress in the processing process and the diffusion bonding process and the factors causing cracking such as oxidation, etc. comprehensively, to make a proper process to control the residual stress in the whole process and prevent TiAl/Ti2The AlNb ring structure diffusion bond developed cracks.
Disclosure of Invention
In order to solve the problem that cracking is caused by only considering the residual stress in the diffusion connection process and neglecting the residual stress in the machining process in the prior art, the invention provides a method for diffusion connection of a Ti-Al alloy annular piece.
The specific process of the invention is as follows:
the method comprises the following steps: TiAl/Ti2Processing of AlNb alloy diffusion connecting piece
The TiAl/Ti2The AlNb alloy diffusion connecting piece comprises a TiAl alloy rim and Ti2AlNb alloy wheel core.
Wherein the TiAl rim inner diameter surface and Ti2The outer diameter surface of the AlNb wheel core is the connecting interface of the two. The TiAl rim inner surface and Ti2The outer surfaces of the AlNb wheel cores are all provided with 3-degree interface inclination angles.
Before the working, the cake as a raw material is subjected to stress relief annealing. The annealing process parameters are as follows: heating to 850 ℃ at the heating rate of 6 ℃/min, preserving heat for 2-6 h and cooling along with the furnace.
The continuity of the whole processing process is ensured in the processing, the interval between different processing procedures is not more than 12h, if the time interval of more than one week exists between the processing procedures, the TiAl alloy wheel rim and Ti are required to be processed2And performing stress relief annealing on the AlNb alloy wheel core. The technological parameters of the stress relief annealing are the same as the annealing technological parameters of the raw materials.
In the gap of each processing procedure, the workpiece is processed,a TiAl alloy rim and Ti2Soaking the AlNb alloy wheel core in alcohol; in the surface fine polishing process, cooling oil is required to be coated on the surface so as to reduce the influence of heat generation on an interface, and the surface cooling oil is reserved so as to ensure that the surface is not polluted and oxidized by impurities in the subsequent transportation process. And (5) flaw detection is carried out after the test piece is processed.
Step two: and (4) pre-processing of assembly.
The pre-assembly treatment comprises TiAl/Ti2The surface treatment of the AlNb alloy diffusion connecting piece and the treatment of the upper and lower graphite pressure heads in the clamp and the vacuum diffusion connecting furnace.
For TiAl/Ti2The surface of the AlNb alloy diffusion connecting piece is treated by surface pickling the surface of the TiAl rim and Ti2The surface of the AlNb wheel core is subjected to oxide layer removal treatment;
the surface of the pair of TiAl rims and Ti2The specific process of carrying out the oxide layer removing treatment on the surface of the AlNb wheel core comprises the following steps:
ultrasonic cleaning: a TiAl alloy rim and Ti2And immersing the AlNb alloy wheel core test piece into acetone for ultrasonic degreasing for 15min, and then immersing into absolute ethyl alcohol for ultrasonic cleaning for 5 min.
Acid washing: and adopting TiAl alloy pickling solution to pickle the TiAl alloy wheel rim for 1 min. By using Ti2Pickling solution of AlNb alloy for Ti2And acid washing the AlNb wheel core for 1 min. If TiAl alloy rim or Ti is coated in the pickling process2The acid-washed surface of the AlNb wheel core obviously turns black, and the AlNb wheel core needs to be taken out immediately and washed by alcohol, and is transferred to a vacuum diffusion connecting furnace for assembly immediately after the alcohol is dried by a blower.
The TiAl alloy pickling solution adopts HNO3HF and distilled water; HNO3HF, distilled water in a ratio of 1:1: 10; the ratio is volume ratio.
The Ti2The AlNb alloy pickling solution also adopts HNO3HF and distilled water; HNO3HF is distilled water in the ratio of 1:1: 50.
The treatment of the fixture and the upper and lower graphite press heads in the vacuum diffusion connecting furnace is to smear a solder stopping agent on the inner side surface of the fixture and the surfaces of the upper graphite press head and the lower graphite press head in the vacuum diffusion connecting furnace.
Step three: clamp and TiAl/Ti2Assembly of AlNb alloy diffusion connecting piece
Assembling silicon nitride/TiAl rim/Ti2When the AlNb wheel core is used, the TiAl wheel rim is placed in the inner cavity of the clamp, the outer circumferential surface of the TiAl wheel rim is in clearance fit with the inner circumferential surface of the clamp, and the Ti is put into the inner cavity of the clamp2An AlNb wheel core is placed in the central hole of the TiAl wheel rim and the inner circumferential surface of the TiAl wheel rim is connected with the Ti2The outer circumferential surface of the AlNb wheel core is attached. The gap between the outer circumferential surface of the TiAl rim and the inner circumferential surface of the jig was 0.2 mm.
Before the clamp is used, the clamp is required to be placed in a vacuum diffusion connecting furnace for heating and air release; heating and degassing by placing the fixture in a vacuum diffusion bonding furnace at 5 × 10-2Heating the vacuum diffusion bonding furnace to over 1000 ℃ under Pa, and then preserving heat for more than or equal to 2 h; and after the heat preservation is finished, cooling the fixture to room temperature along with the furnace, and finishing heating and air releasing of the fixture.
Step four: and (4) diffusion bonding.
Will be equipped with TiAl/Ti2And placing the fixture of the AlNb alloy diffusion connecting piece into a vacuum diffusion connecting furnace. The vacuum diffusion bonding furnace is vacuumized to 5 x 10-3Pa and maintaining the vacuum degree; the furnace temperature is increased to 1000 ℃ in a gradient heating way and is kept for 90min, and after the heat preservation is finished, the furnace temperature is reduced to room temperature in a gradient cooling way, namely the TiAl alloy and the Ti are finished2And diffusion connecting the AlNb alloy annular structural member.
And flaw detection is carried out after the diffusion connection is finished, so that cracking is avoided.
The specific process of the step temperature rise during welding is that the temperature in the vacuum diffusion welding machine furnace is raised to 300 ℃ at the temperature rise rate of 10 ℃/min, and the temperature is kept for 30 min. After the heat preservation is finished, the temperature in the vacuum diffusion welding machine furnace is continuously raised to 600 ℃ at the temperature raising rate of 8 ℃/min, the temperature is kept for 20min, then the temperature is continuously raised to 900 ℃ at the temperature raising rate of 5 ℃/min, the temperature is kept for 10min, and the temperature in the vacuum diffusion welding machine furnace is raised to 1000 ℃ at the temperature raising rate of 5 ℃/min. When the temperature in the vacuum diffusion welding machine furnace rises to 1000 ℃, the temperature is kept for 90 min.
And after the heat preservation is finished, the temperature in the vacuum diffusion welding machine furnace is reduced to the room temperature in a stepped temperature reduction mode. The specific process is as follows: reducing the furnace temperature of the vacuum diffusion welding machine furnace to 900 ℃ at the cooling rate of 2 ℃/min, and preserving the temperature for 10 min; reducing the furnace temperature of the vacuum diffusion welding machine furnace to 800 ℃ at the cooling rate of 3 ℃/min, and preserving the temperature for 30 min; and after the heat preservation is finished, cooling to room temperature along with the furnace.
Thus, the diffusion bonding of the annular member of Ti-Al alloy was completed.
The invention controls the size of the thermal stress by controlling the cooling rate in the high-temperature region, and ensures that the joint is not damaged at high temperature; the effect of eliminating partial residual stress can be achieved by ladder heat preservation in a high-temperature interval, and cracking of a connecting interface caused by overlarge final residual stress is avoided.
In the invention, the method for realizing the diffusion connection of the ring-shaped parts by utilizing the expansion pressure difference provided by the invention creation with the publication number of CN107745178A is taken as an example, the diffusion connection method of the ring-shaped parts provided by the invention is improved, the details in the diffusion connection production process of the complex structural part are explained in detail, and the stress-relief annealing process is added aiming at the intrinsic brittleness of the Ti-Al alloy, so that the method provides guidance for industrial production.
The key point of the invention is to avoid and eliminate the residual stress generated in the processes of mechanical processing and diffusion bonding, eliminate the residual stress generated in the process of mechanical processing through stress relief annealing, and achieve the purpose of eliminating or diffusing the residual stress generated in the bonding as much as possible by removing the surface oxidation layer of the connecting piece to be diffused and controlling the cooling speed after the diffusion bonding. Through the technical measures, the invention avoids residual stress before diffusion bonding as much as possible and eliminates the residual stress after diffusion bonding. Because the residual stress generated before or during the diffusion bonding process can cause microcracks in the Ti-Al alloy with intrinsic brittleness; excessive residual stress can even damage the diffusion bond interface, causing the diffusion bond interface to fracture and even failure of the entire joint. In addition, the magnitude of residual stress is controlled during diffusion bonding while avoiding oxidation of the bonding interface. Because the diffusion of elements can be influenced after the interface is oxidized, the joint connection strength is reduced, the residual stress of the joint is increased, and the failure of the joint is accelerated.
The invention can generate residual stress in the machining stage, namely wire cutting or surface grinding, and the existence of the residual stress can lead the TiAl alloy and Ti2AlNb alloys develop microcracks during processing. The invention eliminates the residual stress through the stress relief annealing part to ensure the TiAl alloy wheel rim and the Ti2The AlNb alloy wheel core has no microcrack before diffusion connection; in the diffusion connection process, the residual stress is controlled by assembling the diffusion connection device with a clamp in a clearance way to avoid the oxidation of a connection interface; during cooling, the cooling rate is reduced in a high-temperature region, and the residual stress is partially eliminated by stepped temperature reduction. In the invention, the stress relief annealing is added in the mechanical processing process, and a mode of stepped temperature reduction and cooling speed control is adopted in the diffusion connection cooling stage, which is not used in industrial production and experimental research.
The quality of the diffusion bonding interface before welding is also an important factor influencing the diffusion bonding effect, the interface quality of a simple structural member is easy to control under the laboratory condition, but how to ensure the interface quality of a complex structural member in the actual production is not mentioned. According to the invention, an acid pickling process is added in the pre-welding treatment stage, so that an oxide layer, impurity oil stains and the like on the surface of the structural member are removed, the quality of a connection interface is improved, and the interface oxidation is prevented.
By adopting the measures, the generation of micro cracks in the TiAl alloy rim processing is effectively avoided; and the phenomenon of the diffusion bonding interface cracking is also improved. As shown in fig. 5, when the conventional diffusion bonding process is adopted, the processing quality of the outer circle of the TiAl alloy rim is extremely poor, and due to the existence of microcracks, the whole structure has to be destroyed, and a part of the outer edge is cut off; after a stress relief annealing process is added in the machining process, the outer circle machining quality of the TiAl alloy wheel rim is obviously improved, and the defects at the boundary are obviously reduced. As shown in fig. 6, when the conventional diffusion bonding method is adopted, the cracking phenomenon of the diffusion bonding interface is very serious; after the measures are taken, the diffusion bonding interface is more stable and has no cracking phenomenon.
The invention is realized by the pair of TiAl alloy wheel rim and Ti2The AlNb alloy wheel core is subjected to proper pre-welding treatment, and a proper assembly process and a proper connection process are determined, so that the cracking phenomenon of an annular structural member in the processes of machining and diffusion connection is avoided, and meanwhile, the bonding strength and the use strength of a diffusion connecting piece are improved.
The invention provides a method for preventing the diffusion bonding cracking completely comprising the whole process from processing to diffusion bonding, detects the flaw at the key node, and is beneficial to more accurately realizing process monitoring in the actual production process, more clearly judging the link of problem generation and realizing process adjustment. The invention also provides reference for welding other alloy annular structural members and preventing welding cracks from being generated by other welding methods of Ti-Al alloy.
Drawings
FIG. 1 is a schematic view of a TiAl rim structure.
FIG. 2 is Ti2And the AlNb wheel core structure is schematic.
Figure 3 is a schematic view of a silicon nitride ceramic chuck.
FIG. 4 is a silicon nitride/TiAl rim/Ti2AlNb wheel core assembly diagram.
Fig. 5 is a graph showing the effect of diffusion bonding under different diffusion bonding process conditions, wherein fig. 5a shows a diffusion bond 4 bonded using a prior art technique; fig. 5b shows a diffusion bond 5 using the inventive bonding.
Fig. 6 is SEM picture of diffusion bonding interface of different diffusion bonding processes, wherein fig. 6a is the bonding interface 6 obtained by using the prior art, and fig. 6b is the bonding interface 7 obtained by using the present invention.
Fig. 7 is a flow chart of the present invention.
In the figure: 1. a silicon nitride ceramic clamp; TiAl wheel rims; 3.Ti2An AlNb wheel core; 4. diffusion connectors of the prior art are used; 5. the diffusion connecting piece of the invention is adopted; 6. a connection interface connected by adopting the prior art; 7. the invention is adopted for connecting the connecting interface.
Detailed Description
The annular part rim metal is TiAl alloy in nameThe component is Ti-45Al-8.5 Nb-0.2W-0.2B-0.3Y; the metal of the wheel core is Ti2The AlNb alloy has a nominal composition of Ti-22Al-25 Nb. The specific process of this embodiment is:
the method comprises the following steps: TiAl/Ti2Processing of AlNb alloy diffusion connecting piece
The TiAl/Ti2The AlNb alloy diffusion connecting piece comprises a TiAl alloy rim and Ti2AlNb alloy wheel core.
Respectively processing TiAl alloy wheel rim and Ti according to design drawing2AlNb alloy wheel core.
Wherein the TiAl rim inner diameter surface and Ti2The outer diameter surface of the AlNb wheel core is the connecting interface of the two. The TiAl rim inner surface and Ti2The outer surfaces of the AlNb wheel cores are all provided with 3-degree interface inclination angles.
Before the working, the cake as a raw material is subjected to stress relief annealing. The annealing process parameters are as follows: heating to 850 ℃ at the heating rate of 6 ℃/min, preserving heat for 2-6 h and cooling along with the furnace.
According to the conventional processing method, the TiAl alloy rim and Ti are processed and manufactured by fast wire cutting, TiAl alloy center punching, slow wire cutting and surface fine polishing2AlNb alloy wheel core. The continuity of the whole processing process is ensured in the processing, namely the interval between different processing procedures is not more than 12 hours, if the time interval of more than one week exists between the processing procedures, the TiAl alloy wheel rim and Ti need to be processed2And performing stress relief annealing on the AlNb alloy wheel core. The technological parameters of the stress relief annealing are the same as the annealing technological parameters of the raw materials.
The test piece is soaked in alcohol in the gap of each processing procedure, cooling oil needs to be coated on the surface in the surface fine polishing procedure, the influence of heat generation on an interface is reduced, the surface cooling oil is reserved, and the fact that the test piece is not polluted and oxidized by impurities in the subsequent transportation process is guaranteed. And (5) flaw detection is carried out after the test piece is processed.
Step two: and (4) pre-processing of assembly.
The pre-assembly treatment comprises TiAl/Ti2The surface treatment of the AlNb alloy diffusion connecting piece and the treatment of the upper and lower graphite pressure heads in the clamp and the vacuum diffusion connecting furnace.
The treatment of the fixture and the upper and lower graphite press heads in the vacuum diffusion connecting furnace is to smear a solder stopping agent on the inner side surface of the fixture and the surfaces of the upper graphite press head and the lower graphite press head in the vacuum diffusion connecting furnace. The solder stop agent is boron nitride.
For TiAl/Ti2The surface of the AlNb alloy diffusion connecting piece is treated by surface pickling the surface of the TiAl rim and Ti2The surface of the AlNb wheel core is subjected to oxide layer removal treatment;
the surface of the pair of TiAl rims and Ti2The specific process of carrying out the oxide layer removing treatment on the surface of the AlNb wheel core comprises the following steps:
ultrasonic cleaning: a TiAl alloy rim and Ti2And immersing the AlNb alloy wheel core test piece into acetone for ultrasonic degreasing for 15min, and then immersing into absolute ethyl alcohol for ultrasonic cleaning for 5 min.
Acid washing: and adopting TiAl alloy pickling solution to pickle the TiAl alloy wheel rim for 1 min. By using Ti2Pickling solution of AlNb alloy for Ti2And acid washing the AlNb wheel core for 1 min. If TiAl alloy rim or Ti is coated in the pickling process2The acid-washed surface of the AlNb wheel core obviously turns black, and the AlNb wheel core needs to be taken out immediately and washed by alcohol, and is transferred to a vacuum diffusion connecting furnace for assembly immediately after the alcohol is dried by a blower.
The TiAl alloy pickling solution adopts HNO3HF and distilled water; HNO3HF, distilled water in a ratio of 1:1: 10; the ratio is volume ratio.
The Ti2The AlNb alloy pickling solution also adopts HNO3HF and distilled water; HNO3HF is distilled water in the ratio of 1:1: 50.
Step three: clamp and TiAl/Ti2Assembly of AlNb alloy diffusion connecting piece
This embodiment employs the ring structure diffusion bonding fixture disclosed in the invention creation application No. 201810351312.5. The jig is a sintered silicon nitride ceramic as shown in fig. 3. The ceramic clamp is a revolving body, the outer circumferential surface of the ceramic clamp is in a step shape, the maximum wall thickness is 50mm, and the minimum wall thickness is 25 mm; the axial length of the maximum wall thickness is equal to the axial length of the minimum wall thickness; the center of the end face of the small-diameter end of the clamp is provided with a groove, and the inner diameter of the groove is slightly larger than the outer diameter of the TiAl wheel rim and is 200 mm; the depth of the groove is equal to the axial length of the TiAl rim, and the thickness of the groove bottom is 20 mm.
Assembling silicon nitride/TiAl rim/Ti2When the AlNb wheel core is used, the TiAl wheel rim is placed in the inner cavity of the clamp 1, the outer circumferential surface of the TiAl wheel rim is in clearance fit with the inner circumferential surface of the clamp, and the Ti is put into the inner cavity of the clamp2An AlNb wheel core 3 is put into the center hole of the TiAl rim and the inner circumferential surface of the TiAl rim is made to contact with the Ti2The outer circumferential surface of the AlNb wheel core is attached. The clearance between the outer circumferential surface of the TiAl wheel rim and the inner circumferential surface of the clamp is 0.2mm, the primary control of the integral stress of diffusion connection is realized by adjusting the clearance distance, the TiAl wheel rim is prevented from cracking in the diffusion connection process, and meanwhile, the residual stress is prevented from being overlarge. After the silicon nitride ceramic is manufactured, the silicon nitride ceramic needs to be placed into a vacuum diffusion connecting furnace to be heated and deflated, so that the silicon nitride ceramic is prevented from polluting the connecting surface in the diffusion connecting process.
The heating and air-releasing are carried out by placing the fixture in a vacuum diffusion bonding furnace in a vacuum state at 5 × 10-2Heating the vacuum diffusion bonding furnace to over 1000 ℃ under Pa, and then preserving heat for more than or equal to 2 h; and after the heat preservation is finished, cooling the fixture to room temperature along with the furnace, and finishing heating and air releasing of the fixture.
Step four: and (4) diffusion bonding.
Will be equipped with TiAl/Ti2And placing the fixture of the AlNb alloy diffusion connecting piece into a vacuum diffusion connecting furnace. The vacuum diffusion bonding furnace is vacuumized to 5 x 10-3Pa and maintaining the vacuum degree; the furnace temperature is increased to 1000 ℃ in a gradient heating way and is kept for 90min, and after the heat preservation is finished, the furnace temperature is reduced to room temperature in a gradient cooling way, namely the TiAl alloy and the Ti are finished2And diffusion connecting the AlNb alloy annular structural member.
And flaw detection is carried out after the diffusion connection is finished, so that cracking is avoided.
The specific process of the step temperature rise during welding is that the temperature in the vacuum diffusion welding machine furnace is raised to 300 ℃ at the temperature rise rate of 10 ℃/min, and the temperature is kept for 30 min. After the heat preservation is finished, the temperature in the vacuum diffusion welding machine furnace is continuously raised to 600 ℃ at the temperature raising rate of 8 ℃/min, the temperature is kept for 20min, then the temperature is continuously raised to 900 ℃ at the temperature raising rate of 5 ℃/min, the temperature is kept for 10min, and the temperature in the vacuum diffusion welding machine furnace is raised to 1000 ℃ at the temperature raising rate of 5 ℃/min. When the temperature in the vacuum diffusion welding machine furnace rises to 1000 ℃, the temperature is kept for 90 min.
And after the heat preservation is finished, the temperature in the vacuum diffusion welding machine furnace is reduced to the room temperature in a stepped temperature reduction mode. The specific process is as follows:
reducing the furnace temperature of the vacuum diffusion welding machine furnace to 900 ℃ at the cooling rate of 2 ℃/min, and preserving the temperature for 10 min; reducing the furnace temperature of the vacuum diffusion welding machine furnace to 800 ℃ at the cooling rate of 3 ℃/min, and preserving the temperature for 30 min; and after the heat preservation is finished, cooling to room temperature along with the furnace.
The size of the thermal stress is controlled by controlling the cooling rate of the high-temperature interval, so that the joint is ensured not to be damaged at high temperature; the effect of eliminating partial residual stress can be achieved by ladder heat preservation in a high-temperature interval, and cracking of a connecting interface caused by overlarge final residual stress is avoided.

Claims (4)

1. A method for preventing Ti-Al series alloy annular parts from being diffused and connected and cracked is characterized by comprising the following specific steps:
the method comprises the following steps: TiAl/Ti2Processing an AlNb alloy diffusion connecting piece;
the TiAl/Ti2The AlNb alloy diffusion connecting piece comprises a TiAl alloy rim and Ti2An AlNb alloy wheel core;
wherein the TiAl rim inner diameter surface and Ti2The outer diameter surface of the AlNb wheel core is a connecting interface of the AlNb wheel core and the AlNb wheel core; the TiAl rim inner surface and Ti2The outer surfaces of the AlNb wheel cores are all provided with 3-degree interface inclination angles;
step two: pretreatment of assembly:
the pre-assembly treatment comprises TiAl/Ti2The surface of the AlNb alloy diffusion connecting piece is treated, and the upper graphite pressure head and the lower graphite pressure head in the fixture and the vacuum diffusion connecting furnace are treated;
for TiAl/Ti2The surface of the AlNb alloy diffusion connecting piece is treated by surface pickling the surface of the TiAl rim and Ti2Deoxidizing the surface of AlNb wheel coreProcessing a chemical layer;
the treatment of the clamp and the upper and lower graphite press heads in the vacuum diffusion connecting furnace is to smear a solder stopping agent on the inner side surface of the clamp and the surfaces of the upper graphite press head and the lower graphite press head in the vacuum diffusion connecting furnace;
step three: clamp and TiAl/Ti2Assembling the AlNb alloy diffusion connecting piece:
assembling silicon nitride ceramic clamp/TiAl wheel rim/Ti2When the AlNb wheel core is used, the TiAl wheel rim is placed in the inner cavity of the clamp, the outer circumferential surface of the TiAl wheel rim is in clearance fit with the inner circumferential surface of the clamp, and the Ti is put into the inner cavity of the clamp2An AlNb wheel core is placed in the central hole of the TiAl wheel rim and the inner circumferential surface of the TiAl wheel rim is connected with the Ti2The outer circumferential surface of the AlNb wheel core is attached; the gap between the outer circumferential surface of the TiAl rim and the inner circumferential surface of the clamp is 0.2 mm;
before the clamp is used, the clamp is required to be placed in a vacuum diffusion connecting furnace for heating and air release; heating and degassing by placing the fixture in a vacuum diffusion bonding furnace at 5 × 10-2Heating the vacuum diffusion bonding furnace to over 1000 ℃ under Pa, and then preserving heat for more than or equal to 2 h; cooling to room temperature along with the furnace after the heat preservation is finished, and finishing heating and air releasing of the clamp;
step four: diffusion bonding:
will be equipped with TiAl/Ti2Placing a fixture of the AlNb alloy diffusion connecting piece into a vacuum diffusion connecting furnace; the vacuum diffusion bonding furnace is vacuumized to 5 x 10-3Pa and maintaining the vacuum degree; the furnace temperature is increased to 1000 ℃ in a gradient heating way and is kept for 90min, and after the heat preservation is finished, the furnace temperature is reduced to room temperature in a gradient cooling way, namely the TiAl alloy and the Ti are finished2Diffusion connection is carried out on the AlNb alloy annular structural member;
flaw detection is carried out after the diffusion connection is finished, and it is ensured that the cracks do not occur;
thus, the diffusion connection of the Ti-Al alloy annular piece is completed;
the specific process of the step temperature rise during the diffusion bonding is that the temperature in a vacuum diffusion welding machine furnace is raised to 300 ℃ at the temperature rise rate of 10 ℃/min, and the temperature is kept for 30 min; after the heat preservation is finished, continuously heating the vacuum diffusion welding machine furnace to 600 ℃ at the heating rate of 8 ℃/min, preserving the heat for 20min, continuously heating to 900 ℃ at the heating rate of 5 ℃/min, preserving the heat for 10min, and heating the vacuum diffusion welding machine furnace to 1000 ℃ at the heating rate of 5 ℃/min;
when the temperature in the vacuum diffusion welding machine furnace rises to 1000 ℃, preserving the heat for 90 min;
after the heat preservation is finished, the specific process of reducing the temperature in the vacuum diffusion welding machine furnace to the room temperature in a step cooling mode is as follows: reducing the furnace temperature of the vacuum diffusion welding machine furnace to 900 ℃ at the cooling rate of 2 ℃/min, and preserving the temperature for 10 min; reducing the furnace temperature of the vacuum diffusion welding machine furnace to 800 ℃ at the cooling rate of 3 ℃/min, and preserving the temperature for 30 min; and after the heat preservation is finished, cooling to room temperature along with the furnace.
2. The method for preventing diffusion bonding cracking of an annular member made of a Ti-Al alloy according to claim 1,
before processing, performing stress relief annealing on the forged cake as a raw material; the annealing process parameters are as follows: heating to 850 ℃ at the heating rate of 6 ℃/min, preserving heat for 2-6 h and cooling along with the furnace;
the continuity of the whole processing process is ensured in the processing, the interval between different processing procedures is not more than 12h, if the time interval of more than one week exists between the processing procedures, the TiAl alloy wheel rim and Ti are required to be processed2Performing stress relief annealing on the AlNb alloy wheel core; the technological parameters of the stress relief annealing are the same as the annealing technological parameters of the raw materials;
in the gap of each processing procedure, TiAl alloy wheel rim and Ti are required to be processed2Soaking the AlNb alloy wheel core in alcohol; in the surface fine polishing process, cooling oil is required to be coated on the surface so as to reduce the influence of heat generation on an interface, and the surface cooling oil is reserved so as to ensure that the surface cooling oil is not polluted and oxidized by impurities in the subsequent transportation process; and (5) flaw detection is carried out after the test piece is processed.
3. The method for preventing diffusion bonding cracking of an annular member made of a Ti-Al alloy according to claim 1,
the surface of the pair of TiAl rims and Ti2The specific process of carrying out the oxide layer removing treatment on the surface of the AlNb wheel core comprises the following steps:
ultrasonic cleaning: a TiAl alloy rim and Ti2Immersing the AlNb alloy wheel core test piece into acetone for ultrasonic degreasing for 15min, and then immersing into absolute ethyl alcohol for ultrasonic cleaning for 5 min;
acid washing: adopting TiAl alloy pickling solution to pickle TiAl alloy rims for 1 min; by using Ti2Pickling solution of AlNb alloy for Ti2Pickling the AlNb wheel core for 1 min; wheel rim of TiAl alloy or Ti in pickling process2The acid-washed surface of the AlNb wheel core obviously turns black, and the AlNb wheel core needs to be taken out immediately and washed by alcohol, and then is transferred into a vacuum diffusion connecting furnace for assembly immediately after the alcohol is dried by a blower.
4. The method for preventing diffusion bonding cracking of an annular member made of a Ti-Al alloy according to claim 3,
the TiAl alloy pickling solution adopts HNO3HF and distilled water; HNO3HF, distilled water in a ratio of 1:1: 10; the proportion is volume ratio;
the Ti2The AlNb alloy pickling solution also adopts HNO3HF and distilled water; HNO3HF is distilled water in the ratio of 1:1: 50.
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