Preparation method of powder metallurgy titanium alloy fastener

Abstract

The invention discloses a preparation method of a powder metallurgy titanium alloy fastener, which comprises the following steps: mixing Ti powder and alloy element powder to obtain mixed powder, carrying out cold isostatic pressing and vacuum sintering on the mixed powder to obtain a sintered bar blank, carrying out hot rolling treatment on the sintered bar blank to obtain a titanium alloy bar, then carrying out phosphating treatment on the titanium alloy bar, cutting into sections to obtain a pre-blank, and carrying out heat treatment on the pre-blank to obtain the powder metallurgy titanium alloy fastener. According to the preparation method, the titanium alloy bar is prepared through the powder metallurgy process, material pores are eliminated through thermoplastic deformation, then the titanium alloy fastener is formed through the cold heading process, and the titanium alloy fastener which is uniform and fine in structure, high in strength, high in toughness, high in strength and high in toughness can be obtained. And the fastener is relatively high in comprehensive mechanical property and relatively high in cost performance. By the adoption of the cold heading process, the turn-milling process is effectively avoided, and the cold heading process has the advantages of being high in productivity, material utilization rate, surface quality and inherent quality and the like and is a process which is low in cost and capable of preparing fasteners with high cost performance.

Description

Technical Field

[0001] The invention belongs to the field of powder metallurgy material forming, and particularly relates to a method for preparing a powder metallurgy titanium alloy fastener. Background Art

[0002] Titanium alloy has a low density (4.51g / cm 3 Titanium alloys are known as "space metals" and "ocean metals" for their advantages, such as being approximately 40% that of steel, high strength (reaching over 1000 MPa), excellent fatigue resistance (fatigue limit twice that of steel), excellent corrosion resistance, good biocompatibility, and non-magnetic properties. They are therefore well-suited for use as fasteners. The weight reduction achieved by titanium alloy fasteners is crucial for improving aircraft and spacecraft propulsion, increasing flight range, saving fuel, and reducing launch costs. In modern aircraft manufacturing, a single aircraft utilizes anywhere from hundreds of thousands to millions of fasteners. For example, the US Galaxy C5 transport aircraft utilizes 1.5 million titanium fasteners, reducing structural weight by 1.2 tons. Titanium alloy fasteners account for 90% of the threaded fasteners on a Boeing 747, reducing the weight of a single aircraft by over 1.8 tons. The aviation industry alone generates an annual demand for over 500 million titanium alloy fasteners. Titanium alloy fasteners are not only in strong demand in the aviation and aerospace sectors, but also, due to their excellent corrosion resistance, have enormous potential for application in shipbuilding (including submarines), as well as in industries such as petroleum, chemical engineering, light industry, electric power, and metallurgy, which are subject to severe corrosive environments. Furthermore, titanium alloy fasteners are widely used in biomedicine, human implants, and high-end consumer goods (such as sporting goods and decorative items).

[0003] Currently, titanium alloy bars for fasteners are primarily produced using ingot metallurgy, a process that includes multiple steps, including vacuum consumable melting, blanking, rolling, and drawing. This process is lengthy, with high energy consumption for melting and high-temperature forging, and significant equipment investment. This results in high material costs for ingot metallurgy. Powder metallurgy, with its advantages of low raw material costs, short process flow, low energy consumption, and minimal equipment investment, offers the potential to significantly reduce material costs. Studies have shown that for certain complex components, powder metallurgy can reduce component costs by 50% to 70%, making it a promising technology for producing low-cost titanium alloy bars for fasteners. While titanium alloys produced using powder metallurgy have a fine and uniform microstructure, their mechanical properties are generally lower than those of materials produced using traditional ingot metallurgy due to the presence of porosity.

[0004] Currently, turning is the primary method of machining titanium alloy fasteners. However, some irregularly shaped parts with significant deformation of the shank and head remain a challenge, creating significant challenges for industrial design. Fastener shanks and heads typically experience deformation of around 50%. Turning, with its raw material made of titanium bar and processed in single pieces, requires equipment such as wire cutting, lathes, milling machines, drilling machines, and tapping machines, resulting in low efficiency. Because the turning and milling process is a major bottleneck, nearly 50% of the process generates titanium shavings, resulting in low material utilization and high final product costs. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to overcome the problems of material waste and low production efficiency caused by the ingot casting process and turning process in preparing fasteners, and to provide a method for preparing powder metallurgy titanium alloy fasteners with simple procedures, high production efficiency and high cost performance.

[0006] In order to solve the above technical problems, the technical solution proposed by the present invention is:

[0007] The present invention discloses a preparation method of a powder metallurgy titanium alloy fastener, comprising the following steps: mixing Ti powder and alloy element powder to obtain a mixed powder, cold isostatic pressing and vacuum sintering the mixed powder to obtain a sintered rod blank, hot rolling the sintered rod blank to obtain a titanium alloy bar, phosphating the titanium alloy bar, and cutting the pre-blank into segments to obtain a cold-headed blank, cold-heading the pre-blank to obtain a cold-headed blank, and tapping the cold-headed blank to obtain the finished product.

[0008] The preparation method of the present invention uses powder metallurgy to produce titanium alloy rods, employs thermoplastic deformation to eliminate material porosity, and then forms titanium alloy fasteners using a cold heading process. This method produces fasteners with uniform and fine microstructure, high comprehensive mechanical properties, and a high cost-effectiveness ratio. The cold heading process effectively avoids turning and milling steps, resulting in high productivity, high material utilization, and high surface and internal quality. This is a low-cost process for producing fasteners with high cost-effectiveness.

[0009] During the actual operation, the cut pre-blanks are sent to a multi-station cold heading machine for cold heading processing, and the formed blanks are inspected. Unqualified blanks are scrapped; the qualified blanks are deburred and placed on the machine tool, and tapped with a wire pusher. After tapping, they are inspected. After passing the inspection, the surface is polished to obtain the finished product, and unqualified ones are scrapped.

[0010] In a preferred embodiment, the alloying element in the alloying element powder is selected from at least one of Ti, Al, V, and Mo, and the alloying element powder is pure metal powder or intermediate alloy powder.

[0011] In a preferred embodiment, the particle size of the Ti powder is -200 to -400 mesh, and the particle size of the alloy element powder is -200 to -300 mesh.

[0012] In the present invention, except for a small amount of inevitable impurity elements, the raw materials do not contain other element components except Ti, Al, V, and Mo; the inevitable trace impurity elements in the raw materials mainly refer to oxygen, and its mass percentage is generally less than 0.5%.

[0013] In a preferred embodiment, the mass fraction of the alloy element powder in the mixed powder is ≤30%.

[0014] In a preferred embodiment, the pressure of the cold isostatic pressing treatment is 100 MPa to 300 MPa, and the holding time is 1 min to 10 min.

[0015] In a preferred embodiment, the temperature of the vacuum sintering treatment is 1200° C. to 1400° C., and the time of the vacuum sintering treatment is 1 hour to 3 hours.

[0016] In a preferred embodiment, the hot rolling treatment temperature is 700-900°C, the deformation per pass is 10%-30%, the total deformation is 50%-400%, and the tempering temperature between passes is 600-900°C.

[0017] In a preferred embodiment, the length of the pre-blank is L=10-120 mm, and the diameter is D=3-15 mm.

[0018] In a preferred embodiment, the number of cold heading passes is ≥ 2, preferably 4 to 6, and the deformation of the cold heading is (Li-Li+1) / Li=20% to 60%, preferably 20% to 40%, i=1, 2, 3... (See Figure 3 ).

[0019] By controlling the deformation of the cold heading process in the above manner, the performance of the final material obtained is optimal.

[0020] Compared with the existing preparation process of titanium alloy fasteners, the present invention has the following advantages:

[0021] (1) The process steps are relatively simple and can be achieved with conventional equipment;

[0022] (2) The use of powder metallurgy to prepare fastener materials improves material utilization, and the structure is more fine and uniform, with excellent comprehensive mechanical properties;

[0023] (3) Compared with the turning process, the cold heading fasteners have high production efficiency, high material utilization rate and high cost performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0025] Figure 1 It is a process flow chart of the present invention.

[0026] Figure 2 It is a temperature-time process curve diagram of the sintering process and the low-temperature hot rolling process of the present invention.

[0027] Figure 3 It is a schematic diagram of the pre-blank and cold heading blank of the present invention.

[0028] Figure 4 This is a photo of the titanium alloy bar prepared after rolling in Example 1 of the present invention.

[0029] Figure 5 This is a photograph of the powder metallurgy titanium alloy fastener prepared in Example 1 of the present invention.

[0030] Figure 6 This is a metallographic photograph of the powder metallurgy titanium alloy fastener prepared in Example 1 of the present invention.

[0031] Figure 7 This is a SEM photograph of the powder metallurgy titanium alloy fastener prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0032] To facilitate understanding of the present invention, the present invention will be described in more comprehensive and detailed form below in conjunction with the accompanying drawings and preferred embodiments. However, the protection scope of the present invention is not limited to the following specific embodiments.

[0033] Unless otherwise defined, all technical terms used hereinafter have the same meanings as those generally understood by those skilled in the art. The technical terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0034] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0035] Example 1:

[0036] A kind of Figure 1 The method for preparing the powder metallurgy titanium alloy fastener of the present invention comprises the following steps:

[0037] (1) Ti powder (oxygen content of 0.35%) with a particle size of -325 mesh and Al-V master alloy powder (oxygen content of 0.47%) with a particle size of -250 mesh were used as raw materials. Except for a small amount of unavoidable impurity oxygen, the raw materials did not contain any other elements except Ti powder and Al-V master alloy powder. Ti powder and Al-V master alloy powder were weighed in a mass ratio of 9:1, and the mass ratio of Al to V in the Al-V master alloy powder was controlled at 6:4. The weighed raw material powders were mixed uniformly in a V-type mixer for 8 hours. The mixing process was protected by inert gas argon.

[0038] (2) The powders fully mixed in step (1) were subjected to cold isostatic pressing, the pressure during the cold isostatic pressing was controlled to be 180 MPa, and the holding time was controlled to be 2 min to obtain a green rod; the green rod was then placed in a vacuum sintering furnace for vacuum sintering, and the vacuum degree was 1×10 -3 Pa, sintering temperature is 1250℃, sintering holding time is 2h, heating rate is controlled at 5℃ / min, and sintered rod blank is obtained after cooling in the furnace;

[0039] (3) The sintered rod obtained in step (2) is subjected to low-temperature hot rolling treatment, the hot rolling temperature is controlled to 850°C, the pass deformation is 20%, the interpass tempering temperature is 800°C, and the total hot rolling deformation is controlled to 321%, and the following is obtained: Figure 4 Powder metallurgy titanium alloy rod shown.

[0040] (4) The titanium alloy rod obtained in step (3) is subjected to surface phosphating treatment and then cut into pre-blanks of Ø12×80 mm.

[0041] (5) The pre-blank obtained in step (4) is subjected to cold heading treatment, and the deformation amount of the cold heading pass is (Li-Li+1) / Li=20%. After 6 deformation passes, the blank is obtained.

[0042] (6) The blank obtained in step (5) is tapped with a wire pusher, and the surface is polished after tapping to obtain the following Figure 5 Finished fastener shown.

[0043] The product of this embodiment was tested by the drainage method, and the density of the powder metallurgy titanium alloy fastener was measured to be 99.4%. The metallographic structure photos and SEM photos of the powder metallurgy titanium alloy fastener prepared in this embodiment are shown as follows: Figure 6 、 Figure 7 As shown by Figure 6 、 Figure 7 It can be seen that the powder metallurgy titanium alloy rod product prepared by the present invention has good density, relatively fine and uniform metallographic structure, and no component segregation.

[0044] Example 2:

[0045] A kind of Figure 1 The method for preparing the powder metallurgy titanium alloy fastener of the present invention comprises the following steps:

[0046] (1) Ti powder (oxygen content of 0.35%) with a particle size of -325 mesh, Al powder (oxygen content of 0.41%) with a particle size of -200 mesh, and V powder (oxygen content of 0.11%) with a particle size of -250 mesh are used as raw materials. Except for a small amount of unavoidable impurity oxygen, the raw materials do not contain other elements except Ti powder and Al-V master alloy powder. Ti powder, Al powder and V powder are weighed in a mass ratio of 45:3:2, and the weighed raw material powders are mixed uniformly in a V-type mixer for 8 hours. The mixing process is protected by inert gas argon.

[0047] (2) The powders mixed thoroughly in step (1) were subjected to cold isostatic pressing, with the pressure during the cold isostatic pressing controlled at 200 MPa and the holding time controlled at 1 min to obtain green rods; the green rods were then placed in a vacuum sintering furnace for vacuum sintering, with a vacuum degree of 1×10 -3 Pa, sintering temperature is 1300℃, sintering holding time is 2h, heating rate is controlled at 5℃ / min, and sintered rod blank is obtained after cooling in the furnace;

[0048] (3) The sintered rod blank obtained in step (2) is subjected to low-temperature hot rolling treatment, the hot rolling temperature is controlled to 850°C, the pass deformation is 20%, the inter-pass tempering temperature is 800°C, and the total hot rolling deformation is controlled to 251%, thereby obtaining a powder metallurgy titanium alloy rod.

[0049] (4) The titanium alloy rod obtained in step (3) is subjected to surface phosphating treatment and then cut into pre-blanks of Ø5×30 mm.

[0050] (5) The pre-blank obtained in step (4) is subjected to cold heading treatment, and the deformation amount of the cold heading pass is (Li-Li+1) / Li=20%. After 6 deformation passes, the blank is obtained.

[0051] (6) The blank obtained in step (5) is tapped with a wire pusher, and after the tapping is completed, the surface is polished to obtain a finished fastener.

[0052] The product of this embodiment was tested by the drainage method, and the density of the powder metallurgy titanium alloy fastener was measured to be 99.1%. The metallographic structure photos and SEM photos of the powder metallurgy titanium alloy fastener prepared by this embodiment show that the titanium alloy rod product prepared by the present invention has good density, a relatively fine and uniform metallographic structure, and no composition segregation.

[0053] Example 3:

[0054] A kind of Figure 1 The method for preparing the powder metallurgy titanium alloy fastener of the present invention comprises the following steps:

[0055] (1) Ti powder (oxygen content of 0.20%) with a particle size of -200 mesh, Mo powder (oxygen content of 0.22%) with a particle size of -250 mesh, and Al-V master alloy powder (oxygen content of 0.47%) with a particle size of -250 mesh are used as raw materials. Except for a small amount of unavoidable impurity oxygen, the raw materials do not contain other elements except Ti powder, Mo powder, and Al-V master alloy powder. Ti powder, Mo powder, and Al-V master alloy powder are weighed in a mass ratio of 35:2:3. The mass ratio of Al to V in the Al-V master alloy powder is controlled at 4:6. The weighed raw material powders are mixed uniformly in a V-type mixer for 8 hours. The mixing process is protected by inert gas argon.

[0056] (2) The powders fully mixed in step (1) were subjected to cold isostatic pressing, the pressure during the cold isostatic pressing was controlled to be 180 MPa, and the holding time was controlled to be 2 min to obtain a green rod; the green rod was then placed in a vacuum sintering furnace for vacuum sintering, and the vacuum degree was 1×10 -3 Pa, sintering temperature is 1300℃, sintering holding time is 2h, heating rate is controlled at 5℃ / min, and sintered rod blank is obtained after cooling in the furnace;

[0057] (3) The sintered rod blank obtained in step (2) is subjected to low-temperature hot rolling treatment, the hot rolling temperature is controlled to 800°C, the pass deformation is 20%, the inter-pass tempering temperature is 800°C, and the total hot rolling deformation is controlled to 200%, thereby obtaining a powder metallurgy titanium alloy rod.

[0058] (4) The titanium alloy rod obtained in step (3) is subjected to surface phosphating treatment and then cut into pre-blanks of Ø8×60mm.

[0059] (5) The pre-blank obtained in step (4) is subjected to cold heading treatment, and the deformation amount of the cold heading pass is (Li-Li+1) / Li=35%. After 4 deformations, the blank is obtained.

[0060] (6) The blank obtained in step (5) is tapped with a wire pusher, and after the tapping is completed, the surface is polished to obtain a finished fastener.

[0061] The product of this embodiment was tested by the drainage method, and the density of the powder metallurgy titanium alloy fastener was measured to be 99.2%. The metallographic structure photos and SEM photos of the powder metallurgy titanium alloy fastener prepared by this embodiment show that the titanium alloy rod product prepared by the present invention has good density, a relatively fine and uniform metallographic structure, and no composition segregation.

[0062] Example 4:

[0063] A kind of Figure 1 The method for preparing the powder metallurgy titanium alloy fastener of the present invention comprises the following steps:

[0064] (1) Ti powder (oxygen content of 0.20%) with a particle size of -200 mesh, Mo powder (oxygen content of 0.22%) with a particle size of -250 mesh, Al powder (oxygen content of 0.41%) with a particle size of -200 mesh, and V powder (oxygen content of 0.11%) with a particle size of -250 mesh are used as raw materials. Except for a small amount of unavoidable impurity oxygen, the raw materials do not contain other element components except Ti powder, Mo powder, Al powder, and V powder; Ti powder, Mo powder, Al powder, and V powder are weighed in a mass ratio of 75:10:6:9, and the weighed raw material powders are mixed uniformly in a V-type mixer for 8 hours. The mixing process is protected by inert gas argon;

[0065] (2) The powders mixed thoroughly in step (1) were subjected to cold isostatic pressing, with the pressure during the cold isostatic pressing controlled at 200 MPa and the holding time controlled at 1 min to obtain green rods; the green rods were then placed in a vacuum sintering furnace for vacuum sintering, with a vacuum degree of 1×10 -3 Pa, sintering temperature is 1250℃, sintering holding time is 2h, heating rate is controlled at 5℃ / min, and sintered rod blank is obtained after cooling in the furnace;

[0066] (3) The sintered rod blank obtained in step (2) is subjected to low-temperature hot rolling treatment, the hot rolling temperature is controlled to 800°C, the pass deformation is 20%, the inter-pass tempering temperature is 800°C, and the total hot rolling deformation is controlled to 256%, thereby obtaining a powder metallurgy titanium alloy rod.

[0067] (4) The titanium alloy rod obtained in step (3) is subjected to surface phosphating treatment and then cut into pre-blanks of Ø10×100 mm.

[0068] (5) The pre-blank obtained in step (4) is subjected to cold heading treatment, and the deformation amount of the cold heading pass is (Li-Li+1) / Li=30%. After 4 deformations, the blank is obtained.

[0069] (6) The blank obtained in step (5) is tapped with a wire pusher, and after the tapping is completed, the surface is polished to obtain a finished fastener.

[0070] The product of this embodiment was tested by the drainage method, and the density of the powder metallurgy titanium alloy fastener was measured to be 99.3%. The metallographic structure photos and SEM photos of the powder metallurgy titanium alloy fastener prepared by this embodiment show that the titanium alloy rod product prepared by the present invention has good density, a relatively fine and uniform metallographic structure, and no composition segregation.

Claims

1. A method for preparing a powder metallurgy titanium alloy fastener, characterized in that: Ti powder and alloy element powder are mixed to obtain mixed powder, the mixed powder is subjected to cold isostatic pressing and vacuum sintering to obtain sintered rod blanks, the sintered rod blanks are hot rolled to obtain titanium alloy bars, and then the titanium alloy bars are phosphated and cut into segments to obtain pre-blanks, the pre-blanks are cold headed to obtain cold forging blanks, and the cold forging blanks are tapped to obtain the finished product.

2. The method for preparing a powder metallurgy titanium alloy fastener according to claim 1, characterized in that: The alloy element in the alloy element powder is selected from at least one of Ti, Al, V, and Mo, and the alloy element powder is pure metal powder or intermediate alloy powder.

3. The method for preparing a powder metallurgy titanium alloy fastener according to claim 1 or 2, characterized in that: The particle size of the Ti powder is -200 to -400 mesh, and the particle size of the alloy element powder is -200 to -300 mesh.

4. The method for preparing a powder metallurgy titanium alloy fastener according to claim 1 or 2, characterized in that: The mass fraction of the alloy element powder in the mixed powder is ≤30%.

5. The method for preparing a powder metallurgy titanium alloy fastener according to claim 1 or 2, characterized in that: The pressure of the cold isostatic pressing treatment is 100 MPa to 300 MPa, and the holding time is 1 min to 10 min.

6. The method for preparing a powder metallurgy titanium alloy fastener according to claim 1 or 2, characterized in that: The temperature of the vacuum sintering treatment is 1200° C. to 1400° C., and the time of the vacuum sintering treatment is 1 hour to 3 hours.

7. The method for preparing a powder metallurgy titanium alloy fastener according to claim 1 or 2, characterized in that: The temperature of the hot rolling treatment is 700-900° C., the deformation amount per pass is 10%-30%, the total deformation amount is 50%-400%, and the tempering temperature between passes is 600-900° C.

8. The method for preparing a powder metallurgy titanium alloy fastener according to claim 1 or 2, characterized in that: The length of the pre-blank is L=10~120mm, and the diameter is D=3~15mm.

9. The method for preparing a powder metallurgy titanium alloy fastener according to claim 1 or 2, characterized in that: The number of passes of the cold heading process is ≥2 times, and the deformation amount of the cold heading process is (Li-Li+1) / Li=20%~60%, i=1, 2, 3...

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