Method for preparing titanium alloy workpiece through near-net forming of titanium hydride powder

Abstract

The invention relates to the technical field of titanium alloy preparation and machining, and particularly discloses a method for preparing a titanium alloy workpiece through near-net forming of titanium hydride powder. The method comprises the steps that after titanium hydride powder and intermediate alloy powder are mixed, cold press molding is conducted under 200-800 MPa, and a pressed blank is obtained; sintering the pressed blank and the mold for the first time at the temperature of 500-1200 DEG C, preserving heat for 10-30 minutes, and then cooling; and the pressed blank is taken out of the mold, secondary sintering is carried out at the temperature of 1200-1400 DEG C, cooling is carried out after heat preservation is carried out for 2-4 hours, and a titanium alloy workpiece is obtained. The method does not include the step of partially dehydrogenating the titanium hydride powder before cold press molding. According to the method, the problem that the titanium hydride pressed blank is easy to crack during demolding is fundamentally solved through the first sintering with the mold by utilizing the volume shrinkage effect in the dehydrogenation process, so that the product percent of pass is greatly improved, and meanwhile, the low hydrogen content (llt of a workpiece is ensured; 0.015%), high density (greater than or equal to 99%) and uniform components.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of preparation and processing of titanium alloy, and particularly relates to a method for preparing a titanium alloy part by adopting near-net-shaping of titanium hydride powder. BACKGROUND

[0002] Titanium alloy plays an irreplaceable role in high-end fields such as aerospace, biomedical, chemical industry and national defense due to its high specific strength, good corrosion resistance and excellent heat resistance. However, traditional titanium alloy processing methods such as melting and casting, forging and the like have problems such as long process flow, low material utilization rate, difficulty in forming complex components and high cost, which seriously restricts the large-scale application and market expansion of titanium alloy.

[0003] To overcome the above bottleneck, powder near-net-shaping technology emerges as the times require. The technology uses metal powder as raw material to realize near-net-shaping manufacturing of components through forming and sintering processes, and has the advantages of high material utilization rate, low production cost and suitability for batch production of complex structures. Since the 1980s, in-depth basic research and engineering exploration have been carried out worldwide around the direction of low-cost titanium alloy powder metallurgy. Among the many powder raw materials, titanium hydride (TiH2) powder is considered as an ideal choice to replace traditional titanium powder because it reduces cost, simplifies process requirements, and improves product sintering performance, including higher density and lower oxygen content. Using titanium hydride powder to prepare titanium alloy, especially Ti-6Al-4V and other commonly used alloys, is conducive to promoting composition homogenization and obtaining high product density after sintering.

[0004] Using titanium hydride powder faces problems such as high powder brittleness, low green strength and large sample shrinkage, and usually adopts raw material pre-dehydrogenation, green body sintering dehydrogenation or warm pressing for treatment. For example, patent CN107034375A discloses a method for preparing high-density titanium products using titanium hydride powder. The method first performs partial dehydrogenation treatment on the titanium hydride powder to obtain unsaturated TiH x powder to improve its pressing performance, and then performs die pressing and vacuum sintering. Patent CN107760897A provides a method for manufacturing titanium and titanium alloy and its parts using titanium hydride sponge as raw material. After powder pressing, it is first rapidly sintered and partially dehydrogenated under inert gas, and then the powder compact after high-temperature sintering and heat preservation is directly and rapidly transferred into an extrusion die or a forging die, and finally completely dehydrogenated in vacuum, thereby improving the density and mechanical properties of the product.

[0005] However, the existing hydrogenated titanium powder metallurgy technology still has significant problems. Since hydrogenated titanium is a non-plastic material, when the green body is pushed out of the mold after cold pressing, stress concentration occurs due to the volume expansion of the green body, resulting in cracks or even breakage, which causes the qualified rate of the product to be relatively low, usually below 85%, which seriously affects the industrial application and cost control of the hydrogenated titanium powder near-net forming preparation of titanium alloy products. Therefore, developing a hydrogenated titanium-based titanium alloy preparation method that can effectively solve the demolding cracking problem, improve the green body integrity, and at the same time ensure the uniformity of the composition and high density, has become a key technical problem that needs to be broken through in the field. SUMMARY

[0006] To solve the problem of cracking of titanium alloy product green body prepared by pressing hydrogenated titanium powder during demolding, the present application provides a method for preparing a titanium alloy product by near-net forming of hydrogenated titanium powder, comprising the following steps:

[0007] (1) Powder mixing: uniformly mix hydrogenated titanium powder and master alloy powder according to the composition ratio of the target titanium alloy;

[0008] (2) Cold pressing: put the uniformly mixed powder in step (1) into a mold, apply a pressure of 200-800 MPa for cold pressing to form a compact;

[0009] (3) Mold sintering: put the compact obtained in step (2) and the mold together into a vacuum or inert gas environment, heat to 500-1200°C at a heating rate of 5-20°C / min, hold for 10-30 minutes, and then cool with the furnace;

[0010] (4) Final sintering: take the compact sintered with the mold in step (3) out of the mold, heat to 1200-1400°C in a vacuum or inert gas environment, hold for 2-4 hours, and then cool with the furnace to obtain a titanium alloy product.

[0011] Further, the pressure for cold pressing in step (2) is 400-500 MPa, and the holding time is 15-20 min.

[0012] Further, the heating rate for mold sintering in step (3) is 8-15°C / min, and the heating temperature is 800-1000°C.

[0013] Further, the heating rate for final sintering in step (4) is 8-15°C / min, and the heating temperature is 1250-1350°C.

[0014] Further, the vacuum degree of the vacuum environment in steps (3) and (4) is 1x10 -3 Pa to 5x10 -4 Pa.

[0015] Further, the inert gas in step (3) and step (4) is argon or helium, and the purity is not less than 99.99%.

[0016] Further, the intermediate alloy powder in step (1) is aluminum-vanadium intermediate alloy powder, and the composition is 58-62% aluminum and 38-42% vanadium by weight percentage; the average particle size of the intermediate alloy powder is 50-100 μm, and the average particle size of the titanium hydride powder is 35-45 μm; and the target alloy is Ti-6Al-4V alloy.

[0017] Further, the hydrogen content of the titanium alloy product is less than 0.015%, and the relative density is more than 99%.

[0018] Compared with the prior art, the method has the following advantages:

[0019] (1) The product qualified rate is greatly improved: the green body is sintered with a mold, so that the compacts complete stress release and size stabilization in the mold, and the problem of easy cracking of the titanium hydride compacts during demolding is fundamentally solved, the product qualified rate is greatly improved, and partial dehydrogenation is also considered;

[0020] (2) The comprehensive performance of the product is excellent: through the synergistic effect of the two-step sintering process, full dehydrogenation (hydrogen content <0.015%) is realized at the same time, densification (relative density ≥ 99%) is promoted, and the alloy composition can be completely solid-solved, so that a high-performance titanium alloy product with dense structure and uniform composition can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 The process flow chart of the preparation method of the present application is shown in the figure;

[0022] Figure 2 The titanium alloy sample prepared in the embodiment of the present application is shown in the figure;

[0023] Figure 3 The cold pressing mold for preparing the titanium alloy green body of the present application is shown in the figure.

[0024] Explanation of reference signs: 1, mold; 2, punch; 3, concave die; 4, mixture of titanium hydride powder and intermediate alloy powder; 5, base. DETAILED DESCRIPTION

[0025] The present application will be further described in detail below in combination with examples and comparative examples, but the embodiments of the present application are not limited thereto. In the following examples, unless otherwise specified, the equipment and methods used are conventional equipment and methods in the art.

[0026] Example 1

[0027] The embodiment provides a preparation method of a Ti-6Al-4V titanium alloy part, and specific steps are as follows.

[0028] (1) Powder mixing: titanium hydride (TiH2) powder with an average particle size of 40 μm and aluminum-vanadium intermediate alloy powder (Al-60V-40) with an average particle size of 75 μm are mixed according to a weight ratio of 90.5:9.5, and a mixer is used for mixing for 4 hours to ensure that the powders are uniform.

[0029] (2) Cold pressing forming: the uniformly mixed powders are loaded into a mold, a pressure of 500 MPa is applied on a vertical hydraulic machine, and pressure maintaining is performed for 15 minutes to press a compact with a predetermined shape.

[0030] (3) First sintering (sintering with a mold): the compact is transferred into a vacuum sintering furnace together with the mold, vacuumizing is performed to 5×10 -4 Pa, then heating is performed to 850 ℃ at a heating rate of 10 ℃ / min, holding for 20 minutes, and then furnace cooling is performed to room temperature. In this process, the compact is subjected to a dehydrogenation reaction, the volume shrinks by about 5%, and the pre-sintered compact is easily taken out from the mold after cooling.

[0031] (4) Second sintering (final sintering): the pre-sintered compact is taken out from the mold and placed in a vacuum sintering furnace (vacuum degree 5×10 -4 Pa), heating is performed to 1300 ℃ at a heating rate of 10 ℃ / min, holding for 3 hours, and then furnace cooling is performed to obtain the final Ti-6Al-4V titanium alloy part.

[0032] Example 2

[0033] The difference between the embodiment and example 1 lies in the process parameters of the first sintering: heating is performed to 500 ℃ at a heating rate of 5 ℃ / min, and holding for 30 minutes. The remaining steps and parameters are completely same as those of example 1.

[0034] Example 3

[0035] The difference between the embodiment and example 1 lies in the process parameters of the first sintering: heating is performed to 1200 ℃ at a heating rate of 20 ℃ / min, and holding for 10 minutes. The remaining steps and parameters are completely same as those of example 1.

[0036] Comparative Example 1

[0037] The difference between the comparative example and example 1 lies in the process parameters of the first sintering: the heating temperature is 300 ℃, and holding for 35 minutes. The remaining steps and parameters are completely same as those of example 1. Due to the too low temperature, the dehydrogenation reaction is insufficient, and the compact is broken when demolding, so that the complete green compact cannot be obtained.

[0038] Comparative Example 2

[0039] The difference between the present comparative example and Example 1 is that the process parameters of the first sintering: the heating temperature is 1400℃, and the holding time is 5 minutes. The remaining steps and parameters are the same as those of Example 1. The excessively high first sintering temperature causes local bonding between the compact and the mold, which makes the demolding difficult and the mold severely damaged.

[0040] Comparative Example 3

[0041] The difference between the present comparative example and Example 1 is that the process parameters of the second sintering: the sintering temperature is 1100℃, and the holding time is 5 hours. The remaining steps and parameters are the same as those of Example 1. The demolded green compact has no macroscopic defects on the surface, but the final sintering temperature is insufficient, the compact is not completely densified, the relative density is only 96.2%, and the diffusion of alloying elements is insufficient.

[0042] Comparative Example 4

[0043] The difference between the present comparative example and Example 1 is that the process parameters of the second sintering: the sintering temperature is 1500℃, and the holding time is 1 hour. The remaining steps and parameters are the same as those of Example 1. The demolded green compact has no macroscopic defects on the surface, but the excessively high second sintering temperature causes the relative density to be 97.7%, and the grains to be abnormally coarse, which significantly affects the plasticity.

[0044] Comparative Example 5

[0045] The difference between the present comparative example and Example 1 is that the cold pressing forming pressure is 100 MPa. The remaining steps and parameters are the same as those of Example 1. The excessively low pressure causes the initial density of the green compact to be too low, and the green compact is broken when it is taken out of the mold before the first sintering.

[0046] The key performances of the prepared parts in the above examples and comparative examples are tested, and the results are shown in Table 1.

[0047] Table 1

[0048] Group Product yield Hydrogen content (wt%) Relative density (%) Demoulding macrodefects Example 1 100％ 0.008 99.5 None Example 2 100％ 0.010 99.1 None Example 3 100％ 0.007 99.3 None Comparative Example 1 70％ - 98.2 Demoulding breakage Comparative Example 2 80％ 0.006 98.9 Surface sticking Comparative Example 3 85％ 0.005 97.3 None Comparative Example 4 75％ 0.004 97.7 None Comparative Example 5 65％ - 93.5 Pressing body breakage

[0049] As shown in Table 2, within the process parameter range of Examples 1 to 3, high-quality titanium alloy parts with a green compact qualified rate of 100%, a hydrogen content of less than 0.015%, and a relative density of more than 99% can be obtained.

[0050] Comparative Example 1 and Comparative Example 5 prove that when the cold pressing pressure or the first sintering temperature is too low, the qualified green compact cannot be obtained. Comparative Example 2 shows that the excessively high first sintering temperature causes new technical problems. Comparative Example 3 and Comparative Example 4 prove that when the second sintering temperature exceeds the preferred range of the present application, although the complete green compact can be obtained, it is difficult to achieve the best balance between the density and the microstructure, and it is difficult to obtain parts with excellent comprehensive performance.

[0051] The above is the preferred embodiment of the present application, any simple modification, equivalent change and modification of the above embodiment according to the technical essence of the present application fall within the protection scope of the present application.

Claims

1. A method for preparing titanium alloy parts using near-net-shape forming of titanium hydride powder, characterized in that, Includes the following steps: (1) Powder mixing: Mix titanium hydride powder and intermediate alloy powder evenly according to the composition ratio of the target titanium alloy; (2) Cold pressing: The powder that was mixed evenly in step (1) is placed into a mold and a pressure of 200-800 MPa is applied for cold pressing to form a blank; (3) Sintering with mold: The pressed blank obtained in step (2) is placed together with the mold in a vacuum or inert gas environment and heated to 500-1200°C at a heating rate of 5-20°C / min, held for 10-30 minutes, and then cooled with the furnace. (4) Final sintering: Take out the compact sintered with mold in step (3) from the mold, heat it to 1200-1400℃ in a vacuum or inert gas environment, hold it for 2-4 hours, and then cool it with the furnace to obtain titanium alloy parts.

2. The preparation method according to claim 1, characterized in that, The pressure for cold pressing in step (2) is 400-500 MPa, and the holding time is 15-20 min.

3. The preparation method according to claim 1, characterized in that, The heating rate of the sintering with mold in step (3) is 8-15℃ / min, and the heating temperature is 800-1000℃.

4. The preparation method according to claim 1, characterized in that, The heating rate for the final sintering in step (4) is 8-15℃ / min, and the heating temperature is 1250-1350℃.

5. The preparation method according to claim 1, characterized in that, The vacuum level of the vacuum environment described in steps (3) and (4) is 1×10⁻⁶. -3 Pa to 5×10 -4 Pa.

6. The preparation method according to claim 1, characterized in that, The inert gas mentioned in steps (3) and (4) is argon or helium with a purity of not less than 99.99%.

7. The preparation method according to claim 1, characterized in that, The intermediate alloy powder mentioned in step (1) is an aluminum-vanadium intermediate alloy powder, which is composed of 58-62% aluminum and 38-42% vanadium by weight percentage; the average particle size of the intermediate alloy powder is 50-100 μm, the average particle size of the titanium hydride powder is 35-45 μm, and the target alloy is a Ti-6Al-4V alloy.

8. The preparation method according to claim 1, characterized in that, The titanium alloy component has a hydrogen content of less than 0.015% and a relative density of more than 99%.

Images