Alpha grain equiaxing method for laser additive manufacturing of titanium-based composite material

Abstract

The invention relates to an alpha crystal grain equiaxing method for a laser additive manufacturing titanium-based composite material, which comprises a heating and cooling treatment process of the titanium-based composite material and a repeated step of the heating and cooling treatment process, and the alpha crystal grain equiaxing titanium-based composite material is obtained by discharging and air cooling, the equiaxed alpha crystal grains are primary alpha crystal grains with an aspect ratio of less than or equal to 3. According to the method, on the basis that the shape of a laser additive manufacturing component is not damaged, an alpha-phase matrix structure with a high-isometric alpha grain proportion is constructed by means of nucleation sites provided by the reinforcement phase and a multi-time heating and cooling system, and alpha grain equiaxing of the laser additive manufacturing titanium-based composite material is achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of microstructure regulation of metal matrix composites. Background Art

[0002] Titanium matrix composites have relatively high specific strength and service temperature. Compared with high-temperature titanium alloys, their service temperature can be increased by 100 - 200 °C. Compared with superalloys, they have better high-temperature resistance and fatigue performance, and the weight reduction is up to 46%. They are ideal metal structural materials integrating high-temperature resistance, high strength and lightweight.

[0003] Compared with traditional manufacturing methods, preparing titanium matrix composites by laser additive manufacturing technology can promote the formation of fine lamellar α or acicular α', which can significantly improve the strength of titanium matrix composites. However, while the strength is improved, the plasticity decreases, resulting in obstacles to its application. Among them, equiaxed and duplex microstructure titanium alloys have relatively high plasticity, and equiaxed α exhibits better comprehensive performance than acicular α'. Its microstructure characteristics are also applicable to the performance improvement of titanium matrix composites. Therefore, the equiaxialization of α grains in laser additive manufacturing titanium matrix composites is an important way to expand the application range of titanium matrix composites.

[0004] Generally speaking, the equiaxialization of α grains in titanium alloys can generally be achieved by hot deformation or heat treatment. The Chinese invention patent with the publication number CN106011538 discloses a method for controlling grain equiaxialization to improve the plasticity of Ti20Zr6.5Al4V titanium alloy. By quenching, rolling and annealing the titanium alloy bars, the volume fraction of equiaxed grains exceeds 85%. However, the deformation process will destroy the original structural form of the component, which conflicts with the near-net-shape characteristics pursued by laser additive manufacturing.

[0005] The Chinese invention patent with the publication number CN113355666A discloses a method for refining and equiaxializing the microstructure of TC18 titanium alloy by laser cladding additive manufacturing. The transformation from coarse columnar grains to equiaxed grains is achieved through cyclic heat treatment. However, due to the existence of reinforcing phases in titanium matrix composites, there are relatively large differences in their microstructures from those of titanium alloys, and this process method is not suitable for laser additive manufacturing of titanium matrix composites either.

[0006] In summary, at present, the equiaxialization of α grains in titanium alloys by using hot deformation and heat treatment processes is not suitable for ceramic phase-reinforced titanium matrix composites. Therefore, the equiaxialization of α grains in laser additive manufacturing titanium matrix composites still belongs to a technical blank. Summary of the Invention

[0007] The object of the present invention is to avoid the deficiencies of the prior art and provide a method for equiaxed grain of α grains in the structure of a laser additive manufactured titanium matrix composite, and the proportion of equiaxed α grains exceeds 75%.

[0008] To achieve the above object, the technical solution adopted by the present invention is: a method for equiaxed grain of α grains in a laser additive manufactured titanium matrix composite, comprising the following steps: Place the titanium matrix composite obtained by laser additive manufacturing in a heat treatment furnace with vacuum or argon protection, heat it at a heating rate of 10 - 15 °C / min until the titanium matrix composite is heated in the furnace to a temperature 40 - 80 °C below the β phase transformation point; Then, continue to heat the titanium matrix composite at a heating rate of 2 - 10 °C / min to a temperature 5 - 10 °C below the β phase transformation point; Finally, cool the titanium matrix composite at a cooling rate of 2 - 10 °C / min to a temperature 40 - 80 °C below the β phase transformation point; At this time, a heating and cooling treatment process of the titanium matrix composite is completed; After repeating the heating and cooling treatment process 3 - 10 times, take it out of the furnace and air-cool it to obtain a titanium matrix composite with equiaxed α grains, wherein the equiaxed α grains are primary α grains with an aspect ratio less than or equal to 3.

[0009] Further, the reinforcing phase of the laser additive manufactured titanium matrix composite is TiB whiskers, and the volume fraction of the reinforcing phase is greater than 1 vol.%; the matrix titanium alloy of the laser additive manufactured titanium matrix composite is Ti65, Ti6242 or Ti55 alloy.

[0010] Further, the volume fraction of the reinforcing phase is 1 - 2.5 vol.%.

[0011] Further, the vacuum environment means that the vacuum degree in the heat treatment furnace is lower than 500 Pa; the argon protection environment means that argon is introduced into the heat treatment furnace and the argon flow rate is controlled to be 0.5 - 1.5 L / min.

[0012] Further, the α phase in the structure of the titanium matrix composite with equiaxed α grains is composed of primary equiaxed α grains, primary rod-shaped α grains and secondary lamellar α grains, the volume fraction of the primary α grains is 20 - 35%, and the proportion of equiaxed α grains is 75 - 95%.

[0013] Further, the method for quantifying the equiaxed α grains is as follows: in the microstructural image of the titanium matrix composite with equiaxed α grains, the adhered α grains are segmented at the concave points, and then the volume fraction of the equiaxed α grains and the volume fraction of the primary α grains are statistically analyzed. Then, the calculation formula for the proportion of the equiaxed α grains is as follows:

[0014] Wherein, is the proportion of the equiaxed α grains, is the volume fraction of the equiaxed α grains, is the volume fraction of the primary α grains, and the units are all %.

[0015] Further, the laser additive manufactured titanium matrix composite is a titanium matrix composite with a length of 50 - 100 mm, a width of 3 - 20 mm, and a height of 10 - 35 mm obtained by single-pass or multi-pass additive manufacturing.

[0016] Further, during the laser additive manufacturing, the laser power is 1500 - 2500 W, the powder feeding rate is 6 - 10 g / min, the scanning rate is 3 - 7 mm / s, the spot diameter is 3 - 6 mm, and the overlapping rate is 40 - 70%.

[0017] Compared with the prior art, the present invention has the following beneficial effects: on the basis of not damaging the shape of the laser additive manufactured component, the present invention utilizes the nucleation sites provided by the reinforcing phase and the multiple heating and cooling regimes to construct an α-phase matrix structure with a high proportion of equiaxed α grains (exceeding 75%), realizing the equiaxialization of the α grains in the laser additive manufactured titanium matrix composite, and the present invention can provide a new idea for the α grain equiaxialization method of other titanium alloys or titanium matrix composites. Description of the Drawings

[0018] Figure 1 is the original microstructure of the 1 vol.% TiBw / Ti65 composite material sample of Specific Example 1 of the present invention; Figure 2 is the microstructure of the 1 vol.% TiBw / Ti65 composite material sample of Specific Example 1 of the present invention after heating and cooling 3 times; Figure 3 is the microstructure of the 1 vol.% TiBw / Ti65 composite material sample of Specific Example 1 of the present invention after heating and cooling 5 times; Figure 4 is the original microstructure of the 2 vol.% TiBw / Ti65 composite material sample of Specific Example 2 of the present invention; Figure 5 is the microstructure of the 2 vol.% TiBw / Ti65 composite material sample of Specific Example 2 of the present invention after heating and cooling 5 times. Detailed implementation manners

[0019] The principles and features of the present invention will be described below in conjunction with the accompanying drawings. The examples given are only used to explain the present invention and are not intended to limit the scope of the present invention.

[0020] In order to achieve the above object, the present invention provides the following detailed implementation manners: Example 1: A method for equiaxedization of α grains in a laser additive manufactured titanium matrix composite, comprising the following steps: Step 1: Using a laser power of 1500 - 2500 W, a powder feeding rate of 6 - 10 g / min, a scanning rate of 3 - 7 mm / s, a spot diameter of 3 - 6 mm, a lap rate of 40 - 70%, and performing single-pass or multi-pass additive manufacturing to obtain a titanium matrix composite with a length of 50 - 100 mm, a width of 3 - 20 mm, and a height of 10 - 35 mm; The reinforcing phase of the laser additive manufactured titanium matrix composite is TiB whiskers, and the volume fraction of the reinforcing phase is greater than 1 vol.%; The matrix titanium alloy of the laser additive manufactured titanium matrix composite is Ti65 alloy.

[0021] Step 2: Place the titanium matrix composite obtained by laser additive manufacturing in a heat treatment furnace with a vacuum degree lower than 500 Pa, and heat it at a heating rate of 10 - 15 °C / min until the titanium matrix composite is heated with the furnace to a temperature 40 - 80 °C lower than the β phase transformation point; Then, continue to heat the titanium matrix composite at a heating rate of 2 - 10 °C / min to a temperature 5 - 10 °C lower than the β phase transformation point; Finally, cool the titanium matrix composite at a cooling rate of 2 - 10 °C / min to a temperature 40 - 80 °C lower than the β phase transformation point; At this time, one heating and cooling treatment process of the titanium matrix composite is completed; After repeating the heating and cooling treatment process 3 - 10 times, take it out of the furnace and air-cool it to obtain a titanium matrix composite with equiaxed α grains, wherein the equiaxed α grains are primary α grains with an aspect ratio less than or equal to 3.

[0022] The α phase in the microstructure of the titanium matrix composite with equiaxed α grains consists of primary equiaxed α grains, primary rod-shaped α grains, and secondary lamellar α grains. The volume fraction of the primary α grains is 20 - 35%, and the proportion of the equiaxed α grains is 75 - 95%.

[0023] Example 2: The same as Example 1, except that the titanium matrix composite obtained by laser additive manufacturing is placed in a heat treatment furnace into which argon is introduced, and the argon flow rate is controlled to be 0.5 - 1.5 L / min.

[0024] Example 3: Identical to Example 1, except that the volume fraction of the reinforcing phase of the laser additive manufactured titanium matrix composite is greater than 1 vol.% or is 1 - 2.5 vol.%. The matrix titanium alloy of the laser additive manufactured titanium matrix composite is Ti6242 alloy.

[0025] Example 4: Identical to Example 1, except that the volume fraction of the reinforcing phase of the laser additive manufactured titanium matrix composite is greater than 1 vol.% or is 1 - 2.5 vol.%. The matrix titanium alloy of the laser additive manufactured titanium matrix composite is Ti55 alloy.

[0026] Example 5: Identical to Example 1, except that the proportion of equiaxed α grains in Example 1 is 75 - 95%, which is obtained by the following quantification method: In the microstructure picture of the α grain equiaxed titanium matrix composite, the adhered α grains are segmented at the concave points, and then the volume fraction of equiaxed α grains and the volume fraction of primary α grains are statistically analyzed. Then, the calculation formula for the proportion of equiaxed α grains is as follows:

[0027] Among them, is the proportion of equiaxed α grains, is the volume fraction of equiaxed α grains, is the volume fraction of primary α grains, and the units are all %.

[0028] As Figures 1 - 5 shown, in order to further illustrate the technical solutions and technical effects of the present invention, the present invention provides the following specific examples: Specific Example 1: A method for equiaxing α grains of a laser additive manufactured titanium alloy composite, comprising the following steps: Step (1): Place a 1 vol.% TiBw / Ti65 composite material sample prepared by laser additive manufacturing technology in a heat treatment furnace filled with argon for protection, with the argon flow rate being 1 L / min, and heat the sample to 1000 °C at a heating rate of 10 °C / min; Step (2): After Step (1), heat the sample to 1060 °C at a heating rate of 10 °C / min; Step (3): After Step (2), cool the sample to 1000 °C at a cooling rate of 2 °C / min; Step (4): Repeat the sample in Steps (2) and (3) 3 times, then take it out of the furnace and air cool to finally obtain a 1 vol.% TiBw / Ti65 composite material sample after heating and cooling 3 times.

[0029] 1vol.% TiBw The original microstructure of the 1vol.% TiBw / Ti65 composite material sample and the microstructure after being treated with Specific Example 1 are respectively as follows Figure 1 and Figure 2 shown. The microstructure pictures of the titanium matrix composite material after heating and cooling three times are imported into the PS software for contrast processing, and the adhered α grains are segmented at the concave points, and then the quantitative software IPP is used to statistically analyze the volume fraction of equiaxed α and the volume fraction of primary α.

[0030] The α-phase quantitative results of the 1vol.% TiBw / Ti65 composite material after being treated with Specific Example 1 are shown in Table 1. w

[0031] Specific Example 2: The same as Specific Example 1, except that the number of heating and cooling times is 5 times.

[0032] Step (1): Place the 1 vol.% TiBw / Ti65 composite material prepared by laser additive manufacturing technology in a heat treatment furnace with argon protection, and the flow rate of the introduced argon is 1 L / min, and heat the sample to 1000 °C at a heating rate of 10 °C / min; Step (2): After Step (1), heat the sample to 1060 °C at a heating rate of 10 °C / min; Step (3): After Step (2), cool the sample to 1000 °C at a cooling rate of 2 °C / min; Step (4): Repeat the sample 5 times in Steps (2) and (3), and then take it out of the furnace and air-cool it to finally obtain the 1vol.% TiBw / Ti65 composite material sample after heating and cooling 5 times.

[0033] The original microstructure of the 1vol.% TiBw / Ti65 composite material sample and the microstructure after being treated with Specific Example 2 are respectively as follows Figure 1 and Figure 3 shown. Statistically analyze the volume fraction of equiaxed α and the volume fraction of primary α of the titanium matrix composite material after heating and cooling 5 times. The α-phase quantitative results of the 1vol.% TiBw / Ti65 composite material after being treated with Specific Example 2 are shown in Table 1.

[0034] Specific Example 3: The same as Specific Example 2, except that the TiBw volume fraction of the laser additive manufacturing TiBw / Ti65 composite material sample is 2vol.%.

[0035] Step (1): Place the 2vol.% TiBw / Ti65 composite material prepared by laser additive manufacturing technology in a heat treatment furnace with argon protection, and the flow rate of the introduced argon is 1 L / min, and heat the sample to 1000 °C at a heating rate of 10 °C / min;​ Step (2): After step (1), heat the sample to 1060 °C at a heating rate of 10 °C / min; Step (3): After step (2), cool the sample to 1000 °C at a cooling rate of 2 °C / min; Step (4): Repeat the sample 5 times in steps (2) and (3), then take it out of the furnace and air-cool it, finally obtaining a 2vol.% TiBw / Ti65 composite material sample after heating and cooling 5 times.

[0036] The original microstructure of the 2vol.% TiBw / Ti65 composite material sample and the microstructure after being treated by Specific Example 3 are respectively as Figure 4 and Figure 5 shown. Statistically analyze the volume fraction of equiaxed α and primary α in the titanium matrix composite after heating and cooling 5 times.

[0037] The α-phase quantitative results of the 2vol.% TiBw / Ti65 composite material treated by Specific Example 3 are shown in Table 1.

[0038] Table 1

[0039] From Table 1 and Figures 1 - 3 the analysis, it can be obtained that the α-phase of the original microstructure of the 1vol.% TiBw / Ti65 composite material sample is all lamellar α. After being treated by the heating and cooling regimes of Specific Example 1 and Specific Example 2, the original α-phase transforms into a mixed structure composed of primary equiaxed α, primary rod-shaped α, and secondary lamellar α.

[0040] Among them, the volume fraction of primary α after heating and cooling 3 times is 24.62%, and the proportion of equiaxed α grains is 87.61%; the volume fraction of primary α after heating and cooling 5 times is 26.29%, and the proportion of equiaxed α grains is 90.00%.

[0041] From Table 1, Figure 4 and Figure 5 the analysis, it can be obtained that the α-phase of the original microstructure of the 2vol.% TiBw / Ti65 composite material sample is also all lamellar α. After being treated by the heating and cooling regime of Specific Example 3, the original α-phase transforms into the same mixed structure as Specific Example 1. The difference is that the volume fraction of primary α is 32.55%. Among them, the proportion of equiaxed α grains is as high as 95.36%, which is 8.84% higher than that of Specific Example 1. This is attributed to the fact that a higher volume fraction of TiBw is beneficial to the equiaxialization of α grains.

[0042] The above results show that the present invention has achieved the equiaxed α grain of the titanium matrix composite by means of multiple heating and cooling regimes, which is beneficial to the improvement of the plasticity of the titanium matrix composite prepared by laser additive manufacturing, and has broad practical application prospects.

[0043] The above are only the preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A method for equiaxing α grains in laser additive manufacturing of titanium-based composite materials, characterized in that: The following steps are involved: The titanium-based composite material obtained by laser additive manufacturing is placed in a heat treatment furnace with vacuum or argon protection, and heated at a heating rate of 10 to 15 °C / min until the titanium-based composite material is heated to a temperature 40 to 80 °C lower than the β phase transition point; Next, the titanium-based composite material is further heated to a temperature 5 to 10° C. lower than the β phase transition point at a heating rate of 2 to 10° C. / min; Finally, the titanium-based composite material is cooled to a temperature 40 to 80°C below the β-transformation point at a cooling rate of 2 to 10°C / min; At this point, the heating and cooling process of the titanium-based composite material is completed; After the heating and cooling process is repeated 3 to 10 times, the composite material is taken out of the furnace and air-cooled, thereby obtaining a titanium-based composite material with equiaxed α grains, wherein the equiaxed α grains are primary α grains with an aspect ratio of less than or equal to 3.

2. The method for equiaxing α grains of titanium-based composite materials by laser additive manufacturing according to claim 1, characterized in that: The reinforcement phase of the laser additively manufactured titanium-based composite material is TiB whiskers, and the volume fraction of the reinforcement phase is greater than 1 vol.%; the matrix titanium alloy of the laser additively manufactured titanium-based composite material is Ti65, Ti6242 or Ti55 alloy.

3. The method for equiaxing α grains of titanium-based composite materials manufactured by laser additive manufacturing according to claim 2, characterized in that: The volume fraction of the reinforcement phase is 1 to 2.5 vol.%.

4. The method for equiaxing α grains of titanium-based composite materials manufactured by laser additive manufacturing according to claim 1, characterized in that: The vacuum environment refers to: the vacuum degree in the heat treatment furnace is lower than 500 Pa; the argon protection environment refers to: argon is introduced into the heat treatment furnace and the argon flow rate is controlled to be 0.5 to 1.5 L / min.

5. The method for equiaxing α grains of titanium-based composite materials by laser additive manufacturing according to claim 1, characterized in that: The α phase in the α-grain equiaxed titanium-based composite material organization consists of primary equiaxed α grains, primary rod-shaped α grains and secondary lamellar α grains, the volume fraction of primary α grains is 20-35%, and the proportion of equiaxed α grains is 75-95%.

6. The method for equiaxing α grains of titanium-based composite materials by laser additive manufacturing according to claim 4, characterized in that: The quantitative method of the equiaxed α grains is as follows: in the microstructure picture of the equiaxed α grain titanium-based composite material, the adhered α grains are segmented at the concave points, and then the volume fraction of the equiaxed α grains and the volume fraction of the primary α grains are counted. Then, the calculation formula of the proportion of the equiaxed α grains is as follows: in, is the proportion of equiaxed α grains, is the volume fraction of equiaxed α grains, is the volume fraction of primary α grains, and the unit is %.

7. The method for equiaxing α grains of titanium-based composite materials produced by laser additive manufacturing according to claim 1, characterized in that: The laser additive titanium-based composite material is a titanium-based composite material with a length of 50-100 mm, a width of 3-20 mm, and a height of 10-35 mm obtained by single-pass or multi-pass additive manufacturing.

8. The method for equiaxing α grains in laser additive manufacturing of titanium-based composite materials according to any one of claims 1 to 7, characterized in that: The laser power during the laser additive process is 1500-2500 W, the powder feeding rate is 6-10 g / min, the scanning rate is 3-7 mm / s, the spot diameter is 3-6 mm, and the overlap rate is 40-70%.

Images