阅读说明：本技术 一种实现激光增材制造钛合金强韧化的方法 (Method for strengthening and toughening titanium alloy manufactured by laser additive ) 是由 张强 张思雨 胡云龙 李卫 林鑫 陈静 于 2020-11-19 设计创作，主要内容包括：本发明公开了一种实现激光增材制造钛合金强韧化的方法,该方法通过控制激光增材制造工艺和后热处理制度获得“全等轴β晶粒+均匀晶内α相”组织,从而实现激光增材制造钛合金的强韧化。该方法步骤如下：首先对激光增材制造钛合金进行初步的工艺参数优化,结合成形过程的冷却控制,实现“全等轴β晶粒+全马氏体/全β相”沉积态组织的制备；随后,采用不同热处理制度使沉积态试样中的马氏体相或β相转变为均匀的α板条,从而得到“全等轴β晶粒+均匀的晶内α相”组织,为保证等轴β晶粒不粗化,热处理温度应低于β相变点；最后,将经不同热处理后的试样加工成标准拉伸样并进行拉伸测试,选择力学性能最优的热处理制度。(The invention discloses a method for strengthening and toughening a titanium alloy manufactured by laser additive manufacturing, which obtains a structure of 'full equiaxial beta crystal grains + uniform intragranular alpha phase' by controlling a laser additive manufacturing process and a post-heat treatment system, thereby realizing the strengthening and toughening of the titanium alloy manufactured by the laser additive manufacturing. The method comprises the following steps: firstly, carrying out primary process parameter optimization on the titanium alloy manufactured by laser additive manufacturing, and combining with the cooling control of the forming process to realize the preparation of a 'full equiaxial beta crystal grain + full martensite/full beta phase' deposition state structure; then, adopting different heat treatment systems to convert martensite phase or beta phase in the deposition state sample into uniform alpha lath, thereby obtaining a structure of 'full equiaxial beta crystal grain + uniform intragranular alpha phase', wherein in order to ensure that equiaxial beta crystal grain is not coarsened, the heat treatment temperature is lower than a beta phase transformation point; and finally, processing the samples subjected to different heat treatments into standard tensile samples, performing tensile test, and selecting a heat treatment system with optimal mechanical properties.)

1. A method for realizing strengthening and toughening of a titanium alloy manufactured by laser additive is characterized by comprising the following steps:

(1) in an inert gas protection chamber, laser is used as a heat source, inert gas is used as a carrier to synchronously convey titanium alloy powder, and the preparation of a structure of 'full equiaxial beta crystal grains + full martensite/full beta phase' is realized through the optimization of additive manufacturing process parameters and the cooling control of a formed piece;

(2) and carrying out heat treatment at a temperature lower than the phase change point of the titanium alloy, and uniformly precipitating an alpha phase on the premise of ensuring that the equiaxed beta crystal grains are not coarsened to prepare the titanium alloy component with a structure of 'fully equiaxed beta crystal grains + uniform intragranular alpha phase'.

2. The method according to claim 1, characterized in that it comprises in particular the steps of:

s1, setting three of four parameters of laser power, spot diameter, scanning speed and powder feeding amount, and performing parameter design by taking another parameter as a variable;

s2, adopting the parameters in S1 to deposit a single-channel single-layer sample, analyzing the surface appearance and the tissue characteristics of the sample, and selecting laser power, spot diameter, scanning speed and powder feeding amount with good surface quality and equiaxed grain appearance as primary selection process parameters;

s3, carrying out single-pass multilayer sample deposition by adopting primary selection process parameters and different lifting amounts, analyzing the surface appearance and the tissue characteristics of the sample, and selecting parameters with good surface quality and equiaxed crystal grains in the shape of crystal grains to obtain the optimized lifting amount;

s4, depositing a plurality of layers of block samples at different lap joint rates, pausing the forming process every several deposited layers to fully cool the deposited part, repeating the process to finish the deposition of the plurality of layers of block samples, carrying out metallographic examination, and selecting the lap joint rate with no defect at the lap joint and equiaxed grain shape as the optimization;

s5, carrying out different heat treatments on the sample, wherein the heat treatment temperature of each stage is not higher than the phase transformation point of the titanium alloy;

and S6, processing the heat treatment sample into a standard tensile sample, then performing tensile test, and selecting a heat treatment system with optimal mechanical property.

3. The method of claim 1 or 2, wherein the beam spot shape of the laser is one or more of circular, linear, rectangular, and elliptical.

4. The method of claim 1 or 2, wherein the titanium alloy powder is selected from one of an alpha titanium alloy, a beta titanium alloy, and an alpha + beta titanium alloy.

5. The method of claim 2, wherein the sample is cooled in step S4 by natural cooling or by external air cooling or water cooling.

6. The method according to claim 2, wherein the influence of the powder feeding amount on the grain morphology is based on the amount of powder actually entering the molten pool, and the judgment of the powder feeding amount is not limited to the number of the powder feeder.

7. The method of claim 2, wherein the laser power is 1000W, the spot diameter is 1.1mm, the scanning speed is 10mm/s, the powder feeding amount is 40r/min, and the lift amount is 0.7 mm.

8. The method of claim 2, wherein the overlap ratio is 40% to 50%.

9. The method according to claim 1 or 2, characterized in that the heat treatment is an annealing treatment, a double annealing or a solution ageing treatment.

10. The method of claim 9, wherein the heat treatment regimen is 750 ℃,1h, WC +630 ℃,4h, AC.

Technical Field

The invention relates to the technical field of metal laser additive manufacturing, in particular to a method for strengthening and toughening titanium alloy manufactured by laser additive manufacturing, and specifically relates to a method for strengthening and toughening titanium alloy manufactured by additive manufacturing by controlling an additive manufacturing forming process and a post-heat treatment system to obtain a structure of 'full equiaxial beta crystal grains + uniform alpha phase'.

Background

The application demand of advanced aerospace equipment on titanium alloy components with high complexity, light weight and structural performance is increasingly urgent, but the traditional technology cannot meet the manufacturing demand of high-end titanium alloy components. Based on the manufacturing idea of dispersion and accumulation, the metal additive manufacturing technology integrating the technologies of computer aided design, numerical control, rapid prototyping and the like can realize the die-free, rapid and full-compact near-net forming of the high-performance metal part with the complex structure, and is an effective means for solving the manufacturing problem of aerospace high-end equipment. Currently, additive manufacturing of titanium alloy components has gained important applications in the aerospace field. However, in the additive manufacturing process, large columnar beta grains and non-uniform alpha phases exist in the titanium alloy component due to high temperature gradient and complex thermal cycle, the structural characteristics seriously influence the mechanical properties of the formed component, and particularly seriously reduce the plasticity in the direction vertical to the growth direction of the columnar grains, so that the method becomes a great obstacle for limiting the application of the technology in more fields. Therefore, the improvement of the toughness of the titanium alloy manufactured by the additive manufacturing by preparing the 'all-equiaxed beta crystal grains + the uniform intragranular alpha phase' becomes a research hotspot in the field. Currently, obtaining fully equiaxial β -grains requires a deformation treatment (journal of metals, 2017,53(9): 1065-. However, the method has obvious disadvantages, such as that the forming equipment is more complicated, the forming of parts with complicated structures is difficult, and the high-temperature solution treatment often causes the coarsening of beta crystal grains, thereby seriously damaging the mechanical properties of the formed parts, and the like.

Disclosure of Invention

The invention aims to solve the defects in the prior art, and the transformation of columnar crystal orientation equiaxial crystals is induced by partially melting powder particles on the premise of not changing the existing equipment and alloy components by regulating and controlling an additive manufacturing and forming process, and meanwhile, the non-uniform temperature of the whole is avoided and the higher cooling speed is kept by cooling and controlling a formed part, so that an all-beta phase or an all-alpha' martensite phase is obtained in a deposition state; and then, combining a post-heat treatment method lower than beta phase transformation, and obtaining the organization characteristics of 'full equiaxial beta crystal grains + uniform intragranular alpha phase' on the premise of avoiding the coarsening of equiaxial beta crystal grains, thereby realizing the strengthening and toughening method of the titanium alloy manufactured by the additive.

The purpose of the invention can be achieved by the following technical scheme.

A method for realizing laser additive manufacturing titanium alloy strengthening and toughening is characterized in that laser is used as a heat source and inert gas is used as a carrier to synchronously convey titanium alloy powder in an inert gas protection chamber, and a titanium alloy component is freely formed without a die; the manufacturing method comprises the steps of optimizing additive manufacturing process parameters and controlling cooling of a formed part to realize preparation of a structure of 'full equiaxial beta crystal grains + full martensite/full beta phase'; then, carrying out post heat treatment at the temperature lower than the phase change point of the alloy, and uniformly precipitating an alpha phase on the premise of ensuring that equiaxed beta grains are not coarsened, thereby realizing the preparation of a structure of 'full equiaxed beta grains + uniform intragranular alpha phase'; and finally, processing the samples subjected to different heat treatments into standard tensile samples, performing tensile test, and selecting a heat treatment system with optimal mechanical properties.

Further, the method comprises the steps of:

s1, setting three of four parameters such as laser power, spot diameter, scanning speed and powder feeding amount, and performing parameter design by taking another parameter as a variable;

s2, performing single-channel single-layer sample deposition by adopting the parameters, analyzing the surface appearance and the tissue characteristics of the sample, and selecting the parameters such as laser power, spot diameter, scanning speed and the like with good surface quality and equiaxed crystal grains in the appearance as the primary selection process parameters;

s3, carrying out single-pass multilayer sample deposition by adopting primary selection process parameters and different lifting amounts, analyzing the surface appearance and the tissue characteristics of the sample, and selecting parameters with good surface quality and equiaxed crystal grains in the shape of crystal grains to obtain the optimized lifting amount;

s4, depositing a plurality of layers of block samples at different lap joint rates, pausing the forming process every several deposited layers to fully cool the deposited part, repeating the process to finish the deposition of the plurality of layers of block samples, carrying out metallographic examination, and selecting the lap joint rate with no defect at the lap joint and equiaxed grain shape as the optimization;

s5, carrying out heat treatment on the sample, wherein the heat treatment temperature in each stage is not higher than the phase transformation point of the alloy;

and S6, processing the heat treatment sample into a standard tensile sample, then performing tensile test, and selecting a heat treatment system with optimal mechanical property.

Further, the shape of the beam spot of the laser is one or more of circular, linear, rectangular and elliptical.

Further, the titanium alloy powder is selected from one of an alpha titanium alloy, a beta titanium alloy, and an alpha + beta titanium alloy.

Further, the cooling method of the sample in step S4 may be natural cooling or external air cooling or water cooling.

Furthermore, the influence of the powder feeding amount on the shape of the crystal grains is based on the amount of powder actually entering the molten pool, and the judgment of the powder feeding amount is not limited to the number of the powder feeder.

Further, the determination of the parameters such as the laser power, the spot diameter, the scanning speed, the lifting amount, the overlapping ratio and the like in the steps S1 to S4 can be directly selected according to previous experience, so that the process steps are simplified.

Further, the laser power is 1000W, the diameter of a light spot is 1.1mm, the scanning speed is 10mm/s, the powder feeding amount is 40r/min, the lifting amount is 0.7mm, and the overlapping rate is 40-50%.

Further, the heat treatment system in step S5 may be annealing treatment, double annealing, solution aging treatment, or the like.

Further, the heat treatment schedule is 750 ℃,1h, WC +630 ℃,4h and AC.

Compared with the prior art, the invention has the following advantages and effects:

(1) the preparation of the fully equiaxial beta crystal grains is realized by regulating and controlling the forming process parameters, the size of the crystal grains is controllable from tens of microns to hundreds of microns, no grain refiner is required to be added, no deformation treatment is required to be combined, and the process is simpler and more flexible.

(2) The heat treatment temperature of the invention is lower than the phase transformation point of the titanium alloy, the heat treatment system is flexible to select, and the controllability of the alpha phase in the crystal from nano level to micron level can be realized on the premise of not changing the shape and the size of the equiaxial beta crystal grains.

(3) The toughening method provided by the invention can simultaneously reduce the anisotropy of the titanium alloy manufactured by the additive.

Drawings

FIG. 1 is a plot of the size and morphology of a single-pass monolayer specimen in example 1 of the present invention.

FIG. 2 is a graph showing the grain morphology of a single-pass multilayer sample at different powder feeding amounts in example 1 of the present invention.

FIG. 3 is a structural morphology of "full equiaxed grain structure + full α' martensite phase" in the Ti17 alloy as-deposited state in example 1 of the present invention.

FIG. 4 is a structural morphology of "holoisometric crystal structure + homogeneous intragranular alpha phase" of the Ti17 alloy in the heat treatment state in the embodiment 1 of the invention.

FIG. 5 is a graph comparing the mechanical properties of Ti17 alloy in example 1 of the present invention with those reported in the literature, wherein H represents the transverse direction and V represents the longitudinal direction; AD represents as-deposited; HT represents a heat treatment state; LSP denotes laser shock.

FIG. 6 is a schematic flow chart of a method for strengthening and toughening a titanium alloy by laser additive manufacturing according to the present invention.

Detailed Description

The following further describes embodiments of the present invention with reference to the examples and the drawings, but the embodiments of the present invention are not limited thereto.

The schematic flow diagram of the method for strengthening and toughening the titanium alloy through laser additive manufacturing is shown in fig. 6.

Example 1

A method for realizing strengthening and toughening of a Ti17 titanium alloy manufactured by laser additive manufacturing comprises the following steps:

the first step is as follows: given a laser power (1000W), a spot diameter (1.1mm), and a scanning speed (10mm/s), the powder feed rate was set to increase from 10r/min to 90r/min by 10 r/min.

The second step is that: the surface topography and texture characteristics of the samples obtained by single pass monolayer deposition using the above parameters are shown in fig. 1.

The third step: and respectively forming single-pass multilayer samples by adopting the powder feeding amount, wherein the lifting amount is determined according to the size of the single-pass deposition layer (70% -90% of the deposition height can be selected). And analyzing the surface appearance and the tissue characteristics of the sample, and selecting parameters with good surface quality and equiaxed grain appearance as the preferred forming parameters. Fig. 2 shows the holoisometric crystal structure obtained by optimizing the process parameters, which are as follows: (laser power: 1000W, powder feeding amount: 40r/min, spot diameter: 1.1mm, scanning speed: 10mm/s, lifting amount: 0.7 mm).

The fourth step: depositing a plurality of layers of block samples, pausing the forming process for 5 minutes when 3 layers are deposited, fully cooling the deposited part, and repeating the process to finish the deposition of the plurality of layers of block samples; a microstructure with "fully equiaxed beta grains + fully martensitic" as shown in figure 3 is obtained.

The fifth step: and (3) carrying out heat treatment on the sample, wherein the heat treatment temperature in each stage is not higher than the phase transformation point of the alloy so as to prevent the coarsening of beta crystal grains. The heat treatment schedule of this example was 750 ℃,1h, WC (water cooling) +630 ℃,4h, AC (air cooling), to obtain the "fully equiaxed β -grains + homogeneous intragranular α -phase" structure shown in fig. 4.

And a sixth step: a sample with a structure of 'full equiaxial beta crystal grains + uniform intragranular alpha phase' is subjected to a tensile test (the tensile test is carried out according to the national standard GB T228.1-2010), and in the tensile process, the equiaxial beta crystal grains effectively block crack propagation, so that the mechanical property of the Ti17 alloy manufactured by laser additive manufacturing is obviously improved. As shown in FIG. 5, the mechanical properties of the Ti17 alloy obtained by the method provided by the invention in the transverse direction and the longitudinal direction are the best properties reported at present (document 1: Trans. non-ferrous Metals Soc. China 26(2016) 2058-.

The above embodiments are preferred embodiments of the present invention, but the present invention is not limited to the above embodiments, and any other changes, modifications, substitutions, combinations, and simplifications which do not depart from the spirit and principle of the present invention should be construed as equivalents thereof, and all such changes, modifications, substitutions, combinations, and simplifications are intended to be included in the scope of the present invention.