CN110405209A - Method for in-situ reduction of residual stress of titanium matrix composites prepared by selective laser melting - Google Patents

Abstract

The invention discloses a method for in-situ reduction of residual stress of titanium-based composite material prepared by selective laser melting. The method includes preparing titanium-based composite material powder. Confluence, the chemical substances include one or more of B boron element, C carbon element and rare earth element; spread one or more layers of titanium-based composite powder on the substrate of the selective laser melting equipment, and perform laser selective melting; After laser selective melting, the solidified surface is subjected to one or more laser remelting; the operation is repeated until the preparation of the titanium-based composite material component is completed. The invention reduces the local thermal effect caused by scanning the powder layer with a high-energy laser beam as a heat source by performing laser remelting on the solidified surface after laser selective melting, so that the reaction of the reinforcement is more thorough and the precipitation of the reinforcement is finer. , reduce the residual stress in the component preparation process, and change the properties of the material.

Description

Method for in-situ reduction of residual stress of titanium matrix composites prepared by selective laser melting

technical field

The invention belongs to the technical field of laser melting reinforcement material manufacturing, and relates to a method for in-situ reduction of residual stress of titanium-based composite materials prepared by selective laser melting.

Background technique

Laser additive manufacturing of titanium alloy parts is to be widely used in aircraft. However, since the selective laser melting process scans the powder layer with a high-energy laser beam as a heat source, this local heat input causes an uneven temperature field, causing local thermal effects, which make the molten pool extremely prone to residual residues during solidification and cooling. stress. Therefore, there will be extremely high residual stress inside the components manufactured by selective laser melting. The existence of residual stress will not only affect the dimensional stability of the component, but also reduce the yield strength, fatigue strength and corrosion resistance of the component, and will directly lead to the brittle failure of the component in severe cases. Residual stress can be reduced by rapidly removing the heat generated by the laser beam, which requires the metal powder material to have a sufficiently high thermal conductivity, which in turn leads to reduced component performance. Therefore, how to reduce and eliminate the residual stress in laser additive manufacturing components without reducing their performance has always been one of the research hotspots in the field of laser processing at home and abroad.

Titanium-based composites not only maintain the excellent properties of titanium, but also have higher specific strength and specific modulus than titanium. Therefore, the research on additive manufacturing of titanium-based composites is also in full swing. However, the plasticity of titanium-based composites is lower than that of titanium alloys. During the additive manufacturing process of titanium-based composites, the residual stress generated is significantly larger than that of titanium alloys, and cracking and warping often occur, resulting in selective laser melting additive manufacturing. Process interrupted.

At present, one way to deal with the residual stress release of selective laser melting of titanium alloys is to preheat the printing substrate, reduce the temperature gradient along the powder deposition direction during the forming process, and weaken the residual stress accumulation, but it is limited by the temperature that the internal devices of the machine can withstand. The preheating temperature loading of commercial selective laser melting additive manufacturing machines is generally lower than 200 °C, which is far lower than the stress annealing temperature of titanium alloys. Therefore, a simple and convenient method is urgently needed to reduce the titanium matrix composite during the manufacturing process. Material residual stress.

SUMMARY OF THE INVENTION

The purpose of the present invention is to overcome the defect of excessive residual stress and easy cracking of titanium-based composite materials prepared in the prior art, and to provide a method for in-situ reduction of residual stress of titanium-based composite materials prepared by selective laser melting.

To achieve the above object, the present invention provides the following technical solutions:

A method for in-situ reduction of residual stress of titanium-based composite material prepared by selective laser melting, comprising the following steps:

Step 1: Prepare a titanium-based composite material powder, the titanium-based composite material powder includes a combination of titanium or a titanium alloy and a chemical substance that generates a reinforcement, and the chemical substance includes one of B, boron, C, and rare earth elements. species and above;

Step 2: Lay one or more layers of titanium-based composite powder on the substrate of the selective laser melting equipment to perform laser selective melting;

Step 3. Perform one or more laser remelting on the solidified surface after the laser selected area is melted;

Step 4: Repeat steps 2 to 3 until the preparation of the titanium-based composite material component is completed.

The residual stress in the prepared titanium-based composite material component is reduced by 40% to 85% compared with the component prepared by not performing laser remelting on the solidified surface after selective laser melting.

The reinforcing body selected in the present invention contains more than one of boron element, carbon element and rare earth element, and the reinforcing body generated by in-situ reaction is more than one of TiB, TiC and rare earth oxide, wherein, the tensile strength of TiB and TiC is more than one. The strength is much greater than that of titanium, and its Young's modulus of elasticity is 4 to 5 times that of titanium, and its Poisson's ratio and density are similar to those of titanium and titanium alloys. The thermal expansion coefficient and thermodynamic compatibility are 50% higher than those of titanium and titanium alloys. Inside, it can be a good reinforcement for titanium-based materials. The rare earth elements in the reinforcement react with oxygen to form stable high melting point compounds, which are dispersed in the matrix material and can play a role in dispersion strengthening, which is beneficial to improve the high temperature instantaneous strength and lasting strength of the matrix material. In addition, rare earth elements and Oxygen binding in the matrix material reduces the oxygen content in the matrix material, which is beneficial to improve the thermal stability of the matrix material.

In the present invention, one or more additives containing boron element, carbon element and rare earth element are selected, and the reinforcements generated with the titanium-based material are TiB, TiC, La ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ , Ce ₂ O ₃ , Er ₂ O ₃ and Gd ₂ O ₃ , the present invention selects the above substances as the reinforcing body of the titanium-based material of the present invention because the above reinforcing bodies have better performance and the best matching degree with the titanium alloy. After laser remelting of the solidified surface after selective laser melting, the local thermal effect caused by the scanning of the powder layer by the high-energy laser beam as the heat source can be reduced, the reaction of the reinforcement can be more thorough, and the precipitation of the reinforcement can be made smaller, which is beneficial to Heterogeneous nucleation hinders the growth of dendrites in the same direction and interrupts the growth of dendrites, thereby reducing the residual stress in the component fabrication process and changing the properties of the material.

As the preferred technical solution:

A method for reducing residual stress of titanium matrix composites prepared by in-situ selective laser melting as described above, the titanium alloy is TC4 powder, IMI834 powder, IMI679 powder, IMI685 powder, Ti-6246 powder, Ti-6242 powder, Ti1100 Powder, BT36 powder, TC11 powder, Ti-55 powder, Ti60 powder or Ti600 powder. The protection scope of the present invention is not limited to this, and only some feasible materials are listed here, and other suitable titanium-containing materials can also be applied to the present invention.

In the above-mentioned method for reducing residual stress of titanium-based composite material prepared by selective laser melting in situ, the reinforcing body accounts for 0.1-20% of the total volume of the titanium-based composite material powder. The addition amount of the chemical substance to generate the reinforcement can be adjusted within a certain range according to the actual situation, but the adjustment range should not be too large, the addition amount is too large, it is easy to cause the residual stress of the titanium matrix composite material to be too large, resulting in component cracking , affecting the product quality, the addition amount is too small, it is difficult to significantly improve other properties of titanium matrix composites such as wear resistance, flame resistance and elastic modulus.

A method for reducing the residual stress of titanium-based composite material prepared by in-situ selective laser melting as described above. Matrix composite material blank, and then use the atomization method to make the powder. The preparation method of the titanium-based composite material powder is not limited to this, and the present invention only takes this as an example, and other suitable preparation methods can also be applied to the present invention.

A method for reducing residual stress of titanium-based composite material prepared by selective laser melting in situ as described above, the chemical substances are set to boron (B), carbon (C), B ₄ C (boron carbide), titanium diboride One or more of (TiB ₂ ), rare earth (Re) and rare earth oxide (ReX); the rare earth elements in the rare earth and rare earth oxide are all La, Nd, Y, Ce, Er or Gd.

Its reaction equation with titanium to generate reinforcement is as follows:

Ti+B=TiB;

Ti+C=TiC;

5Ti+B ₄ C=TiC+4TiB;

Ti+TiB ₂ =2TiB;

Re+O=Re ₂ O ₃ ;

Ti+2ReX+3O=TiX+Re ₂ O ₃ .

A method for reducing the residual stress of titanium-based composite materials prepared by in-situ selective laser melting as described above, laying a layer of titanium-based composite material powder on the substrate of the selective laser melting equipment, performing laser selective melting, and then after laser selective melting The solidified surface is subjected to one or more laser remelting;

Alternatively, lay multiple layers of titanium-based composite material powder on the substrate of the selective laser melting equipment, perform selective laser melting respectively, and then perform one or more laser remelting on the solidified surface after selective laser melting.

Among them, the number of times of laser remelting is not more than five times, and the laser selection area corresponding to each laser remelting contains at most five layers of titanium-based composite material powder, which can be determined according to the performance requirements of the titanium-based composite material components to be prepared.

A method for in-situ reduction of residual stress of titanium-based composite material prepared by selective laser melting as described above, the process parameters of selective laser melting are set as laser power 150-400 W, powder thickness 30-50 μm, and spot diameter 50-80 μm , the scanning speed is 600～1500mm/s, and the preheating temperature of the substrate is 30～200℃;

The process parameters of the laser remelting are set as laser power 150-400 W, powder thickness 30-50 μm, spot diameter 50-80 μm, and scanning speed 600-1500 mm/s. Specifically, it can be determined according to the performance requirements of the titanium-based composite material components to be prepared.

Beneficial effects:

The method of preparing the titanium-based composite material by laser remelting significantly reduces the residual stress of the prepared titanium-based composite material. Compared with ordinary metal alloy materials, the titanium-based composite material of the present invention has more complex components, and the influence of laser remelting on each component is different. It is not known what effect it will have on the titanium-based composite material. : After laser remelting, the precipitation of reinforcement will be affected.

The present invention selects one or more additives containing boron element, carbon element and rare earth element, and the resulting titanium-based material reinforcement is TiB, TiC, La ₂ O ₃ , Nd ₂ O ₃ , Y ₂ O ₃ , Ce ₂ O ₃ , Er ₂ O ₃ or Gd ₂ O ₃ , the present invention selects the above substances as the titanium-based material reinforcement of the present invention because the above reinforcement has excellent performance and the best matching degree with the titanium alloy. The present invention selects the above substances as the reinforcing body of the titanium-based material of the present invention because the above reinforcing body has better performance and has the best matching degree with the titanium alloy. Because of the local thermal effect caused by the high-energy laser beam as the heat source scanning the powder layer, the reaction of the reinforcement can be more thorough, the precipitation of the reinforcement can be smaller, which is conducive to the formation of heterogeneous nucleation, hinders the growth of dendrites in the same direction, and breaks the The dendrite growth is reduced, the residual stress in the component preparation process is reduced, the incidence of cracks is greatly reduced, the properties of the material are changed, the precision of the titanium matrix composite component is improved, and its application range is broadened. The preparation method of the invention has the advantages of simple operation, low cost, high efficiency, strong adaptability, and great application prospect.

Detailed ways

The specific embodiments of the present invention will be further described below.

Example 1

A method for reducing the residual stress of titanium-based composite materials prepared by selective laser melting in situ, the specific steps are as follows:

(1) The matrix alloy for preparing the titanium-based composite material is pure titanium, and the reinforcing body is a fiber hybrid reinforced composite material with a volume ratio of TiB of 0.2%. By uniformly combining pure titanium and the powder of the chemical element to generate the reinforcement, the in-situ reaction formula is: Ti+TiB ₂ =2TiB, the required titanium-based composite material blank is prepared by vacuum smelting, and then made by atomization method. Powder, the reinforcement in the titanium matrix composite powder accounts for 0.2% of the total volume of the titanium matrix composite powder;

(2) Preparation of titanium matrix composite components:

(2.1) Lay a layer of titanium-based composite powder for selective laser melting;

(2.2) Laser remelting is performed on the solidified surface after laser selective melting, and the number of remelting is 1 time;

(2.3) Repeat steps (2.1) and (2.2) until the titanium matrix composite component is prepared;

Among them, the process parameters of selective laser melting are: laser power 150W, powder thickness 40μm, spot diameter 50μm, scanning speed 600mm/s, substrate preheating temperature 30℃; the process parameters of remelting are the same as those of selective laser melting.

XRD was used to measure the residual stress of the prepared titanium-based composite component, and the prepared titanium-based composite component had no cracks, and its residual stress was reduced by 50% compared with the component prepared without laser remelting.

Example 2

A method for reducing the residual stress of titanium-based composite materials prepared by selective laser melting in situ, the specific steps are as follows:

(1) The matrix alloy used for preparing the titanium matrix composite material is TC4, the reinforcement is TiC whose volume ratio is Vol 2.5%, and TiB whose volume ratio is Vol 2.5%. The titanium alloy is uniformly combined with the powder of the chemical element that generates the reinforcement, and its in-situ reaction is Ti+C=TiC 5Ti+B ₄ C=TiC+4TiB, and the desired titanium-based composite material blank is prepared by vacuum smelting. The powder made by the atomization method, the reinforcement in the titanium matrix composite powder accounts for 5% of the total volume of the titanium matrix composite powder;

(2) Preparation of titanium matrix composite components:

(2.1) Lay a layer of titanium-based composite powder for selective laser melting;

(2.2) Laser remelting is performed on the solidified surface after laser selective melting, and the number of remelting is 3 times;

(2.3) Repeat steps (2.1) and (2.2) until the titanium matrix composite component is prepared;

Among them, the process parameters of selective laser melting are: laser power 180W, powder thickness 40μm, spot diameter 70μm, scanning speed 1200mm/s, substrate preheating temperature 100℃; the process parameters of remelting are the same as those of selective laser melting.

The obtained titanium-based composite component has no cracks, and the test method and parameters of its residual stress are the same as in Example 1, which is 80% lower than that of the component without laser remelting.

Example 3

A method for reducing the residual stress of titanium-based composite materials prepared by selective laser melting in situ, the specific steps are as follows:

(1) IMI834 is selected as the base alloy for preparing the titanium-based composite material, the reinforcement is TiB whose volume ratio is 3.6%, and the volume ratio of La ₂ O ₃ is 1.1%. The titanium alloy is uniformly combined with the powder of the chemical elements that generate the reinforcement, and its in-situ reaction is Ti+B=TiB, Ti+2ReX+3O=TiX+Re ₂ O ₃ , and the desired titanium base is prepared by vacuum smelting The composite material blank, and then the powder made by the atomization method, the reinforcement in the titanium matrix composite material powder accounts for 4.7% of the total volume of the titanium matrix composite material powder;

(2) Preparation of titanium matrix composite components:

(2.1) Lay a layer of titanium-based composite material powder, perform selective laser melting, and repeat the operation to prepare three layers of laser selective melting layer;

(2.2) Laser remelting is performed on the solidified surface after laser selective melting, and the number of remelting is 1 time;

(2.3) Repeat steps (2.1) and (2.2) until the titanium matrix composite component is prepared;

Among them, the process parameters of selective laser melting are: laser power 280W, powder thickness 50μm, spot diameter 60μm, scanning speed 1000mm/s, substrate preheating temperature 80℃.

The obtained titanium-based composite component has no cracks, and the test method and parameters of its residual stress are the same as those in Example 1, which are 40% lower than those obtained without laser remelting.

Example 4

A method for reducing the residual stress of titanium-based composite materials prepared by selective laser melting in situ, the specific steps are as follows:

(1) Ti-6242 is selected as the matrix alloy for preparing the titanium-based composite material, and the reinforcing body is TiB whose volume ratio is Vol 2.4%, TiC whose volume ratio is Vol 0.6%, and Gd ₂ O ₃ whose volume ratio is Vol 0.5% . By combining the titanium alloy with the powders of chemical elements that generate reinforcements uniformly, the in-situ reactions are Ti+B=TiB, Ti+C=TiC, Re+O=Re ₂ O ₃ , 5Ti+B ₄ C=TiC+ 4TiB, prepared into the required titanium-based composite material blank by vacuum smelting, and then made into powder by atomization. The reinforcement in the titanium-based composite material powder accounts for 3.5% of the total volume of the titanium-based composite material powder;

(2) Preparation of titanium matrix composite components:

(2.1) Lay a layer of titanium-based composite material powder, perform selective laser melting, and repeat the operation to prepare three layers of laser selective melting layer;

(2.2) Laser remelting is performed on the solidified surface after laser selective melting, and the number of remelting is 5 times;

(2.3) Repeat steps (2.1) and (2.2) until the titanium matrix composite component is prepared;

Among them, the process parameters of selective laser melting are: laser power 400W, powder thickness 50μm, spot diameter 80μm, scanning speed 1500mm/s, substrate preheating temperature 200℃.

The obtained titanium-based composite component has no cracks, and the test method and parameters of its residual stress are the same as those in Example 1, which are 85% lower than those obtained without laser remelting, and the dimensional accuracy and mechanical properties are obtained. Qualified titanium matrix composite components.

Example 5

A method for reducing the residual stress of titanium-based composite materials prepared by selective laser melting in situ, the specific steps are as follows:

(1) Ti-5553 is selected as the matrix alloy for preparing the titanium-based composite material, and the reinforcing body is TiB whose volume ratio is Vol 7.5%, TiC whose volume ratio is Vol 7.5%, and Y ₂ O ₃ whose volume ratio is Vol 5% . By combining the titanium alloy and the powder of the chemical elements that generate the reinforcement uniformly, the in-situ reaction is Ti+C=TiC; Ti+TiB ₂ =2TiB; Ti+2ReX+3O=TiX+Re ₂ O ₃ , which is smelted by vacuum. The required titanium-based composite material blank is prepared, and then the powder is made by the atomization method. The reinforcement in the titanium-based composite material powder accounts for 20% of the total volume of the titanium-based composite material powder;

(2) Preparation of titanium matrix composite components:

(2.1) Lay a layer of titanium-based composite material powder, perform selective laser melting, and repeat the operation to prepare five layers of laser selective melting layer;

(2.2) Laser remelting is performed on the solidified surface after laser selective melting, and the number of remelting is 5 times;

(2.3) Repeat steps (2.1) and (2.2) until the titanium matrix composite component is prepared;

Among them, the process parameters of selective laser melting are: laser power 380W, powder thickness 40μm, spot diameter 80μm, scanning speed 1100mm/s, substrate preheating temperature 120℃.

The obtained titanium-based composite component has no cracks, and the test method and parameters of its residual stress are the same as those in Example 1, which are 50% lower than those obtained without laser remelting, and the dimensional accuracy and mechanical properties are prepared. Qualified titanium matrix composite components.

Comparative Example 1

A method for reducing residual stress of titanium-based composite materials prepared by in-situ selective laser melting. The steps are basically the same as those in Example 5. Significant large cracks appear in composite components.

It can be found by comprehensive analysis of Example 5 and Comparative Example 1 that the present invention realizes the reduction of residual stress in the component through the interaction of suitable additives and remelting. The melting times will affect the magnitude of the residual stress, and the reduction of the residual stress can only be achieved by selecting the additive and remelting of the present invention.

Examples 6 to 12

A method for in-situ reduction of residual stress of titanium matrix composites prepared by selective laser melting, the steps are basically the same as those in Example 5, the difference is that the components of the matrix and reinforcement and the residual stress of the final product are reduced, and the differences are shown in the following table , the residual stress drop in the table below refers to the percentage reduction of the residual stress in the titanium matrix composite component compared to the component without laser remelting.

matrix Additives Residual stress drop (%) Example 6 BT36 TiC, Vol 0.1% 52% Example 7 TC11 Nd₂O₃, Vol 5% 70% Example 8 Ti60 TiB+Er₂O₃,Vol 7.5% 66% Example 9 Ti600 Ce₂O₃+TiC Vol 3.5% 73% Example 10 IMI679 TiB+TiC+Y₂O₃, Vol 12% 59% Example 11 IMI685 TiB+TiC+La₂O₃, Vol 18% 53% Example 12 Ti-6246 TiB+TiC Vol 15% 55%

Although the specific embodiments of the present invention have been described above, those skilled in the art should understand that these are only examples, and various changes may be made to these embodiments without departing from the principle and essence of the present invention. Revise.

Claims (7)

1. a method for reducing residual stress of titanium-based composite material prepared by selective laser melting in situ, is characterized in that comprising the following steps: Step 1: Prepare a titanium-based composite material powder, the titanium-based composite material powder includes a combination of titanium or a titanium alloy and a chemical substance that generates a reinforcement, and the chemical substance includes one of B boron element, C carbon element and rare earth element. species and above; Step 2: Lay one or more layers of titanium-based composite powder on the substrate of the selective laser melting equipment to perform laser selective melting; Step 3. Perform one or more laser remelting on the solidified surface after the laser selected area is melted; Step 4: Repeat steps 2 to 3 until the preparation of the titanium-based composite material component is completed. The residual stress in the prepared titanium-based composite material component is reduced by 40% to 85% compared with the component prepared by not performing laser remelting on the solidified surface after selective laser melting. 2 . The method for in-situ reduction of residual stress of titanium-based composite material prepared by selective laser melting according to claim 1 , wherein: after the titanium-based composite material powder is combined with a chemical substance for generating a reinforcement through titanium or titanium alloy , prepared into titanium-based composite material blanks by vacuum smelting, and then powdered by atomization. 3 . The method for in-situ reduction of residual stress of titanium-based composite material prepared by selective laser melting according to claim 2 , wherein the generated reinforcement comprises TiB, TiC, La ₂ O ₃ , Nd ₂ O ₃ , One or more of Y ₂ O ₃ , Ce ₂ O ₃ , Er ₂ O ₃ and Gd ₂ O ₃ . 4 . The method for in-situ reduction of residual stress of titanium-based composite material prepared by selective laser melting according to claim 3 , wherein the reinforcing body accounts for 0.1-20% of the total volume of the titanium-based composite material powder. 5 . 5. The method for in-situ reduction of residual stress of titanium-based composite material prepared by selective laser melting according to claim 1, characterized in that: a layer of titanium-based composite material powder is laid on the substrate of the selective laser melting device, and laser selective melting is performed. , and then perform one or more laser remelting on the solidified surface after laser selective melting; Alternatively, lay multiple layers of titanium-based composite material powder on the substrate of the selective laser melting equipment, perform selective laser melting respectively, and then perform one or more laser remelting on the solidified surface after selective laser melting. 6 . The method for in-situ reduction of residual stress of titanium-based composite materials prepared by selective laser melting according to claim 5 , wherein the number of times of the laser remelting is not more than five times, and the laser selective area corresponding to each laser remelting is not more than five times. 7 . Contains up to five layers of titanium matrix composite powder. 7 . The method for in-situ reduction of residual stress of titanium-based composite materials prepared by selective laser melting according to claim 5 , wherein the process parameters of the selective laser melting are set to laser power of 150-400 W, and powder thickness of 30- 50μm, spot diameter 50～80μm, scanning speed 600～1500mm/s, preheating temperature of substrate 30～200℃; The process parameters of the laser remelting are set as laser power 150-400 W, powder thickness 30-50 μm, spot diameter 50-80 μm, and scanning speed 600-1500 mm/s.