CN114669751B - Preparation method of crack-free nickel-titanium-copper alloy for additive manufacturing - Google Patents

Abstract

A preparation method of crack-free nickel-titanium-copper alloy for additive manufacturing comprises the steps of firstly calculating the thermal cracking tendency in the range of target alloy components, selecting the alloy component with the lowest thermal cracking tendency for proportioning and smelting, and preparing nickel-titanium-copper alloy powder by a gas atomization method; designing a 'grid lapping' parameter optimization structure, modeling the structure of the 'grid lapping' parameter optimization structure and the part structure, designing a position and a support, and carrying out slicing treatment; keeping the original coordinates of the model unchanged, setting a printing path and a scanning strategy, inputting process parameters, and copying the set engineering file into SLM equipment; then debugging equipment is debugged, the lamella is printed firstly to form a new substrate, and then parts are printed; when the temperature of the substrate is reduced to below 70 ℃, taking down the substrate with the printing piece, and placing the substrate in a furnace for heat preservation; and finally, cutting the printed piece from the substrate and grinding to obtain the nickel-titanium-copper alloy. According to the invention, the printing cracks are eliminated through component design, process parameter optimization and structural design, and the nickel-titanium-copper alloy with high density, good formability and excellent comprehensive performance is prepared.

Description

Preparation method of crack-free nickel-titanium-copper alloy for additive manufacturing

Technical Field

The invention relates to the technical field of metal additive manufacturing, in particular to a preparation method of a crack-free nickel-titanium-copper alloy for additive manufacturing.

Background

Nickel titanium based alloys are the most widely used shape memory alloys at present. Among them, the nitinol thin film and the spring show a high power ratio, a high recoverable stress, and excellent fatigue properties, and are widely used in microactuator devices and spring brakes. However, the nickel-titanium-copper shape memory alloy prepared by the traditional processing technology has high cost and complex process, and is difficult to realize the manufacture of complex structures. Selective Laser Melting (SLM) is used as a 3D printing method for accurately controlling forming, the smoothness and the geometric accuracy of parts can be guaranteed, and the manufacture of the structure-function integrated shape memory alloy can be realized. Therefore, the SLM technology is considered as a key technology for the preparation of the new generation of nitinol.

However, as a rapid solidification process, the complicated thermal history (high temperature inside the molten pool and high cooling speed on the boundary of the molten pool) in the forming process of manufacturing some alloy parts by adopting the SLM technology can cause the non-equilibrium solidification to be intensified, and the alloy is repeatedly remelted, so that the residual stress in the printed alloy is high, thereby being easy to generate deformation and cracking and influencing the comprehensive performance of the alloy. Particularly, for the preparation of NiTiCu alloy by adopting SLM process, the Cu element has high reflectivity, and the precipitated phase generated in the solidification process can cause alloy embrittlement, so that the cracking problem becomes the biggest obstacle of the application of the NiTiCu alloy.

Disclosure of Invention

The invention aims to solve the technical problem of providing a preparation method of a crack-free nickel-titanium-copper alloy for additive manufacturing, which is characterized in that target alloy components with lower crack sensitivity are preferably selected through component design, process parameters and a scanning strategy are optimized on the basis of adopting a selective laser melting technology, and unique structural design is carried out, so that alloy cracks in a 3D printing forming process are effectively reduced, and the nickel-titanium-copper alloy with good formability and excellent comprehensive performance is prepared.

In order to solve the technical problems, the invention adopts the following technical method: a preparation method of a crack-free nickel-titanium-copper alloy for additive manufacturing comprises the following steps:

step S1, component design: calculating the hot cracking tendency in the range of target alloy components based on a Hill solidification model and a crack sensitive factor calculation method, and selecting the alloy component with the lowest hot cracking tendency for batching;

step S2, preparing powder: smelting and ingot casting are carried out according to the alloy components selected in the step S1 to obtain a nickel-titanium-copper alloy bar, then nickel-titanium-copper pre-alloy powder is obtained through an air atomization method, screening treatment is carried out on the nickel-titanium-copper pre-alloy powder, and then vacuum drying is carried out to obtain nickel-titanium-copper alloy powder;

s3, three-dimensional structure modeling: designing a 'grid lapping' parameter optimization structure, respectively carrying out 3D modeling on the 'grid lapping' parameter optimization structure and a part structure by using NX-10 and Materialise-Magics3 software, designing a position, supporting, and carrying out slicing treatment, wherein the thickness of a sheet layer is layered according to the minimum layer thickness of 0.01 mm;

s4, setting process parameters: keeping the original coordinates of the model constructed in the step S3 unchanged, setting a printing path to be a melting channel layer by layer printing, scanning a strategy to be a strip partition and interlayer rotation, inputting process parameters optimized by adopting a 'mesh lapping' parameter optimization structure model, and copying a set engineering file into SLM equipment;

step S5, printing and forming: firstly, debugging equipment, introducing argon, and preheating a substrate; printing a lamella with the thickness of 1mm and the same component as the component of the part in advance to form a new substrate, and then finishing the printing of the part; cooling the substrate to below 70 ℃, taking down the substrate with the printing piece, placing the substrate in a furnace for heat preservation, and performing stress relief annealing; and finally, cutting the printed part from the substrate, and grinding the surface of the part to obtain the nickel-titanium-copper alloy part.

Further, after obtaining the nickel-titanium-copper alloy bar material in the step S2, putting the nickel-titanium-copper alloy bar material into a small-sized vacuum induction gas atomization powder making device, controlling the oxygen content in the whole process within 600ppm, preparing nickel-titanium-copper pre-alloy powder through a gas atomization method, sieving the nickel-titanium-copper pre-alloy powder through a 200-mesh screen to remove large-particle powder, and then putting the nickel-titanium-copper pre-alloy powder into a vacuum drying oven at 100 ℃ to dry for more than 2 hours to obtain the nickel-titanium-copper alloy powder with the particle size of 15-53 mu m and the sphericity of more than 95%.

Further, in step S3, when the NX-10 and the Materialise-Magics3 software are used for carrying out 3D modeling on the part structure, a 'bullnose' structure is arranged on the edge of the part, and the radius of the bullnose is 2-4mm.

Further, in step S3, when the part structure is subjected to 3D modeling by using NX-10 and Materialise-Magics3 software, a 'fillet' structure is arranged at the contact part of the part and the substrate, and the radius of the fillet is 2-4mm.

Still further, in step S3, the method for designing the "mesh lap joint" parameter optimization structure is as follows:

firstly, arranging the decomposed selective laser melting process parameters into an orthogonal table, constructing a 22mm multiplied by 29mm multiplied by 4mm cuboid with a 2mm chamfer angle, equally dividing the cuboid into 12 independent blocks with the size of 8mm multiplied by 4mm before slicing, wherein the adjacent grids contain a 1mm lap joint area, copying a module, reasonably arranging the modules, and assigning the process parameters in the orthogonal table to 24 independent blocks in sequence to obtain a 'grid lap joint' parameter optimization structure.

Still further, in step S3, when 3D modeling is performed on the "mesh lap" parameter optimization structure using NX-10 and Materialise-Magics3 software, process parameters are optimized in an orthogonal table form, three parameters among laser power, scanning speed, scanning pitch, and spot diameter are controlled to be constant values, and another parameter is changed to determine the optimal range of each parameter.

Further, in step S3, the optimized process parameters are: the laser power is 100-240W, the scanning speed is 800-1600mm/s, the scanning interval is 60-120 μm, the spot diameter is 60-100 μm, and the powder layer thickness is 50 μm.

Further, in step S4, the width of the stripe in the stripe division and interlayer rotation is 4-10mm, the interlayer rotation angle is 67 °, and the initial scan angle is 0-57 °.

Further, in step S5:

when debugging equipment, cleaning a powder bin of the SLM equipment, closing a bin door of a forming chamber, introducing argon, setting the preheating temperature of a substrate to be 180 ℃ when the oxygen content in the forming chamber is lower than 300ppm, when the temperature of the substrate rises to 150 ℃, sending the nickel-titanium-copper alloy powder prepared in the step S2 into the SLM equipment, manually spreading the powder, and executing a printing program when the spreading of the powder is smooth and the flowability is good;

when printing a part, selecting a nickel-titanium alloy substrate as a printing substrate, firstly printing a 1mm thick sheet layer with the same components as the part on the substrate by SLM equipment, remelting the sheet layer twice on the upper layer, and cooling the sheet layer to the temperature of the substrate to be used as a new substrate; then, according to the slice data set in the step S4, automatic powder spreading scanning is started to print parts, when the manufacturing of one layer is finished, the workbench is lowered by one powder spreading layer thickness, the scraper flattens the nickel-titanium-copper alloy powder again, the manufacturing of the next layer is carried out, the circulation is continuously carried out until the printing of the whole part is finished, if the serious warping occurs, the printing of the corresponding process is stopped, in the printing process, argon is introduced into the forming chamber, the content of oxygen is reduced to be below 300ppm, the air pressure is kept to be 10-20mbar, convection blowing is kept in the forming chamber, the air speed of an air outlet is changed according to the quantity of residues, and impurity residues are removed;

and after printing is finished, stopping heating the substrate, reducing the pressure in the forming chamber when the temperature of the substrate is reduced to below 70 ℃, removing residual powder, taking down the substrate with the printed piece, placing the substrate and the printed piece in a vacuum furnace or a 200 ℃ furnace filled with inert gas for heat preservation for 2h, performing stress relief annealing, then performing air cooling to room temperature, cutting the printed piece from the substrate by utilizing wire cutting, treating the surface of the part by using an automatic grinding machine, and grinding oxide skin formed by wire cutting to obtain the nickel-titanium-copper alloy part.

Preferably, the nickel-titanium-copper alloy powder comprises the following components in percentage by mass: nickel-45.04 wt.%, copper-10.01 wt.%, silicon-0.10 wt.%, oxygen-0.054 wt.%, aluminum-0.10 wt.%, iron-0.04 wt.%, chromium-0.05 wt.%, cobalt-0.008 wt.%, molybdenum-0.04 wt.%, zirconium-0.02 wt.%, unspecified further elements, each < 0.02wt.%, total < 0.10wt.%, balance titanium.

According to the preparation method of the crack-free nickel-titanium-copper alloy for additive manufacturing, provided by the invention, cracks in 3D printing are eliminated through component design, process parameter optimization and structural design, so that the nickel-titanium-copper alloy with the advantages of no cracks on the surface, high density, good formability and excellent comprehensive performance is prepared. Specifically, the invention provides an alloy component with low crack sensitivity by efficiently screening target alloy components based on a Hill solidification model and a crack sensitivity factor calculation method proposed by Kou. In addition, the invention provides a frame for efficiently optimizing process parameters, which decomposes the process parameters by adopting an orthogonal table and is matched with an autonomously designed 'mesh lapping' parameter optimization structure, so that the energy density can be regulated and controlled in a large range in one-time printing, the quality of a printed sample is efficiently evaluated, and the optimal parameter range is obtained. Furthermore, the invention firstly provides a structural design method for reducing internal stress, avoiding warping and eliminating cracks, and the design of printing a substrate and rounding is introduced into the structure of the part, so that the stress concentration on the part can be obviously reduced on the premise of not changing the original process parameters, and the warping and cracking of the part can be effectively prevented. In summary, the invention firstly provides an efficient process optimization strategy and a structure design method based on the selective laser melting technology, which can effectively eliminate cracks of the nickel-titanium-copper alloy formed by 3D printing and prepare the nickel-titanium-copper alloy with good formability and excellent comprehensive performance. The invention provides a new feasible process for preparing the nickel-titanium-copper alloy with the complex structure, and is expected to expand the application range of the nickel-titanium-copper alloy.

Drawings

FIG. 1 is a flow chart of a method for preparing a crack-free nickel-titanium-copper alloy for additive manufacturing according to the present invention;

FIG. 2 is a schematic diagram illustrating the calculation results of crack sensitivity factors of nickel-titanium-copper alloys with different components in the preparation method of crack-free nickel-titanium-copper alloys for additive manufacturing according to the present invention;

FIG. 3 is a schematic diagram of a scanning strategy in the method for preparing a crack-free Ni-Ti-Cu alloy for additive manufacturing according to the present invention;

FIG. 4 is a schematic view of a nickel-titanium-copper alloy printed according to example 1 of the present invention;

FIG. 5 is a schematic view of a nickel-titanium-copper alloy printed according to example 2 of the present invention;

FIG. 6 is a schematic view of a nickel-titanium-copper alloy printed according to example 3 of the present invention;

FIG. 7 is a surface scanning electron microscope image of a shaped nickel-titanium-copper alloy prepared by SLM in examples 1-3 of the present invention (in the drawing, (a), (c) are the planar regions perpendicular to the manufacturing direction (X-Y) and parallel to the manufacturing direction (X-Z) of example 3-b, (b) is the planar region perpendicular to the manufacturing direction (X-Y) of example 2-a, and (d) is the planar region parallel to the manufacturing direction (X-Z) of example 3).

Detailed Description

In order to facilitate understanding of those skilled in the art, the present invention will be further described with reference to the following examples and drawings, which are not intended to limit the present invention.

The method mainly eliminates the cracks of the parts in the 3D printing process through component design, process parameter optimization and structure design, so that the nickel-titanium-copper alloy with good formability and excellent comprehensive performance is prepared, which is the key for expanding the application of the nickel-titanium-copper shape memory alloy and has wide practical value. The present invention will be described in detail with reference to examples.

Example 1

A preparation method of a crack-free nickel-titanium-copper alloy for additive manufacturing is shown in figure 1 and comprises the following steps:

step S1, component design: based on the Hill coagulation model and Kou et al [ S.Kou Acta Materialia 88 (2015) 366-374]The proposed method for calculating the crack sensitivity factor uses the thermodynamic calculation software Pandat https:// computherm]Calculating the hot cracking tendency in the range of the target alloy components, as shown in fig. 2, as a calculation result of crack sensitive factors of nickel-titanium-copper alloys with different components, selecting the alloy component with the lowest hot cracking tendency for batching, specifically, in this example 1, the selected alloy components are, by mass percent: nickel-45.04 wt.%, copper-10.01 wt.%, silicon-0.10 wt.%, oxygen-0.054 wt.%, aluminum-0.10 wt.%, iron-0.04 wt.%, chromium-0.05 wt.%, cobalt-0.008 wt.%, molybdenum-0.04 wt.%, zirconium-0.02 wt.%, unspecified further elements, each of ≦ 0.02wt.%, total ≦ 0.10wt.%, the balance titanium. Wherein the main component titanium has a purity of 99.995% and

the nickel is 99.995% pure and

the purity of the high-purity nickel columnar particles and the copper is 99.99 percent

The pure copper particles of (1).

Step S2, preparing powder: and (4) carrying out smelting and ingot casting according to the alloy components selected in the step S1 to obtain the nickel-titanium-copper alloy bar with uniform components. Then putting the nickel-titanium-copper alloy bar into a small-sized vacuum induction gas atomization powder making device, controlling the oxygen content within 600ppm in the whole process, preparing nickel-titanium-copper prealloy powder through a gas atomization method, then sieving the nickel-titanium-copper prealloy powder through a 200-mesh screen, removing large particle powder, then putting the nickel-titanium-copper prealloy powder into a vacuum drying oven at 100 ℃ for drying for more than 2 hours, and obtaining the nickel-titanium-copper alloy powder with the particle size of 15-53 mu m and the sphericity of more than 95%, wherein the nickel-titanium-copper alloy powder is good in fluidity.

S3, modeling the three-dimensional structure

S31, designing a grid lap joint parameter optimization structure: the decomposed selective laser melting process parameters are listed in an orthogonal table, as shown in table 1 and table 2, a cuboid which is inverted with a 2mm fillet and is 22mm multiplied by 29mm multiplied by 4mm in size is constructed, the cuboid is equally divided into 12 independent blocks which are 8mm multiplied by 4mm before slicing, a 1mm lap joint area is contained between adjacent grids, a module is duplicated and reasonably arranged, the process parameters in the orthogonal table are sequentially assigned to the 24 independent blocks, and a set of efficient 'grid lap joint' parameter optimization structure is obtained.

Table 1 parameter optimization orthogonal table a

TABLE 2 orthogonal table b for parameter optimization

S32, structural design: the structure combining the printing substrate and the fillet is adopted.

Selecting a nickel-titanium alloy substrate as a printing substrate, firstly printing four 1 mm-thick lamella layers with the same components as the parts on the substrate by SLM equipment, remelting the upper layer twice, and cooling to the temperature of the substrate to obtain a new substrate, wherein the new substrate can reduce the internal stress between the substrate and the printing parts and prevent warping; a10 mm x 5mm part is formed on each new substrate, and a fillet with a radius of 2mm is provided at the contact portion of the part and the new substrate. On the base plate, the four parts are rotated clockwise by 15 ° forming an inclination with the direction of travel of the scraper.

S33, modeling: and respectively carrying out 3D modeling on the grid lapping parameter optimization structure and the part structure by using NX-10 and Materialise-Magics3 software, designing positions and supports, and carrying out slicing treatment, wherein the thickness of the sheet layer is layered according to the minimum layer thickness of 0.01 mm.

When NX-10 and Materialise-Magics3 software are used for carrying out 3D modeling on a 'grid lapping' parameter optimization structure, process parameters are optimized in an orthogonal table form, 48 process parameters are printed at one time during optimization, the quality of a printed sample is efficiently evaluated, specifically, three parameters of laser power, scanning speed, scanning distance and spot diameter are controlled to be constant values, the other parameter is changed, the optimal range of the other parameter is determined, and the optimized process parameter range is as follows: the laser power is 100-240W, the scanning speed is 800-1600mm/s, the scanning interval is 60-120 mu m, the spot diameter is 60-100 mu m, and the powder layer thickness is 50 mu m.

S4, setting process parameters: keeping the original coordinates of the model constructed in the step S3 unchanged, setting a printing path to be a melting channel layer-by-layer printing, and setting a scanning strategy to be a strip partition and interlayer rotation, as shown in fig. 3, wherein the strip width is 4mm, the interlayer rotation angle is 67 degrees, the initial scanning included angle is 0 degree, and the process parameters optimized in the step S33 are selected as follows:

(a) The laser power is 140W, the scanning speed is 1000mm/s, the scanning interval is 60 mu m, the spot diameter is 60 mu m, and the powder layer thickness is 50 mu m;

(b) The method comprises the following steps The laser power is 130W, the scanning speed is 1000mm/s, the scanning interval is 80 μm, the spot diameter is 60 μm, and the powder layer thickness is 50 μm;

(c) The method comprises the following steps The laser power is 135W, the scanning speed is 1000mm/s, the scanning interval is 80 mu m, the spot diameter is 60 mu m, and the powder layer thickness is 50 mu m;

(d) The method comprises the following steps The laser power is 160W, the scanning speed is 1000mm/s, the scanning interval is 100 μm, the spot diameter is 60 μm, and the powder layer thickness is 50 μm.

And copying the set engineering file into SLM equipment, wherein the SLM equipment selects a BLT-A320 selective laser melting metal 3D printer.

Step S5, printing and forming

S51, equipment debugging: cleaning a powder bin of the SLM equipment, closing a bin door of a forming chamber, introducing argon, setting the preheating temperature of a substrate to be 180 ℃ when the oxygen content in the forming chamber is lower than 300ppm, feeding the nickel-titanium-copper alloy powder prepared in the step S2 into the SLM equipment when the temperature of the substrate is raised to 150 ℃, manually spreading the powder, and executing a printing program when the spreading is smooth and good in fluidity;

s52, printing parts: after the SLM equipment prints a new substrate, automatic powder spreading scanning and printing of parts are started according to slice data set in the step S4, when manufacturing of one layer is completed, the workbench descends by one powder spreading layer thickness, namely 50 micrometers, the scraper flattens nickel-titanium-copper alloy powder again, here, the scraper selects a 40-steel hard scraper to manufacture the next layer, the next layer is manufactured continuously and circularly until the printing of the whole part is completed, if severe warping occurs, the printing of the corresponding process is stopped, and it is noted that in the printing process, argon is introduced into the forming chamber, in order to protect argon, the content of oxygen needs to be reduced to be below 300ppm, the air pressure is kept to be 10-20mbar, in addition, convection air blowing is kept in the forming chamber, the air outlet air speed is changed according to the quantity of residues, and impurity residues are removed.

S53, post-processing: after printing is finished (as shown in fig. 4), stopping heating the substrate, reducing the pressure in the forming chamber when the temperature of the substrate is reduced to below 70 ℃, removing residual powder, taking down the substrate with the printing piece, placing the substrate and the printing piece in a vacuum or 200 ℃ furnace filled with inert gas for heat preservation for 2 hours, performing stress relief annealing, and then performing air cooling to room temperature. And cutting the printed part from the base plate by using wire cutting, processing the surface of the part by using an automatic grinding machine, and grinding the oxide skin formed by the wire cutting to obtain the nickel-titanium-copper alloy part with a smooth and bright surface.

And (5) cutting off part of the part obtained in the step (S53), grinding and polishing the part, shooting the surface appearance, and testing the mechanical property and the phase transition behavior. In this example 1, the scanning topography of the nitinol obtained by using the process parameter (b) is shown in fig. 7 (a, c), and the alloy properties are as follows: vickers Hardness (HV) of 302.1HV _5.0 The compressive strength (. Sigma.) was 683.42MPa, the elongation (. Delta.) was 6.21%, and the phase change hysteresis was 12.1 ℃.

Example 2

A preparation method of a crack-free nickel-titanium-copper alloy for additive manufacturing is disclosed, which is different from example 1 only in that:

1) The structure designed in step S32 is: the structure combining the 'external fillet' and the 'internal fillet' is adopted. Specifically, in step S33, when the part structure is 3D modeled by using NX-10 and material-Magics 3 software, four parts are constructed on the substrate, wherein three parts are truncated pyramids with an upper surface of 25mm × 25mm, a lower surface of 30mm × 30mm and a height of 8mm, a fillet with a radius of 3mm is constructed on the edge of the three parts, another part is a common truncated cone with an upper surface radius of 12mm and a lower surface radius of 15mm, and fillets with a radius of 3mm are arranged at the contact parts of all the parts and the substrate. On the base plate, the four parts are rotated 15 ° clockwise, forming an inclination with the direction of travel of the blade.

2) When the process parameters are set in step S4: keeping the original coordinates of the model constructed in the step S3 unchanged, setting a printing path to be a melting channel layer-by-layer printing, and setting a scanning strategy to be a strip partition and interlayer rotation, wherein the strip width is 4mm, the interlayer rotation angle is 67 degrees, the initial scanning included angle is 57 degrees, and the process parameters optimized in the step S33 are selected as follows:

a) The method comprises the following steps The laser power is 130W, the scanning speed is 1000mm/s, the scanning interval is 80 μm, the spot diameter is 60 μm, and the powder layer thickness is 50 μm;

(b) The method comprises the following steps The laser power is 135W, the scanning speed is 1000mm/s, the scanning interval is 80 mu m, the spot diameter is 60 mu m, and the powder layer thickness is 50 mu m;

(c) The method comprises the following steps The laser power is 140W, the scanning speed is 1000mm/s, the scanning interval is 80 μm, the spot diameter is 60 μm, and the powder layer thickness is 50 μm;

(d) The method comprises the following steps The laser power is 150W, the scanning speed is 1100mm/s, the scanning interval is 80 μm, the spot diameter is 60 μm, and the powder layer thickness is 50 μm.

And copying the set engineering file into SLM equipment, wherein the SLM equipment selects a BLT-A320 selective laser melting metal 3D printer.

3) In step S53, the finished nitinol is printed as shown in fig. 5.

4) In this embodiment 2, a scanning topography of the nitinol alloy obtained by using the process parameters (b) is shown in fig. 7 (b), and the alloy properties are as follows: vickers Hardness (HV) 317.5HV _5.0 The compressive strength (sigma) was 847.75MPa, the elongation (delta) was 7.46%, and the phase change hysteresis was 11.1 ℃.

Example 3

A preparation method of a crack-free nickel-titanium-copper alloy for additive manufacturing is disclosed, which is different from example 1 only in that:

1) The structure designed in step S32 is: the method comprises the following steps that a combined structure of a printing substrate, an excircle corner and an inner fillet corner is adopted, a nickel-titanium alloy substrate is selected as the printing substrate, an SLM device firstly prints a sheet layer which is 1mm thick, 80mm long and 80mm wide and has a fillet and the same components as parts on the substrate, the sheet layer is remelted twice on the upper layer and cooled to the temperature of the substrate to serve as a new substrate, and the new substrate can reduce the internal stress between the substrate and the printing parts and prevent warping; a part is constructed on a new substrate, the part is a frustum with an upper surface of 50mm multiplied by 50mm, a lower surface of 60mm multiplied by 60mm and a height of 8mm, a fillet of 4mm is arranged on the edge of the part, and a fillet of 4mm is arranged at the contact part of the part and the substrate.

2) When the process parameters are set in step S4: keeping the original coordinates of the model constructed in the step S3 unchanged, setting a printing path as a melting channel layer-by-layer printing, and setting a scanning strategy as a strip partition and interlayer rotation, wherein the strip width is 4mm, the interlayer rotation angle is 67 degrees, the initial scanning included angle is 57 degrees, the process parameters optimized in the step S33, namely the laser power is 135W, and the scanning speed is 135W1000mm/s, a scanning interval of 80 μm, a spot diameter of 60 μm, a powder layer thickness of 50 μm, and an energy density of 33.75J/mm ³ 。

3) In step S53, the finished nitinol is printed as shown in fig. 6.

4) The scanning topography of the nitinol alloy obtained in this example 3 is shown in fig. 7 (d), and the alloy properties are as follows: vickers Hardness (HV) of 310.5HV _5.0 The compressive strength (. Sigma.) was 885.76MPa, the elongation (. Delta.) was 7.21%, and the phase transition retardation was 12.7 ℃.

The following table 3 shows the density comparison of the nickel-titanium-copper alloy obtained by the printing and the process parameters used in each of examples 1 to 3.

Table 3 process parameters and density comparisons used in examples 1-3

As can be seen from comparison between table 3 and fig. 4, in the scanning strategy of embodiment 1, the initial angle is 0 °, and since the scanning path needs to avoid the direction of the air outlet, only 2 scanning directions are overlapped with each other in the actual printing process, which causes stress concentration at the corners of the part and warpage. Example 2-3 the initial angle in the scanning strategy was 57 °, 5 scan directions were present during the actual printing process, and saw-tooth grain boundaries could be formed between the layers, hindering crack propagation, and significantly improving the ductility of SLM-formed NiTiCu alloys. The process parameters have great influence on the formability and the compactness of the alloy in a printing state, and the energy density is more than 33.5J/mm ³ Can obtain a printing sample with the density meeting the requirement.

FIG. 7 is a surface scanning electron micrograph of a shaped nickel-titanium-copper alloy prepared by SLM, wherein (a) and (c) are the planar regions perpendicular to the manufacturing direction (X-Y) and parallel to the manufacturing direction (X-Z) of example 3-b, respectively; (b) Is the planar area of example 2-a perpendicular to the direction of manufacture (X-Y); (d) Example 3 is a planar area parallel to the direction of manufacture (X-Z). Wherein, no crack exists on the X-Y plane, a small amount of pores can be seen, a small amount of component segregation exists, and the whole structure is uniform. No crack on the X-Z plane, less pores and component segregation along the bottom of the molten pool, good integral formability and uniform structure. As can be seen from the figure 7, the method adopts the selective laser melting technology, and introduces the component design, the process optimization and the structure design method, so that the prepared nickel-titanium-copper alloy has no crack and good formability.

Generally, the nickel-titanium-copper alloy block printed by the method has the density as high as 99.1 +/-0.1%, no surface crack, no obvious large-size defect (such as a hole, a crack or an inclusion), uniform tissue and good formability. The phase transition temperature range of the nickel-titanium-copper alloy block is 12.1-40.0 ℃, the phase transition lag (Af-Ms) is 11.1-12.7 ℃, and the narrow phase transition lag effect is good. In addition, the hardness of the nickel-titanium-copper alloy block can reach 317.5 +/-7.6 HV _5.0 The compression strength is 885.76 +/-20.3 MPa, the compression strain is 7.36 +/-0.34 percent, and the mechanical property is good.

The above embodiments are preferred implementations of the present invention, and besides, the present invention can be implemented in other ways, and any obvious substitutions without departing from the concept of the present invention are within the protection scope of the present invention.

Some of the drawings and descriptions of the present invention have been simplified to facilitate the understanding of the improvements over the prior art by those skilled in the art, and other elements have been omitted from this document for the sake of clarity, and it should be appreciated by those skilled in the art that such omitted elements may also constitute the subject matter of the present invention.

Claims (3)

1. A preparation method of a crack-free nickel-titanium-copper alloy for additive manufacturing is characterized by comprising the following steps:

step S1, component design: calculating the hot cracking tendency in the range of target alloy components based on a Hill solidification model and a crack sensitive factor calculation method, and selecting the alloy component with the lowest hot cracking tendency for batching;

the nickel-titanium-copper alloy powder comprises the following components in percentage by mass: nickel-45.04 wt.%, copper-10.01 wt.%, silicon-0.10 wt.%, oxygen-0.054 wt.%, aluminum-0.10 wt.%, iron-0.04 wt.%, chromium-0.05 wt.%, cobalt-0.008 wt.%, molybdenum-0.04 wt.%, zirconium-0.02 wt.%, unspecified further elements, each of ≦ 0.02wt.%, total ≦ 0.10wt.%, the balance titanium;

step S2, preparing powder: smelting and ingot casting are carried out according to the alloy components selected in the step S1 to obtain a nickel-titanium-copper alloy bar, then nickel-titanium-copper pre-alloy powder is obtained through an air atomization method, screening treatment is carried out on the nickel-titanium-copper pre-alloy powder, and then vacuum drying is carried out to obtain nickel-titanium-copper alloy powder;

s3, modeling a three-dimensional structure: designing a 'grid lapping' parameter optimization structure, respectively carrying out 3D modeling on the 'grid lapping' parameter optimization structure and a part structure by using NX-10 and Materialise-Magics3 software, designing a position, supporting, and carrying out slicing treatment, wherein the thickness of a sheet layer is layered according to the minimum layer thickness of 0.01 mm;

the method for designing the 'mesh lapping' parameter optimization structure comprises the following steps: firstly, putting decomposed selective laser melting process parameters into an orthogonal table, constructing a 22mm multiplied by 29mm multiplied by 4mm cuboid with a 2mm chamfer angle, equally dividing the cuboid into 12 independent blocks with the size of 8mm multiplied by 4mm before slicing, wherein 1mm lap joint areas are arranged between adjacent grids, copying modules, reasonably arranging the modules, and assigning the process parameters in the orthogonal table to 24 independent blocks in sequence to obtain a 'grid lap joint' parameter optimization structure;

when NX-10 and Materialise-Magics3 software are used for carrying out 3D modeling on the 'mesh lapping' parameter optimization structure, the process parameters are optimized in an orthogonal table form, three parameters of laser power, scanning speed, scanning interval and spot diameter are controlled to be constant values, the other parameter is changed, and the optimal range of each parameter is determined;

when the part structure is subjected to 3D modeling by using NX-10 and Materialise-Magics3 software, an 'external fillet' structure is arranged on the edge of the part, the radius of the external fillet is 2-4mm, and an 'internal fillet' structure is arranged at the contact part of the part and the substrate, and the radius of the internal fillet is 2-4 mm;

s4, setting process parameters: keeping the original coordinates of the model constructed in the step S3 unchanged, setting a printing path to be a melting channel layer by layer printing, setting a scanning strategy to be a strip partition and interlayer rotation, wherein the strip width of the strip partition and interlayer rotation is 4-10mm, the interlayer rotation angle is 67 degrees, the initial scanning included angle is 0-57 degrees, inputting process parameters optimized by adopting a grid lapping parameter optimization structure model, copying the set engineering file into SLM equipment, and the optimized process parameters are as follows: the laser power is 135-140W, the scanning speed is 1000-1100mm/s, the scanning interval is 60-100 mu m, the spot diameter is 60-100 mu m, and the powder layer thickness is 50 mu m;

step S5, printing and forming: firstly, debugging equipment, introducing argon, and preheating a substrate; printing a lamella with the thickness of 1mm and the same component as the component of the part in advance to form a new substrate, and then finishing the printing of the part; cooling the substrate to below 70 ℃, taking down the substrate with the printing piece, placing the substrate in a furnace for heat preservation, and performing stress relief annealing; and finally, cutting the printed part from the substrate, and grinding the surface of the part to obtain the nickel-titanium-copper alloy part.

2. The method for preparing the crack-free nickel-titanium-copper alloy for additive manufacturing according to claim 1, wherein the crack-free nickel-titanium-copper alloy for additive manufacturing comprises the following steps: in the step S2, after obtaining the nickel-titanium-copper alloy bar, putting the nickel-titanium-copper alloy bar into a small vacuum induction gas atomization powder making device, controlling the oxygen content in the whole process to be within 600ppm, preparing nickel-titanium-copper prealloying powder through a gas atomization method, then sieving the nickel-titanium-copper prealloying powder through a 200-mesh screen to remove large-particle powder, and then putting the nickel-titanium-copper prealloying powder into a 100 ℃ vacuum drying oven to be dried for more than 2 hours to obtain the nickel-titanium-copper alloy powder with the particle size of 15-53 mu m and the sphericity of more than 95%.

3. The method for preparing the crack-free nickel-titanium-copper alloy for additive manufacturing according to claim 2, wherein the method comprises the following steps: in step S5:

when debugging equipment, cleaning a powder bin of the SLM equipment, closing a bin door of a forming chamber, introducing argon, setting the preheating temperature of a substrate to be 180 ℃ when the oxygen content in the forming chamber is lower than 300ppm, when the temperature of the substrate rises to 150 ℃, sending the nickel-titanium-copper alloy powder prepared in the step S2 into the SLM equipment, manually spreading the powder, and executing a printing program when the spreading of the powder is smooth and the flowability is good;

when a part is printed, a nickel-titanium alloy substrate is selected as a printing substrate, the SLM equipment firstly prints a 1mm thick lamella which has the same components as the part on the substrate, and the lamella is remelted twice on the upper layer and cooled to the temperature of the substrate to be used as a new substrate; then, according to the slice data set in the step S4, automatic powder spreading scanning is started to print parts, when the manufacturing of one layer is finished, the workbench is lowered by one powder spreading layer thickness, the scraper flattens the nickel-titanium-copper alloy powder again, the manufacturing of the next layer is carried out, the circulation is continuously carried out until the printing of the whole part is finished, if the serious warping occurs, the printing of the corresponding process is stopped, in the printing process, argon is introduced into the forming chamber, the content of oxygen is reduced to be below 300ppm, the air pressure is kept to be 10-20mbar, convection blowing is kept in the forming chamber, the air speed of an air outlet is changed according to the quantity of residues, and impurity residues are removed;

and after printing is finished, stopping heating the substrate, reducing the pressure in the forming chamber when the temperature of the substrate is reduced to below 70 ℃, removing residual powder, taking down the substrate with the printed piece, placing the substrate and the printed piece in a vacuum furnace or a 200 ℃ furnace filled with inert gas for heat preservation for 2h, performing stress relief annealing, then performing air cooling to room temperature, cutting the printed piece from the substrate by utilizing wire cutting, treating the surface of the part by using an automatic grinding machine, and grinding oxide skin formed by wire cutting to obtain the nickel-titanium-copper alloy part.

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