阅读说明：本技术 一种大可回复应变NiTi合金的激光增材制造方法 (Laser additive manufacturing method of NiTi alloy with large recoverable strain ) 是由 丰焱 王硕 万雪曼 于 2020-10-28 设计创作，主要内容包括：本发明涉及一种大可回复应变NiTi合金的激光增材制造方法,以NiTi合金板为基材,分别采用CO_2激光器和半导体激光器两种不同的能量源,通入高纯氩气将成形室内气氛的氧含量控制在100ppm以内,采用十字交叉扫描策略以同轴送粉方式将粒度为50μm-150μm的NiTi合金粉连续熔融沉积在基材上；沉积过程选取较大的激光束光斑直径、高的激光功率,在一定送粉率下通过控制激光功率、扫描速率以获得相对较高的能量输入,进而得到成形致密的NiTi合金块材,保证了成形样品的力学性能等同甚至优于同成分铸、锻态NiTi合金样品；该工艺制备的NiTi合金块材具备较强的择优取向(<001>∥沉积方向),保证了成形样品优异的超弹回复性能及形状记忆效应。(The invention relates to a laser additive manufacturing method of a NiTi alloy with large recoverable strain, which takes a NiTi alloy plate as a base material and respectively adopts CO 2 Two different energy sources of a laser and a semiconductor laser are introduced, high-purity argon is introduced to control the oxygen content of the atmosphere in a forming chamber to be within 100ppm, and NiTi alloy powder with the granularity of 50-150 mu m is continuously fused and deposited on a base material by adopting a cross scanning strategy and a coaxial powder feeding mode; in the deposition process, a larger laser beam spot diameter and high laser power are selected, and relatively higher energy input is obtained by controlling the laser power and the scanning rate under a certain powder feeding rate, so that a formed compact NiTi alloy block is obtained, and the mechanical property of a formed sample is ensured to be equal to or even superior to that of a cast or forged NiTi alloy sample with the same composition; the NiTi alloy block material prepared by the process has stronger preferred orientation (<001>/. deposition direction), ensures excellent superelastic recovery properties and shape memory effects for the shaped samples.)

1. A laser additive manufacturing method of a NiTi alloy with large recoverable strain is characterized by comprising the following steps:

step 1: drying NiTi alloy powder for 2-3 hours at 100-120 ℃ under the vacuum condition of being less than or equal to 0.1Pa, cooling to room temperature, taking out and putting into a powder feeder;

step 2: placing and fixing the NiTi alloy base material in a forming chamber, keeping the oxygen content of the atmosphere in the forming chamber within 100ppm under the circulation action of high-purity argon, and forming;

and step 3: starting a laser energy source, wherein the laser power is 1000-1800W, the scanning speed is 400-1000 mm/min, the laser energy source starts to act under the control of a numerical control workbench, a powder feeding nozzle feeds NiTi alloy powder onto a NiTi base material at the powder feeding speed of 9-11.5 g/min for deposition, the laser energy source and the powder feeding nozzle are synchronously lifted by 0.15-0.5 mm after the deposition of a first layer is finished, and the NiTi alloy powder is continuously deposited and formed by a crisscross scanning path;

and 4, step 4: and after the forming is finished, closing the laser system and the powder feeding system, waiting for the sample to be cooled to room temperature, turning off the high-purity argon gas, taking out the base material from the forming chamber, and cutting the NiTi alloy sample by utilizing wire cut electrical discharge machining to obtain the laser additive of the NiTi alloy with large recoverable strain.

2. The laser additive manufacturing method of the NiTi alloy with large recoverable strain according to claim 1, wherein: the particle size range of the NiTi alloy powder is 50-150 mu m.

3. The laser additive manufacturing method of the NiTi alloy with large recoverable strain according to claim 1 or 2, wherein the laser additive manufacturing method comprises the following steps: the total atomic weight of two elements of the alloy powder Ni + Ti is less than or equal to 100at percent.

4. The laser additive manufacturing method of the NiTi alloy with large recoverable strain according to claim 1 or 2, wherein the laser additive manufacturing method comprises the following steps: the alloy powder is prepared by adopting an electrode induction gas atomization technology.

5. The laser additive manufacturing method of the NiTi alloy with large recoverable strain according to claim 1, wherein: the laser energy source is a laserline LDF6000 type semiconductor laser or a CP4000 type CO₂A laser.

Technical Field

The invention belongs to the field of advanced manufacturing of materials, and relates to a laser additive manufacturing method of a high recoverable strain NiTi alloy. In particular to a method for preparing a sample with preferred orientation (<001 >/deposition direction) so that the sample has excellent superelasticity and shape memory effect; has better metallurgical fusion and excellent mechanical property.

Background

The NiTi alloy with the near-equal atomic ratio belongs to one of shape memory materials, and has excellent superelasticity, shape memory effect, good mechanical property, biocompatibility and other properties, so that the NiTi alloy is widely applied to the fields of aviation, engineering, medical treatment and the like. The traditional method for preparing and processing the NiTi alloy is difficult to directly obtain a component with a complex shape and excellent intelligent characteristics, and greatly limits the further application of the alloy.

The laser additive manufacturing is based on the idea of dimension reduction, converts a complex three-dimensional component into a two-dimensional plane, and can prepare any complex component theoretically, which brings great possibility for the shape design of materials. The laser powder bed process has the advantages of high forming precision, good surface quality and the like, but based on the inherent properties of the NiTi alloy, the NiTi alloy is easy to generate macroscopic cracking when the NiTi alloy is formed by adopting the laser powder bed process such as Selective Laser Melting (SLM), which seriously limits the forming process window, and the process has lower forming speed and smaller formed sample size and is difficult to meet the requirement of forming large-scale components. Compared with a laser powder bed process, the additive manufacturing process based on laser synchronous powder feeding has the advantages of high forming speed, high formed part density, good mechanical property and the like, can be used for quickly producing large-size and complex-shape components, is applied to the direct forming of NiTi alloy, can overcome the limitation of the traditional preparation and processing method of NiTi alloy and the laser additive manufacturing method of the powder bed process on the shape and size of the component, and widens the application field of the alloy. The laser near net shape (LENS) additive manufacturing process based on laser synchronous powder feeding has the advantages, but compared with NiTi alloy prepared in a traditional mode, the obtained product or component has lower strain recovery rate and cannot meet the use requirement.

Materials prepared using laser additive manufacturing techniques typically have a certain preferred orientation, which, if properly utilized, is highly advantageous for specific material applications. For the NiTi alloy with the parent phase of a body-centered cubic structure, the Schmidt factors of <001> {110} and <001> {100} under compression loading are 0 and are 'hard orientation', the orientation is not beneficial to the starting of a sliding system, the accumulated plastic deformation in the loading process can be greatly reduced, the recovery rate after loading can be obviously improved, and the functional characteristics of the NiTi alloy are improved. However, the preferred orientation is closely related to the thermal history of the preparation process, and the NiTi alloy with stronger specific preferred orientation can be obtained by parameter optimization.

Therefore, the limitation of the traditional NiTi alloy preparation and processing method and the laser additive manufacturing method by the powder bed process on the shape and the size of the component is urgently needed to be broken through, appropriate laser additive manufacturing process parameters are explored, and the NiTi alloy with large recoverable strain is developed.

Disclosure of Invention

Technical problem to be solved

In order to avoid the defects of the prior art, the invention provides a laser additive manufacturing method of a NiTi alloy with large recoverable strain, which can quickly form a large-size NiTi alloy member without macroscopic defects and can obtain a super-elastic recovery rate of over 90% when pre-compression loading strain is 10%; at low temperature (martensite state), when the pre-compression loading strain is 12%, the temperature is heated to be higher than the temperature of the parent phase, and the shape memory recovery rate reaches or approaches 100%; the tensile sample had a post-fracture elongation of over 15%.

Technical scheme

A laser additive manufacturing method of a NiTi alloy with large recoverable strain is characterized by comprising the following steps:

step 1: drying NiTi alloy powder for 2-3 hours at 100-120 ℃ under the vacuum condition of being less than or equal to 0.1Pa, cooling to room temperature, taking out and putting into a powder feeder;

step 2: placing and fixing the NiTi alloy base material in a forming chamber, keeping the oxygen content of the atmosphere in the forming chamber within 100ppm under the circulation action of high-purity argon, and forming;

and step 3: starting a laser energy source, wherein the laser power is 1000-1800W, the scanning speed is 400-1000 mm/min, the laser energy source starts to act under the control of a numerical control workbench, a powder feeding nozzle feeds NiTi alloy powder onto a NiTi base material at the powder feeding speed of 9-11.5 g/min for deposition, the laser energy source and the powder feeding nozzle are synchronously lifted by 0.15-0.5 mm after the deposition of a first layer is finished, and the NiTi alloy powder is continuously deposited and formed by a crisscross scanning path;

and 4, step 4: and after the forming is finished, closing the laser system and the powder feeding system, waiting for the sample to be cooled to room temperature, turning off the high-purity argon gas, taking out the base material from the forming chamber, and cutting the NiTi alloy sample by utilizing wire cut electrical discharge machining to obtain the laser additive of the NiTi alloy with large recoverable strain.

The particle size range of the NiTi alloy powder is 50-150 mu m.

The total atomic weight of two elements of the alloy powder Ni + Ti is less than or equal to 100at percent.

The alloy powder is prepared by adopting an electrode induction gas atomization technology.

The laser energy source is a laserline LDF6000 type semiconductor laser or a CP4000 type CO₂A laser.

Advantageous effects

The invention provides a laser additive manufacturing method of a high recoverable strain NiTi alloy, which is based on a laser synchronous powder feeding process, wherein a deposition system comprises a laser, a numerical control workbench, a high-precision powder feeding system, an inert atmosphere forming chamber and the like. Taking a NiTi alloy plate as a base material, and respectively adopting CO₂Two different energy sources of a laser and a semiconductor laser are introduced, high-purity argon is introduced to control the oxygen content of the atmosphere in a forming chamber to be within 100ppm, and NiTi alloy powder with the granularity of 50-150 mu m is continuously fused and deposited on a base material by adopting a cross scanning strategy and a coaxial powder feeding mode; deposition processSelecting a larger laser beam spot diameter and high laser power, and obtaining relatively higher energy input by controlling the laser power and the scanning rate under a certain powder feeding rate so as to obtain a formed compact NiTi alloy block material, thereby ensuring that the mechanical property of a formed sample is equal to or even superior to that of a cast or forged NiTi alloy sample with the same composition; the NiTi alloy block material prepared by the process has stronger preferred orientation (<001>/. deposition direction), ensures excellent superelastic recovery properties and shape memory effects for the shaped samples.

Compared with NiTi alloy formed by other technologies, the invention has the following beneficial effects:

the laser additive manufacturing method of the NiTi alloy with large recoverable strain provided by the invention has the advantages of large forming process window, good formability, no macrocracks on the surface, no large-size metallurgical defects inside, high density and capability of quickly forming large-size components.

The NiTi alloy bulk material prepared by the process has stronger preferred orientation (<001 >/deposition direction).

The formed piece has excellent functional characteristics, the superelasticity can reach the level of NiTi alloy prepared by the traditional method, and when the precompression loading strain is 10%, the superelasticity recovery of more than 90% can be obtained; the shape memory effect is excellent, the strain amount of the pre-compression loading reaches 12% at low temperature (in a martensite state), the pre-compression loading strain amount is unloaded and then heated to a parent phase, and the strain recovery rate reaches or approaches 100%; further, the tensile sample had a post-fracture elongation of more than 15%.

Drawings

FIG. 1(a) is a schematic view of a deposition process, (b) is a schematic view of a laser scanning path, wherein the z-direction is the deposition direction and x and y are the laser scanning directions;

FIG. 2 is a DSC curve of a sample of the shaped alloy of example 1;

FIG. 3 is a polar view of a xoy plane of a sample of the shaped alloy of example 1;

FIG. 4 is a uniaxial compressive stress-strain curve for a shaped alloy sample of example 1, the compressed sample being taken along the xoz or yoz plane;

FIG. 5 is a uniaxial compressive stress-strain curve at low temperature for the formed alloy sample of example 1, the compressive sample being taken along the xoz or yoz plane;

FIG. 6 is a uniaxial tensile stress-strain curve of a sample of the shaped alloy of example 1, the tensile sample being taken along the xoy plane.

Detailed Description

The invention will now be further described with reference to the following examples and drawings:

the method is carried out on laser synchronous powder feeding forming equipment, and a large-size NiTi alloy sample which is good in forming property and compactness and has excellent functional characteristics of preferred orientation (<001 >/deposition direction) is obtained by adjusting process parameters. A laser additive manufacturing method of a NiTi alloy with large recoverable strain is provided.

Example 1

The first step is as follows: the NiTi alloy powder has a particle size range of 50-150 μm and is prepared by an electrode induction gas atomization technology. Drying NiTi alloy powder at 120 deg.c in vacuum (not more than 0.1Pa) for 2 hr, cooling to room temperature, taking out and setting in powder feeder.

The second step is that: the NiTi alloy base material with the size of 120mm multiplied by 10mm is placed and fixed in a forming chamber, under the circulation action of high-purity argon, the oxygen content of the atmosphere in the forming chamber is within 100ppm, and the forming is started.

The third step: starting a laserline LDF6000 type semiconductor laser, selecting a light spot with the diameter of 3mm, starting to act at the laser power of 1200W and the scanning speed of 800mm/min under the control of a numerical control workbench, sending NiTi alloy powder to a NiTi alloy base material for deposition at the powder sending speed of 11.5g/min by using a powder sending device taking high-purity argon as powder carrying airflow, wherein the overlapping rate is about 50%, after the deposition of a first layer is finished, a laser energy source and a powder sending nozzle are synchronously lifted to the height of about 0.4mm, and the NiTi alloy powder is continuously deposited and formed by a crisscross scanning path (shown in figure 1).

The fourth step: and after the forming is finished, closing the laser system and the powder feeding system, waiting for cooling to room temperature, closing the high-purity argon introduced into the forming chamber, taking the base material out of the forming chamber, and cutting the NiTi alloy component by wire electrical discharge machining to obtain a formed sample.

Differential thermal analysis was performed on the sample obtained in example 1 to obtain a DSC phase transition curve as shown in fig. 2, which was found to be in a mother phase state at room temperature; electron back-scattered diffraction analysis of the xoy plane of the sample obtained in example 1 gave a polar pattern as shown in FIG. 3, with a pronounced (<001 >/. deposition direction) preferential orientation of the sample; the sample obtained in example 1 is subjected to a superelasticity test, as shown in fig. 4, the compression loading strain is 10%, and the recovery rate is as high as 95%; the shape memory performance of the sample obtained in example 1 was tested, and the loading-unloading curve is shown in fig. 5; the tensile mechanical property test of the sample obtained in example 1 showed that the elongation after fracture reached 17%, as shown in fig. 6.

Example 2

The first step is as follows: the NiTi alloy powder has a particle size range of 50-150 μm and is prepared by an electrode induction gas atomization technology. Drying NiTi alloy powder in a vacuum (less than or equal to 0.1Pa) environment at 110 ℃ for 2 hours, cooling to room temperature, taking out and putting into a powder feeder.

The second step is that: the NiTi alloy base material with the size of 120mm multiplied by 10mm is placed and fixed in a forming chamber, under the circulation action of high-purity argon, the oxygen content of the atmosphere in the forming chamber is within 100ppm, and the forming is started.

The third step: starting CP4000 type CO₂The laser selects a light spot with the diameter of 2mm, the laser starts to act at the laser power of 1500W and the scanning speed of 800mm/min under the control of a numerical control workbench, a powder feeding device with high-purity argon as powder carrying airflow sends NiTi alloy powder to a NiTi base material at the powder feeding speed of 11g/min for deposition, the lapping rate is about 50%, after the deposition of the first layer is finished, a laser energy source and a powder feeding nozzle are synchronously lifted to the height of about 0.3mm, and the NiTi alloy powder is continuously deposited and formed by a crisscross scanning path (shown in figure 1).

The fourth step: and after the forming is finished, closing the laser system and the powder feeding system, waiting for cooling to room temperature, closing the high-purity argon introduced into the forming chamber, taking the base material out of the forming chamber, and cutting the NiTi alloy component by wire electrical discharge machining to obtain a formed sample.

Example 3

The first step is as follows: the NiTi alloy powder has a particle size range of 50-150 μm and is prepared by an electrode induction gas atomization technology. Drying NiTi alloy powder at 120 deg.c in vacuum (not more than 0.1Pa) for 2 hr, cooling to room temperature, taking out and setting in powder feeder.

The second step is that: the NiTi alloy base material with the size of 120mm multiplied by 10mm is placed and fixed in a forming chamber, under the circulation action of high-purity argon, the oxygen content of the atmosphere in the forming chamber is within 100ppm, and the forming is started.

The third step: starting CP4000 type CO₂The laser selects a light spot with the diameter of 2mm, the laser starts to act at the laser power of 1700W and the scanning speed of 680mm/min under the control of a numerical control workbench, a powder feeding device with high-purity argon as powder carrying airflow sends NiTi alloy powder to a NiTi base material at the powder feeding speed of 9g/min for deposition, the lapping rate is about 50%, after the deposition of the first layer is finished, a laser energy source and a powder feeding nozzle are synchronously lifted to the height of about 0.15mm, and the NiTi alloy powder is continuously deposited and formed by a crisscross scanning path (shown in figure 1).

The fourth step: and after the forming is finished, closing the laser system and the powder feeding system, waiting for cooling to room temperature, closing the high-purity argon introduced into the forming chamber, taking the base material out of the forming chamber, and cutting the NiTi alloy component by wire electrical discharge machining to obtain a formed sample.

Examples 1 and 3 the superelasticity, shape memory effect and tensile mechanical properties are shown in table 1, wherein the shape memory effect is loaded in the low temperature martensitic state, after unloading the temperature is raised above the martensitic reverse transformation temperature and the amount of strain recovered is recorded. The data in the table show that the NiTi alloy sample formed by the method has excellent functional characteristics and mechanical properties.

TABLE 1