A device and method for quantitatively evaluating the thermal cracking sensitivity of high-entropy alloys under a laser deposition process

Abstract

The present application belongs to the technical field of laser additive manufacturing, and particularly relates to a device and method for quantitatively evaluating the thermal cracking sensitivity of high-entropy alloys under laser deposition process. The fixed support of the device is formed by connecting the upper and lower plates through connecting rods, the upper and lower plates being arranged in parallel, the upper die limiting block is located on the top of the lower plate, and the upper die is installed between the two upper die limiting blocks; the power loading device is provided with a servo motor and a servo cylinder, which are installed at the bottom of the upper plate of the fixed support, the output end of the servo cylinder is installed with a horizontal U-shaped pressure head, and the laser deposition substrate is placed above the upper die limiting block and corresponds to the upper die. The present application can determine the critical strain and solidification temperature interval of the alloy, and other thermal cracking tendency indexes, accurately evaluate the thermal cracking sensitivity of the alloy, and guide the research and application of various metals.

Description

Technical Field

[0001] This invention belongs to the field of laser additive manufacturing technology, specifically relating to a testing device and method for quantitatively evaluating the hot cracking sensitivity of high-entropy alloys under laser deposition processes. Background Technology

[0002] Laser additive manufacturing (such as laser deposition and selective laser melting) is a disruptive metal processing technology that has emerged in recent years. Compared with traditional subtractive manufacturing, it has significant advantages in the manufacturing of complex integral parts, lightweight engineering, and material utilization. However, currently only a small number of commercial alloys (such as IN718, Ti6Al4V, and AlSi10Mg) can be formed using laser additive manufacturing. Most alloys with poor weldability (such as 7-series aluminum alloys, most nickel-based superalloys, and high-entropy alloys) are not suitable for the rapid heating and cooling process of laser additive manufacturing, and are prone to hot cracking. This will significantly reduce the fatigue strength of components and may even lead to component fracture failure.

[0003] During laser deposition, the high cooling rate and large temperature gradient cause the alloy solidification structure to tend to form continuously epitaxial, coarse columnar crystals. Narrow voids easily form between these parallel columnar crystals. In the later stages of solidification (solidity > 0.9%), the fluidity of the liquid metal is poor, making it difficult to backfill and shrink. The liquid film between the dendrites opens under thermal stress, leading to the formation of micro-hot cracks. Therefore, the formation process of hot cracks is complex, involving the interaction between thermal stress, solidification shrinkage, and liquid backfill, and is influenced by numerous factors. These influencing factors can generally be divided into thermodynamic factors and intrinsic alloy properties. Among them, the temperature gradient during alloy solidification and the solid / liquid interface migration rate are the main thermodynamic factors for hot crack formation, while the coefficient of thermal expansion, the width of the solid-liquid phase line, and intermetallic compounds are the essential factors for hot cracking. Therefore, effectively evaluating the hot cracking susceptibility of laser-deposited alloys under the influence of various factors is key to solving the hot cracking problem.

[0004] Currently, methods for evaluating the hot cracking susceptibility of alloys under additive manufacturing processes such as laser deposition mainly include metallographic microstructure observation and non-destructive testing techniques such as industrial computed tomography (CT). Metallographic microstructure observation determines the hot cracking susceptibility of the alloy by statistically analyzing the number of cracks in the field of view and calculating the crack density. However, this method has a certain degree of randomness in its statistical results and can only provide a qualitative or semi-quantitative evaluation of the alloy's hot cracking susceptibility. On the other hand, non-destructive testing techniques such as industrial CT cannot detect samples with limited size, and the test results are difficult to distinguish the cause of crack formation (hot cracking or cold cracking, etc.). Summary of the Invention

[0005] To address the shortcomings of existing technologies, the first objective of this invention is to provide a quantitative evaluation device for the hot cracking susceptibility of high-entropy alloys under laser deposition processes. This device can determine hot cracking tendency indicators such as the critical strain and solidification temperature range for hot crack formation in the alloy. Furthermore, based on the high-entropy alloy hot cracking susceptibility testing device under laser deposition processes, the second objective of this invention is to provide a quantitative evaluation method for the hot cracking susceptibility of high-entropy alloys under laser deposition processes. This device and method can accurately evaluate the magnitude of the alloy's hot cracking susceptibility, thereby guiding the research and development and application of various metals.

[0006] The technical solution of this invention is:

[0007] A quantitative evaluation device for assessing the hot cracking sensitivity of high-entropy alloys under laser deposition processes is disclosed. The device comprises a fixed support, a dynamic loading device, a servo driver, a U-shaped indenter, a laser deposition substrate, punches with different radii of curvature, a punch limiting block, and a non-contact temperature measurement device. The specific structure is as follows:

[0008] The fixed bracket consists of an upper base plate and a lower base plate arranged parallel to each other and connected by a connecting rod. The punch limiting block is located on the top of the lower base plate, and the punch is installed between the two punch limiting blocks. The power loading device is equipped with a servo motor and a servo cylinder, which are installed at the bottom of the upper base plate of the fixed bracket. A horizontal U-shaped pressure head is installed at the output end of the servo cylinder. The U-shaped pressure head is placed on the laser deposition substrate, and the bottom of the two side rods of the U-shaped pressure head corresponds to the two sides of the upper surface of the laser deposition substrate. The laser deposition substrate is placed above the punch limiting block, and the bottom middle of the laser deposition substrate corresponds to the punch. When external restraint is applied to the laser deposition substrate through the U-shaped pressure head, the non-contact temperature measuring device corresponds to the position point on the laser source moving path where external restraint is applied.

[0009] The aforementioned quantitative evaluation device for the hot cracking sensitivity of high-entropy alloys under laser deposition process involves the following external constraint application process: A servo cylinder moves up and down under program control, driving a U-shaped pressure head, threadedly connected and suspended above the punch limiting block, to apply external constraint to the laser deposition substrate. The magnitude of the external constraint is determined by the radius of curvature of the punch placed between the punch limiting blocks, and the relationship between the two is ε = (t / 2H) × 100%, where: ε is the reinforcing strain (%); t is the thickness of the laser deposition substrate (mm); and H is the radius of curvature of the punch (mm). When the U-shaped pressure head moves downward at a constant speed for a certain distance, causing the lower surface of the laser deposition substrate to adhere to the upper surface of the punch, it is considered that a corresponding external constraint has been applied to the laser deposition substrate.

[0010] The aforementioned quantitative evaluation test device for the hot cracking sensitivity of high-entropy alloys under laser deposition process uses a non-contact temperature measuring device, which is a thermal imager or an infrared thermometer. By aiming the non-contact temperature measuring device at the position point on the moving path of the laser source where an external constraint is applied, the cooling curve of the alloy solidification process at that position point can be obtained.

[0011] The aforementioned quantitative evaluation device for the hot cracking sensitivity of high-entropy alloys under laser deposition process controls the up-and-down movement of the servo cylinder by programming the servo driver of the servo motor, thereby controlling the direction, distance, speed and delay loading time of the U-shaped indenter.

[0012] The aforementioned quantitative evaluation test device for the hot cracking sensitivity of high-entropy alloys under laser deposition process includes a fixed bracket that provides support for the dynamic loading device and fixes the position of the punch.

[0013] A quantitative method for evaluating the hot cracking susceptibility of high-entropy alloys under laser deposition processes includes the following steps:

[0014] Step 1: Preparation of substrate for laser deposition test. The pre-prepared alloy powder is deposited into the trapezoidal groove of the substrate for laser deposition using a laser deposition process.

[0015] Step 2: Preparation for adjustable restraint test. Place the laser deposition substrate between the U-shaped indenter and the punch, and adjust the positions of the U-shaped indenter, the laser deposition substrate, and the temperature measuring device. The temperature measuring point is located at the loading point.

[0016] Step 3: Set adjustable restraint test parameters, including the delayed loading time, the U-shaped indenter descent distance, and the descent speed.

[0017] Step 4: Simultaneously start the laser and external load loading device to cause the alloy to be evaluated to remelt under the action of the high-energy laser beam. During the laser remelting process of the alloy, external restraint is applied at a designated position.

[0018] Step 5: After remelting is complete, remove the test laser deposition substrate, replace the punch with a different radius of curvature, and repeat steps 1 to 4. Keep the power and scanning speed of laser remelting constant.

[0019] Step 6: After the experiment, measure the maximum crack length L of the hot crack at the loading point under different external constraints. MCL To obtain the key indicator for hot cracking sensitivity evaluation—the solidification cracking temperature range (SCTR) of the alloy—the time required for crack initiation is equal to the maximum crack length above saturation strain divided by the cooling rate R. The laser remelting rate is represented by V. The SCTR is then calculated using the following formula:

[0020]

[0021] Where: SCTR is the solidification cracking temperature range of the alloy, in °C; LMCL denoted as maximum crack length (μm); R as cooling rate (℃ / s); and V as laser remelting rate (mm / s).

[0022] In the quantitative evaluation method for the hot cracking sensitivity test of high-entropy alloys under laser deposition process, in step 1, the thickness of the substrate used for laser deposition is 2-5 mm.

[0023] In the quantitative evaluation method for the hot cracking sensitivity of high-entropy alloys under laser deposition process, in step 3, the delayed loading time corresponds to the time when the laser source starts to move to the loading point, and the U-shaped indenter descent speed is 150-300 mm / s.

[0024] In the quantitative evaluation method for the hot cracking sensitivity of high-entropy alloys under laser deposition process, step 4, the designated position during the laser remelting process of the alloy is the geometric center of the substrate used for laser deposition.

[0025] In the quantitative evaluation method for the hot cracking sensitivity of high-entropy alloys under laser deposition process, step 5 includes the following parameters: laser remelting power: 500–1000 W; scanning speed: 5–10 mm / s; and applied strain: 0.5–5%.

[0026] The design concept of this invention is:

[0027] Adjustable restraint testing is an effective method for quantitatively evaluating hot crack susceptibility in welding. It typically employs large hydraulic machinery to apply external restraint, resulting in high equipment costs and poor portability. Compared to the large hydraulic machinery used in adjustable restraint testing in welding, this invention utilizes a servo-controlled electronic device for loading, which is not only lower in cost but also more lightweight and portable. This is particularly suitable for evaluating the hot crack susceptibility of alloys in on-site localized directional repair and remanufacturing processes such as laser deposition. Furthermore, no research has been reported on using adjustable restraint testing to evaluate the hot crack susceptibility of laser-deposited alloys. Compared to current methods for evaluating the hot crack susceptibility of alloys in additive manufacturing processes such as laser deposition, this invention proposes a quantitative evaluation method that introduces adjustable restraint testing into the evaluation of hot crack susceptibility of alloys in laser deposition processes, providing strong support for the development of alloy compositions suitable for laser additive manufacturing processes.

[0028] The apparatus and technical method of this invention draw on the adjustable restraint test in the welding field, and have the following advantages over existing technologies:

[0029] 1. The mushy region at the tail of the molten pool is subjected to tensile stress applied by an external load, resulting in solidification hot cracks (which can be clearly observed at the loading point of the sample). This avoids the randomness of hot cracking. Compared with the microstructure observation method, this method can clearly and accurately analyze hot cracking.

[0030] 2. This invention enables a quantitative evaluation of hot crack sensitivity by measuring the maximum hot crack length and combining it with the temperature changes during alloy solidification.

[0031] 3. The welding process exhibits a significant base material dilution phenomenon, which essentially evaluates the compatibility between the welding material and the base material. However, this method is closer to the actual working conditions of laser additive manufacturing. The melting area and heat-affected zone during deposition are much smaller than those during welding, which can significantly reduce the influence of the base material on the alloy composition.

[0032] 4. This invention adjusts the types and proportions of elements in the laser-deposited alloy powder to make the composition of the alloy to be evaluated continuously adjustable, thereby achieving a quantitative evaluation of the influence of alloy element content on hot cracking sensitivity and determining the alloy composition with the best hot cracking resistance under laser deposition. Attached Figure Description

[0033] Figure 1 This is a structural diagram of the laser deposition alloy hot cracking sensitivity testing device of the present invention. In the figure, 1 is a fixed bracket (11 upper base plate, 12 connecting rod, 13 lower base plate), 2 is a servo motor, 3 is a servo electric cylinder, 4 is a U-shaped pressure head, 5 is a substrate for laser deposition, 6 is a punch, and 7 is a punch limiting block.

[0034] Figures 2(a)-(c) show FeCoCrNi and FeCoCrNiTi. 0.2 ,FeCoCrNiTi 0.2 - A stereomicroscopic image of a hot-cracked TiC high-entropy alloy.

[0035] Figures 3(a)-(c) show FeCoCrNi and FeCoCrNiTi. 0.2 ,FeCoCrNiTi 0.2 - Maximum crack length curve of TiC high-entropy alloy. In the figure, the horizontal axis Augmented strain represents the reinforcing strain (%), the vertical axis Maximum crack Length (MCL) represents the maximum crack length (μm), crack is the crack, and crack fitting is the crack fitting curve.

[0036] Figure 4 FeCoCrNi, FeCoCrNiTi 0.2 ,FeCoCrNiTi 0.2 - Solidification cracking temperature range (SCTR) curve of TiC high entropy alloy. In the figure, the horizontal axis Temperature represents temperature (°C), and the vertical axis Augmented strain represents reinforcement strain (%). Detailed Implementation

[0037] The technical solution of the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings. The following embodiments are merely preferred embodiments of the present invention and are not intended to limit the present invention in other ways. Any person skilled in the art may make equivalent modifications to the disclosed technical content to create equivalent embodiments. Any simple modifications or equivalent changes made to the following embodiments based on the technical essence of the present invention without departing from the scope of the present invention are within the protection scope of the present invention.

[0038] like Figure 1 As shown, the laser-deposited alloy hot cracking sensitivity testing device of the present invention mainly includes a fixed bracket 1, a power loading device (servo motor 2, servo cylinder 3), a servo driver, a U-shaped pressure head 4, a laser deposition substrate 5, punches with different radii of curvature 6, a punch limiting block 7, and a non-contact temperature measuring device such as a thermal imager or infrared thermometer. The specific structure is as follows:

[0039] The fixed bracket 1 mainly provides support for the power loading device and fixes the position of the punch 6. The fixed bracket 1 is formed by the upper base plate 11 and the lower base plate 13, which are arranged in parallel to each other and connected by a connecting rod 12. The punch limiting block 7 is located on the top of the lower base plate 13, and the punch 6 is installed between the two punch limiting blocks 7.

[0040] The power loading device consists of a servo motor 2 and a servo cylinder 3 mounted on the bottom of the upper base plate 11 of the fixed bracket 1. A horizontal U-shaped pressure head 4 is mounted on the output end of the servo cylinder 3. The U-shaped pressure head 4 is placed on the laser deposition substrate 5. The bottom of the two side rods of the U-shaped pressure head 4 corresponds to the two sides of the upper surface of the laser deposition substrate 5 (sample). The laser deposition substrate 5 is located above the punch limiting block 7, and the bottom middle of the laser deposition substrate 5 corresponds to the punch 6. This is equivalent to bending the sample at three points through the U-shaped pressure head 4 and the punch 6. By programming the servo driver of the servo motor 2, the servo cylinder 3 is controlled to move up and down, thereby controlling the movement direction, movement distance, movement speed and delay loading time of the U-shaped pressure head 4.

[0041] The external restraint application process is as follows: the servo cylinder 3 is moved up and down by program control, driving the U-shaped indenter 4, which is threadedly connected and suspended above the punch limiting block 7, to apply external restraint to the specimen. The magnitude of the external restraint is determined by the radius of curvature of the punch 6 placed between the punch limiting blocks 7, and the relationship between the two is ε=(t / 2H)×100%, where: ε is the reinforcing strain (%), t is the specimen thickness (mm), and H is the radius of curvature of the punch (mm). When the U-shaped indenter 4 moves downward at a constant speed for a certain distance, causing the lower surface of the specimen to fit against the upper surface of the punch 6, it is considered that the corresponding external restraint has been applied to the specimen.

[0042] By aiming a non-contact temperature measurement device at a point on the moving path of the laser source where external constraint is applied, the cooling curve of the alloy solidification process at that point can be obtained. This device primarily provides external constraint (strain) and measures the cooling curve during the alloy solidification process in laser-deposited alloy hot cracking sensitivity evaluation tests.

[0043] Example 1

[0044] In this embodiment, a quantitative evaluation method for the hot cracking sensitivity of high-entropy alloys under laser deposition processes is provided to test the hot cracking sensitivity of FeCoCrNi metal powder. A FeCoCrNi substrate with trapezoidal grooves is selected as the base material, and FeCoCrNi metal powder is used as the filler material. The particle size of the FeCoCrNi metal powder is between 45 μm and 105 μm. The testing method includes the following steps:

[0045] Step 1: Preparation of test samples. The pre-prepared alloy powder was deposited into the trapezoidal groove of the base material using laser deposition technology (sample thickness is 2 mm).

[0046] Step 2: Preparation for the adjustable restraint test. Place the deposited base material between the U-shaped indenter and the punch, and adjust the positions of the U-shaped indenter, base material, and temperature measuring device (the temperature measuring point is located at the loading point).

[0047] Step 3: Set adjustable restraint test parameters, including the delayed loading time (the delayed loading time corresponds to the time when the laser source starts moving to the loading point), the U-shaped indenter descent distance, and the descent speed (150 mm / s).

[0048] Step 4: Simultaneously start the laser and external load loading device to cause the alloy to be evaluated to remelt under the action of the high-energy laser beam. During the laser remelting process of the alloy, external restraint is applied at a designated position (usually the geometric center of the sample).

[0049] Step 5: After remelting is complete, remove the test sample, replace the punch with a different radius of curvature, and repeat steps 1 to 4. Keep the power and scanning speed of laser remelting constant (remelting power: 600W, scanning speed: 5mm / s, enhanced strain: 0.5-5%).

[0050] Step 6: After the experiment, measure the maximum crack length (L) of the hot crack at the loading point under different external constraints. MCL The solidification cracking temperature range (SCTR) of an alloy, a key indicator for evaluating hot cracking susceptibility, can be obtained by using the laser (μm) as an approximation. Assuming the time required for crack formation is equal to the maximum crack length above saturation strain divided by the cooling rate (R, ℃ / s), and the laser remelting rate is represented by V (mm / s), the SCTR can be calculated using the following formula:

[0051]

[0052] In this embodiment, L MCL R is the maximum crack length, taken as 1260 μm; R is the cooling rate, taken as 529 °C / s; V is the laser remelting rate, taken as 5 mm / s.

[0053] In step one, the deposited sample must maintain a smooth overall surface. The distance between the U-shaped indenter and the punch should be equal to the sample thickness, ensuring sample stability during laser remelting.

[0054] Example 2

[0055] In this embodiment, a quantitative evaluation method for the hot cracking sensitivity of high-entropy alloys under laser deposition processes is used to test FeCoCrNiTi. 0.2 Due to the thermal cracking sensitivity of metal powders, FeCoCrNi substrates with trapezoidal grooves were selected as the base material and FeCoCrNiTi. 0.2 Metal powder as filler material, FeCoCrNiTi 0.2 The metal powder particle size is between 45 μm and 105 μm. The test method includes the following steps:

[0056] Step 1: Preparation of test samples. The pre-prepared alloy powder was deposited into the trapezoidal groove of the base material using laser deposition technology (sample thickness is 2 mm).

[0057] Step 2: Preparation for the adjustable restraint test. Place the deposited base material between the U-shaped indenter and the punch, and adjust the positions of the U-shaped indenter, base material, and temperature measuring device (the temperature measuring point is located at the loading point).

[0058] Step 3: Set adjustable restraint test parameters, including the delayed loading time (the delayed loading time corresponds to the time when the laser source starts moving to the loading point), the U-shaped indenter descent distance, and the descent speed (150 mm / s).

[0059] Step 4: Simultaneously start the laser and external load loading device to cause the alloy to be evaluated to remelt under the action of the high-energy laser beam. During the laser remelting process of the alloy, external restraint is applied at a designated position (usually the geometric center of the sample).

[0060] Step 5: After remelting is complete, remove the test sample, replace the punch with one of different radii of curvature, and repeat steps 1 to 4. Keep the power and scanning speed of laser remelting constant (remelting power: 600W, scanning speed: 5mm / s, enhanced strain: 0.5-5%).

[0061] Step 6: After the experiment, measure the maximum crack length (L) of the hot crack at the loading point under different external constraints. MCLThe solidification cracking temperature range (SCTR) of an alloy, a key indicator for evaluating hot cracking susceptibility, can be obtained by using the laser (μm) as an approximation. Assuming the time required for crack formation is equal to the maximum crack length above saturation strain divided by the cooling rate (R, ℃ / s), and the laser remelting rate is represented by V (mm / s), the SCTR can be calculated using the following formula:

[0062]

[0063] In this embodiment, L MCL R is the maximum crack length, taken as 1099 μm; R is the cooling rate, taken as 541 °C / s; V is the laser remelting rate, taken as 5 mm / s.

[0064] In step one, the deposited sample must maintain a smooth overall surface. The distance between the U-shaped indenter and the punch should be equal to the sample thickness to ensure sample stability during laser remelting.

[0065] Example 3

[0066] In this embodiment, a quantitative evaluation method for the hot cracking sensitivity of high-entropy alloys under laser deposition processes is used to test FeCoCrNiTi. 0.2 Due to the thermal cracking sensitivity of TiC metal powder, FeCoCrNi substrate with trapezoidal grooves was selected as the base material and FeCoCrNiTi 0.2 TiC metal powder is used as the filler material, FeCoCrNiTi 0.2 - The TiC metal powder particle size is between 45 μm and 105 μm. The testing method includes the following steps:

[0067] Step 1: Preparation of test samples. The pre-prepared alloy powder was deposited into the trapezoidal groove of the base material using laser deposition technology (sample thickness is 2 mm).

[0068] Step 2: Preparation for the adjustable restraint test. Place the deposited base material between the U-shaped indenter and the punch, and adjust the positions of the U-shaped indenter, base material, and temperature measuring device (the temperature measuring point is located at the loading point).

[0069] Step 3: Set adjustable restraint test parameters, including the delayed loading time (the delayed loading time corresponds to the time when the laser source starts moving to the loading point), the U-shaped indenter descent distance, and the descent speed (150 mm / s).

[0070] Step 4: Simultaneously start the laser and external load loading device to cause the alloy to be evaluated to remelt under the action of the high-energy laser beam. During the laser remelting process of the alloy, external restraint is applied at a designated position (usually the geometric center of the sample).

[0071] Step 5: After remelting is complete, remove the test sample, replace the punch with one of different radii of curvature, and repeat steps 1 to 4. Keep the power and scanning speed of laser remelting constant (remelting power: 600W, scanning speed: 5mm / s, enhanced strain: 0.5-5%).

[0072] Step 6: After the experiment, measure the maximum crack length (L) of the hot crack at the loading point under different external constraints. MCL The solidification cracking temperature range (SCTR) of an alloy, a key indicator for evaluating hot cracking susceptibility, can be obtained by using the laser (μm) as an approximation. Assuming the time required for crack formation is equal to the maximum crack length above saturation strain divided by the cooling rate (R, ℃ / s), and the laser remelting rate is represented by V (mm / s), the SCTR can be calculated using the following formula:

[0073]

[0074] In this embodiment, L MCL R is the maximum crack length, taken as 1313 μm; R is the cooling rate, taken as 528℃ / s; V is the laser remelting rate, taken as 5 mm / s.

[0075] In step one, the deposited sample must maintain a smooth overall surface. The distance between the U-shaped indenter and the punch should be equal to the sample thickness to ensure sample stability during laser remelting.

[0076] The three examples evaluated FeCoCrNi and FeCoCrNiTi, respectively. 0.2 ,FeCoCrNiTi 0.2 -The thermal cracking sensitivity of TiC high-entropy alloy powders. Figure 2 shows the thermal cracking sensitivity of FeCoCrNi and FeCoCrNiTi. 0.2 ,FeCoCrNiTi 0.2 The morphology of the hot-cracked TiC high-entropy alloy is clearly visible, showing that the cracks are distributed on the sample surface and extend from the solid-liquid interface fusion zone into the solid phase region. Furthermore, the hot cracking phenomenon intensifies with increasing strain. Figure 3 shows the morphology of FeCoCrNi and FeCoCrNiTi alloys. 0.2 ,FeCoCrNiTi 0.2 The trend of maximum crack length in the TiC high-entropy alloy shows that the maximum crack length reaches its saturation value at saturation strains of 1.5%, 3%, and 2.5%, respectively. Figure 4 As shown, the SCTRs obtained from the maximum crack length, cooling curve, and welding speed are 133℃, 119℃, and 139℃, respectively.

[0077] The results show that this invention can achieve quantitative evaluation of the hot cracking sensitivity of alloys under additive manufacturing processes such as laser deposition. This is of great significance for revealing the hot cracking mechanism of alloys under this process and solving the hot cracking problem, and can provide strong support for the widespread application of laser additive manufacturing technology.

Claims

1. A testing device for quantitatively evaluating the hot cracking sensitivity of high-entropy alloys under laser deposition processes, characterized in that, The device includes a fixed bracket, a power loading device, a servo driver, a U-shaped pressure head, a substrate for laser deposition, punches with different radii of curvature, punch limiting blocks, and a non-contact temperature measurement device. The specific structure is as follows: The fixed bracket consists of an upper base plate and a lower base plate arranged parallel to each other and connected by a connecting rod. The punch limiting block is located at the top of the lower base plate, and the punch is installed between the two punch limiting blocks. The power loading device is equipped with a servo motor and a servo cylinder, which are installed at the bottom of the upper base plate of the fixed bracket. A horizontal U-shaped pressure head is installed at the output end of the servo cylinder. The U-shaped pressure head is placed on the laser deposition substrate, and the bottom of the two side rods of the U-shaped pressure head corresponds to the two sides of the upper surface of the laser deposition substrate. The laser deposition substrate is placed above the punch limiting block, and the bottom middle of the laser deposition substrate corresponds to the punch. When external restraint is applied to the laser deposition substrate through the U-shaped pressure head, the non-contact temperature measuring device corresponds to the position point on the laser source moving path where external restraint is applied. The external constraint application process is as follows: A servo cylinder moves up and down under program control, driving a U-shaped pressure head, threadedly connected and suspended above the punch limiting blocks, to apply external constraint to the laser deposition substrate. The magnitude of the external constraint is determined by the radius of curvature of the punches placed between the punch limiting blocks, and the relationship between the two is... ε =(t / 2H)×100%, where: ε To enhance strain, %; t is the thickness of the laser deposition substrate, mm; H is the radius of curvature of the punch, mm; when the U-shaped indenter moves downward at a constant speed for a certain distance so that the lower surface of the laser deposition substrate is in contact with the upper surface of the punch, it is considered that a corresponding external constraint has been applied to the laser deposition substrate. By programming the servo driver of the servo motor, the servo electric cylinder can be controlled to move up and down, thereby controlling the direction, distance, speed and delay loading time of the U-shaped pressure head. The non-contact temperature measuring device is a thermal imager or an infrared thermometer. By aiming the non-contact temperature measuring device at the position point on the moving path of the laser source where an external constraint is applied, the cooling curve of the alloy solidification process at that position point can be obtained. The fixed bracket provides support for the power loading device and fixes the position of the punch.

2. A method for quantitatively evaluating the hot cracking susceptibility of high-entropy alloys under laser deposition processes using the apparatus described in claim 1, characterized in that, Includes the following steps: Step 1: Preparation of the substrate for laser deposition test. The pre-prepared alloy powder is deposited into the trapezoidal groove of the substrate for laser deposition using a laser deposition process. Step 2: Preparation for adjustable restraint test. Place the laser deposition substrate between the U-shaped indenter and the punch, and adjust the positions of the U-shaped indenter, the laser deposition substrate, and the temperature measuring device. The temperature measuring point is located at the loading point. Step 3: Set adjustable restraint test parameters, including the delayed loading time, the U-shaped indenter descent distance, and the descent speed. Step 4: Simultaneously start the laser and external load loading device to cause the alloy to be evaluated to remelt under the action of the high-energy laser beam. During the laser remelting process of the alloy, apply external restraint at the designated position. Step 5: After remelting is complete, remove the test laser deposition substrate, replace the punch with a different radius of curvature, and repeat steps 1 to 4. Keep the laser remelting power and scanning speed constant. Step 6: After the test, measure the maximum crack length of the hot crack at the loading point under different external constraints. L MCL To obtain the key indicator for hot cracking sensitivity evaluation—the solidification cracking temperature range (SCTR) of the alloy—the time required for crack initiation is equal to the maximum crack length above saturation strain divided by the cooling rate. R Laser remelting speed V If so, the SCTR is calculated using the following formula: Where: SCTR is the solidification cracking temperature range of the alloy, in °C; L MCL The maximum crack length is in μm; R Cooling rate, ℃ / s; V denoted as laser remelting velocity, mm / s.

3. The method for quantitatively evaluating the hot cracking sensitivity of high-entropy alloys under laser deposition process according to claim 2, characterized in that, In step 1, the thickness of the substrate used for laser deposition is 2~5mm.

4. The method for quantitatively evaluating the hot cracking sensitivity of high-entropy alloys under laser deposition process according to claim 2, characterized in that, In step 3, the delayed loading time corresponds to the time when the laser source begins to move to the loading point position, and the descent speed of the U-shaped pressure head is 150~300mm / s.

5. The method for quantitatively evaluating the hot cracking sensitivity of high-entropy alloys under laser deposition process according to claim 2, characterized in that, In step 4, the designated position during the alloy laser remelting process is the geometric center of the substrate used for laser deposition.

6. The method for quantitatively evaluating the hot cracking sensitivity of high-entropy alloys under laser deposition process according to claim 2, characterized in that, In step 5, the laser remelting power is 500~1000W, the scanning speed is 5~10mm / s, and the applied strain is 0.5~5%.

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