CN113814413A

CN113814413A - Preparation method for manufacturing crack-free high-temperature alloy with controllable strength and toughness by laser additive manufacturing

Info

Publication number: CN113814413A
Application number: CN202111118943.0A
Authority: CN
Inventors: 王大威; 刘丰刚; 刘奋成; 黄春平
Original assignee: Wuhan Institute of Technology; Nanchang Hangkong University
Current assignee: Wuhan Institute of Technology; Nanchang Hangkong University
Priority date: 2021-09-24
Filing date: 2021-09-24
Publication date: 2021-12-21
Anticipated expiration: 2041-09-24
Also published as: CN113814413B

Abstract

The invention relates to a preparation method of a high-temperature alloy with controllable strength and toughness and no crack by laser additive manufacturing, which comprises the following steps: forming GH3536 powder on a high-temperature alloy forging base plate layer by layer through a synchronous powder feeding laser additive manufacturing system in an inert atmosphere protection environment, pausing for a period of time between adjacent channels in the process of forming the GH3536 powder layer by layer, and pausing for a period of time after 2 layers are deposited; and heating the manufactured sample to 1050-1300 ℃ for solution treatment, keeping the temperature for a period of time, and cooling the sample to room temperature by water. The solution treatment process can effectively control the form of the Laves phase, so that the Laves phase is converted into dispersed grains after heat treatment from a continuous strip in a deposition state, the plasticity of the material is greatly improved while a certain strength is maintained, the strength and elongation of GH3536 alloy manufactured by laser additive manufacturing are strengthened and matched, and a foundation is provided for the application of the GH3536 alloy.

Description

Preparation method for manufacturing crack-free high-temperature alloy with controllable strength and toughness by laser additive manufacturing

Technical Field

The invention relates to the field of metal material preparation and heat treatment thereof, in particular to a preparation method of a high-temperature alloy which is free of cracks and controllable in strength and toughness and manufactured by laser additive manufacturing.

Background

The GH3536 alloy is a solid solution strengthening type nickel-based high-temperature alloy, has good durability and creep property after being used for a long time at the temperature of below 900 ℃, has a short-term working temperature of 1080 ℃, also has excellent oxidation resistance and corrosion resistance, and is widely applied to manufacturing of hot end parts of aero-engines. With the development of high-performance aircraft engines, the requirements of light weight and integration are provided for the structure of the aircraft engine, and the problems of high design difficulty, long processing period, material waste and the like exist in the traditional manufacturing technology, so that the innovative development of the aircraft engine technology is restricted.

The laser additive manufacturing can realize the near-net-shape free manufacturing of high-performance metal parts with complex structures, and gradually becomes an important way for manufacturing key parts of aerospace. As a representative laser additive manufacturing technology, the synchronous powder feeding laser additive manufacturing technology (laser three-dimensional forming) has the advantages of high deposition efficiency, good forming performance, high-performance accurate repair of metal parts and the like, and is widely applied to manufacturing and repairing high-performance complex metal parts such as high-temperature alloy, titanium alloy, high-strength steel and the like.

Because the synchronous powder feeding laser additive manufacturing is a non-equilibrium near-rapid solidification process, a molten pool is subjected to rapid melting and solidification in the forming process, and the laser three-dimensional forming nickel-based superalloy has an uneven structure of epitaxial growth. In addition, in the nickel-based superalloy with high Nb and Mo contents, the Nb and Mo elements which are refractory at the end of solidification are easily concentrated in the liquid phase, and harmful Laves phases are generated. The formation of Laves consumes a large amount of Nb and Mo elements in the matrix, so that the solid solution strengthening effect of the matrix is reduced, and the Laves phase as a hard and brittle topological closely-packed phase (TCP) can seriously affect the tensile plasticity, fracture toughness, fatigue and creep property of the alloy, and simultaneously can easily become a crack nucleation base point and an expansion channel, so that the GH3536 high-temperature alloy generates cracks.

Therefore, a preparation method of nickel-based high-temperature alloy which has no crack and satisfies the use requirements of strength and plasticity needs to be found.

Disclosure of Invention

Based on the defects of the prior art, the invention aims to provide a preparation method of a high-temperature alloy which is free of cracks and controllable in strength and toughness by laser additive manufacturing, so as to reduce the volume fraction of a Laves phase in a deposition area and change the form distribution of the Laves phase, thereby improving the strength and plasticity of the high-temperature alloy by additive manufacturing.

The technical scheme for solving the technical problems is as follows: a preparation method for manufacturing a high-temperature alloy with controllable strength and toughness and no crack by laser additive manufacturing comprises the following steps:

s100, forming GH3536 powder on a high-temperature alloy forging base plate layer by layer through a synchronous powder feeding laser additive manufacturing system in an inert atmosphere protection environment, pausing for a period of time between adjacent steps in the process of forming the GH3536 powder layer by layer, and pausing for a period of time after 2 layers are deposited;

s200, heating the manufactured sample to 1050-1300 ℃ for solution treatment, keeping the temperature for a period of time, and cooling the sample to room temperature by water.

On the basis of the technical scheme, the invention can be further improved as follows.

Further, the high-temperature alloy forging base plate is In718 alloy or GH3536 alloy.

Furthermore, in the process of forming GH3536 powder layer by layer, the deposition is suspended for 3-10 s after one layer is deposited, then the adjacent deposition is performed, meanwhile, the deposition is suspended for 30-100 s after 2 layers are deposited, then the next layer is deposited, and the steps are repeated in a circulating way.

Furthermore, in the process of forming GH3536 powder layer by layer, the deposition is paused for 5s after one layer is deposited, the adjacent deposition is performed again, the deposition is paused for 60s after 2 layers are deposited, the next layer is deposited, and the steps are repeated in a circulating way.

Further, a light source in the synchronous powder feeding laser additive manufacturing system is semiconductor laser or fiber laser, the laser power is 1000W-3000W, the diameter of a light spot is 3 mm-5 mm, the laser scanning speed is 6 mm/s-12 mm/s, the powder feeding amount is 6 g/min-20 g/min, the constrained gas flow is 5L/min-12L/min, the Z-axis single-layer lifting amount is 0.2 mm-1 mm, and the lap joint rate is 40% -60%.

Furthermore, the size of GH3536 powder is 50-150 μm;

the raw material powder comprises the following components in percentage by mass:

cr: 20 wt% -23 wt%, Fe: 17 wt% -20 wt%, Mo: 8 wt% -10 wt%, Co: 0.5 wt% to 2.5 wt%, W: 0.2 wt% -1.5 wt%, Al: 0.3 wt% -0.5 wt%, C: 0.05 wt% -0.2 wt%, Si: 0.05 wt% -0.5 wt%, Mn: 0.05 wt% -0.5 wt%, and the balance of Ni.

Furthermore, the GH3536 powder comprises the following components in percentage by mass:

cr: 22.23 wt%, Fe: 17.22 wt%, Mo: 9.71 wt%, Co: 1.63 wt%, W: 0.56 wt%, Al: 0.32 wt%, C: 0.85 wt%, Si: 0.087 wt%, Mn: 0.072 wt% and the balance of Ni.

Further, the inert atmosphere is argon and the oxygen content is less than 200 ppm.

Furthermore, a heating furnace is adopted for heating the sample, the temperature control precision is +/-1 ℃, and the temperature rise rate is 10 ℃/min.

Further, the heating furnace is a box-type resistance furnace.

Further, step S200 is:

the manufactured sample is heated to 1075-1225 ℃ for solution treatment, and is cooled to room temperature after heat preservation for 1 hour.

Further, in step S100:

the prepared deposition-state sample has no cracks, pores and poor fusion, the structure is columnar grains and fine dendrites, and a strip-shaped continuous Laves phase exists between the dendrites.

Further, in step S200:

after the solid solution treatment, the microstructure of the high-temperature alloy manufactured by the laser additive shows that columnar crystals are recrystallized and transformed into fine isometric crystals, and the dendrite segregation basically disappears.

Further, in step S200:

after the solution treatment, the microstructure of the high-temperature alloy manufactured by the laser additive shows that a strip-shaped continuous Laves phase is gradually dissolved into a matrix, the quantity of brittle Laves phases is obviously reduced, and the brittle Laves phases are converted into discontinuous particles beneficial to mechanical properties.

In the environment with argon atmosphere protection, laser emitted by a laser source is gathered on a substrate to be locally melted to form a molten pool, meanwhile, powder is synchronously fed into the molten pool through a powder feeding device through airflow restriction, the powder is rapidly melted after entering the molten pool, meanwhile, a laser beam continuously moves to continuously generate a new molten pool, and the molten pool on a sweeping path is rapidly solidified on the surfaces of relatively large base materials and test pieces due to the movement of the heat source; in the deposition process, in order to prevent the sample from generating cracks caused by excessive heat accumulation, the deposition is stopped for 5s after one deposition, and then adjacent passes are deposited; meanwhile, after 2 layers are deposited, pausing for 60s, depositing the next layer, and repeating the steps in a circulating way to obtain a GH3536 alloy sample for laser additive manufacturing of a three-dimensional entity;

the GH3536 deposition state sample prepared by the method has good forming quality, no cracks and air holes exist, the structure of the GH3536 deposition state sample is typical thick columnar crystal growing along the deposition direction, the width of the columnar crystal is about 35-400 microns, the interior of the columnar crystal grain is mainly of a columnar dendritic crystal structure, the spacing of primary dendritic crystal arms is about 8-12 microns, the growth direction of the dendritic crystal does not strictly grow along the deposition direction, and a certain included angle exists between the primary dendritic crystal arms and the deposition direction; the sedimentary sample structure has an obvious zonal structure, the dendrite on the upper part of the zonal boundary is smaller, the secondary dendrite arm is not developed, and the dendrite on the lower part of the zonal boundary is coarser, and the secondary dendrite arm is more developed; the top of the deposited sample is an equiaxed dendritic structure; obvious micro segregation exists among dendrites of the GH3536 alloy manufactured by laser additive manufacturing, and a chain-shaped white Laves phase is precipitated among the dendrites; the Laves phase is generally considered as a brittle phase which seriously influences various mechanical properties of the alloy; solution treatment is generally carried out at 1100 ℃ for the In718 alloy to eliminate the Laves phase; the research finds that the Laves phase is difficult to eliminate by adopting the conventional solid solution treatment, the chain-shaped Laves phase is converted into dispersed particles by carrying out the solid solution treatment at a higher temperature, and meanwhile, the content of the Laves phase can be controlled, so that part of the Laves phase is solid-dissolved in a matrix, therefore, a proper heat treatment process can be selected according to the performance requirement of laser additive manufacturing high-temperature alloy, and the controllability of the strength and the elongation of the laser additive manufacturing high-temperature alloy is realized.

The process has the advantages that:

1. according to the preparation method of the high-temperature alloy with controllable strength and toughness and no crack in the laser additive manufacturing process, provided by the embodiment of the invention, through pause between adjacent channels and pause after 2 layers are deposited, the residual stress in the sample is reduced, and a GH3536 sample with good quality and no defects such as cracks and air holes can be obtained;

2. the temperature is kept at 1050-1300 ℃, so that coarse columnar crystals of a deposition state sample are dissolved, the sample is recrystallized, the crystal grain form is converted into isometric crystals, a large amount of annealing twin crystals appear in the sample, the crystal grains are further refined, and the aims of improving the structure and optimizing the alloy performance are fulfilled;

3. according to the invention, appropriate heat energy is input into the laser additive manufacturing high-temperature alloy to melt the Laves phase back into the matrix, and the form is changed from a continuous chain shape to a dispersed granular shape, so that the stress concentration in the stretching process is reduced, and the plasticity of the alloy is greatly improved;

4. the preparation method is simple and low in cost, and is an efficient method for improving the mechanical property of the laser additive manufactured high-temperature alloy.

Drawings

Fig. 1 is a schematic diagram of a laser additive manufacturing GH3536 process and scan path;

fig. 2 is a laser additive manufacturing GH3536 as-deposited structure;

fig. 3 is a laser additive manufacturing GH3536 as deposited Laves phase morphology;

fig. 4 shows Laves phase morphology under different solution treatments for laser additive manufacturing of GH 3536: (a)1075 deg.C; (b)1125 deg.C; (c)1175 deg.C; (d)1225 deg.C;

fig. 5 shows room temperature tensile properties of laser additive manufactured GH3536 at different solution treatments: (a) engineering stress-strain curves; (b) tensile strength and elongation.

Detailed Description

The principles and features of this invention are described below in conjunction with the following drawings, which are set forth by way of illustration only and are not intended to limit the scope of the invention.

Example 1

A method for preparing a high-temperature alloy with controllable strength and toughness and no crack by laser additive manufacturing takes GH3536 alloy with alloy components shown in Table 1 as an example, and introduces the processing method of the invention in detail:

TABLE 1 alloy composition (wt%) of materials used in examples of the present invention

Ni	Cr	Fe	Mo	Co	W	Al	C	Si	Mn
										48.086	22.23	17.22	9.71	1.63	0.56	0.32	0.085	0.087	0.072

The preparation process of the crack-free high-temperature alloy with controllable strength and plasticity specifically comprises the following steps:

1) placing GH3536 alloy spherical powder with the size of 50-150 mu m into a powder feeder;

2) putting an In718 high-temperature alloy substrate into a processing chamber filled with argon atmosphere, fixing the processing chamber on a workbench, controlling the oxygen content to be below 200ppm through argon replacement, and starting synchronous powder feeding laser additive manufacturing to obtain the high-temperature alloy with the forming size of 65mm multiplied by 60mm multiplied by 15 mm;

3) the laser used is a semiconductor laser, GH3536 powder is fused and deposited on an In718 substrate on a 6kW laser additive manufacturing system provided with a five-axis linkage numerical control machine tool, a cladding layer with the width of 2mm and the height of 0.2mm is prepared by moving a laser beam along the X direction, the cladding layer is paused for 5s, then the laser beam is deviated to the Y direction for 1mm, a cladding layer with the width of 2mm and the height of 0.2mm is prepared on adjacent passes, the cladding layer is paused for 5s, and the process is repeated to prepare a cladding layer with the size of 65mm multiplied by 60mm multiplied by 0.2 mm;

4) the process of step 3) was repeated to prepare a 2 nd layer of cladding having dimensions of 65mm by 60mm by 0.2mm, with a pause of 60 seconds thereafter. By analogy, each cladding is suspended for 5s, cladding 2 layers is suspended for 60s, and finally the block sample with the size of 65mm multiplied by 60mm multiplied by 15mm is obtained; the forming process is shown in figure 1;

the laser additive manufacturing process parameters are as follows: the laser power is 2000W, the diameter of a light spot is 5mm, the laser scanning speed is 8mm/s, the powder feeding amount is about 8.5g/min, the restricted gas flow is 8L/min, the Z-axis single-layer lifting amount is 0.2-0.3 mm, and the overlapping rate is 50%. In the forming process, high-purity argon gas with the purity of 99.99 percent is used as protective gas and powder conveying gas to protect a molten pool, and a powder conveying nozzle is adopted in the powder conveying process;

the obtained GH3536 deposition alloy manufactured by laser additive manufacturing has no defects of cracks, air holes and the like, the tensile strength of a sample is 652MPa, the elongation is 30%, the microstructure of the sample is shown in figure 2, coarse austenite columnar grains are presented, and fine dendrites are arranged inside the grains;

5) 5 test pieces with the size of 5mm multiplied by 5mm are cut out of the prepared crack-free GH3536 sample by adopting wire electrical discharge machining for solution treatment: putting the first sample in a box-type resistance furnace, heating to 1075 ℃ at the heating rate of 10 ℃/min, preserving the heat for 1h, and then cooling to room temperature by water, wherein the microstructure of the sample is shown in figure 4(a), and the chain-shaped Laves phase just begins to dissolve;

putting the second sample in a box-type resistance furnace, heating to 1125 ℃ at the heating rate of 10 ℃/min, preserving the heat for 1h, and then cooling to room temperature by water, wherein the microstructure of the second sample is shown in figure 4(b), and the chain-shaped Laves phase is further dissolved to be chain-shaped;

placing the third sample in a box-type resistance furnace, heating to 1175 deg.C at a heating rate of 10 deg.C/min, maintaining for 1h, and cooling with water to room temperature to obtain a microstructure shown in FIG. 4(c) wherein the chain-like Laves phase dissolves to form spherical particles;

putting the fourth sample in a box-type resistance furnace, heating to 1225 ℃ at a heating rate of 10 ℃/min, preserving the temperature for 1h, and then cooling to room temperature by water, wherein the microstructure of the fourth sample is shown in figure 4(e), and only a small amount of Laves phase particles exist; austenite grains are recrystallized and present as equiaxed grains;

and (3) putting the fifth sample in a box-type resistance furnace, heating to 1200 ℃ at the heating rate of 10 ℃/min, preserving the temperature for 1h, and then cooling to room temperature by water, wherein the microstructure is shown in figure 4(d), the number of the granular Laves phases is reduced compared with that of the granular Laves phases at 1175 ℃, and the austenite grains are recrystallized and appear as isometric grains.

The room-temperature tensile strength, elongation and stress-strain curves of the laser additive manufactured GH3536 alloy after solution treatment at different temperatures in the embodiment are shown in FIG. 5;

the curves at the tail end in the left diagram of fig. 5 refer to: as-deposited, 1075 ℃, 1125 ℃, 1175 ℃, 1200 ℃, 1225 ℃;

on the same abscissa in the right-hand graph of fig. 5, the left column denotes ultimateensilbenterlength and the right column denotes Elongation.

It can be seen that with the increase of the solid solution temperature, the tensile strength is increased and then decreased, and reaches the maximum value at 1200 ℃, in the temperature increasing process, as the Laves phase is melted back into the matrix, the quantity of the brittle Laves phase is obviously reduced, the shape is changed from a chain shape into a spherical shape or a granular shape, and simultaneously the residual stress of the sample and the stress concentration in the stretching process are reduced, so that the plasticity is gradually increased, and the strength and the elongation of the laser additive manufacturing high-temperature alloy after the solid solution treatment are greatly improved compared with those of the deposition state sample, therefore, a proper heat treatment method can be selected according to the performance requirements of the target laser additive manufacturing high-temperature alloy, so that the controllability of the strength and the plasticity is realized.

Example 2

2) putting an In718 high-temperature alloy substrate into a processing chamber filled with argon atmosphere, fixing the processing chamber on a workbench, controlling the oxygen content to be below 200ppm through argon replacement, and starting synchronous powder feeding laser additive manufacturing to obtain the high-temperature alloy with the forming size of 65mm multiplied by 10 mm;

3) the laser is a fiber laser, GH3536 powder is fused and deposited on an In718 substrate on a laser additive manufacturing system provided with a five-axis linkage numerical control machine tool, a cladding layer with the width of 2mm and the height of 0.3mm is prepared by moving a laser beam along the X direction, the cladding layer is paused for 5s, then the laser beam is shifted to the Y direction for 1mm, a cladding layer with the width of 2mm and the height of 0.2mm is prepared on adjacent passes, the cladding layer is paused for 5s, and the process is repeated to prepare a cladding layer with the size of 65mm multiplied by 60mm multiplied by 0.2 mm;

4) the process of step 3) was repeated to prepare a 2 nd layer of cladding having dimensions of 65mm by 60mm by 0.2mm, with a pause of 60 seconds thereafter. By analogy, each cladding is paused for 5s, and the cladding of 2 layers is paused for 60s, so that a block sample with the size of 65mm multiplied by 10mm is finally obtained. The laser additive manufacturing process parameters are as follows: the laser power is 1800W, the diameter of a light spot is 5mm, the laser scanning speed is 6mm/s, the powder feeding amount is about 8.5g/min, the restricted gas flow is 8L/min, the Z-axis single-layer lifting amount is 0.2-0.3 mm, and the overlapping rate is 50%. In the forming process, high-purity argon gas with the purity of 99.99 percent is used as protective gas and powder conveying gas to protect a molten pool, and a powder conveying nozzle is adopted in the powder conveying process;

the obtained GH3536 deposition alloy manufactured by laser additive manufacturing presents coarse austenite columnar grains, and fine dendrites are arranged in the grains;

5) cutting 5 samples with the size of 5mm multiplied by 5mm from the prepared crack-free GH3536 sample by adopting wire electrical discharge machining for solution treatment, putting the first sample in a box-type resistance furnace, raising the temperature to 1200 ℃ at the temperature rise rate of 10 ℃/min, preserving the temperature for 1h, and then cooling the sample to room temperature by water.

The alloy in the embodiment has 721MPa of tensile strength and 46% of elongation after solution treatment.

Example 3

2) putting an In718 high-temperature alloy substrate into a processing chamber filled with argon atmosphere, fixing the processing chamber on a workbench, controlling the oxygen content to be below 200ppm through argon replacement, and starting synchronous powder feeding laser additive manufacturing to obtain the high-temperature alloy with the forming size of 50mm multiplied by 10 mm;

3) the laser used is a semiconductor laser, GH3536 powder is fused and deposited on an In718 substrate on a 6kW laser additive manufacturing system provided with a five-axis linkage numerical control machine tool, a cladding layer with the width of 2mm and the height of 0.3mm is prepared by moving a laser beam along the X direction, the cladding layer is paused for 5s, then the laser beam is deviated to the Y direction for 1mm, a cladding layer with the width of 2mm and the height of 0.2mm is prepared on adjacent passes, the cladding layer is paused for 5s, and the process is repeated to prepare a cladding layer with the size of 65mm multiplied by 60mm multiplied by 0.2 mm;

4) the process of step 3) was repeated to prepare a 2 nd layer of cladding having dimensions of 65mm by 60mm by 0.2mm, with a pause of 60 seconds thereafter. By analogy, each cladding is paused for 5s, cladding 2 layers are paused for 60s, and finally a block sample with the size of 50mm multiplied by 10mm is obtained;

the laser additive manufacturing process parameters are as follows: the laser power is 2500W, the diameter of a light spot is 5mm, the laser scanning speed is 10mm/s, the powder feeding amount is about 10g/min, the restricted gas flow is 8L/min, the Z-axis single-layer lifting amount is 0.2-0.3 mm, and the overlapping rate is 50%. In the forming process, high-purity argon gas with the purity of 99.99 percent is used as protective gas and powder conveying gas to protect a molten pool, and a powder conveying nozzle is adopted in the powder conveying process;

The alloy in this example was solution treated to have a tensile strength of 732MPa and an elongation of 45%.

Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention, and that variations, modifications, substitutions and alterations can be made to the above embodiments by those of ordinary skill in the art within the scope of the present invention.

Claims

1. A preparation method for manufacturing a high-temperature alloy with controllable strength and toughness and no crack by laser additive manufacturing is characterized by comprising the following steps:

2. The method for preparing the high-temperature alloy with controllable strength and toughness and without cracks through laser additive manufacturing according to claim 1, wherein the high-temperature alloy forging substrate is an In718 alloy or a GH3536 alloy.

3. The method for preparing the high-temperature alloy with controllable strength and toughness and without cracks through laser additive manufacturing according to claim 1, wherein in the process of layer-by-layer forming of the GH3536 powder, after each deposition of one layer, the deposition is paused for 3s to 10s, then the adjacent deposition is paused for 30s to 100s, after each deposition of 2 layers, the next layer is deposited, and the steps are repeated in a cycle.

4. The method for preparing the high-temperature alloy with controllable strength and toughness and without cracks through laser additive manufacturing according to claim 1, 2 or 3, wherein a light source in the synchronous powder feeding laser additive manufacturing system is a semiconductor laser or an optical fiber laser, the laser power is 1000W-3000W, the spot diameter is 3 mm-5 mm, the laser scanning speed is 6 mm/s-12 mm/s, the powder feeding amount is 6 g/min-20 g/min, the constraint gas flow rate is 5L/min-12L/min, the Z-axis single-layer lifting amount is 0.2 mm-1 mm, and the lap joint rate is 40% -60%.

5. The method for preparing the high-temperature alloy with controllable strength and toughness and without cracks through laser additive manufacturing according to claim 1, 2, 3 or 4, wherein the GH3536 powder size is 50-150 μm;

6. The method of claim 1, wherein the inert atmosphere is argon and the oxygen content is less than 200 ppm.

7. The method for preparing the high-temperature alloy with controllable strength and toughness and no crack through laser additive manufacturing according to claim 1, wherein a heating furnace is adopted for heating the sample, the temperature control precision is +/-1 ℃, and the temperature rise rate is 10 ℃/min.

8. The method of claim 7, wherein the furnace is a box-type resistance furnace.

9. The method for preparing the high-temperature alloy with controllable strength and toughness and without cracks through the laser additive manufacturing according to claim 1, wherein the step S200 is as follows: