CN117161405A - Method for obtaining a large number of equiaxed crystals for 3D printing titanium alloy multistage cyclic heat treatment and application thereof - Google Patents
Method for obtaining a large number of equiaxed crystals for 3D printing titanium alloy multistage cyclic heat treatment and application thereof Download PDFInfo
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- 238000010438 heat treatment Methods 0.000 title claims abstract description 152
- 229910001069 Ti alloy Inorganic materials 0.000 title claims abstract description 59
- 238000000034 method Methods 0.000 title claims abstract description 57
- 239000013078 crystal Substances 0.000 title claims abstract description 53
- 238000010146 3D printing Methods 0.000 title claims abstract description 24
- 125000004122 cyclic group Chemical group 0.000 title claims description 25
- 238000001816 cooling Methods 0.000 claims abstract description 94
- 239000000956 alloy Substances 0.000 claims abstract description 28
- 229910045601 alloy Inorganic materials 0.000 claims description 16
- 229910000734 martensite Inorganic materials 0.000 claims description 6
- 239000000203 mixture Substances 0.000 claims description 4
- 238000000354 decomposition reaction Methods 0.000 claims description 3
- 238000010309 melting process Methods 0.000 claims description 3
- 229910001040 Beta-titanium Inorganic materials 0.000 claims description 2
- 230000009286 beneficial effect Effects 0.000 abstract description 5
- 238000010924 continuous production Methods 0.000 abstract description 2
- 238000013461 design Methods 0.000 abstract description 2
- 238000000110 selective laser sintering Methods 0.000 description 22
- XKRFYHLGVUSROY-UHFFFAOYSA-N Argon Chemical compound [Ar] XKRFYHLGVUSROY-UHFFFAOYSA-N 0.000 description 18
- 239000000463 material Substances 0.000 description 10
- 229910052786 argon Inorganic materials 0.000 description 9
- 238000004519 manufacturing process Methods 0.000 description 5
- 230000008569 process Effects 0.000 description 5
- 238000012360 testing method Methods 0.000 description 5
- 238000000137 annealing Methods 0.000 description 4
- 238000002844 melting Methods 0.000 description 4
- 230000008018 melting Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 239000000654 additive Substances 0.000 description 2
- 230000000996 additive effect Effects 0.000 description 2
- 229910052751 metal Inorganic materials 0.000 description 2
- 239000002184 metal Substances 0.000 description 2
- 239000000843 powder Substances 0.000 description 2
- 238000012545 processing Methods 0.000 description 2
- 230000001105 regulatory effect Effects 0.000 description 2
- 238000011160 research Methods 0.000 description 2
- 230000007704 transition Effects 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 1
- 238000012512 characterization method Methods 0.000 description 1
- 230000001276 controlling effect Effects 0.000 description 1
- 230000007797 corrosion Effects 0.000 description 1
- 238000005260 corrosion Methods 0.000 description 1
- 230000007547 defect Effects 0.000 description 1
- 230000007123 defense Effects 0.000 description 1
- 230000008021 deposition Effects 0.000 description 1
- 238000005516 engineering process Methods 0.000 description 1
- 238000002474 experimental method Methods 0.000 description 1
- 230000006872 improvement Effects 0.000 description 1
- 239000000155 melt Substances 0.000 description 1
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Abstract
The invention provides a 3D printing titanium alloy multistage circulation heat treatment method for obtaining a large number of equiaxed crystals, which adopts a stepped circulation heat treatment method in three temperature intervals, and the multi-step temperature rise and fall are more beneficial to the spheroidization of alpha crystal grains, so that the equiaxed crystal grains with higher proportion are obtained. In the method, the adjustable range of each parameter is wide, a large number of equiaxed crystal tissues are obtained, and the required mechanical properties can be obtained by arbitrarily changing the heat treatment temperature and the final cooling initial temperature of each stage. The titanium alloy material treated by the method provided by the invention has the advantages that the equiaxial crystal proportion is more than 20%, more preferably, 27.6% -36.8%, the comprehensive mechanical property of the titanium alloy material can be obviously improved, and the prepared titanium alloy material has the advantages of high tensile strength, high yield strength, good extensibility and the like. The invention has reasonable design, simple method steps, easy operation, continuous production realization and wide popularization and application prospect.
Description
Technical Field
The invention belongs to the technical field of titanium alloy additive manufacturing, and particularly relates to a method for obtaining a large number of equiaxed crystal 3D printing titanium alloy multistage circulation heat treatment and application of the method for obtaining a large number of equiaxed crystal 3D printing titanium alloy multistage circulation heat treatment.
Background
Selective laser melting (Selective laser melting, SLM) is an additive manufacturing technique based on three-dimensional model data that selectively melts metal powder layer by layer using a high energy laser beam and directly obtains parts having arbitrary shapes. The technology has the advantages of high precision, high forming speed, wide printable material range and the like, and can realize personalized customization according to different requirements of users. After printing, the unmelted metal powder can be reused, which greatly reduces the production cost. Titanium alloy is widely applied to the fields of aerospace, biomedical treatment, ships, national defense and the like because of high specific strength, good biocompatibility, strong corrosion resistance, low elastic modulus and excellent fatigue performance. The titanium alloy produced by the traditional method has a plurality of limitations such as difficult processing, low material utilization rate, long production period, high production cost and the like, so that the titanium alloy prepared by adopting the SLM (selective laser sintering) process has gained more and more attention in recent years. Due to the very fast cooling speed of the SLM process (10 4 -10 6 K/s), columnar crystals grown in the deposition direction and needle-like Marshall's inside thereof are generally present in the shaped sampleThe body, resulting in high strength and low elongation of the material, can not meet the industrial application requirements.
A large number of experiments show that the comprehensive mechanical properties of the material can be obviously improved by obtaining a certain proportion of equiaxed crystals in a microstructure. Plastic deformation + annealing is the most commonly used method to sphere the microstructure, but this is not applicable to SLM as a "near net shape" technique. Therefore, heat treatment becomes the only effective post-treatment means. The most commonly used heat treatment method for SLM forming titanium alloys at present is a single annealing treatment, i.e. the sample is kept at a certain temperature for a period of time and then cooled down to room temperature by air or furnace. Although a certain proportion of equiaxed crystals can be obtained in a sample by the method, the extensibility of the material cannot be improved significantly due to the small number.
In general, any proportion of equiaxed crystals below the upper limit of the desired equiaxed crystal proportion can be obtained only if the upper limit of equiaxed crystals obtained by the heat treatment regime exceeds the desired equiaxed crystal proportion. Correspondingly, the higher the obtained equiaxed crystal proportion is, the wider the regulation and control range of mechanical properties is, and the applicable use environment is also wider. On the basis, when the strength of the titanium alloy material is required to be higher, the proportion of the equiaxed crystal can be properly reduced; when the titanium alloy is required to have higher plasticity, the proportion of the equiaxed crystals can be increased, so that the flexible regulation and control of the mechanical properties of the titanium alloy material can be realized.
Based on the method, a method for performing heat treatment on the 3D printing titanium alloy capable of obtaining a large number of equiaxed crystals is provided, and has important significance for improving the mechanical properties of alloy materials, and is also a technical problem to be solved.
Disclosure of Invention
One of the purposes of the invention is to provide a method for obtaining a plurality of equiaxed crystals of 3D printed titanium alloy through multistage cyclic heat treatment.
The second object of the invention is to provide a 3D printing titanium alloy with a large number of equiaxed crystals and excellent mechanical properties.
One of the achievement purposes of the invention adopts the technical proposal that: a method for obtaining a plurality of equiaxed crystals of a 3D printed titanium alloy for multi-stage cyclic heat treatment is provided, comprising the steps of:
s1, placing the titanium alloy prepared by 3D printing in an inert atmosphere, and placing in T 1 Performing first heat treatment at the temperature for a certain time to obtain a first sample;
s2, heating the first sample to T 2 Performing a second heat treatment at a temperature for a certain time, and heating to T 3 Performing third heat treatment for a certain time at the temperature to obtain a second sample;
s3, cooling the second sample to T along with the furnace 2 Performing fourth heat treatment at temperature for a certain time, and cooling to T along with the furnace 1 A temperature;
s4, repeating the steps S1-S3 for a plurality of times until a third sample of equiaxed crystals with the required proportion is obtained;
the T is 1 At a temperature higher than the martensitic decomposition temperature of the titanium alloy, T 3 The temperature is lower than the beta transus temperature of the titanium alloy, and T 1 <T 2 <T 3 。
The general thought of the multistage circulation heat treatment method provided by the invention is as follows:
since the selective laser melting (Selective laser melting) SLM process cools very fast, the sample forms very fine needle-like martensite and contains a large number of dislocations, twins, and substructures. In the initial stage of multi-stage cyclic heat treatment, acicular martensite is decomposed and converted into alpha and beta phases; due to the presence of the above-mentioned crystallographic defects, grain boundary splitting occurs in a part of the α laths. As the number of cycles increases, the grain boundary splitting gradually deepens until the lath breaks completely. These broken laths gradually coarsen and eventually form equiaxed crystals as the heat treatment proceeds. Preferably, in step S4, the number of repetitions of steps S1-S3 is 2-15, more preferably, the number of repetitions of steps S1-S3 is 4-9.
Compared with the conventional single annealing treatment mode (i.e. the sample is kept at a certain temperature for a period of time and then cooled by air or by a furnace to room temperature), the invention adopts the stepped circulation heat treatment method in three temperature intervals, the multi-step heating and cooling are more beneficial to the spheroidization of alpha grains, and the circulation times can be regulated and controlled as required, thereby obtainingA higher proportion of equiaxed grains is obtained. In the selection of three temperature intervals, the invention defines T 1 At a temperature higher than the martensitic decomposition temperature of the titanium alloy, T 3 The temperature is lower than the beta transus temperature of the titanium alloy, and T 1 <T 2 <T 3 . Wherein T is 1 The temperature is set to ensure that martensite is decomposed and converted into alpha phase, which is beneficial to the occurrence of subsequent spheroidization; t (T) 3 The setting of the temperature is to consider that when the temperature exceeds the beta phase transition point, the microstructure is obviously coarsened, so that the comprehensive mechanical property of the material is obviously reduced; t (T) 2 Between T 1 And T 3 The transition effect can be achieved, so that the alpha phase of the lath is split more fully, and more equiaxed crystals can be formed; at the same time, intermediate temperature T 2 The arrangement of (2) can also effectively reduce the T 3 Processing time of temperature, if T is not set 2 Temperature, sample is required to be at T 3 The heat is preserved for a longer time at the temperature to ensure the formation of equiaxed crystals, and long-time high-temperature treatment easily causes the growth of crystal grains, resulting in the reduction of the strength of the material.
In the method, the microstructure with different proportions can be obtained by adjusting the annealing temperature and the final cooling initial temperature of each section, so as to obtain the part with controllable mechanical properties.
Further, the 3D printing is a selective laser melting process; the titanium alloy is near alpha titanium alloy or alpha+beta titanium alloy. In the invention, the titanium alloy is prepared by adopting a selective laser melting process, and the grain boundary alpha phase does not exist in the sample, so that any subsequent treatment is not needed to eliminate the grain boundary alpha phase, the treatment flow is simplified, and the treatment efficiency is improved.
Preferably, said T 1 The temperature is 700-800 ℃, T 2 The temperature is 800-900 ℃, T 3 The temperature is 900-1000 ℃. More preferably, T is 80 ℃ or less 2 -T 1 ≤120℃，80℃≤T 3 -T 2 ≤120℃。
Preferably, the heating rate is 8-12 ℃/min. The time of the first heat treatment, the second heat treatment and the third heat treatment is 1-3 h, and the three heat treatment times can be the same or different. Specifically, the adjustment can be performed according to the actually required comprehensive mechanical properties.
Preferably, the furnace cooling rate is 2-8 ℃/min.
Further, the method for obtaining a plurality of 3D printing titanium alloy multi-stage cyclic heat treatment of equiaxed crystals provided by the invention further comprises the following steps: and S5, cooling the third sample to room temperature.
In the present invention, the heat treatment temperature after completion of step S4 is T 1 At a lower temperature, the third sample consisted essentially of equiaxed alpha phases and short rod-like alpha phases. If the third sample is directly air-cooled to room temperature, the microstructure is more T 1 Without significant changes. A great number of researches show that on the basis of obtaining the expected equiaxed crystal with the proportion, different cooling modes are selected for the third sample, so that the effect of auxiliary regulation and control of the equiaxed crystal proportion can be achieved, and further the effect of further regulating and controlling the mechanical property of the titanium alloy material can be achieved. In the step S5 of the invention, the microstructure with different proportions can be obtained by heating the third sample to different temperatures (the proportion of the beta phase is different) and then cooling the third sample, so that the regulation and control of the mechanical properties of the final sample are realized.
Preferably, step S5 includes: first, the third sample is put at T 1 Performing a first heat treatment at a temperature for a certain time, and then heating to T 2 Performing a second heat treatment at a temperature for a certain time, and heating to T 3 And performing third heat treatment for a certain time at the temperature, and then air-cooling to room temperature. Research has found that when at T 3 When the temperature is cooled to room temperature, the beta phase of the sample is higher in proportion, and the beta phase can be converted into strip-shaped alpha phase, so that the finally prepared material has higher mechanical strength.
Preferably, step S5 includes: first, the third sample is put at T 1 Performing a first heat treatment at a temperature for a certain time, and then heating to T 2 Performing a second heat treatment at a temperature for a certain time, and heating to T 3 Performing a third heat treatment at a temperature for a certain time, and then cooling to T along with the furnace 2 Performing a fourth heat treatment at a temperature for a certain time, and finally taking out the blankCool to room temperature.
Preferably, step S5 includes: first, the third sample is put at T 1 Performing a first heat treatment at a temperature for a certain time, and then heating to T 2 Performing a second heat treatment at a temperature for a certain time, and heating to T 3 Performing a third heat treatment at a temperature for a certain time, and then cooling to T along with the furnace 2 Performing fourth heat treatment at temperature for a certain time, and cooling to T along with the furnace 1 And (5) taking out the mixture at the temperature, and finally taking out the mixture for air cooling to the room temperature.
Preferably, the fourth heat treatment is performed for 1 to 3 hours.
In the above operation, the temperature of the sample after the completion of the cycle of step S4 is gradually raised to T 3 And then, different cooling means are adopted to regulate and control the proportion of the equiaxed crystal and the secondary alpha lath in the final sample so as to obtain the required mechanical property. In the multistage circulation heat treatment method provided by the invention, the heating stage of heat treatment is a process of dissolving and converting alpha phase into beta phase, and the cooling stage is a process of converting beta phase into alpha 0 phase; in the step S5, the cooling modes and cooling rates are different, so that the morphology of the α1 phase converted from the β phase is also different, and the mechanical properties are also different. Unlike the cooling mode of the cyclic heat treatment in the step S4, the cooling rate in the air cooling step in the step S5 is higher, the beta phase is directly converted into the alpha 2 phase of the sheet, the equiaxed alpha phase can provide good plasticity, and the alpha phase of the sheet can provide higher strength. In the invention, the proportion of the equiaxed alpha phase to the alpha phase of the lamellar is controlled by adjusting the air cooling at different temperatures, so that a final sample with expected mechanical strength is obtained.
The second technical scheme adopted for realizing the purpose of the invention is as follows: there is provided a 3D printed titanium alloy made according to the method of one of the objects of the present invention. According to the invention, by adjusting various parameters in the multistage cyclic heat treatment method, the equiaxial crystal regulation and control of any proportion can be realized, so that the comprehensive mechanical properties of the titanium alloy material are optimized.
In some better embodiments, the 3D printing titanium alloy treated by the method provided by the invention has the equiaxed crystal proportion of 21.4% -36.8%, excellent comprehensive mechanical property, the tensile strength of 880-939 MPa, the yield strength of 731-850 MPa and the elongation of 14.4% -17.2%.
Compared with the prior art, the invention has the beneficial effects that:
(1) According to the method for obtaining the multi-stage cyclic heat treatment of the 3D printing titanium alloy with a large number of equiaxed crystals, which is provided by the invention, the multi-stage cyclic heat treatment is adopted to obtain the titanium alloy prepared by the SLM with a large number of equiaxed crystal structures, and the comprehensive mechanical properties of the material are obviously improved.
(2) The invention has wide adjustable range of each parameter, and can obtain the required mechanical property by arbitrarily changing the heat treatment temperature and the final cooling initial temperature of each stage.
(3) The invention has reasonable design, simple method steps, easy operation, continuous production realization and wide popularization and application prospect.
Drawings
FIG. 1 is a schematic illustration of a method for multi-stage cyclic heat treatment of 3D printed titanium alloys to obtain a plurality of equiaxed crystals in accordance with the present invention;
FIG. 2 is a photograph showing the microstructure of the SLM TA15 alloy of example 1 of the present invention after 4 cycles of multi-stage cyclic heat treatment;
FIG. 3 is a photograph showing the microstructure of the SLM TA15 alloy of example 2 of the present invention after 9 cycles of multi-stage cyclic heat treatment;
FIG. 4 is a photograph showing the microstructure of the SLM TC4 alloy of example 3 of the present invention after 4 cycles of multi-stage cyclic heat treatment;
FIG. 5 is a photograph showing the microstructure of the SLM TC4 alloy of example 4 of the present invention after 9 cycles of multi-stage cyclic heat treatment;
FIG. 6 is a photograph showing the microstructure of the SLM TA15 alloy of example 5 of the present invention after 4 cycles of multi-cycle heat treatment.
Detailed Description
The technical solutions of the present invention will be clearly and completely described in connection with the embodiments, and it is obvious that the described embodiments are only some embodiments of the present invention, not all embodiments. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
It should be noted that, without conflict, the embodiments of the present invention and features of the embodiments may be combined with each other.
The invention will be further illustrated, but is not limited, by the following examples.
The main parameters involved in examples 1-9 are shown in Table 1 below:
TABLE 1
Example 1
A multistage cyclic heat treatment method for obtaining a large number of equiaxed crystals and remarkably improving the plasticity of 3D printing titanium alloy comprises the following steps:
step 1: heating a heat treatment furnace filled with high-purity argon to 750 ℃, and then placing a TA15 alloy sample prepared by SLM into the furnace to start heat treatment;
step 2: the sample obtained in the step 1 is kept at 750 ℃ for 1h, then is heated to 850 ℃ with the heating rate of 10 ℃/min, is kept at 1h, is heated to 950 ℃ with the heating rate of 10 ℃/min, and is kept at 1h;
step 3: cooling the sample obtained in the step 2 to 850 ℃ at a cooling rate of 6 ℃/min along with a furnace, preserving heat for 1h, and then cooling to 750 ℃ at a cooling rate of 6 ℃/min along with the furnace;
step 4: repeating the step 2 and the step 3 for 4 times in total;
step 5: and (3) carrying out the heat treatment in the step (2) on the sample obtained in the step (4) again, cooling to 850 ℃ along with the furnace, preserving heat for 1h, cooling to 750 ℃ along with the furnace, and taking out and cooling to room temperature immediately to obtain a final finished product.
Example 2
A multistage cyclic heat treatment method for obtaining a large number of equiaxed crystals and remarkably improving the plasticity of 3D printing titanium alloy comprises the following steps:
step 1: heating a heat treatment furnace filled with high-purity argon to 750 ℃, and then placing a TA15 alloy sample prepared by SLM into the furnace to start heat treatment;
step 2: the sample obtained in the step 1 is kept at 750 ℃ for 1h, then is heated to 850 ℃ with the heating rate of 10 ℃/min, is kept at 1h, is heated to 950 ℃ with the heating rate of 10 ℃/min, and is kept at 1h;
step 3: cooling the sample obtained in the step 2 to 850 ℃ at a cooling rate of 6 ℃/min along with a furnace, preserving heat for 1h, and then cooling to 750 ℃ at a cooling rate of 6 ℃/min along with the furnace;
step 4: repeating the step 2 and the step 3 for 9 times in total;
step 5: and (3) carrying out the heat treatment in the step (2) on the sample obtained in the step (4) again, cooling to 850 ℃ along with the furnace, preserving heat for 1h, cooling to 750 ℃ along with the furnace, and taking out and cooling to room temperature immediately to obtain a final finished product.
Example 3
A multistage cyclic heat treatment method for obtaining a large number of equiaxed crystals and remarkably improving the plasticity of 3D printing titanium alloy comprises the following steps:
step 1: heating a heat treatment furnace filled with high-purity argon to 750 ℃, and then placing a TC4 alloy sample prepared by the SLM into the furnace to start heat treatment;
step 2: the sample obtained in the step 1 is kept at 750 ℃ for 1h, then is heated to 850 ℃ with the heating rate of 10 ℃/min, is kept at 1h, is heated to 950 ℃ with the heating rate of 8 ℃/min, and is kept at 1h;
step 3: cooling the sample obtained in the step 2 to 850 ℃ at a cooling rate of 4 ℃/min along with a furnace, preserving heat for 1h, and then cooling to 750 ℃ at a cooling rate of 4 ℃/min along with the furnace;
step 4: repeating the step 2 and the step 3 for 4 times in total;
step 5: and (3) carrying out the heat treatment in the step (2) on the sample obtained in the step (4) again, cooling to 850 ℃ along with the furnace, preserving heat for 1h, cooling to 750 ℃ along with the furnace, and taking out and cooling to room temperature immediately to obtain a final finished product.
Example 4
A multistage cyclic heat treatment method for obtaining a large number of equiaxed crystals and remarkably improving the plasticity of 3D printing titanium alloy comprises the following steps:
step 1: heating a heat treatment furnace filled with high-purity argon to 750 ℃, and then placing a TC4 alloy sample prepared by the SLM into the furnace to start heat treatment;
step 2: the sample obtained in the step 1 is kept at 750 ℃ for 1h, then is heated to 850 ℃ with the heating rate of 10 ℃/min, is kept at 1h, is heated to 950 ℃ with the heating rate of 8 ℃/min, and is kept at 1h;
step 3: cooling the sample obtained in the step 2 to 850 ℃ with a cooling rate of 2 ℃/min, preserving heat for 1h, and then cooling to 750 ℃ with the cooling rate of 2 ℃/min;
step 4: repeating the step 2 and the step 3 for 9 times in total;
step 5: and (3) carrying out the heat treatment in the step (2) on the sample obtained in the step (4) again, cooling to 850 ℃ along with the furnace, preserving heat for 1h, cooling to 750 ℃ along with the furnace, and taking out and cooling to room temperature immediately to obtain a final finished product.
Example 5
A multistage cyclic heat treatment method for obtaining a large number of equiaxed crystals and remarkably improving the plasticity of 3D printing titanium alloy comprises the following steps:
step 1: heating a heat treatment furnace filled with high-purity argon to 750 ℃, and then placing a TA15 alloy sample prepared by SLM into the furnace to start heat treatment;
step 2: the sample obtained in the step 1 is kept at 750 ℃ for 1h, then is heated to 850 ℃ with the heating rate of 10 ℃/min, is kept at 1h, is heated to 950 ℃ with the heating rate of 12 ℃/min, and is kept at 1h;
step 3: cooling the sample obtained in the step 2 to 850 ℃ at a cooling rate of 5 ℃/min along with a furnace, preserving heat for 1h, and then cooling to 750 ℃ at a cooling rate of 5 ℃/min along with the furnace;
step 4: repeating the step 2 and the step 3 for 4 times in total;
step 5: and (3) carrying out the heat treatment in the step (2) on the sample obtained in the step (4) again, and taking out the sample immediately and cooling the sample to room temperature to obtain a final finished product.
Example 6
A multistage cyclic heat treatment method for obtaining a large number of equiaxed crystals and remarkably improving the plasticity of 3D printing titanium alloy comprises the following steps:
step 1: heating a heat treatment furnace filled with high-purity argon to 750 ℃, and then placing a TA15 alloy sample prepared by SLM into the furnace to start heat treatment;
step 2: the sample obtained in the step 1 is kept at 750 ℃ for 2 hours, then is heated to 850 ℃ with the heating rate of 10 ℃/min, is kept at 2 hours, is heated to 950 ℃ with the heating rate of 10 ℃/min, and is kept at 2 hours;
step 3: cooling the sample obtained in the step 2 to 850 ℃ at a cooling rate of 8 ℃/min along with a furnace, preserving heat for 2 hours, and then cooling to 750 ℃ at a cooling rate of 8 ℃/min along with the furnace;
step 4: repeating the step 2 and the step 3 for 6 times in total;
step 5: and (3) carrying out the heat treatment in the step (2) on the sample obtained in the step (4) again, cooling to 850 ℃ along with a furnace, preserving heat for 2 hours, and taking out and cooling to room temperature immediately to obtain a final finished product.
Example 7
A multistage cyclic heat treatment method for obtaining a large number of equiaxed crystals and remarkably improving the plasticity of 3D printing titanium alloy comprises the following steps:
step 1: heating a heat treatment furnace filled with high-purity argon to 700 ℃, and then placing a TA15 alloy sample prepared by SLM into the furnace to start heat treatment;
step 2: the sample obtained in the step 1 is kept at 700 ℃ for 1h, then is heated to 800 ℃ with the heating rate of 10 ℃/min, is kept at 1h, is heated to 900 ℃ with the heating rate of 10 ℃/min, and is kept at 1h;
step 3: cooling the sample obtained in the step 2 to 800 ℃ at a cooling rate of 8 ℃/min along with a furnace, preserving heat for 1h, and then cooling to 750 ℃ at a cooling rate of 8 ℃/min along with the furnace;
step 4: repeating the step 2 and the step 3 for 4 times in total;
step 5: and (3) carrying out the heat treatment in the step (2) on the sample obtained in the step (4) again, cooling to 800 ℃ along with the furnace, preserving heat for 1h, cooling to 700 ℃ along with the furnace, and taking out and cooling to room temperature immediately to obtain a final finished product.
Example 8
A multistage cyclic heat treatment method for obtaining a large number of equiaxed crystals and remarkably improving the plasticity of 3D printing titanium alloy comprises the following steps:
step 1: heating a heat treatment furnace filled with high-purity argon to 800 ℃, and then placing a TA15 alloy sample prepared by SLM into the furnace to start heat treatment;
step 2: the sample obtained in the step 1 is kept at 800 ℃ for 1h, then is heated to 900 ℃ with the heating rate of 10 ℃/min, is kept at 1h, is heated to 970 ℃ with the heating rate of 10 ℃/min, and is kept at 1h;
step 3: cooling the sample obtained in the step 2 to 900 ℃ at a cooling rate of 8 ℃/min along with a furnace, preserving heat for 1h, and then cooling to 800 ℃ at a cooling rate of 8 ℃/min along with the furnace;
step 4: repeating the step 2 and the step 3 for 4 times in total;
step 5: and (3) carrying out the heat treatment in the step (2) on the sample obtained in the step (4) again, cooling to 900 ℃ along with the furnace, preserving heat for 1h, cooling to 800 ℃ along with the furnace, and taking out and cooling to room temperature immediately to obtain a final finished product.
Example 9
A multistage cyclic heat treatment method for obtaining a large number of equiaxed crystals and remarkably improving the plasticity of 3D printing titanium alloy comprises the following steps:
step 1: heating a heat treatment furnace filled with high-purity argon to 730 ℃, and then placing a TC4 alloy sample prepared by the SLM into the furnace to start heat treatment;
step 2: the sample obtained in the step 1 is kept at 730 ℃ for 3 hours, then is heated to 830 ℃ with the heating rate of 10 ℃/min and then is kept at 3 hours, and then is heated to 930 ℃ with the heating rate of 10 ℃/min and is kept at 3 hours;
step 3: cooling the sample obtained in the step 2 to 830 ℃ at a cooling rate of 6 ℃/min along with a furnace, preserving heat for 3 hours, and then cooling to 730 ℃ at a cooling rate of 6 ℃/min along with the furnace;
step 4: repeating the step 2 and the step 3 for 9 times in total;
step 5: and (3) carrying out the heat treatment in the step (2) on the sample obtained in the step (4) again, cooling to 830 ℃ along with the furnace, preserving heat for 3 hours, cooling to 730 ℃ along with the furnace, and taking out and cooling to room temperature immediately to obtain a final finished product.
Performance testing and characterization
(one) microscopic morphology and equiaxed Crystal ratio
Figures 2-6 show microstructure pictures of titanium alloy samples of examples 1-5 of the present invention after various cycles. As can be seen from fig. 2-6, the microstructure of the titanium alloy materials treated in examples 1-5 is composed of equiaxed alpha grains, rod-shaped alpha grains, lath alpha grains, and a small amount of residual beta phase. The alpha grains with different shapes can be seen to have smaller sizes, and the small grain sizes are beneficial to the improvement of the material strength.
Further, the equiaxed crystal ratio in the titanium alloy material of each example was calculated as shown in the following table 2:
TABLE 2
As can be seen from the above table, the equiaxed crystal ratio in the microstructure of the samples treated in examples 1 to 9 is higher than 20%, wherein the equiaxed crystal ratio in examples 2, 3, 4, 6 and 9 is more than 30%.
(II) mechanical Property test
The titanium alloy materials treated in examples 1-5 were subjected to comprehensive mechanical property tests, the test items including: tensile strength, yield strength, and elongation. The results of each test are shown in table 3 below:
TABLE 3 Table 3
As can be seen from the above table, the data,
the titanium alloy material treated by the method provided by the invention has excellent comprehensive mechanical properties on the basis of having a higher proportion of equiaxed crystals, the tensile strength is 880-939 MPa, the yield strength is 750-850 MPa, and the elongation is 13.7% -17.2%. The multi-stage circulation heat treatment scheme provided by the invention can effectively spheroidize microstructure, and provides a brand new method for optimizing the tissue performance of the 3D printing titanium alloy.
The foregoing is merely illustrative of the preferred embodiments of the present invention and is not intended to limit the embodiments and scope of the present invention, and it should be appreciated by those skilled in the art that equivalent substitutions and obvious variations may be made using the teachings of the present invention, which are intended to be included within the scope of the present invention.
Claims (10)
1. A method for obtaining a plurality of equiaxed crystals of a 3D printed titanium alloy for multi-stage cyclic heat treatment, comprising the steps of:
s1, placing the titanium alloy prepared by 3D printing in an inert atmosphere, and placing in T 1 Performing first heat treatment at the temperature for a certain time to obtain a first sample;
s2, heating the first sample to T 2 Performing a second heat treatment at a temperature for a certain time, and heating to T 3 Performing third heat treatment for a certain time at the temperature to obtain a second sample;
s3, cooling the second sample to T along with the furnace 2 Performing fourth heat treatment at temperature for a certain time, and cooling to T along with the furnace 1 A temperature;
s4, repeating the steps S1-S3 for a plurality of times until a third sample of equiaxed crystals with the required proportion is obtained;
the T is 1 At a temperature higher than the martensitic decomposition temperature of the titanium alloy, T 3 The temperature is lower than the beta transus temperature of the titanium alloy, and T 1 <T 2 <T 3 。
2. The method of claim 1, wherein the 3D printing is a selective laser melting process; the titanium alloy is near alpha titanium alloy or alpha+beta titanium alloy.
3. The method of claim 1, wherein said T 1 The temperature is 700-800 ℃, T 2 The temperature is 800-900 ℃, T 3 The temperature is 900-1000 ℃.
4. The method of claim 1, wherein the rate of temperature rise is 8-12 ℃/min.
5. The method of claim 1, wherein the furnace cooling rate is 2-8 ℃/min.
6. The method according to claim 1, characterized in that the method further comprises the steps of:
and S5, cooling the third sample to room temperature.
7. The method of claim 6, wherein step S5 comprises: first, the third sample is put at T 1 Performing a first heat treatment at a temperature for a certain time, and then heating to T 2 Performing a second heat treatment at a temperature for a certain time, and heating to T 3 And performing third heat treatment for a certain time at the temperature, and then air-cooling to room temperature.
8. The method of claim 6, wherein step S5 comprises: first, the third sample is put at T 1 Performing a first heat treatment at a temperature for a certain time, and then heating to T 2 Performing a second heat treatment at a temperature for a certain time, and heating to T 3 Performing a third heat treatment at a temperature for a certain time, and then cooling to T along with the furnace 2 And performing fourth heat treatment for a certain time at the temperature, and finally taking out and air cooling to room temperature.
9. The method of claim 6, wherein step S5 comprises: first, the third sample is put at T 1 Performing a first heat treatment at a temperature for a certain time, and then heating to T 2 Performing a second heat treatment at a temperature for a certain time, and heating to T 3 Performing a third heat treatment at a temperature for a certain time, and then cooling to T along with the furnace 2 Performing fourth heat treatment at temperature for a certain time, and cooling to T along with the furnace 1 And (5) taking out the mixture at the temperature, and finally taking out the mixture for air cooling to the room temperature.
10. A 3D printed titanium alloy produced according to the method of any one of claims 1-9, wherein the 3D printed titanium alloy has an equiaxed grain ratio of greater than 20%.
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