A heat treatment method for improving tensile properties of TC4 titanium alloy

Abstract

The application provides a heat treatment method for improving the tensile property of TC4 titanium alloy, and comprises the following steps: placing a treated TC4 titanium alloy sample in a heat treatment furnace to heat to below a beta phase transition temperature for solid solution and heat preservation; then, cooling to a certain temperature in the furnace according to a set cooling speed, and immediately water quenching; placing the quenched sample in the heat treatment furnace again to heat to below the beta phase transition temperature for aging and heat preservation for a period of time, and then cooling; the TC4 titanium alloy sample is made by plasma arc deposition and synchronous rolling additive manufacturing. In conclusion, the application combines the characteristics of subcritical annealing for regulating primary phase and large-scale microstructure and solid solution and aging for regulating secondary phase and small-scale microstructure, and the microstructure obtained after heat treatment comprises equiaxed primary alpha, discontinuous grain boundary alpha, secondary phase and alpha / beta interface phase, so that the tensile property of the TC4 titanium alloy is significantly improved.

Description

Technical Field

[0001] This invention relates to the field of plasma arc additive manufacturing of TC4 titanium alloy, and particularly to a heat treatment method for improving the tensile properties of TC4 titanium alloy. Background Technology

[0002] Titanium alloys, especially TC4, possess excellent mechanical properties, such as higher specific strength than common steel and aluminum alloys, making them widely used in the aerospace field where weight reduction is crucial. However, titanium's low thermal conductivity and high chemical reactivity limit the speed of cutting tools to avoid heat buildup causing tool adhesion and reduced part precision. Therefore, traditional forming methods (plastic forming, machining, etc.) are characterized by long forming cycles, low material utilization, and high production costs. Traditional methods for forming titanium alloys are based on the concepts of equal-material or subtractive forming. To avoid the drawbacks of traditional methods, additive manufacturing (AM) methods based on additive forming and rapid near-net-shape forming can be adopted. Wire and Arc Additive Manufacturing (WAAM) is a technology that uses an electric arc heat source to melt metal wires and deposit them layer by layer along a given path to create solid parts. However, due to the repeated and rapid thermal cycles involved in the arc additive manufacturing process, including melting, solidification, and α / β solid-state phase transformation, TC4 titanium alloy exhibits coarse columnar β crystals and an inhomogeneous microstructure, resulting in anisotropic tensile properties and low elongation. Common control methods include optimizing deposition parameters, designing alloy composition, combining with other processes, and post-deposition heat treatment.

[0003] Combined process control methods typically involve integrating deposition with plastic deformation, which is more effective than optimizing deposition parameters and designing alloy composition in achieving equiaxed and grain-refining effects on primary columnar β grains. Rolling, in particular, can generate greater plastic deformation than ultrasonic impact. While combined plasma arc deposition and rolling achieve homogenization of primary β grains, significant room for control remains regarding the primary α phase, which constitutes over 80% of the microstructure at room temperature. Furthermore, to further improve performance, it is necessary to study the microstructure at small scales: secondary phases and the α / β interface phase, which significantly influence tensile properties. Therefore, the characteristics of the α phase determine the room-temperature tensile properties of TC4 titanium alloy. Patent CN108374136B discloses a heat treatment method to improve the strength and plasticity of TC4 titanium alloy. This method employs solution treatment followed by cold deformation and finally aging treatment. The principle behind this method is that the cold deformation process accumulates nucleation motive force for the aging process, resulting in a fine and uniformly distributed microstructure.

[0004] Heat treatment is an important way to regulate the microstructure and properties of TC4 titanium alloys, controlling element diffusion processes and cooling rates. Previous research has established standard heat treatment regimes for TC4 titanium alloys, with common regimes based on the forged microstructure (biaxial or equiaxed structure). Since the microstructure and properties of TC4 after heat treatment are closely related to its initial microstructure, and TC4 titanium alloys manufactured using composite additive manufacturing exhibit unique microstructure characteristics different from forged or Widmanstätten structures, a heat treatment method suitable for the unique microstructure of TC4 titanium alloys manufactured using plasma arc composite additive manufacturing is needed. However, the heat treatment method in the aforementioned patent only regulates the secondary α phase and cannot regulate the characteristics of the α phase used. Summary of the Invention

[0005] In view of this, the present invention proposes a heat treatment method to improve the tensile properties of TC4 titanium alloy. The method adopts a combination of subcritical annealing and solution aging treatment, which can control the microstructure of TC4 titanium alloy produced by plasma arc composite additive manufacturing and improve the tensile properties of TC4 titanium alloy produced by plasma arc composite additive manufacturing.

[0006] The technical solution of this invention is implemented as follows:

[0007] This invention provides a heat treatment method for improving the tensile properties of TC4 titanium alloy, comprising the following steps:

[0008] S1 placed the treated TC4 titanium alloy sample in a heat treatment furnace and heated it to below the β phase transformation temperature for solution treatment and heat preservation.

[0009] S2 furnace-cools the TC4 titanium alloy sample after solution treatment and heat preservation to a certain temperature at a set cooling rate, and then immediately water-quenches it.

[0010] S3 involves placing the quenched TC4 titanium alloy sample back into a heat treatment furnace, heating it to below the β-phase transformation temperature, holding it at that temperature, and finally cooling it. In this invention, the cooling temperature is 20-25℃.

[0011] Based on the above technical solution, preferably, in step 1, the processing method for the TC4 titanium alloy sample is as follows: take a sample with dimensions of 12×8×5mm. 3 The TC4 titanium alloy was subjected to a process where the oxide layer was removed using 200# silicon carbide sandpaper, and then sealed in a quartz glass tube. The TC4 titanium alloy sample was formed by additive manufacturing using plasma arc deposition combined with simultaneous rolling (hereinafter referred to as: plasma arc composite additive manufacturing TC4 titanium alloy).

[0012] More preferably, the solution temperature is below the β-phase transformation temperature, specifically 10-20°C lower. It should not be too low, as an excessively low solution temperature will result in less α-phase transformation into β-phase during solution treatment. In this invention, the solution treatment temperature is 940-950°C, and the solution treatment time is 1.5-3 hours.

[0013] Based on the above technical solutions, preferably, in step 2, the cooling rate is lower than the general furnace cooling rate, set to 0.5-1℃ / min, and the quenching temperature is 900℃. More preferably, the cooling rate is set to 0.8-0.9℃ / min.

[0014] Based on the above technical solutions, preferably, in step 3, the temperature during aging and heat preservation is below the β-phase transformation temperature and varies around the α-phase transformation temperature, ranging from 550-860℃, and the aging and heat preservation time is 1.5-3 hours. More preferably, the temperature during aging and heat preservation is 600-720℃.

[0015] The principle of this invention is as follows:

[0016] This invention targets the plasma arc composite additive manufacturing of TC4 titanium alloy. To combine the excellent microstructure obtained by subcritical annealing and solution aging, two heat treatment processes are combined. In order to obtain discontinuous grain boundaries α to improve plasticity, solution is performed at subcritical high temperature to consume a large amount of primary grain boundary α. During cooling, secondary grain boundary α particles are formed between the primary grain boundary α particles, and the entire grain boundary α morphology is discontinuous.

[0017] To obtain equiaxed primary α phase, furnace cooling during cooling can ensure that the secondary α phase precipitates and grows slowly on the remaining lamellar α phase, promoting the formation of equiaxed α phase;

[0018] To obtain a large amount of dispersed secondary α and α / β interface phases, the aging temperature should be increased as much as possible during the aging stage to promote the full decomposition of martensite α and the formation of α / β interface phases. However, the aging temperature should not exceed 860℃. Above this temperature, the α and β contents change drastically.

[0019] The heat treatment method of the present invention has the following advantages over the prior art:

[0020] 1. Since the initial microstructure of the material to be heat-treated has a great influence on the microstructure and properties after heat treatment, the same heat treatment method applied to TC4 titanium alloys with different microstructure characteristics will result in different microstructure and properties. Therefore, this invention is for heat treatment of TC4 titanium alloys manufactured by plasma arc composite additive manufacturing, and the resulting microstructure has the characteristics of a cast or forged microstructure.

[0021] 2. Targeting the characteristics and properties of TC4 titanium alloy manufactured using plasma arc composite additive manufacturing, a combined subcritical annealing and solution aging method is employed. This method leverages the principles of subcritical annealing to control primary phases and large-scale microstructure, and solution aging to control secondary phases and small-scale microstructure. This results in a microstructure with equiaxed primary α phases, discontinuous grain boundary α phases, secondary phases, and α / β interface phases. Therefore, this method can control all α phase characteristics, achieving the transformation from lamellar primary α phases to equiaxed primary α phases and from discontinuous grain boundary α phases to continuous grain boundary α phases, resulting in dispersed secondary phases and small-scale α / β interface phases. This method eliminates the need for additional deformation treatment, utilizing the nucleation motive force accumulated during heat treatment to generate the desired microstructure, making the process operation more consistent and easier to control. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 Images showing the microstructure of TC4 titanium alloy in Example 1 of this invention;

[0024] Figure 2 Images showing the tensile properties of TC4 titanium alloy in Example 1 of this invention;

[0025] Figure 3 Images showing the microstructure of TC4 titanium alloy in Example 2 of this invention;

[0026] Figure 4 Images showing the tensile properties of TC4 titanium alloy in Example 2 of this invention;

[0027] Figure 5 Images showing the microstructure of TC4 titanium alloy in Example 3 of this invention;

[0028] Figure 6 Images showing the tensile properties of TC4 titanium alloy in Example 3 of this invention;

[0029] Figure 7 Images showing the microstructure of TC4 titanium alloy in Example 4 of this invention;

[0030] Figure 8 The image shows the tensile properties of TC4 titanium alloy in Example 4 of this invention. Detailed Implementation

[0031] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0032] Example 1

[0033] (1) Take the dimensions as 12×8×5mm 3 The oxide layer of TC4 titanium alloy was removed using 200# silicon carbide sandpaper, and the sample was then placed in a quartz glass tube for sealing. The treated sample was then heated to 940℃ in a heat treatment furnace and held at that temperature for 2 hours.

[0034] (2) After the holding time is reached, the cooling rate is set to 0.8℃ / min, the quenching temperature is 900℃, and water quenching is performed immediately after the above temperature is reached.

[0035] (3) Remove the oxide layer from the quenched sample with 200# silicon carbide sandpaper and seal it in a quartz glass tube. Then put it back into the heat treatment furnace and heat it to 600℃ for aging and holding for 1.7h. Then take it out and let it cool in the air.

[0036] In this embodiment, the TC4 titanium alloy has a yield strength of 970 MPa, a tensile strength of 1062 MPa, and an elongation of 12.4%.

[0037] Example 2

[0038] (1) Take the dimensions as 12×8×5mm 3 The oxide layer of TC4 titanium alloy was removed using 200# silicon carbide sandpaper, and the sample was then placed in a quartz glass tube for sealing. The treated sample was then heated to 950°C in a heat treatment furnace and held at that temperature for 2.5 hours.

[0039] (2) After the holding time is reached, the cooling rate is set to 0.9℃ / min, the quenching temperature is 900℃, and water quenching is performed immediately after the above temperature is reached.

[0040] (3) Remove the oxide layer from the quenched sample with 200# silicon carbide sandpaper and seal it in a quartz glass tube. Then put it back into the heat treatment furnace and heat it to 720°C. The aging and holding time is 2 hours. Then take it out and let it cool in the air.

[0041] In this embodiment, the TC4 titanium alloy has a yield strength of 926 MPa, a tensile strength of 1023 MPa, and an elongation of 12.1%.

[0042] Example 3

[0043] (1) Take the dimensions as 12×8×5mm 3 The oxide layer of TC4 titanium alloy was removed using 200# silicon carbide sandpaper, and the sample was then placed in a quartz glass tube for sealing. The treated sample was then heated to 950°C in a heat treatment furnace and held at that temperature for 1.5 hours.

[0044] (2) After the holding time is reached, the cooling rate is set to 0.5℃ / min, the quenching temperature is 900℃, and water quenching is performed immediately after the above temperature is reached.

[0045] (3) Remove the oxide layer from the quenched sample with 200# silicon carbide sandpaper and seal it in a quartz glass tube. Then put it back into the heat treatment furnace and heat it to 550°C for aging and holding for 1.5 hours. Then take it out and let it cool in the air.

[0046] In this embodiment, the TC4 titanium alloy has a yield strength of 902 MPa, a tensile strength of 1005 MPa, and an elongation of 14.1%.

[0047] Example 4

[0048] (1) Take the dimensions as 12×8×5mm 3 The oxide layer of TC4 titanium alloy was removed using 200# silicon carbide sandpaper, and the sample was then placed in a quartz glass tube for sealing. The treated sample was then heated to 940℃ in a heat treatment furnace and held at that temperature for 3 hours.

[0049] (2) After the holding time is reached, the cooling rate is set to 1℃ / min, the quenching temperature is 900℃, and water quenching is performed immediately after the above temperature is reached.

[0050] (3) Remove the oxide layer from the quenched sample with 200# silicon carbide sandpaper and seal it in a quartz glass tube. Then put it back into the heat treatment furnace and heat it to 860°C for 3 hours. Then take it out and let it cool in the air.

[0051] In this embodiment, the TC4 titanium alloy has a yield strength of 909 MPa, a tensile strength of 1002 MPa, and an elongation of 15.7%.

[0052] As can be seen from the above four embodiments, the TC4 titanium alloys prepared by this invention all have a yield strength of over 902 MPa, a tensile strength of over 1002 MPa, and an elongation of over 12.1%. Therefore, the TC4 titanium alloys obtained by the heat treatment method of this invention have good yield strength and tensile strength, and can achieve excellent performance with a good balance between strength and elongation.

[0053] Comparative Example 1

[0054] Ion arc composite additive manufacturing of TC4 titanium alloy without any heat treatment.

[0055] Comparative Example 2 samples are different

[0056] Based on Example 1, the sample was replaced with cast TC4 titanium alloy, and all other steps were the same.

[0057] Comparative Example 3 replaces step two with a processing method found in the prior art.

[0058] Based on Example 1, step two is replaced; the specific steps after the replacement are as follows:

[0059] (1) Take the dimensions as 12×8×5mm 3 The oxide layer of TC4 titanium alloy was removed using 200# silicon carbide sandpaper, and the sample was then placed in a quartz glass tube for sealing. The treated sample was then heated to 940℃ in a heat treatment furnace and held at that temperature for 2 hours.

[0060] (2) After solution treatment and heat preservation, the sample was water-cooled to room temperature, and the cooled TC4 titanium alloy was subjected to 5% cold plastic deformation.

[0061] (3) Remove the oxide layer from the quenched sample with 200# silicon carbide sandpaper and seal it in a quartz glass tube. Then put it back into the heat treatment furnace and heat it to 600℃ for aging and holding for 1.7h. Then take it out and let it cool in the air.

[0062] Comparative Example 4: Solution Temperature Adjustment

[0063] Based on Example 2, the solution temperature was adjusted to 980°C.

[0064] Comparative Example 5: Solution Temperature Adjustment

[0065] Based on Example 2, the solution temperature was adjusted to 920°C.

[0066] Comparative Example 6: Different Aging Temperatures

[0067] Based on Example 1, the aging temperature was adjusted to 450℃.

[0068] Comparative Example 7: Different Aging Temperatures

[0069] Based on Example 1, the aging temperature was adjusted to 880℃.

[0070] The samples in Comparative Example 8 were different, and the solution treatment temperature was adjusted.

[0071] Based on Example 1, the sample was replaced with cast TC4 titanium alloy, and the solution treatment temperature was adjusted to 920℃; all other steps were the same.

[0072] The aging temperature was adjusted, unlike that of the 9th comparative sample.

[0073] Based on Example 1, the sample was replaced with cast TC4 titanium alloy, and the aging temperature was adjusted to 880℃; all other steps were the same.

[0074] The samples in Comparative Example 10 were different, and the solution treatment temperature and aging temperature were adjusted.

[0075] Based on Example 1, the sample was replaced with cast TC4 titanium alloy, and the solution treatment temperature was adjusted to 920℃ and the aging temperature was adjusted to 880℃; all other steps were the same.

[0076] Adjustment of solution temperature and aging temperature in Comparative Example 11

[0077] Based on Example 2, the solution temperature was adjusted to 980°C and the aging temperature was adjusted to 880°C. Comparative Example 12 replaced step two with a prior art processing method and adjusted the solution temperature.

[0078] Based on Example 1, step two is replaced; the specific steps after the replacement are as follows:

[0079] (1) Take the dimensions as 12×8×5mm 3 The oxide layer of TC4 titanium alloy was removed using 200# silicon carbide sandpaper, and the sample was then placed in a quartz glass tube for sealing. The treated sample was then heated to 980℃ in a heat treatment furnace and held at that temperature for 2 hours.

[0080] (2) After solution treatment and heat preservation, the sample was water-cooled to room temperature, and the cooled TC4 titanium alloy was subjected to 5% cold plastic deformation.

[0081] (3) Remove the oxide layer from the quenched sample with 200# silicon carbide sandpaper and seal it in a quartz glass tube. Then put it back into the heat treatment furnace and heat it to 600℃ for aging and holding for 1.7h. Then take it out and let it cool in the air.

[0082] Comparative Example 13 replaces step two with a processing method found in the prior art and adjusts the aging temperature.

[0083] Based on Example 1, step two is replaced; the specific steps after the replacement are as follows:

[0084] (1) Take the dimensions as 12×8×5mm 3The oxide layer of TC4 titanium alloy was removed using 200# silicon carbide sandpaper, and the sample was then placed in a quartz glass tube for sealing. The treated sample was then heated to 940℃ in a heat treatment furnace and held at that temperature for 2 hours.

[0085] (2) After solution treatment and heat preservation, the sample was water-cooled to room temperature, and the cooled TC4 titanium alloy was subjected to 5% cold plastic deformation.

[0086] (3) Remove the oxide layer from the quenched sample with 200# silicon carbide sandpaper and seal it in a quartz glass tube. Then put it back into the heat treatment furnace and heat it to 450°C for aging and holding for 1.7 hours. Then take it out and let it cool in the air.

[0087] The performance of the TC4 titanium alloy prepared in the comparative example was tested, and the specific test results are shown in Table 1.

[0088] Table 1. Performance test results of TC4 titanium alloys prepared in the examples and comparative examples.

[0089]

[0090]

[0091] The performance test results of the TC4 titanium alloy prepared by the comparative example show that the tensile properties of the TC4 titanium alloy prepared by the heat treatment method of the present invention are significantly improved, thus exhibiting excellent tensile properties.

[0092] In addition, the heat treatment method proposed in this invention is applicable to a wide range of microstructures, especially the microstructure of TC4 titanium alloy manufactured by arc additive manufacturing, and is also applicable to the microstructure of TC4 titanium alloy manufactured by laser and electron beam additive manufacturing.

[0093] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A heat treatment method for improving the tensile properties of TC4 titanium alloy, characterized in that, The method comprises the following steps: S1: heating the processed TC4 titanium alloy to below the beta phase transition temperature for solid solution heat preservation in a heat treatment furnace; S2: furnace cooling the TC4 titanium alloy after the solid solution heat preservation to a certain temperature at a set cooling speed, and immediately water quenching; S3: placing the TC4 titanium alloy after the quenching treatment in the heat treatment furnace again, heating to below the beta phase transition temperature for aging heat preservation, and finally cooling; The TC4 titanium alloy is formed by plasma arc deposition and synchronous rolling of additive manufacturing; In the S1 step, the temperature during the solid solution heat preservation is 940-950 DEG C, and the time for the solid solution heat preservation is 1.5-3h; In the S2 step, the cooling speed is 0.8-0.9 DEG C / min, and the quenching temperature is 900 DEG C; In the S3 step, the temperature during the aging heat preservation is 550-860 DEG C, and the time for the aging heat preservation is 1.5-3h.

2. The heat treatment method for improving the tensile property of TC4 titanium alloy according to claim 1, characterized in that: The processing method of the TC4 titanium alloy is as follows: taking TC4 titanium alloy with a size of 12*8*5mm 3 , removing the oxide layer with sandpaper with a mesh number of 200#, and then sealing and processing.

3. The heat treatment method for improving the tensile property of TC4 titanium alloy according to claim 1, characterized in that: In the S3 step, the temperature during the aging heat preservation is 600-720 DEG C.

Images