Treatment method of Ti2AlNb alloy casting

Abstract

According to the treatment method of the Ti2AlNb alloy casting, firstly, the Ti2AlNb alloy casting is subjected to hot isostatic pressing treatment under the conditions that the pressure ranges from 130 MPa to 200 MPa and the temperature ranges from 1100 DEG C to 1250 DEG C, then heat treatment is carried out under the conditions that the temperature ranges from 850 DEG C to 995 DEG C and the time ranges from 30 min to 120 min, through hot isostatic pressing treatment, the defects of holes in the Ti2AlNb alloy casting are eliminated, and the heat treatment efficiency is improved. And moreover, a foundation is laid for tissue regulation and control in subsequent heat treatment, the synergistic effect of coarse lamellar and fine lamellar tissues is achieved, and the problems that the Ti2AlNb alloy is low in plasticity, poor in plasticity, prone to cracking, difficult to repair welding, difficult to machine, prone to cracking in the using process and the like are solved. Test results show that the plasticity of the Ti2AlNb alloy casting is effectively improved, and the application potential of the Ti2AlNb alloy casting in the fields of aviation, aerospace, weaponry and the like is improved.

Description

Technical Field

[0001] The invention relates to the technical field of metal casting, and in particular to a processing method for a Ti2AlNb alloy casting. Background Art

[0002] Ti2AlNb alloy is an intermetallic compound, composed of ionic bonds or covalent bonds and metallic bonds. It has material properties between metals and ceramics, and its intrinsic plasticity is lower than that of metal materials. The composition range of Ti2AlNb alloy is usually Ti-(18%~30%)Al-(12.5%~30%)Nb (at.%). According to the Nb content, it is divided into two generations: the first generation, when Nb<25at.%, is composed of B2+O+α2 three phases, called the first generation O phase alloy; the second generation, when Nb≥25at.%, is composed of B2+O phase, called the second generation O phase alloy. The presence of O phase and α2 phase not only plays a strengthening role, but also avoids the problem of coarse grains and poor plasticity of single B2 phase. Studies have shown that the ordered orthogonal O phase has a greater strengthening effect than the α2 phase, which can significantly improve the creep resistance of the alloy. Moreover, since the O phase, α2 phase and B2 are mutually coherent, the O phase and α2 phase formed during the solidification and heat treatment process appear in laths of different thicknesses.

[0003] At present, the relevant data published at home and abroad show that the performance control methods of Ti2AlNb alloy castings are mainly based on composition, casting process, hot isostatic pressing, and heat treatment process control methods. However, current research in related fields at home and abroad shows that the elongation of Ti2AlNb alloy castings after room temperature tensile fracture is difficult to reach more than 3%, which limits the engineering application of Ti2AlNb alloy. On the one hand, it is difficult to meet the high-temperature service requirements of Ti2AlNb alloy components. Under high-temperature load conditions, cracking is prone to occur, reducing the service life of components. On the other hand, the plasticity is too poor, and the castings are prone to cracking after welding repair. A large number of fluorescent cracks are easily formed in the welding area, and the metallurgical quality is difficult to meet the delivery requirements of castings; if the plasticity is too low, it will also affect the quality of the machined surface and reduce the surface integrity of the casting. For the highly stress-sensitive Ti2AlNb alloy, the service life of its castings is greatly reduced.

[0004] The above problems have largely limited the engineering application of high-temperature lightweight Ti2AlNb alloy castings. However, as the power and temperature of aerospace aircraft engines continue to increase, key high-temperature components are constantly required to reduce component density and increase component specific strength. It is urgent to develop lightweight high-temperature materials that can be used in engineering applications to replace high-density high-temperature alloys and improve the thrust-to-weight ratio and power-to-weight ratio of aircraft engines. Using Ti2AlNb alloy materials to replace high-temperature alloys in the 650℃~750℃ range can greatly improve the maneuverability and combat effectiveness of aircraft and meet the requirements of the military industry for aerospace vehicles. Therefore, improving the plasticity of Ti2AlNb alloy castings can broaden its application in aviation, aerospace, weapons and equipment and other fields. Summary of the invention

[0005] In view of this, the present invention provides a processing method for Ti2AlNb alloy castings. The processing method provided in the present application can increase the elongation of the Ti2AlNb alloy castings to more than 6%, thereby greatly improving the plasticity thereof.

[0006] The present application provides a method for treating a Ti2AlNb alloy casting, comprising the following steps:

[0007] a) subjecting the Ti2AlNb alloy casting to hot isostatic pressing, wherein the hot isostatic pressing pressure is 130MPa-200MPa and the temperature is 1100°C-1250°C;

[0008] b) subjecting the casting obtained in step a) to heat treatment at a temperature of 850° C. to 995° C. and for a time of 30 min to 120 min.

[0009] In some specific implementations, in step a), the hot isostatic pressing treatment is performed at a pressure of 150 MPa to 170 MPa, a temperature of 1100° C. to 1250° C., and a time of 2 h to 6 h.

[0010] In some specific implementations, the heating rate of the hot isostatic pressing process is 2° C. / s to 10° C. / s.

[0011] In some specific implementations, in step a), the Ti2AlNb alloy casting is placed in an anti-deformation tooling for hot isostatic pressing.

[0012] In some specific implementations, in the step b), the heat treatment is carried out at a temperature of 930° C. to 980° C. and for a time of 60 min to 90 min.

[0013] In some specific implementations, in step b), the casting obtained in step a) is placed in an anti-deformation tool for heat treatment.

[0014] In some specific implementations, the following steps are further included between step a) and step b):

[0015] The casting obtained in step a) is surface treated.

[0016] In some specific implementations, before step a), the method further includes:

[0017] Pretreatment of Ti2AlNb alloy castings.

[0018] In some specific implementations, the pretreatment is selected from at least one of sand blasting, shot blasting, acid washing, alkali washing or water washing.

[0019] In some specific implementations, the composition of the Ti2AlNb alloy casting includes:

[0020] 18at% to 30at% Al;

[0021] 12.5 at% to 30 at% Nb;

[0022] The remainder of Ti.

[0023] The processing method of Ti2AlNb alloy castings provided in the present application is to first perform hot isostatic pressing on the Ti2AlNb alloy castings at a pressure of 130MPa to 200MPa and a temperature of 1100°C to 1250°C, and then perform heat treatment at a temperature of 850°C to 995°C and a time of 30min to 120min. The hot isostatic pressing treatment not only eliminates the internal hole defects of the Ti2AlNb alloy castings, but also lays the foundation for the subsequent heat treatment to achieve organizational regulation, realize the synergistic effect of coarse lamellae and fine lamellae organizations, and solve the problems of low plasticity, poor plasticity, easy cracking, difficult repair welding, difficult processing, and easy cracking during use of the Ti2AlNb alloy. The test results show that the room temperature tensile elongation after fracture of the casting body treated by the method provided in the present application can reach more than 6%, and the tensile strength can reach more than 900MPa; the room temperature tensile elongation after fracture of the sample cast in the same furnace as the casting can reach more than 5%, and under the condition of 650℃, the tensile strength can reach more than 700MPa and the elongation can reach more than 6%, which effectively improves the plasticity of Ti2AlNb alloy castings and enhances its application potential in military and civilian fields, especially in aviation, aerospace, weapons and equipment and other fields. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 The cross-sectional microstructure of the test bar prepared in Example 1;

[0025] Figure 2 The cross-sectional microstructure of the test bar prepared in Example 2;

[0026] Figure 3This is a fluorescence detection photograph of the Ti2AlNb alloy sample. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0029] In addition, the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly indicating the number of technical features indicated. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, "multiple" means two or more, unless otherwise clearly and specifically defined. In addition, the terms "installed", "connected" and "connected" should be understood in a broad sense, for example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal connection of two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0030] The present application provides a method for treating a Ti2AlNb alloy casting, comprising the following steps:

[0031] a) subjecting the Ti2AlNb alloy casting to hot isostatic pressing, wherein the hot isostatic pressing pressure is 130MPa-200MPa and the temperature is 1100°C-1250°C;

[0032] b) subjecting the casting obtained in step a) to heat treatment at a temperature of 850° C. to 995° C. and for a time of 30 min to 120 min.

[0033] The present application first performs hot isostatic pressing on the Ti2AlNb alloy casting, which, on the one hand, eliminates the internal pore defects of the Ti2AlNb alloy casting, and on the other hand, provides a basis for the second step of heat treatment. In some specific implementations, the Ti2AlNb alloy casting is a Ti2AlNb alloy casting of various complex structures prepared using various types of shells such as ceramic molds, graphite molds, and metal molds, and the present application has no special restrictions on it. In some specific implementations, the composition of the Ti2AlNb alloy casting includes: 18at% to 30at% Al; 12.5at% to 30at% Nb; the balance Ti. The present application has no special restrictions on the preparation method of the Ti2AlNb alloy casting, and it can be prepared according to the method familiar to those skilled in the art according to the needs, such as induction melting, arc melting, cold hearth furnace, plasma furnace and other melting and pouring methods.

[0034] Before hot isostatic pressing of the Ti2AlNb alloy casting, the present application preferably pre-treats the Ti2AlNb alloy casting to remove sand, scale, contamination, etc. on the surface of the casting. In some specific implementations, the pre-treatment is selected from at least one of sand blasting, shot peening, pickling, alkali washing or water washing, and those skilled in the art can select a suitable pre-treatment process according to the surface state of the Ti2AlNb alloy casting.

[0035] Before hot isostatic pressing of Ti2AlNb alloy castings, the present application first places the Ti2AlNb alloy castings in an anti-deformation tooling, and then performs hot isostatic pressing. The present application has no special restrictions on the anti-deformation tooling, which can be selected according to the structure, size and placement of the castings. The material that does not react with the castings and does not deform at high temperatures can be used to prevent the castings from deforming during hot isostatic pressing and heat treatment.

[0036] The Ti2AlNb alloy casting and the anti-deformation device are subjected to hot isostatic pressing in a hot isostatic pressing device, which, on the one hand, eliminates the internal pore defects of the Ti2AlNb alloy casting, and on the other hand, provides a basis for the second step of heat treatment. In some specific implementations, the pressure of the hot isostatic pressing treatment is 130MPa~200MPa, preferably 150MPa~170MPa; the temperature is 1100℃~1250℃, preferably 1150℃~1220℃; the time is 2h~6h, preferably 3h~4h. The present application first fills the hot isostatic pressing device with protective gas such as argon, then heats up to the hot isostatic pressing temperature and pressure, and cools after heat preservation and pressure maintenance. In some specific implementations, the heating rate is 2℃ / s~10℃ / s, preferably 3℃ / s~8℃ / s. In some specific implementations, the cooling may be cooling to below 300° C. before taking out of the furnace, or first cooling to below 500° C. and then introducing an inert gas, such as argon, to cool to below 300° C. before taking out of the furnace.

[0037] After the hot isostatic pressing treatment is completed, the present application preferably performs internal defect detection, for example, by using X-ray, real-time imaging or CT methods to confirm whether all the internal looseness, shrinkage holes and other hole-like defects have been pressed.

[0038] After the internal defect detection is completed, the qualified castings are further subjected to heat treatment. Before the heat treatment, the castings after hot isostatic pressing are preferably subjected to surface treatment. In some specific implementations, the purpose of the surface treatment is to clean again and remove stains, dust, etc. The present application has no particular restrictions on the surface treatment method, which can be selected from sand blasting, shot peening, pickling, alkali washing or water washing, etc.

[0039] After the surface treatment is completed, the obtained casting is heat treated in a heat treatment device. In some specific implementations, the casting is placed in an anti-deformation tooling for heat treatment, which is not repeated in this application. In some specific implementations, the temperature of the heat treatment is 850°C to 995°C, preferably 930°C to 980°C, more preferably 970°C to 980°C, and the time is 30min to 120min, preferably 60min to 90min. In some specific implementations, the heating rate is 2°C / s to 10°C / s, preferably 3°C / s to 8°C / s. After the heat treatment is completed, the obtained casting can be cooled. In some specific implementations, the cooling can be cooling to below 300°C with the furnace or first cooling to below 500°C and then introducing an inert gas, such as cooling to below 300°C with argon gas.

[0040] The processing method of Ti2AlNb alloy castings provided in the present application is to first perform hot isostatic pressing on the Ti2AlNb alloy castings at a pressure of 130MPa to 200MPa and a temperature of 1100°C to 1250°C, and then perform heat treatment at a temperature of 850°C to 995°C and a time of 30min to 120min. The hot isostatic pressing treatment not only eliminates the internal hole defects of the Ti2AlNb alloy castings, but also lays the foundation for the subsequent heat treatment to achieve organizational regulation, realize the synergistic effect of coarse lamellae and fine lamellae organizations, and solve the problems of low plasticity, poor plasticity, easy cracking, difficult repair welding, difficult processing, and easy cracking during use of the Ti2AlNb alloy. The test results show that the room temperature tensile elongation after fracture of the casting body treated by the method provided in the present application can reach more than 6%, and the tensile strength can reach more than 900MPa; the room temperature tensile elongation after fracture of the sample cast in the same furnace as the casting can reach more than 5%, and under the condition of 650℃, the tensile strength can reach more than 700MPa and the elongation can reach more than 6%, which effectively improves the plasticity of Ti2AlNb alloy castings and enhances its application potential in military and civilian fields, especially in aviation, aerospace, weapons and equipment and other fields.

[0041] The processing method of the Ti2AlNb alloy casting provided in the present application is described in detail below in conjunction with the embodiments.

[0042] In the following examples and comparative examples, the Ti2AlNb alloy is Ti-22Al-25Nb (at.%).

[0043] Example 1

[0044] 1) Using investment casting ceramic shell to prepare Ti2AlNb alloy blank test rod with a diameter of 15 mm and a length of 100 mm;

[0045] 2) Sandblast and alkali wash the surface of the test rod to remove surface contamination such as mold shell and oil stains;

[0046] 3) Place the test bar on the anti-deformation tooling, load it into the hot isostatic pressing furnace, and process it according to process system A shown in Table 1. After the isostatic pressing furnace is evacuated, it is filled with argon gas, and the temperature and pressure are raised to 1160°C and 170MPa at the same time. After the heat and pressure are maintained for 4 hours, it is cooled to below 300°C and taken out of the furnace;

[0047] 4) Use real-time imaging method to detect internal defects of the test rod;

[0048] 6) Use sand blowing + light pickling method to treat the surface of the test rod to remove the surface contamination layer and stain layer;

[0049] 7) Treat according to process system A shown in Table 1, place the cleaned test rod in a heat treatment furnace, evacuate to below 3 Pa, heat to 980°C, keep warm for 60 minutes, cool to below 500°C with the furnace, fill with argon, cool to below 300°C and take out of the furnace.

[0050] 8) After the heat-treated test bar is processed into a tensile specimen, the cross-sectional microstructure of the test bar is characterized and its mechanical properties are tested. The results are shown in Figure 1 and Table 2, Figure 1 Table 2 is the cross-sectional microstructure of the test rod prepared in Example 1. Table 3 is the mechanical property test results of the test rods prepared in the example and the comparative example.

[0051] Example 2

[0052] 1) Using investment casting ceramic shell, a Ti2AlNb alloy casting with a diameter of 500 mm and a height of 780 mm and an attached casting sample with a diameter of 15 mm and a length of 100 mm were prepared;

[0053] 2) The surface of the casting and the attached casting sample is subjected to sand blasting, alkali washing and pickling to remove the surface contamination layer, oil stains, etc.;

[0054] 3) Place the casting and the attached casting sample on the anti-deformation tooling, load it into the hot isostatic pressing furnace, and treat it according to the process system B shown in Table 1. After the isostatic pressing furnace is evacuated, it is filled with argon gas, and the temperature and pressure are increased to 1090℃ and 150MPa at the same time. After the heat and pressure are maintained for 3h, it is cooled to below 300℃ and taken out of the furnace.

[0055] 4) Use X-ray detection method to detect internal defects of castings and cast samples;

[0056] 6) Perform surface sandblasting treatment on the casting and the attached casting sample again to remove the surface contamination layer and stain layer;

[0057] 7) According to process system B shown in Table 1, the cleaned castings and cast samples are placed in a heat treatment furnace, evacuated to below 3 Pa, heated to 970 ° C, kept at this temperature for 90 min, and then cooled to below 300 ° C and taken out of the furnace.

[0058] 8) Characterize the cross-sectional microstructure of the test bar, and test the mechanical properties of the heat-treated test bar after processing it into a tensile specimen. The results are shown in Figure 2 and Table 2, Figure 2 2 is the cross-sectional microstructure of the test rod prepared in Example 2. Table 2 is the mechanical property test results of the test rods prepared in the example and the comparative example.

[0059] After heat treatment, the castings were visually inspected, the surface pits were polished, and then the welding was repaired by argon arc welding. Then, the repaired area was tested by fluorescence. The test results were as follows: Figure 3 As shown, Figure 3 This is a fluorescence detection photo of the Ti2AlNb alloy sample, where: Figure 3 (a) is a fluorescence inspection photo before repair welding. Figure 3 (b) is a fluorescence detection photo after soldering. Figure 3 It can be seen that after the above-mentioned hot pressing + heat treatment process, the fluorescence display of the argon arc welding repair area of ​​the Ti2AlNb alloy sample has no microcrack defects.

[0060] Comparative Examples 1 to 4

[0061] Referring to the method of Example 1, the Ti2AlNb alloy blank test bar was processed according to the process system provided in Table 1. The mechanical property test results are shown in Table 2.

[0062] Table 1 Process system provided in the embodiment

[0063]

[0064]

[0065] Table 2 Mechanical properties test results of the test bars prepared in the embodiments and comparative examples

[0066]

[0067] It can be seen from Tables 1 and 2 that the room temperature tensile elongation after fracture of the casting body treated by the method provided in the present application can reach more than 6%, and the tensile strength can reach more than 900 MPa; the room temperature tensile elongation after fracture of the sample cast in the same furnace as the casting can reach more than 5%, and under the condition of 650°C, the tensile strength can reach more than 700 MPa and the elongation can reach more than 6%, which effectively improves the plasticity of Ti2AlNb alloy castings and enhances its application potential in military and civilian fields, especially in aviation, aerospace, weapons and equipment and other fields.

[0068] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for treating a Ti2AlNb alloy casting, characterized in that: The following steps are involved: a) subjecting the Ti2AlNb alloy casting to hot isostatic pressing, wherein the hot isostatic pressing pressure is 130MPa-200MPa and the temperature is 1100°C-1250°C; b) subjecting the casting obtained in step a) to heat treatment at a temperature of 850° C. to 995° C. and for a time of 30 min to 120 min.

2. The processing method according to claim 1, characterized in that: In the step a), the hot isostatic pressing treatment is performed under a pressure of 150 MPa to 170 MPa, at a temperature of 1100° C. to 1250° C., for a time of 2 h to 6 h.

3. The processing method according to claim 2, characterized in that: In the step a), the heating rate of the hot isostatic pressing treatment is 2°C / s to 10°C / s.

4. The processing method according to claim 3, characterized in that: In the step a), the Ti2AlNb alloy casting is placed in an anti-deformation tooling for hot isostatic pressing.

5. The processing method according to claim 1, characterized in that: In the step b), the heat treatment temperature is 930° C. to 980° C., and the time is 60 min to 90 min.

6. The processing method according to claim 5, characterized in that: In the step b), the casting obtained in the step a) is placed in an anti-deformation tool for heat treatment.

7. The processing method according to any one of claims 1 to 6, characterized in that: The step between step a) and step b) also includes: The casting obtained in step a) is surface treated.

8. The processing method according to claim 7, characterized in that: Before step a), the method further comprises: Pretreatment of Ti2AlNb alloy castings.

9. The processing method according to claim 7, characterized in that: The pretreatment is selected from at least one of sand blasting, shot blasting, acid cleaning, alkali cleaning or water cleaning.

10. The processing method according to any one of claims 1 to 6, characterized in that: The composition of the Ti2AlNb alloy casting comprises: 18at% to 30at% Al; 12.5 at% to 30 at% Nb; The remainder of Ti.

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