Ti al alloy and forging method thereof

Abstract

The application discloses a TiAl alloy and a forging method thereof, and belongs to the technical field of alloy material processing, and the method comprises the following steps: melting and preparing a TiAl alloy ingot, a main system of the TiAl alloy is Ti-Al-Mn-X, wherein X is at least one of Mo, W and Nb elements; the TiAl alloy ingot is subjected to heating and holding treatment; under a non-sheathed and non-isothermal environment, the TiAl alloy ingot is processed to a preset size according to a length-diameter ratio of the TiAl alloy ingot and a forging mode is selected. The TiAl alloy is forged under the non-sheathed and non-isothermal conditions, and the technical effect of reducing the forging cost of the TiAl alloy is realized.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of alloy material processing, and particularly relates to a TiAl alloy and a forging method thereof. BACKGROUND

[0002] Compared with traditional Fe and Ni-based alloys, the TiAl alloy has low density, high specific strength, high specific modulus, good high-temperature fatigue resistance, creep resistance and corrosion resistance, and is a competitive strategic structural material in the fields of aerospace, advanced ships, unmanned aerial vehicles and engines of automobiles.

[0003] Since the TiAl alloy belongs to intermetallic compounds, the effective hot working window is narrow, and the deformation temperature and deformation rate are extremely harsh in the actual hot forging deformation process, that is, special hot forging deformation processes such as near-isothermal or package are generally required, and the problem of high forging cost exists. SUMMARY

[0004] The main purpose of the present application is to provide a TiAl alloy and a forging method thereof, and to solve the problem of high forging cost caused by the need for special hot forging deformation process of the current TiAl alloy.

[0005] To achieve the above-mentioned purpose, the present application provides a forging method of a TiAl alloy, which comprises the following steps:

[0006] Melting and preparing a TiAl alloy ingot, wherein the main system of the TiAl alloy is Ti-Al-Mn-X, and X is at least one of Mo, W and Nb elements;

[0007] Performing heating and holding treatment on the TiAl alloy ingot;

[0008] Forging the TiAl alloy ingot under a non-packaged and non-isothermal environment, and processing the TiAl alloy ingot to a preset size.

[0009] Optionally, the composition of the TiAl alloy ingot comprises 41.0%-46.0% of Al, 1.0%-4.0% of Mn, 0.1%-6.0% of X, 0.1%-0.3% of B, 0.1%-0.3% of C, 0%-0.3% of Si, 0-0.1% of Y, and the balance of Ti, in terms of atomic percentage.

[0010] Optionally, X is 2.0%-3.5% of Nb and / or 0.3%-1.5% of Mo and / or 0.1%-1.0% of W.

[0011] Optionally, the element composition deviation of Ti, Al and Mn in the TiAl alloy ingot is less than 0.2wt.%, and the element composition deviation of W, Mo and Nb is less than 0.1wt.%.

[0012] Optionally, the TiAl alloy ingot further comprises impurity elements O, N and H, wherein the content of O is less than 0.08wt.%, the content of N is less than 0.0020wt.% and the content of H is less than 0.0020wt.%.

[0013] Optionally, the step of forging the TiAl alloy ingot comprises:

[0014] If the length-diameter ratio of the TiAl alloy ingot is greater than 1.5, the TiAl alloy ingot is directly elongated forged;

[0015] If the length-diameter ratio of the TiAl alloy ingot is less than or equal to 1.5, the TiAl alloy ingot is upset forged or elongated forged after upsetting.

[0016] Optionally, the elongation forging and upsetting forging adopt a forging press, and the reduction speed of the forging press is 10-60mm / s.

[0017] Optionally, the forging mode is multi-fire multi-pass forging, and the final forging temperature of each fire is greater than 1100℃.

[0018] Optionally, the cumulative deformation of the TiAl alloy ingot is greater than 50%.

[0019] In addition, to achieve the above-mentioned purpose, the application also provides a TiAl alloy prepared by the above-mentioned forging method of the TiAl alloy.

[0020] The TiAl alloy and the forging method thereof provided by the application adopt Ti-Al-Mn-X as the main alloy system, wherein X is at least one of Mo, W and Nb elements, which improves the thermal deformation of the TiAl alloy in a high-temperature environment, widens the hot working window of the TiAl alloy, and also ensures good oxidation resistance of the TiAl alloy, so that the requirement for the forging condition can be reduced, and the forging is performed by using a relatively simple non-sleeved non-isothermal forging mode, and the alloy forgings meeting the use requirements are obtained after forging, which greatly reduces the forging cost. BRIEF DESCRIPTION OF DRAWINGS

[0021] Figure 1 It is a flowchart of an embodiment of the forging method of the TiAl alloy of the application;

[0022] Figure 2 It is an appearance diagram of the cast bar before forging in embodiment 1 of the application;

[0023] Figure 3 It is a scene diagram of heating of the cast bar in embodiment 1 of the application;

[0024] Figure 4 The scene schematic diagram for the first forging of the casting rod in the embodiment 1 of the present application;

[0025] Figure 5 The scene schematic diagram for the second forging of the casting rod in the embodiment 1 of the present application;

[0026] Figure 6 The appearance diagram of the casting rod after forging in the embodiment 1 of the present application;

[0027] Figure 7 The appearance diagram of the casting ingot before forging in the embodiment 2 of the present application;

[0028] Figure 8 The appearance diagram of the 1 / 2 casting ingot in the embodiment 2 of the present application;

[0029] Figure 9 The scene schematic diagram for the fifth forging of the casting ingot in the embodiment 2 of the present application;

[0030] Figure 10 The appearance diagram of the casting ingot after forging in the embodiment 2 of the present application.

[0031] The implementation, functional features and advantages of the present application will be further explained with reference to the embodiments and the accompanying drawings. DETAILED DESCRIPTION

[0032] It should be understood that the specific embodiments described herein merely exemplify the present application and do not limit the present application.

[0033] Since TiAl alloy belongs to intermetallic compound, the effective hot working window is narrow, and the actual hot forging deformation process has extremely harsh requirements on the deformation temperature and deformation rate, i.e. generally requires special hot forging deformation processes such as near-isothermal or package. For example, there is a processing method suitable for hot forging deformation of Ti-48Al-2Cr-2Nb alloy, which requires to simultaneously meet the conditions of 5mm thick Q235 package and near-isothermal double, and the strain rate of hot forging deformation is only 0.3mm / s. Such hot forging deformation method often has high requirements on the forging equipment conditions, and has problems such as complicated process, low efficiency and high cost, which greatly limits the commercial application process of TiAl alloy deformation parts.

[0034] In order to reduce the manufacturing cost of TiAl alloy parts, it is urgent to develop a process method which can realize low-cost hot forging deformation of TiAl alloy. Around this theme, a method of hot forging deformation of TiAl alloy under the condition of no package has appeared, which reduces the forging deformation cost of TiAl alloy to a certain extent, but still requires preheating treatment of TiAl alloy blank, 2-3mm thick glass lubricating powder rolling coating after preheating treatment, and need for insulation cotton layer and other processes, which will also greatly make the TiAl alloy forging deformation still have problems such as complicated process and low deformation efficiency.

[0035] The purpose of this invention is to provide a simple, fast, and universally applicable low-cost forging method for TiAl alloys, namely a forging deformation method that does not require billet pretreatment or isothermal cladding, which will strongly promote the large-scale application of TiAl alloys.

[0036] This invention provides a forging method for TiAl alloys, referring to... Figure 1 , Figure 1 This is a schematic flowchart of an embodiment of the forging method for TiAl alloy of the present invention.

[0037] In this embodiment, the forging method of the TiAl alloy includes:

[0038] Step S10: Melt and prepare TiAl alloy ingots, wherein the main system of the TiAl alloy is Ti-Al-Mn-X, and X is at least one of Mo, W and Nb elements;

[0039] The smelting of TiAl alloy ingots can employ either a single vacuum induction process or a combination of vacuum induction and vacuum consumable smelting. Vacuum induction refers to a metallurgical method that uses electromagnetic induction to generate eddy currents within a metal conductor to heat the furnace charge under vacuum conditions, allowing for precise control of the alloy composition. Vacuum consumable smelting involves using the material to be smelted as one electrode and a water-cooled copper crucible as the other under vacuum. An arc is ignited between the two electrodes, and the material is melted by the high temperature of the arc and drips into the crucible, gradually melting and solidifying into an ingot. Both of these smelting methods are applicable to the smelting of TiAl alloy ingots.

[0040] In some feasible embodiments, the composition of the TiAl alloy ingot, by atomic percentage, comprises 41.0%-46.0% Al, 1.0%-4.0% Mn, 0.1%-6.0% X, 0.1%-0.3% B, 0.1%-0.3% C, 0%-0.3% Si, 0-0.1% Y, with the balance being Ti. X may be 2.0%-3.5% Nb and / or 0.3%-1.5% Mo and / or 0.1%-1.0% W, i.e., any combination of one or more of the above elements.

[0041] In the case of a Ti-Al-Mn-X main system, X can be any one or a combination of Mo, W, and Nb. Mn is a β-phase stabilizing element, which is beneficial for the forging deformation of TiAl alloys under normal conditions. However, Mn, like Ti and Al, will oxidize in high-temperature oxidizing environments, leading to oxidative corrosion of the matrix. Therefore, adding Mo, W, or Nb elements to promote Al diffusion in the matrix and inhibit TiO2 formation can improve the high-temperature oxidation resistance of the alloy. The proportion of X in the alloy varies slightly depending on the element X. Although Mo, W, or Nb elements can promote Al diffusion in the matrix, excessive addition can also have certain effects. For example, with a high Nb content, brittle ω-phase (Ti4Al3Nb) is easily precipitated in the alloy. In addition, TiAl alloys with high Nb content have poor hot workability. Even if high-temperature hot working can be achieved, it often requires harsh conditions such as cladding or isothermal treatment, making the processing steps complex. Therefore, it is necessary to control the composition of X element within a suitable range to ensure the hot workability of TiAl alloys.

[0042] In some feasible implementations, the elemental composition deviations of Ti, Al, and Mn in the TiAl alloy ingot are less than 0.2 wt.%, and the elemental composition deviations of W, Mo, and Nb are less than 0.1 wt.%. The TiAl alloy ingot also includes impurity elements O, N, and H, wherein the O content is less than 0.08 wt.%, the N content is less than 0.0020 wt.%, and the H content is less than 0.0020 wt.%.

[0043] The deviation in elemental composition can be controlled during the smelting process by adjusting the process and parameters. This ensures that the alloy composition is as close as possible to the theoretically designed proportions. For example, the melting rate of the furnace charge can be gradually increased, and the heating power can be gradually raised to ensure smooth melting and thorough degassing of the charge. In the middle and later stages of melting, the heating power can be appropriately increased to accelerate the melting rate and shorten the melting time. Furthermore, in the final stage of melting and the initial stage of refining, the charge can be fully boiled to deoxidize, denitrify, dehydrogenate, and remove inclusions.

[0044] Step S20: The TiAl alloy ingot is subjected to heating and heat preservation treatment;

[0045] Post-melting heating and holding treatment can regulate the microstructure. The heating and holding temperature can be selected within the α+β two-phase region, between 1300℃ and 1380℃, for a holding time of 10-60 minutes. This temperature is based on the assumption that the cross-sectional temperature of the ingot uniformly reaches 1300℃-1380℃. The set holding temperature and holding time will vary depending on the ingot's size. Because the length-to-diameter ratio of the ingot differs, the time required for uniform heating at the same holding temperature varies; therefore, the temperature and time can be set according to the ingot's length-to-diameter ratio.

[0046] Step S30, forging the TiAl alloy ingot in a non-canned, non-isothermal environment, and processing the TiAl alloy ingot to a preset size.

[0047] Canned processing refers to a method of processing metal in a can with a certain shape, often combined with hot isostatic pressing method. Isothermal forging is a forging method with the same temperature of the mold and the formed piece, with mold heating and temperature control device. The forging in the present embodiment does not use the above process and can be performed in an atmospheric environment. The forging in the present embodiment can be operated using a forging press, placing the ingot in the processing position of the forging press, and pressing the ingot to a certain size by the forging hammer. The reduction speed of the forging press can be 10-60 mm / s. During the forging process, the microstructure inside the ingot also changes at the microscale. Controlling the reduction speed within an appropriate range can improve the performance of the alloy and avoid cracking and other problems.

[0048] In some feasible embodiments, if the length-diameter ratio of the TiAl alloy ingot is greater than 1.5, the TiAl alloy ingot is directly elongated; if the length-diameter ratio of the TiAl alloy ingot is less than or equal to 1.5, the TiAl alloy ingot is upset forged or first upset and then elongated. The TiAl alloy ingot can be prepared into different shapes with different length-diameter ratios. The length-diameter ratio refers to the ratio between the length direction size of the ingot and the diameter direction size perpendicular to the length direction. The ingot with a large length-diameter ratio can be in the shape of a cast rod, which is relatively long and thin. In the case where the length-diameter ratio of the ingot is greater than 1.5, the elongation forging process is suitable for further increasing the length of the cast rod to produce rod-shaped TiAl alloy. In the case where the length-diameter ratio of the ingot is less than or equal to 1.5, the ingot can be directly processed into a plate by upsetting forging, or first upsetting forging and then elongation forging to a preset size. The preset size refers to the size of the finished material piece, which can be determined according to actual needs. Upsetting forging can break the columnar crystals in the alloy, optimize the microstructure, and improve the performance of the alloy.

[0049] The equipment used for drawing and upsetting forging can be a forging press, with a pressing speed of 10-60 mm / s during the forging process. The forging method is multi-pass, multi-fire forging, with a final forging temperature greater than 1100℃ for each pass. After one forging pass, the ingot can be reheated to 1300℃-1380℃ and held for 5-20 minutes, then forged again using the same forging parameters as the previous passes until the designed finished size is achieved. After multiple passes, the total deformation of the forging is greater than 50%. In the forging process, "one fire" refers to one heating cycle, while "pass" indicates the number of times the ingot is processed. Forging is the process of processing a large-volume ingot into a small-volume forging. In this embodiment, when the temperature is sufficient and the deformation of the forging meets the requirements, multiple passes can be performed per forging pass to fully utilize the heating temperature and reduce the number of heating cycles. Generally, multiple forging passes can be performed in the early stages of forging, while single-pass forging can be performed when there is a significant temperature loss during subsequent processing.

[0050] In this embodiment, Ti-Al-Mn-X is used as the main alloy system, where X is at least one of Mo, W, and Nb elements. This improves the hot deformation properties of TiAl alloy under high-temperature conditions, broadens the hot working window of TiAl alloy, and also ensures the good oxidation resistance of TiAl alloy. Therefore, the requirements for forging conditions can be reduced, and a simpler uncoated, non-isothermal forging method can be used for forging. After forging, alloy forgings that meet the usage requirements are obtained, which greatly reduces the forging cost.

[0051] Example 1

[0052] Melted using a vacuum induction furnace A 21kg alloy casting rod. Figure 2 This is a drawing of the appearance of the cast rod before forging, such as... Figure 2 As shown, the open shrinkage cavity at the top of the casting was removed, and the length of the casting after removing the shrinkage cavity is 980 mm. The alloy system is Ti-43Al-2Mn-0.5Mo (at.%), and the impurity content in the alloy is O: 0.062 wt.%, N: 0.0018 wt.%, and H: 0.0010 wt.%.

[0053] The obtained casting rod is placed in an induction heating furnace, where it reaches 1350°C within one hour and is held at that temperature for 30 minutes. Then, a hydraulic high-speed forging machine is used to forge the heated alloy casting rod.

[0054] First forging: Original dimensions Casting rod. Figure 3 A schematic diagram of a scenario for heating a casting rod, as shown below. Figure 3 As shown, during the heating process, one end of the bar is placed into the induction heating furnace, and the temperature is rapidly increased to 1350℃ and held for 20 minutes. Figure 4A schematic diagram illustrating the first forging stage of the casting process, as shown below. Figure 4 As shown, the heated cast Ti-Al-Mn-Mo alloy bar is placed on a 60t hydraulic forging press and forged multiple times with small deformation using a 4Cr5MoSiV1 alloy hammer from the heated end to knead the looseness in the center of the bar. The pressing speed is 50mm / s, and the bar is forged into a square ingot with a size of 68mm×65mm and a length of 670mm after forging. The hot-deformed bar is then cut off and quickly returned to the furnace for heating and holding for 10 minutes.

[0055] Second forging: Figure 5 This is a schematic diagram illustrating the second forging process of the casting rod, as shown below. Figure 5 As shown, the 68mm×65mm square ingot, after being held at 1350℃ for 10 minutes, was forged again at a pressing speed of 50mm / s. After multiple pressings, it was forged into a 43mm×46mm square ingot with a length of 1500mm. Then it was cut into three sections of bar stock with a length of about 500mm. The three sections of bar stock were quickly returned to the furnace and heated to the forging temperature and held for 10 minutes.

[0056] The third forging: After holding at 1350℃ for 10 minutes, the 43mm×46mm square ingot is forged again at a pressing speed of 50mm / s until it becomes a 37mm×42mm square ingot with a length of 640mm. Then it is quickly returned to the furnace to be heated to the forging temperature and held for 5 minutes.

[0057] Fourth forging: The 37mm×42mm square ingot, after being kept at a certain temperature, is forged and corner-trimmed to finally obtain a square bar of approximately 40mm×40mm. Figure 6 As shown.

[0058] The tensile properties of the unclad TiAl alloy forged bar prepared in Example 1 are as follows: At room temperature, the tensile strength R... m =900~950MPa, yield strength R p0.2 =700~800MPa, elongation A=1~2%; tensile strength R at 800℃ m =550~600MPa, yield strength R p0.2 =300~350MPa, elongation A=10~15%.

[0059] Example 2

[0060] Figure 7 This is a drawing of the ingot's appearance before forging, such as... Figure 7A 5 kg ingot of Ti-42Al-3.5Mn-0.8W-0.2B-0.1Y alloy was vacuum induction melted as shown. The impurity element contents in the ingot were O: 0.0570 wt.%, N: 0.0016 wt.%, H: 0.0010 wt.%, respectively. The ingot was cut in half, and the lower half of the ingot (1 / 2 ingot) was retained for forging, as shown in FIG. 1. Figure 8

[0061] The obtained ingot was placed in a muffle furnace, and heated to 1310°C in one hour and held for 10 minutes. The heated alloy ingot was then forged using a hydraulic quick forging machine.

[0062] First forging pass: original size The inverted cone 1 / 2 ingot was placed on a 60t hydraulic forging machine and elongated using a 4Cr5MoSiV1 alloy hammer head at a ram speed of 50 mm / s to form a 75 mm x 65 mm x 150 mm square ingot. The ingot was then rapidly reheated and held for 10 minutes.

[0063] Second forging pass: the 75 mm x 65 mm x 150 mm square ingot was upset forged at a ram speed of 50 mm / s to form a 90 mm x 100 mm x 80 mm square ingot. The ingot was then rapidly reheated in a furnace and held for 10 minutes at the forging temperature.

[0064] Third forging pass: the 90 mm x 100 mm x 80 mm square ingot was elongated and then upset forged at a ram speed of 50 mm / s to form a 90 mm x 75 mm x 95 mm square ingot. The ingot was then rapidly reheated in a furnace and held for 10 minutes at the forging temperature.

[0065] Fourth forging pass: the 90 mm x 100 mm x 80 mm square ingot was elongated and forged at a ram speed of 50 mm / s to form a 130 mm x 90 mm x 60 mm square ingot. The ingot was then rapidly reheated in a furnace and held for 5 minutes at the forging temperature.

[0066] Fifth forging pass: the 130 mm x 90 mm x 60 mm square ingot was elongated and forged at a ram speed of 50 mm / s to form a 190 mm x 100 mm x 40 mm square ingot. The ingot was then rapidly reheated in a furnace and held for 5 minutes at the forging temperature, as shown in FIG. 2. Figure 9

[0067] ​​Sixth forging: the 190 mm x 100 mm x 40 mm square ingot after holding at 1310 °C for 5 minutes was elongated at a reduction speed of 50 mm / s to a 240 mm x 105 mm x 30 mm plate, then the plate was rapidly reheated to the forging temperature and held for 5 minutes.

[0068] Seventh forging: the 240 mm x 105 mm x 30 mm plate after holding at 1310 °C for 5 minutes was elongated at a reduction speed of 50 mm / s to a 285 mm x 110 mm x (20-27) mm plate, then the plate was rapidly reheated to the forging temperature and held for 5 minutes.

[0069] Eighth forging: the 285 mm x 110 mm x (20-27) mm plate after holding at 1310 °C for 5 minutes was elongated at a reduction speed of 50 mm / s to a 310 mm x 110 mm x (20-15) mm plate.

[0070] The tensile properties of the forged TiAl alloy plate prepared in Example 2 were as follows: (1) for the transverse tensile specimen, at room temperature, the tensile strength R m = 820-850 MPa, the yield strength R p0.2 = 770-800 MPa, and the elongation A = 0.8-1.5%; at 800 °C, the tensile strength R m = 550-600 MPa, the yield strength R p0.2 = 300-350 MPa, and the elongation A = 20-30%; (2) for the longitudinal tensile specimen, at room temperature, the tensile strength R m = 950-1000 MPa, the yield strength R p0.2 = 870-900 MPa, and the elongation A = 1-1.5%; at 800 °C, the tensile strength R m = 600-650 MPa, the yield strength R p0.2 = 350-400 MPa, and the elongation A = 10-15%.

[0071] The same process was applied to the remaining two ingots to obtain the finished forged plate, as shown in Table 2. Figure 10

[0072] ​It should be noted that, in this text, the term "comprising", "including" or any other variant thereof is intended to cover a non-exclusive inclusion, so that a process, method, article or system that includes a list of elements not only includes those elements, but also includes other elements not expressly listed, or inherent to such process, method, article or system. Without more limitations, the element defined by the statement "comprising a" does not exclude the presence of other identical elements in the process, method, article or system that includes the element.

[0073] The above-mentioned embodiment numbers of the application are only for description, not representing the advantages and disadvantages of the embodiments.

[0074] The above is only the preferred embodiment of the application, and does not limit the patent scope of the application. Any equivalent structure or equivalent process transformation made by using the content of the application specification and drawings, or directly or indirectly applied in other related technical fields, is also included in the patent protection scope of the application.

Claims

1. A forging method for a TiAl alloy, characterized in that, The forging method of the TiAl alloy includes the following steps: TiAl alloy ingots are prepared by smelting. The main system of the TiAl alloy is Ti-Al-Mn-X, wherein X is at least one of Mo, W, and Nb. The composition of the TiAl alloy ingot, by atomic percentage, includes 41.0%-46.0% Al, 1.0%-4.0% Mn, 0.1%-6.0% X, 0.1%-0.3% B, 0.1%-0.3% C, 0%-0.3% Si, 0-0.1% Y, and the balance being Ti. X is 2.0%-3.5% Nb and / or 0.3%-1.5% Mo and / or 0.1%-1.0% W. The elemental composition deviation of Ti, Al, and Mn in the TiAl alloy ingot is less than 0.2 wt.%, and the elemental composition deviation of W, Mo, and Nb is less than 0.1 wt.%. The TiAl alloy ingot is subjected to heat treatment and heat preservation. The TiAl alloy ingot is forged in an uninsulated, non-isothermal environment to process it to a preset size, wherein the cumulative deformation of the TiAl alloy ingot during forging is greater than 50%.

2. The forging method of TiAl alloy as described in claim 1, characterized in that, The TiAl alloy ingot also contains impurity elements O, N and H, wherein the content of O is less than 0.08 wt.%, the content of N is less than 0.0020 wt.%, and the content of H is less than 0.0020 wt.%.

3. The forging method of TiAl alloy as described in claim 1, characterized in that, The step of forging the TiAl alloy ingot includes: If the length-to-diameter ratio of the TiAl alloy ingot is greater than 1.5, then the TiAl alloy ingot is directly drawn and forged. If the length-to-diameter ratio of the TiAl alloy ingot is less than or equal to 1.5, the TiAl alloy ingot shall be subjected to upsetting forging or upsetting followed by drawing forging.

4. The forging method of TiAl alloy as described in claim 3, characterized in that, Forging and upsetting are carried out using a forging press with a pressing speed of 10-60 mm / s.

5. The forging method of TiAl alloy as described in claim 3, characterized in that, The forging method is multi-fire, multi-pass forging, with the final forging temperature of each pass exceeding 1100℃.

6. A TiAl alloy, characterized in that, The TiAl alloy was prepared by the forging method described in any one of claims 1-5.

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