Large-size titanium-based intermetallic compound ingot low-stress melting method

Abstract

The present application relates to a large-size titanium-based intermetallic compound ingot production technology, in particular to a large-size titanium-based intermetallic compound ingot low-stress melting method. Step one: uniformly mixed raw materials are pressed into electrode blocks; step two: the electrode blocks are welded outside the furnace to form consumable electrodes; step three: first vacuum consumable melting is performed to obtain primary ingots; step four: two groups of primary ingots obtained in step three are welded in the furnace; step five: second vacuum consumable melting is performed to obtain secondary ingots; step six: third vacuum consumable melting is performed to obtain tertiary ingots; step seven: the tertiary ingots obtained in step six are subjected to surface turning processing to obtain industrial-grade large-size titanium-based intermetallic compound finished ingots. By controlling the melting power and using the shallow-pool slow-cooling method, the present application can obtain low-stress ingots with smaller residual stress, ensure the integrity of the ingots, and increase the overall ingot size.

Description

Technical Field

[0001] This invention relates to the production technology of large-size titanium-based intermetallic compound ingots, specifically a low-stress melting method for large-size titanium-based intermetallic compound ingots. Background Technology

[0002] Titanium-based intermetallic compounds are lightweight, high-temperature structural materials with advantages such as light weight, high specific strength, high temperature resistance, and corrosion resistance. They can be used at temperatures of 700–1000℃, making them an important alternative material for high performance and lightweight applications in aero-engines, automotive engine rotating parts, and next-generation weapons and high-tech products.

[0003] As a substitute for nickel-based superalloys, titanium-based intermetallic compounds have been applied to hot-end components of aerospace and automotive engines operating at 600–800°C. More than 30 years ago, GE in the United States used its self-developed cast 4822 alloy, with a nominal composition of Ti-48Al-2Nb-2Cr (atomic fraction, %), as the last two stages of the low-pressure turbine blades in its GEnx™ engine, applied to the Boeing 787 commercial airliner. Furthermore, SNECMA in France used 4822 alloy as the low-pressure turbine blades for its next-generation LEAP™ engine, applied to the Boeing 737, Airbus A320, and COMAC C919 passenger aircraft. In recent years, P&W in the United States and MTU in Germany have used forged TNM alloy, with a nominal composition of Ti-43.5Al-4Nb-1Mo-0.1B, as the final stage blades of its new geared turbofan engine GTFTM. In 1999, Mitsubishi in Japan applied TiAl alloy as a turbocharger turbine for civilian buses. The 47.5Al alloy developed by the my country Iron and Steel Research Institute has passed the over-temperature and over-speed tests and engine durability tests for automotive turbochargers, and is now undergoing full-road condition testing on vehicles.

[0004] As the application fields of titanium-based intermetallic compounds continue to expand, the production and quality of large-size ingots are receiving increasing attention from enterprises. The preparation of titanium-based intermetallic compound ingots mainly involves three processes: vacuum arc melting, plasma beam melting, and induction solidification melting. Compared to the other two melting methods, vacuum arc melting is more suitable for melting large-size ingots.

[0005] During vacuum arc melting, uneven distribution of solidification shrinkage in different parts of the ingot leads to residual stress of varying degrees. During solidification and cooling, differences in cooling rates in different parts of the ingot result in inconsistent linear shrinkage across different regions at any given time. As this difference in linear shrinkage increases, the various parts of the ingot become mutually restrictive in their cooling, thus generating residual stress within the ingot. The root cause of this residual stress lies in the misalignment resulting from uneven deformation within the material. As the ingot size increases, the degree of misalignment caused by uneven deformation within the material becomes greater, leading to an increase in residual stress.

[0006] As a brittle titanium-based intermetallic compound structural material, it exhibits weak damage tolerance and crack propagation resistance. Excessive residual stress during the melting and solidification cooling processes can lead to ingot cracking and eventual ingot rupture. Sometimes, excessive residual stress causes cracking during the next melting and electrode welding process; sometimes, cracking occurs during the melting heating process; and sometimes, cracking occurs during the cooling process. These phenomena can all result in ingot scrapping or even melting accidents. Therefore, the melting of large-sized titanium-based intermetallic compound ingots has become a major challenge limiting the application and development of alloy materials. Currently, the diameter of large-sized titanium-based intermetallic compound ingots that can be melted in my country does not exceed 320 mm, which restricts the development and application of large-sized titanium-based intermetallic compound ring forgings in my country. Summary of the Invention

[0007] To address the problems in the prior art, the present invention aims to provide a low-stress melting method for large-size titanium-based intermetallic compound ingots. This method employs multiple vacuum consumable melting processes, solidifying the ingots in a water-cooled copper crucible. It is applicable to the melting of large-size ingots of titanium-based intermetallic compounds such as TiAl, Ti3Al, and Ti2AlNb.

[0008] The technical solution of this invention is:

[0009] A low-stress melting method for large-size titanium-based intermetallic compound ingots includes the following steps:

[0010] Step 1: Prepare and mix the raw materials according to the requirements of GB / T 39816 for casting master alloy electrodes of titanium and titanium alloys, and press the uniformly mixed raw materials into electrode blocks in a large forging press.

[0011] Step 2: The electrode blocks pressed in Step 1 are welded outside the furnace to form consumable electrodes;

[0012] Step 3: Perform a first vacuum consumable electrode melting process on the electrode obtained in Step 2 to obtain a primary ingot. The parameters for the first vacuum consumable electrode melting process are as follows: melting vacuum degree: ≤1Pa; melting voltage: 20~30V; melting current: 2~5kA; arc stabilizing current (DC): 1~5A; cooling water flow rate: 200~500L / min; cooling time after melting: ≥5h; primary ingot diameter: φ200~φ220mm.

[0013] Step 4: Perform in-furnace welding on the two sets of primary castings obtained in Step 3. Welding vacuum degree: 0.1~1Pa; welding voltage: 15~25V; welding current: 1~3kA;

[0014] Step 5: Perform a second vacuum arc remelting on the φ200~φ220mm ingot obtained in Step 4 to obtain a secondary ingot. The parameters for the second vacuum arc remelting are as follows: melting vacuum degree: ≤1Pa; melting voltage: 25~35V; melting current: 5~10kA; arc stabilizing current (DC): 1~5A; cooling water flow rate: 200~500L / min; outlet water temperature: 30~40℃; melting speed: 5~15kg / min; depth of the molten pool edge: 50~200mm; cooling time after melting: ≥7h; diameter of the secondary ingot: φ300~φ320mm.

[0015] Step Six: Perform a third vacuum consumable melting on the φ300~φ320mm ingot obtained in Step Five to obtain a third ingot. The parameters for the third vacuum consumable melting are as follows: melting vacuum degree: ≤1Pa; melting voltage: 25~35V; melting current: 5~10kA; arc stabilizing current (DC): 1~5A; cooling water flow rate: 200~500L / min; melting speed: 5~10kg / min; molten pool depth: 50~150mm; cooling time after melting: ≥7h; diameter of the third ingot: φ370~φ380mm.

[0016] Step 7: Perform surface turning on the three ingots obtained in Step 6 to obtain industrial-grade large-size titanium-based intermetallic compound finished ingots.

[0017] In the low-stress melting method for large-size titanium-based intermetallic compound ingots, step six includes N vacuum self-consumption meltings between the third vacuum self-consumption melting and obtaining the three ingots, where N is an integer greater than or equal to 1. The melting process parameters are the same as in step six. The upper and lower positions of the head and bottom are swapped in adjacent vacuum self-consumption meltings.

[0018] The low-stress melting method for large-size titanium-based intermetallic compound ingots involves controlling the melting voltage and current during vacuum consumable melting and using a shallow melting pool for slow cooling to obtain low-stress ingots with minimal residual stress. After room temperature residual stress testing, the axial stress is ≤400MPa and the circumferential stress is ≤300MPa.

[0019] The low-stress melting method for large-size titanium-based intermetallic compound ingots described above can melt ingots with a diameter of up to 380 mm.

[0020] In the low-stress melting method for large-size titanium-based intermetallic compound ingots described above, in step one, the electrode block is made of sponge titanium, aluminum briquettes, and intermediate alloy raw materials, with an aluminum content of 30-50 at%.

[0021] The low-stress melting method for large-size titanium-based intermetallic compound ingots produced ingots without large-size shrinkage cavities, macroscopic segregation, macroscopic cracks, inclusions, or other macroscopic defects.

[0022] The low-stress melting method for large-size titanium-based intermetallic compound ingots described above results in an ingot microstructure typically composed of γ(TiAl) phase and α2(Ti3Al) phase.

[0023] The low-stress melting method for large-size titanium-based intermetallic compound ingots described herein has an ingot alloy operating temperature of 700–1000℃.

[0024] The design concept of this invention is:

[0025] This invention proposes a low-stress melting method for large-sized titanium-based intermetallic compound ingots. The method employs multiple vacuum consumable melting processes, solidifying the ingot in a water-cooled copper crucible. By controlling the melting voltage and current and using a shallow molten pool for slow cooling, low-stress ingots with minimal residual stress can be obtained. Low residual stress in the ingot prevents cracking during cooling and avoids the ingot from falling into the molten pool and causing a "crucible explosion" during subsequent melting and heating, thus preventing arc extinction or even production accidents. Using the shallow molten pool for slow cooling, ingot diameters up to 380 mm can be melted.

[0026] This invention employs a shallow-pool process to smelt large-sized titanium-based intermetallic compounds, characterized by precise control of the molten pool depth. By controlling the shallow pool, the temperature gradient between the molten alloy and the solidified ingot is reduced, thereby decreasing the total residual stress after solidification. Furthermore, this process alters the interface morphology of the molten pool in traditional vacuum arc remelting, transforming it from a deep-valley interface to a shallow-valley interface with a shallower axial direction. This effectively reduces the axial residual stress component and lowers the overall residual stress of the ingot. Because the shallow-pool smelting process yields ingots with lower residual stress, cracks and fissures are less likely to occur during smelting and after solidification. Therefore, this process ensures safety and stability during ingot solidification and produces titanium-based intermetallic compound ingots larger than those obtained with traditional methods, while maintaining ingot quality and yield.

[0027] The advantages and beneficial effects of this invention are:

[0028] This invention provides a method for preparing φ380mm industrial titanium-based intermetallic compound ingots, applicable to the preparation of 450kg~600kg industrial titanium-based intermetallic compound alloy ingots, filling a technological gap in my country's field of industrial titanium-based intermetallic compound ingots with diameters of φ320mm and above. This invention achieves large-size industrial-grade titanium-based intermetallic compound alloy ingots by repeatedly melting with vacuum consumable electrodes and rationally controlling melting process parameters to reduce the residual stress level on the ingot surface. Attached Figure Description

[0029] Figure 1 This is a simulation diagram of the molten pool distribution in the third vacuum self-consuming melting process of Example 1.

[0030] Figure 2 This is a simulation diagram of the molten pool distribution in the third vacuum self-consuming melting process of Example 2.

[0031] Figure 3 This is a schematic diagram showing the location for measuring residual stress in the ingot in the embodiment.

[0032] Figure 4 The figures show the comparative results of axial residual stress tests on ingots in the examples. In the figures, ingot 1 represents Example 1, and ingot 2 represents Example 2.

[0033] Figure 5 The figures show the comparative results of circumferential residual stress tests on ingots in the examples. In the figures, ingot 1 represents Example 1, and ingot 2 represents Example 2. Detailed Implementation

[0034] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings, so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0035] Example 1:

[0036] In this embodiment, a TiAl-4822 alloy ingot is prepared, with a nominal composition of Ti-48Al-2Cr-2Nb (at%). The preparation process is as follows:

[0037] (1) The required alloy of TiAl-4822 was prepared into a φ180mm consumable electrode by electrode pressing and welding;

[0038] (2) The consumable electrode is melted once to prepare a φ220mm ingot. The process parameters of the first melting in the embodiment are: vacuum degree 0.5Pa, melting voltage 25V, melting current 3kA, arc stabilizing current 3A, cooling water flow rate 350L / min, and cooling time after melting 8h. The resulting ingot is defined as a first ingot.

[0039] (3) The two sets of primary castings were welded in the furnace. The welding vacuum degree was 0.3 Pa; the welding voltage was 20 V; and the welding current was 2 kA.

[0040] (4) The obtained φ220mm ingot is subjected to a second vacuum self-consumption melting to obtain a secondary ingot; the parameters of the second vacuum self-consumption melting are: melting vacuum degree: 0.5Pa; melting voltage: 35V; melting current: 8kA; arc stabilizing current is DC: 3A; cooling water flow rate: 400~500L / min; melting speed: 15~20kg / min; melting pool depth: 100~600mm; cooling time after melting: 10h; secondary ingot diameter: φ300mm.

[0041] (5) The obtained φ300 ingot is subjected to a third vacuum self-consumption melting process to obtain a third ingot; the parameters of the third vacuum self-consumption melting process are as follows: melting vacuum degree: 0.5Pa; melting voltage: 35V; melting current: 8kA; arc stabilization current: DC: 3A; cooling water flow rate: 400~500L / min; melting speed: 15~20kg / min; melting pool depth: 100~600mm; cooling time after melting: 10h; diameter of the third ingot: φ380mm.

[0042] In this embodiment, the titanium-based intermetallic compound ingot is free of large-sized shrinkage cavities, macroscopic segregation, macroscopic cracks, inclusions and other macroscopic defects. Its typical microstructure consists of γ(TiAl) phase and α2(Ti3Al) phase, with the as-cast γ(TiAl) phase having a volume fraction of about 90% and the α2(Ti3Al) phase having a content of about 10%.

[0043] Example 2:

[0044] In this embodiment, a TiAl-4822 alloy ingot is prepared, with a nominal composition of Ti-48Al-2Cr-2Nb (at%). The preparation process is as follows:

[0045] (1) The required alloy of TiAl-4822 was prepared into a φ180mm consumable electrode by electrode pressing and welding;

[0046] (2) The consumable electrode is melted once to prepare a φ220mm ingot. The process parameters of the first melting in the embodiment are: vacuum degree 0.5Pa, melting voltage 25V, melting current 3kA, arc stabilizing current 3A, cooling water flow rate 350L / min, and cooling time after melting 8h. The resulting ingot is defined as a first ingot.

[0047] (3) The two sets of primary castings were welded in the furnace. The welding vacuum degree was 0.3 Pa; the welding voltage was 20 V; and the welding current was 2 kA.

[0048] (4) The obtained φ220mm ingot is subjected to a second vacuum self-consumption melting to obtain a secondary ingot; the parameters of the second vacuum self-consumption melting are: melting vacuum degree: 0.5Pa; melting voltage: 25V; melting current: 5kA; arc stabilizing current is DC: 2A; cooling water flow rate: 300~400L / min; melting speed: 5~8kg / min; melting pool depth: 100~200mm; cooling time after melting: 10h; secondary ingot diameter: φ300mm.

[0049] (5) The obtained φ300 ingot is subjected to a third vacuum self-consumption melting process to obtain a third ingot; the parameters of the third vacuum self-consumption melting process are as follows: melting vacuum degree: 0.5Pa; melting voltage: 25V; melting current: 5kA; arc stabilization current: DC: 2A; cooling water flow rate: 300~400L / min; melting speed: 5~8kg / min; melting pool depth: 50~150mm; cooling time after melting: 10h; diameter of the third ingot: φ380mm.

[0050] In this embodiment, the titanium-based intermetallic compound ingot is free of large-sized shrinkage cavities, macroscopic segregation, macroscopic cracks, inclusions and other macroscopic defects. Its typical microstructure consists of γ(TiAl) phase and α2(Ti3Al) phase, with the as-cast γ(TiAl) phase having a volume fraction of about 90% and the α2(Ti3Al) phase having a content of about 10%.

[0051] Table 1 shows the comparison results of smelting process parameters and residual stress in Examples 1 and 2.

[0052] Table 1

[0053]

[0054] like Figures 1-2 The figure shows the simulation results of the molten pool distribution in the third vacuum consumable melting process using the process parameters of Examples 1 and 2. In the figure, areas with a solid fraction below 0.6 represent the molten pool, while areas with a solid fraction above 0.6 represent solidified TiAl-4822 alloy ingots. The lower part of the molten pool represents the solidified TiAl-4822 alloy ingot, and the upper part represents the location of the ingot to be filled. From these two molten pool depth diagrams, it can be seen that the molten pool depth in low-stress melting is shallower compared to the traditional melting process.

[0055] For two identical TiAl-4822 ingots prepared by the methods of Examples 1 and 2, the residual stress at the same location on both ingots was measured using the drilling method. Figure 3 As shown, residual stress was compared at three points on the ingot: top, middle, and bottom. The points were located as follows: point 1 was 100mm from the top of the ingot, point 2 was in the middle, and point 3 was 100mm from the bottom of the ingot. The drilling depth at each point was 5-10mm.

[0056] like Figures 4-5 As shown, the results of residual stress tests for the two ingots are compared. The bar graph of the residual stress test results shows that, compared with the traditional melting method, the ingots obtained using the low-stress melting method have approximately 40%–50% lower axial residual stress and approximately 30%–40% lower circumferential residual stress.

[0057] The results of the embodiments show that by controlling the melting power and using a shallow melting pool and slow cooling method, the present invention can obtain a low-stress ingot with less residual stress, ensuring the integrity of the ingot while increasing the overall ingot size. The diameter of the melted ingot can reach 380mm, and the alloy service temperature is 700~1000℃.

Claims

1. A method for low-stress melting of large-size titanium-based intermetallic compound ingots, characterized in that, Includes the following steps: Step 1: Prepare and mix the raw materials according to the requirements of GB / T 39816 for casting master alloy electrodes of titanium and titanium alloys, and press the uniformly mixed raw materials into electrode blocks in a large forging press. Step 2: The electrode blocks pressed in Step 1 are welded outside the furnace to form consumable electrodes; Step 3: Perform a first vacuum consumable electrode melting process on the electrode obtained in Step 2 to obtain a primary ingot. The parameters for the first vacuum consumable electrode melting process are as follows: melting vacuum degree: ≤1Pa; melting voltage: 20~30V; melting current: 2~5kA; arc stabilizing current (DC): 1~5A; cooling water flow rate: 200~500L / min; cooling time after melting: ≥5h; primary ingot diameter: φ200~φ220mm. Step 4: Perform in-furnace welding on the two sets of primary castings obtained in Step 3. Welding vacuum degree: 0.1~1Pa; welding voltage: 15~25V; welding current: 1~3kA; Step 5: Perform a second vacuum arc remelting on the φ200~φ220mm ingot obtained in Step 4 to obtain a secondary ingot. The parameters for the second vacuum arc remelting are as follows: melting vacuum degree: ≤1Pa; melting voltage: 25~35V; melting current: 5~10kA; arc stabilizing current (DC): 1~5A; cooling water flow rate: 200~500L / min; outlet water temperature: 30~40℃; melting speed: 5~15kg / min; depth of the molten pool edge: 50~200mm; cooling time after melting: ≥7h; diameter of the secondary ingot: φ300~φ320mm. Step Six: Perform a third vacuum consumable melting on the φ300~φ320mm ingot obtained in Step Five to obtain a third ingot. The parameters for the third vacuum consumable melting are as follows: melting vacuum degree: ≤1Pa; melting voltage: 25~35V; melting current: 5~10kA; arc stabilizing current (DC): 1~5A; cooling water flow rate: 200~500L / min; melting speed: 5~10kg / min; molten pool depth: 50~150mm; cooling time after melting: ≥7h; diameter of the third ingot: φ370~φ380mm. Step 7: Perform surface turning on the three ingots obtained in Step 6 to obtain industrial-grade large-size titanium-based intermetallic compound finished ingots. In the vacuum consumable melting process, the melting voltage and current are controlled, and a shallow melting pool slow cooling method is adopted to obtain a low-stress ingot with less residual stress. After room temperature residual stress testing, the axial stress is ≤400MPa and the circumferential stress is ≤300MPa. The typical microstructure of the ingot consists of γ(TiAl) phase and α2(Ti3Al) phase, and the service temperature of the ingot alloy is 700~1000℃.

2. The low-stress melting method for large-size titanium-based intermetallic compound ingots according to claim 1, characterized in that, In step six, between the third vacuum consumable melting and the three ingots, there are also N vacuum consumable meltings, where N is an integer greater than or equal to 1. The melting process parameters are the same as in step six; the upper and lower positions of the head and bottom are swapped in two adjacent vacuum consumable meltings.

3. The low-stress melting method for large-size titanium-based intermetallic compound ingots according to claim 1 or 2, characterized in that, The diameter of the smelted ingot reaches 380mm.

4. The low-stress melting method for large-size titanium-based intermetallic compound ingots according to claim 1 or 2, characterized in that, In step one, the electrode block is made of sponge titanium, aluminum briquettes and intermediate alloy raw materials, with an aluminum content of 30-50 at%.

5. The low-stress melting method for large-size titanium-based intermetallic compound ingots according to claim 1 or 2, characterized in that, The ingot as a whole is free of large-sized shrinkage cavities, macroscopic segregation, macroscopic cracks, inclusions, and other macroscopic defects.

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