Short-process low-cost titanium alloy plate and preparation method thereof

Abstract

The invention discloses a short-process low-cost titanium alloy plate and a preparation method thereof, and relates to the field of titanium alloy material preparation and structure property control. With Ti-Al-Cr-Fe-Zr as a research object, the preparation method comprises the following steps: (1) proportioning, smelting and pouring according to alloy components; (2) the alloy ingot is subjected to isothermal three-way forging at 950-970 DEG C, the squatting deformation is 30-50%, the drawing deformation is 20-40%, and the alloy ingot is air-cooled to the room temperature after four-heating-number forming; and then hot rolling is conducted at the temperature of 775-790 DEG C, the total deformation is 75%, the single-pass deformation is 12.5%, remelting heat preservation is conducted for 10-15 min between passes, finally air cooling is conducted to the room temperature, and the short-process low-cost high-strength plastic titanium alloy plate which is uniform in structure, excellent in performance and capable of inducing martensite phase transformation under the stress effect is obtained.

Description

Technical Field

[0001] This invention relates to the field of titanium alloy material preparation and microstructure and property control, and in particular to a low-cost, short-process, high-strength ductile titanium alloy sheet based on the stress-induced martensitic phase transformation mechanism and its preparation method. Background Technology

[0002] Titanium is a lightweight and high-strength material. Due to its high strength and toughness, durability and low density, as well as good biocompatibility, it is widely used in high-end fields such as aerospace, military, marine engineering and medical fields. Although titanium is a metal with excellent performance, the high cost of its processing greatly limits the development of titanium alloys.

[0003] However, judging from the current performance of low-cost titanium alloys developed by various countries, their comprehensive mechanical properties are still significantly insufficient. It is generally difficult to simultaneously achieve the target of a tensile strength of 1.3 GPa and an elongation greater than 10%, matching strength and ductility. Existing low-cost titanium alloys are subject to many limitations in alloy element system design, and the short-process preparation is prone to compositional segregation and microstructure inhomogeneity, resulting in performance fluctuations and limited mechanical properties. It is worth noting that when the β phase in a titanium alloy is in a low thermodynamic and elastic stability state, stress-induced martensitic transformation can occur under applied stress, transforming the original dislocation slip mechanism into a transformation-induced plasticity mechanism, thereby significantly improving the synergy between plasticity and strength. This mechanism provides a new approach for the microstructure design of low-cost titanium alloys. However, stress-induced martensitic transformation usually has a low initiation stress, and its yield strength is often below 800 MPa, making it difficult to meet high strength requirements. Therefore, how to introduce a stress-induced martensitic transformation mechanism in a low-cost system while effectively improving the yield strength, achieving a synergistic optimization of high strength and high plasticity, has become a key technical challenge that urgently needs to be overcome in the field of low-cost titanium alloys. Summary of the Invention

[0004] This invention addresses the problem of plasticity mismatch in the high-strength state of existing low-cost titanium alloys by providing a low-cost, short-process high-strength ductile titanium alloy based on the stress-induced martensitic phase transformation mechanism and its preparation method.

[0005] To achieve the above objectives, a low-cost, short-process, high-strength ductile titanium alloy preparation process based on stress-induced martensitic phase transformation mechanism is provided. The mass percentages of each component in the alloy are as follows: Al: 5.9 wt.%-6.1 wt.%, Cr: 5.8 wt.%-6.1 wt.%, Fe: 1.1 wt.%-1.2 wt.%, Zr: 0.18 wt.%-2.2 wt.%, with the balance being Ti, and the impurity content of N, H, and O ≤0.13 wt.%.

[0006] The specific steps are as follows:

[0007] (1) According to the alloy mass percentages Al: 5.9 wt.%-6.1 wt.%, Cr: 5.8 wt.%-6.1 wt.%, Fe: 1.1 wt.%-1.2 wt.%, Zr: 0.18 wt.%-2.2 wt.% and the balance Ti, weigh out the raw materials grade 0 sponge titanium (≥99.7%), high-purity aluminum particles (≥99.99%), pure chromium particles (≥99.5%), high-purity iron particles (≥99.98%) and sponge zirconium (≥99.5%), place the above raw materials in the corresponding crucibles, and then place them in the resistance furnace and heat to 120 ℃ to remove the internal moisture of the billet;

[0008] (2) Mix the dehydrated blanks evenly, gradually and evenly place them into the mold, and press them into cylindrical blanks on a hydraulic press;

[0009] (3) Place the cylindrical billet in a cleaned vacuum induction melting furnace and vacuum it. Then bake it for 2-4 minutes under argon protection at a power of 40-60 kW. Then melt it at a power of 160-180 kW so that the melt suspension time is 45-90s. To make the composition uniform, the ingot is melted three times. Finally, it is placed in a preheated mold for casting to obtain the alloy ingot.

[0010] (4) After removing the riser from the alloy ingot obtained in step (3), perform β single-phase forging; the specific steps are as follows: The ingot was placed in a resistance furnace at 950~970 ℃ and held for 60 min. Steps The ingot, after being kept at a suitable temperature, is transferred to a forging machine for the first stage of forging deformation, with a deformation rate of 0.01 s. -1 The ingot is subjected to one roughing and one drawing process. The deformation amount of roughing is 30%~50%, and the deformation amount of drawing is 20%~40%. During the forging process, the billet is deformed in three directions (for example, roughing in one direction and drawing in the other two directions). Then the steps The obtained forging billet is returned to the step Hold in a resistance furnace at 950~970 ℃ for 10~15 min, and then proceed with the next step. The forging method involves reheating the sample at 950-970℃ after the sample temperature decreases, for a total of [number missing] cycles. The process involves four forging steps; ④ After the final forging, the material is air-cooled to room temperature.

[0011] (5) Hot-roll the alloy forging (pre-rolled part) obtained in step (4); the specific steps are as follows: The pre-rolled part was placed in a resistance furnace at 775~790 ℃ (α+β two-phase region) and held for 60 min; Steps The pre-rolled parts with insulation are transferred to the twin-roll mill, where the deformation amount per pass is 12.5% ​​for rolling deformation. Between passes, the parts are returned to the furnace at 775~790 ℃ for 10~15 min for a total of six passes. After the last pass, the parts are directly air-cooled to room temperature, and finally, a titanium alloy sheet with a total deformation amount of 75% is obtained.

[0012] Further step (3) First, a relatively low vacuum is extracted, and then a high vacuum is extracted to 10⁻²-10⁻¹ Pa before argon gas purging and melting.

[0013] In the further step (3), the material is first dried for 3 minutes at a power of 50 kW under argon protection.

[0014] In the further step (4), the resistance furnace is raised to 950°C and held at that temperature for 60 minutes.

[0015] In the further step (5), the resistance furnace is raised to 780°C and held at that temperature for 60 minutes.

[0016] In further step (5), the deformation amount of each pass is 12.5% ​​for rolling deformation. The passes are then reheated in the furnace for 10 minutes. After the last pass, the material is directly air-cooled to room temperature, and finally a titanium alloy plate with a total deformation amount of 75% is obtained.

[0017] The aforementioned short-process, low-cost, high-strength PVC-TiO2 alloy sheet does not require subsequent heat treatment. Its tensile properties at room temperature can reach excellent levels with tensile strength greater than 1290 MPa, yield strength greater than 1250 MPa, and elongation exceeding 12%.

[0018] During room temperature stretching, this alloy is capable of undergoing a stress-induced martensitic transformation (as shown in the attached figure). Figure 4 As shown in the figure, the β phase shears under stress to form nanoscale orthorhombic martensite (α), thereby providing strong work hardening ability, making the work hardening rate of the alloy exceed 1000 MPa (as shown in the attached figure). Figure 3 As shown in the figure, this mechanism effectively delays the occurrence of necking, enabling the alloy to maintain high yield strength (>1250 MPa) while still possessing excellent plasticity, thus achieving a synergistic improvement in strength and plasticity.

[0019] This invention addresses a short-process, low-cost, high-strength titanium alloy preparation method. During the composition design stage, the proportions of β-stabilizing elements (such as Cr and Fe) are rationally controlled, and β-single-phase forging is performed (forging after holding at 950-970 °C, with the forging deformation occurring at temperatures precisely covering the alloy's β-transformation temperature of 880-900 °C). Furthermore, a controlled metastable β-phase structure is formed during hot rolling and subsequent cooling. This metastable β-phase exhibits high stress sensitivity and phase transformation activity at room temperature or under applied loads, enabling stress-induced martensitic transformation at high stress levels, significantly enhancing the alloy's work hardening capability. By precisely controlling the stability of the β-phase, this invention achieves a "controlled metastable" design for the β-phase: maintaining structural stability under conventional forming and service conditions, while triggering a controllable martensitic transformation under higher stress or plastic deformation conditions. This controlled metastable β-phase structure not only endows the material with excellent strength-plasticity synergy but also avoids the drawback of low yield strength in traditional stress-induced martensitic titanium alloys. Therefore, this invention can obtain low-cost titanium alloy plates with both high strength and high plasticity without the need for complex heat treatment processes.

[0020] The advantages of the technical solution of this invention are:

[0021] This invention achieves controlled metastable design of the β phase by rationally controlling the proportion of β-stabilizing elements (Cr, Fe) based on a short-process preparation. This allows the alloy to maintain structural stability under normal service conditions, while undergoing a controllable stress-induced martensitic transformation under applied high stress loads, significantly improving work hardening capacity and uniformity of plastic deformation. This mechanism effectively overcomes the shortcomings of traditional stress-induced martensitic transformation titanium alloys, such as low yield strength, and the mismatch between strength and plasticity in traditional low-cost titanium alloys. The material achieves excellent comprehensive properties, including tensile strength >1290 MPa, yield strength >1250 MPa, and elongation >12%, without the need for complex heat treatments such as solution treatment and aging. This short-process, low-cost, high-strength, and high-plasticity titanium alloy not only achieves a synergistic improvement in strength and plasticity but also has significant advantages such as simplified process, low cost, and strong industrial applicability. Attached Figure Description

[0022] Figure 1 Schematic diagram of low-cost, short-process thermomechanical processing of titanium alloy plates;

[0023] Figure 2 Engineering stress-engineering strain curves of low-cost, short-process titanium alloy plates.

[0024] Figure 3 Work hardening curve of low-cost, short-process titanium alloy sheet

[0025] Figure 4TEM images of the microstructure of low-cost, short-process titanium alloy sheet after room temperature stretching Detailed Implementation

[0026] The technical solution of the present invention will be further described below with reference to the accompanying drawings and embodiments, but the present invention is not limited to the following embodiments:

[0027] Example 1:

[0028] 1. Weigh out raw materials of grade 0 sponge titanium (≥99.7%), high-purity aluminum particles (≥99.99%), pure chromium particles (≥99.5%), high-purity iron particles (≥99.98%), and sponge zirconium (≥99.5%) according to the mass percentages of Al: 6.03 wt.%, Cr: 6 wt.%, Fe: 1.2 wt.%, Zr: 2 wt.%, and balance Ti. Place the above raw materials in the corresponding crucibles, and then place them in an electric resistance furnace and heat to 120 °C to remove the internal moisture of the billet.

[0029] 2. Mix the dehydrated blanks evenly, gradually and evenly place them into the mold, and press them into cylindrical blanks on a hydraulic press.

[0030] 3. Place the cylindrical billet in a cleaned vacuum induction melting furnace and vacuum it. Then bake it for 3 minutes under argon protection at a power of 50 kW, and then melt it at a power of 170 kW, so that the melt suspension time is 75 s. To ensure uniform composition, the ingot is melted three times. Finally, it is placed in a preheated mold for casting to obtain an alloy ingot of φ60 mm × 120 mm.

[0031] IV. After removing the riser from the alloy ingot obtained in step ③, forge it in the β single-phase region (the β transformation temperature of the alloy is 896 ℃). The specific steps are as follows: (1) Place the ingot in a resistance furnace at 950 ℃ and keep it at that temperature for 60 min; (2) Transfer the ingot that has been kept at that temperature in step (1) to a forging machine for the first forging deformation, with a deformation rate of 0.01 s. -1 , the ingot is roughed once and drawn once, the deformation amount of roughing is 30% and the deformation amount of drawing is 40%; (3) the forging billet obtained in step (2) is then placed back into the resistance furnace of 950 ℃ in step (1) for 15 min and the forging method of step (2) is carried out; during the forging process, the billet is deformed in three directions. When the sample temperature drops, the sample is placed back into the furnace (950 ℃) for heat preservation. A total of four forgings are carried out; (4) after the last forging is completed, it is air-cooled to room temperature;

[0032] Fifth, cut the alloy forging obtained in step four into pre-rolled parts with dimensions of 40*40*20mm, and then hot roll them. The specific steps are as follows: (1) Place the pre-rolled parts in a resistance furnace at 780 ℃ and keep them warm for 60 min; (2) Transfer the pre-rolled parts that have been kept warm in step (1) to a twin-roll mill, and roll them with a single-pass deformation of 12.5%. The parts are then returned to the furnace (780 ℃) and kept warm for 10 min between passes. A total of six passes are performed. After the last pass, the parts are directly air-cooled to room temperature. Finally, a plate with a total deformation of 75% and a size of approximately 5*120*50mm is obtained.

[0033] The aforementioned short-process, low-cost, high-strength PVC-TiO2 alloy sheet does not require subsequent heat treatment. Its tensile properties at room temperature can reach excellent levels with tensile strength greater than 1290 MPa, yield strength greater than 1250 MPa, and elongation exceeding 12%.

[0034] During room temperature tensile testing, this alloy undergoes stress-induced martensitic transformation. The β phase shears under stress to form a nanoscale martensitic structure, thus providing strong work hardening capability, resulting in a work hardening rate exceeding 1000 MPa (see attached figure). Figure 3 As shown in the figure, this mechanism effectively delays the occurrence of necking, enabling the alloy to maintain high yield strength (>1250MPa) while still possessing excellent plasticity, thus achieving a synergistic improvement in strength and plasticity.

[0035] This invention addresses a short-process, low-cost, high-strength titanium alloy preparation method. During the composition design stage, the proportions of β-stabilizing elements (such as Cr and Fe) are rationally controlled to induce a controlled metastable β-phase structure in the alloy during hot rolling and subsequent cooling. This metastable β-phase exhibits high stress sensitivity and phase transformation activity at room temperature or under applied loads, enabling stress-induced martensitic transformation under high stress levels and significantly enhancing the alloy's work hardening capability. By precisely controlling the stability of the β-phase, this invention achieves a "controlled metastable" design for the β-phase: maintaining structural stability under conventional forming and service conditions, while triggering a controllable martensitic transformation under higher stress or plastic deformation conditions. This controlled metastable β-phase structure not only endows the material with excellent strength-plasticity synergy but also avoids the low yield strength of traditional stress-induced martensitic titanium alloys. Therefore, this invention provides a low-cost titanium alloy sheet with both high strength and high plasticity without the need for complex heat treatment processes.

[0036] The mechanical properties of the short-process, low-cost titanium alloy sheet prepared in Example 1 were tested, with the tensile direction of the sample parallel to the rolling direction. The test results are shown in Table 1, and the stress-strain curves are as follows: Figure 2 As shown, the work hardening curve is as follows: Figure 3As shown in the figure. The results show that this alloy exhibits excellent comprehensive mechanical properties, with high yield strength, tensile strength, and good elongation. To further analyze its deformation mechanism, the microstructure of a sample approximately 3 mm from the fracture surface of the plate from Example 1 after room temperature tensile fracture was observed using TEM, as shown in the figure. Figure 4 As shown in the figure. The results indicate that during tensile deformation, the β phase in the alloy underwent a significant martensitic transformation under external stress, verifying the existence of the stress-induced martensite mechanism in the alloy of this invention.

[0037] Table 1. Room temperature tensile mechanical properties after rolling at 780℃

[0038] UTS / MPa YS / MPa Elongation / % Implementation 1305.2 1271.3 12.2

Claims

1. A short process low cost titanium alloy sheet material, characterized by, Ti-Al-Cr-Fe-Zr alloy, each component element of which has a mass percentage of Al: 5.9 wt.%-6.1 wt.%, Cr: 5.8 wt.%-6.1 wt.%, Fe: 1.1 wt.%-1.2 wt.%, Zr: 0.18 wt.%-2.2 wt.% and the balance of Ti, and the impurity content of N, H and O is ≤0.13 wt.%. 0.18 wt.%-2.2 wt.% and the balance of Ti, and the impurity content of N, H and O is ≤0.13 wt.%.

2. The method of claim 1, wherein the short process low cost titanium alloy material is prepared by the steps of: The method comprises the following steps ​ (1) according to the mass percentage of Al: 5.9 wt.%-6.1 wt.%, Cr: 5.8 wt.%-6.1 wt.%, Fe: 1.1 wt.%-1.2 wt.%, Zr: 0.18 wt.%-2.2 wt.% and the balance of Ti, respectively, 0-grade titanium sponge with a purity of ≥99.7%, high-purity aluminum particles with a purity of ≥99.99%, pure chromium particles with a purity of ≥99.5%, high-purity iron particles with a purity of ≥99.98% and zirconium sponge with a purity of ≥99.5% are weighed, the above raw materials are placed in corresponding crucibles, and then placed in a resistance furnace for heating to remove moisture inside the blank; (2) the moisture-removed blank is uniformly mixed and gradually and uniformly placed in a mold and pressed into a cylindrical blank on a hydraulic press; (3) the cylindrical blank is placed in a cleaned vacuum induction melting furnace, vacuumized, then baked at a power of 40-60 kW for 2-4 min under argon protection, and then melted at a power of 160-180 kW, so that the suspension time of the melt is 45-90 s, the ingot is melted for three times to make the composition uniform, and finally cast into a preheated mold to obtain an alloy ingot; In step (4), baking is first performed at a power of 50 kW for 3 min under argon protection. (4) After removing the riser from the alloy ingot obtained in step (3), perform β single-phase forging; the specific steps are as follows: The ingot was placed in a resistance furnace at 950~970 ℃ and held for 60 min. Steps The ingot, after being kept warm, is transferred to a forging machine for the first step of forging deformation, with a deformation rate of 0.01 s. -1 The ingot is subjected to one roughing and one drawing process. The deformation amount of roughing is 30%~50%, and the deformation amount of drawing is 20%~40%. During the forging process, the billet is deformed in three directions (for example, roughing in one direction and drawing in the other two directions). Then the steps The obtained forging billet is returned to the step Hold in a resistance furnace at 950~970 ℃ for 10~15 min, and then proceed with the next step. The forging method involves reheating the sample at 950-970℃ after the sample temperature decreases, for a total of [number missing] cycles. The process involves four forging steps; ④ After the final forging, the material is air-cooled to room temperature. (5) The alloy forge piece obtained in step (4) is subjected to hot rolling; the specific steps are as follows: The pre-rolled piece is placed in a resistance furnace at 775-790 ℃ and kept for 60 min; The pre-rolled piece is kept for 60 min in a resistance furnace at 775-790 ℃; The pre-rolled piece is transported to double-roller rolling and is subjected to rolling deformation with a single-pass deformation of 12.5%, and is reheated in a furnace at 775-790 ℃ for 10-15 min between passes, and is subjected to a total of six passes, and is directly air-cooled to room temperature after the last pass, and finally a titanium alloy plate with a total deformation of 75% is obtained.

3. The method of claim 2, wherein, Step (3) is first performed under a relatively low vacuum, and then under a high vacuum to 10 -2 -10 -1 Pa, and then argon gas is filled and smelted.

4. The method of claim 2, wherein, In step (4), the resistance furnace is raised to 950℃ and kept at this temperature for 60 min.

5. The method of claim 2, wherein, In step (5), the resistance furnace is raised to 780℃ and kept at this temperature for 60 min.

6. The method of claim 2, wherein, In step (5), the deformation amount of each pass is 12.5% for rolling deformation, the furnace is kept for 10 min between passes, and after the last pass, the sample is directly air-cooled to room temperature, and finally a titanium alloy plate with a total deformation of 75% is obtained.

7. The method of claim 2, wherein, During the room temperature tensile process of the obtained alloy, stress-induced martensite phase change occurs in the alloy, the β phase is sheared to form nanoscale rhombohedral martensite α" under stress, thereby providing strong work hardening capacity, and the work hardening rate of the alloy exceeds 1000 MPa.

8. The method of claim 2, wherein, ​

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