High-strength and low-yield-ratio laser cladding forming near-alpha type titanium alloy and heat treatment method of high-strength and low-yield-ratio laser cladding forming near-alpha type titanium alloy

Abstract

The invention discloses a laser cladding forming near-alpha type titanium alloy with high strength and low yield ratio. The laser cladding forming near-alpha type titanium alloy is prepared from, by mass, 5.0%-8.0% of Al, 2.0%-5.0% of Mo, 1.0%-3.0% of Zr, 0.1%-1.0% of Si, x is smaller than or equal to 0.5%, x is other impurity elements including Fe, C, N, H and O, and the balance Ti. The heat treatment method of the titanium alloy comprises multi-stage heat treatment including annealing, solid solution, water quenching and aging. According to the method, the laser cladding forming near-alpha type titanium alloy with high strength and low yield ratio is obtained by controlling the components of the laser cladding forming near-alpha type titanium alloy and regulating and controlling the structure of the laser cladding forming near-alpha type titanium alloy and the morphology and the size of the alpha phase by combining with multi-stage heat treatment, so that the safety and the reliability of the titanium alloy are improved, and the production cost is reduced. The method is suitable for the fields of ocean engineering, petrochemical engineering, transportation, sports equipment and biomedical treatment.

Description

Technical Field

[0001] The present invention belongs to the technical field of titanium alloy heat treatment, and particularly relates to a laser cladding formed near-α titanium alloy with high strength and low yield ratio and a heat treatment method thereof. Background Art

[0002] Laser cladding forming technology is a near-net-shape additive manufacturing technology that has been widely studied in recent years. Additive manufacturing can break through the limitations of traditional manufacturing, enabling the manufacturing of complex structures, integrated forming, and customized design; and through near-net-shape forming, the processing links can be reduced, thereby improving material utilization rate and reducing costs. Compared with other additive manufacturing technologies, laser cladding forming technology has the characteristics of not requiring a mold and being able to quickly repair or replace key components, so it has attracted much attention in the fields of aerospace, marine ships, military, etc.

[0003] Titanium alloys are widely used in important fields such as aerospace, ocean engineering, petrochemical industry, etc. The yield ratio is an important mechanical index that affects the processing and engineering applications of titanium alloys. However, currently, the yield ratios of titanium alloys used in engineering applications are generally high, that is, the yield strength is close to the fracture strength, resulting in an increase in the utilization rate of titanium alloys but a significant reduction in safety and reliability. Therefore, a lower yield ratio is beneficial to improving the safety and reliability of materials, and at the same time, a low yield ratio can also reduce the cold forming performance of titanium alloys. With the increasing demand for the service safety and reliability of titanium alloys and the processing requirements of various complex components, exploring the preparation method of low-yield-ratio titanium alloys is of great significance for further expanding the application of titanium alloys. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a laser cladding formed near-α titanium alloy with high strength and low yield ratio in view of the above-mentioned deficiencies of the prior art. This method controls the composition of the laser cladding formed near-α titanium alloy, and combines multi-stage heat treatment including annealing, solution treatment, water quenching, and aging to regulate the microstructure and the morphology and size of the α phase of the laser cladding formed near-α titanium alloy, so as to improve both its strength and toughness, and obtain a laser cladding formed near-α titanium alloy with high strength and low yield ratio, solving the problem of the reduction in safety and reliability caused by the relatively high yield ratio of existing titanium alloys.

[0005] To solve the above technical problem, the technical solution adopted by the present invention is: a laser cladding formed near-α titanium alloy with high strength and low yield ratio, which is characterized by including the following components in mass percentage: Al 5.0% - 8.0%, Mo 2.0% - 5.0%, Zr 1.0% - 3.0%, Si 0.1% - 1.0%, x ≤ 0.5%, where x is other impurity elements including Fe, C, N, H, O, and the balance is Ti.

[0006] Generally, the raw materials used for the laser cladding forming of the near-α type titanium alloy of the present invention are titanium alloy powders. There is no binding or caking phenomenon in the titanium alloy powders, and they have good sphericity. There are no holes on the powder surface, and the particle size is mainly 80μm - 110μm.

[0007] The laser cladding forming process parameters of the laser cladding forming near-α type titanium alloy of the present invention are as follows: laser power 6kW - 8kW, scanning speed 800mm / min - 1200mm / min, powder feeding speed 1000g / H - 1200g / H, overlap ratio 30% - 50%.

[0008] Meanwhile, the present invention also discloses a heat treatment method for the laser cladding forming near-α type titanium alloy with high strength and low yield ratio. It is characterized in that by performing multi-stage heat treatment on the laser cladding forming near-α type titanium alloy including annealing, solution treatment, water quenching and aging, the microstructure and the morphology and content of the α phase of the laser cladding forming near-α type titanium alloy are regulated to obtain a laser cladding forming near-α type titanium alloy with high strength and low yield ratio.

[0009] The above heat treatment method is characterized in that the multi-stage heat treatment includes the following steps:

[0010] Step 1: Heat the laser cladding forming near-α type titanium alloy to 500°C - 600°C and hold for 4h - 10h for annealing, and then air cool;

[0011] Step 2: Heat the laser cladding forming near-α type titanium alloy air cooled in Step 1 to T β -10°C and hold for 1h - 4h, and then furnace cool to T β -20°C - T β -120°C and hold for 1h - 4h for solution treatment, and then water cool; the T β is the β phase transformation point temperature of the laser cladding forming near-α type titanium alloy, in °C;

[0012] Step 3: Age the laser cladding forming near-α type titanium alloy water cooled in Step 2 at 200°C - 400°C for 1h - 8h, and then air cool.

[0013] The above heat treatment method is characterized in that the regulated laser cladding forming near-α type titanium alloy has a basket weave structure composed of rod-shaped α and ultrafine lamellar α.

[0014] The above heat treatment method is characterized in that the room temperature mechanical properties of the laser cladding forming near-α type titanium alloy with high strength and low yield ratio are as follows: tensile strength Rm≥1000MPa, yield strength R p0.2 ≥600MPa, elongation after fracture A≥8%, yield ratio 0.6 - 0.8.

[0015] The present invention has the following advantages compared with the prior art:

[0016] 1. By controlling the composition of the laser cladding formed near-α titanium alloy and combining multi-stage heat treatment including annealing, solution treatment, water quenching and aging, the initial structure in the laser cladding formed near-α titanium alloy, namely the ultrafine lamellar α+α' structure, is transformed into short rod α phase with a volume fraction of about 20% - 40% and α' phase with 60% - 80% after stress relief annealing, solution treatment in two-phase region and water quenching. After further low-temperature aging, martensite partially decomposes to obtain the basket weave structure of short rod α+ultrafine α s +ultrafine β structure.

[0017] 2. The short rod α phase in the heat-treated laser cladding formed near-α titanium alloy of the present invention has a transformation-induced plasticity effect during the deformation process, generating a large number of twins and occurring the dynamic "Hall-Petch" effect, which greatly improves its strength. And the nano-scale ultrafine α s +ultrafine β structure improves both its strength and toughness, thereby reducing the yield ratio and obtaining a laser cladding formed near-α titanium alloy with high strength and low yield ratio.

[0018] 3. The tensile strength Rm≥1000MPa, yield strength R p0.2 ≥600MPa, elongation after fracture A≥8%, and yield ratio 0.6 - 0.8 of the heat-treated laser cladding formed near-α titanium alloy of the present invention. It has the characteristics of high strength and low yield ratio, improves the safety and reliability of the titanium alloy, and has wide application value in the fields of ocean engineering, petrochemical industry, transportation, sports equipment and biomedicine, etc.

[0019] The technical solution of the present invention will be further described in detail below with reference to the drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is the metallographic structure diagram of the heat-treated laser cladding formed near-α titanium alloy with high strength and low yield ratio in Embodiment 1 of the present invention.

[0021] Figure 2 It is the metallographic structure diagram of the heat-treated laser cladding formed near-α titanium alloy in Comparative Example 1 of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0022] Embodiment 1

[0023] The nominal composition of the laser cladding formed near-α titanium alloy with high strength and low yield ratio in this embodiment is Ti-6.5Al-3.5Mo-1.5Zr-0.3Si, including the following components by mass percentage: Al 6.5%, Mo 3.5%, Zr 1.5%, Si 0.3%, x≤0.5%, where x is other impurity elements including Fe, C, N, H, O, and the balance is Ti;

[0024] The laser cladding forming process parameters of this laser cladding formed near-α titanium alloy are: laser power 6 kW, scanning speed 1000 mm / min, powder feeding speed 1000 g / h, and overlap ratio 30%.

[0025] The heat treatment method of the laser cladding formed near-α titanium alloy in this embodiment includes the following steps:

[0026] Step 1: Heat the laser cladding formed near-α titanium alloy to 540 °C and hold for 6 h for annealing, then air cool;

[0027] Step 2: Heat the laser cladding formed near-α titanium alloy after air cooling in Step 1 to 1005 °C and hold for 1 h, then furnace cool to 960 °C and hold for 1.5 h for solution treatment, then water cool;

[0028] Step 3: Age the laser cladding formed near-α titanium alloy after water cooling in Step 2 at 250 °C for 6 h, then air cool to obtain the laser cladding formed near-α titanium alloy with high strength and low yield ratio.

[0029] Figure 1 This is the metallographic structure diagram of the laser cladding formed near-α titanium alloy with high strength and low yield ratio after heat treatment in this embodiment. From Figure 1 It can be seen that the structure of this titanium alloy is a basketweave structure composed of rod-shaped α and ultrafine lamellar α.

[0030] After testing, the room temperature mechanical properties of the laser cladding formed near-α titanium alloy with high strength and low yield ratio in this embodiment are: tensile strength Rm = 1115 MPa, yield strength R p0.2 = 716 MPa, elongation after fracture A = 18.5%, reduction of area Z = 36%, and yield ratio is 0.64.

[0031] Comparative Example 1

[0032] The nominal composition of the laser cladding formed near-α titanium alloy in this comparative example is Ti-6.5Al-3.5Mo-1.5Zr-0.3Si, including the following components by mass percentage: Al 6.5%, Mo 3.5%, Zr 1.5%, Si 0.3%, x≤0.5%, where x is other impurity elements including Fe, C, N, H, O, and the balance is Ti;

[0033] The laser cladding forming process parameters of this near-α type titanium alloy by laser cladding are as follows: laser power 6 kW, scanning speed 1000 mm / min, powder feeding speed 1000 g / h, and overlap ratio 30%.

[0034] The heat treatment method of the near-α type titanium alloy by laser cladding in this comparative example includes the following steps:

[0035] Step 1: Heat the near-α type titanium alloy by laser cladding to 540 °C, hold for 6 h for annealing, and then air-cool;

[0036] Step 2: Heat the near-α type titanium alloy by laser cladding after air-cooling in Step 1 to 960 °C, hold for 1.5 h for solution treatment, and then water-cool to obtain the heat-treated near-α type titanium alloy by laser cladding.

[0037] After testing, the room temperature mechanical properties of the heat-treated near-α type titanium alloy by laser cladding in this example are as follows: tensile strength Rm = 1115 MPa, yield strength R p0.2 = 429 MPa, elongation after fracture A = 15%, reduction of area Z = 33%, and yield ratio is 0.38.

[0038] Figure 2 This is the metallographic structure diagram of the heat-treated near-α type titanium alloy by laser cladding in this comparative example. From Figure 2 it can be seen that the structure of this titanium alloy is a lamellar structure. Rapid cooling results in a decrease in the thickness of the lamellar α phase, and a large amount of residual β phase between the lamellae undergoes martensitic transformation.

[0039] Comparing Example 1 with Comparative Example 1, it can be known that for the near-α type titanium alloy by laser cladding using conventional annealing and solution heat treatment in Comparative Example 1, both the yield strength and the yield ratio are relatively low, not only lower than the yield ratio of 0.9 of conventional titanium alloys, but also lower than the minimum yield ratio of 0.4 for normal use of titanium alloys, and thus cannot meet the requirements of engineering applications; while for the near-α type titanium alloy by laser cladding after multi-stage heat treatment in the present invention, the yield strength is significantly increased, and the elongation and reduction of area also increase to a certain extent. The yield ratio is increased to 0.64, which is much lower than the conventional yield ratio of 0.9 and higher than the minimum yield ratio of 0.4 for normal use of titanium alloys. Combining Figure 1 and Figure 2 it can be seen that the multi-stage heat treatment method of the present invention increases the width of the lamellar α in the near-α type titanium alloy by laser cladding (as shown in Figure 1 and Figure 2 ), and the large-sized lamellar α makes the titanium alloy have a higher yield strength, and the plasticity and toughness also increase to a certain extent. Thus, on the premise of meeting the requirements of engineering applications, the yield strength of the titanium alloy is effectively increased and its yield ratio is reduced, thereby improving the safety and reliability of its use.

[0040] Example 2

[0041] The nominal composition of the laser cladding formed near-α type titanium alloy in this example is Ti-7.8Al-4.5Mo-3Zr-0.5Si, including the following components by mass percentage: Al 7.8%, Mo 4.5%, Zr 3%, Si 0.5%, x 0.5%, x≤0.3%, x is other impurity elements including Fe, C, N, H, O, and the balance is Ti;

[0042] The laser cladding forming process parameters of this laser cladding formed near-α type titanium alloy are: laser power 6kW, scanning speed 1000mm / min, powder feeding speed 1000g / H, and overlap ratio 30%.

[0043] The heat treatment method of the laser cladding formed near-α type titanium alloy in this example includes the following steps:

[0044] Step 1: Heat the laser cladding formed near-α type titanium alloy to 580°C and hold for 10h for annealing, then air cool;

[0045] Step 2: Heat the laser cladding formed near-α type titanium alloy air cooled in Step 1 to 1005°C and hold for 4h, then furnace cool to 990°C and hold for 4h for solution treatment, then water cool;

[0046] Step 3: Age the laser cladding formed near-α type titanium alloy water cooled in Step 2 at 400°C for 2h, then air cool to obtain the laser cladding formed near-α type titanium alloy with high strength and low yield ratio.

[0047] After testing, the room temperature mechanical properties of the laser cladding formed near-α type titanium alloy with high strength and low yield ratio in this example are: tensile strength Rm = 1072MPa, yield strength R p0.2 = 830MPa, elongation after fracture A = 9%, reduction of area Z = 20%, and yield ratio is 0.77.

[0048] Comparative Example 2

[0049] The nominal composition of the laser cladding formed near-α type titanium alloy in this comparative example is Ti-7.8Al-4.5Mo-3Zr-0.5Si, including the following components by mass percentage: Al 7.8%, Mo 4.5%, Zr 3%, Si 0.5%, x 0.5%, x≤0.3%, x is other impurity elements including Fe, C, N, H, O, and the balance is Ti;

[0050] The laser cladding forming process parameters of this laser cladding formed near-α type titanium alloy are: laser power 6kW, scanning speed 1000mm / min, powder feeding speed 1000g / H, and overlap ratio 30%.

[0051] The heat treatment method of the laser cladding formed near-α type titanium alloy in this comparative example includes the following steps:

[0052] Step 1: Heat the laser cladding formed near-α type titanium alloy to 580 °C, hold for 10 h for annealing, and then air cool;

[0053] Step 2: Heat the laser cladding formed near-α type titanium alloy after air cooling in Step 1 to 990 °C, hold for 1.5 h for solution treatment, and then water cool to obtain the heat-treated laser cladding formed near-α type titanium alloy.

[0054] After testing, the room temperature mechanical properties of the heat-treated laser cladding formed near-α type titanium alloy in this comparative example are: tensile strength Rm = 1372 MPa, yield strength R p0.2 = 1207 MPa, elongation after fracture A = 2%, reduction of area Z = 4%, and yield ratio is 0.88.

[0055] It can be seen from Example 2 and Comparative Example 2 that, compared with the laser cladding formed near-α type titanium alloy with conventional annealing and solution heat treatment in Comparative Example 2, the yield strength of the laser cladding formed near-α type titanium alloy after multi-stage heat treatment in Example 2 increases significantly, and the elongation and reduction of area also increase to a certain extent, and the yield ratio decreases.

[0056] The above are only the preferred embodiments of the present invention and do not impose any limitations on the present invention. Any simple modifications, changes, and equivalent variations made to the above embodiments according to the technical essence of the invention still fall within the protection scope of the technical solution of the present invention.

Claims

1. A laser cladding formed near-α titanium alloy with high strength and low yield ratio, characterized in that: The invention comprises the following components in percentage by mass: Al 5.0% to 8.0%, Mo 2.0% to 5.0%, Zr 1.0% to 3.0%, Si 0.1% to 1.0%, x≤0.5%, x is other impurity elements including Fe, C, N, H, O, and the balance is Ti.

2. A heat treatment method for the high-strength and low-yield ratio laser cladding-formed near-α-type titanium alloy as claimed in claim 1, characterized in that: By subjecting the laser cladding formed near-α titanium alloy to multi-stage heat treatment including annealing, solid solution, water quenching and aging, the microstructure of the laser cladding formed near-α titanium alloy and the morphology and content of the α phase are regulated to obtain a laser cladding formed near-α titanium alloy with high strength and low yield ratio.

3. The heat treatment method according to claim 2, characterized in that: The multi-stage heat treatment comprises the following steps: Step 1: heating the laser cladding formed near-α titanium alloy to 500°C to 600°C and keeping the temperature for 4h to 10h for annealing, followed by air cooling; Step 2: Heat the laser cladding formed near-α titanium alloy after air cooling in step 1 to T β Keep at -10℃ for 1h~4h, then cool to T β -20℃~T β -120℃ for 1h~4h, solid solution, and then water cooling; β is the β phase transition temperature of the near-α titanium alloy formed by laser cladding, in °C; Step 3: ageing the laser cladding-formed near-α titanium alloy after water cooling in step 2 at 200° C. to 400° C. for 1 h to 8 h, and then air-cooling.

4. The heat treatment method according to claim 2, characterized in that: The regulated near-α-type titanium alloy formed by laser cladding has a basket structure composed of rod-shaped α and ultra-fine lamellar α.

5. The heat treatment method according to claim 2, characterized in that: The room temperature mechanical properties of the high-strength and low-yield ratio laser cladding-formed near-α-type titanium alloy are as follows: tensile strength Rm≥1000MPa, yield strength R p0.2 ≥600MPa, elongation after break A≥8%, yield strength ratio 0.6~0.8.

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