A dual annealing heat treatment process for simultaneously improving strength and ductility of alpha or near-alpha titanium alloys

Abstract

This invention discloses a dual annealing heat treatment process that simultaneously improves the strength and plasticity of α-type or near-α-type titanium alloys, belonging to the field of metal material heat treatment technology. The titanium alloy forgings or rolled plates are first held at 40°C–80°C below the β-phase transformation temperature for 20–40 minutes; then furnace cooled to 10°C–30°C above the recrystallization temperature and held for 90–180 minutes; finally, furnace cooled to room temperature. This invention activates the recrystallization process within the alloy through a first-step short-time high-temperature annealing, followed by a second-step long-time low-temperature annealing at a temperature slightly above the recrystallization temperature, ensuring complete recrystallization while controlling excessive grain growth. Compared to conventional annealing, this process yields fully recrystallized equiaxed α-grains with smaller grain sizes. This allows α-type or near-α-type titanium alloys to maintain high strength while possessing excellent plasticity. This invention solves the problem that traditional heat treatment methods often fail to simultaneously meet the service requirements for strength and plasticity in α-type or near-α-type titanium alloys, and has significant engineering implications.

Description

Technical Field

[0001] This invention is a dual annealing heat treatment process that simultaneously improves the strength and plasticity of α-type or near-α-type titanium alloys, belonging to the field of heat treatment technology for metallic materials. Background Technology

[0002] Titanium alloys are widely used in aerospace, weaponry, and marine transportation due to their low density, high specific strength, and excellent comprehensive properties. Alpha-type or near-alpha-type titanium alloys, in particular, are extensively used in aero-engines due to their excellent mechanical properties, creep resistance, and corrosion resistance at high temperatures. For example, Ti-Al-Zr-Sn-Mo-Nb-Si titanium alloys, with β-stabilizing elements not exceeding 2% and Si content as high as 0.5%, exhibit excellent high-temperature mechanical properties and creep resistance by introducing small amounts of β-phase and silicide precipitates. They are widely used in high-temperature components of aero-engines, such as the disks and blades of the R / R Spey engine and the compressors of the Boeing 757. However, the room-temperature mechanical properties of alpha-type or near-alpha-type titanium alloys are not outstanding. While alloys treated with conventional annealing exhibit good ductility, their strength is low. Solution-aging heat treatment results in higher strength but significantly deteriorates ductility. Conventional heat treatment processes struggle to achieve a balance between strength and ductility in alpha-type or near-alpha-type titanium alloys. With the rapid development of aero-engine performance requirements and the increasingly harsh service environment, higher requirements have been placed on the room temperature mechanical properties of materials for various high-temperature components, which has greatly limited the application of α-type or near-α-type titanium alloys in aero-engines. Summary of the Invention

[0003] To address the mismatch between room temperature strength and plasticity in α-type or near-α-type titanium alloys after conventional heat treatment, this invention provides a dual annealing heat treatment process that can simultaneously improve the strength and plasticity of α-type or near-α-type titanium alloys, enabling their room temperature mechanical properties to meet service requirements.

[0004] The technical solution of the present invention is as follows:

[0005] This invention provides a dual annealing heat treatment process that simultaneously improves the strength and plasticity of α-type or near-α-type titanium alloys. The specific steps are as follows:

[0006] Step 1: Obtain the recrystallization temperature (T) of the alloy 再结晶 The phase transition temperature (T) from the β phase to the α phase. β );

[0007] Step 2: Heat the α-type or near-α-type titanium alloy forgings or rolled plates to T. β Keep warm at 40℃~80℃ for 20min~40min;

[0008] Step 3: Cool in the furnace to T 再结晶Hold at 10℃~30℃ for 90min~180min, then cool to room temperature with the furnace.

[0009] Furthermore, in step 1, differential scanning calorimetry (DSC) is used to obtain the T of the alloy. 再结晶 and T β ;

[0010] Furthermore, in step 2, after the furnace reaches the specified temperature, the titanium alloy forging or rolled plate sample is placed inside. Based on experience, the sample heat penetration time is approximately ζ min, where ζ is the value corresponding to the sample thickness (in mm). The holding time is started after the sample has been fully heated.

[0011] Furthermore, in step 3, the furnace cooling rate is controlled between 3°C / min and 8°C / min.

[0012] Furthermore, the α-type or near-α-type titanium alloy described in this invention has a β-phase stability coefficient (K). β Titanium alloys with a strength less than 0.25, K β The calculation formula is as follows:

[0013]

[0014] Among them, C n For the mass fraction of β-stable elements, C Kn Table 1 below lists the critical concentrations of commonly used β-stable elements to correspond to their respective critical concentrations:

[0015] Table 1 Critical concentrations of commonly used β-stable elements

[0016] <![CDATA[Critical concentration C K , wt.%]]> 10 15 36 40 7 5 6.4 7 9

[0017] The principle of this invention is as follows:

[0018] Titanium alloy forgings or rolled plates undergo partial dynamic recrystallization after hot working, but the density of defects such as vacancies, dislocations, and stacking faults remains high. Therefore, annealing is often performed after hot working to eliminate defects and improve the mechanical properties of the alloy. This invention employs a dual annealing process, distinct from conventional annealing methods. First, a high-temperature, short-time annealing activates the recrystallization process within the alloy. Then, furnace cooling to near the recrystallization temperature allows for long-time recrystallization annealing, ensuring complete recrystallization within the alloy. After heat treatment using this process, the microstructure of the titanium alloy consists of equiaxed α grains and grain boundary β phases. The equiaxed α grains are almost defect-free, resulting in excellent plastic deformation capacity. Due to the lower recrystallization temperature, the equiaxed α grains grow at a slower rate. Simultaneously, the grain boundary β phase pins and hinders interface migration, suppressing the growth of equiaxed α grains. Consequently, the equiaxed α grain size is smaller, resulting in a significant grain refinement strengthening effect and a substantial increase in strength. Therefore, this invention's dual annealing heat treatment process can simultaneously improve the strength and plasticity of α-type or near-α-type titanium alloys.

[0019] Compared with the prior art, the beneficial effects of the dual annealing heat treatment process provided by the present invention, which simultaneously improves the strength and plasticity of α-type or near-α-type titanium alloys, are as follows:

[0020] The dual annealing process for α-type or near-α-type titanium alloys described in this invention, compared to ordinary annealing processes, achieves significant grain refinement under conditions of complete recrystallization of the titanium alloy, thus simultaneously improving both strength and plasticity. This invention overcomes the problem of the mutual constraint between strength and plasticity in α-type or near-α-type titanium alloys after traditional heat treatment, achieving an excellent balance of strength and plasticity, thus broadening the application prospects of such titanium alloys and possessing significant engineering implications. Attached Figure Description

[0021] Figure 1 This is a comparison diagram of the microstructure of the alloy in Example 1 after undergoing the double annealing heat treatment of the present invention and ordinary annealing heat treatment;

[0022] Figure 2 This is a comparison chart of the mechanical properties of the alloy in Example 2 after undergoing the double annealing heat treatment of the present invention and ordinary annealing heat treatment. Detailed Implementation

[0023] The following is a detailed description of a dual annealing heat treatment process that simultaneously improves the strength and plasticity of α-type or near-α-type titanium alloys, provided by the present invention, with reference to the accompanying drawings and embodiments.

[0024] The following examples demonstrate the double annealing process provided by this invention on two different α-type or near-α-type titanium alloys, while ordinary annealing at the same temperature and time is performed for comparison, in order to illustrate the beneficial effects of this invention.

[0025] Example 1

[0026] The main steps of the present invention for performing a dual annealing heat treatment on near-α type titanium alloy Ti-6.5Al-1Mo-1V-2Zr (TA15) rolled sheet to simultaneously improve the strength and plasticity of α type or near-α type titanium alloys are as follows:

[0027] (1) The T of TA15 alloy was determined by DSC. β Approximately 985℃, T 再结晶 Approximately 765℃;

[0028] (2) Heat the TA15 alloy rolled plate to 940℃ and hold for 30 minutes;

[0029] (3) Cool the TA15 alloy rolled plate to 780°C in the furnace, hold for 120 minutes, and then cool to room temperature in the furnace.

[0030] In contrast, the same batch of TA15 alloy rolled plates underwent ordinary annealing heat treatment: the rolled plates were heated to 940℃ and held for 120 minutes, and then furnace cooled to room temperature.

[0031] The microstructure of the alloys in both states was characterized, and the results are as follows: Figure 1 As shown in the figure, statistical analysis of the ESBD inverse pole figure reveals that after the double annealing heat treatment provided by this invention, the grain size of the primary α phase in the TA15 alloy is 6.56 μm; after ordinary annealing heat treatment, the grain size of the primary α phase in the TA15 alloy is 18.38 μm. It can be observed that the grain size obtained by the double annealing heat treatment process provided by this invention is significantly refined compared to the ordinary annealing process. This results in a tensile strength of 1056 MPa and an elongation of 19.0% for the alloy after double annealing, while the tensile strength of the alloy after ordinary annealing is 953 MPa and the elongation is 14.8%. Therefore, the double annealing heat treatment process provided by this invention simultaneously improves the strength and plasticity of the TA15 alloy.

[0032] Example 2:

[0033] The main steps of the dual annealing heat treatment provided by this invention for near-α type titanium alloy Ti-8Al-1Mo-1Cr-1Zr-0.1C forgings to simultaneously improve the strength and plasticity of α type or near-α type titanium alloys are as follows:

[0034] (1) The T of Ti-8Al-1Mo-1Cr-1Zr-0.1C alloy was determined by DSC. β Approximately 1057℃, T 再结晶 Approximately 805℃;

[0035] (2) Heat the Ti-8Al-1Mo-1Cr-1Zr-0.1C alloy forging to 1015℃ and hold for 20 min;

[0036] (3) Cool the Ti-8Al-1Mo-1Cr-1Zr-0.1C alloy forging to 830℃ in the furnace, hold for 90 minutes, and then cool to room temperature in the furnace.

[0037] In contrast, the same batch of Ti-8Al-1Mo-1Cr-1Zr-0.1C alloy forgings were subjected to ordinary annealing heat treatment: the rolled plate was heated to 1015℃ and held for 90 minutes, and then furnace cooled to room temperature.

[0038] Microstructure characterization was performed on the two alloy states: After the double annealing heat treatment provided by this invention, the primary α phase grain size of the Ti-8Al-1Mo-1Cr-1Zr-0.1C alloy was 7.13 μm; after ordinary annealing heat treatment, the primary α phase grain size of the Ti-8Al-1Mo-1Cr-1Zr-0.1C alloy was 15.26 μm. Similarly, the double annealing heat treatment process provided by this invention significantly refined the grains compared to ordinary annealing. The tensile strength of the alloy after double annealing was 1096 MPa, and the elongation was 27.4%, while the tensile strength of the alloy after ordinary annealing was 1042 MPa, and the elongation was 17.6%. The stress-strain curves of the alloys in the two states are shown below. Figure 2 As shown, the dual annealing heat treatment process provided by this invention simultaneously improves the strength and plasticity of the Ti-8Al-1Mo-1Cr-1Zr-0.1C alloy.

[0039] The above description is merely a preferred embodiment of the present invention and does not limit the implementation and protection scope of the present invention. Those skilled in the art should realize that any equivalent substitutions and obvious changes made based on the description and illustrations of the present invention should be included within the protection scope of the present invention.

Claims

1. A dual annealing heat treatment process that simultaneously improves the strength and plasticity of α-type or near-α-type titanium alloys, characterized in that, The microstructure of the α-type or near-α-type titanium alloy consists of an α phase and a grain boundary β phase. The double annealing heat treatment process includes the following steps: Step 1: Obtain the recrystallization temperature T of the titanium alloy 再结晶 Phase transition temperature T from β phase to α phase β ; Step 2: Heat the α-type or near-α-type titanium alloy forgings or rolled plates to T. β Keep warm at 40℃~80℃ for 20min~40min; Step 3: Cool in the furnace to T 再结晶 Hold at 10℃~30℃ for 90min~180min, then cool to room temperature with the furnace.

2. The dual annealing heat treatment process for simultaneously improving the strength and plasticity of α-type or near-α-type titanium alloys as described in claim 1, characterized in that: The alloy used is an α-type or near-α-type titanium alloy, i.e., the β-phase stability coefficient K. β Less than 0.

25.

3. The dual annealing heat treatment process for simultaneously improving the strength and plasticity of α-type or near-α-type titanium alloys as described in claim 1, characterized in that: In step 1, differential scanning calorimetry (DSC) is used to obtain the T of the alloy. 再结晶 and T β .

4. The dual annealing heat treatment process for simultaneously improving the strength and plasticity of α-type or near-α-type titanium alloys as described in claim 1, characterized in that: In step 3, the furnace cooling rate is controlled at 3℃ / min to 8℃ / min.

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