A method for regulating a titanium alloy cellular microstructure

Abstract

The application is a kind of cell-like microstructure regulation method of titanium alloy, which obtains the cell-like characteristic microstructure of equiaxial alpha phase and boundary beta phase after the continuous step converter heat treatment of the titanium alloy blank with duplex structure formed by forging, and can obtain good matching of strength and plasticity, and has better impact load performance. The application can obviously improve the comprehensive mechanical properties of the titanium alloy blank by applying the continuous step converter heat treatment process to the titanium alloy blank with duplex structure formed by forging to complete microstructure regulation and optimization.

Description

Technical Field

[0001] This invention relates to a method for controlling the cellular microstructure of titanium alloys, belonging to the field of metal material preparation. Background Technology

[0002] Titanium alloys are lightweight metallic structural materials with excellent comprehensive properties, typically characterized by low density, high specific strength, high corrosion resistance, and weldability. The lightweight, high strength, good toughness, and corrosion resistance of titanium alloys can meet the comprehensive performance requirements of aero-engine and aircraft structures, effectively ensuring the structural strength and damage resistance of components, and playing a crucial role in the leapfrog development of related equipment.

[0003] The balance between strength and plasticity is crucial for the microstructure control of titanium alloys. Especially under high-speed impact loads, fully realizing the strength and plasticity potential of titanium alloys has always been an important research direction in this field, which is closely related to the microstructure factors of titanium alloys. Existing conventional hot working and heat treatment methods generally control the alloy's microstructure and mechanical properties by refining grains and controlling phase types and proportions. Summary of the Invention

[0004] This invention addresses the aforementioned existing technical situation by providing a method for controlling the cellular microstructure of titanium alloys. Its purpose is to fully utilize the strength and plasticity potential of titanium alloys under high-speed impact loads, achieve microstructure control and optimization, and improve the comprehensive mechanical properties of titanium alloy billets.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] The method for controlling the cellular microstructure of titanium alloys according to the present invention is characterized in that: the method is completed by solution treatment followed by continuous stepped converter heat treatment, and the steps are as follows:

[0007] Step 1: Requirements for the condition of titanium alloys before heat treatment

[0008] Determine the phase transformation temperature T of the titanium alloy to be heat-treated;

[0009] The titanium alloy billet to be heat-treated is forged below the phase transformation point at a forging temperature of T-20℃~T-50℃ and a forging deformation of not less than 20%. The minimum outer diameter dimension D of the titanium alloy billet is measured.

[0010] The titanium alloy billet to be heat-treated has a dual-state microstructure, including a matrix microstructure of equiaxed α phase and β transformed phase with a volume fraction of not less than 5%;

[0011] Deformation treatment within this temperature range can yield a relatively uniform and fine bimorphic structure, while accumulating a certain amount of deformation energy, providing the original tissue basis and transformation driving force for the formation of cellular tissue during subsequent heat treatment.

[0012] Prepare two heat treatment furnaces, namely heat treatment furnace 1 and heat treatment furnace 2;

[0013] Step 2: First-stage solution heat treatment of the α+β two-phase region

[0014] The titanium alloy billet is placed in heat treatment furnace 1 and heated at a temperature lower than the phase transformation point temperature T but higher than the forging temperature used in step one for forging the titanium alloy billet. After reaching a stable state, a heat treatment process is performed, with the holding time t1 determined according to formula 1:

[0015] (0.4D-30)min≤t1≤(0.4D+30)min Formula 1

[0016] Step 3: Second Stage α+β Two-Phase Region Converter Heat Treatment

[0017] Heat furnace 2 is heated to T-140℃~T-100℃ and stabilized. The titanium alloy billet that has undergone heat treatment in step two is then rapidly transferred to heat furnace 2, with a transfer time of less than 30 seconds. Subsequently, it is held at the temperature in heat furnace 2, and the holding time t2 is determined according to formula 2:

[0018] t2=0.4D min Formula 2

[0019] Step 4: Third Stage α+β Two-Phase Region Converter Heat Treatment

[0020] Adjust the heating temperature of heat treatment furnace 1 to T-240℃~T-200℃ and reach a stable state. Quickly transfer the titanium alloy billet that has completed the heat treatment in step three to heat treatment furnace 1. The transfer time should be less than 30s. Then, hold it in heat treatment furnace 1. The holding time t3 is determined according to formula 3:

[0021] t3=0.6D min Formula 3

[0022] Step 5, Fourth Stage Stabilization Converter Heat Treatment

[0023] Heat furnace 2 is heated to T-300℃~T-250℃ and stabilized. The titanium alloy billet that has undergone heat treatment in step four is then rapidly transferred to heat furnace 2, with a transfer time of less than 30s. Subsequently, it is held at the temperature in heat furnace 2 for a holding time t4, which is determined by formula 4.

[0024] t4=(0.75~1)D Equation 4

[0025] After completion, remove from the oven and air cool to room temperature.

[0026] The features and advantages of the technical solution of this invention are as follows:

[0027] 1. Through multi-stage converter heat treatment design, the phase transformation driving force brought about by deformation energy storage and temperature difference is fully utilized. After continuous stepped converter heat treatment, a cellular microstructure with equiaxed α phase and boundary β phase is obtained, which can simultaneously achieve a good match between strength and plasticity and has better impact load resistance.

[0028] 2. This method utilizes the phase transformation characteristics of titanium alloys and can be completed using a conventional heat treatment furnace, making it highly feasible and widely applicable in practical applications. Attached Figure Description

[0029] Figure 1 Metallographic images of TA15 titanium alloy bars before heat treatment in this embodiment of the invention.

[0030] Figure 2 This is a photograph of the cellular microstructure of equiaxed α-phase and boundary β-phase of TA15 titanium alloy bars after heat treatment in an embodiment of the present invention. Detailed Implementation

[0031] The present invention will be further described in detail below with reference to embodiments.

[0032] This embodiment takes TA15 titanium alloy bars as an example. The steps for preparing TA15 titanium alloy bars using the continuous stepped converter heat treatment method designed in this invention are as follows:

[0033] Step 1: Requirements and Assessment of the Condition of TA15 Titanium Alloy Bars Before Heat Treatment

[0034] The minimum outer diameter (D) of the TA15 titanium alloy bar billet to be heat-treated is 400 mm, with an equiaxed α-phase content of 45%, and the remainder being a β-transformed phase matrix. The phase transformation temperature (T) of the TA15 titanium alloy bar billet to be heat-treated was determined to be 1010℃. The final forging temperature of this TA15 titanium alloy bar billet before heat treatment was T-50℃, and the forging deformation was not less than 40%. Its microstructure is as follows: Figure 1 As shown;

[0035] Prepare two heat treatment furnaces, namely heat treatment furnace 1 and heat treatment furnace 2;

[0036] Step 2: First-stage solution heat treatment of the α+β two-phase region

[0037] The titanium alloy billet was placed in heat treatment furnace 1 and heated to 980℃. After reaching a stable state, it was subjected to heat treatment and solution heat treatment for holding time t1 of 180min.

[0038] Step 3: Second Stage α+β Two-Phase Region Converter Heat Treatment

[0039] Heat the heat treatment furnace 2 to 900℃ and reach a stable state. Then, quickly transfer the titanium alloy billet that has completed the heat treatment in step two to the heat treatment furnace 2. The transfer time is 25s. Then, hold it in the heat treatment furnace 2 for 160min.

[0040] Step 4: Third Stage α+β Two-Phase Region Converter Heat Treatment

[0041] The heating temperature of heat treatment furnace 1 is adjusted to 780℃ and stabilized. The titanium alloy billet that has completed the heat treatment in step three is quickly transferred to heat treatment furnace 1. The transfer time is 20s. Then, it is held in heat treatment furnace 1 for 240min.

[0042] Step 5, Fourth Stage Stabilization Converter Heat Treatment

[0043] Heat the heat treatment furnace 2 to 740°C and reach a stable state. Quickly transfer the titanium alloy billet that has completed the heat treatment in step four to the heat treatment furnace 2. The transfer time is 25 seconds. Then, hold it in the heat treatment furnace 2 for 300 minutes. After completion, remove it from the furnace and air cool it to room temperature.

Claims

1. A method for controlling the cellular microstructure of titanium alloys, characterized in that: This method is accomplished through solution treatment followed by continuous stepped converter heat treatment, and the steps are as follows: Step 1: Requirements for the condition of titanium alloys before heat treatment Determine the phase transformation temperature T of the titanium alloy to be heat-treated; The titanium alloy billet to be heat-treated is forged below the phase transformation point at a forging temperature of T-20℃~T-50℃, with a forging deformation of not less than 20%, and the minimum outer diameter Dmm of the titanium alloy billet is measured. The titanium alloy billet to be heat-treated has a dual-state microstructure, including a matrix microstructure of equiaxed α phase and β transformed phase with a volume fraction of not less than 5%; Prepare two heat treatment furnaces, namely heat treatment furnace 1 and heat treatment furnace 2; Step 2: First-stage solution heat treatment of the α+β two-phase region The titanium alloy billet is placed in heat treatment furnace 1 and heated at a temperature lower than the phase transformation point temperature T but higher than the forging temperature used in step one for forging the titanium alloy billet. After reaching a stable state, a heat treatment process is performed, with the holding time t1 determined according to formula 1: (0.4D-30)min≤t1≤(0.4D+30)min Formula 1 Step 3: Second Stage α+β Two-Phase Region Converter Heat Treatment Heat furnace 2 is heated to T-140℃~T-100℃ and stabilized. The titanium alloy billet that has undergone heat treatment in step two is then rapidly transferred to heat furnace 2, with a transfer time of less than 30 seconds. Subsequently, it is held at the temperature in heat furnace 2, and the holding time t2 is determined according to formula 2: t2=0.4D min Formula 2 Step 4: Third Stage α+β Two-Phase Region Converter Heat Treatment Adjust the heating temperature of heat treatment furnace 1 to T-240℃~T-200℃ and reach a stable state. Quickly transfer the titanium alloy billet that has completed the heat treatment in step three to heat treatment furnace 1. The transfer time should be less than 30s. Then, hold it in heat treatment furnace 1. The holding time t3 is determined according to formula 3: t3=0.6D min Formula 3 Step 5, Fourth Stage Stabilization Converter Heat Treatment Heat furnace 2 is heated to T-300℃~T-250℃ and stabilized. The titanium alloy billet that has undergone heat treatment in step four is then rapidly transferred to heat furnace 2, with a transfer time of less than 30s. Subsequently, it is held at the temperature in heat furnace 2 for a holding time t4, which is determined by formula 4. t4=(0.75~1)D Equation 4 After completion, remove from the oven and air cool to room temperature.

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