多尺度层状组织结构对TC21钛合金力学性能的影响

Effect of the Multiscale Lamellar on Mechanical Properties of TC21 Titanium Alloy

选用典型的高强韧TC21钛合金,利用基于伪调幅分解机制的"Step-quenching"热处理工艺调控和优化多尺度层状组织结构及其力学性能。利用SEM、TEM等研究多尺度层状组织结构的微观组织形貌、断口表面形貌、横截面裂纹扩展形貌等特征。结果表明,等温淬火温度对α相析出行为和合金力学性能有强烈影响。将试样在930℃固溶1 h,分别在0、400、600℃温度范围等温保温2 h后水冷到室温,次生α相的宽度逐渐增加,硬度先增加后稍有降低,在400℃保温的硬度达到最高值;将试样在880、930和960℃固溶1 h,并在400℃等温保温2 h后水冷至室温,分别获得粗片层组织、多尺度层状组织和细片层组织,合金的硬度和强度随固溶温度的升高依次增加。然而,多尺度片层组织表现出优异的抗裂纹扩展能力,其断裂韧度高达104 MPa·m^(1/2),显著高于粗片层组织(67 MPa·m^(1/2))和细片层组织(33 MPa·m^(1/2)),机制分析结果表明这归因于滑移难以穿过相界面、曲折的裂纹扩展路径和裂纹偏转等特性。

TC21 titanium alloy with high strength and toughness was selected,and the heat treatment process of“Step-quenching”was used to regulate and optimize the multi-scale lamellar microstructure and its mechanical properties.The microstructure morp hology,fracture morphology and cross-section crack propagation morphology of multi-scale lamellar microstructure were investigated by SEM and TEM.The results show that the isothermal quenching temperature has a strong influence on theαphase precipitation behavior and the mechanical properties of the alloy.The samples were solution treated at 930℃for 1 h,and then step-quenched at temperature of 0℃to 600℃for 2 h,and cooled to room temperature.With the increase of temperature,the width of secondaryαlath phase gradually increases,and the hardness first increases and then decreases slightly,among which the hardness at 400℃being the highest.The samples were solution treated from 880℃to 960℃for 1 h and aged at 400℃for 2 h with water cooling to room temperature.Thus,coarse lamellar,multi-scale lamellar and fine lamellar microstructures were obtained,and the hardness and strength of the alloy increase successively.However,due to its tortuous crack propagation path and crack deflection characteristics,the multi-scale lamellar microstructure shows excellent crack propagation resistance(K_(Q)=104 MPa·m^(1/2)),which is significantly higher than those of the coarse lamellar(K_(Q)=67 MPa·m^(1/2))and the fine lamellar microstructure(K_(Q)=33 MPa·m^(1/2)).