多尺度层状组织结构TC21钛合金及其对力学性能的影响研究

Multiscale Lamellar TC21 Titanium Alloy And Its Effect On Mechanical Properties

摘要:

本文选用典型的高强韧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1h，分别在0℃-600℃ 温度范围等温保温2小时后水冷到室温，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；将试样从880℃-960℃固溶1h，并在400℃等温保温2h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104MPa?m1/2，显著高于粗片层组织（67MPa?m1/2）和细片层组织（33MPa?m1/2），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。

Abstract:

In this paper, 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 morphology, 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 the α phase precipitation behavior and the mechanical properties of the alloy. The samples were solution treated at 930 ℃ for 1h, and then step-quenched with temperature from 0 ℃ to 600 ℃. With the increasing of temperature, the width of secondary α lath phase gradually increased, and the hardness first increased and then decreased slightly, among which the hardness at 400 ℃ being the highest. The samples were solution treated from 880 ℃ to 960 ℃ for 1h and aged at 400 ℃ for 2h with water cooling to room temperature. Thus, coarse lamellar, multi-scale lamellar and fine lamellar microstructure were obtained respectively, and the hardness and strength of the alloy increased successively. However, due to its tortuous crack propagation path and crack deflection characteristics, the multi-scale lamellar microstructure showed excellent crack propagation resistance (KQ=104 MPa?m1/2) which was significantly higher than the coarse lamellar (KQ=67 MPa?m1/2) and the fine lamellar microstructure (KQ=33 MPa?m1/2).