选区激光熔化TC11钛合金的动态压缩行为与强化机制

Dynamic Compression Behavior and Strengthening Mechanism of Selective Laser Melted TC11 Titanium Alloy

摘要:

采用选区激光熔化（selective laser melting, SLM）技术制备的TC11钛合金具有优异的比强度，在航空航天领域具有广阔的应用前景。本研究通过对水平和垂直两个方向沉积成形的SLM TC11钛合金进行准静态拉伸和动态压缩力学实验，研究了SLM TC11钛合金系列应变率下的力学行为；基于EBSD测试，探究了晶界强化和位错强化机制对SLM TC11钛合金动态压缩强度的影响。研究结果表明，SLM TC11钛合金准静态拉伸时，因水平沉积成形试件中的晶界α_GB易汇聚裂纹从而表现出更低的塑性；SLM TC11钛合金动态压缩时表现出显著的应变率强化效应和较强的宏观各向同性，绝热温升引起的热软化与应变硬化的竞争导致流变应力塑性阶段呈现“平台”段特征；通过动态压缩试件的晶粒尺寸和几何必要位错密度统计分析，发现位错强化机制是SLM TC11钛合金动态压缩时的主要强化机制。本研究综合考虑应变硬化、应变率强化效应和热软化效应的影响，提出一种具有比J-C本构方程更高精度的J-C modified本构方程，可准确地描述SLM TC11钛合金的动态力学行为。

Abstract:

TC11 titanium alloy manufactured by selective laser melting (SLM) technique has excellent specific strength and broad application prospects in the aerospace field. By conducting quasi-static tensile and dynamic compressive mechanical experiments on SLM TC11 titanium alloy that built in horizontal and vertical direction, the mechanical behavior of SLM TC11 titanium alloy under series strain rate loads was investigated. Based on EBSD testing, the effects of grain boundary strengthening and dislocation strengthening mechanisms on the dynamic compressive strength of SLM TC11 titanium alloy were explored. The results indicate that the grain boundaries α_GB in the horizontally deposited specimens tends to aggregate cracks then exhibit lower plasticity during quasi-static tension. SLM TC11 titanium alloy exhibits significant strain rate strengthening effect and strong macroscopic isotropy during dynamic compression. Adiabatic temperature rise will cause thermal softening, which competes with strain hardening and then leads to a "plateau" characteristic in the flow stress plastic stage. Through statistical analysis of grain size and geometrically necessary dislocation density of dynamic compression specimens, it is found that the dislocation strengthening mechanism is the main strengthening mechanism of SLM TC11 titanium alloy during dynamic compression. Taking into account the effects of strain hardening, strain rate strengthening, and thermal softening, a J-C modified constitutive equation with accuracy higher than that of the J-C constitutive equation is proposed, which can accurately describe the dynamic mechanical behavior of SLM TC11 titanium alloy.