钛合金六方马氏体α′的特殊金相腐蚀行为及机理

A special metallographical corrosion behavior and its mechanism of hexagonal martensite α′ for titanium alloys

摘要:

六方马氏体α′具有特殊金相腐蚀行为，即：部分晶粒内部组织经腐蚀后无明显对比度，而部分晶粒腐蚀特征较明显，其内部细长的α′相呈十字正交排列。本文基于OM、AFM、EBSD等手段，分析了α′金相腐蚀行为的内在机理。研究发现：原始β相淬火析出α′时具有三组正交析出方向，若金相观察面同某一晶粒中三组正交析出方向的任意一组平行或近似平行，则该组α′片必为十字正交排列或平行排列。此时，α′片同金相观察面垂直，界面纵深大，腐蚀深度大，故呈现深腐蚀特征。对于给定晶粒，两种排列方式可同时存在，故整体呈现正交排列方式。

Abstract:

Hexagonal martensite α′ gets special metallographical corrosion behavior: the inner microstructure of some grains shows unobvious contrast after corrosion, however, some other grains have obvious corrosion character, namely the inner vimineous α′ array orthogonally. In present work, the mechanism of this corrosion behavior was studied based on OM, AFM and EBSD analyses. It’s found that: there are three groups of orthogonal precipitation directions of α′ when transformed from original β phase, if the metallographical observation surface is parallel or near-parallel to any one of the three groups of orthogonal precipitation directions, then this group of α′ plates must array orthogonally or parallelly. Under this circumstance, α′ plates are perpendicular to the observation surface, thus the α′/α′ interfaces are deep, which leads to deep corrosion depth, and finally deep corrosion characters are shown. For a given grain, the two arrangement modes of α′ plates can exist simultaneously, which appears orthogonal array mode as a whole.