粘结相相变机制的研究

Study on Mechanism of Phase Transformation in Binder Phase

为了进一步了解粘结相在硬质合金中松弛应力、协调两相应变状态的作用,本文用透射电镜对Co基合金在不同状态下的微观结构进行了观察研究。结果表明:⒈Co相中常见的结构缺陷主要是层错和孪晶。烧结态下以层错为主,淬火态及回火态则两者并存,且孪晶数量大大增加。⒉冷却时粘结相中发生的马氏体型相变是通过层错形核机制由面心立方α-Co逐渐转变成密排六方ε-Co的,两者的取向关系是:(111)α-Co//(0001)ε-Co,[110]α-Co//[2110]ε-Co。⒊孪晶界阻碍了层错的扩展,不利于马氏体相变的进行,增加了α-Co的稳定性。⒋粗略推断,导致ε-Co开始生成的临界层错密度约为每隔75层原子面插入一层层错面,临界层错间距约为15纳米。

In order to further understanding the action of binder phase to relax stress and coordinate strain state between two phases in cemented carbide,observation and study have been carried out on microstructure of Co-based alloy at different conditions with TEM in the paper.The results show:1.Common structure defects in Co phase are mainly stacking fault and twin.Stacking fault is the main defect in sintered state.Both of them exist in quenched state and tempered state,and twin quantities increase greatly.2.During cooling the martensitic phase transformation taken placed in biner phase is gradual transition into h.c.p. ε-Co from f.c.c. α-Co by stacking fualt form core mechanism.Orientation relationship between the two is:(111) α-Co//(0001) ε-Co, α-Co// ε-Co.3.Twin boudary restrained the expansion of stacking fault,unfavouable to the progress of martensitic phase transformation,and increased the strbility of α-Co.4.Roughly infer that critical stacking fault density which ε-Co begins to form is approximately one stacking fault for every 75 close packed atom planse,critical stacking fault distance is about 15nm.