两相黄铜中的形变孪晶与微空洞的形成

On the Void Formation and Deformation Twin in H62 Two-phase Brass

利用扫描电镜、透射电镜及正电子湮没技术,系统地观测了两相黄铜的形变结构,发现形变孪晶对微空洞形核与微空洞长大的影响是不同的。按照Mahajan的孪晶机制,分别讨论了这两种不同影响的微观机制,并将分析结果与微空洞的实际测试数据加以对照比较,发现两者吻合较好。

The deformation structure of H62 two-phase brass (with 38% of Zn in wt.) has been studied by various microscopic analyses and positron annihilation. One of the aims is to understand the influence of deformation twins on void formation. Special attention has been paid to the different behaviours of twins in connection with the nucleation and the growth of voids. It is shown that void nucleation is accelerated by the deformation twins formed at the grain boundaries of a phase and the void growth is retarded by the twins. An explanation is made using the model of continuous emitting dislocations as suggested by Mahajan. The theoretical value of critical strain for void nucleation can be estimated bywhere M-Taylor factor, M= 3.06; σc-strength of α grain boundary; σT-backward stress to α boundaries when deformation twins were formed; N-number of twin dislocations; α-angle between twin and boundaries; γ-fault energy of α phase; b-Burgers vector of twin dislocations; k-strengthening coefficient of strain hardening, σ = kεn; n-strain hardening exponent. The estimated value of critical strain for void nucleation coincides quite well with the experimental data.