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A sort of special dislocation configuration was deformation-induced in an Fe-Ni-V-C alloy by in-situ elongation tests of TEM. The cooling in-situ observations, as well as the SADPs from the region of the special dislocation configurations, proved that they are martensitic nuclei. In martensitic transformation, a nucleus changed into a small martensitic sub-plate, and a group of parallel sub-plates that formed from a group of parallel nuclei made up a big martensitic plate Martensitic transformation involved opposite shear between adjacent martensitic nuclei. By using the reduced-cell method, the crystallographic structure of observed martensitic nuclei was indexed as a face-centered orthogonal (FCO) lattice, which was explained by the nucleation mechanism proposed by the present authors. The crystallographic analysis confirmed that the defect faulting involved in martensitic nucleation took place among three close pakked planes, instead of between two adjacent planes as an ordinary stacking fault. 相似文献
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用十字型缺口试样和WOL缺口试样分别在压应力和拉应力下研究了黄铜在氨水中的应力腐蚀。实验表明,无论那种试样,在压应力下均能产生应力腐蚀。拉、压应力腐蚀门槛值之比K_(SCC)(压)/K_(SCC)(拉)分别等于5.9(WOL试样)和5.5(十字型试洋)。拉应力腐蚀是穿晶断裂。压应力腐蚀断口和K_1有关,当K_1较低时是典型的沿晶断口,而当K_1较高时则是混合断口。电镜观察表明,双向压应力下位错塞积在晶界和孪晶界;在双向拉应力下则晶内位错密度高于晶界,且晶界位错不呈塞积群。 相似文献
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