TEM observation of dynamic distortion in 2Y-PSZ/steel composites

Abstract 2Y-PSZ/steel composites have been sintered by vacuum hot-pressing. The microstructure was studied by TEM after the composites were impacted at the average strain of 1.0×103 S−1 by split Hopkinson method. The results showed that the phase transformation from γ to α′ occurred in the matrix of TRIP steel under dynamic loading. Dynamic mechanical properties of 2Y-PSZ/steel composites were improved because of the transformation of distortion induced Martensite. The morphology of Martensite induced by distortion was mainly twins. The sub-structure of Martensite was mainly twins. But there was no mid-ridge and distortion twins comptetely expanded to the whole Martensite. Moreover, there was dislocation Martensite at the same sample. The inhomogeneous spread of stress wave in 2Y-PSZ/steel composites led to the different dimension of twins Martensite. When dynamic distortion was relatively efficient, Martensitic dimension and twins distance were increased and the second twins would occur. ZrO2 grains are finely distributed in matrix TRIP steel, which improved the dynamic flow stress of 2Y-PSZ/steel composites. Moreover, ZrO2 could undergo tetragonal→monoclinic phase transformation, which would improve the dynamic yield strength of the composites. But when the content of ZrO2 exceeded 20 vol.%, it would restrain the transformation of dynamic distortion induced Martensite in TRIP steel and led to the decrease of the dynamic mechanical properties of 2Y-PSZ/steel composites.