Papers by Author: Zhe Feng Zhang

Abstract: The deformation mechanisms of various kinds of single crystals and bicrystals during the process of equal channel angular pressing (ECAP) have been paid more attention world wide. This paper reviews the recent progresses in the understanding of the deformation mechanisms of single crystals and bicrystals subjected to one-pass ECAP, and discusses the effect of initial crystallographic orientation and grain boundary on the microstructural evolution of these crystals. Based on those experimental results and analysis, it is suggested that in addition to the shear deformation along the intersection plane (IP) of ECAP die, the shear along the normal of IP also plays an important role in affecting the microstructural evolution and deformation mechanisms of these single crystals and bicrystals.

Abstract: The microstructures of pure Cu processed by equal channel angular pressing (ECAP) from 4 to 24 passes were investigated. It was found that the microstructures of Cu samples with a small number of ECAP passes (4-8) were not inhomogeneous and the fraction of high-angle grain boundary (HAGB) was low (25~43%). While for the samples with many number of ECAP passes (12-24), the grains became more equiaxed-like and the GB misorientations exhibited double-peak distribution with high fraction (51~64%) of HAGB. It was dislocation cells formed in large grains of the few-pass samples, but subgrains in the many-pass samples. These characterizations suggested that ultrafine-grained (UFG) microstructures in the few-pass samples were not fully accomplished, while it was obtained after many passes (>12). It is believed that dynamic recovery during processing for many passes was attributed to the formation of UFG microstructures.

Abstract: Ti₃SiC₂ has been widely investigated for their intriguing physical and mechanical properties [1]. In the past decades, dense and pure polycrystalline Ti₃SiC₂ has been fabricated by some techniques [1,2]. Studies on deformation and fracture behavior at elevated temperature showed that Ti₃SiC₂ exhibited substantial plasticity with high strength [3]. It is pointed out that Ti₃SiC₂ can be possibly used for some contact applications, such as bearings, for its relative high compression strength, self-lubricating and machinability [1]. In the present paper, fatigue crack-growth rates and Hertzian contact damage of Ti₃SiC₂ were studied. Shielding ability of Ti₃SiC₂ was investigated specially in the small crack region. Damage evolution and strength degradation under Hertzian contact were studied to reveal damage behavior and mechanisms in Ti₃SiC₂.