Papers by Author: Shou Xin Li

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: For many applications, the understanding of very long life fatigue in materials becomes extremely important. In this study, the fatigue behavior of bearing steel GCr15 (conforming to AISI 52100) at very high number of cycles has been examined. Experiments on hourglass specimens were conducted in air at room temperature, for fully reversed loading condition (R=-1), using a piezoelectric fatigue testing machine operating at a frequency of 20kHz. The results indicate that the S-N data does not reach a horizontal asymptote (signifying the fatigue limit) at 107 cycles, as conventionally believed, and that the material can fracture up to 109 cycles. Therefore, to quote a fatigue limit at 107 cycles may not hold good for the material studied. The influence of defects (such as inclusions) on the crack initiation and fracture was analyzed by scanning electron microscopy.

Abstract: The room temperature tensile strength and ductility of Mg-3.3%Li alloy were improved simultaneously by two kinds of different equal channel angular pressing (ECAP) treatments. Microstructural analyses showed that grain refinement and texture modification are the principal reasons for the improvement of mechanical properties.

Abstract: Ultrafine-grained (UFG) pure Cu processed by equal channel angular pressing (ECAP) was subjected to cyclic deformation and subsequent ageing treatment at room temperature (RT) in order to investigate the stability of defects and grain size. Cyclic deformation for 1000 cycles at RT leads to a large decrease of internal stress. X-ray diffraction (XRD) shows that the stability of defects and grain size at RT in as-cyclic deformed sample is lower than that in as-processed sample and that a reduction of internal stress takes place prior to grain growth. TEM observations show that the microstructural evolution during ageing is characterized by normal grain growth accompanied with recovery within grain interior.