Papers by Author: Kwai S. Chan

Abstract: First–principle computational methods have been utilized to compute the diffusion mobility of Mo, Cr, Fe, and W. A local density-based full-potential linearized augmented plane wave (FLAPW) code, named WIEN2K, was utilized to compute the electronic structure and total energy of an n-atom supercell with atom positions designed to simulate the desired diffusion processes. The computational procedure involves the calculations of the energy for vacancy formation and the energy barrier for solute migration in the host metal. First-principles computational results of the energy of vacancy formation, solute migration energy, activation energy for self-diffusion, as well as diffusion of Mo, Cr, Fe, and W solutes in Ni and vice versa are presented and compared against experimental data from the literature.

Abstract: The fracture behavior of Nb-based in-situ composites is reviewed to elucidate the effects of alloy additions on the fracture process in multiphase alloys. The overview paper summarizes the current understanding of the processes by which alloying addition and microstructure alter the near-tip deformation and fracture mechanism, and presents a methodology for predicting the fracture toughness of the constituent phases and the composite. The alloying effects observed in Nb-based in-situ composites can be attributed to changes in dislocation mobility in the metallic solid solution matrix that provides ductile phase toughening in the composites. The size, volume fraction, and the continuity of the intermetallic phases dictate the fracture path and impact significantly the facture toughness of the in-situ composites.