Papers by Author: H. Kaffash

Abstract: Fabrication of alloys in the solid state via mechanical alloying (MA) process has been studied by earlier researchers. The effects of milling time and impact force, defined as the ball-to-powder weight ratio (BPR), on the elemental diffusion during synthesis of nanostructured Fe-50at.%Cu alloy via MA process were evaluated in the current work. X-ray diffraction patterns revealed that increasing the milling time and impact force give rise to increasing the micro-strain, lattice parameter and decreasing the crystallite size during the MA process. Furthermore, scanning electron microscopy (SEM) was utilized not only for evaluating the microstructure of the milled powder particles but also for proving this claim that during MA process, the mutual diffusion of Cu and Fe has occurred. The interpretation of data resulted have been discussed in details.

Abstract: NiTi alloys containing more than 55%wt nickel undergo precipitation of Ni4Ti3, Ni3Ti2, and Ni3Ti phases during various heat treatments which could have a great effect on the chemical composition of the matrix and behavior of alloy. In this investigation, a NiTi alloy with Ti-57.5%wt nickel content, produced by vacuum induction melting in a graphite crucible, were subjected to the homogenization heat treatments in 1100oC and for various time periods (0.5, 1, 2, and 4 hours). The subsequent cooling was conducted in different cooling media (furnace and air) in order to examine the effect of cooling rate. Microstructural investigations show Ni4Ti3 particles with bimodal size distribution in furnace cooling. Differential scanning calorimetry demonstrates the correlation between homogenization time and transformation temperatures of the alloy.