Joining and microstructural development of Ni-Al-Ti sheets under ball collisions

Ni-Al-Ti sheets were fabricated using a ball-collision technique at room temperature in an ambient atmosphere. The 0.5 mm thick Ni, Al and Ti foils were stacked and fixed at the top of a vibration chamber and ball-treated for durations of between 5 and 30 min. The microstructural evolution of the sheets was investigated as a function of the processing time and the mass of the ball. Joining of materials was considered to have occurred when materials at the interface plasticized, flowed and came into intimate contact under the high pressure developed by the ball collisions. The key parameters of the process were impact energy and processing time. Larger balls with higher impact energy were more effective for joining, and smaller balls were more effective for grain refinement. The transformation difference in grain refinement was attributed to the impact frequency, which appeared to be higher for the smaller balls. Ball collisions may have refined the grains of the Ni and Ti sheets to the nanometer scale, thereby destroying the initial rolling texture and inducing the formation of the fiber texture. The formation and stability of the 〈1 1 1〉 fiber texture in Ni were affected by the ball mass.