Microstructure evolution of Cr coatings on Cu substrates prepared by mechanical alloying method

Mechanical alloying method was applied to fabricate Cr coating on Cu substrate at room temperature under ambient atmosphere, using a planetary ball mill with different milling durations. The formation of coating was a result of combined effects of mechanically induced plastic deformation, grain refinement, and deposition caused by the repeated collisions of milling balls along with powder particles. The microstructural features of the coatings were drastically affected by the treatment time. The results illustrated that at the selected processing conditions especially the rotation speed of 350 rpm and milling time of 7 h, a fully dense, uniform and metallurgically bonded coating was successfully fabricated on the substrate. The intermixing and the interdiffusion of elements at interface were critical for joining of the dissimilar materials under the ball collisions. The maximum hardness of the coatings reached 626 HV0.05 tested by Vickers hardness, showing a six times improvement upon the substrate. The friction and wear property were also improved with the reinforcing coating.