Experimental investigation and response surface methodology of mechanical milling time effect on the microstructure, densification and microhardness of nanostructured copper

Suitable condensation of mechanically milled powders is among the substantial procedures to achieve superior mechanical and physical properties. Depending on the milling conditions, time and other related parameters, mechanical milled powders possess specific morphology, work-hardening capability, and sintering behavior; hence, microstructure and condensation properties are highly dependent to milling time. In this study, copper powder was mechanically milled for different milling times and subsequently, sintered at high temperature under the Argon atmosphere. The influence of milling time on microstructure, condensation, and microhardness of the samples was experimentally investigated and the related statistical models were proposed. It was found that increasing the milling time leads to the reduction of relative density and grains size and increment of imposed lattice microstrain and microhardness. The improved hardness of the milled samples by increasing milling time is related to the grain size refinement and their higher stability during the sintering treatment. Additionally, to predict the relative density and microhardness of the sintered samples, some polynomial mathematical models were successfully developed. The analysis of variance confirmed that the suggested models can be satisfactorily applied for prediction of the relative density and microhardness. The obtained relationships can be potentially extended to estimate the densification and hardness of the other sintered mechanically milled metals. (paper)