Effect of ball milling treatment on the microstructure and microhardness of Nb-25Cr alloy

Samples of Nb-25Cr alloy were ball milled for durations of 12 h, 24 h, 36 h and 48 h. The effect of processing time on the microstructure and microhardness of Nb-25Cr alloy was investigated. The experimental results show that a deformation layer is obtained on the surface of the treated Nb-25Cr alloy samples. The deformation layer thickness correlates directly with the processing time. The ball milling treatment led to the emergence of cracks on the surface of the 48 h treated specimen due to strain and strain rate. Broad width XRD (X-ray diffraction) peaks with weak intensity and FWHM (full width at half-maximum) increasement indicate that the surface microstructure of Nb-25Cr alloy is refined. A gradual microstructure refinement on the surface of Nb-25Cr alloy is observed, corresponding to the higher strain energy introduced into the surface layer with extended processing times. Improvement in microhardness of Nb-25Cr alloy is due to microstructure refinement and work hardening effects. The microhardness of the 48 h treated specimen fell abruptly due to the cracks on the sample surface.