Structural analysis and densification study of the mechanically alloyed Cr50Ni50powders

Nanocrystalline Cr(50)Ni(50)material was obtained by high-energy ball milling from pure Cr and Ni powders in a planetary ball-mill P7 under argon atmosphere at ambient temperature. Microstructural, structural, morphological, magnetic, and densification properties were studied by X-ray diffraction, scanning electron microscopy, magnetic measurements, and cold compaction followed by sintering. The Rietveld refinement of the X-ray diffraction pattern reveals after 1 h of milling the formation of the disordered fcc-Ni (Cr) solid solution in addition to pure Cr and Ni. After 25 h of milling, the interdiffusion between Cr and Ni atoms leads to the formation of a mixture of disordered fcc-Ni(Cr) and bcc-Cr(Ni) solid solutions. The average thickness of the grain boundaries of bcc-Cr(Ni) and fcc-Ni(Cr) is of about 3.5 and 2.3 nm, respectively. The morphological observations reveal the fragile aspect of the powder particles which is explained by their fragmentation at different stages of the milling process.The existence of small magnetic particles which are typically single domains is evidenced byM(r)/M-s(0.1-0.5) values. The porosity fraction of the cold compacted powders is about 25% then decreases to about 12% after sintering at 1250 degrees C for 2 h. The Vickers microhardness values of the milled powders for 25 h evolute from 1045 to 1280H(v)while those of the sintered powders vary in the range 716 to 995H(v).