Characterization and Synthesis of Co(ss)/WSi2-CoWSi Nanocomposite by Mechanical Alloying and Subsequent Sintering

In this study, Co_(ss)/WSi₂-CoWSi nanocomposite was synthesized via mechanical alloying and heat treatment. In order to fabricate bulk composite, 50-h-milled powders were cold pressed and subsequently sintered at 1150 °C for 4 h in Ar atmosphere. Phase development and structural changes were investigated by x-ray diffraction technique and scanning electron microscopy. After various milling times, the powders were investigated by differential thermal analysis and microhardness measurements. The starting powder mixture has two allotropic structures of Co (fcc and hcp). After 10-h milling, an allotropic transformation takes place in Co (fcc to hcp), and a composite microstructure consisting of cold-welded Co, W, and Si phases is formed. After 20 h, new peaks related to WSi₂ appeared in x-ray diffractograms. Increasing milling time to 50 h caused the formation of (Co, W, and Si) solid solution, WSi₂, and CoWSi phases. DTA analysis of 30- and 50-h-milled powders confirmed an increase in the degree of ordering. The 50-h-milled powders exhibited high microhardness value of about 1050 HV_0.1. XRD result of sintered material demonstrated that only ordered Co_(ss)/WSi₂-CoWSi nanostructured composite is present. Consolidated sample showed 12% porosity. Nanoindentation results showed that the sintered composite an exhibited a high hardness of 700 HV_0.1 with an elastic modulus of 107 GPa.