Hossein Sedaghati - Materials and Metallurgical Engineering Department, Iran University of Science and Technology (IUST)
M. Tamizifar - Materials and Metallurgical Engineering Department, Iran University of Science and Technology (IUST)

The effect of CaO on the formation of β- and γ-zirconia nanoparticles from α-zirconia was investigated and their stability evaluated via mechanical activation. α-ZrO۲+۸.۵wt%CaO powder was milled for ۲-۱۵۰ hours with ball-to-powder weight ratios (BPWR) of ۴۰:۱ and ۶۰:۱. Structural evaluations were conducted using X-Ray diffraction and scanning electron microscope (SEM). Thermal analysis was carried out using Differential Scanning Calorimetry (DSC). Results showed that, γ-zirconia (with a cubic structure) was obtained by ball milling of α-ZrO۲+۸.۵wt%CaO at room temperature. It was found that α to γ phase transformation began after two hours of milling and completed after ۴۸ hours with a BPWR of ۴۰:۱. Moreover, the Williamson-Hall equation indicated that the particle size of α-ZrO۲+۸.۵wt%CaO was reduced to ۵۰ nanometers and reached its equilibrium point after ۲۴ hours of milling and was unchanged after that. In addition, DSC analysis showed that β-zirconia and γ-zirconia were unstable in pure ZrO۲ powder, while CaO addition led to the stabilization of ZrO۲ as β-zirconia and γ-zirconia after ball milling.

WC–Co, Cemented carbide, Nano-structured hard-metal, Hot pressing, Wear