Investigation of the Structural and Mechanical Properties of MicroNano Sized Al2O3 & cBN Composites
Alumina-cubic boron nitride (cBN) composites were prepared using the spark plasma sintering(SPS) technique. Alpha-alumina powders with particle sizes of ~15mm and~150mm were used as the matrix while cBN particles with and without nickel coating were used as reinforcement agents. The amounts of both coated and uncoated cBN reinforcements for each type of matrix were varied between 10 to 30 wt%. The powder materials were sintered at a temperature of 1400°C under a constant uniaxial pressure of 50 MPa. We studied the effect of the size of the starting alumina powder particles, as well as the effect of the nickel coating, on the phase transformation from cBN to hBN (hexagonal boron nitride) and on the thermo-mechanical properties of the composites. In contrast to micro-sized alumina, utilization of nano-sizedalumina as the starting powder was observed to have played a pivotal role in preventing the cBN-to-hBN transformation. The composites prepared using nano-sized alumina with nickel-coated 30wt% cBN showed the highest relative density of 99% along with the highest Vickers hardness(Hv2) value of 29 GPa. Because the compositions made with micro-sized alumina underwent the phase transformation from cBN to hBN, their relative densification as well as hardness values were relatively low (20.95-22.86 GPa). However, coating nickel on the cBN reinforcement particles hindered the cBN-to-hBN transformation in the micro-sized alumina matrix, resulting in improved hardness values of up to 24.64 GPa.
This paper highlights application of the C-Therm TCi Thermal Conductivity Analyzer.
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