Sintering of Aluminium Nitride

Abstract

Aluminium nitride (AlN) sublimates at 2450°C under ordinary pressure without forming liquid phase. It has been believed that AlN products with sufficiently high density and mechanical strength for commercial uses have not been able to obtain by sintering moulded AlN powder.In this paper, it is described that AlN rods with high strength and low porosity were produced by sintering fine AlN powder.The process of sintering of AlN powder was observed. Sample rods 8mm in diameter and 15mm in length were formed of raw powder of particle size 4.4, 1.5 and 0.78μ in average, respectively. The pressure of forming was 5t/cm2, and the samples were sintered at the temperature range from 1600° to 2000°C in N2 atmosphere at 760mmHg. The time of sintering ranged from 10 to 240min. Density, flexural strength and shrinkage of sintered rods were measured in relation with sintering time, temperature and the particle size of raw powder. The structure of sintered rods were examined microscopically.Shrinkage, density and flexural strength of the samples increased with increase of sintering temperature. At constant soaking temperature, they increased rather rapidly in the early stage and slowly in the later stage of sintering. In the process of densification, crystal grains in sintered rods grew concurrently, and the rate of grain growth was faster with finer particle size of raw powder and higher sintering temperature. At the final stage of sintering, it was observed that the mechanical strength fell with increase of grain size.