Mechanical strength of ultra-fine Al-AlN composites produced by a combined method of plasma-alloy reaction, spray deposition and hot pressing

Ultra-fine Al-AlN composites with high packing density were produced by the simple sequential process consisting of nitrogen plasma-alloy reaction, spray deposition and hot-pressing. The AlN content, V_f, was controlled in the range below about 40 vol % by changing the nitrogen partial pressure in the plasma-alloy reaction. The density of the Al-AlN composite with V_f=36% after hot-pressing for 7.2 ks at 673 K was 2.96 Mg m^-3 which is nearly the same as the theoretical density. The constituent phases were f c c aluminium and hexagonal AlN and their lattice parameters are nearly the same as those of pure aluminium and AlN phases. The grain size and interparticle spacing of the AlN particles were as small as about 90 and 50 nm, respectively. The Vickers hardness number, Young's modulus and compressive strength of the dense Al-AlN composite were 193, 112 GPa and 628 MPa, and the high hardness above 100 was maintained in the temperature range below 673 K. It was therefore concluded that the sequential process is a useful technique to produce ultra-fine metal-ceramic composites with high mechanical strengths.