Abstract
With graphite, 45 steel and copper as substrates respectively, Ti(C,N)-TiB2 composite ceramic preforms with micro/nanometric grains were prepared by self-reactive sprayed forming technology. The cooling rate of spray particles deposited on different substrates was calculated by finite element method. The influence of cooling rate on morphology of micro/nanometric grains of Ti(C,N)-TiB2 composite ceramic preforms was studied by means of SEM, XRD and EDS. The results showed that the average cooling rates of particles deposited on the three kinds of substrates were 7.0×107°C/s, 8.1×107°C/s and 10.7×107°C/s respectively. The extremely quick cooling rate was the essential reason why the spray formed preforms were composed of micro/nanometric grains. The TiC0.3N0.7 grains in preforms deposited on three kinds of substrates all took on anomalous equiaxed grains. Quicker the cooling rates of the deposited particles were, smaller the grains were. The grain size of them was all less than 3μm. Whereas the influence of cooling rate on the morphology of the TiB2 grains was great. When with graphite as substrate, TiB2 took on rod-like grains with big length to diameter ratio. When with 45 steel as substrate, it took on near equiaxed grains. And when with copper as substrate, it took on lamina grains with thickness of about 100nm due to the extremely quick cooling rate and the extremely large degree of supercooling. That’s because with the change of the cooling rates, the remaining time of the liquid phases is different, so as to the growing time of the grains along the habit plane is also very different.
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