Development of Heat Resistant Ni_3Al Base Cermet Using Mechanical Alloying Process.

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Ni_3Al (Ni-24.5 mol%Al-0.3mol%B) matrix composite alloys with 20,40,60 and 80vol%TiC particles and a matrix alloy with 0vol%TiC were produced by mechanical alloying - hot press process using pure Ni, pure Al and TiC powders. Details of phenomenon like morphological change of powders during mechanical alloying process were studied. Also, the microstructures and the mechanical properties as well as the oxidation properties of sintered specimens were investigated. Fine powder particles with diameter of less than 10mum were produced by mechanical alloying. Sintered composite alloys were found that they consist of Ni_3Al matrix with small amount of Ni solid solution and uniformly dispersed TiC particles. Although the plastic strain was observed for the 0vol% - 40vol%TiC alloys at any temperature investigated, 60vol% and 80vol%TiC alloys deformed plastically only at higher temperatures than 673K and 1073K,respectively. The flow stresses for alloys with 0vol% - 40vol%TiC exhibited the plateau region from 400K to 700K,and then decreased markedly. It was revealed that the strain rate sensitivity exponent (m value) for the base matrix alloy was over 0.4, indicating the development of superplastic deformation. On the other hand, the composite alloys with TiC particles showed lower m values than 0.3. Mass gain during oxidation test at 1273K increased with TiC volume fraction. While the thickness of the scale observed for the matrix alloy was very thin and composed of only Al_2O_3, TiC containing alloy formed the thick scale consisting of both Al_2O_3 and TiO_2.