Abstract:In order to develop the liquid phase sintering process of WC−Ni₃Al−B composites, the preparation process of WC+Ni₃Al prealloyed powder by reaction synthesis of carbonyl Ni, analytical purity Al and coarse WC powders was investigated. DSC and XRD were adopted to study the procedure of phase transformation for the 3Ni+Al and 70%WC+(3Ni+Al) mixed powders in temperature ranges of 550−1200 °C and 25−1400 °C, respectively. The results demonstrate that the formation mechanism of Ni₃Al depends on the reaction temperature. Besides WC phase, there exist Ni₂Al₃, NiAl and Ni₃Al intermetallics in the powder mixture after heat treatment at 200−660 °C, while only NiAl and Ni₃Al exist at 660−1100 °C. Homogeneous WC+Ni₃Al powder mixture can be obtained in the temperature range of 1100−1200 °C. The WC−30%(Ni₃Al−B) composites prepared from the mixed powders by conventional powder metallurgy technology show nearly full density and the shape of WC is round. WC−30%(Ni₃Al−B) composites exhibit higher hardness of 9.7 GPa, inferior bending strength of 1800 MPa and similar fracture toughness of 18 MPa·m^1/2 compared with commercial cemented carbides YGR45 (WC−30%(Co−Ni−Cr)).

Key words: WC−Ni₃Al−B composites; Ni₃Al intermetallic; liquid phase sintering; mechanical properties