Liquid-phase sintering and properties of Cr3C2/NiCr cermets

Abstract

Liquid-phase sintering of Cr3C2/NiCr cermets was investigated as a function of Cr3C2 content (55-95 wt%) at a constant Ni-to-Cr ratio of 4. Specimens cold-isostatically pressed at 230 MPa were sintered in a vacuum and in the presence of a liquid phase, at 1300 degrees C for 15 and 30 min. Specimens with a carbide content of <75% were heavily distorted due to excessive liquid phase formed during sintering, but those with a higher carbide content were densified to near theoretical density (>98%) within 15 min. The density of the successfully sintered specimens decreases slightly with increasing carbide content and sintering time. Using X-ray diffraction analysis and scanning electron micrographs, it was revealed that the microstructures consisted of a prismatic Cr3C2 phase and a metallic binder phase. The hardness of the samples increased with increasing carbide content, whereas the transverse rupture strength decreased. The decrease in strength is attributed to the reduction in the metallic binder content and to poor densification. It was shown that almost fully-densified Cr3C2/NiCr cermets with carbide contents of 75-95 wt% could be produced in a vacuum through the liquid-phase sintering process at a low temperature, such as 1300 degrees C, for a sintering time as short as 15 min. (C) 1998 Published by Elsevier Science S.A.