In sintered WC-Ni alloys containing 6, 10 wt. % Ni, effects of sintering temperature and time on the density and mechanical properties have been investigated. Mixtures of WC (1.42㎛) and Ni (4.0㎛) powder have been compacted at 31 MPa. The compacts have been packed into graphite boat in mixed alumina-carbon powder and sintered in hydrogen atmosphere.
Firstly, sintering temperature has been varied from 1300℃ to 1550℃ while sintering time has been fixed for 20 min. The alloy sintered at 1450℃ show the maximum density and hardness.
Then specimens have been sintered for various times at 1450℃. The maximum density is achieved after sintering from 20 min to 40 min for WC-6% Ni, and after a few minute for WC-10% Ni alloy.
Specimens of maximum density also show maximum TRS and hardness at both compositions. The maximum hardness for WC-6% Ni and WC-10% Ni alloy are $R_A$92.1 and $R_A$89.1, respectively, while the maximum TRS are about 1020 MPa and 1040 MPa, respectively. The hardness of these WC-Ni alloys are comparable to that of WC-Co alloys. But TRS of WC-6% Ni alloy is about 70% of conventional WC-6% Co alloy.
Upon over-sintering, the grain growth and pore formation increase remarkably in the outer region of specimen. This phenomenon is attributed to carbon diffusing into the specimen. The grain growth and pore formation probably cause the decrease of density and mechanical properties.
