Processing of ZrC–Mo Cermets for High Temperature Applications, Part II: Pressureless Sintering and Mechanical Properties

Abstract

Pressureless sintering of ZrC–Mo cermets was investigated in a He/H2 atmosphere and under vacuum. A large density increase was observed for specimens with >20 vol% Mo after heating at 2150°C for 60 min in a He/H2 atmosphere. The increase in density was attributed to the formation of Mo2C during heating and its subsequent eutectic reaction with Mo, which produced rounded ZrC grains in a Mo–Mo2C matrix. Sintering in vacuum did not produce the same increase in density, due to the lack of Mo2C formation and subsequent lack of liquid formation, which resulted in a microstructure with irregular ZrC grains with isolated areas of Mo. Mechanical properties testing showed a decrease in Young's modulus with increasing Mo content that was consistent with the models presented. Flexure strength of ZrC–Mo cermets sintered in He/H2 atmosphere materials increased with increasing Mo content from 320 MPa at 20 vol% Mo to 410 MPa at 40 vol% Mo. Strength was predicted by adapting theories developed previously for WC–Co cermets.

Microstructure and thermal conductivity of Mo–TiC cermets processed by hot isostatic pressing

“…Thus, lot of studies dealed with high temperature mechanical property enhancement of these cermets by adjusting carbide to ceramic volume ratio [10][11][12][13][14][15][16][17][18][19][20][21]. Most of the time, composites were produced by arc-melting [10][11][12]14,17], leading to more or less fine eutectictype microstructure according to the phase diagram.…”

“…Most of the time, composites were produced by arc-melting [10][11][12]14,17], leading to more or less fine eutectictype microstructure according to the phase diagram. Uniaxial pressing [13], pressureless sintering [18], hot isostatic pressing [19,20] and even spark plasma sintering [21] were also proposed. On a mechanical point of view, the use of Mo/Nb-TiC/ZrC composites should be consistent with the GFR design requirements.…”

Microstructure and mechanical properties of hot-pressed ZrC–Ti–CNTs composites

“…Driven by the applied pressure during sintering, the relatively soft Ti grains can be squeezed into the pockets left by the ZrC grain skeleton and then act as a binder agent to promote densification. The similar densification mechanism could also be found in the other ultra-high temperature ceramics [5,20].…”

Diffusion and solid solution formation between the binary carbides of TaC, HfC and ZrC

“…They possess interesting engineering properties such as high melting points (TaC: 3983°C; HfC: 3693°C; ZrC: 3445°C) high hardness values (TaC:~19 GPa; HfC:~20.0 GPa; ZrC:~25.5 GPa), high electrical conductivities and high elastic moduli (TaC: 537 GPa; HfC: 425 GPa; ZrC: 400-440 GPa). So, they are capable of withstanding temperatures exceeding 1600°C in an aggressive environment [1][2][3][4]. The characteristic of the carbides of Groups IV and V is their mutual solubility [5].…”