Mechanical properties of large TiC-Mo-Ni cermet tiles

The mechanical properties of large, commercially produced plates of a 14 vol% nickel bonded TixMo1-xC cermet have been assessed in order to determine their viability for impact and structural applications. Keene et al. (Agnew et al., 2017 [6]) have recently characterized the phase fractions and composition, microstructure (particle size and contiguity), density, and residual stress. Samples tested in the as processed, stress relieved and hot isostatic pressed (HIP) conditions revealed no discernible trends with post-processing. Pulse-echo ultrasonic velocity measurements indicated the Young's and shear elastic moduli of the cermet to be 382 and 155 GPa respectively; consistent with Hill composite estimates. The combination of a moderately low theoretical density of 5520 kg/m3, combined with a high compressive strength of 2.7 GPa and fracture toughness of 16.1 ± 1.7 MPam, indicated the material holds promise for some structural applications. However, the low bend strength of only 538 ± 109 MPa, combined a with a low Weibull modulus of approximately 6.3 were indicative of a highly stochastic material that seriously impedes its use in such applications. The random occurrence of large pockets of insufficient binder (a form of shrinkage porosity) between essentially spherical carbide particles contributed to the low Weibull modulus, but did not account for the low average flexural strength. Instead, a high carbide particle contiguity factor was shown to be responsible for the low local toughness and decrease of the critical flaw length to that of cracked carbide particle crack. The structure-property relationships shown to describe the present material were used to construct a graphical Pareto optimization map to examine the strength - toughness relationships of this material system as the hard particle diameter and volume fraction were varied. The development of improved processing approaches that reduce contiguity and porosity are necessary for this material to fulfill its significant potential.