Pulsed electric current sintering of TiC-Ultimet powders and effect of binder content on microstructure and mechanical properties

TiC-Ultimet® powders were prepared with Ultimet® (54Co-26Cr-9Ni-5Mo-3Fe-2W) contents of 12, 25, and 40 wt%, by Spex ball milling under argon atmosphere. They were compacted with pulsed electric current sintering (1473-1548 K, 5-8 min, 50 MPa). Density of the samples (Ø20, Ø25, Ø40 mm) was studied by Archimedes method. Microstructures were analyzed using optical microscopy, SEM, and XRD. Mechanical properties were studied with instrumented indentation tests. Fracture toughness was evaluated by determining K_IC in HV30 tests. The critical crack initiation load (P_cr) was measured by instrumented Vickers indentation test. Density of the samples increased with processing temperature. During processing Ultimet® was partially melted and distributed evenly among the carbides. This composite structure has high hardness of 2100-2400 HV1 independent of the Ultimet® content. Although these composites are quite brittle their ductility is better than that of pure TiC.