Mechanical properties and microstructures of TiCN/nano-TiB2/TiN cermets prepared by spark plasma sintering

Abstract

The effects of TiN and nano-TiB2 additions to titanium carbonitride (TiCN-WC-Cr3C2-Co)-based cermets processed by spark plasma sintering (SPS) are identified. The TiN and nano-TiB2 additions were varied from 0 to 15 wt% to ascertain their combined effects on the mechanical properties. Scanning electron microscopy (SEM) revealed the combined chemical composition of the new phases formed during sintering. The hardness and fracture toughness values were recorded. Increase in the fracture toughness value with TiN addition was more compared with the nano-TiB2 addition. In contrast, the hardness values were higher for the cermets formed with the nano-TiB2 addition. Sintered bodies were made as tool inserts that meet SNGN120408 standard tool configuration. Using these tools, EN24 work-piece was turned at different cutting speeds of 11.87, 29.68, 71.46, 163.88 m/min under conditions of dry cutting. The performance was evaluated. Cutting force as well as surface roughness of the work-piece after machining was measured. For all cutting tools, initially the cutting force was high but it tended to decrease at higher cutting speeds. In addition, for all the tools, at higher cutting tools the surface roughness values were uniformly minimal. The cermet with a composition 55TiCN-15WC-10Co-5Cr3C2–15nanoTiB2 (all in wt%), in particular, showed a balanced enhancement in both fracture toughness (6.8 MPa m1/2) and Vickers hardness (18 GPa) values. The surface finish of the work-piece was also the best after machining when a tool of the above composition was used.