Wear and mechanical properties of spark plasma and liquid phase sintered WC and NbC based cemented carbide inserts

The effects on the mechanical properties, thermal behaviour, response to cutting forces and wear mechanisms have been investigated for different manufacturing processes and materials for cemented carbide inserts. Spark plasma sintering (SPS) has been compared with liquid phase sintering (LPS), including NbC substitution for WC inserts, Ni and Fe3Al substitution for the Co binder, and with Cr3C2, Mo2C and TiC additions. The comparisons were conducted for coolant-free hard-turning and interrupted milling. Turning was carried out on 440B martensitic stainless steel (X90CrMoV18, 408 HV or 71.3 HRA) and interrupted milling was conducted on a structural steel (SABS 1431: 300WA, 184 HV or 55.1 HRA). The turning speed was varied from 80-120 m/min with a depth of cut between 0.5-1 mm, while the milling speed was varied from 100-250 m/min with a depth of cut of 1 mm. The cutting edge temperature (>1000 °C) was measured using a thermal camera (30 thermal readings per second) and force measurements were made by a Kistlerdynamometer attached to the workpiece clamp. During turning, both SPS and LPS WC inserts had lower flank wear rate (FWR) values than the NbC inserts at all speeds. The LPS inserts had lower FWR values than the SPS inserts at low speeds, but the opposite occurred at high speeds. However, during milling, the NbC-12Co (ie NbC with 12 wt.%Co binder alloy) insert had a lower FWR than the SPS WC-10Co insert at 100 m/min and performed better than both the SPS and LPS WC-10Co at 250 m/min. Additions of TiC and Mo2C to the WC inserts lowered FWR and improved the crater wear resistance in both turning and milling. No crater wear was observed in the NbC inserts due to its low solubility in the alloys. During hard turning, the NbC-12Co inserts performed better than the NbC-12Fe3Al inserts. Wear was investigated by optical microscopy and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM), and the results are explained by the composition and mechanical properties of the inserts. (AU) Copy ight © 2018 Companhia Brasileira de Metalurgia e Mineração (CBMM) All rights reserved