Development and performance evaluation of self-lubricating cemented carbide

Abstract

Nowadays, there is a trend in the industry to reduce or even eliminate the use of cutting fluid in machining operations. The high costs of purchasing, using, and disposing of fluids and problems related to environmental pollution and operator health favor the dry-cutting technique. However, in some machining processes, lubrication is required. In this cases, solid lubrication may be a solution. The present study investigated the development of self-lubricating cutting tool materials by adding graphite in WC – 10 wt% Co cemented carbide and how this graphite affects the sample's mechanical properties and wear behavior. The WC - 10 wt% Co cemented carbide was prepared by spark plasma sintering (SPS), and solid graphite lubricant was added at different concentrations. The samples were mixed in a high-energy ball mill and sintered at 1200 °C under 40 MPa. Microstructure, hardness, fracture toughness, and wear analyses were performed on the samples to understand the effect of graphite addition on sintered material properties. The chemical composition of the samples was analyzed by XRD and Raman spectroscopy. The wear measurement was performed by analyzing the volume of material lost by the samples during the pin-on-disk tests. Profilometry analyzes of the samples before and after the tests made it possible to measure the volume of lost material, allowing to verify the influence of the addition of solid lubricant on the wear rate of the samples. The results of the mechanical tests show that the highest hardness and the modulus of elasticity were 1578 HV and 870 GPa, respectively. The wear presented by the samples with 1% of graphite was up to 9 times less than the standard samples. The wear mechanisms are micro-cracking and fragmentation of WC grains; however, the presence of a solid lubricant avoids the steel counterpart material transfer for the pin surface. Also, it was observed the formation of a graphite and oxide tribolayer on the worn disc surface during the tests, thus avoiding excessive wear.