In the present work, the surface integrity and flank wear of uncoated cermet inserts in dry turning of AISI 1045 steel were evaluated. Three-dimensional techniques were used to assess the surface roughness. Previously, finite element analysis was carried out to predict the cutting forces and heat distribution in the chip formation region. Cutting speed and feed were the parameters varied in the experiments. Feed is decisive in the final quality of the turned surface and cutting speed had little influence on this aspect. The surface was significantly damaged with the progression of the insert flank wear. Considering an average flank wear VB_B of 0.1 mm, a tool life of 35 min was achieved using a cutting speed of 175 m/min, and of 23 min for a cutting speed of 275 m/min. Abrasive wear was predominant during the experiments. No microstructure defects were observed, as well as crack propagation or accentuated deformations near the machined surface region. Therefore, the dry turning of 1045 steel with cermet inserts route has proven extremely viable from the standpoints of tool life, surface integrity, chip formation, and sustainability.

The dispersion stability of carbon-based solid lubricants/lubricating oils remains a challenge to overcome. Recently, novel processing routes were developed to obtain 2D turbostratic graphite particles via solid-state reactions between B₄C and Cr₃C₂ (GBC) and between SiC and Fe (GSF) that present outstanding tribological properties in a dry scenario, as well as functionalized graphene (GNH). This work investigated the suspension stability of GBC and GSF particles (0.05 wt.%) dispersed in a low-viscosity polyol ester lubricating oil and their tribological performance. Ammonia-functionalized graphene (GNH) particles were also used as a reference. In order to evaluate the dispersion stability, in addition to the classical digital image technique, a much more assertive, reliable, quantitative and rarely reported in the literature technique was used, i.e., the STEP^TM (Space and Time-resolved Extinction Profiles) technology. Reciprocating sphere-on-flat tribological tests were carried out, in which before contact, 0.2 μL of pure oil and suspension (POE + 0.05 wt.% of solid lubricant) was applied on a flat surface. The results showed that the GBC particles remained remarkably stable and reduced the sphere wear rate by 61.8%. From the tribosystem point of view, the presence of GBC and GSF reduced the wear rate by 18.4% and 2.2%, respectively, with respect to the pure oil, while the GNH particles increased the wear rate by 4.2%. Furthermore, the wear rate was improved due to the highly disordered carbon tribolayer formation identified on both surfaces.

Powder metallurgy is a competitive technology to produce ferrous near net shape parts for diverse engineering applications. However, their inherent porosity increases the susceptibility to oxidation and sealing their surface is mandatory to avoid premature degradation. Alongside, polymer derived ceramics (PDCs), such as silicon-carbonitride, have drawn attention concerning their high temperature and chemical stability. However, PDCs undergo volume shrinkage during ceramization that leads to defect formation. The shrinkage can be compensated by the addition of fillers, which are also capable of tailoring the ceramic resulting properties. This work evaluates the processing of PDC-based coatings loaded with ZrO₂ and glass fillers to compensate for the shrinkage, densify the coating and seal the sintered steel surface. Therefore, polymeric slurries were sprayed onto sintered steel substrates, which were pyrolyzed at different temperatures for microstructural and oxidation resistance evaluation. Microstructural modifications caused by the enhanced glass viscous flow during pyrolysis at 800 °C resulted in more homogeneous, dense and protective coatings, which reduced the mass gain up to 40 wt% after 100 h of oxidation at 450 °C in air in comparison to the uncoated substrate. Moreover, no macrocracks or spallation were detected, confirming the feasibility of PDC composite barrier coatings for sintered steels.