Comparative analysis of dry sliding wear behavior of nanocrystalline diamond (NCD) films and NCD films coated with a thin Al 2 O 3 layer (Al 2 O 3 /NCD) is the main goal of the present study. Plasma-enhanced chemical vapor deposition (PECVD) and atomic layer deposition (ALD) methods were used to prepare the NCD and alumina films, respectively. Sliding wear tests were conducted at room temperature (RT), 300 and 450 • C in air. Independent of type of specimen, superlubricating behavior with the coefficient of friction (COF) in the range of 0.004-0.04 was found for the tests at 300 • C. However, the COF value measured on the Al 2 O 3 /NCD films in the tests at 450 • C is lower than that for the NCD film. A relatively short run-in period and a stable COF value of about 0.15 were observed at this temperature for the Al 2 O 3 /NCD films. The width of the wear scars measured on the Al 2 O 3 /NCD films after the tests at 450 • C is significantly smaller in comparison with the NCD film. The apparent wear volume of the wear scar on the NCD film tested at 450 • C was noticeably higher than that on the Al 2 O 3 /NCD films.

Mechanical and tribological properties of the hard-multilayer TiN-AlTiN/nACo-CrN/AlCrN-AlCrO-AlTiCrN coating deposited on WC-Co substrate were investigated. The sliding tests were carried out using ball-on-disc tribometer at room (25 °C) and high temperatures (600 and 800 °C) with Al2O3 balls as counterpart. Nano-scratch tests were performed at room temperature with a sphero-conical diamond indenter. The surface morphology and chemical composition were investigated with scanning electron microscopy (SEM), energy-dispersive spectrometry (EDS) and in-situ high-temperature X-ray diffraction (HT-XRD). The phase transition from fcc-(Al,Cr)2O3 into α-(Al,Cr)2O3 was observed at about 800 °C. The results of the tribological tests depends on the temperature, the lowest apparent and real wear volumes were observed on the coating after the test at 800 °C along with the smallest coefficient of friction (COF). The plastic deformation of the coating was confirmed in sliding and nano-scratch tests. The nano-scratch tests revealed the dependence of COF value on the temperature of the sliding tests.

The focus is on the oxidation resistance and tribological performance of ta-C and Al2O3/ta-C coatings. The wear tests were carried out on the ball on disc tribometer at room (25 °C) and high (400, 450 and 500 °C) temperatures in ambient air with Si3N4 balls as counterbodies. Scanning electron microscopy and Raman spectroscopy were used to analyze the surface morphology and chemical bonding, respectively. The Al2O3/ta-C coating exhibited better oxidation resistance and tribological performance at elevated temperatures than the ta-C coating. The Raman analysis revealed that a thin alumina layer suppresses structural changes in the ta-C coating at elevated temperatures, thus preserving the sp3 content.

This study describes deformation behavior and fracture during compression and tension at high temperatures of ferritic/martensitic 13CrMoNbV steel. Hot compression and tensile tests were carried out in the temperature range of 1100–1275 °C with a thermomechanical simulator Gleeble 3800. The true stress and ultimate tensile strength decrease with an increase in the deformation temperature. The modified Arrhenius-type constitutive model was built for 13CrMoNbV ferritic/martensitic steel using the experimental stress–strain compression data. The modified Rice and Tracy ductile fracture criteria were calculated using finite element simulation of the tensile test at different temperatures. The comparison between experimental and computed force vs. displacement curves shows high predictability of the deformation and fracture models for ferritic/martensitic 13CrMoNbV steel.