Solid lubricant behavior of MoS2 and WSe2-based nanocomposite coatings

Tribological coatings made of MoS2 and WSe2 phases and their corresponding combinations with tungsten carbide (WC) were prepared by non-reactive magnetron sputtering of individual targets of similar composition. A comparative tribological analysis of these multiphase coatings was done in both ambient air (30–40% relative humidity, RH) and dry nitrogen (RH<7%) environments using the same tribometer and testing conditions. A nanostructural study using advanced transmission electron microscopy of the initial coatings and examination of the counterfaces after the friction test using different analytical tools helped to elucidate what governs the tribological behavior for each type of environment. This allowed conclusions to be made about the influence of the coating microstructure and composition on the tribological response. The best performance obtained with a WSex film (specific wear rate of 2 × 10−8 mm3 N–1m–1 and a friction coefficient of 0.03–0.05) was compared with that of the well-established MoS2 lubricant material.The Spanish Ministry of Economy, Industry and Competitiveness [projects n° MAT2010-21597-C02-01, MAT2011-29074-C02-01; MAT2015-65539-P; MAT2015-69035-REDC], Junta de Andalucía [P10-TEP-67182] and Spanish National Research Council (CSIC) [201560E013] are acknowledged for their financial support

Tribological properties of nitrogen implanted and boron implanted steels

Samples of a steel with high chrome content was implanted separately with 75 keV nitrogen ions and with 75 keV boron ions. Implanted doses of each ion species were 2-, 4-, and 8 {times} 10{sup 17}/cm{sup 2}. Retained doses were measured using resonant non-Rutherford Backscattering Spectrometry. Tribological properties were determined using a pin-on-disk test with a 6-mm diameter ruby pin with a velocity of 0.94 m/min. Testing was done at 10% humidity with a load of 377 g. Wear rate and coefficient of friction were determined from these tests. While reduction in the wear rate for nitrogen implanted materials was observed, greater reduction (more than an order of magnitude) was observed for boron implanted materials. In addition, reduction in the coefficient of friction for high-dose boron implanted materials was observed. Nano-indentation revealed a hardened layer near the surface of the material. Results from grazing incidence x-ray diffraction suggest the formation of Fe{sub 2}N and Fe{sub 3}N in the nitrogen implanted materials and Fe{sub 3}B in the boron implanted materials. Results from transmission electron microscopy will be presented

Thermo-Electric Detection of Early Fatigue Damage in Metals

There are numerous nondestructive inspection methods which can be used to detect and quantitatively characterize advanced fatigue damage following crack initiation. However, crack nucleation occurs at a much smaller microstructural scale following a more or less extended period of gradual material degradation which remains beyond the reach of known eddy current, ultrasonic, and other inspection methods. Before crack initiation, fatigue degradation remains an elusive process leading to distributed crystal defects on the scale of individual grains and grain boundary imperfections. This gradual evolution of early fatigue damage first results in increasing dislocation density, formation of slip bands, microplasticity, cold work, etc., then leads to crack nucleation at multiple sites. Following crack nucleation the growing microcracks ultimately coalesce into larger detectable fatigue cracks, but current NDE methods cannot detect the often quite serious preexisting fatigue damage in the material before this point

Microstructure et frottement d’un acier à roulement implanté d’ions azote

L’acier à roulement 100 C6 (1 % C, 1.5% Cr) est implanté d’ions azote (40 keV) sous diverses conditions de fluence et de température.Les microstructures obtenues sont étudiées par diffraction X sous incidence rasante. Cette analyse permet de mettre en évidence la formation de nitrures de type ε orientées différemment selon la température d’implantation. Cette température joue également un rôle sur le comportement en frottement et usure : les meilleurs résultats sont obtenus avec des traitements effectués entre 100 °C et 150 °C. L’usure se produit essentiellement par oxydation (frottement sec) et la diffraction X permet de différencier les comportements observés lors des essais

Characterization of TiN/B-C-N multilayers by transmission electron microscopy, ion beam backscattering, and low angle x-ray diffraction

The effects of Ar ion irradiation on the structure and stability of multilayered DC sputtered thin films of TiN/B-C-N have been studied. An increase of the bilayer repeat length to a maximum of 12.8% and departure of nitrogen from the film was observed indicating the interdiffusion between TiN and B-C-N layers. For the highest dose (5 {times} 10{sup 16} ions/cm{sup 2}) the multilayered structure partly disappears. The various mechanisms are discussed in terms of stress-driven diffusion and viscous flow of atoms