The Friction and Wear Behaviours of Inconel 718 Superalloys at Elevated Temperature

Machine parts made of nickel-based alloys usually work in high-temperature service environments such as aircraft turbines. The mechanical properties and antioxidant properties of materials tend to be reduced at high temperatures. Therefore, it is of great practical significance to reveal the wear mechanisms of materials at different temperatures. In the present investigation, the tribological behaviour of an Inconel 718 superalloy at different temperatures was investigated. First, the coefficient of friction curves obtained under different test conditions were analysed in detail to illustrate the dynamic change process of friction at high temperature. Next, the morphology of the wear surface, surface morphology of friction pairs and material transfer during friction were analysed via scanning electron microscopy 3D morphology and energy dispersive spectroscopy measurements to reveal the wear mechanisms of materials in a high-temperature environment. Finally, the microstructure of the cross section of the wear tracks was analysed by using optical microscopy electron back-scattered diffraction etc., to clarify the mechanisms of crack initiation and material removal. The results show that the friction properties of the Inconel 718 superalloy have differences at different test temperatures. Although increasing the test temperature does not necessarily aggravate the wear of the material, the oxidation of the wear surface during the friction process significantly increases. In addition, when the contact load increases, the thickness of the oxide layer and wear of the material simultaneously increase.

Basic Bio-Tribological Performance of Insulating Si3N4-Based Ceramic as Human Body Replacement Joints

The paper presents an in-depth study of the bio-tribological performance on silicon nitride matrix ceramic composites containing hexagonal boron nitride (hBN) with different content. Ultra-high molecular weight polyethylene (UHMWPE) under simulated body fluid lubrication, and the simulated body fluid-lubricated sliding tests were performed on a universal friction and wear tester. The results showed that the incorporation of hBN into silicon nitride matrix reduced the friction coefficients from 0.27 for Si3N4/UHMWPE pair to 0.16 for Si3N4-20%hBN/UHMWPE with full immersion in simulated body fluid lubrication. Scanning electron microscopy (SEM), laser scanning microscope, X-ray photoelectron spectroscopy (XPS) were utilized to characterize the wear surface. The analysis results indicated that, with simulated body fluid lubrication, the interfacial between hBN and Si3N4 facilitated the wear pits to form on the wear surface, and the residual wear particles deposited in the pits. Then, tribochemical products were formed on the wear surface, which protected and smoothed the wear surface of the sliding pair in the simulated body fluid.

Selected Methods and Applications of Anti-Friction and Anti-Wear Surface Texturing

The constant development of environmental protection causes the necessity to increase the efficiency of machines. By increasing the efficiency of machines, energy losses can be limited, leading to lower energy consumption. Friction reduction leads to an increase in efficiency and a decrease in wear. In this paper, selected surface texturing methods, such as burnishing and abrasive jet machining, with their limitations are presented. Thanks to those processes, various surface textures can be obtained. Examples of applications of these methods for friction and wear reduction are shown.

Analysis of Wear Resistance of Borided Steel C45

The wear resistance of diffusion coatings in conditions of specific pressures of 3, 7 and 10 MPa was studied. The boride coatings were prepared by means of diffusion methods using C45 steel as the substrate material. Research on the microstructure and redistribution of chemical elements on wear surface of a borided layer was carried out. It was found that the boride coatings should be used under a specific pressure of 7 MPa. It was found that the wear of friction couple coating of steel C45 under specific pressure of 3 MPa proceeds according to the oxidation wear mechanism, while under specific pressures of 7 and 10 MPa the abrasive wear prevails. The wear-induced segregation of atoms in coatings was studied using secondary mass-spectroscopy method (SIMS). Increased C, O, and B concentrations were noticed at the wear surface on depth from 50 to 2000 Å. The secondary wear-induced structure formation on the wear surface resulted in high wear resistance of diffusion borided coatings.