Fretting tribological performance of DLC, TiAlN and DLC/TiAlN coatings deposited on carburized 18CrNi4A steel

To improve the fretting wear performance of 18CrNi4A steel, DLC, TiAlN and DLC/TiAlN coatings were deposited on the surface of carburized 18CrNi4A steel, respectively. The microstructure morphologies, chemical compositions, and mechanical properties of these coatings were evaluated. The fretting tribological properties of pad/flat contact pairs for carburized 18CrNi4A steel, DLC, TiAlN and DLC/TiAlN coatings were investigated in different lubricant environments including dry sliding and #RIPP 7254 aviation grease. The results show that DLC, TiAlN and DLC/TiAlN coatings deposited on the carburized 18CrNi4A steel surface can improve surface roughness, hardness, fracture toughness and resistance to plastic deformation. DLC, TiAlN and DLC/TiAlN coatings deposited on the surface of carburized 18CrNi4A steel can make the surface of the substrate have excellent fretting wear properties. DLC and DLC/TiAlN coatings have lower coefficient of friction and better fretting wear resistance than TiAlN coatings in dry sliding condition, and DLC/TiAlN coatings have the lowest wear rate in #RIPP 7254 grease lubrication condition. In addition, the wear mechanisms of carburized 18CrNi4A steel, DLC, TiAlN and DLC/TiAlN coatings in dry sliding and #RIPP 7254 aviation grease conditions were analyzed.

Influence of the taper on the fretting wear of the femoral stem-femoral head taper junction in total hip prosthesis

Purpose The purpose of this paper is to study the roughness effect on the fixation of taper junction components and surfaces wear in terms of taper surface design. The roughness of the femoral heads’ taper and of the femoral stems’ trunnions can influence the fretting wear of the taper junction. Design/methodology/approach It was analysed whether a microgrooved taper surface of the femoral stem trunnion improves the fixation and reduces the wear rate at the taper junction of the hip prosthesis. Two models have studied: a femoral head with a smooth tapered surface combined with a microgrooved stem trunnion and a femoral head with a smooth tapered surface combined with a trunnion that had a smooth surface of the tapered. To compare the wear evolution between these two models, a computerised finite element model of the wear was used. Findings The results obtained after analysis carried out during millions of loading cycles showed that the depth of the linear wear and the total material loss were higher for the femoral heads joined with microgrooved trunnions. The main conclusion of this paper is that the smooth surfaces of the taper and of the trunnions will ensure a better fixation at the taper junction, and therefore, will reduce the volumetric wear rates. Originality/value A higher fixation of the taper junction will reduce the total hip prosthesis failure and, finally, it will improve the quality and durability of modular hip prostheses.

The Role of Stress–Strain State of Gas Turbine Engine Metal Parts in Predicting Their Safe Life

The influence of various factors on the workability of critical metallic parts of a gas turbine engine (GTE) is analysed and systematized. As shown, compressor blades fail as a result of foreign-objects’ damage, gas corrosion, and erosion. Compressor blade roots in most cases fail due to fretting wear caused by vibrations, while the fir-tree rim of turbine discs fails due to low-cycle fatigue (LCF) damage and creep. An increase in the radial gaps between the rotor and stator of the turbine reduces the thrust force and causes changes in the gas-dynamic loading of the engine components. Additional oxidation of metal parts is observed under the action of hot gases from the combustion chamber. The principles of material selection for manufacturing turbine blades and disks, concepts of alloying heat-resistant alloys, and modern methods of surface engineering due to applying protective oxidation-resistant coatings, in particular, chemical vapour deposition (CDV), physical vapour deposition (PVD), air plasma spraying (APS), etc., are also described. To predict the lifetime of turbine disks, it is proposed to use the modified Walker model and Miner’s rule. To specify the time before the failure of the metal blades of the turbine, it is proposed to use the finite element method. To monitor the working-surfaces’ deformations of the gas turbine engine, it is recommended to use optical-digital methods.