Tribological Behavior of Stellite 720 Coating under Block-on-Ring Wear Test

Stellite 720 is a high-carbon Co-Cr-Mo alloy, designed for severe wear/corrosion environments. This article presents a study of the Stellite 720 coating on stainless steel 304 under block-on-ring wear test. The coating is deposited through a slurry/powder metallurgy sintering process. Micro-hardness indentation test is conducted on the cross section of the coating specimen to investigate the hardness of individual phases of the coating material and the dilution effect of the substrate material on the coating layer. The tribological behavior of the coating under low and high load wear is investigated. The worn surfaces of the coating specimens are analyzed using a Philips XL30S FEG scanning electron micro- scope (SEM) with an EDAX energy dispersive X-ray (EDX) spectroscopy system. The experimental results are discussed to explore the wear mechanisms of the Stellite 720 coating under block-on-ring wear.

Flow-Field of an Axisymmetric Lobed Mixer

The flow-field of a fuel/air mixing system with an axisymmetric lobed mixer was numerically investigated. Large-scale streamwise vortices are formed immediately downstream of the mixer trailing edge, stretched further downstream, and finally broken into fragments where more intense mixing occurs. Both numerical and experimental results indicate that the length required for streamwise vortices breakdown in the confined flow-field of an axisymmetric lobed mixer is much shorter than that in the case of planar lobed mixers subject to parallel freestreams. For the conditions studied, the streamwise vortices start to breakdown at three wavelengths downstream of the mixer trailing edge.

Analytical modeling of oxide thickness variation of metals under high temperature solid-particle erosion

The paper presents a study of model development for predicting the oxide thickness on metals under high temperature solid-particle erosion.The model is created based on the theory of solid-particle erosion that characterizes the erosion damage as deformation wear and cutting wear,incorporating the effect of the oxide scale on the eroded surface under high temperature erosion.Then the instantaneous oxide thickness is the result of the synergetic effect of erosion and oxidation.The developed model is applied on a Ni-based Al-containing(Ni–Al)alloy to investigate the oxide thickness variation with erosion duration of the alloy at high temperatures.The results show that the thickness of the oxide scale on the alloy surface increases with the exposure time and temperature when the surface is not attacked by particles.However,when particles impact on the alloy surface,the oxide thickness is reduced,although oxidation is continuing.This indicates that oxidation does not benefit the erosion resistance of this alloy at high temperatures due to the low growth rate of the oxide.

Modeling study of solid-particle erosion with consideration of particle velocity dependent model parameters

An advanced erosion model that correlates two model parameters—the energies required to remove unit mass of target material during cutting wear and deformation wear,respectively,with particle velocity,particle size and density,as well as target material properties,is proposed.This model is capable of predicting the erosion rates for a material under solid-particle impact over a specific range of particle velocity at the impingement angle between 0◦and 90◦,provided that the experimental data of erosion rate for the material at a particle velocity within this range and at impingement angles between 0◦and 90◦are available.The proposed model is applied on three distinct types of materials:aluminum,perspex and graphite,to investigate the dependence behavior of the model parameters on particle velocity for ductile and brittle materials.The predicted model parameters obtained from the model are validated by the experimental data of aluminum plate under Al2O3 particle impact.The significance and limitation of the model are discussed;possible improvements on the model are suggested.