A study on the erosion and erosion-oxidation of metal matrix composites
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Doctoral thesis (monograph)
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Date
2003-10-31
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Mcode
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en
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108, [2]
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Abstract
The potential of metal matrix composites (MMCs) as new generation erosion and erosioncorrosion resistant materials is investigated. As a type of wear attack, erosion involves destructive impact of free-moving particles on a solid. The high-strain-rate and hence adiabatic deformation conditions that the target surface experiences during erosion are often the reasons behind the poor correlation of erosion rate with static mechanical properties of the targets, imparting difficuties on erosion study. On the other hand, a good correlation exists between erosion rate and the thermophysical properties of the target. This, however, suggests limited possibilities of enhancing erosion resistance on a monolithic alloy. A literature study at the beginning elaborates the complex of erosion as a physical phenomenon, and lies the theoretical base for the experiment. In the experiment, nickel-chromium superalloy- and heat resistant steel-based composites are manufactured through a powder metallurgy route. Ceramic particles are added at different volume fractions as the reinforcements. Efforts are made to optimise the powder mixing and powder consolidation procedures to ensure a homogeneous microstructure and full densification of the final composites. Two types of erosion tester are used in the study: a centrifugal erosion tester is for the erosion tests at room temperature, and a gas-blast erosion tester is for the erosion-oxidation tests at high temperature. With the gas-blast tester, both the temperature and oxygen concentration is controlled to simulate real application situations. The discussion is focused on the tests under a 60° angle of impact. Optical and SEM (scanning electron microscopy) observations are carried out on the eroded surfaces to assess the damage pattern and general behaviour of the studying composites. Meanwhile, on cross-sectioned specimens the bonding and material dissolution at the matrix/reinforcement interfacial regions and the deformation situation at the sub-surfaces are examined by EDS (energy dispersion spectroscopy) and microhardness measurements to reveal the erosion mechanisms of the composites. The experimental results suggest that the strain localisation mode is valid in describing erosion process of a ductile metal, but may need modifications when applying to MMCs. The erosion response of a MMC system is determined by not only the internal parameters of the composites, but also external factors involving all parameters of erosion. In addition, this study provides useful guidelines to the selection of composite systems having high erosion resistance for industrial applications and to the future study as well.Description
Keywords
MMC, metal matrix composites, erosion, erosion-corrosion, reinforcement, erosion-oxidation, room temperature, high temperature