Elevated temperature erosion studies on some materials for high temperature applications

Abstract

<p>The surface degradation of materials due to high temperature erosion or combined erosion-corrosion is a serious problem in many industrial and aeronautical applications. As such, it has become an important design consideration in many situations. The materials investigated in the present studies are stainless steels, Ti-6Al-4V, alumina ceramics, with and without silicate glassy phase, and zirconia. These are some of the potential materials for use in the high temperature erosive-corrosive environments;The erosion or erosion-corrosion experiments were performed in a high temperature sand-blast type of test rig. The variables studied included the temperature, material composition, heat treatment condition, impingement velocity and angle, erodent concentration, etc. The morphological features of the eroded or eroded-corroded surfaces, substrate deformation, and oxide characteristics were studied by optical and scanning electron microscopy, X-ray diffraction, energy dispersive X-ray spectroscopy, thermogravimetric analysis. The scratch test, single ball impact, and indentation tests were used to understand the behavior of oxide film in particle impacts;Based on these investigations, the understanding of the mechanisms involved in the mechanical or combined mechanical and chemical actions in erosion was developed. The analysis focused on the interactions among factors such as the temperature-dependent properties of materials, microstructure including the role of multiple phases in ceramics, high temperature erosion characteristics, cracking fracture of ceramics, oxidation rate, and the composition, structure, and properties of oxide scales. The enhanced corrosion rate from erosion damage, the effect of corrosion on material mass loss, and enhanced erosion rate at high temperatures were interpreted in terms of the above factors;This dissertation is composed of five major parts which present various aspects of high temperature erosion and erosion-corrosion based on the investigations on the three kinds of materials for high temperature applications;PARTS I and II are the investigations of high temperature erosion-corrosion behavior of ferritic, austenitic, martensitic and precipitation hardening stainless steels. PART III deals with SEM studies of the material damage in alumina ceramics by single and multiple particle impacts. PART IV extends the above studies on alumina ceramics to high temperature environment. PART V covers the high temperature erosion-corrosion behavior of Ti-6Al-4V. In contrast to other materials studied in this thesis, the titanium alloy undergoes rapid oxidation at elevated temperatures.</p>