High-performance Load-bearing Alloys

Abstract: The aim of this thesis is to study advanced metallic alloys as load-bearing componentsfor engineering and biomedical applications. The investigations have been focusing onthe improvement of the properties and performance of existing materials as well assynthesizing and developing completely new materials. This thesis covers alloy design,microstructure characterizations, mechanical and electrochemical tests, together withevaluating the tribocorrosion performances under the combined action of wear andcorrosion. The thesis consists of three parts:In part one (paper I and II), two types of multicomponent Ti-Fe-Sn-Nb alloys weredeveloped showing superior mechanical properties with distinct microstructures. Firstlythe hypoeutectic alloy consisting of ductile dendrites and ultrafine eutectic presentedsuperior yield strength and enhanced ductility compared to those of bulk metallicglasses (BMGs). Secondly, the β-type alloys completely retaining of β-Ti phasedisplayed outstanding plasticity without sacrificing the high mechanical strength.In part two (paper III), a series of Ti-based glassy alloys containing no biological toxicelements e.g. Ni, Cu and Al, were designed by a novel method coupling thermodynamiccalculations and topological instability criterion. A self-consistent thermodynamicdatabase was constructed based on the CALPHAD (Calculation of Phase Diagrams)approach. The experimental verifications matched reasonably well with the theoreticalcalculation, suggesting this method provides an effective approach for glass formingpredictions.In part three (paper IV and V), the degradation mechanisms of the load-bearing Zrbased BMGs were evaluated under the effects of tribological wear and electrochemicalcorrosion. Comparatively the tribo-electrochemical performances of the surfacemodified (plasma nitriding or diamond-like carbon) conventional metallic biomaterialsi.e. medical grade pure Ti, stainless steel and CoCrMo alloys, were investigated in linewith that of the BMGs.