ON THE DISCONTINUOUS YIELDING PHENOMENA OBSERVED IN A NB-TI-AL ALLOY

Alloys based on niobium have many attractive mechanical properties whi ch make them candidate materials for use in high-temperature corrosive environments. In this work, alloys containing additions of titanium a nd aluminum have been studied since these elements provide improved ox idation resistance and lower density. This paper describes the discont inuous yielding phenomena which are observed in Nb-40Ti-15Al. A yield- point is seen after aging at intermediate temperatures, and serrated y ielding is seen on tensile testing at various temperatures. Various ex periments are described which indicate that a Portevin-Le-Chatelier-ty pe effect occurs in this alloy. Evidence will be presented from which it is argued that this serrated yielding is caused by the dynamic prec ipitation and dissolution of the omega-phase. (C) 1998 Published by El sevier Science Limited. All rights reserved.