Reflections on creep: A review of the mst archive

Abstract

Amongst many themes embedded in Materials Science and Technology (MST), the phenomenon of creep has remained a significant component, seamlessly continuing from the journals through which MST was directly descended. The Journal of the Iron and Steel Institute (JISI), from its founding in 1869, recorded procedures to manufacture steels to withstand arduous conditions to improve the performance of furnaces and engines. The problem of creep was identified and its exploration included its occurrence in non-ferrous metals and alloys with results on these published in the Journal of the Institute of Metals (JIM). The sensitivity of creep to materials' processing as well as to chemical composition was soon apparent. The brief commentary here outlines some of the main features in this area as reported by the successive line of journals, but it gives no more than a taste the wealth of information, ideas and proposals they contain.Early studies were necessarily empirical but became more focused by progressively controlling parameters that led to variable results. The shape of the strain versus time curve at constant uniaxial stress and temperature was a prominent consideration with formulae proposed for its description. 1 Such attention has continued with increasing sophistication 2 aided by the data processing power of computers. Experimental results and the capability of their extrapolation are vital ingredients in attempting to make realistic prediction of long term behaviour to times greatly in excess of those feasible in laboratory testing. Within relatively narrow ranges of material composition and microstructure and of imposed conditions such efforts have made valuable progress but the high sensitivity of the creep process to both internal and external variables indicates that unique relationships to cover a wider range of conditions are unlikely to emerge in a simple, precise and accurate form.Many contributions have aimed at interpretation of creep behaviour. [16][17][18][19] These were aided by substantial support for basic scientific research in the post-war years that encouraged studies 20-24 on metals with well characterised microstructures and accurately known levels of impurity. Much of this work was nevertheless driven by practical and commercial needs, urgently seeking data and better understanding of the behaviour of materials under severe conditions and in entirely new environments such as those inherent in nuclear power generation. Papers concerned with these areas have necessarily invoked extensive understanding of broad areas of metallurgy. As well as enhancing surface reactions, elevated temperatures allow precipitates to coarsen, grain boundaries to migrate and shear, impurities to segregate, dislocations to climb as well as glide, vacancies to be created, diffuse, condense and be absorbed.