Experimental study by pyrometry of Portevin-Le Ch(a)over-captelier plastic instabilities - Type A to type B transition

The dynamic strain aging phenomenon which occurs in some materials under certain temperature and strain rate conditions can cause a localization of the plastic strain in the form of Portevin-Le Ch (a) over cap telier (PLC) bands. According to the strain rate and the temperature, the spatiotemporal pattern of these bands changes and three main types of band are identifiable (types A-C). The increment of plastic strain associated with each band causes an increment in temperature which can be measured by infrared pyrometry. This experimental technique was used in this paper to study the PLC phenomenon in an aluminium-copper alloy at ambient temperature and to visualize the strain localization patterns. Some characteristics of these bands are measured: bandwidth, slope angle, increment of plastic strain in the band, time between two band formations, time of band formation, propagation velocity of the bands, band spacing... The evolution of these characteristics according to the strain enables us to suggest an explanation of the type A-type B transition. (C) 2007 Elsevier B.V. All rights reserved.