Cyclically induced grain growth within shear bands investigated in UFG Ni by cyclic high pressure torsion. Issue 23 (25th July 2017)

• Record Type: Journal Article
• Authors: Kapp, Marlene Walpurga; Renk, Oliver; Leitner, Thomas; Ghosh, Pradipta; Yang, Bo; Pippan, Reinhard
• Is Part Of: Journal of materials research. Volume 32:Issue 23(2017)
• Page Start: 4317
• Page End: 4326
• Publication Date: 2017-07-25
• Subjects: nanostructured, -- fatigue, -- structural; Materials -- Research -- Periodicals; 620.1105
• DOI: 10.1557/jmr.2017.273
• Languages: English
• ISSNs: 0884-2914

Abstract

Abstract: Abstract : Structural instabilities of nanocrystalline and ultrafine-grained (UFG) materials have been recognized as a major challenge during cyclic loading, especially in the low cycle fatigue regime. Although a severe deterioration of the mechanical properties has been reported during cyclic deformation, quantification of the softening portion solely due to grain coarsening was not possible. It will be demonstrated that cyclic high pressure torsion (CHPT) is a versatile method to enable direct measurement of the impact of grain coarsening on cyclic softening, as failure of the sample is prevented. Here, CHPT experiments have been performed on 99.99% UFG nickel. Grain coarsening similar to conventional uniaxial fatigue experiments was observed and could be studied up to large cyclic accumulated macro strains of 50. The correlation of electron back scatter diffraction images with microhardness measurements facilitated quantification of the cyclic softening as a consequence of grain growth for the very first time. Further, structural investigations revealed distinctly enhanced grain coarsening within shear bands. Thus, the cyclic strain seems to be the most important parameter controlling mechanically driven boundary migration during cyclic loading at low homologous temperatures.