Assessment of Mechanical Property Gradients after Impact-Bases Surface Treatments using Nano-Compression Testing

Author:  D. Tumbajoy-Spinela, c, X. Maederb, J. Michlerb, S. Descartesc, J.M. Bergheaud, V. Lacaillee, C. Langladef, G. Kermouchea*
Source:  ICSP-13
Doc ID:  2017032
Year of Publication:  2017
Abstract:  
Introduction: Mechanical surface treatments are known to improve wear and fatigue resistance of metallic materials. In the case of conventional impact treatments (shot-peening [1]-[2], SMAT [3]), the surface is exposed to repeated mechanical loadings, producing near-surface severe plastic deformation (SPD). It leads to a local progressive refinement of the microstructure [2]-[3], commonly known as tribologically transformed structure (TTS) [4], and thus to a graded in-depth strengthening. Micro-percussion testing [5]-[6] appears to be an interesting model case scenario to emulate these conventional treatments and go further on micro-structural and mechanical characterization. For this technique, every impact is made at the same position by a rigid conical indenter, controlling the number, angle and velocity of each impact. The aim of this paper is to describe and compare the mechanical and micro-structural gradients resulting of these two treatments. More precisely, three main goals are considered: (i) characterize the transformed surfaces; (ii) quantify the mechanical gradient in-depth by the means of local micro-mechanical testing (micro-pillar compression [7]-[8]); and (iii) compare both impact treatment effects evaluating the possibility to emulate industrial techniques with micro-percussion. This investigation is carried out using a pure α-iron.