Laser shock peening of Ti-17 titanium alloy: Influence of process parameters

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2012, Vol.532, p.362-372
• Main Authors: Cellard, C., Retraint, D., François, M., Rouhaud, E., Le Saunier, D.
• Format: Article
• Language: English
• Subjects: Applied sciences; Curvature; Design of experiments (DoE); Engineering Sciences; Exact sciences and technology; Hardness; Incremental hole drilling; Lasers; Metals. Metallurgy; Peening; Polishing. Blast cleaning; Process parameters; Production techniques; Residual stress; Roughness; Surface treatment; Titanium base alloys; Work-hardening; X-ray diffraction
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2011.10.104

► Laser shock peening parameters studied through a design of experiments. ► Laser fluence, pulse duration, number of impacts and sample thickness are studied. ► The observed work hardening is low, the roughness is lightly affected. ► A significant part of hardness increase is due to compressive residual stresses. ► High tensile residual stresses can appear on thin laser shocked specimens. The influence of the process parameters of laser shock peening was investigated on specimens made of an aeronautic titanium alloy: Ti–5Al–2Sn–2Zr–4Cr–4Mo (Ti-17). In order to quantify the effect of relevant process parameters, an experimental design was carried out. It is based on a full factorial design with four factors (laser fluence, pulse duration, number of impacts and thickness of the sample) and two levels for each factor. The process is characterised with the following variables: the depth of the impacts, the roughness of the treated surface, the hardening of the material (itself evaluated with the hardness and X-ray diffraction peak width), the residual stresses left in the sample and the global curvature of the sample. It is found that all the parameters have an influence on the residual stresses and that laser shock peening has no influence on roughness and low influence on work-hardening. The variables are then analysed in order to evaluate correlations. The increase in hardness is found to be essentially due to compressive residual stresses, cold work-hardening having only a small effect. In thin specimens, the stress redistribution due to self-equilibrium leads to tensile residual stresses at the treated surface and to large deformations of the specimens.