Surface Modifications of a Ti6Al4V Alloy by a Laser Shock Processing

Abstract

The influence of the Laser Shock Processing (LSP) on the morphology, microstructure and surface layer properties of a Ti6Al4V alloy has been studied. Residual stresses were assessed as well. For the Laser Shock Processing a 1 KW, high-power Q-switched Nd:YAG laser was used. During the process the surface of the investigated material was covered by series of single, partially overlapping impulses. The laser power density was a 1 GW/cm 2 and a pulse duration of 18 ns. The microstructure and the phases presented in the surface layer of the treated material were analysed by optical, scanning and transmisssion electron microscopy as well as by X-ray diffractometry. The X-ray diffractometry was also use to determine the residual stresses. It has been found that the laser shock processing can cause plastic deformation and generate the compressive residual stresses into the treated surface of a Ti6Al4V alloy.

Laser modification of the materials surface layer – a review paper

“…The nanohardness values measured on the polished cross-sections showed that the hardness of the layer contained martensite and a high density of dislocations (approximately up to 0.5 mm) which was much higher (varied between 360 -480 nHV) than that of the matrix (290 nHV). Also the Young's modulus values of the investigated internal deformed surface layer (140 GPa) was slightly higher than that of the matrix (127 GPa)-as reference see [124,126].…”

“…Water decreases the expansion of plasma in the surrounding atmosphere and produces up to ten time's higher pressure on the material surface. The pressure propagating into the treated material as a shock wave can induce microstructural changes, cause a high increase of dislocation density, influence the surface roughness of the material as well as produce high residual surface compressive stresses [122][123][124][125]. If the surface is insulated from the increasing temperature by a protective absorbing layer, the laser treatment becomes purely mechanical.…”

“…When the shock wave generation occurs together with surface ablation and melting, the treatment becomes thermo-mechanical [123]. Rozmus-Gornikowska et al [124] examined the effect of the laser shock processing on microstructure, mechanical properties, residual stress level and roughness of the surface layer of a Ti6Al4V titanium alloy. The sample surfaces for the laser processing were prepared using the standard metallographic procedure of grinding and polishing.…”

“…Schematic representation of the laser shock processing (a) metal target with absorbing and water overlays (b) shock wave generation by laser beam after Ref. [124] The process was performed in an air atmosphere. Before laser processing, the Ti6Al4V alloy samples showed a homogeneous microstructure with very fine grains of α and β phases.…”

Fatigue life enhancement of high reliability metallic components by laser shock processing

“…Although the technique was initially developed for the improvement of the fatigue cracking resistance of materials used in the aeronautic applications (specifically Aluminum alloys), Titanium alloys and different types of stainless steels are being extensively investigated in the frame of different areas of application, especially the aerospatial sector itself but also in the nuclear, automotive and biomedical sectors on the basis of the commercial availability of new powerful laser sources able to provide intensities exceeding the GW/cm 2 level [5][6][7][8][9][10].…”