Effect of Multiple Laser Shock Processing on Microstructure and Mechanical Properties of Ti-5Al-4Mo-4Cr-2Sn-2Zr Titanium Alloy

Abstract

Abstract The effects of the impact times and laser energy on the mechanical properties and microstructures of the Ti-5Al-4Mo-4Cr-2Sn-2Zr titanium alloy during multiple laser shock processing (LSP) were investigated. Residual stress and microhardness were tested on the samples to analyze the mechanical properties, and X-ray diffraction (XRD) and transmission electron microscope (TEM) observation was conducted to study micro-structural evolution. It's found that laser energy and impact number have an influence on the residual stresses and the hardness. Both the hardness and the residual stress of Ti-5Al-4Mo-4Cr-2Sn-2Zr titanium alloy have been improved, forming a severe plastic deformation layer, and increasing of impact number or laser energy will improve the amplitude and enhance affected depth. XRD tests of the specimen surfaces with different impacts and power density show that the positions of diffraction peaks do not change, but the Bragg diffraction peaks broaden. The TEM observation indicates that a layer of nanocrystalline with a size of 30∼60 nm has been fabricated on the surface of the titanium alloy after 3 impacts, and adopts random orientation. Dislocation activity is the main reason of the grain refinement for Ti-5Al-4Mo-4Cr-2Sn-2Zr titanium alloy.