Abstract
Mechanical properties, such as residual stress, micro-hardness and fatigue performance, of the Ti-5Al-4Mo-4Cr-2Sn-2Zr titanium alloy were improved via the laser peening without coating (LPwC) with a water-penetrable wavelength of 532 nm and pulse duration of 10 ns. In this paper, three kinds of laser energy, namely 85, 110 and 160 mJ were used to process the samples. The titanium alloy samples were also peened with different impact times (1, 3 or 5 impacts) at the energy of 85 mJ. The micro-hardness and residual stress distribution results provided that LPwC can introduce compressive residual stress (CRS) and also induce hardening of the target materials. Further, micro-hardness and CRS showed the increasing trends when the laser impact times increased. However, the CRS and micro-hardness decreased while the laser energy increased from 110 to 160 mJ, which was attributed to the dynamic equilibrium between the thermal and mechanical effects of LPwC. High cycle fatigue strength of the titanium alloy was significantly improved from 360 to 490.3 MPa after three impacts LPwC. The strengthening mechanism of fatigue strength subjected to LPwC was a combined effect between the laser-induced CRS and the high-density dislocations.
Highlights
Ti-5Al-4Mo-4Cr-2Sn-2Zr titanium alloy, named as Ti-17, has been widely used as compressor fan blades and blisks in the aero-engine due to its excellent mechanical and physical properties such as high strength-to-weight ratio, light weight and good toughness as well as excellent corrosion and wear resistance [1,2,3,4]
As a new technique Laser peening without coating (LPwC) is that developed by Mukai et al in based on the conventional laser shock peening (LSP) [15]
The results revealed that the surface residual stress was compressive for all the specimens after LPwC
Summary
Ti-5Al-4Mo-4Cr-2Sn-2Zr titanium alloy, named as Ti-17 (service temperature ≤400 ◦ C), has been widely used as compressor fan blades and blisks in the aero-engine due to its excellent mechanical and physical properties such as high strength-to-weight ratio, light weight and good toughness as well as excellent corrosion and wear resistance [1,2,3,4]. Umapathi and Swaroop [32] investigated the effect of different laser power density and different peening times on the microstructure and residual stress as well as micro-hardness distribution of TC6 titanium alloys. To the best of our knowledge, the present work is the first study to report the effect of LPwC with different laser energies and impact times on the mechanical properties as well as microstructures of Ti-5Al-4Mo-4Cr-2Sn-2Zr dual phase titanium alloy. Motivated by the above observations, the influence of LPwC with different laser parameters (impact times and laser energy) on the mechanical properties, like micro-hardness and residual stress distribution as well as the high cycle fatigue strength, will be explored in this work. This work can be utilized to optimize the laser processing parameters so as to enhance the mechanical properties of titanium alloy and extend the applications of titanium alloy in various fields
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