Nanocrystallization in the Duplex Ti-6Al-4V Alloy Processed by Multiple Laser Shock Peening

Abstract

Laser shock peening of titanium alloys has been widely applied in the aerospace industry. However, little is known of the nanocrystalline formation characteristics and mechanisms. In this investigation, a nanocrystalline layer was formed in the duplex Ti-6Al-4V titanium alloy surface region by means of multiple pulsed laser shock peening (LSP). The phase transition and residual stress characteristics of LSP samples were analyzed with X-ray diffraction (XRD) and scanning electron microscopy (SEM). Transmission electron microscopy (TEM) was used to characterize the microstructure and morphologies. As the number of laser pulses increased for each location, higher grain refinement was observed. Micro-hardness testing showed that hardness increased with the number of pulses delivered to each location due to the formation of nanocrystalline layers and high dislocation density in the samples, and a gradient variation of the micro-hardness was obtained. In addition, mechanical twins and different dislocation configurations were formed in the α phase region while only dense dislocation tangles were observed in the β phase region after multiple laser pulse impacts.

Laser Shock Processing on Metal

“…An example is shown here by Zhou et al [3] of microstructural modifications at the nanoscale range obtained on a Ti-6Al-4V (α + β) titanium alloy. Using the Scherrer-Wilson method for analyzing X-ray diffraction peak broadening, microstrains and average grain sizes of laser-peened diffracting zones were estimated and subjected to TEM microstructural observations.…”

“…They provide interesting insights into the beneficial effects of temperature on laser-shock-induced plastic deformations. Considering LSP temperature ranges up to 160 • C and a 6061 (Al0.9Mg0.6Si) alloy, warm laser peening (WLP) trials were carried out with 2 mm diameter impacts, a 50% overlap, and a glass confining medium [3]. Such WLP trials evidence a 20% decrease of surface compressive stresses, but deeper affected layers and large hardening effect (up to +55% HV for a WLP at 130 • C).…”

“…The following fields are covered in the seven selected papers: materials' behavior and phase transformations under high strain rate (Amadou et al [1]), new loading conditions with ultra-short pulses (Petronic et al [2]) surface modifications induced by laser peening including recrystallization effects (Zhou et al [3]) and warm laser peening (Huang et al [4], Chen et al [5]), and novel applications of LSP such as water droplet erosion resistance (Gujba et al [6]) or impact spot welding (Liu et al [7]). The wide variety of topics related to LSP highlights the extraordinary dynamism and enthusiasm of the growing international LSP community.…”

Improvement of Damping Property and Its Effects on the Vibration Fatigue in Ti6Al4V Titanium Alloy Treated by Warm Laser Shock Peening

“…This generally results in high residual tensile stress on the surface [2,3], which is not conducive to the improvement of fatigue life. Laser shock peening at room temperature (RT-LSP) has been proved to be an effective technology to improve the fatigue resistance of materials by the high compressive residual stress (CRS) [4,5].…”

Impact-Sliding Tribology Behavior of TC17 Alloy Treated by Laser Shock Peening

“…These materials commonly exhibit excellent properties, such as high strength to weight ratio, excellent toughness, and outstanding corrosion resistance [1,2]. TC17 titanium alloy has been widely used to manufacture aero-engine fans, compressor disks, jetengine blades, and other important parts of advanced aircrafts [3,4].…”