Abstract
Laser shock peening (LSP) is an innovative surface treatment process with the potential to change surface microstructure and improve mechanical properties of additively manufactured (AM) parts. In this paper, the influences of LSP on the microstructure and properties of Ti–6Al–4V (Ti64) titanium alloy fabricated via selective laser melting (SLM), as an attractive AM method, were investigated. The microstructural evolution, residual stress distribution and mechanical properties of SLM-built Ti64 samples were characterized before and after LSP. Results show that the SLM sample was composed of single hcp α’ phase, which deviates from equilibrium microstructure at room temperature: α + β phases. The LSP significantly refines the grains of α’ phase and produces compressive residual stress (CRS) of maximum magnitude up to −180 MPa with a depth of 250 μm. Grain refinement of α’ phase is attributed to the complex interaction of dislocations and the intersection of deformation twinning subjected to LSP treatment. The main mechanism of strength and micro-hardness enhancement via LSP is ascribed to the effects of CRS and α’ phase grain refinement.
Highlights
Ti–6Al–4V (Ti64) alloy is a low density, α + β dual-phase titanium alloy, which exhibits high strength, excellent corrosion resistance and bio-compatibility, and is applied in the aerospace, biomedical and automotive industries [1,2]
But no obvious cracks were observed in the Ti64 samples
3a, which deviates from equilibrium microstructure at room β phase exists, as shown in Figure 3a, which deviates from equilibrium microstructure at room temperature: phases.Such
Summary
Ti–6Al–4V (Ti64) alloy is a low density, α + β dual-phase titanium alloy, which exhibits high strength, excellent corrosion resistance and bio-compatibility, and is applied in the aerospace, biomedical and automotive industries [1,2]. The unique conditions in the SLM process lead to coarse grain size and tensile residual stress (TRS) [7,8]. Laser shock peening (LSP) is an innovative post-processing technology, which adopts a high power laser with short pulses to apply on the material surface to produce compressive residual stress (CRS) [12]. Guo et al [17] reported that the tensile strength of Ti64 alloy parts constructed via wire arc AM was improved with LSP. Some important issues, such as stress state, surface roughness and microstructure evolution and their effect on mechanical properties of AM metallic parts treated via LSP, are still pending. The microstructure evolution, residual stress, micro-hardness and tensile strength of SLM-manufactured Ti64 alloy before and after LSP were analyzed. This study will promote the applications of the SLM-manufactured titanium alloy parts
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