Tensile behavior of Ti-6Al-4V alloy fabricated by selective laser melting: effects of microstructures and as-built surface quality

Abstract

T i-6Al-4V is a typical α+β duplex-phase titanium alloy with outstanding specific strength, corrosion resistance and bio-compatibility, which has been widely applied in biomedical, aerospace, automotive, energy, chemical, and other industries [1] . However, the poor machinability and high cost of Ti-6Al-4V using a traditional processing route limit its more extensive application. Furthermore, the production of titanium alloy by conventional processing technology leads to Abstract: Selective laser melting (SLM) is a powerful additive manufacturing (AM) technology, of which the most prominent advantage is the ability to produce components with a complex geometry. The service performances of the SLM-processed components depend on the microstructure and surface quality. In this work, the microstructures, mechanical properties, and fracture behaviors of SLM-processed Ti-6Al-4V alloy under machined and as-built surfaces after annealing treatments and hot isostatic pressing (HIP) were investigated. The microstructures were analyzed by optical microscope (OM), scanning electron microscope (SEM) and transmission electron microscopy (TEM). The mechanical properties were measured by tensile testing at room temperature. The results indicate that the as-deposited microstructures are characterized by columnar grains and fi ne brittle martensite and the asdeposited properties present high strength, low ductility and obvious anisotropy. After annealing at 800-900°C for 2-4 h and HIP at 920°C/100MPa for 2 h, the brittle martensite could be transformed into ductile lamellar (α+β) microstructure and the static tensile properties of SLM-processed Ti-6Al-4V alloys in the machined condition could be comparable to that of wrought materials. Even after HIP treatment, the as-built surfaces could decrease the ductility and reduction of area of SLM-processed Ti-6Al-4V alloys to 9.2% and 20%, respectively. The crack initiation could occur at the columnar grain boundaries or at the as-built surfaces. The lamellar (α+β) microstructures and columnar grains could hinder or distort the crack propagation path during tensile tests.

The Relationship of Fracture Mechanism between High Temperature Tensile Mechanical Properties and Particle Erosion Resistance of Selective Laser Melting Ti-6Al-4V Alloy

“…It can be seen that the strength of 400-AC is significantly higher than that of AS. According to previous reports [23,24], the tensile strength can be improved by the precipitation of α phases in the grains or on the boundaries, and the residual stress is also reduced by a 400 °C heat treatment, so the strength of 400-AC is higher than that of AS. The β phases begin to precipitate, and the strength gradually decreases with increases in the heat treatment temperature, and the strength is similar to AS at 600 °C, but the strength at 800 °C is lower than that of AS because the α' phases are completely transformed into the α+β phases.…”

“…It can be seen that the strength of 400-AC is significantly higher than that of AS. According to previous reports [23,24], the tensile strength can be improved by the precipitation of α phases in the grains or on the boundaries, and the residual stress is also reduced by a 400 • C heat treatment, so the strength of 400-AC is higher than that of AS. The room temperature tensile properties of AS, 400-AC, 600-AC, and 800-AC are shown in Figure 7, with the mean value of the mechanical properties list in Table 4.…”

Microstructure, Mechanical Properties, and Constitutive Models for Ti–6Al–4V Alloy Fabricated by Selective Laser Melting (SLM)

“…The as-printed Ti-6Al-4V has considerably lower fatigue life with respect to the wrought material, which should be attributed to the residual stress, internal porosity, low surface quality, and microstructure [11]. To enhance the mechanical performance, various heat treatments [12,13] have been attempted to eliminate the residual stress and regulate the microstructure, hot isostatic pressing (HIP) [14] was applied to close the internal defects, and surface post-treatment [15] including shot peening, electro-polishing, sandblasting, and machining was adopted to decrease the surface roughness. After surface finishing and heat post-treatments such as HIP, the fatigue performance of SLM-deposited Ti-Al-4V could be equivalent to that of the wrought material.…”

“…ε vs. ln σ and ln . ε vs. σ according to Equations (12) and (13), respectively. The activation energy Q is the average of the slope of curves ln[sinh(ασ)] vs. Q/nRT and A was determined by the intercepts of these curves for a given strain rate according to Equation (14).…”

Particle Erosion Induced Phase Transformation of Different Matrix Microstructures of Powder Bed Fusion Ti-6Al-4V Alloy Flakes

“…Titanium alloys are widely applied in environments susceptible to erosion, including blades, turbines, and desalination pipeline [1]. Among them, Ti-6Al-4V is the most representative among the α + β titanium alloys [2,3], which possesses excellent specific strength, fracture toughness, corrosion resistance, and bio-compatibility [4]. However, its low thermal conductivity and high reactivity features, which result in its poor machinability characteristics, make it difficult to undertake further exploitation [5].…”