Abstract
Ti-6Al-4V (TC4) titanium alloy parts were successfully fabricated by laser melting deposition (LMD) technology in this study. Proper normalizing temperatures were presented in detailed for bulk LMD specimens. Optical microscope, scanning electron microscopy, X-ray diffraction, and electronic universal testing machine were used to characterize the microstructures, phase compositions, the tensile properties and hardness of the TC4 alloy parts treated using different normalizing temperature. The experimental results showed that the as-fabricated LMD specimens’ microstructures mainly consisted of α-Ti phase with a small amount of β-Ti phase. After normalizing treatment, in the area of α-Ti phase, the recrystallized length and width of α-Ti phase both increased. When normalizing in the (α + β) phase field, the elongated primary α-Ti phase in the as-deposited state was truncated due to the precipitation of β-Ti phase and became a short rod-like primary α-Ti phase. In as-fabricated microstructure, the β-Ti phase was precipitated between different short rod-shaped α-Ti phases distributed as basketweave. After normalizing treatment at 990 for two hours with subsequent air cooling, the TC4 titanium alloy had significant different microstructures from original sample produced by LMD. The normalizing treatment methods and temperature can be qualified as a prospective heat treatment of titanium alloy fabricating by laser melting deposition.
Highlights
Titanium alloys are widely used in aerospace and biomedical fields due to their high tensile strength and fatigue strength, low elastic modulus and density, high temperature performance, and good corrosion resistance [1,2,3]
The reason of weak diffraction peaks of the β-Ti phase is that the normalizing temperature in the single phase region of α-Ti phase has not got into the α + β phase region
Nearby the fusion line the optical microstructures of the as-deposited samples are coarse columnar
Summary
Titanium alloys are widely used in aerospace and biomedical fields due to their high tensile strength and fatigue strength, low elastic modulus and density, high temperature performance, and good corrosion resistance [1,2,3]. Laser melting deposition (LMD) is a rapid solidification forming technology based on layer-by-layer melting materials [10,11]. Heat treatment was widely conducted by many researchers to improve the mechanical properties of titanium alloy produced by LMD. Gerrit et al [24] reported the phase fraction and tensile properties of TC4 titanium alloys parts with extensive heat treatment temperatures via a laser melting deposition process. Their results indicate that the heat treatment can eliminate the residual stress and improve its mechanical properties [25]. The microstructure and mechanical properties of the original titanium alloy prepared by laser melting deposition and different normalizing conditions are compared. The formation mechanisms of tensile fracture under different temperatures were explored to improve the laser melting deposition in the future
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