This study presents the investigation on how heat treatment parameters, which are temperature, cooling method, and residence time, influence the microstructural and hardness properties of Ti6Al4V components produced on Ti6Al4V substrate using high speed selective laser melting technique. Heat treatment was performed on the produced samples before they were characterized for microstructure and hardness. The microstructure of the as-built sample contained large columnar β-grains that were filled with martensite α’ phase and had a high hardness of 383 ± 13 HV. At 1000 °C and residence time of maximum 4 h, better heat treatment parameters were seen for the selective laser melting (SLM) produced Ti6Al4V sample since an improved lamellar α + β microstructure was obtained at this condition. This microstructure is known to have improved tensile properties.

This work presents the microstructural investigation of an in situ synthesized TiB/Ti6Al4V-ELI composite that was manufactured with additive manufacturing (AM) technique known as laser metal deposition (LMD). A single-track sample was manufactured by adding TiB₂ to Ti6Al4V-ELI at mass deposition volume of 5% and characterized for microstructure and hardness. It was found that in situ reaction promoted the formation of quasi-continuous network microstructure of TiB whiskers with a needle-like morphology, in a martensitic α′ matrix. Furthermore, the manufactured TiB/Ti6Al4V-ELI presented two different grain growth morphologies, with smaller and large TiB network grains observed at the top and bottom of the sample, respectively, due to heat travelling direction. A high hardness of 513 HV was observed at the top of the sample, which was reduced to 483 HV at the bottom, promoted by grain growth. Graphical abstract

This study investigated the effect of in-situ alloying of Ti6Al4V and TiB₂ during laser metal deposition for microstructure, hardness and tensile properties enhancement. It was found that the addition of TiB₂ at powder feed rates of range 0.1–0.3 rpm resulted in the formation of TiB whiskers with columnar and equiaxed network morphologies, in a lamella α + β matrix. By increasing TiB₂ at 0.4–0.5 rpm, a complete dissolution of the equiaxed and columnar network morphologies were achieved. The dissolution led to a random distribution of formed TiB whiskers, resulting in enhanced hardness and ultimate tensile strength (UTS), with the 0.5 rpm giving the highest hardness and UTS values of 511 ± 13 HV and 1745 MPa, respectively.

This study presents the investigation of the influence of heat treatment on microstructure, hardness and tensile properties of high-speed selective laser melted Ti6Al4V components. Heat treatment was performed to obtain an improved microstructure with enhanced hardness and tensile properties. It was found that the acicular martensitic α′ structure on the as-built sample lead to high hardness, yield strength and ultimate tensile strengths of 389±10 HV0.3, 949 ± 10 MPa and 1045 ± 3 MPa, respectively,with a low ductility of 5%. Heat treatment transformed the martensitic α′ structure into lamella α + β phases, with heat treatment at 1000 °C resultingin the most improved hardness and ductility from 389 ± 10 HV0.3 and 5% to 325 ± 20 HV0.3 and 13%, and a decrease in yield and ultimate tensile strength from 949 ± 10 MPa and 1045 ± 13MPa to 835 ± 11 MPa and 911 ± 5 MPa, respectively.

This study presents the investigation of TiB distribution characteristics on the microstructure of in-situ synthesized TiB/Ti6Al4V single-track composites manufacture with laser metal deposition. Ti6Al4V alloy was reinforced by adding TiB₂ceramic at mass volumes of 0%, 1% and 2% for microstructure modification and mechanical properties enhancement. The TiB/Ti6Al4V composite was characterized using optical microscope (OM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD) and microhardness. It was found that the addition of TiB₂resulted in the transformation of the prior β-grain into two types of morphologies of dendritic and columnar microstructures. Furthermore, the increase in the amount of TiB₂resulted in the reduction of the volume fraction of β-Ti phase, with the in situ formed TiB replacing and occupying the β-Ti positions. Deposition at 2% promoted the formation of unmelted TiB₂particles which promoted hardness increase to 496 ± 17 HV.