Tensile Properties and Microstructures of Laser-Formed Ti-6Al-4V

Abstract

The room temperature tensile properties of Ti-6Al-4V alloy prepared under two different processing routes were evaluated and compared. One group of samples was prepared by conventional casting-forging-rolling into flat plates. The other group was prepared by using TritonÕs Laser Free-Form Fabrication (LF3)Ô processes, i.e., a laser was used to melt pre-alloyed powders of the required metallic composition as they were dropped onto a moveable substrate programmed to move in such a manner as to form a solid alloy plate. Five populations of Ti-6Al-4V were evaluated: a standard wrought form, an as-deposited form, a machined as-deposited form, a heat-treated as-deposited form, and a machined as-deposited and heattreated form. The poorest mechanical properties occurred with the rough surfaces, likely due to existing microcracks and stress concentrations. The LF3Ô as-deposited material had mechanical properties comparable to, if not higher than, the mechanical properties of the wrought material. Further evaluations of the laser-formed material for complex spacecraft piece parts were warranted, specifically in regards to improving the surface finish of the materials.

Microstructure and Texture of Ti‐6Al‐4V Direct Laser Deposits

“…It has been reported in welding processes that significant variant selection can occur due to the thermo-mechanical stresses resulting from welding [17], as DLD is a similar process to welding it seems likely that similar thermomechanical stresses and therefore variant selection could occur under certain deposition conditions. Tensile fracture analysis Direct laser deposition of Ti-6Al-4V has been shown by other studies to produce comparable or better mechanical properties than that of wrought or forged Ti-6Al-4V [5,7,8]. Similarly in this study a marked increase of 20% in the UTS and 0.2% proof strength has been produced over wrought Ti-6Al-4V.…”

“…In both reported cases the heat treatment was 950-980 C followed by furnace cooling. This heat treatment procedure has shown in both cases to cause a marked coarsening effect on the Widmanstätten microstructure and by Alcisto et al [7], a minimising of porosity which they attributed to the increased ductility. Lutjering [6] presents data that indicates an optimum cooling rate for Widmanstätten microstructures, increasing cooling rates beyond this causes a rapid ductility reduction.…”

“…Heat treatment, in the + region of the phase diagram, of deposited Ti-6Al-4V structures has been shown to increase the ductility [7,8]. In both reported cases the heat treatment was 950-980 C followed by furnace cooling.…”

“…Deposition of Ti-6Al-4V has been shown to produce an anisotropic component evaluated through tensile testing; this has mainly been attributed to microstructural morphology variation, lack of fusion and porosity [5]. Despite this it has been observed that deposited Ti-6Al-4V with a fine + Widmanstätten microstructure can produce properties that exceed those of wrought and forged Ti-6Al-4V [5,[7][8][9]. Further to microstructural variations and porosity, crystallographic textures can also strongly affect material properties.…”

Understanding Additive Manufacturing Part Performance Through Modeling and Laboratory Experiments

“…1,2 The technology involves joining of materials to build parts strand by strand, and layer upon layer. 3 As such, parts fabricated by AM processes have different mechanical behaviors compared to those produced by conventional manufacturing technologies such as injection molding and casting. Since students often rely on AM for parts fabrication in courses and capstone projects, 4,5 and industries could adopt AM for distributed manufacturing and production of parts on-demand, 6,7 AM education is of critical importance.…”