Abstract
Dislocations play a central role in determining strength and flow properties of metals and alloys. Diffusionless phase transformation of β→α in Ti6Al4V during the Direct Metal Laser Sintering (DMLS) process produces martensitic microstructures with high dislocation densities. However, heat treatment, such as stress relieving and annealing, can be applied to reduce the volume of these dislocations. In the present study, an analysis of the X-ray diffraction (XRD) profiles of the non-heat-treated and heat-treated microstructures of DMLS Ti6Al4V(ELI) was carried out to determine the level of defects in these microstructures. The modified Williamson–Hall and modified Warren–Averbach methods of analysis were used to evaluate the dislocation densities in these microstructures. The results obtained showed a 73% reduction of dislocation density in DMLS Ti6Al4V(ELI) upon stress relieving heat treatment. The density of dislocations further declined in microstructures that were annealed at elevated temperatures, with the microstructures that were heat-treated just below the β→α recording the lowest dislocation densities.
Highlights
The aerospace and biomedical industries have recently undergone considerable technological advancement in relation to new processes of manufacturing
Misorientation distribution and analysis of X-ray diffraction (XRD) profiles for evaluation of dislocation densities in five different microstructures of Ti6Al4V(ELI) produced by Direct Metal Laser Sintering (DMLS) technology were carried out here, with the following conclusions: The percentage fractions of the High Angle Grain Boundaries (HAGBs) accounted for the majority of misorientation angles (>95%)
Samples type C did not show any trace of Low Angle Grain Boundaries (LAGBs); the frequencies of LAGBS in samples A and B were less than 1%, while in samples D and E they were higher at 2.5% and
Summary
The aerospace and biomedical industries have recently undergone considerable technological advancement in relation to new processes of manufacturing. Titanium alloys have been used extensively as biomedical implants (orthopaedic prostheses and dental applications), and in the manufacturing of aircraft gas turbine engine components [3] This is mainly due to their excellent properties of high specific strength (strength normalised by density), good fracture toughness, high fatigue performance, outstanding corrosion resistance and superior biocompatibility [3,4]. These alloys have excellent mechanical properties, they are very difficult to machine and require specialised equipment and procedures during casting. This is mainly due to their low thermal conductivity [5] and the acute reactivity of molten titanium with crucibles
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