Continuous and pulsed selective laser melting of Ti6Al4V lattice structures: Effect of post-processing on microstructural anisotropy and fatigue behavior

Abstract

Additive manufacturing technologies in general and laser powder bed fusion (L-PBF) in particular have been on the rise in different applications, including biomedical implants. The effects of the various l-PBF process parameters on the microstructure and properties of Ti6Al4V lattice structures have been studied before. However, the relationship between the different modes of laser scanning and the resulting microstructure, internal imperfections, and surface morphology is still underexplored. In this study, the aforementioned parameters and their effect on the compressive mechanical properties and fatigue behaviour of lattice titanium have been studied for both continuous and pulsed laser scanning modes. Moreover, the influence of various combinations of post-processing treatments, such as hot isostatic pressing (HIP), sandblasting, and chemical etching, on the quasi-static mechanical properties and fatigue endurance of the resulting materials were investigated. It was found that continuous laser strategy results in fewer imperfections and higher fatigue resistance, while pulsed laser showed a more homogenous microstructure; likely leading to a more isotropic behaviour. Furthermore, the continuous mode showed larger prior β grains preferentially oriented in the building direction, while pulsed specimens exhibited finer equiaxed grains with no preferred orientations. The highest level of fatigue life was obtained by using an optimized combination of HIP, sandblasting, and chemical etching.

Highlights

There is a strong relationship between the laser scanning modes and the resulting microstructure, surface morphology and mechanical response.•

Continuous laser strategy results in larger and preferentially oriented prior β grains, fewer imperfections and higher fatigue resistance.•

Inter-beads failure was detected for pulsed laser, contrary to the continuous mode featuring mostly nodes intersections failures.•

Local stress normalization was found to be the most effective method to study the mechanical response of lattice structures.•

A combination of HIP, sand blasting, and chemical etching was found the most effective in improving the fatigue response of lattice structures.

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