Abstract
Selective Laser Melting (SLM) is of great interest to the aerospace industry due to its ability for producing components with complex geometries. The laser melting process induces a high cooling rate (105-107 K/s) and a germination by epitaxy which leads to a columnar microstructure. In the case of Ti-6Al-4V the rate of cooling from the β domain generates a martensitic α’ structure made up of fine needles. The present work describes the microstructural, textural and mechanical heterogeneities along the building direction of Ti-6Al-4V samples produced by SLM with two strategies that have different melt pool size. Characterizations show that both strategies lead to a martensitic microstructure but only the SLM with the greater melting area allows to get homogeneous hardness, texture and β grain size (reconstructed by ARPGE) along building direction.
Highlights
The Selective Laser Melting (SLM) powder bed process is probably the most attractive technique for building parts with a high degree of complexity as indicated in the work by Kruth et al [1]
The microstructure exhibits some domains which correspond to the prior β gain structure and they are larger for the Laser Boost (LB) process (Fig. 2(d)) compared to those obtained with the Classical Linear (CL) strategy (Fig.2 (b))
The melt flow rate of LB strategy is more than three times higher than CL strategy with a larger melting area, the LB strategy is interesting due to a faster melting process
Summary
The Selective Laser Melting (SLM) powder bed process is probably the most attractive technique for building parts with a high degree of complexity as indicated in the work by Kruth et al [1]. The high cooling rate of the SLM process generates Ti-6Al-4V parts with predominant martensitic α′ microstructure where prior β grains grow epitaxially throughout the deposition layers. The β grain solidification is influenced by the laser scan strategy and the β phase has a strong〈100〉texture along its grain growth direction parallel to the Z-axis [4] [5]. This rapid solidification behavior is due to large thermal gradients along the building direction that generates the parts with high strength and low ductility, residual stresses and solidification texture that induce anisotropy in the final product [6] [7]. The quantification of β-phase was performed using X-ray diffraction to follow the microstructure evolution along building direction and mechanical properties were characterized by micro hardness
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