Abstract
Surface remelting/skin scanning of components is generally performed during the selective laser melting (SLM) process to improve the surface quality of a part. However, the chemical effects of surface remelting are not well understood. In this study, cuboidal parts fabricated with and without laser remelting were characterised using scanning electron microscopy (SEM), surface profilometry and X-ray photoelectron spectrophotometry (XPS). The SEM images showed a low-amplitude undulating pattern was observed on both surfaces. The surface chemistries of the surface remelted/skin scanned (SK) and non-surface remelted/non-skin scanned (NSK) samples were observed to significantly differ in their elemental composition. The thickness of the surface oxide layer of the SK surface was double that of the NSK surface. Also, the contribution of the major alloying elements, including titanium and aluminium, on the surface oxide layer varied for both NSK and SK surfaces. The surface chemistry of the NSK and SK surface was significantly different to a conventionally forged (CF) Ti6Al4V surface. The rate of decrease of oxide with depth was in the order of CF>NSK>SK. Although surface remelting is useful in rendering improved surface quality, its impact on surface chemistry should be carefully considered.
Highlights
Selective laser melting (SLM) is a metal-based additive manufacturing (AM) technique capable of fabricating parts directly from three dimensional (3D) computer models
Both the No skin scan (NSK) and SK surfaces showed some particles partially melted to the surface; the number of particles partially melted to the SK surface was fewer than the NSK surface
The partially sintered particles observed on the top horizontal surface might be due to the blowing of metal particles into the laser melted zones by the argon gas flow in the build chamber
Summary
Selective laser melting (SLM) is a metal-based additive manufacturing (AM) technique capable of fabricating parts directly from three dimensional (3D) computer models. Due to its increased geometrical freedom, the use of SLM to fabricate customised designs with complex internal and external structures is explored widely for various applications including in the automotive, aerospace and biomedical industries (Gibson et al, 2010). SLM is widely regarded as an enabler of direct manufacture of end-use parts. Vaithilingam et al (2015) observed a surface roughness (Ra) of 17.6 m ± 2 m for Ti6Al4V components fabricated using Renishaw’s AM 250 SLM machine. Alrbaey et al (2014) reported a Ra value of 12.4 m ± 3 m for stainless steel components fabri- SLM has numerous advantages over conventional manufacturing such as moulding, die casting etc., the surface quality of a part produced by SLM is generally inferior. Vaithilingam et al (2015) observed a surface roughness (Ra) of 17.6 m ± 2 m for Ti6Al4V components fabricated using Renishaw’s AM 250 SLM machine. Alrbaey et al (2014) reported a Ra value of 12.4 m ± 3 m for stainless steel components fabri-
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