Analysis of laser power/scan speed combinations on constant energy density: Correlation of roughness-density and structure-property of additively manufactured Ti-6Al-4 V alloy

Abstract

The present work mainly addresses the influence of laser power (LP) and scan speed (SS) variations within constant energy density (CED) on Titanium alloy (Ti-6Al-4V) fabricated through laser powder bed fusion (L-PBF) process. The samples were fabricated with five different combinations of LP and SS with variations from 150 to 370 W and 475 to 1170 mm/s respectively within CED of 44 J/mm³. Strong inter-relationship observed between the outer surface topography and the interior part density showed that a sample with minimum roughness parameters (R_a= 0.88 µm) exhibiting higher relative density (99.15% ± 0.12). Decrease in the roughness parameters such as 47.61% of R_a, 53.01% of R_q, 63.56% of R_z and 74.76% of R_t was seen from the samples S₁ to S₄ as the LP and SS gradually increased within CED beyond which it again increased. Decrease in the melt track width was seen with simultaneous increase in LP and SS, and revealing a narrow melt track of range between 235.8 and 241.4 μm with high LP (370 W) and high SS (1170 mm/s) combination. Conversely, at low LP (150 W) and low SS (475 mm/s), the moving heat source provided enough time for melting resulted in a wider scan track of range between 307.9 and 311.5 µm. XRD pattern showed identical peaks in all the samples with noticeable peak shift despite the change in LP and SS at CED. EBSD analysis revealed more than 97% of martensite (α′) phases and also strong texture along the <0001 > direction. The presence of more amount of needle shaped martensitic structure led to higher ultimate tensile strength (UTS) of more than 1145 MPa in all the samples. However, notable uncertainty was observed between the samples in the percentage of elongation due to the presence of porosity.