Remelt processing and microstructure of selective laser melted Ti25Ta

In this study, elemental powder mixtures of Ti25Ta, an alloy with promise for orthopaedic applications, were processed using Selective Laser Melting (SLM), an emerging manufacturing method for bespoke implants. Material density and homogeneity was investigated as a function of laser scan speed and scanning strategy. Dense (>99.99%), pore free material was obtained at optimised processing parameters and a ‘remelt’ scan strategy improved melting of the Ta powders, avoiding keyhole formation. Tensile and ultrasonic modulus testing of the SLM Ti25Ta revealed that the processed material had a similar yield strength to SLM commercially pure Ti, namely 426 ± 15 MPa, with a significant reduction of elastic modulus to 65 ± 5 GPa. The remelt scan strategy increased the yield strength to 545 ± 9 MPa, without altering the elastic modulus, however reduced the elongation from 25 ± 1 to 11 ± 4%. TEM analysis revealed the microstructure consisted of predominantly hexagonal α′ martensite with a limited amount of orthorhombic α′′ martensite formed in the Ta-rich regions near partially melted Ta particles, specifically facilitated by enhanced diffusion occurring during the remelt scan. The composition range for the α′′ phase was observed to be approximately 40–50 wt% Ta. Electron back-scattered imaging (BSI) and back scattered diffraction (EBSD) revealed the formation of the prior β grains with close to equiaxed morphology and a slight texture in the α′ martensite. The application of the remelt scan disrupted the prior β grain structure and resulted in randomly oriented α′ laths.