Additively manufactured Ti-6Al-4V/Ta bimetal: from neutron diffraction residual stress analysis to wear and bioproperty testings

Powder bed fusion-laser beam prepared Ti-6Al-4V/Ta bimetals can be well-suited for advanced biomedical applications. However, a few issues remain unsolved, including (a) understanding of residual stress distribution and its level in as-printed bimetal; and (b) wear and bio properties of the bimetal. This study aims to address these points through a series of investigations, including residual stress analysis by neutron diffraction, printing optimization, and analysis of heat treatment effect on the properties. It was discovered that the residual stress is highly related to the temperature gradient and Young’s modulus. In the interface region of the as-printed bimetal, the residual stress was reduced and inverted compared to the as-printed Ta alone, changing from ~ (140-180) MPa (tensile) to ~ (30-70) MPa (compressive), which may have helped the Ta layer bond effectively with the Ti-6Al-4V matrix. Meanwhile, a high residual stress (~ 390 MPa) in the Ti-6Al-4V part of the as-printed bimetal justifies the need for heat treatment. After heat treatment, the bimetal exhibited good biocompatibility and much improved wear and corrosion resistance compared to Ti-6Al-4V alone. These improvements may be attributed to the formation of tantalum oxide during friction and corrosion processes. Ta layer can also improve the biocompatibility due to its intrinsic noncytotoxic feature.