Biomedical <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" altimg="si38.svg" display="inline" id="d1e781"> <mml:mi>β</mml:mi> </mml:math> -titanium alloys from pure metal powders - Key role of Sn during additive manufacturing

Additive manufacturing of β -Ti alloys offers a transformative pathway for the development of patient-specific implants tailored to the individual’s needs. While β -Ti alloys are able to reduce stress-shielding effects, the inherent thermal treatment during the manufacturing process inevitably leads to elastic stiffening and embrittlement due to the formation of ω i s o precipitates. In this study, we show that ternary additions of Sn (3 at.%) to a Ti-12at.%Cr alloy, produced by in-situ alloying of elemental powders during laser powder bed fusion, mitigate the effects of thermal history by impeding the decomposition process during repeated thermal cycling that precedes the ω transformation. While the Sn-free alloy underwent a pronounced ω i s o formation accompanied by an increase in Young’s modulus of ≈ 30 % already during printing, the Sn-added alloy maintained a lower Young’s modulus of ≈ 83 ± 5 GPa with no apparent ω i s o precipitation, similar to the conventionally produced alloy. This greatly improved resistance to cyclic reheating is also sustained during long-term low-temperature ageing, whereas the ω i s o formation proceeded unhindered in the Sn-free alloy. In addition to retaining its favourable elastic properties, the alloy exhibited a high corrosion stability in a simulated physiological environment with a current density below 4 µA cm −2 around the body potential. These results highlight the key role that Sn can play in alloy design for additive manufacturing routes. The mitigating effect of Sn as a ternary addition to β -Ti alloys enables their reliable printing, with in-situ alloying approaches opening up possibilities for multi-material alloys compositionally tuned in order to respond to local loading conditions. • Homogeneous TiCr3Sn alloys were printed by in-situ alloying using rescanning strategies. • The addition of Sn mitigates the ω -embrittlement caused by inherent thermal cycling. • Sn-added alloys maintained a lower Young’s modulus of 83 ± 5 GPa due to ω i s o -suppression. • Very limited ω i s o formation even after long-term ageing at 250 °C. • High corrosion stability in PBS at 37 °C around the body potential.