Torsional and Fracture Behavior of Selective Laser-Melted Ti6Al4VAlloy for High-Torsion and Large-Cycle Loading Applications

Because of its exceptional mechanical strength, thermal stability, and precision, selective laser melting (SLM) is finding widespread adoption in additive manufacturing (AM). In particular, the SLM processing of Ti6Al4V alloy is well-suited for applications that require high-performance with weight savings, high structural integrity, and durability for long-term applications. However, the wide range of process parameters and complex thermo-physical phenomenon involved significantly affect its torsional and torsional-fatigue properties. This study investigates the torsional performance and fracture behavior of SLM-printed Ti6Al4V alloy components under static torsional loading and high-cycle fatigue conditions. The tests were performed through 3D-printing of samples to investigate the mechanical response properties and fracture behavior of SLM-Ti6Al4V samples under torque-controlled conditions, followed by fractography analysis. Unique mechanical response characteristics were observed in the torsional stress–strain loading curves. The torsional performance parameters at the neck point were determined to be: torsional yield shear stress (τ y ) of 588 MPa, ultimate torsional shear stress (τ u ) of 1108 MPa at a twist angle of 24.58°, a shear modulus (G) of 42.85 GPa, and torsional shear stiffness of 1.7 kNm/rad. The ultimate shear stress (τ u ) is higher than what is reported so far, while the torsional yield shear stress (τ y ) obtained here is comparable to previous SLM components and higher than the wrought alloy values. Post-peak region behavior and fractography surface morphology features showed strain softening behavior as the crucial cause of the fractured surface of the Ti6Al4V alloy samples. Similarly, the torsional-fatigue strength of the SLM-Ti6Al4V alloy sample was found to be in the range of 97 MPa and 145 MPa under 100,000 cycles. These findings confirm that the torsional properties of the SLM-Ti6Al4V samples meet the performance requirements for demanding high-performance applications, offering reliable strength and stability under torsional loading conditions.