Orientation-dependent mechanical strength and fatigue crack growth behaviour of commercially hot-rolled Ti Grade 2

The orientation-dependent mechanical and fatigue crack growth (FCG) behaviour of commercially hot-rolled Ti Grade 2 (Ti Gr.2) was investigated through tensile testing, hardness measurements, FCG experiments, and microstructural characterisation. Specimens were extracted along the LT and TL orientations relative to the rolling direction to evaluate anisotropy in the as-received condition. The results reveal clear orientation-dependent differences in yield strength, ultimate tensile strength, hardness, and strain-hardening behaviour, attributable to interstitial elements and microstructural heterogeneity developed during hot rolling. The LT orientation exhibits higher tensile strength (YS = 591 ± 0.34 MPa, UTS = 675 ± 1.95 MPa) and hardness (315 ± 1.79 HV), whereas the TL orientation (YS = 448 ± 6.80 MPa, UTS = 621 ± 6.42 MPa; 292 ± 1.51 HV) shows a higher strain-hardening rate, promoting more uniform deformation and greater ductility. Pronounced anisotropy was also observed in the FCG behaviour, with the LT orientation exhibiting a lower Paris law exponent ( m = 3.35 ± 0.06) than the TL orientation ( m = 3.82 ± 0.33), indicating superior crack-growth resistance along the LT direction. Fractographic analysis further revealed orientation-dependent differences in crack-path characteristics and fracture features across the crack-growth regimes. The estimated conditional fracture toughness values (K Q ≈ 26 MPa·m 1/2 ) were comparable for both orientations, suggesting that fracture is controlled by the bulk α-Ti matrix. Overall, the results demonstrate that the mechanical response and FCG resistance of commercially hot-rolled Ti Gr.2 are strongly governed by material orientation, providing further insight into anisotropy effects in structural Ti Gr.2.