Static and Fatigue Characteristics of Heat-Treated Ti–6Al–3Mo–2Zr–2Sn–2Nb–1.5Cr–0.1Si Alloy

Static and fatigue characteristics of Ti–6Al–3Mo–2Zr–2Sn–2Nb–1.5Cr–0.1Si (TC21 Ti-alloy) in as-received and heat-treated conditions were investigated at ambient temperature. Two solution treatment cycles were applied on as-received TC21 samples. The first treatment was done below β-transus temperature (Tβ) at 920 °C/15 min and the second one above β-transus temperature (Tβ) at 1020 °C/15 min followed by water quenching. Both groups of samples were aged at 600 °C for 4 h before being air-cooled. The treated samples at 920 °C showed an equiaxed α + β structure. However, a complete martensitic structure was obtained in the treated samples at 1020 °C. In addition, secondary α-platelets (αs) precipitated inside retained β-phase (βr) due to aging process. The treated samples at 920 °C revealed the best tensile properties (tensile strength, 1447 MPa, and elongation, 8%). Theoretical study using Solidworks simulation program showed a fatigue limit of 709 MPa for as-received smooth samples. The treated samples at 920 °C obtained the highest fatigue limit of 866.5 MPa. However, the treated samples at 1020 °C revealed the lowest fatigue limit of 598.5 MPa. The as-received notched samples recorded a fatigue limit of 392 MPa by a decrease in the fatigue limit of about 45% compared with the as-received smooth samples. The experimental study using rotary bending fatigue machine recorded the best fatigue limit of 782.5 MPa for treated samples at 920 °C. As-received and treated samples at 1020 °C achieved fatigue limits of 651 and 546 MPa, respectively. The as-received notched samples showed a reduction in fatigue limit by approximately 43% from 625 to 359 MPa. Hence, the treated samples at 920 °C showed the best fatigue properties. The difference between theoretical and experimental fatigue values was less than 10% in four studied conditions.