الفهرس | Only 14 pages are availabe for public view |
Abstract In this work, the effect of strain hardening and aging processes on microstructure examination, tensile test and fatigue performance was studied on cast TC21 titanium samples with a chemical composition of Ti-6.1Al-2.96Mo-2.11Nb1.98Sn-2.05Zr-1.44Cr-0.1Si. The samples were classified into four groups: where the first group was as-cast samples, the second group was swaged+annealed samples, the third group was aged samples at 575ºC for 4hr on swaged+annealed samples. The fourth group was obtained by applying plastic deformation (strain hardening) process by 2%,3% and 4% strain on swaged samples at room temperature using a universal tensile testing machine. Then aging process was applied on the strain hardened samples at 575ºCfor 4 hr. By applying aging process at 575oC for 4 hr, secondary α-platelets were precipitated in the transformed β-phase. Maximum hardness of (HV440) was achieved for the 4%def.+aging samples. However, minimum hardness of (HV320) was recorded for as-cast condition. The highest ultimate tensile strength of (1311 MPa) was obtained for 4% def.+aged samples due to the presence of high amount of dislocation density as well as precipitation of secondary α-platelets in the residual β-phase. The lowest ultimate tensile strength of (1020 MPa) was reported for the as-cast samples. Maximum elongation of 14% was observed for 4% def.+aging samples and minimum elongation of 3% was obtained for the as-cast samples. Hence, strain hardening plus aging process can enhance considerably the elongation up to 366% and 133% in case of applying 4% def.+aging process on TC21 Ti-alloy compared to as-cast samples and aged samples without applying plastic deformation respectively. Theoretical study using Solid Works and Ansys software’s programs was carried out for estimating endurance limits for investigated samples. For validating the theoretical results, experimental test was carried out using rotating bending fatigue testing machine on three selected conditions of swaged, 2%def.+aged and 4%def.+aged. Maximum estimated fatigue strength of (783 and 775 MPa) was obtained for 4%def.+aged samples in Solid Works and Ansys software’s respectively and the experimental one was (755 MPa). Hence, the difference between estimated and experimental endurance limit for 4%def.+aged samples was less than of 3%. Minimum estimated fatigue strength of (278 and 272 MPa) was recorded for as-cast condition in Solid Works and Ansys software’s respectively due to minimum hardness and tensile strength. |