الفهرس 
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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.