TITLE:
Fatigue Performance of Heat Treated TC21 Ti-Alloy
AUTHORS:
Ramadan N. Elshaer, Khaled M. Ibrahim, Azza F. Barakat, Reham R. Abbas
KEYWORDS:
TC21 Ti-Alloy, Solution Treatment, Microstructure, Hardness, Tensile, Fatigue
JOURNAL NAME:
Open Journal of Metal,
Vol.9 No.2,
June
30,
2019
ABSTRACT: TC21 is
considered a new titanium alloy that is used in aircraft applications as a
replacement for the famous Ti-6Al-4V alloy due to its high strength. The effect
of single and duplex stage heat treatments on fatigue behavior of TC21 Ti-alloy
(Ti-6Al-2Sn-2Zr-3Mo-1Cr-2Nb-0.09Si, wt.%) was investigated. Two heat treatment
cycles were applied on as-received TC21 Ti-alloy. The first cycle was called
single stage heat treatment (SSHT). The other cycle was named duplex stage heat
treatment (DSHT). Typical microstructures of SSHT & DSHT composed of
primary equiaxed α phase, residual β phase and secondary α phase (αs). Secondary α phase was precipitated in the residual β phase due to low cooling rate using air cooling and aging treatment.
Morphology of α phase does not change after solution treatments, while their volume
fraction and grain size were changed. SSHT showed the highest fatigue strength
of 868 MPa due to high tensile strength, hardness and existing of high
percentages of residual β phase in the microstructure. However, DSHT reported lower fatigue
strength of 743 MPa due to increasing grain size of α phase. The fracture surface of fatigue samples showed cleavage ductile
fracture mode for both heat treatment cycles.