Investigation on monotonic and cyclic stress–strain characteristics of Ti–2Al–2.5Zr alloy

The monotonic and cyclic deforming regularity of Ti–2Al–2.5Zr alloy rod, tube and profiled tube (PT) specimen was determined at room temperature (RT). The effects of tension speed, V, cycle number, N, strain ratio, R, strain amplitude, εa and specimen shape on tensile and cyclic deforming behavior and characteristics were analyzed. The stress–strain relation equations under monotonic and cyclic loading, and the fatigue life prediction equations of Ti–2Al–2.5Zr alloy were established. The structure and fracture were also observed with optical and scanning electron microscope (OM, SEM). The tensile properties of Ti–2Al–2.5Zr alloy are related with V and specimen shape. At R=0.1, the cyclic stress–strain curves of tube and rod appear as cyclic softening. But the rod (at R=−l) and PT (at R=0) behave as cyclic softening at low εa value (≤9.0%), whereas they appear as cyclic hardening at high εa value (>2.0%). The fatigue life of Ti–2Al–2.5Zr alloy determined with tube is lower than that with rod. The twinning is closely related to εa, N value, etc. The tensile fractures show typical dimple features. There are many irregular crystalline convexes in fatigue fractures where many secondary cracks, fatigue striations and holes also exist.