Yingying Zong

Hot deformation behavior and microstructure evolution of TC4 titanium alloy

Abstract The hot deformation behavior of Ti-6Al-4V (TC4) titanium alloy was investigated in the temperature range from 650 °C to 950 °C with the strain rate ranging from 7.7×10−4 s−1 to 7.7×10−2 s−1. The hot tension test results indicate that the flow stress decreases with increasing the deformation temperature and increases with increasing the strain rate. XRD analysis result reveals that only deformation temperature affects the phase constitution. The microstructure evolution under different deformation conditions was characterized by TEM observation. For the deformation of TC4 alloy, the work-hardening is dominant at low temperature, while the dynamic recovery and dynamic re-crystallization assisted softening is dominant at high temperature.

The formation mechanism of tear strips on stretched Ti-22Al-25Nb alloy sheets

This paper reports the presence of tear strips on the surface of a Ti-22Al-25Nb alloy sheet stretched at 960 °C. The test piece reveals a “bamboo”-shaped pattern on its surface, which severely affects the quality of the alloy. Microstructure analysis indicates that the formation mechanism of the tear strip is related to both the rich α2 phase layer and the interfacial B2 phase dynamic recrystallization layer between the α2 phase layer and the substrate metal.

Influence of Mo content on microstructure and mechanical properties of β-containing TiAl alloy

Abstract The influence of Mo content on the microstructure and mechanical properties of the Ti-45Al-5Nb- x Mo-0.3Y ( x =0.6, 0.8, 1.0, 1.2) alloys was studied using small ingots produced by non-consumable electrode argon arc melting. The results show that small quantities of β phase are distributed along γ/α 2 lamellar colony boundaries as discontinuous network in the TiAl alloys owing to the segregation of Mo element. The γ phase forms in the interdentritic microsegregation area when the Mo addition exceeds 0.8%. The β and γ phases can be eliminated effectively by subsequent homogenization heat treatment at the temperature above T α . The evolution of the strength, microhardness and ductility at different Mo contents under as-cast and as-homogenization treated conditions was analyzed, indicating that excessive Mo addition is prone to cause the microsegregation, thus decreasing the strength and microhardness obviously, which can be improved effectively by subsequent homogenization heat treatment.

Relation between Short-term Creep and Stress Relaxation of Titanium Alloy at High Temperature

Creep or stress relaxation is considered as a main mechanism of reducing the springback of titanium alloy sheet during thermal forming process.So far,the difference and relation between the two phenomena have not been clearly explored.In this paper,tests of short term creep and stress relaxation of Ti6Al4V alloy were conducted at high temperature.The microstructure of the tested alloy was observed by using TEM.Effects of temperature,stress and time on creep and stress relaxation behavior were studied,respectively.The correlation and difference between the two phenomena were compared based on relations of creep strain- time and strain rate- time.Results show that creep behavior is controlled by atom diffusion at low temperature under low stress;by dislocation slide and climb at high temperature under high stress.The stress relaxation behavior is mainly governed by dislocation climb.The predicted stress relaxation behavior based on the creep data shows a good agreement with the experiment.