Cheng-n Li

Effect of Boron Addition on Microstructure and Property of Low Cost Beta Titanium Alloy

A study on effect of boron addition on microstructure and property of low cost beta Ti-Al-Cr-Fe-B alloys are undertaken in the present. The Ti-Al-Cr-Fe alloys were developed as low cost beta Ti alloys for automotive springs, based on Molybdenum equivalency. Low priced Cr-Fe master alloys were introduced as beta stabilizing alloying elements for lowering cost, and elastic modulus. The boron addition is introduced in to refine the ingot microstructure and thus simplify hot working, which should lead to a cost reduction. On the other hand, the Ti-B compositions are able to restrict beta grain growth during heat treatments. So it can increase strength and microstructural stability. The mechanical tests show that the boron modified alloy has good tensile properties in solution condition. Moreover, the alloy can obtain well-balanced high strength levels with acceptable ductility after modulated aging treatment.

A Study on Microstructures and Hardening Behaviors of Ti-12.1Mo-1Fe Alloy

Ti-Mo-Fe alloy was developed as low cost beta Ti alloys for automotive springs, and designed based on Molybdenum equivalency and Bo-Md molecular orbital method. Low priced Mo-Fe master alloys were introduced as alloying elements for the cost and elastic modulus reduction. A laboratory scale ingot was melted by ISM (Induction Skull Melting). Then, microstructure characterization and hardening behavior of a new designed Ti-12.1Mo-1Fe alloy during solution and aging treatment were investigated in the present study by microscopy, X-ray diffraction and hardness test. The results showed that ω phase played a more important role than a phase in hardening. The hardening due to ω phase can lead to high hardness about 470 Hv. However, the coarse a phase resulted in hardness below 300 Hv. On the other hand, the alloy exhibited fast aging response due to high diffusion rate of Fe element in the Ti matrix.