Heat Treatment of Low Cost Beta Titanium Alloy Produced by Investment Casting

Document Type : Original Article

Authors

1 Mechanical Engineering Department, Faculty of Engineering, Suez University, Suez- Egypt

2 Mechanical Engineering Department,Faculty of Engineering, Helwan University, Helwan- Egypt

Abstract

Beta (β) Ti-alloys are promising class of Ti-alloys for high performance structural applications, thanks to their high strength to weight ratios and outstanding corrosion resistance. In the current work, Ti-4.5Fe-7Cr low cost beta Ti-alloy was produced by investment casting. DSC test was carried out to determine the transformation temperatures. The influence of solution treatment and aging temperatures on microstructure and mechanical properties were studied. Six heat treatment cycles were carried out, two solution treatment cycles in β- and α+β-range at 900 °C and 750 °C, respectively, and four precipitation hardening cycles, i.e. α+β-aging at 450 °C and 650 °C after solution treating at both 900 °C and 750 °C. Microstructure examination, XRD analysis and compression test had been conducted to investigate the influence of the different heat treatment regimes on the proposed alloy. Solution treatment at 900 °C results in coarser β-grain size than at 750 °C; hence lower strength. Strengthening by α-phase precipitation and grain refinement was achieved during aging. Aging at 650 °C results in higher strength than at 450 °C although coarser grain size, this is attributed to stronger effect of precipitation hardening of α-phase at 650 °C as a result of its higher amount than at 450 °C. The designed alloy shows high strength and excellent malleability, i.e. the alloy reveals superior plastic deformability, where specimens did not reveal any fracture; and the compression tests were interrupted at a compressive strain of 33%; therefore, this alloy may find applications as a healthcare, automotive or aerospace material.

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