Optimization of Low-Cost Ti-35421 Titanium Alloy: Phase Transformation, Bimodal Microstructure, and Combinatorial Mechanical Properties

Abstract

A sophisticated understanding of phase transformations and microstructure evolution is crucial in mechanical property optimization for the newly developed low-cost Ti-35421 (Ti-3Al-5Mo-4Cr-2Zr-1Fe wt.%) titanium alloy. The phase transformations in dual-phase Ti-35421 were studied by experiments and thermo-kinetic modeling. The phase transformation reactions and temperature ranges were determined as β→αlamellar [410–660 °C], αlamellar→β [660–740 °C], αlath→β [740–825 °C]. The Gibbs-Thomson effect and multicomponent diffusivities were proven to be responsible for the distinguishing behaviors of growth and dissolution between two α phases. The aging temperature of 540 °C was optimized based on calculations. It introduced a bimodal microstructure containing stubby α lamellae and β matrix. The mechanical properties of bimodal Ti-35421 were tested and compared with baseline alloy Ti-B19 and other near-β titanium alloys. The 540 °C aged alloy exhibits an optimal combination of mechanical properties with tensile strength of 1313 MPa, yield strength of 1240 MPa, elongation of 8.62%, and fracture toughness of 75.8 MPa·m1/2. The bimodal Ti-35421 shows comparable performance to Ti-B19 but has lower cost in raw materials and processing. The results also demonstrate that thermo-kinetic modeling can effectively be utilized in tailoring microstructure and enhancing mechanical properties.

Effect of Mo addition on the pitting resistance of TiMn alloys in Hanks’ solution

“…Many studies have been aimed at reducing the price of Ti alloys without sacrificing its properties. Iron, which is much cheaper than V, Nb and Mo, was used to develop Ti1.5Al6.8Mo4.5Fe alloy demonstrating improved mechanical properties at reduced raw material and processing costs [4]. Manganese (Mn), traditionally exploited as alloying element for many alloys and is cheaper than Fe and aluminum (Al), was also used for developing TiMn alloys with interesting mechanical properties [5][6][7], such as Ti (8)(9)(10)(11)(12)(13)Mn alloys that possess Youngʼs modulus, hardness and tensile strength close to or better than those of annealed Ti6Al4V ELI [8].…”

High-Temperature Deformation Behavior and Microstructural Characterization of Ti-35421 Titanium Alloy

“…The chemical composition of Ti-35421 alloy is to replace 5 wt% V in TB-19 with 1 wt% Fe while the total Mo equivalent stays the same for Ti-35421 alloy. Ti-35421 alloy has a high strength of 900-1450 Mpa, and medium elongation 6-15% [20]. As the new alloy has just been designed, the workability is still missing.…”