High-Strength Titanium-Based Alloy for Low-Temperature Superplastic Forming
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s://doi.org/10.1007/s11661-020-06058-8 The Minerals, Metals & Materials Society and ASM International 2020
I. A.V. MIKHAYLOVSKAYA, A.D. KOTOV, M.N. SITKINA, and A.I. BAZLOV are with the National University of Science and Technology ‘‘MISiS’’, Leninsky Prospekt, 4, Moscow, Russian Federation 119049. Contact e-mail: [email protected] A.O. MOSLEH is with the National University of Science and Technology ‘‘MISiS’’ and also with the Shoubra Faculty of Engineering, Benha University, Shoubra St. 108, Shoubra, P.O. 11629, Cairo, Egypt. P. MESTRE-RINN is with the Ecole Nationale Supe´rieure des Mines de Saint-Etienne,158 Cours Fauriel, 42100 Saint-Etienne, France. D.V. LOUZGUINE-LUZGIN is with the WPI Advanced Institute for Materials Research, Tohoku University, Sendai 980-8577, Japan and also with the MathAM-OIL, National Institute of Advanced Industrial Science and Technology (AIST), Sendai 980-8577, Japan. Manuscript submitted June 9, 2020; accepted October 5, 2020.
METALLURGICAL AND MATERIALS TRANSACTIONS A
INTRODUCTION
DUE to their high strength and corrosion resistance, titanium alloys are widely used in aeronautic, transportation engineering, medicine, and chemical engineering, with the Ti-6Al-4V alloy being the most common one.[1] Many studies have been conducted to optimize the production of Ti alloys parts by reducing the temperature and stress needed to achieve superplastic forming (SPF), known as a good technique to produce complex-shaped parts with a unique geometry.[2–8] The important forming parameters are strain rate and temperature. The desirable strain rate is above 10 4 to 10 3 s 1. The SPF temperature for conventional
titanium alloys sheets is usually around 820 C to 950 C.[1,9–12] For the main aircraft titanium-based alloy Ti-6Al-4V, the SPF temperature ranges from 825 C to 950 C.[1,13] The decreasing of the forming temperature is the most important task for superplastic Ti alloys.[13–16] The formability is improved in two ways. The first approach is the formation of ultrafine grains obtained by thermomechanical treatment, including severe plastic deformation (SPD).[2,7,17–20] After SPD, Ti alloys demonstrate a uniform ultrafine-grained structure, a low-temperature superplasticity at 500 C to 700 C,[15,21–23] a steady flow, and, as a result, excellent formability, though the SPD methods seriously increase the product cost, in addition to size limitations. The second approach is based on a decrease of the b-transus temperature due to alloying with b-stabilizing elements and decrease the content of a-stabilizing Al.[24,25] Addressed alloying by b-stabilizing elements with high tracer diffusivities,[24,26–28] such as Fe, Ni, and Cr, facilitate the accommodation of grain boundary sliding (GBS) at low temperatures. Several recently developed Ti-0.75Al-0.5V-2.75Fe-0.25Ni-1Mo-0.05B, Ti-1.5Al1.5V-2.75Fe-0.25Ni-3Mo-0.1B, and Ti-2.25Al-1.5V-0.25Fe2.75Ni-2Mo-0.15Si alloys[24] exhibit superplasticity at 650 C to 750 C. However, due to low Al content, room temperature strength of these alloys is rather
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