Friction Stir Processing of Beta C and Ti-185: A Unique Pathway to Engineer Microstructures for Exceptional Properties i
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SINCE the early 2000s, the use of titanium alloys in the aerospace, automotive, chemical, petrochemical, biomedical, and defense industries increased markedly due to their attractive properties such as lightweight (about 60 pct lighter than steels), excellent corrosion resistance, bio-compatibility, and good ballistic resistance.[1,2] In recent times, b titanium alloys have become widely explored candidates of choice because of their wide range of property combinations. Figure 1 illustrates the uses of b Ti alloys in various industries. Applications of b alloys are driven by significant weight
VEDAVYAS TUNGALA, ANIKET K. DUTT, DEEP CHOUDHURI, and RAJIV S. MISHRA are with the Center for Friction Stir Processing, Department of Materials Science and Engineering, University of North Texas, Denton, TX 76207. Contact e-mail: [email protected] SESH A. TAMIRISAKANDALA is with Arconic Titanium & Engineered Products, 1000 Warren Avenue, Niles, OH 44446. KYU C. CHO and RAYMOND E. BRENNAN are with the Weapons and Materials Research Directorate, U.S. Army Research Laboratory, Aberdeen Proving Grounds, MD 21005. Manuscript submitted March 1, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
savings due to superior specific strength (strength-toweight ratio) leading to significant life-cycle cost savings. The primary challenge in the research and development of b alloys is to enhance strength while retaining acceptable fracture properties. Rapid grain growth in b alloys during conventional thermo-mechanical processing (TMP) due to high diffusion rates in the b phase and associated anisotropy constrains the maximum achievable mechanical properties and applications of b alloys. The current study explores the application of a novel deformation technique, friction stir processing (FSP), to b Ti alloys to overcome these issues. FSP is currently used for many Al,[3–8] Mg,[9,10] and Cu[11] alloys. Progress in the application of FSP to Ti alloys has been slow due to limited availability of tool materials that can withstand high temperatures and loads generated during the process. Numerous authors have investigated the FSP of the workhorse a + b titanium alloy, Ti-6Al-4V (Ti-64), using tools such as W,[12,13] W-Re,[14–20] Mo-based,[21] polycrystalline boron nitride,[22] WC-Co,[23] and lanthanated W.[24] Recent works on FSP of titanium alloys show the enhanced mechanical properties due to microstructural evolution.[25–29] Studies on the FSP of b titanium alloys are
Fig. 1—Overview of the usage of b titanium alloys in various industries.
scanty. Leinart et al.[30] studied the effect of FSP on the microstructure and mechanical properties of Ti-15V-3Cr-3Al-3Sn (Ti-15-3), a metastable b alloy used in environmental control systems (e.g., ducting on Boeing 777 and Airbus A380). A fully recrystallized b grain microstructure was obtained after FSP, with a grain size in the range 10 to 20 lm, developed as a result of dynamic recovery followed by meta-dynamic recrystallization.[30] Another study on Ti-15-3 reported the grain structure evo
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