Microstructure and Texture Evolution During Sub-Transus Thermomechanical Processing of Ti-6Al-4V-0.1B Alloy: Part I. Hot
- PDF / 4,161,677 Bytes
- 19 Pages / 593.972 x 792 pts Page_size
- 80 Downloads / 217 Views
UM alloys, owing to their high specific strength, good corrosion properties, and excellent fracture resistance, are known as one of the most important structural materials for aerospace and chemical industries.[1] Most of the titanium alloy products are obtained by casting followed by wrought processing since the ascast titanium alloys possess coarse microstructural features and strong crystallographic texture.[2,3] These two attributes are considered unfavorable for optimal processing; therefore, many attempts have been made to overcome these limitations. Significant success in this regard has been incurred through hypoeutectic boron addition to various titanium alloys, most notably to the (a + b) alloy Ti-6Al-4V.[4–6] The unalloyed microstructure of Ti-6Al-4V consists of a (P63mmc) and b (Im3m) phases wherein the a lamellae form colony structure within prior b grains with the b phase being sandwiched between the a lamellae. Microstructural studies on the cast Ti-6Al-4V alloy containing various levels of boron addition in the
SHIBAYAN ROY, formerly Ph.D. Student with the Department of Materials Engineering, Indian Institute of Science, Bangalore, India, is now Post-doctoral Researcher with the Institut fu¨r Werkstoffwissenschaft und Werkstofftechnik, Chemnitz University of Technology, Chemnitz, Germany. SATYAM SUWAS, Associate Professor, is with the Department of Materials Engineering, Indian Institute of Science. Contact e-mail: [email protected] Manuscript submitted May 31, 2012. Article published online March 15, 2013 METALLURGICAL AND MATERIALS TRANSACTIONS A
hypoeutectic range reveal Widmansta¨tten a colony structure within the prior b grain with significant refinement for both prior b grain and a colony sizes compared with the base alloy without boron.[5] In boron-containing alloys, the TiB phase form as whiskers with aspect ratio ~8 to 9 preferentially at the prior b grain boundaries forming a necklace-like arrangement. Microstructure of the base alloy contains thick grain boundary a layer (~10 lm), whereas the alloy with boron show marked reduction in this micro-constituent size.[6] Godfrey et al.[7] showed significant improvement in tensile strength and ductility, for mechanically alloyed Ti-6Al-4V with hypereutectic boron powder, similar to that expected in wrought Ti-6Al-4V. Zhu et al.,[4] on the other hand, reported that the tensile ductility of cast Ti6Al-4V alloy cannot be improved with hypoeutectic boron addition. A more recent study by Sen et al.[8] showed that with the refinement in the microstructure, the yield and ultimate tensile strengths increase significantly, although ductility drops after 0.1 wt pct boron addition. In-situ tensile testing of a boron-modified Ti6Al-4V alloy at room temperature and 753 K (480 C) revealed higher tensile and ultimate strengths for this alloy with a ductile fracture mode at quasi-static tensile elongations equivalent to conventional Ti-6Al-4V.[9] Elevated temperature (728 K or 455 C) cyclic loading of Ti-6Al-4V-0.1B alloy (wt pct) castings exhibited
Data Loading...
