Effects of Thermomechanical Processing and Heat Treatment on the Tensile and Creep Properties of Boron-Modified Near Alp
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TITANIUM alloys with minor boron additions have attracted considerable attention in recent years because of their attractive mechanical and wear properties. The alloys exhibit superior yield and ultimate tensile strengths as compared with their base alloys (without boron addition) with similar or marginally lower elongation-to-failure.[1–18] Titanium alloys with minor boron additions exhibit higher elastic modulus resulting in superior stiffness.[19–21] Addition of small amounts of boron to titanium alloys also leads to considerable refinement in grain size[6,7,14,19,20,22–25] as well as mitigation of grain boundary alpha[6,7,19,20,22] resulting in enhanced processing capability. While these alloys have found various commercial applications such as exhaust valves of automotive engines,[6,7,26] the potential of these alloys for aerospace applications has not yet been systematically explored, although titanium alloys are extensively used for aero-engine applications.[27] The requirements of higher thrust-to-weight ratio and efficiency for aero-engines demand alloys with superior elevated temperature capabilities. In this regard, a study of the mechanical behavior of these alloys at elevated temperature assumes considerable significance as the application temperature of titanium alloys range from 573 K to 873 K (300 °C to 600 °C), especially in the compressor section of an aero-engine. VIVEK CHANDRAVANSHI, Scientist, is with the Titanium Alloy Group, Defence Metallurgical Research Laboratory, Hyderabad 500 058, Andhra Pradesh, India. Contact e-mail: [email protected] R. SARKAR, Scientist, is with the Electron Microscopy Group, Defence Metallurgical Research Laboratory. S.V. KAMAT, Scientist, is with the Mechanical Behaviour Group, Defence Metallurgical Research Laboratory. T.K. NANDY, Scientist, is with the Powder Metallurgy Group, Defence Metallurgical Research Laboratory. Manuscript submitted August 2, 2011. Article published online September 26, 2012 METALLURGICAL AND MATERIALS TRANSACTIONS A
Several studies have been carried out in the literature to understand the high-temperature creep behavior of titanium alloys containing minor additions of boron.[6–8,17] The effect of boron on the elevated temperature creep behavior of Ti-6Al-4V alloy was studied by Boehlert et al.[6] The primary objective of their investigation was to determine whether the refinement in as-cast grain size as a result of boron addition led to degradation or enhancement of elevated temperature properties. Boron addition was found to improve the creep resistance of Ti-6Al-4V alloy significantly, and this was attributed to load sharing by TiB whiskers. A study carried by Chen and Boehlert[7] in as-cast Ti-6Al-2Sn-4Zr-2Mo-0.1Si alloy also showed that boron addition caused an improvement in the creep properties although the improvement was not as significant as that observed in Ti-6Al-4V. A similar study was also carried out on powder metallurgy (PM)-processed Ti-6Al-4V with 1 wt pct boron addition.[8] Significant improvement in creep properties
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