Solidification Behavior in Newly Designed Ni-Rich Ni-Ti-Based Alloys
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OVER the past few decades, Ni-Ti alloys (Nitinol)[1–4] have extensively been researched due to existence of the unique and improved properties including high strength at elevated temperature, good workability, excellent corrosion resistance, shape memory effect, etc. The search for novel advanced materials with better mechanical properties has led to continuous drive in the scientific community.[5] Recently, it has been reported[6–9] that bulk nano/ultrafine eutectic alloy with micron-scale dendritic phases is a promising material; exhibiting improved and well-balanced combination of strength and ductility required for niche applications. Sufficiently large number of studies has been reported in the literature on the development of these types of
SUMANTA SAMAL, formerly Ph.D. Student with the Department of Materials Science and Engineering, Indian Institute of Technology Kanpur, Kanpur, Uttar Pradesh 208016, India, is now Institute Postdoctoral Fellow with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras, Chennai, Tamil Nadu 600036, India. KRISHANU BISWAS, Professor, is with the Department of Materials Science and Engineering, India Institute of Technology Kanpur. Contact e-mail: kbiswas@ iitk.ac.in GANDHAM PHANIKUMAR, Professor, is with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology Madras. Manuscript submitted April 20, 2016. METALLURGICAL AND MATERIALS TRANSACTIONS A
composite microstructure in Ti-based multicomponent alloys such as Ti-Fe-Sn,[10–12] Ti-Fe-Co,[13,14] Ti-CuNi-Sn-Nb/Ta[6,15,16] by proper selection of the alloying elements and their concentration. However, very limited studies[17–19] have been reported on the Ni-based multicomponent alloys so far. To the best of the authors’ knowledge, the equilibrium Ni-rich Ni-Ti-based multicomponent alloy phase diagram is not available, and thus, it is very tedious to predict the phase formation and microstructure evolution in the Ni-rich Ni-Ti-based multicomponent alloys. Therefore, one needs to investigate systematically the effect of addition of alloying elements to near-eutectic Ni-Ti binary alloy (as indicated by dotted line in Figure 1) with an aim to obtain clear understanding of the phase formation in these alloys. It is to be noted that the detailed mechanical properties of Ni-rich Ni-Ti-based alloys has been reported in the earlier publication (Table I),[20] revealing that fine tuning the composition by addition of alloying elements in the alloy would lead well-balanced mechanical properties (ultimate strength ~2 GPa and ductility ~13 pct). The objective of the current investigation is to explore the novel approach to achieve in-depth understanding of the phase formation and microstructure evolution of the investigated Ni-rich Ni-Ti-based alloys by the systematic addition of different alloying elements such as Cu, Co, and Ta in the Ni-rich Ni-Ti binary alloy. The purpose of
the present manuscript is to understand the solidification behavior of the multicomponent Ni-Ti-
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