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Indian Institute of Science

1. Tiwary, Chandra Sekhar. Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys.

Degree: PhD, Faculty of Engineering, 2018, Indian Institute of Science

The thesis introduces a novel alloy system based on submicron distributions of intermetallic phases realised through eutectic solidification in the ternary system Ni-Al-Zr. Various compositions in this system comprising of intermetallic phases distributed in different eutectic structures show ultra-high strength at temperatures upto 700°C combined with reasonable tensile plasticity, exceptional oxidation resistance and high temperature structural stability. Intermetallics have long been used in high temperature alloys systems such as in the classical Ni-base superalloys that derive their strength from nanoscale dispersions of the aluminide, Ni3Al(γ’) in a matrix of disordered fcc Ni (γ), alloyed with expensive, high density refractory elements such as Re and Ru. The high temperature applications of intermetallics derive from their strength retention to high temperatures, creep resistance enabled by low diffusion rates, and attractive oxidation resistance based on high concentration of elements such as Al that forms stable oxides. Several decades of effort on the development of new generation of intermetallic alloys through the 80’s and 90’s have gone unrewarded, with the exception of TiAl based alloys that are now used in recent generation aircraft engines. The promise of intermetallics as high temperature candidate materials is limited by their poor ductility or toughness arising from several intrinsic properties such as low grain boundary cohesive strength (in the case of Ni3Al) or an insufficient number of slip systems (as in NiAl) or extrinsic effects such as embrittlement by hydrogen (Fe3Al) that derive fundamentally from the existence of directionality in bonding. However, low ductility or toughness can often be alleviated by limiting the length scale for slip. We have therefore examined the possibility of combining intermetallics in the form of eutectic structures, potentially limiting slip lengths within each intermetallic constituent. Eutectic structures in binary systems limit the choice of intermetallic combinations so that finding such combinations with engineering potential is difficult. On the other hand combinations of three elements or more would enable a significantly larger set of permutations of eutectic intermetallics, provided the constituent binary phase diagrams contain either eutectic or peritectic reactions involving intermetallic phases, as well as intermediate intermetallic phases. The ternary Ni-Al-Zr system met our criterion in several ways. The Ni-Al binary phase diagram shows a peritectic reaction from liquid and NiAl (Pm 3m, B2 with a lattice parameter of 0.288nm) to form Ni3Al (Pm 3m, L12 with a lattice parameter of 0.356 nm), intermetallics that have been extensively investigated in earlier literature. The Ni-Zr system shows a peritectic reaction between liquid and the Ni7Zr2 (C12/m1 with a lattice parameters a=0.469nm, b=0.823nm, c=1.219nm) phase to form the intermetallic Ni5Zr (F 43m with a lattice parameter of 0.670nm). Further the NiAl and Ni7Zr2 are both intermediate phases… Advisors/Committee Members: Chattopadhyay, K (advisor), Banerjee, Dipankar (advisor).

Subjects/Keywords: Intermetallic Alloys; Nickel-Aluminium-Zirconium Eutectic Alloys; Ni-Al-Zr Alloys; Ternary Alloys; Intermetallic Eutectic Composites; Metallurgy

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APA (6th Edition):

Tiwary, C. S. (2018). Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys. (Doctoral Dissertation). Indian Institute of Science. Retrieved from http://etd.iisc.ac.in/handle/2005/2991

Chicago Manual of Style (16th Edition):

Tiwary, Chandra Sekhar. “Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys.” 2018. Doctoral Dissertation, Indian Institute of Science. Accessed January 23, 2021. http://etd.iisc.ac.in/handle/2005/2991.

MLA Handbook (7th Edition):

Tiwary, Chandra Sekhar. “Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys.” 2018. Web. 23 Jan 2021.

Vancouver:

Tiwary CS. Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys. [Internet] [Doctoral dissertation]. Indian Institute of Science; 2018. [cited 2021 Jan 23]. Available from: http://etd.iisc.ac.in/handle/2005/2991.

Council of Science Editors:

Tiwary CS. Microstructural, Mechanical and Oxidation Behavior of Ni-Al-Zr Ternary Alloys. [Doctoral Dissertation]. Indian Institute of Science; 2018. Available from: http://etd.iisc.ac.in/handle/2005/2991

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