Year of Publication

2010

Degree Name

Master of Science in Mechanical Engineering (MSME)

Document Type

Thesis

College

Engineering

Department

Mechanical Engineering

First Advisor

Dr. Haluk E. Karaca

Abstract

Among the potential high temperature shape memory alloys, due to its low cost, medium ductility and high work output NiTiHf seems to be the most promising HTSMA for a wide range of applications in the 100-250ºC. A detailed investigation into the shape memory properties and transformation behavior for the Ni-rich HTSMA with the compositions of Ni45.3Cu5Ti29.7Hf20, Ni50.3Ti29.7Hf20 and Ni45.3Pd5Ti29.7Hf20 was carried out. It is possible to form Ni-rich precipitates in Ni-rich NiTiHf alloys and tailor the TTs by heat treatments that results in increased strength and stable response at high temperatures. The coherent Ni-rich precipitates deplete the Ni content from the matrix increasing the transformation temperatures and strengthen the material by hindering the dislocation motion. The effect of aging on the microstructure, shape memory and mechanical properties are revealed. Optimum aging conditions have been found determined to get the most favorable combination of high transformation temperatures with stable and good shape memory properties. The Ni50.3Ti29.7Hf20 and Ni45.3Pd5Ti29.7Hf20 aged at 500ºC-600 ºC were found to be formidable candidates for high temperature applications.

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