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Effect of Aging and Alloying on Wear Characteristics of Nitinol Based Alloys

Yellappa M1, G V Krishnareddy2, Uday M1, Gowtham K1, and Puneet U1
1.Assistant Professor, Mechanical Department, SJBIT, Bangalore-60, India
2.Lecturer, Mechanical Department, Govt Polytechnic, Bangalore, India

Abstract— NiTiNOL is an alloy of roughly 50% Nickel and 50% Titanium. NiTiNOL derives its name from its chemical components and its founders: Ni (Nickel) + Ti (Titanium) + NOL (Naval Ordinance Lab). It has good biocompatibility and good magnetic resonance imaging opacity, making it ideally suited for design of biomedical implantable. In the present work, alloy samples with varying percentage of ternary alloys are vacuum cast in vacuum arc melting furnace and the alloy samples are heat-treated at different low temperatures keeping the time (1hour) constant and tested for hardness wear behavior of the samples. The wear characteristics are predicted for as cast samples as well as heat treated samples by carrying out Adhesive wear as well as Abrasive wear tests as per ASTM Standards. The hardness seems to increase with different aging temperatures (oC) conditions. The Vickers hardness is low for the as-cast samples of both the compositions but gradually increases with increase in the heat-treatment temperatures up to 350oC possibly due to formation of transition precipitates but there is a decrease in the hardness at 400oC possibly because of NiTi formation. Abrasive specific wear rates show a trend that is exactly the inverse of Vickers hardness. The wear rates tend to decrease from ascast condition up to 350oC heat-treatment, and increase in the samples heat-treated at 400oC. The Vickers hardness of the samples is seen to go up gradually with an increase in the aluminum content, also the effect of heat –treatment will reduce the internal stresses and eliminate coring. The marginal hardness increase may be due to the Ni-Ti composition moving towards stoichiometry by precipitation of excess Ni or Ti in the form of suitable precipitates. Abrasive wear of the specimens is seen to increase both with an increase with the cooper content and the heat-treatment temperature, for different reasons. The specific wear rate for the samples is seen to go up accordingly with the abrasive wear since the ductility of the samples may be lowered considerably with an increased addition of aluminum to the NiTi matrix.

Index Terms— Adhesive Wear, Abrasive Wear, Vickers Hardness, Heat-treatment

Cite: Yellappa M, G V Krishnareddy, Uday M, Gowtham K, and Puneet U, " Effect of Aging and Alloying on Wear Characteristics of Nitinol Based Alloys," International Journal of Mechanical Engineering and Robotics Research, Vol. 3, No. 2, pp. 311-320, April 2014.