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Daniel Coughlin

  • Room #439
    116 W Nineteenth Ave
    Columbus, OH 43210

About

Daniel is a member of Michael Mills' group. Characterization of NiTiHf shape memory alloys has become important due to their useful mechanical properties, high temperature applications, and lower cost than other shape memory alloys with similar characteristics.  A certain microstructure and mechanical properties are obtained when Hf is added to NiTi and a proper aging cycle is used.  The alloys analyzed for this research all had 20(at.)% Hf with varying Ti concentrations (29(at.)%, 29.7(at.)%, 30(at.)%, and 30.5(at.)%).  To determine the effect of aging on the behavior of these alloys isothermal constant strain rate compression testing was performed at temperatures above the austenite finish temperature.  Tests were run at temperatures of Af+10ºC, Af+30ºC, Af+50ºC, Af+70ºC, Af+90ºC for each alloy.  This revealed that the alloy strength and the temperature range for pseudoelasticity versus austenite plasticity was strongly influenced by aging for the Ni-rich alloys.  Additionally, electron microscopy has revealed precipitates rich in hafnium with a novel ordered structure relative to the B2 austenite phase form during aging.

(a )HAADF HRSTEM image of a precipitate in a 51Ni–29Ti–20Hf alloy along the [011]B2 direction, (b) magnified image of (a).