The effects of mechanical alloying conditions on hydrogen interaction characteristics and microstructure of mixtures of titanium, magnesium, and nickel

Keywords

Mechanical alloying; Metals -- Effect of temperature on; Hydrogen interaction characteristics; Mechanical alloying; Microstructure of mechanically alloyed material; Temperature effect on mechanical alloying

Abstract

The effect of mechanical alloying conditions on the hydrogen interaction characteristics and microstructure of mechanically alloyed titanium-magnesium-nickel mixtures was studied. The milling energy, time, atmosphere, and starting temperature were varied to investigate the effect of milling conditions on the hydrogen storage properties and microstructure of the mechanically alloyed Ti-Mg-Ni systems. The hydrogen interaction properties, including weight percent hydrogen and hydrogen onset temperatures, of the mechanically alloyed Ti-Mg-Ni mixtures were determined using differential scanning calorimetry (DSC). Microstructural characterization of the samples was preformed using scanning electron microscopy/x-ray dispersive spectrometry (SEM/XEDS) and focus ion-beam (FIB) milling. Significant differences were observed in the microstructures and hydriding onset temperatures of the Ti-Mg-Ni mixtures mechanically alloying under the different milling conditions. Increased milling energy resulted in an increase in the weight percent hydrogen uptake of the Ti-Mg-Ni mixtures. The transition of the Ti-Mg-Ni system from a ductile-brittle to a ductile-ductile system was also observed under the elevated milling energy conditions. Hydriding onset temperatures and weight percent hydrogen uptake decreased with increased milling times for the Ti-Mg-Ni mixtures milled under low energy conditions. The weight percent hydrogen uptake for mixtures milled under high energy conditions was increased. The

Ti-Mg-Ni mixture prepared using a pre-milled Ti and Ni sample exhibited a more refined microstructure and significantly reduced hydriding onset temperatures. Varying the milling atmosphere in the high energy system not only resulted in increased hydrogen storage capacity, but also converted the Ti-Mg-Ni mixtures to a ductile-brittle system. It was observed that the milling start temperature had a dramatic affect on the microstructure of the Ti-Mg-Ni mixtures. The microstructures of the Ti-Mg-Ni mixtures transitioned from those of a ductile-ductile system to those of a ductile brittle system as the milling start temperature was decreased from ambient to -40°C. Reducing the initial milling start temperature not only resulted in increased weight percent hydrogen uptake of the Ti-Mg­Ni mixtures, but also reduced hydriding onset temperatures. The results of this work indicate that a large degree of control over the samples was obtained by varying the mechanical alloying parameters. Significant alteration of the microstructure, transformations from a ductile-brittle system to a ductile-ductile system and vise versa, as well as drastic changes in the hydrogen weight percent stored and hydriding onset temperatures of the samples were obtained by controlling the mechanical alloying parameters.

Notes

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Graduation Date

2003

Advisor

Hampton, Michael D.

Degree

Master of Science (M.S.)

College

College of Arts and Sciences

Department

Chemistry

Format

PDF

Pages

106 p.

Language

English

Length of Campus-only Access

None

Access Status

Masters Thesis (Open Access)

Identifier

DP0028725

Subjects

Arts and Sciences -- Dissertations, Academic; Dissertations, Academic -- Arts and Sciences

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