Date of Final Oral Examination (Defense)

5-2010

Type of Culminating Activity

Thesis

Degree Title

Master of Science in Materials Science and Engineering

Department

Materials Science and Engineering

Major Advisor

Dr. Megan Frary

Abstract

Spark plasma sintering (SPS) is reported to produce materials with properties superior to those that result from conventional processing techniques. Spark plasma sintering is also reported to process materials at lower temperatures and in a shorter time than other processes, which may facilitate the synthesis of materials that are traditionally difficult to process. While the properties of materials that result from SPS processing have been studied, there is not a thorough understanding of the evolution of the microstructure in response to SPS process parameters. A comparison of the microstructure of nickel produced by SPS at varying ramp rate, temperature, dwell time, and applied pressure, and nickel produced at varying time and temperature by conventional sintering (CS) techniques is made. Material properties that are compared include: density, hardness, porosity, average grain size, and grain boundary character. Evaluations of the activation energy of sintering, plastic flow, and modeling using a hotpress equation of SPS nickel are also performed to elucidate the mechanism of sintering. The results from this study are expected to give insight into more complex material systems processed with SPS.

The specimens processed by SPS reach higher density at lower temperatures than those processed by CS techniques. The hardness of SPS nickel is linearly related to the density, consistent with results from foams. The hardness and porosity results also indicate that radial temperature gradients do exist during SPS processing of nickel. The average grain sizes do not change significantly with SPS process conditions except at high temperatures or for long dwell times. Approximations of the grain growth rate of SPS nickel are higher than for CS nickel. The grain boundary character is stable during both SPS and CS processing, with significant increases in the Σ3 and special fractions only occurring at the longest times and highest temperatures. The activation energy of sintering indicates that SPS nickel densifies by diffusional processes. A hot-press model is also used to help identify the sintering mechanism, but the model is insufficient to explain the SPS process. The microstructural evolution of nickel is different during processing with SPS and with CS techniques.

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