Title page for etd-0426117-103718


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URN etd-0426117-103718
Author Wei-Yu Tsai
Author's Email Address No Public.
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Department Materials and Optoelectronic Science
Year 2016
Semester 2
Degree Ph.D.
Type of Document
Language English
Title Microstructures and properties of nano-grain refined 304 stainless steel and ceramic-powder inserted Al processed by ultrasonic surface mechanical attrition treatment
Date of Defense 2017-05-25
Page Count 193
Keyword
  • surface mechanical attrition treatment
  • grain refinement
  • fine grain strengthening
  • ultrasonic mechanical coating and armoring
  • heat dissipation coating
  • Abstract In this research, we used Ultrasonic shot peening equipment as the tool, conducting nano-crystallization and surface mechanical coating experiments. Detailed experimental methods, results and discussion are presented separately as SMAT and UMCA parts in the manuscript.
    For the first part, the analytic modeling and one experimental assess of the ultrasonic surface mechanical attrition treatment (SMAT) are presented. The bombarding ball speed, induced energy, and the resulting sample hardness, experienced depth and grain size are incorporated into this model, based on harmonic longitudinal vibration motion of ultrasonic-wave-driven ball impact onto the sample surface. An experimental assessment by using a stainless steel flat sample is conducted, and the comparison of the model and experiment is reported. There appear some optimum SMAT working parameters for the best SMAT effect, locating within the ranges of 1-2 mm for the ball size, 8-10 m/s for the ball speed, 4-5x102 s-1 for the strain rate, and 70-75 mJ for the input energy. Beyond the optimum SMAT parameters, the sample surface would be subject to bombarding micro-cracking and the grain size would not be further reduced. Instead, the grain size becomes larger and the hardness becomes lower. The benefits from SMAT would become lower.
    We used 1050 aluminum alloys, which often serve as heat sink in light-emitting diode (LED) lighting, are inherent with a high thermal conductivity, but poor thermal total emissivity. Thus, high emissive coatings on the Al substrate can enhance the thermal dissipation efficiency of radiation. In this study, the ultrasonic mechanical coating and armoring (UMCA) technique was used to insert various ceramic combinations, such as Al2O3, SiO2, graphite and carbon nanotube to enhance thermal dissipation. Analytic models have been established to couple the thermal radiation and convection on the sample surface through heat flow equations. A promising match has been reached between the theoretical estimations and experimental measurements. With the adequate insertion of ceramic powders, the heat can be transferred to thermal radiation and emitted. The temperature of the Al plates and heat sinks can be lowered by 5–11°C, which is highly favorable for applications requiring cooling components.
    Advisory Committee
  • Shian-Ching Jang - chair
  • Che-Hsin Lin - co-chair
  • Hsuan-Kai Lin - co-chair
  • Cheng-Tang Pan - co-chair
  • Chih-Ching Huang - advisor
  • Files
  • etd-0426117-103718.pdf
  • Indicate in-campus at 2 year and off-campus access at 2 year.
    Date of Submission 2017-05-30

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