Title page for ETD etd-09212011-234908


Type of Document Master's Thesis
Author Holt, Susan Marie
URN etd-09212011-234908
Title Effect of Processing Parameters on Bond Strength and Effective Plasticity in Al2O3-TiB2 Composites
Degree Master of Science
Department Materials Science and Engineering
Advisory Committee
Advisor Name Title
Logan, Kathryn V. Committee Chair
Pickrell, Gary R. Committee Member
Reynolds, William T. Jr. Committee Member
Keywords
  • Titanium Diboride
  • bond strength
  • effective plasticity
  • Alumina
Date of Defense 2011-09-09
Availability unrestricted
Abstract
Alumina-titanium diboride (Al2O3-TiB2) composites have high temperature, wear, and impact resistance that could be useful in high performance applications. Determining the effect of processing parameters on relative bond strength and effective plasticity may contribute to optimization and predictability of performance in the Al2O3-TiB2 system. Al2O3-TiB2 composites were obtained from a collection of samples that were created during a separate ongoing research program being conducted by Dr. Kathryn V. Logan. The Logan samples were initially formed by hot pressing powders produced using Self-Propagating High Temperature synthesis (SHS) of Al, TiO2, and B2O3 powders or manual mixing (MM) of Al2O3 and TiB2 powders. Samples were then fractured using standard single edge notched beam (SENB) fracture toughness testing. The obtained fractured surfaces were examined using Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray Spectroscopy (EDS). Relative amounts of transgranular and intergranular fracture of Al2O3 and TiB2 grains were determined. Transgranular fracture was used as a measure of relative bond strength. Other samples were obtained from the Logan collection to conduct nano-indentation measurements on polished sample surfaces in Al2O3 grains and in TiB2 grains. Indent locations were verified using SEM. Reduced modulus, final displacements, and fracture toughness for indents in Al2O3 grains and in TiB2 grains were determined from nano-indentation curves. Reduced modulus was used as a measure of relative bond strength. Final displacement and fracture toughness were used as measures of relative effective plasticity. Analysis of Variance (ANOVA) using Taguchi arrays was conducted using the powder processing factor (SHS vs. MM) and the predominant microstructure factor (TiB2 grains surrounding Al2O3 grains vs. TiB2 grains distributed amongst Al2O3 grains) when examining the effect of processing parameters on relative bond strength as measured by amount of transgranular fracture. Analysis of Variance (ANOVA) using Taguchi arrays was conducted using the powder processing factor (SHS vs. MM), the predominant microstructure factor (TiB2 grains surrounding Al2O3 grains vs. TiB2 grains distributed amongst Al2O3 grains), and the indented phase factor (Al2O3 vs. TiB2) when examining the effect of processing parameters on relative bond strength as measured by nano-indentation reduced modulus and both measures of relative effective plasticity. Powder processing was significant for the relative bond strength measures, but was not significant for the relative effective plasticity measures. Predominant microstructure was significant for all measures except relative effective plasticity as measured by fracture toughness, for which none of the factors and interactions were significant. The interaction between powder processing and predominant microstructure was significant for most of the relative bond strength measures and for relative effective plasticity as measured by final displacements. Indented phase was significant for the nano-indentation measures except nano-indentation fracture toughness, although the significance for nano-indentation fracture toughness was just below the critical level. The interaction between powder processing and indented phase and the interaction between predominant microstructure and indented phase were only significant for the relative bond strength measure using nano-indentation reduced modulus. The interaction between powder processing, predominant microstructure, and indented phase was significant for the nano-indentation measures except nano-indentation fracture toughness. The optimum level for powder processing was predominantly manual mixing. The optimum level for predominant microstructure was predominantly TiB2 grains surrounding Al2O3 grains. The optimum level for indented phase was predominantly TiB2.
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