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Synthesis, Microstructure, And Mechanical Behavior Of Fe-Cu Composites, Jin-Woo Jeon

Masters Theses

The synthesis, microstructure, and mechanical properties of ball-milled nanocrystalline (nc) Fe powder and immiscible Fe-Cu alloy composites are investigated in this thesis. Experimental approaches are described for the characterization of the grain size and hardness of nc Fe powders and the internal stress state of bulk Fe-Cu alloy composites are presented.

The grain size measurements of ball-milled Fe powders obtained from the XRD line broadening analysis (15 nm) and TEM observation (18 nm) showed good agreement between two results. From the nanoindentation tests, the hardness values of the ball-milled Fe powders were increased from 3.5 to 10.5 GPa as the …

An Experimental Evaluation Of The Constant Β Relating The Contact Stiffness To The Contact Area In Nanoindentation, Jeremy Harper Strader

Masters Theses

Measurements of mechanical properties by nanoindentation with triangular pyramidal indenters like the Berkovich rely heavily upon the relationship between the contact stiffness, S, the contact area, A, and the reduced elastic modulus, E_r . This relationship is often written in the form: S = 2βEr(A/π)1/2, where βis a constant that depends on the geometry of the indenter. Although the most common values for βused in experimental measurements are 1.000 and 1.034, various theoretical analyses have yielded values as small as 1.00 or as large as 1.2, depending on the assumptions made to model the deformation. Here the most appropriate …

Effect Of Hydrogenon On Mechanical Behavior Of A Zircaloy-4 Alloy, Elena Garlea

Masters Theses

Hydride formation is one of the main degradation mechanisms of zirconium alloys in hydrogen-rich environments. When sufficient hydrogen is present, zirconiumhydride precipitates can be formed. Cracking of the brittle hydrides near a crack tip can initiate the growth of a crack leading to the premature failure of the material. Hydride formation is believed to be enhanced by the presence of residual or applied stresses. Therefore, the increase in the stress field ahead of a crack tip may promote precipitation of additional hydrides. In order to verify these phenomena, the effect of internal stresses on the zirconium-hydride-precipitate formation, and in turn, …

The Development Of Qualification Standards For Cast Super Duplex Stainless Steel (2507 Wrought Equivalent), Vasudevan Hariharan

Masters Theses

The objective of the program is to determine the suitability of ASTM A923 “Standard Test methods for Detecting Detrimental Intermetallic Phase in Wrought Duplex Austenitic-Ferritic Stainless Steels” for 25 Cr Cast Super Duplex Stainless Steels (ASTM A890-5A).

Different tests were carried out on the materials procured from various steel foundries as stated in the ASTM A923. The foundries were designated as Foundry A, B, C and D. All the materials were foundry solution annealed. Materials from Foundry D were solution heat treated at The University of Tennessee also and then they were subjected to heat treatment schedule which was derived …

Microstructural Evolution Of Tial-Intermetallic Alloys Containing W And B, Lan Huang

Masters Theses

The TiAl alloys have been considered as promising candidates for structural-materials applications at around 800⁰C. In this work, new TiAl alloys, containing tungsten (W) and boron (B), have been developed. Using the scanning-electron microscopy (SEM), electron-microprobe, and transmission-electron microscopy (TEM), the effects of W and B on the microstructural evolution of TiAl alloys, including the colony size and lamellar spacing, were analyzed. It is important to point out that fine uniform microstructures (with the colony size smaller than 50 mm) can be conveniently developed after Hot-Isostatic Pressing (HIP) the as-cast alloys at 1,250⁰C and 150 MPa …

Fundamental Studies Of Stabilization Of Polyacrylonitrile Precursor, Stephen Alan White

Masters Theses

The purpose of this study was to examine the stabilization of polyacrylonitrile precursor. Currently, the stabilization of polyacrylonitrile is the limiting step in the production of carbon fibers because of its cost and time requirements. By furthering the understanding of the stabilization process, it may be possible to reduce the cost and time required, allowing the widespread use of carbon fiber in several industries to be achieved.

In this study, the effects of temperature, time, environment, and pressure on the stabilization of polyacrylonitrile were examined. Once fiber samples were heat treated, four experimental techniques were used to examine the samples. …

Investigation Of A Phase Transition In Pure And Magnesia- And Titania-Substituted Hexacelsian, Melanie Jean Kirkham

Masters Theses

Hexacelsian, the hexagonal polymorph of BaAl_{2Si2O8, experiences a phase transition near 300ºC with an accompanying large volume change, which can lead to cracking and thermal shock, limiting the potential applications of hexacelsian. It has previously been reported that certain additions, including MgO and TiO2, can suppress the undesirable phase transition. Room-temperature neutron and high-temperature X-ray diffraction have been used to study the structure and thermal behavior of hexacelsian, both pure and substituted with varying amounts of MgO and TiO2. The diffraction data of the pure sample was refined using the}

P-3 space group. Attempting to refine the substituted sample …