Theses and Dissertations - Department of Metallurgical and Materials Engineering

Permanent URI for this collection

https://ir.ua.edu/handle/123456789/122

Browse

Now showing 1 - 7 of 7

The investigation of accumulative roll bonding for processing TI/Al multilayered composite targets for perforation testing
(University of Alabama Libraries, 2015) Stokes, Derrick D.; Acoff, Viola L.; University of Alabama Tuscaloosa
Multilayered composites (MLCs) processed using accumulative roll bonding (ARB) have great potential as candidates for perforation testing. In the current study, multilayered composites comprised of alternating layers of titanium and aluminum have been investigated. Since the ARB process has been shown to induce anisotropy, the Ti/Al MLCs were first subjected to quasi-static loading to determine the effects of anisotropy. The MLCs were then subjected to perforation testing using projectiles with various apex angles. The effects of perforation testing were studied in terms of varying ballistic parameters and characterization of the fracture surfaces of the MLCs. The results of this study show that ARB-processed Ti/Al MLCs are promising for use in ballistic and impact applications.
Investigation of influencing factors in liquid metal embrittlement of advanced high strength steel
(University of Alabama Libraries, 2019) Massie, Daniel Joseph Woodson; Brewer, Luke N.; University of Alabama Tuscaloosa
This thesis explored the influence of temperature, steel type, galvanization method, and macro-strain level on the sensitivity of advanced high strength steels (AHSS) to zinc-based liquid metal embrittlement (LME). It is critical to understand the influencing factors of LME because zinc coatings are commonly used to protect steel parts from corrosion, and the use of advanced high strength steel in the automotive industry is increasing. Electro-galvanized and zinc free samples of a transformation induced plasticity steel, TBF1180, and a complex phase steel, CP1200, were studied to examine the sensitivity of each to LME. Hot-dip galvanized samples of CP1200 were examined alongside the electro-galvanized samples to investigate the effect of coating method on the LME effect. Hot tension tests were performed and ductility trough graphs were created for all samples to examine the effect of these factors on LME during fracture. Additionally, small-strain tensile tests were designed and performed on the steels to examine LME crack nucleation. From the results it was determined that LME response is temperature and steel dependent. It was shown that TBF 1180 nucleated LME cracks at 600 °C while CP1200 did not. It was also determined that hot-dip galvanized coatings more readily nucleate LME cracks than electro-galvanized coatings. Finally, these results suggest that macro-plastic deformation may not be required to initiate an LME response.
Investigation of liquid metal embrittlment in advanced high strength steels
(University of Alabama Libraries, 2018) Briant, Nathaniel P.; Brewer, Luke N.; University of Alabama Tuscaloosa
This thesis explored the susceptibility of ferritic/bainitic, advanced high strength steels to zinc-based liquid metal embrittlement (LME). The understanding of the causes and effects of LME is critical because of the common use of zinc coatings for corrosion protection and an increased used of advanced high strength steels in industries such as automotive. Transformation induced plasticity steels, TBF 1180 and TRIP 700, and a complex phase steel, CP 1200, were studied to assess their susceptibility to LME during hot tensile tests. Comparisons between stress versus strain curves collected with and without zinc coatings at various temperatures and strain rates were used to determine the effect of the zinc-based embrittlement on the mechanical properties of these steels. The stress versus strain curves were collected using uniaxial hot tensile tests in a Gleeble 1500D thermal-mechanical simulator from Dynamic Systems Inc. The fracture modes were studied using scanning electron microscopy and energy-dispersive X-ray spectrometry (EDS). From the results it was determined that all three steels demonstrated LME at temperatures between 800 C and 900 C and nominal strain rates of 1.3 and 0.13 strain per second. The fracture mode for all LME cracks was found to be intergranular.
Oxidation behavior of refractory complex concentrated alloys: computational and experimental studies
(University of Alabama Libraries, 2019) Hunter, Brett Matthew; Weaver, Mark L.; University of Alabama Tuscaloosa
In recent years, high entropy alloys (HEAs) and, more specifically, refractory complex concentrated alloys (RCCAs) have been of increased interest due to their potential as replacements in high temperature environments. This dissertation work has systematically investigated the phase equilibria and oxidation resistance of an alloy system with the basis AlHfNbTiZr. The three alloys investigated in the five-component system were all found to contain a single phase microstructure composed of B2 while the seven component alloy was comprised of a B2 and C14 Laves phase. While the oxidation behavior was parabolic for all alloys studied, the five component alloys exhibited 2-stage parabolic behavior compared to a single stage in the seven-component alloy. The oxidation behavior was governed by a combination of thermodynamics and kinetics with regards to diffusion of oxygen into the system. The five component alloys were found to form an external scale comprised of a ZrTiO4-based structure containing all five elements in their respective stoichiometry. Internal oxidation also occurred in these alloys and exhibited a relationship between diffusion of cations out of the alloy and diffusion of anions into the alloy. However, the seven-component alloy did not form an external scale and was governed completely by oxygen diffusion into the alloy and thermodynamic factors as to the composition of the scale. This work has furthered the fundamental understanding of the oxidation behavior of RCCAs and the accuracy of modelling on the phase equilibria of these alloys.
Phase transformations during cooling of automotive steels
(University of Alabama Libraries, 2017) Padgett, Matthew Chase; Brewer, Luke N.; University of Alabama Tuscaloosa
This thesis explores the effect of cooling rate on the microstructure and phases in advanced high strength steels (AHSS). In the manufacturing of automobiles, the primary joining mechanism for steel is resistance spot welding (RSW), a process that produces a high heat input and rapid cooling in the welded metal. The effect of RSW on the microstructure of these material systems is critical to understanding their mechanical properties. A dual phase steel, DP-600, and a transformation induced plasticity bainitic-ferritic steel, TBF-1180, were studied to assess the changes to their microstructure that take place in controlled cooling environments and in uncontrolled cooling environments, i.e. resistance spot welding. Continuous cooling transformation (CCT) diagrams were developed using strip specimens of DP-600 and TBF-1180 to determine the phase transformations that occur as a function of cooling rate. The resulting phases were determined using a thermal-mechanical simulator and dilatometry, combined with light optical microscopy and hardness measurements. The resulting phases were compared with RSW specimens where cooling rate was controlled by varying the welding time for two-plate welds. Comparisons were drawn between experimental welds of DP-600 and simulations performed using a commercial welding software. The type and quantity of phases present after RSW were examined using a variety of techniques, including light optical microscopy using several etchants, hardness measurements, and x-ray diffraction (XRD).
Texture evolution of niobium, aluminum, and titanium in Ti-Al-Nb composites processed by accumulative roll bonding
(University of Alabama Libraries, 2012) Qu, Peng; Acoff, Viola L.; University of Alabama Tuscaloosa
Multilayered Ti/Al/Nb composites were produced by the accumulative roll bonding (ARB) process utilizing pure Ti, Al and Nb element sheets. Up to four cycles of ARB were applied to the composites. The microstructure and texture evolution of the elemental Nb, Al and Ti phase was studied by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM) and electron backscattered diffraction (EBSD). Nanoindentation was performed as well. Nb and Ti layers necked and fractured as the number of ARB passes increased. After four ARB cycles, a nearly homogeneous distribution of Nb and Ti layers in an Al matrix was achieved. The as-received Nb sheet exhibited a fully lamellar structure and had a strong cold rolling texture. After subjecting to ARB, slight grain refining was observed and the high angle grain boundary (HAGB) fraction was increased. The intensity of the α-fiber texture was weakened while that of the γ-fiber texture was strengthened during ARB. The texture evolution was attributed to partial recrystallization during the ARB process as a result of adiabatic heating. In the Al phase, grain refinement occurred with increased ARB cycles as a result of the increased fraction of HAGBs. Strong recrystallization texture occurred for samples subjected to increased ARB cycles as a result of the adiabatic heating produced. The shear bands at the Ti/Al interface reduced the intensity of the cold rolling fiber textures of Al. There was no evidence of shear component from the orientation distribution function (ODF) results. Twinning was observed in the Ti phase for all stages of deformation but had little influence on microstructure. Grain refinement was achieved as a result of the accommodating of shear bands to the limited slip system of Ti. Recrystallization occurred at higher ARB cycles as a result of adiabatic heating. The Schmid factor shows that Basal and prismatic slip systems dominate at low ARB cycles, while at higher deformation, the first-order and second-order pyramidal slips are active.
The texture-structure relationship in ti-al-nb multilayered composites processed by accumulative roll bonding
(University of Alabama Libraries, 2014) Zhou, Liming; Acoff, Viola L.; University of Alabama Tuscaloosa
Multilayered Ti/Al/Nb composites were processed by the accumulative roll bonding (ARB) process using elemental foils of titanium, aluminum, and niobium. The rolled multilayered composites (MLCs) were prepared by ARB process up to two ARB cycles. The microstructure and texture evolution of the Ti, Al, and Nb in the MLCs were studied utilizing X-ray diffraction (XRD) and scanning electron microscopy (SEM) equipped with electron backscattered diffraction (EBSD). The characterizations of crystallographic texture and microstructure were conducted using a creative approach; a layer by layer method on the rolling plane Texture evolution in the MLCs produced by symmetric rolling and asymmetric rolling was also studied in a layer by layer manner. In addition to studying the texture evolution of the Nb in the MLCs produced by the ARB process, the Bingham distribution was used to model the orientation distribution function (ODF) by employing MTEX, a quantitative texture analysis toolbox for Matlab®. This provided a bridge for the gap between experiments and Bingham modeling in terms of the crystallographic texture. As the numbers of ARB cycles increased, the microstructures tended to be heterogeneous through the thickness. Also, the texture development of the mating layers in the MLCs exhibited multiple texture domination rather than random. Furthermore, the developed textures of the layers in the MLCs during the ARB process were significantly different from that produced by conventional rolling. The characteristic textures formed in the MLCs subjected to the ARB process implied that the partial recrystallization and recovery occurred as a result of the adiabatic heat. The shear and compressive strain distributions were inhomogeneous through the thickness. Thus, the texture developments of the layers in the MLCs suggested a strong locational dependence. Where, the surface and the middle layers tended to form textures attributed to the shear, while, the transitory layers tended to form texture components induced by the compression.

UA cloudflare authentication

Browse

Browsing Theses and Dissertations - Department of Metallurgical and Materials Engineering by Author "Barkey, Mark E."

Results Per Page

Sort Options