A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfillment of the requirements for the degree of Doctor of Philosophy.‘ Johannesburg, August 2017 / Fe-B-C composites were produced, from boron carbide and iron powders, using spark plasma sintering. This provided information on the effects of rapid sintering on densification, composition and the microstructure of the materials produced. The composition range included a selection high Fe contents (69.3, 78 and 80.9 vol. % Fe-B4C) and high B4C concentrations (1, 3, 5 vol. % Fe-B4C). The properties of the materials were investigated to determine the potential for using relatively cheap Fe and B4C powders to produce hard, wear resistant materials. High Fe-B4C composites were sintered at 900, 1000 and 1100°C at 60 MPa. Densification increased with increasing temperature and at 1100° each composition achieved ≥ 97 % densification. The materials reacted during sintering with the main phases observed being Fe2B and Fe3(B,C) whilst additional phases formed were FeB, C and Fe23(B,C)6.Comparing the phases that were produced to Fe-B-C phase diagrams showed deviations from expected compositions, indicating the non-equilibrium nature of producing the composites using SPS. Although the composites were not at equilibrium, all the B4C reacted and could not be maintained, even with fast heating and cooling rates. The properties of the materials were dependent on both densification and the phases that were present after sintering. Materials containing higher amounts of the Fe2B phase showed higher hardness and fracture toughness results, up to 13.7 GPa and 3.5 MPa.m0.5 respectively for the 69.3 vol. % Fe-B4C. The materials were sensitive to grain and pore growth which negatively affected properties at 1100°C. The transverse rupture strength of 388.3 MPa for 80.9 vol. % Fe-B4C composite was the greatest, and showed evidence of both intergranular and transgranular fracture. The strength was affected by a fine dispersion of porosity at the grain boundaries, throughout the material, and free carbon in the structure was detrimental to the strength of the 69.3 % Fe-B4C. The wear rates were lower using Si3N4 wear balls compared to stainless steel balls, where 69.3 vol. % Fe-B4C showed the best wear rates, 8.9×10-6 mm3/Nm (stainless steel ball) and 1.77×10-6 mm3/Nm (Si3N4 ball), due to the higher Fe2B composition and free carbon acting as a lubricant during sliding. 1, 3 and 5 vol. % Fe-B4C composites were sintered to densities above 97 % of theoretical at 2000°C and 30 MPa. The formation of a transient FeB liquid phase assisted densification. 1 % Fe-B4C attained hardness and fracture toughness up to 33.1 GPa and 5.3 MPa.m0.5 with a strength of 370.5 MPa. Thermal mismatch between the FeB phase and B4C caused high residual stresses at the interface which led to cracking and pull-out of the FeB phase. Residual carbon at the grain boundary interface exacerbated the pull-out effect. Increasing Fe and the subsequent FeB phase had an embrittling effect. The materials suffered severe wear of up to 36.92×10-6 mm3/Nm as a result of the pull-out with the remaining porosity acting as a stress raiser. 20 vol. % of the Fe in each system was substituted with Ti to reduce the presence of residual carbon. Although in some case the properties of the respective compositions improved, residual carbon was still present in the composites. / MT2018

Thesis (M.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by Paul Dudley Hartung. / M.S.

Thesis (B.S.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1981. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by David Alan Stephenson. / B.S.

Thesis. 1977. Mech.E.--Massachusetts Institute of Technology. Dept. of Mechanical Engineering. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Includes bibliographical references. / by K. Subramanian. / Mech.E.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Vita. / Includes bibliographical references. / by Hyo-Chol Sin. / Ph.D.

In electrical contacts, thin films of nickel and gold or silver are traditionally plated on top of a copper base plate to provide corrosion resistance and wear protection. Most recently, the rising cost of noble metals and intensified competition in manufacturing technology has driven the industry towards thinner plating layers, which gives rise to questions regarding how interfacial contact and wear is affected by plating thickness and material characteristics. This study uses a combination of finite element analysis and ex-situ wear measurement to determine the effect of gold plating thickness on wear performance under linear reciprocating sliding contact. Correlations between predicted and measured results lead to insight into the stress state within the multi-layer system under contact conditions as well as a wear map for gold platings that can be used to inform future connector designs. The middle layer material, Ni, is relatedly inexpensive, but takes a relatively long time to deposit. Because this deposition time has a direct influence on the cost of manufacturing, it is important to reduce the Ni thickness as well. This project thus determines how different combinations of Ni and Au properties influence wear and subsurface layer exposure, which is critical for determining the makeup of future, low-cost, connector designs.

The objective of this work has been to investigate the applicability of the gas gun to study the armature-rail interface wear characteristics relevant to rail gun operations. The approach involved developing constitutive models for armature materials (aluminum 6061) as well as oxygen-free high-thermal conductivity copper as the rail material. Taylor rod-on-anvil impact experiments were performed to validate the accuracy of constitutive strength models by correlating predictions of dynamic simulations in ANSYS AUTODYN with experimental observations. An optical comparator was used to discretize the cross sectional deformation profile of each rod-shaped sample. Parameters of the Johnson-Cook strength model were adjusted for each material to match deformation profiles obtained from simulations with profiles obtained from impact experiments. The fitted Johnson-Cook model parameters for each material were able to give overall deformed length and diameter values within 2% of the experimentally observed data. Additional simulations were then used with the validated strength model parameters to design the geometry involving cylindrical rods of armature material accelerated through a concentric cylindrical extrusion die made of copper, to emulate the interface wear effects produced in a rail gun operation. Experiments were conducted using this geometry and employing both the 7.62mm and 80mm diameter gas guns. Microstructural analysis was conducted on interfaces of the recovered samples from both designs. Hardness measurements were also performed along the interface layer to evaluate the structure formation due to solid-state wear or melt formation. The stress and strain conditions resulting in the observed microstructural effects were correlated with predictions from numerical simulations performed using the validated material models. The overall results illustrate that the stress-strain conditions produced during acceleration of Al through hollow concentric copper extrusion die, result in interface deformation and wear characteristics that are influenced by velocity. At velocities (less than 800m/s), interface wear leads to formation of layer dominated by solid-state alloying of Cu and Al, while higher velocities produce a melted and re-solidified aluminum layer. Hence, use of different armature (Al-based) and rail (Cu-based) materials can be evaluated with the gas-gun set-up employed in the current work to study the effects of interface wear ranging from formation melt layer to solid-state alloying as a function of material properties and velocity.

No description available.

Thesis (M.S.)--University of Texas at El Paso, 2008. / Title from title screen. Vita. CD-ROM. Includes bibliographical references. Also available online.

Thesis (Ph. D.)--Ohio State University, 2008. / Title from first page of PDF file. Includes bibliographical references (p. 189-198).