Date of Award

1995

Publication Type

Doctoral Thesis

Degree Name

Ph.D.

Department

Mechanical, Automotive, and Materials Engineering

Keywords

Engineering, Metallurgy.

Supervisor

Alpas, A. T.

Rights

info:eu-repo/semantics/openAccess

Abstract

The purpose of this work was to study the dry sliding wear properties of aluminum matrix composites A356Al-SiC, 6061Al-Al$\sb2$O$\sb3$, 2014Al-SiC, with 0-20 pct. volume fraction reinforcement. Experiments were performed with a load range of 1 to 450 N and a sliding velocity range of 0.1 to 5.0 m/s. Two types of counterface materials, namely SAE52100 bearing steel and mullite, were used. Three different wear rate regimes were observed in the composites. These were: (i) regime I (ultra mild wear regime), which occurred at low loads and low sliding velocities, where ceramic particles acted as load bearing elements. In this region increasing the particle size and volume fraction of particles improved the wear resistance of the composites. (ii) In regime II (mild wear regime) that covered mid-range loads, there was no significant difference between the wear rates of the unreinforced and the reinforced alloys. In this regime, particles at the contact surfaces fractured and shear forces were transmitted to the aluminum matrix. Wear proceeded by a subsurface delamination process. In addition to promoting subsurface cracking, particles also caused the abrasion of the aluminum matrix. (iii) The transition from regime II (mild wear) to regime III (severe wear) occurred at higher loads and/or higher sliding velocities when the contact surface temperature exceeded a critical value. The transition loads and temperatures were higher in the composites compared to the unreinforced Al alloys. Increasing particle size improves the wear resistance in regime I and delays transition to regime II. However there is no obvious difference in the wear resistances of the composites reinforced with different particle sizes in regime II and regime III. Increasing the volume percent or particles delays the transitions between regime I and regime II as well as between regime II between III. Subjecting the materials to wear against a mullite counterface, which has a smaller thermal conductivity than a counterface made of steel, led to the occurrence of severe wear at lower loads. Different types of wear maps, including wear regime maps, wear rate maps, wear temperature maps and wear mechanism maps, have been constructed by considering the applied mechanical parameters such as the load and the sliding velocity. These maps provide a convenient way to summarize wear rate controlling mechanisms in metal matrix composites. To study the plastic deformation and damage accumulation below the contact surfaces, new metallographic techniques have been developed and used to determine the magnitude of the shear strains and the microhardness gradients in near surface regions. Under dry sliding wear conditions, both the magnitude of plastic strains and the depth of heavily deformed zones increased with sliding distance and applied load. The flow stress and the plastic strains in the deformed zones are shown to obey a Voce type work hardening law. A model based on the hypothesis that delamination cracks leading to the generation of wear debris are formed by the coalescence of voids at a critical depth below the worn surfaces has been proposed. It is shown that the critical depth for maximum rate of damage accumulation is determined by a competition between the plastic strain which enhances void growth and the hydrostatic pressure which suppresses it.Dept. of Mechanical, Automotive, and Materials Engineering. Paper copy at Leddy Library: Theses & Major Papers - Basement, West Bldg. / Call Number: Thesis1995 .Z42. Source: Dissertation Abstracts International, Volume: 57-07, Section: B, page: 4675. Adviser: A. T. Alpas. Thesis (Ph.D.)--University of Windsor (Canada), 1995.

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