| An investigation of the wear behaviour of the dispersed phase in lubricated sliding and rolling wear of in-situ prepared {dollar}rm TiBsb2{dollar} particle reinforced 2024 T4 Al alloy matrix composites against 52100 steel and pearlitic nodular cast iron respectively has been undertaken. Results are compared with those of a powder metallurgy SiC particle reinforced 2124 T4 Al alloy matrix composite. In sliding contact, 0.3 {dollar}rmmu m{dollar} {dollar}rm TiBsb2{dollar}-MMC showed slightly less wear than 1.3 {dollar}rmmu m{dollar} {dollar}rm TiBsb2{dollar}-MMC for the same volume fraction of the reinforcement. Due to strong interfacial bonding, the {dollar}rm TiBsb2{dollar} particles on the wear track were polished and particle pull-out was largely absent. However, particle pull-out and subsequent third-body wear were the major wear mechanisms in lubricated sliding of the SiC-MMC. The wear of the steel mating surfaces worn against the {dollar}rm TiBsb2{dollar}-MMCs was minor. In rolling contact, the smaller, 0.3 {dollar}rmmu m{dollar} size {dollar}rm TiBsb2{dollar}-MMG showed five times higher weight loss than the 1.3 {dollar}rmmu m{dollar} {dollar}rm TiBsb2{dollar}-MMC for the same content of reinforcement, however, the wear of the cast iron was opposite. A high density of surface cracks was present on the wear track of the 0.3 {dollar}rmmu m{dollar} {dollar}rm TiBsb2{dollar}-MMC but not on the 1.3 {dollar}rmmu m{dollar} MMC. The significance of strong particle/matrix interfacial bonding and particle size effect on the wear behaviour of MMCs in lubricated sliding and rolling wear is discussed.; Short crack behaviour needs to be the basis for contact fatigue wear models and this was addressed in the thesis. The Double Slip Plane (DSP) crack model was solved numerically to examine the effect of extensive plasticity ahead of the crack tip on the threshold stress intensity for crack propagation, {dollar}rm Ksb{lcub}A,cr{rcub}.{dollar} By accounting for dislocation crack tip shielding, it is shown that below a critical crack length, {dollar}rm Ksb{lcub}A,cr{rcub}{dollar} is not constant, but rather decreases with decreasing crack length. A method to calculate crack propagation rates based on dislocation density distributions is presented. The DSP model can be further modified to account for crack/particle interactions which are encountered in rolling wear of metal matrix composites. |
