Characterisation and Modelling of Normal and Compound Impact Wear in Common Engineering Alloys

Impact wear is one of the types of wear that have been least researched previously and therefore data on the causes is still quite scarce. It occurs in many engineering and industrial components, posing severe wear problems and limiting service life, but has not been studied as frequently as other wear mechanisms (e.g., abrasion, adhesion, erosive). Impact wear also occurs widely in industrial machinery such as valves, bearings and cams used in energy, metallurgy, petroleum industry and electric power applications, and tools used in mining for rock drilling. Knowing what and how different impact wear parameters affect the wear intensity would be helpful to gaining better understanding of their effects on the impact wear and eventually longer optimal life of the equipment.
The work presented in this thesis aimed to investigate the previously undetermined contribution of the ‘zero wear’ volume for five metallic alloys under repetitive normal impact with point contact geometry. These materials are: austenitic stainless steel AISI 304; medium carbon steel (EN8); ductile cast iron (EN-GJS-600-3); aluminium alloy (AlSi9Cu3) and phosphor bronze (PB102).
The mechanical performance and wear resistance of these materials were assessed using an impact hammering wear rig, while the wear scar features were examined using microscopy techniques and 3D profilometry of the surfaces through use of an Alicona SL in addition to both Vickers hardness and microhardness tests. The analysis of the wear scars suggests that zero wear volume (volume loss due to compression and specimen surface moving in space to a different location but remains in the contact zone) is the main contributor to the total volume ‘loss’ for all materials, and, for specific materials, plastic flow volume and bulk hardness could be a significant parameter in characterising zero wear volume and scar depth.
The research also focused on the crucial role of impact angle for three metal alloys: two types of austenitic stainless steel (AISI 304 and AISI 316) and medium carbon steel (EN8). Wear resistance and mechanical performance were evaluated using the same techniques as utilised for zero wear volume and metallurgical characterisation was achieved through surface and subsurface examination for plastic deformation, grain size, crack initiation and propagation on both the surface and subsurface, and eventually cracks types (intergranular or transgranular). The results suggest that the impact wear damage mechanism changed depending on the impact angle and it has a significant effect on the wear loss of tested materials and the depth of plastic region and deformed grains.
Microhardness profiles for the wear scar were plotted for all ductile materials during this work for both surface and subsurface under different impact angles using an automated hardness tester (Struers Durascan). The results suggest that the hardening value and depth are inversely proportional to impact angle and reduced significantly from normal impact 90° to compound impact 60° and 45°.
Finally, the research developed a new predictive model extracted from the experimental work on both AISI types, 304 and 316, and the EN8 medium carbon steel that was compared with other published papers, taking into consideration the role of impact angle during impact throughout the calculation of both the normal and tangential components of impact force.