Lamellar graphite iron (LGI) is commonly used in diesel engine applications such as piston rings–cylinder liner where an excellent combination of physical and tribological properties is essential to avoid scuffing and bore polishing issues. The excellent tribological behaviour of LGI alloys is related to the graphite lamellas, which act as solid lubricant agents by feeding onto the tribosurfaces under sliding conditions. However, increasingly tighter emissions and fuel economy legislations and the higher demands on enhanced power and durability have encouraged both engine designers and manufacturers to introduce pearlitic compacted graphite irons (CGI) as an alternative material replacing LGI, although the poor machinability of pearlitic CGI alloys compared to the LGI remains a challenge. The focus of this study is placed on investigating how the microstructure of LGI and CGI alloys affects their mechanical and tribological properties. This was initially undertaken by investigating representative, worn lamellar cast iron piston rings taken from a two-stroke large-bore heavy-duty diesel engine. As known that it is tribologically essential to keep the graphite open under sliding conditions, in particular under starved lubrication regimes or unlubricated conditions to avoid scuffing issues; however, this study revealed the closure of a majority of graphite lamellas; profoundly for those lamellas that were parallel to sliding direction; due to the severe matrix deformation caused by abrasion. Both microindentation and microscratch testing, which were used to crudely simulate the abrasion under starved lubricated condition in combustion chamber, suggested a novel mechanism of activating the graphite lamellas to serve as lubricating agents in which the matrix deformation adjacent to the graphite initially resulted in fracturing and then extrusion of the graphite lamellas. Additionally, in order to investigate the relation between matrix constituents, mechanical properties and machinability of cast iron materials, solution-strengthened CGI alloys were produced with different levels of silicon and section thicknesses. The results showed significant improvements in mechanical properties and machinability while deteriorating the ductility. Moreover, multiple regression analysis, based on chemical composition and microstructural characteristics was used to model the local mechanical properties of high Si ferritic CGI alloys, followed by implementing the derived models into a casting process simulation which enables the local mechanical properties of castings with complex geometries. Very good agreement was observed between the measured and predicted microstructure and mechanical properties.

In order to successfully incorporate the tremendous possibilities of nanoscale applications into devices and manufacturing, significant studies need to be conducted of the properties and mechanics of materials of this small scale. In this thesis, the effect of repeated scanning of KBr, aluminum, and gold was studied by using a nanoindenter and Atomic Force Microscope (AFM) in varying environments. Additional research was performed to study the environmental effects of gold film scratching using a Taber Shear/Scratch Tester. Scanning of KBr single crystal surface in air with a diamond tip in the Hysitron Triboindenter formed surface ripples 100 nm high, 1 micron apart. It has been observed that the nanoripple's initial height and period increase with the number of repeated scans. The surface ripples form perpendicular to the scanning direction, beginning at the bottom of sloped samples and working their way up the entire scan area. The addition of water to a wear experiment on gold film produced considerably deeper wear areas than its ambient air counterpart in both scanning machines. Scratch testing with a conical diamond tip of 77 µm radius with 125 g normal load also produced deeper wear tracks in water than in ambient air conditions. Several mechanisms may be responsible for the ripples formation, including dislocation dynamics, chatter, piezo hysteresis and others. Most likely there is a combination of effects, with a clear differentiation between nanoripple's origination and propagation. Mechanisms responsible for rippling, including system dynamic response and stick slip behavior are investigated. Topography modification appears to be the main result of ambient wear tests at the nanoscale, whereas much higher wear rate and nanoripples are observed in water. It is possible that this moisture is assisting grain fracture and pull off.

The cutting action of a single abrasive grain was investigated using a combination of high-speed scratch tests and finite element models. The high-speed scratch tests were unique in that the cutting conditions of a grinding operation were closely replicated. Two geometries were tested: a round-nosed stylus to approximate a 15-grit abrasive grain and a flat-nosed stylus to approximate a worn 46-grit abrasive grain. The three-dimensional finite element model was unique in that a hybrid Euler-Lagrange method was implemented to efficiently model the interaction between an abrasive grain and a workpiece. The finite element model was initially validated using indentation tests to remove the complexities of relative motion from the validation process. The validation was completed through comparisons to the experimental scratch tests. The results of the analysis revealed several key findings. Rubbing, plowing, and cutting do not display distinct transitions; rather, they coexist with different weightings depending on the scratching speed and the depth of cut. The normal forces increased for a given depth of cut as the scratching speed was increased due to strain-rate hardening of the workpiece. The tangential forces decreased for a given depth of cut as the scratching speed was increased due to a reduction in the coefficient of friction and a change in the cutting mechanics from plowing to cutting. The change in the cutting mechanics was investigated by analyzing the evolution of the scratch profiles as the depth of cut and scratching speed were changed. It was found that higher scratching speeds produced less material pile-up and this was attributed to a change in the cutting mechanics. Due to the change in the cutting mechanics, the specific energy decreased as the depth of cut and scratching speed were increased. A numerical case study revealed that reducing the grain size resulted in: lower forces, lower specific energies, and smaller volumes of subsurface stresses. The finite element model was adapted to work in conjunction with the flat-nosed stylus creating the first model capable of simulating the cutting of an abrasive grain in three dimensions.

The goal of this work is to understand how the wear and deformation mechanisms of hardmetalinserts change when the cobalt binder phase is replaced with a dierent metal or analloy. The focus is on inserts for steel turning. The work presented in this licentiate thesisconsists of the rst steps.Cobalt is the most common binder phase in hardmetal tools based on tungsten carbide asthe hard phase. Metallic cobalt powder, present during the manufacturing, has been associatedwith lung diseases and an increased risk for lung cancer if inhaled. Therefore it is importantto investigate alternative binders as one possible solution.This work studies binder phase alloys from the iron-nickel-cobalt system. These alloyscan be either austenitic, martensitic or a mixture of the two phases. By changing the binderphase composition to change the crystal structure it is possible to tailor the macroscopic mechanicalproperties of the material. It is also possible to tailor the composition in such a waythat the binder is transformation toughening, forming martensite as a response to mechanicaldeformation.The majority of inserts for steel turning are coated, and it is important to investigate if thehardmetals with alternative binder can be coated and if the coating adhesion is sucient forsteel turning.Four dierent alternative binder alloys and one reference with cobalt binder coated bychemical vapour deposition were investigated by scratch testing to determine the adhesion.The scratch test adhesion was sucient on all samples, but signicant variations in coatingadhesion were found.One alternative binder with 86wt%Ni and 14wt%Fe and a reference with cobalt binder manufacturedto mimic state of the art turning inserts were tested in steel turning. The alternativebinder grades had a lower resistance to plastic deformation and this was attributed to earlyaking of the coating due to a lower coating adhesion. Focused ion beam and scanning electronmicroscopy were used to study the deformation of the hard metal in the used cuttinginserts.