The effect of crystallinity upon the friction and wear of graphites

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Application of wear resistant coatings by the brush plating technique

The development of cobalt molybdenum and cobalt tungsten brush plating electrolytes is described. Their optimum compositions and operating conditions for commercial applications have been determined. The effects of composition, pH, applied voltage, stylus speed and pressure upon deposit composition and efficiency have been investigated. Transmission and Scanning Electron Microscopy have been employed to study the cobalt alloy deposits produced. Evaluation of the wear resistant properties of the cobalt alloys developed in this work was carried out in the laboratory using a pin and disc technique and a simulated hot forging test, and by industrial trials involving the "on site" plating of hot forging dies and cold pressing tools. It was concluded that the electrolytes developed in tl1is work enabled cobalt alloys containing 6% Mo or 8% W to be deposited at 17-20V. Brush plated cobalt deposits possessed a mixed CPU and FCC crystallographic structure at room temperature. The application of 13µm of either of the cobalt alloys resulted in improved wear performance in both pin and disc and simulated hot forging tests. The results of the industrial trials indicated that by the use of these alloys, the life of hot forging dies may be increased by 20-100%. A commercial forging organisation is using electrolytes developed in this work to coat dies prior to forging nimonic alloys. Reductions in forging temperature and improved forging qualities have been reported. Cold pressing tools coated with the alloys showed a reduced tendency to "pick-up" and scoring of the pressed panels. Reports of a reduced need for lubrication of panels before pressing have also been received.

Wear of abrasion resisting materials

The wear behaviour of a series of chromium containing white irons has been investigated under conditions of high stress grinding abrasion using a specimen on track abrasion testing machine. The measured abrasion resistance of the irons has been explained in terms of microstructure and hardness and with respect to the wear damage observed at and beneath abraded surfaces. During abrasion material removal occurred by cracking and detachment from the matrix of eutectic carbides as well as by penetration and micromachining effects of the abrasive grits being crushed at the wearing surface. Under the particular test conditions used martensitic matrix structures gave higher resistance to abrasion than austenitic or pearlitic. However, no simple relationship was found between general hardness or matrix microhardness at wear surfaces and abrasion resistance, and the test yielded pessimistic results for austenitic irons. The fine structures of the 15% Cr and 30% Cr alloys were studied by thin foil transmission electron microscopy. It was found that both the matrix and carbide constituents could be thinned for examination at 100 Kv using conventional dishing followed by ion beam thinning. Flany of the rodlike eutectic N7C3 carbides were seen to consist of clusters of scalier rods with individual 117C3 crystals quite often containing central cores of matrix constituent. 3oth eutectic and secondary N7C3 carbides were found to contain stacking faults on planes normal to the basal plane. In the eutectic carbides in the 30A Cr iron there was evidence of an in-situ PI7C3 C. transition which had taken place during the hardening heat treatment of this alloy. In the as-cast austenitic matrix iron strain induced martensite was produced at the wear surface contributing to work hardening. The significance of these findings have been discussed in relation to wear performance.

Some clinical aspects of the eye in extended contact lens wear

The limbal vascular response to extended contact lens wear was examined in a group comparative study initially intended to last eighteen months. After six months all patients wearing contact lenses had presented with micro-epithelial cysts. This unanticipated occurrence of the micro-epithelial-cysts necessitated termination of the study, and limited the quantity of data collected. However, sufficient results were available to allow a limited description of •the vascular response to this form of contact lens wear. Interpretations of the date collected ore discussed in relation to suggested vasostimulating factors in the cornea. The micro-epithelial cysts observed after extended wear were classified and their rate of recovery recorded. A further clinical study was undertaken to observe cysts in both contact lens - and non contact lens-wearing eyes. Cysts were observed in every category of patient, although the characteristic patterns varied. These observations of micro-epithelial cysts are discussed with respect to the aetiopathogeneses of corneal epithelial cystic disorders. Subsequently, attempts were made to induce cysts in rabbit corneae by extended contact lens wear. Clinical observations revealed cyst-like appearances. Histological sections did not contain cysts but did exhibit signs characteristic •of cystic disorders of the corneal epithelium. In general, the results from the study indicate that extended wear is subjectively acceptable to contact lens wearers. However, the objective findings of significant vascular changes, micro-epithelial cysts and cases of acute red eye response cast considerable doubt on the recommendation of extended wear contact lenses for purely cosmetic applications.

An investigation of the relationship between temperature, forces and tool wear in turning and drilling

Developing a means of predicting tool life has been and continues to be a focus of much research effort. A common experience in attempting to replicate such efforts is an inability to achieve the levels of agreement between theory and practice of the original researcher or to extrapolate the work to different materials or cutting conditions to those originally used. This thesis sets out to examine why most equations or models when replicated do not give good agreements. One reason which was found is that researchers in wear prediction, their predictions are limited because they generally fail to properly identify the nature of wear mechanisms operative in their study. Also they fail to identify or recognise factors having a significant influence on wear such as bar diameter. Also in this research the similarities and differences between the two processes of single point turning and drilling are examined through a series of tests. A literature survey was undertaken in wear and wear prediction. As a result it was found that there was a paucity in information and research in the work of drilling as compared to the turning operation. This was extended to the lack of standards that exist for the drilling operation. One reason for this scarcity in information on drilling is due to the complexity of the drilling and the tool geometry of the drill. In the comparative drilling and turning tests performed in this work, the same tool material; HSS, and similar work material was used in order to eliminate the differences which may occur due to this factor. Results of the tests were evaluated and compared for the two operations and SEM photographs were taken for the chips produced. Specific test results were obtained for the cutting temperatures and forces of the tool. It was found that cutting temperature is influenced by various factors like tool geometry and cutting speed, and the temperature itself influenced the tool wear and wear mechanisms that act on the tool. It was found and proven that bar diameter influences the temperature, a factor not considered previously.

Do ‘passive’ medical titanium surfaces deteriorate in service in the absence of wear?

Globally, more than 1000 tonnes of titanium (Ti) is implanted into patients in the form of biomedical devices on an annual basis. Ti is perceived to be ‘biocompatible’ owing to the presence of a robust passive oxide film (approx. 4 nm thick) at the metal surface. However, surface deterioration can lead to the release of Ti ions, and particles can arise as the result of wear and/or corrosion processes. This surface deterioration can result in peri-implant inflammation, leading to the premature loss of the implanted device or the requirement for surgical revision. Soft tissues surrounding commercially pure cranial anchorage devices (bone-anchored hearing aid) were investigated using synchrotron X-ray micro-fluorescence spectroscopy and X-ray absorption near edge structure. Here, we present the first experimental evidence that minimal load-bearing Ti implants, which are not subjected to macroscopic wear processes, can release Ti debris into the surrounding soft tissue. As such debris has been shown to be pro-inflammatory, we propose that such distributions of Ti are likely to effect to the service life of the device.

Wear resistance of surface treated metal-working tools

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