We present a description of the design, construction and operation of a magnet system comprising of 2 HTS coils separated by 164 mm, that can encompass a plasma coating module. The coil system ...comprises of two winding packages of 3 pancake pairs of BSCCO (bismuth strontium calcium copper oxide)/Ag tape. These are mounted such that they are in optimum thermal contact with an Edwards Coolstar Coldhead, model 6/30, which is attached to a Cryodrive 3.0 compressor unit. This allows operation of the magnets down to 20 K. The windings provide superconducting ampere turns for an iron core. The main objective of this project is to explore the replacement of high energy density permanent magnets with electromagnets in order (a) to achieve higher fields and (b) to be able to vary the field in time during a given coating process.
Evaluation of the wear resistance for tools and dies, particularly for coated components, is a challenging task in surface engineering testing. Pin‐on‐disc is a widely employed method in the ...literature; its result is rather associated with the friction aspect of the samples than wear resistance for components. A microabrasive test has been suggested recently to assess the wear resistance of hard coatings. The key point in that is to simulate the aspect which is close to the factor of the industrial performance for most of the components. This paper aims to compare pin‐on‐disc tests and microabrasive methods. Two hard coatings of CrN and CrSiN were deposited using a closed field unbalanced magnetron sputter ion plating system. SiC was used as the abrasive particle in the slurry. Results show that the abrasive wear rates of the CrN coatings changed sensitively with the depositing parameters. At the same time, the specific wear rate from pin‐on‐disc test was not able to pick up the change of wear endurance of the coatings. A hole drilling test indicates that the number of holes increases significantly when the abrasive wear rate is lower than a certain critical value. It is concluded that the microabrasive test is an appreciable method in practice to evaluate the wear resistance of hard coatings.
In the past, MoS
2 coatings deposited by sputtering have consisted of a first few layers with a dense coherent structure followed by an open columnar structure, with only the first few layers ...providing any wear resistance. The high ion-current densities at low substrate bias voltages, characteristic of the closed-field unbalanced magnetron sputter ion-plating system, produce MoS
2 coatings that are dense, coherent and adherent with very good tribological properties. The tribological properties of these coatings have been tested by using reciprocating and pin-on-disc friction and wear machines, and the results are presented. The properties of the coatings were improved by optimising the deposition parameters, in particular by reducing the amount of water vapour present in the atmosphere of the coating system. It has been found that the properties can be further improved by the co-deposition of small amounts of metal with the MoS
2. The equipment and deposition methods are described. The MoS
2/metal composite coatings were harder, much more wear-resistant and also less sensitive to water vapour in the testing atmosphere. They gave excellent wear resistance at loads as high as 140
N on the reciprocating wear tester using a 6
mm diameter WC pin. The coefficient of friction was as low as 0.02 at a humidity of 40%, and the coatings and adhesion scratch tests indicated critical loads of >120
N. The composite coatings have been studied by micro hardness testing, scratch adhesion testing, pin-on-disc and reciprocating friction and wear tests. The structure of the coatings was studied by optical microscopy and scanning electron microscopy of normal sections and taper sections produced by ball cratering techniques. Some applications, including the coating of cutting and forming tools, are described.
The deployment of a vascular stent during angioplasty has greatly reduced the risks of restenosis. However, the presence of the device still induces a host response as well as a mechanical action on ...the blood vessel wall and an alteration of the haemodynamics. Platelet and inflammatory cells can adhere on the stent surface and be activated to produce biochemical signals able to stimulate an excessive proliferation of the smooth muscle cells with the consequent obstruction of the vessel lumen. For these reasons, the host response to two of the materials used in stent manufacture, stainless steel and diamond-like carbon, was investigated in vitro. The data showed that stainless steel induced a higher level of host response both in terms of platelet aggregation and macrophage activation. However, the spreading of inflammatory cells was more accentuated on diamond-like carbon. The inflammatory cells produced levels of platelet-derived growth factor, a key signal in smooth muscle cell proliferation, similar to stainless steel thus suggesting that carbon coatings may not be able to prevent restenosis.
