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Sprayed metal coatings are an alternative means of effectively protecting steel structures and equipment exposed to severe environments where other coatings, such as paint, are unsuitable or provide only temporary protection. Selecting the most suitable material for a given application is a very important step in achieving success. For resistance to corrosive environments, zinc and aluminium are the most successful and widely used coatings, both being anodic to iron and steel. The performance of sprayed metal coatings is a function of the environment, coating thickness, adhesion, density and the type of sealer used. The mechanism of adhesion is mainly mechanical, the bond strength being dependent on the application process chosen and standard of surface preparation. This paper describes the results of research work associated with hot sprayed aluminium applied by combustion flame and electric arc processes using compressed air and argon carrier gases. Studies included ductility and adhesion tests, scanning electron microscopy of surfaces and cross sections, and Auger surface analyses.

METALLISING or metal spraying is carried out by heating powder or wire in the flame of a gun and then projecting it on to a suitably prepared surface to form a coating.

The paper's aim is to investigate the sand slurry erosive wear behaviour of Ni‐Cr‐Si‐B coating deposited on mild steel by flame spraying process under different test conditions.

Flame sprayed coatings of Ni‐Cr‐Si‐B were developed on mild steel substrate The slurry pot tester was used to evaluate wear behaviour of the coating and mild steel. The erosive wear test was conducted using 20 and 40 per cent silica sand slurry at three rotational speeds (600, 800 and 1,000 rpm).

Slurry erosive wear of the coating showed that in case of 20 per cent silica sand slurry weight loss increases with increase in rotational speed from 600 to 1,000 rpm while in case of 40 per cent silica sand slurry weight loss first increases with increase in rotational speed from 600 to 800 rpm followed by marginal decrease in weight loss with further increase in rotational speed from 800 to 1,000 rpm. Increase in wear resistance due to thermal spray coating of Ni base alloy on mild steel was quantified as wear ratio (weight loss of mild steel and that of coating under identical erosion test conditions). Wear ratio for Ni‐Cr‐Si‐B coating was found in range of 1.4‐2.8 under different test conditions. The microstructure and microhardness study of coating has been reported and attempts have been to discuss wear behaviour in light of microstructure and microhardness. Scanning electron microscope (SEM) study of wear surface showed that loss of material from the coating surface takes place by indentation, crater formation and lip formation and its fracture.

It would assist in estimating the erosion wear performance of flame sprayed Ni‐Cr coatings and their affects of wear resistance.

Erosion wear of flame sprayed coatings in sand slurry media medium is substantiated by extensive SEM study.

This study aims to investigate the effect of post heat treatment on mechanical properties of NiCrBSi coatings, which were applied on 316L stainless steel using high-velocity oxygen-fuel (HVOF) and flame spray techniques.

The properties of coatings were investigated by metallographic characterizations as well as wear, micro-hardness and adhesion tests.

The micro-hardness results showed that the coatings considerably increased the sub-layer hardness. In addition, regarding the wear test results, it can be seen that heat treatment increased wear resistance of the coatings. These thermal sprayed coatings are usually re-melted by post heat treatment, leading to improvement in tribological properties. The results obtained revealed that re-melting procedure improved the metallurgical bonding in the substrate\coating interface.

Microstructure defects resulting from thermal spraying such as pores and unmelted particles can be eliminated by post heat treatment. This process can considerably improve the corrosion and wear resistances of the thermal sprayed coatings.

The reduction of wear by the use of sprayed surface coatings holds considerable potential at a time when Industry is becoming more conscious of the need to reduce its operating costs. Control of wear is unlikely to become a true science due to the arbitrary nature of the conditions that produce the effect and although no truly economic solution exists for completely preventing surface degradation, it can be minimized to acceptable limits. It is the purpose of this article to present an approach to the use of sprayed surface coatings in tribological situations. Common wear types are briefly described and the philosophy behind the protective surface layer in relation to surface geometry is outlined. The performance of sprayed coatings in adhesive and abrasive wear situations is evaluated and discussed. In addition, the use of sprayed deposits for lubricated bearing surfaces is considered as well as the application of low friction coatings by the spray method.

FLAME spraying, which is basically the heat softening of fusible materials and their projection on to a prepared base material to form a surface coating, has undergone many advances since the effect was observed in the early 1900s and a newcomer to give the process more flexibility is now introduced by Metco.

With present‐day moulding and extrusion techniques there is a wide range of articles that can be made from solid plastics and there is an ever‐increasing market for these products in industry and the home. Despite the attractive finish of these plastics articles and their ability to withstand corrosion and mechanical damage, there are objections to the use of the solid material for some applications. From an engineering point of view, there are difficulties of rigidity and mechanical strength, whilst economy also rules out the use of solid plastics in many cases, since, whilst it may be possible to mass‐produce large quantities of moulded plastics articles for domestic use, where there is a very large market potential, it is another thing to produce small runs of specialised engineering products economically. For these reasons there is an ever‐increasing demand for plastics finishes to both standard and purpose made metal goods either to protect the base metal or to produce an attractive finish.

This paper aims to verify weather atmospheric plasma spray (APS) in situ remelting posttreatment is effective for densifying the porous FeCoCrMoCBY amorphous alloy (FAA) coating and improving the antiabrasion and anticorrosion performances or not.

APS was used to deposit and in situ densify FAA coating on the 40Cr substrate. Scanning electron microscope, X-ray diffractometer, energy dispersive spectroscopy, neutral salt spray, hardness and wear behavior test were used to evaluate the densifying effects.

APS remelting technology can effectively improve the hardness of the coating by reducing the porosity. After remelting at 30 kW power, the hardness of the coating increased by about 260 HV0.2 and the porosity decreased to 2.78%. The amorphous content of the coating is 93.9%, which is about 3.5% lower than original powders. The electrochemical impedance spectrum and neutral salt spray test results show that APS remelting can reduce the corrosion rate by about 62.7%.

APS remelting method is firstly proposed in this work to replace laser remelting or laser cladding methods. APS remelting method can effectively improve the corrosion and abrasion resistance of the FAA coating by increasing the densification with much low recrystallization, which is big progress for application of FAA coatings.

By means of dip‐ or spray‐coating with polythene powder, a complete protective covering can be applied in one operation to metal articles of the most complex shape, such as the soap and sponge rack shown overleaf. Dip‐coating in particular is a process which can be carried out with very simple equipment, yet on the other hand it is adaptable to mass production requirements.