Aluminum alloy has been gradually utilized in cylinder block instead of ferrous casting material for weight reduction in automobile industry these days. In order to acquire more weight reduction, a new liner-less technology - without cast iron liner used - is putting into practice in the fields of aluminum cylinder block and the target is for diesel engine. However, diesel fuel's impurity "sulfur" element and corrosive attack risk, such as sulfuric acid generated to the surface of liner is higher than gasoline fuel. Because of such disadvantage, wear and corrosion resistances applied to the inner cylinder-bore are required in order to achieve this liner-less aluminum cylinder block. This research is intended to accomplish both wear and corrosion performances using plasma thermal spray technology and to verify the feasibility of application to actual engine bore. A newly-developed ferrous powder (Fe-C-Ni-Cr-Cu-V-B alloy) revealed extremely excellent corrosion and wear resistances, compared with currently used bulk casting materials such as Fe-C-Si-B alloy and Fe-C-Si-Mo-B alloy for cylinder liner. For the last time, the new ferrous alloy powder was applied to actual engine bore by using Rota-Plasma spray coating. The experimental results with engine bore presented potential equivalent to current engine bore.

Since about the year 2000, cast aluminum automobile engine blocks have been coated in production lines using internal plasma spraying technology. Using this approach, the coefficient of friction between the cylinder wall and the piston assembly can be reduced to 30% and oil consumption is reduced of a factor two in comparison with cast iron. The extremely low wear rate of the friction elements increases engine life and reduces maintenance costs. The fuel consumption of the cars can be reduced from 2 to 4% in the case of gasoline and diesel engines. The coating costs are strongly dependent on production volume. For high volume production, the costs can be similar to those for cast iron liners. This paper reviews results from laboratory and field tests evaluating the performance and cost efficiency of plasma sprayed engine block liners.

The excellent wear-resistant performance of cast iron coatings considerably depends on the formation of graphite structure with an inherent self-lubricating property. In the present study, two types of cast iron powders produced by gas- (GA) and water-atomization (WA) were deposited on an aluminium alloy substrate by atmospheric DC plasma spraying. WA powders are generally characterized by high oxygen content, irregular appearance and inexpensiveness compared with those of GA powders. Although alloying elements of silicon and aluminium work as a strong graphitizer and anti-oxidizer, graphite structures are not recognized in coatings sprayed with as-atomized high silicon and aluminium powders. Therefore, either pre-annealing of powders or post-annealing of coatings is required to achieve cast iron coatings containing graphite structure. A marked decrease in graphite occurs to the coatings with pre-annealed GA powder, since there exists precipitated graphite mainly on a GA powder surface. A short period of post-annealing is also valuable for graphitization. The weak oxide layers are observed in coating cross-sections with GA and WA powder, however, their oxidized levels are much lower than those with bearing steel powder containing low silicon and aluminium. Hence, graphitized cast iron coatings sprayed with inexpensive WA powder exhibit a splendid anti-wear performance.

The application of wear resistant coatings onto the wall of aluminium engine cylinder bores by thermal spray have seen much development over the last 10 years, with regards to both equipment design and also to the material system used. While the technology has been successful in allowing the implementation of aluminium engine blocks into mass production, there is still room for improvement. One area that can be improved is the preparation of the substrate material in order to allow a good adhesion of the thermal spray coating. Grit blasting, a traditional preparation technique, is undesirable for a mass production environment due to the risk of the assembly areas becoming contaminated with grit. Therefore, an alternative method has been sought that can offer a suitable bond strength without introducing potential risks in the manufacture line. In this study, NiAl bond coats were sprayed onto aluminium substrates using the Plasma Transferred Wire Arc (PTWA) coating system developed by Ford Motor Company. A variety of surface preparation techniques, including traditional and some more novel methods, were used and analysed with respect to bond strength, ease of application and cost.