Shot peening is a well known process that is used widely as a reaction to fatigue failures and as a design tool to avoid them in the first instance. The choice of whether to use peening as a ‘curative’ or a ‘preventative’ treatment depends on how well understood the components are that the process is applied to, although peening processes are applied at some of the highest levels of motorsport as a curative. The magical powers of peening are due to the residual...
Phosphate coatings have been covered in a couple of previous surface treatment articles. In the first of these articles, we looked mainly at engine applications, including piston rings, camshafts and so on. In the second article, we looked in slightly more depth at some of the advantages and disadvantages of phosphating. The design engineer or metallurgist who recommends this type of coating needs to be aware of the potential problems with hydrogen embrittlement of high-strength steels...
It would be wrong to say that conversion treatments such as chromating aren’t used in race engines, but they certainly aren’t used as widely as on race transmissions. One of its main uses in engine parts is the passivation of components with metallic platings such as zinc or cadmium. Chromating on top of these metallic platings prevents early oxidation of the plating – zinc itself, for example, is highly reactive. Plating works by using zinc, say, as a sacrificial coating,...
Where aluminium components might be subjected to wear in a race engine or transmission, hard anodising is often specified as a surface treatment. This process converts the existing surface to a thick oxide structure; the main difference between decorative anodising treatments and hard anodising is the thickness of this oxide layer. The anodised layer thickness may be specified and there is a ‘half and half’ rule that can be used to predict component growth. Half of the oxide...
Chemical machining is a technique that removes material through the interaction between chemicals and a metallic workpiece. Electrochemical machining (also widely referred to as ECM) offers an alternative to electro-discharge machining (EDM) and is suitable for cutting a variety of materials including very hard alloys. Compared to EDM, there are several practical advantages. The surface finish possible with ECM is typically better than with EDM: ECM can produce mirror-finished parts. EDM...