Material choices for Formula One
Formula One is often said to be the pinnacle of motorsport, which is true in many ways, as the cars are the most optimised and highly developed. So utterly unrelenting is development that nobody who aims to compete at the highest level would dream of using the championship-winning car from the previous year. However, the engines have ‘suffered’ from a development freeze: after the 2006 season they were gradually neutered by having a reduced rev limit and a requirement to be more durable. They are certainly not what they might have been had the rules been more open.
Con rod materials have therefore remained as they were in 2007, unless someone has convinced the FIA that their material is at the root of reliability woes. The new engine formula in 2014 however offers the possibility to use something different. There is no telling what materials will be used; all we know of the engines are a few quotes from the manufacturers and some computer images of the units themselves.
Titanium has been widely used for motorsport rods for many years, and talking to a rod expert in the past few years, his feeling has been that titanium still offers the optimum rod – for a given application, the titanium rod would be lightest. Although there are many titanium alloys which could be considered, the ‘workhorse’ Ti-6Al-4V has for many years been the material of choice.
Steels are perhaps not a particularly glamorous choice for motorsport con rods, but they do offer several advantages over titanium, which means that the mass differential between the two is not as great as we might imagine from looking at some basic properties. Whatever steels would be chosen for a Formula One rod, it would probably not be one from which commercially available steel rods are made. Although there are cost constraints in Formula One, the teams can afford to spend more on their materials and components than the average motorsport engine suppliers.
On the face of it, these might be the limits of our material choices. The provisional 2014 rules state: “Connecting rods must be manufactured from iron or titanium-based alloys”; the rules further define what this means: “X Based Alloy [for example, Ni-based alloy] – X must be the most abundant element in the alloy on a %w/w basis. The minimum possible weight percent of the element X must always be greater than the maximum possible of each of the other individual elements present in the alloy.”
So, if we think about it, this offers some significant scope for development. The definitions of other types of materials would allow a titanium or iron alloy to contain a significant proportion, but less than 50%, by volume of intermetallics. Such intermetallics, for example titanium aluminide or iron aluminide, can offer significant advantages over conventional alloys. Before it was banned, titanium aluminide found favour in Formula One for valves, as it was stiffer and less dense than the titanium it replaced. It has been used as a con rod material in motorsport, although not widely. A proportion of 49% by volume of titanium aluminide in a titanium alloy would be legal under the FIA definition, and would be much stiffer than a conventional Ti alloy. High-aluminide content titanium alloys were developed with Formula One in mind some years ago, and are commercially available, though not in large quantities.
Iron aluminide was the subject of a lot of research in the 1980s but fell from favour after companies realised it was not going to be able to replace expensive superalloys. However, it remains an attractive material and there are development projects with the aim of producing high-strength, high-stiffness, ductile iron aluminide materials industrially.
Written by Wayne Ward