Aluminium-berylliumTags : advanced-materials
Previous articles have mentioned a few materials that are used for pistons, and the subject was also covered in a recent Race Engine Technology article on pistons. But there is one material that has been hailed by one piston design expert I spoke to as being ideal here - aluminium-beryllium. Blessed with a combination of desirable properties that may be present individually in other materials, it would almost certainly have been the material of choice now, had it not been banned by the FIA. Such was its importance that it was banned in an era when materials development was very free. In fact, 2010 marks a decade since the controversial decision to ban it.
In 2000, the editor of Race Engine Technology Ian Bamsey wrote in Racer, "Since 1998, Ilmor has manufactured pistons from an aluminium-beryllium alloy, thereby reducing their weight by a third, possibly more, and gaining enhanced thermal conductivity. The cost of this alloy, and the fact that fine beryllium dust particles arguably constitute a health hazard, has led to an effective ban on its use, imposed by the FIA. Under pressure from McLaren and Mercedes, however, this ruling, for which Ferrari lobbied hard, has been postponed to the end of the current season."
In granular form beryllium is indeed hazardous to health. There is a disease associated with it called berylliosis and this is a chronic condition affecting the lungs. Beryllium is used widely in racing engines, in copper-beryllium alloys, and herein lies the key to its safe use. The beryllium in valve seats is alloyed with copper, so it is soluble in copper and is not simply embedded particles of beryllium within the copper matrix. On the other hand, aluminium-beryllium is a metal-matrix composite, with finely divided beryllium reinforcement held in an aluminium matrix, so it is more hazardous.
But I have heard a rumour from more than one source that a certain team objected to the use of this material after it was refused an exclusive supply of it for its own use. Only then, I'm told, did the team's objections on health and cost grounds become so strong. Ron Dennis, whose McLaren team benefited from using aluminium-beryllium pistons from 1998 to 2000, insisted that all of the health risk lay in the manufacture of the parts, not in their use. The material is still used in many applications to this day, albeit outside motorsport.
The reason this material proved to be ideal as a piston material lies in its mechanical properties when compared with those of standard materials. Beryllium has a very low density of 1.85 g/cm3. With an atomic number of four, it is the second metal (if one discounts hydrogen) in the Periodic Table after lithium. It is also very stiff, with an elastic tensile modulus in excess of 280 Gigapascals (GPa). By comparison a typical aluminium alloy has a density of 2.7 g/cm3 and a modulus of 72GPa.
The specific modulus (modulus divided by density) for beryllium is almost 470% greater than that of aluminium. Beryllium's thermal conductivity is also greater than that of a popular aluminium piston alloy by a large margin. So adding beryllium to an aluminium alloy would have some very positive effects. A typical commercially available aluminium-beryllium alloy has a specific stiffness 250% greater than a good piston alloy, and 44% greater thermal conductivity.
The one downside that has been described to me is that, when pistons fail in service, there is very little chance of the source of the failure being proven. Such is the material's lack of ductility that it is said to give the appearance of having shattered.
So where else might we have expected to find a material with such properties? Cylinder liners are a good application to look at here. At the time, the linerless block had yet to become the norm in Formula One, and both aluminium and steel liners were in use. Aluminium-beryllium would surely have supplanted both, giving significant advantages in stiffness and mass, and it would certainly have been the material of choice for some valvetrain components in the universally used (at least in Formula One) pneumatic valve return systems. There are certainly other applications where we might have seen it used, had it not been outlawed.
Outside motorsport, the most popular applications of these materials are in satellites, where low launch mass is important, and in large optical instruments such as reflecting telescopes - the superb image here of Jupiter was taken by a space-based telescope. One such instrument, the James Webb Space Telescope, is scheduled for launch in 2014 and is technologically possible because of materials such as aluminium-beryllium. Its aim is to study the very earliest galaxies formed in the Universe, which rather puts race teams squabbling over materials into context.
Fig. 1 - Satellites and optical instruments are popular applications of Al-Be alloys. Images like this are, in part, thanks to their use
Written by Wayne Ward