A sputter bearing from MAHLE can be recognised by the label ‘SPUTTER' stamped at the back (see picture) – and the "m" that is well-known in workshops.

Sputter bearings are indispensable for high performance diesel and petrol engines. But what is sputtering actually? How is it done? And why? MAHLE aftermarket news is answering here the most important questions on this topic.

Sputtering – what is it?
In a vacuum container with just some traces of noble gas, a positively charged anode and a negatively charged cathode that is covered with a metal layer are located, together with the threematerial bearing that is to be sputtered. A voltage is applied between cathode and anode. Electrons are accelerated towards the anode and ionize the noble gas atoms. The noble gas atoms that are now positively charged are then accelerated towards the cathode and knock out atoms from the metal layer covering the cathode. This will also release secondary electrons that will in turn ionize more noble gas atoms. This results in a mixture of free electrons, positive ions and neutral particles of the noble gas – a so-called steady state plasma. The neutral atoms that were knocked out of the metal layer of the cathode, condense then as thin, extremely resistant metal coating on the bearing surface.

1. Supply of argon (plasma gas) 2. Ion flow 3. Atomic material flow (dispersion)

What is the purpose of friction bearings?
Rotating shafts such as crankshafts, camshafts, rocker arm shafts and balancer shafts operate in engine blocks and connecting rods. Bearings provide support to these parts. The mechanical load on the bearings is respectively high – at ignition pressures up to 200 bar for instance. But this is not all. Internal combustion engines are refined continuously, specific engine performance is increased and size is reduced – and thereby also the size of the bearing surfaces. At the same time, the oil change intervals are extended successively. All this increases the mechanical loads on the bearings.

What are the particular loads on bearings?
The specific surface loads, especially for connecting rod bearings and main bearings, have significantly increased in recent years. For engines with diesel direct injection, surface pressures up to 120 N/mm2 have to be managed in the bearings. Conventional two- or three-material bearings with galvanically applied bearing layers reach their limits here. For modern engines, bearing materials with significantly increased fatigue strength and reduced wear rate are therefore required, especially in the mixed friction range. At the same time, good corrosion resistance has to be assured, also at higher temperatures.

	Solid bearings Solid bearings are made completely from bearing metal that consists of special alloys.
	Two-material bearings Two-material bearings are used for low to medium loads in petrol and naturally aspirated diesel engines in passenger vehicles. They consist of a steel backing, an intermediate layer and a layer of bearing metal. Mainly aluminum alloys are used as bearing metal.
	Three-material bearings Three-material composite bearings are mainly used in engines under heavier loads. They consist of a steel backing, a bearing layer, a barrier layer and the sliding layer. Sputter bearings are special three-material bearings with significantly increased hardness and wear-resistance due to a special production method (sputtering).

Why is a sputter bearing the right solution?

A sputter bearing is composed of a three-material composite bearing which has a bearing layer that is not applied galvanically but by means of cathode sputtering. This coating method works only in a high vacuum. Smallest particles are knocked from the sputter cathode and propelled onto the bearing surface by means of high voltage. The coating is fine-grained, finely dispersed and adheres extremely well to the substrate material. Due to the small grain size, the produced layers are extremely hard with high yield strength and outstanding wear properties.

Where are sputter bearings used?
For highly loaded bearings, the bearing couples consist always of a sputter bearing and a conventional three-material bearing. The sputter bearing is used at the higher load end and the softer three-material bearing is used opposite. For connecting rod bearings, the sputter bearing is therefore fitted in direction rod and the three-material bearing in direction bearing cap. For main bearings this is exactly the other way round. The sputter bearing is here used in the bearing cap and the three-material bearing in direction engine block.

How can you recognize a sputter bearing?
Considering how complex and complicated the coating process is and how impressive the performance, it is difficult to see the difference in the sputtered bearings. They look completely ordinary. To make it possible to recognize the sputtered half-bearings, the sputter bearings are marked with the identification ‘SPUTTER'. This ensures correct fitting, especially as the correct assembly position of the sputtered bearing shells is crucial for reliable working and the service life of the bearings.

Why are sputter bearings and three-material bearings always combined in pairs?

One of the reasons is the high production cost for the sputter coating. At the location with low load, they are not necessary and are therefore not fitted. The second reason is the extreme hardness of the sputter layer, which does not tolerate engine oil contaminations. However, the softer three-material bearing can embed dirt particles in its galvanized bearing layer and renders them therefore harmless.

Why sputter bearings from the expert?
As the world's largest piston manufacturer and development partner of the automotive and engine industry, MAHLE is highly competent in research, testing and production of engine components.

Sputter bearings are also used in the following engines:

Audi/VW series TDI: 1.9 / 2.0 / 2.5 / 4.0 / 5.0 l
Audi petrol engines: 6.0 l (W12) / 1.8 l (225 hp)
MAN: D2865
Mercedes-Benz commercial vehicles: BR 400, BR 500, BR 900
Mercedes-Benz passenger vehicles: CDI-engines BR 600
PSA series HDI: 1.4 / 1.6 / 2.0 / 2.2 / 2.7 l