Titanium compressor impellers

Modern commercial vehicle turbochargers are subject to very high loads due to the wide range of applications they are used in. In many cases where there are extreme loads, a compressor impeller made of an aluminum alloy determines the service life of the turbocharger. In particular, material fatigue can result from extreme loads, especially when the loads are cyclical loads occurring at low frequencies. This phenomena is also known as low cycle fatigue (LCF).

Various measures can be taken to increase the service life. For example, the circumferential speed of the compressor impeller can be reduced by changing the aerodynamic design of the impeller or by controlling or reducing the charging pressure. High-strength aluminum, for example, that manufactured using the HIP technique, is often used to reduce variations in the strength of the material. The high-end solution using aluminum consists of milled compressor wheels which were also developed by BorgWarner Turbo Systems.

The increasing number of engine applications with high cyclical loads as well as the necessity to have higher charging pressures to remain within the stricter emission regulations have made an additional innovation step beyond the moulded aluminum compressor wheels necessary. In order to provide a customer with a technology that can withstand these loads and also ensure a service life that is just as long as it would be under standard conditions, BorgWarner Turbo Systems initiated a special development program.

The demands on the compressor impeller stated above make it necessary to use higher quality materials since the potential for improvement inherent in aluminum is just not sufficient anymore. The engineers at BorgWarner Turbo Systems decided to use a titanium alloy that is not only very hard, but also provides an excellent strength-to-thickness ratio.

With the titanium compressor impeller, BorgWarner Turbo Systems is now able to offer different compressor impeller technologies for special application requirements and special cyclical loads. In this manner the customer can select between cast or moulded aluminum compressor impellers or between cast or moulded titanium compressor wheels depending on the area of application.