Endurance and composition and microstructure effects on endurance of TiAl used in turbochargers

Turbochargers for passenger vehicle diesel engines were manufactured using turbine wheels made from two different TiAl alloys (low-Nb and high-Nb), and were fitted to a 2.5 1 diesel engine for engine endurance testing at 1123 K up to 600 h. Damage to the turbine wheels was subsequently investigated, and the endurance of the TiAl alloys in an actual operating environment was evaluated. In addition, the effects of chemical composition and microstructure on endurance were considered. Oxidation proceeded relatively slowly during endurance testing, and even the low-Nb alloy (which has poorer anti-oxidation properties) showed satisfactory endurance. However, the low-Nb alloy did exhibit erosion of the wheel blade tips, which was not found in the case of the high-Nb alloy. The likely cause of this erosion is collision with fine objects, and the fully lamellar structure marked by very fine colony size and narrow lamellar spacing which was formed in the wheel blades of the high-Nb alloy is thought to have resulted in the superior endurance that was observed. (C) 1999 Elsevier Science Ltd. All rights reserved.