Technology, properties and applications of intermetallic gamma-TiAl based alloys

This paper reviews industrial scale thermomechanical and near-net shape pro cessing of gamma-TiAl based alloys ("gamma alloys"). The progress achieved in forging of large ingots, rolling of sheets from forged ingots as well as HIPed powders, single and multistep extrusion of ingots and HIPing of prea lloyed powders to near-net shape parts is presented. The impact of the diff erent prematerial routes on process economy and the quality of semi-finishe d products will be discussed. The problems which arise when heat treatments are transferred from small lab furnaces to large industrial furnaces are o utlined. The superplastic behaviour of gamma-TiAl sheet material is describ ed and results of superplastic forming are presented. Different joining tec hniques have been screened for gamma-TiAl based alloys including laser weld ing, brazing and solid-state diffusion bonding. Although the oxidation resi stance of gamma alloys is remarkably higher than that of gamma alloys the n eed for reliable oxidation resistant coatings for long-term application at temperatures > 700 degrees C is anticipated. Results of cyclic oxidation te sts on coated gamma-TIAl samples are presented. Finally, some potential app lication fields for gamma-TiAl alloys are outlined.