THE DEVELOPMENT OF SHEET GAMMA TiAl TECHNOLOGY UNDER THE ENABLING PROPULSION MATERIALS/HIGH SPEED CIVIL TRANSPORT (EPM/HSCT) PROGRAM

摘要

The sheet gamma TiAl technology is one of several new and challenging technologies successfully developed and demonstrated under the recently terminated NASA sponsored Enabling Propulsion Materials/High Speed Civil Transport (EPM/HSCT) program [1-3]. As a part of the overall program, the objective of the present effort was to design and fabricate the divergent flap of the nozzle by offering a weight reduction technology, enabling the EPM/HSCT to meet the weight goals for the HSCT engine. The designers chose gamma TiAl for its lightweight, high modulus, and elevated temperature properties to design the divergent flap of an extremely large exhaust nozzle required to reduce exhaust and noise pollution. This paper reviews diverse technologies that were developed to fabricate the nozzle subelement using gamma TiAl sheet. These include: production of large sheets, hot-die forming of sheets into corrugations, joining of sheets by brazing and diffusion bonding as well as by rivets, evaluation of microstracture and mechanical properties of sheets and joints, fabrication of a nozzle subelement involving brazing of large corrugations to face sheets, nondestructive evaluation of braze quality, and bend testing of the subelement. The sheet gamma TiAl technology was successfully transferred to BFGoodrich Aerospace Aerostructure group (BFGA/AG) for manufacturing of industrial scale nozzle components. Since the termination of the EPM/HSCT program in 1999, use of sheet gamma TiAl is being explored for several other aerospace applications and critical technologies are being developed to support their needs. These are: nozzle tiles for gas turbine engines, back structures for scramjets for space applications, heat shields for helicopters, and thermal protection systems for the reusable launch vehicles (RLV), to name a few. Additional technologies such as superplastic forming/diffusion bonding, laser joining and drilling, waterjet machining, and fabrication of honeycomb structures are being developed in order to support these activities.