Near net shape production of monolithic and composite high temperature ceramics by hot isostatic pressing (HIP)

Improved properties of high temperature ceramics in general are achieved by compositional and processing research and development-compatible with sint ering and forming needs. Pressure can be used to increase the driving force for densification and with hot isostatic pressing (HIP) the form can be cl osely controlled, even of complex shaped parts, like turbine wheels. Recent development within the EUREKA-AGATA hybrid electric car gas turbine projec t shows that improved high temperature material properties can be achieved, while at the same time fabricating components like combustion parts and tu rbine wheels, to near-net-shape. For such components a highly uniform green powder body is desired. Combined with a type of encapsulation during HIP, which does not create shear stresses at the surface of the green body durin g the shrinkage/sintering to full density, but at the same time prevents pe netration into the body, optimal near-net-shape results can be achieved. Re cent studies, e.g. by TEM, have confirmed that some encapsulation glass con stituents can form new compounds with silicon nitride, at the very surface, which appear to help develop these desired characteristics. Non-homogeneou s and nonisotropic ceramics, like fiber reinforced composites, may be fabri cated using rigid, shape controlling tools on one or several sides. Particu larly for large (and curved) panels such use of a hot isostatic press can b e an advantage. (C) 1999 Elsevier Science Ltd. All rights reserved.