Functional Gradient Materials

Functional gradient materials (FGMs) have a microstructurally graded transition in composition (e.g. zirconia to a nickel based superalloy). The graded transition eliminates problems associated with a discrete interface such as poor mechanical strength and transport losses. They are being actively pursued by the engineering community, particularly in Japan, as a means of taking advantage of two different materials within the same monolithic body. A versatile process for preparing FGMs is under development at ACR. The process is based on a solid freeforming (SFF) process from a computer virtual image. A solid body is built up from a polymerizable suspension which is deposited from a moving nozzle. The suspension comprises of a mixture of two streams fed from two computer-controlled extruders through a static mixer. The freeformed body is then processed like a traditional ceramic or powdered metallurgy green body. In Phase I the current method will be extended to produce large, "6x6", plates of FGMs. This will involve the use of a dual-headed extruder to fill molds with metal and ceramic gel-casting formulations. Of particular interest in Phase I will be the preparation of unique structural materials designed either to have outstanding thermal protection or wear resistance. Materials systems that will be investigated include combinations of alumina, partially stabilized zirconia, titanium carbide, titanium diboride, tungsten carbide, stainless steel, Inconel X and NiAl. This technology has potential for producing large ??Ms by a novel, flexible and rapid manufacturing technique. Such a method will have important ramifications allowing various combinations of ceramics and metals to be quickly evaluated and introduced as tailored materials for numerous defense and commercial applications.