Design and synthesis of functionally graded composites: the BiB_2/NiAl system

摘要

Functionally graded composites have been studied using finite element analysis (FEA) and by synthesizing TiB_2/NiAl compositionally graded specimens. The FEA studies have been used to obtain the distribution of residual stress as a function of the composite architecture (nature of gradation). The combustion synthesis technique in conjunction with hot pressing was employed to obtain the composites. Vickers microhardness at room temperature and 900 deg C was measured across the graded composite, as a function of volume fraction of TiB_2 (V_(TiB_2)). It was observed that the room temperature hardness varies linearly with V_(TiB_2) but many become nonlinear with V_(TiB_2) at elevated temperature, depending on the microstructure. Specifically, it appears that the hardness at elevated temperature depends sensitively on the distribution of TiB_2 particles. The reasons for this deviation, and the role of residual stresses in governing the mechanical properties are discussed.