High Temperature Deformation and Fracture Mechanisms in Monolithic andParticulate Reinforced Nickel Aluminide Processed by Spray Atomization and Co-Deposition

摘要

Intermetallic-matrix composites (IMCS) have the potential of combining matrixproperties of oxidation resistance and high temperature stability with reinforcement properties of high specific strength and modulus. The purpose of the present investigation is to develop a better understanding of the nature of creep fracture mechanisms in a Ni3A1 composite reinforced with both TiB2 and SiC particulates. In the present study, creep rupture specimens were tested under constant stresses ranging from 180 to 350 MPa in vacuum at 760 deg C. Examinations of tested specimen cross-sections reveal that the high temperature damage in the unreinforced material is comprised of the plastic growth of pre-existing microcracks while damage in the composite is manifested by the nucleation and growth of cavities. The microstructural observations reveal that most of the cavities he on the grain boundaries of the Ni3A1 matrix as opposed to the large TiB2/Ni3A1 interfaces, suggesting that cavities nucleate at fine carbides that lie on the Ni3A1 grain boundaries as a result of the decomposition of the SiCp. This observation accounts for the longer rupture times for the monolithic Ni3A1 as compared to those for the Ni3AI/SiCp/TiB2 IMC.