Processing and microstructure of Nano-Mo/Al2O3 composites from MOCVD and fluidized bed

Abstract

The process utilizing metal-organic chemical vapor deposition (MOCVD) was conducted in a fluidized Al₂O₃ powder bed for the preparation of nano-Mo ceramic composites. During the process, Mo species were deposited in fine Al₂O₃ ceramic powder using a pyrolysis of Mo carbonyl. The composition and crystallinity of the intermediate phases of Mo₂C_xO_y, and the microstructure of the coated particles and coated layer were analyzed using XRD/SEM/TEM techniques. The granulated powder was then treated by H₂ reduction, pressureless sintering or hot-pressing in a vacuum, which could achieve densities better than 99% T.D. The densification, wear, and microstructural properties of the dense nano Mo-composites were then investigated and discussed. It is seen that the nano-inclusion of Mo grains inhibited the grain growth of the alumina matrix, which had a mean grain size of either 4.9 μm or 1.2 μm, as the volume fraction of Mo increased from 0 vol% to 5 vol%. The wear resistance of the nano-Mo/Al₂O₃ was approximately 2 times better than that of pure Al₂O₃. Through an understanding of the pyrolysis of Mo(CO)₆ and grain growth kinetics of Mo-species growth kinetics, the morphology and size of the Mo grains in ceramic composites can be modified.