Use of plasma spraying in the manufacture of continuously graded and layered/graded molybdenum disilicide/alumina composites

摘要

Plasma spraying was used to produce continuously graded and graded/layered structures of molybdenum disilicide (MoSi{sub}2) and alumina (Al{sub}2O{sub}3). These functionally graded materials (FGMs) were achieved by manipulating the powder hoppers and plasma torch translation via in-house created computer software. The resultant microstructures sprayed uniformly and were crack free. The interface between MoSi{sub}2 and Al{sub}2O{sub}3 was continuous and no evidence of debonding or cracking at the interface was found. The mechanical strength of these sprayed materials was evaluated using C-ring samples (in diametrical compression). Weibull analysis conducted on the C-ring data indicated that the continuously graded samples were slightly stronger and had a significantly narrower strength distribution than the graded/layered samples. Although the average strength values of both types of functionally graded samples were closer to those of monolithic MoSi{sub}2, the fracture energy of the graded samples was significantly larger (～2-3 times) compared with the monolithic materials. Scanning electron microscopy (SEM) conducted on the fracture surfaces of the FGMs illustrated a wavy and tortuous crack path through the composite cross section of the sample, with extensive crack kinking. This study has two important results. First, we demonstrated the ability to produce such functionally graded composite ceramic microstructures using a conventional plasma spraying process. Second, we quantified the improvements in mechanical performance provided by these FGMs over conventional monolithic materials.