Effects of different BN grades on the machinability of Si3N4-MoSi2-BN composites

The effects of the addition of 20 vol% hexagonal boron nitride (h-BN) on the surface finishing and machinability of a Si3N4-5 vol% MoSi2 hot-pressed matrix were studied using three commercial BN powders with different particle sizes and impurity contents. After preparation of the specimens, the surface finishing of the BN-containing composites was much lower than the starting matrix. The materials' machinability was quantitatively assessed by turning and drilling tests. In the severe turning tests, the wear resistance of the BN-containing composites was three times lower than the starting matrix without any BN size effect. In the mild drilling tests, the resistance of the composites was influenced by the BN grade, but without any obvious relationship to the BN pockets size. The impurities content of the starting BN powder could be the main factor affecting the machinability of the composites