Friction and Wear Behavior of Alumina Composites with In-Situ Formation of Aluminum Borate and Boron Nitride

Wear and friction properties of Al(2)O(3) composite reinforced with in-situ formed aluminum borate (9Al(2)O(3)·2B(2)O(3)) and hexa-boron nitride (h-BN) have been investigated. The initial constituents for the composites were Al(2)O(3), AlN, and H(3)BO(3). The H(3)BO(3) was used as a source of B(2)O(3), where B(2)O(3) reacted with AlN and Al(2)O(3) to form in-situ h-BN and 9Al(2)O(3)·2B(2)O(3). Based on the thermodynamic calculation and phase transformation, four different compositions were selected. First, the powders were mixed by ball milling followed by compaction at 10 MPa. The compacted pellets were sintered at 1400 °C in vacuum. The composites were characterized using X-ray diffraction followed by hardness measurement and reciprocating sliding test against alumina and steel balls. The X-ray diffraction results revealed the formation of in situ phases of 9Al(2)O(3)·2B(2)O(3) and h-BN that improved the tribological properties. By comparing the tribological performance of different composites, it was found that the hard 9Al(2)O(3)·2B(2)O(3) phase maintains the wear resistance of composites, whereas the coefficient of friction is highly dependent on the counter ball. Against alumina ball, the lowest coefficient of friction was observed for the composites with maximum h-BN concentration and minimum aluminum borate concentration, whereas the opposite trend was observed against the steel ball.