Sol-gel gamma -Al2O3 coating was deposited onto surfaces of aluminum borate
whiskers to control the spinel reactions between whiskers and matrix alloy
s. High-resolution electron microscopy (HREM) observations of the whisker d
efects and coating structure in the squeeze-cast Al(18)B(4)O(33)w/gamma -Al
2O3/6061Al composite were carried out. Stacking faults and edge dislocation
s in the whiskers were directly observed, and zigzag anti-phase boundaries
were also found. A deformation of whiskers along sectional direction was ob
served, which was determined to be a source of in situ fracture of whiskers
. The sol-gel gamma -Al2O3 coating was a nanocrystalline material with an a
verage grain size of 5 nm. (C) 2001 Kluwer Academic Publishers.