Ja. Cornie et al., IMPROVING MECHANICAL-PROPERTIES OF NEXTEL 610 REINFORCED AL-224 ALLOYTHROUGH THETA-PHASE PRECIPITATION AT THE FIBER-MATRIX INTERFACE, Materials science & engineering. A, Structural materials: properties, microstructure and processing, 162(1-2), 1993, pp. 135-142
A novel approach toward axial and transverse composite strengthening t
hrough controlled delamination of interfaces in alumina fiber reinforc
ed Al-(224.2) is presented. During annealing at 350-degrees-C, seconda
ry CUAl2 (0) precipitates coarsen preferentially at the fiber-matrix i
nterface. Observations of fiber pull-out indicate that the interface d
elamination and crack bridging mechanism for axial toughening was acti
vated by coarsening of theta precipitates to a critical size and distr
ibution. The peak sigma11 of 972 MPa (91% of rule of mixtures (ROM)) a
fter 10 h at 350-degrees-C correlates with a minimum in the mean free
distance between theta precipitates and a minimum in transverse streng
th sigma22. However, thermal exposures for longer than 100 h at 350-de
grees-C resulted in an increase in sigma22 to 345 MPa and an acceptabl
e decrease in sigma11 to 70% of ROM (724 MPa). This value of sigma22 i
s comparable with wrought 2xxx-T7 alloys, and is extremely high for mo
st continuously reinforced metal matrix composite applications. The in
crease in sigma2 correlates with an increase in the metal-fiber bond a
rea fraction at the interface, which results from theta precipitate co
arsening.