Fiber damage and high temperature tensile properties of Al2O3 fiber reinforced NiAl-matrix composites with and without hBN-interlayer

The fiber damage caused by thermal residual stress in NiAl-matrix composites reinforced by single-crystal Al2O3 fibers (sapphire) was studied. In the NiAl/Al2O3 (Vf = 0.3) composites, more fibers were broken into shorter segments because of the larger thermal axial compressive stress exerted on the fibers which was caused by the different thermal expansion coefficients of Al2O3 fibers and NiAl matrix. An increasing fiber volume fraction or addition of an hBN-interlayer decreased the thermal axial compressive stress and thus reduced the fiber damage. The tensile strength of NiAl/Al2O3 (Vf = 0.3) composites at 1100 °C reaches only about 80 MPa owing to the fiber strength degradation caused by severe fiber damage. By contrast, NiAl/Al2O3 (Vf = 0.5) composites showed a tensile strength of about 200 MPa at 1000 °C and 140 MPa at 1100 °C. The NiAl/BN/Al2O3 (Vf = 0.3) composites had a tensile strength of only 30 MPa at 1100 °C because of the low bonding strength between fiber and matrix and thus, ineffective load transfer.