INSITU MEASUREMENTS OF THE MECHANICAL-PROPERTIES OF ALUMINIDE COATINGS

A novel technique was used to measure the mechanical properties of surface diffusion coatings which, unlike overlay coatings, cannot be evaluated from bulk samples. Coatings on thin foil samples over a wide range of thicknesses were prepared and a technique related to a law of mixtures approach was used to obtain the elastic modulus, yield stress, fracture stress and strains to failure for NiAl coatings over the temperature range 20-1000-degrees-C. The yield stress decreases from 360 to 60 MPa, the fracture stress from 156 to 44 MPa and Young's modulus from 350 to 100 GPa, over the temperature range 20-1000-degrees-C. The ductile-brittle transition temperature (DBTT) of these coatings was measured and its variation with thickness determined.