Cathodoluminescence imaging of oxidised zirconium alloys

Cathodoluminescence (CL) imaging techniques have been applied to the characterisation of the zirconium oxide films formed from binary Zr alloy matrices using a homemade CL imaging system attached to an Hitachi S-570 scanning electron microscope (SEM). Evidence from the CL images shows the involvement of the individual Zircaloy alloying elements in the luminescence process. β-annealed and slow-cooled samples which have strongly segregated alloying elements at their grain boundaries showed strong CL signals from these areas. Use of this heat treatment was necessary to compensate for the low resolution of the equipment. Strong CL signals were observed also from cracks in the oxides on some alloys and are believed to be caused by the redistribution of iron to the region adjacent to the crack, but below the original surface. Increasing redistribution of Fe with increasing oxidation temperature is seen in the CL images. The cyclic behaviour observed in the weight gain measurements is also observed in the CL intensity measurements. Experimental data from this investigation support the theory that this phenomenon is caused by the successive formation of cracks parallel and normal to the plane of the metal matrix.