화학공학소재연구정보센터
Journal of Materials Science, Vol.33, No.16, 4101-4104, 1998
Measurement of the hardness distribution in sapphire/NiAl composites using continuous indentation
A variety of fibre coatings have been modelled as a means to reduce the thermal residual stresses in sapphire/NiAl composites, including the use of molybdenum as a compliant layer. However, no experimental studies have been performed to quantify the effect of these coatings on the residual stresses. Measuring the effect of the coatings in real composites is a difficult task given the limitations of the most common residual stress measurement methods, such as X-ray and neutron diffraction. In this study, a continuous indentation system was used to measure a spatial hardness distribution both within the molybdenum fibre coatings and the NiAl matrix. Because it has been shown that residual stresses effect the apparent hardness of a material, the hardness distribution should be indicative of the local residual stress state in the sample. The measured hardness distributions showed distinct trends, including an increasing hardness in the molybdenum as the NiAl interface is approached, a substantial increase in NiAl hardness at the fibre/coating boundary, and a decrease in NiAl hardness that is proportional to the distance from the fibre/coating boundary. The potential utility of continuous indentation systems for mapping the residual stresses in composites is briefly discussed.