RESIDUAL STRESS MEASUREMENTS AT THE METAL/CERAMIC INTERFACE USING MODELLING OF NEUTRON DIFFRACTION SPECTROMETER

摘要

The aim of this work is to improve some experimental techniques dedicated to the evaluation of residual stress (RS). These methods have been applied to a sample consisting of a glassy ceramic coating moulded on a metallic substrate (palladium-silver alloy) used in dental applications. Knowing the residual stress distributions is very important to determine the lifetime of the sample. We will describe a new approach to evaluate the RS at interfaces and in the bulk of materials, using neutron diffraction techniques. The RS in a glassy ceramic coated on metallic substrate are generated by the manufacturing process. They are present in the two materials. The RS depend principally on the thermal treatments imposed to the sample and they could have a very strong influence to the lifetime of the sample and in particular for the existing bounding between the metal and the ceramic. Moreover, the mechanical proprieties of glassy ceramic are known to be affected by proprieties of particle dispersed throughout the glassy matrix. The difference in the coefficients of thermal expansion (CTE) that exists between a ceramic and a metallic material could also be at the origin of a stress field. The first part of this paper concerns a development of a numerical simulation, of whole two-axis neutron spectrometers. This programme allows correcting systematic errors due to the great parasitic peak shifts which appear when the measurements are carried out at the interface between two different materials. The second part of this paper leads on the experimental determination of RS by neutron diffraction in the ceramic and metallic materials. These measurements were performed using different European facilities: D1A spectrometer at ILL (Grenoble, F) and E3 at BENSC-HMI (Berlin, D) for the analysis of the palladium substrate, and G5.2 spectrometer at LLB (CEA-Saclay, F) for the characterisation of the glassy ceramic coating.