A SYNCHROTRON X-RAY-DIFFRACTION STUDY OF THE LOCAL RESIDUAL STRAINS AROUND A SINGLE INCLUSION IN AN AL W METAL-MATRIX COMPOSITE/

An X-ray technique for local measurements of the internal residual str ess near inclusions in metal-matrix composites (MMCs) is presented. Th e technique utilizes medium- to high-energy monochromatic X-rays from a synchrotron source and a combination of slits on the entry and exit sides of the sample in order to determine the strains from small volum es deep within the composite sample, The strains of the individual mat rix grains are sampled and averaged, allowing for a much improved spat ial resolution. An analyzer is used in order to avoid well-known syste matic errors related to geometry and stability of the beam. First resu lts are obtained on a model system consisting of a 500 mu m continuous W fiber imbedded in an Al matrix. Two specimens were investigated wit h typical Al grain sizes of 1 mm and 30 mu m. With a gage volume of 10 x 10 x 170 mu m(3), we obtained count rates on the order of 5000 cps and an accuracy in the strain measurements of Delta epsilon less than or equal to 5 x 10(-5). For both specimens, we found no variations of the radial and transverse strain components with the distance to the f iber, indicating either a complete debonding of the system, a very wea k interface, or interface deterioration due to chemical reaction. Intr agranular strain fluctuations on the order off epsilon = +/- 10(-4) we re found to build up close to the grain boundaries. For the specimen w ith the smaller Al grain size, sampling data from approximately 15 gra ins at the same distance to the fiber was sufficient for averaging out the intergranular fluctuations. Finally, we observe effects from the conventional metallurgic sample preparation up to 400 mu m from the su rface, emphasizing the relevance of bulk techniques.