Modification of surfaces in brazing of Al2O3-metal joints

Abstract

AB3:Tutkimuksessa tutkittiin alumiinioksidi/metalli liitosten toimivuutta. Tätä verrattiin alumiinioksidi/alumiinioksidi liitoksiin. Liitoksille tehtiin vetovoimatestit ja rakenteet tutkittiin SEM- ja EDS-tutkimuksilla. Todettiin alumiinioksidi/alumiinioksidi liitokset kestäviksi. Alumiinioksidi/pinnoite liitokset todettiin hieman heikoimmiksi. Alumiinioksidi/Fe52 liitokset todettiin myös kestäviksi, vaikka hajonta olikin suurta.

In this study the wetting and adhesion of brazed A1203/metal joints were investigated. Because of the poor wetting of metals on ceramic surface tayloring of the surface has to be done prior to brazing. The surface of A1203 was modified by using coatings containing an element, like Ti, which facilitates the wetting phenomena of a non-reactive brazing alloy at the ceramic surface. Also the commercial active brazing alloys were used for brazing of the test joints for comparison. In the case of active brazing alloys, the modification happens through the chemical reactions between the ceramic surface and the brazing alloy.- Both alumina/metal and alumina/alumina joints were brazed and characterized. The joints were tested with shear strength test, and the joint structures were inspected by SEM and EDS examinations.-In the microstructural study it was observed that coatings activate non-reactive brazing alloys forming a thin reaction layer at the ceramic interface, and the formed joints were mainly sound.-The shear strength results obtained from the similar A1203/AI203 joints were good. The shear strength of the joints brazed with the Al-braze/coating combination was somewhat lower and exhibited large scatterthan the values obt- The strength of the dissimilar joints, A1203/metal, was decreased by the build up of the thermal residual stresses due to the higher mismatch in the joints than in the similar ones. The test results with the active brazing alloy were, however, good. In the case of AI203/Fe52 joints, with the highest mismatch, there was the highest scatter in the results as well.