The effect of a homogenizing optic on residual stresses and shear strength of laser brazed ceramic/steel-joints
I. Südmeyer, H. Besser, M. Grein,
B. Liesching, M. Rohde, J. Schneider
Proc. SPIE, Band 7921,
Seiten 792108 (2011)
Oxide and non oxide ceramics (Al2O3, SiC) were brazed to commercial steel with active filler alloys using a CO2-laser (lamda = 10.64 ?m). Two different laser intensity profiles were used for heating up the compound: A laser output beam presenting a Gaussian profile and a homogenized, nearly top head profile were applied for joining the compounds in an Argon stream. The temperature distribution with and without the homogenizing optic was measured during the process and compared to the results of a finite element model simulating the brazing process with the different laser intensity profiles. Polished microsections were prepared for characterization of the different joints by scanning electron micrographs and EDXanalysis. In order to evaluate the effects of the different laser intensity profiles on the compound, the shear strengths of the braze-joints were determined. Additionally residual stresses which were caused by the gradient of thermal expansion between ceramic and metal were determined by finite element modeling. The microsections did not exhibit differences between the joints, which were brazed with different laser profiles. However the shear tests proved, that an explicit increase of compound strength up to 34 MPa of the ceramic/metal joints can be achieved with the top head profile, whereas the joints brazed with the Gaussian profile achieved only shear strength values of 24 MPa. Finally tribological pin-on-disc tests proved the capability of the laser brazed joints with regard to the application conditions.