Evaluation of residual stresses during brazing of Al2O3-ZrO2 to cemented tungsten carbide

In the context of the assembly of a cutting tool for wood machining, this article proposes to evaluate the residual stress in a ceramic plate (Al₂O₃-ZrO₂) induced by a brazing step with a cemented tungsten carbide (WC-Co) through a brazing filler (Ag-Cu-Ti). The residual stresses were evaluated using neutron and X-ray diffraction method. Moreover, a mathematical model was used in the case of a three layer assembly, which is based on mechanical properties such as: the thermal coefficient, the Young's modulus, the Poisson's ratio and the thickness of each layer. The observation of the chemical mapping of the brazing filler before and after the assembly, using energy dispersive X-ray spectroscopy (EDX), showed the chemical migration of the titanium to the ceramic oxide and the tungsten carbide. It was estimated that the brazed assembly is under a flexural stress, with a maximum in a compressive stress area near the brazing joint which reaches 85.6 MPa. This stress value reaches 12% of the bending strength allowed by the ceramic (716 MPa). The discussion proposes to highlight the limits of each method. The mathematical model has however shown good accuracy to give a first estimated residual stress in the ceramic plate.