SummaryPaper, mainly constituted of cellulose fibres, often contains mineral fillers. These fillers increase some of the properties of the paper (whiteness, printability, etc.) and are cheaper than the cellulose fibres. Nevertheless, the fillers reduce the mechanical properties of the sheet. Paper presents an anisotropy corresponding to three main directions. This anisotropy characterises the sheet mechanical properties, structure and filler distribution. Analyses of the cross section of the paper sheet with a low-vacuum scanning electron microscope with an energy dispersive spectrometer analysis module can show this distribution. The procedure developed consists in analysing discrete profiles to build the mean profile known as filler Z-distribution for each of the fillers. To develop this method, problems such as determination of the surface points, the number of points to analyse to define a cross section profile and the time required for the test, have been solved. Paper is sensitive to electron irradiation. In order to avoid deterioration of the material and to obtain satisfactory results, the time span for analyses is restricted to 40 s with a 12 kV electron beam accelerating voltage. Monte Carlo simulations are used to determine the diffusion cloud size and thus to determine the number of points that constitute a profile. The samples are gold sputtered and, with the aid of backscattered imaging, the coated surface allows determination of the sample surface points.

This study evaluated the residual stresses induced by brazing and grinding submicron Al 2 O 3 , using different methods. Energy dispersive x-ray spectrometry analysis (EDX) of 72Ag-Cu filler and filler/WC-Co interface showed evidence of atomic diffusion and possible formation of titanium oxide layers between the joint and the bonding materials. An analytical model supported by the finite element method (FEM) based on strain determination due to the difference in variation of thermal expansion was used to assess the stress distribution at the coupling interface and in bulk materials. The model took into account the evolution of the YoungÕs modulus and of the thermal expansion with temperature. The model could be used to follow strain and stress evolutions of the bonded materials during the cooling cycle. The maximum stress rose above 2300 MPa at the center of the 100 3 100 3 3 mm ceramic plates. The residual stresses on the external surface of ceramic were investigated by x-ray diffraction (XRD) and indentation fracture method (IFM). After brazing and grinding the plate, the principal stresses were 128.1 and 94.9 MPa, and the shear stress was 220.1 MPa. Microscopic examination revealed grain pull-out promoted by the global residual stresses induced by the brazing and grinding processes. The surface stresses evaluated by the different methods were reasonably correlated.

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 (Al 2 O 3 -ZrO 2 ) 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. K E Y W O R D S ceramic-metal systems, modeling/model, neutron diffraction, stress, X-ray methods How to cite this article: Contarato F, Bach M, Krier J, Gobled A, Mille P. Evaluation of residual stresses during brazing of Al 2 O 3 -ZrO 2 to cemented tungsten carbide. Int J Appl Ceram Technol. 2020;17:990-997.

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