Étude et modélisation du comportement des émaux lors du matriçage finition des aubes en alliage de titane

摘要

During the hot stamping (around 940°C) of titanium alloy blades, some surface defects can occur. Lubrication of this process is provided by graphite spray on tools and enamel coating (thickness around 100 μm) on workpieces. Coating is deposited on cold workpiece and is composed with organic adhesives and metallic oxides. After bibliographic analysis, we study coating film evolution during process on samples or pieces (blades, "saucers") . Heating induces marked decreasse of the film thickness and gives it properties very near those of metallic glasses. However, residual porosity and roughness on the surface are observed and classical viscosity measurement methods cannot be used. Defect is a local accumulation of enamel and graphite and result of few parameters combination: too large film thickness and residual porosity, too high tool temperature, lubricant damage... It results from enamel's flow from centre to side of contact which breaks the crust of coating out side the contact. In order to measure enamel coating viscosity, we develop two tests based on isothermal deformation of coated metal : low temperature indentation gives the brittle-ductile transition temperature (corresponding to 101 0 Pas about ) and high temperature compression gives an estimation of enamel viscosity starting from measurement of t rapped film thickness. Checking and improvement of the experimental procedure are performed with standard glass, with geometry samples evolution (film between tool and sample between two samples) and numerical simulation (Forge2® multi-mat.) in order to correct Wilson's theory. We develop a non- isothermal crushing test of cylinder on lateral surface for studying the effect of the lubricant, the enamel thickness and the tool temperature on friction and final enamel thickness distribution. Numerical simulation (Forge3®) provides value of friction and allows to analyse the thickness film evolution: It depends on metal surface extension, surface temperature and contact pressure gradients. The equation describing the enamel flow along the interface metal/tool is established and its resolution starting from numerical data provided by the stamping simulation (surface temperature, contact pressure, friction shear stress) could estimate the evolution of the enamel thickness distribution along stamping process and defect apparition probability .