Micromechanical investigations and modelling of a Copper–Antimony-Alloy under creep conditions

• Creep of pure Cu single crystals and of a coarsed grained Cu-1 wt.% Sb alloy at 823 K.
• Metallographic and a crystallographic assessment of the Cu–Sb test specimens.
• Measurements of grain boundary sliding and estimation of the sliding viscosity.
• Development of a micromechanical polycrystal model for finite element analysis.
• Fitting of the micromechanical model to the experimental creep data.

In many practical applications, creep damage is the limiting factor of a component’s lifetime. A micromechanical model of creep induced grain boundary damage is proposed, which allows for the simulation of creep damage in a polycrystal within the framework of finite element analysis. The model considers grain boundary cavitation and sliding according to a micromechanically motivated cohesive zone model while creep deformation of the grains is described following the slip system theory. The model can be applied to idealised polycrystalline structures, such as a Voronoi tessellation or, like demonstrated here, to real grain structures of miniature creep specimens. Creep tests with pure Cu single crystals and with a coarse-grained polycrystalline Cu-1 wt.% Sb alloy at 823 K have been performed and used to calibrate the polycrystal model. The grain structure of the polycrystalline Cu–Sb specimens has been revealed by the EBSD method. Extensive grain boundary sliding and cavitation has been observed in the crept specimens. Grain boundary sliding has been found to promote wedge-type damage at grain boundary triple junctions and to contribute significantly to the total creep strain. Furthermore, the assumed stress sensitivity of the models grain boundary cavity nucleation rate strongly influences the development of wedge-type damage.