a b s t r a c tSimulations of the deformation of microstructures at high homologous temperatures have been carried out using a Crystal Plasticity Finite Element (CPFE) model to predict texture and grain structure deformation in Face-Centred-Cubic (FCC) metals deformed under conditions representative of hot forming operations. Results show that the model can quantitatively predict the location and intensity of the main deformation texture components of a AA5052 aluminium alloy deformed at 300 C under Plane Strain Compression (PSC). Simulations also reasonably predict the range of strain values measured using microgrids in the microstructure of a Fe-30wt%Ni alloy deformed at 1000 C using a new experimental procedure. However, the model fails to reproduce accurately intra-granular strain distribution patterns. Results at room temperature, after a tensile test carried out inside a Scanning Electron Microscope (SEM) on the same model alloy, show a much closer match between simulation and experimental results. Despite discrepancies for some local deformation features, the model predicts the formation of intense deformation bands running at 45 with respect to the tensile axis and located along the same grain boundaries as in the experiment. Results, therefore, highlight the limitations of deterministic CPFE simulations for situations where the grain size to sample thickness ratio is small and for which the sub-surface grain geometry strongly affects surface strains. They also show that reliable predictions of the statistical response of a polycrystalline aggregate can be obtained for the hot deformation of metals which controls microstructure evolution during the processing of metals.

A new experimental procedure has been developed to study micro-crack formation at the surface of compression specimens deformed at high temperature under thermomechanical conditions representative of hot forming operations for steels. Damage formation in a Fe-30wt%Ni alloy has been studied in relation to strain distributions measured at the scale of the microstructure using a microgrid technique. 20 μm-pitch microgrids have been deposited at the surface of a tapered specimen designed to generate critical levels of stress triaxiality representative to those leading to edge cracking in hot rolled steel products. The specimen was deformed using a revised plane strain compression test carried out under vacuum in a Gleeble machine at 1000°C. The grid distortion after the test has then been analysed to produce strain distribution maps which show local strain values ranging from 0 to 75 % for an applied compression of 25 %. Strain localisation has been commonly observed along grain boundaries where damage is initiated at high temperature. Results therefore provide new insight into the early stages of damage formation at the surface of hot rolled products.