Isothermal compression of the GH4169 nickel based superalloy was carried out at a Thermecmaster-Z simulator at deformation temperatures of 930-1050uC at intervals of 20uC, strain rate of 0 . 1-50 . 0 s 21 and maximum height reduction of 60 . 0%. The deformation behaviour of the GH4169 superalloy in isothermal compression was characterised based on the stress-strain behaviour analysis. Constitutive equations described the flow stress as a function of strain rate, strain and deformation temperature were proposed for the isothermal compression of the GH4169 superalloy and a close agreement between the calculated and experimental stress-strain curves is achieved.

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Laser dynamic flexible forming (LDFF) is a novel high velocity forming (HVF) technology, in which the foil metal is loaded by laser shock wave. Strain localization is readily to occur around the bulge edge, which will result in the ultimate dynamic failure. In this work, the microstructures before and after dynamic fracture are characterized by transmission electron microscopy (TEM) to investigate the dynamic failure mechanism. The plastic deformation regions of copper foil are composed of shock compression, strain localization and bulge. Microstructure refinement was observed in three different plastic deformation regions, particularly, dynamic recrystallization (DRX) occurs in the strain localization and bulge regions. In bulge region, extremely thin secondary twins in the twin/matrix (T/M) lamellae are formed. The microstructure features in the strain localization region show that superplastic flow of material exists until fracture, which may be due to DRX and subsequent grain boundary sliding (GBS) of the recrystallized grains. The grain coarsening in strain localization region may degrade the material flowing ability which results in the dynamic fracture.

Laser pre-shocking (LPS) was introduced into the laser dynamic flexible micropunching process to refine the grain size of a workpiece to improve the forming quality of punched parts. T2 copper foils with five different grain sizes and seven different laser power densities with and without LPS were used for the experiment. The results showed that the grains are refined and the average surface roughness decreases after LPS. For copper foils annealed at 650 °C, the value of decreases from 0.430 to 0.363 µm. The increase in laser energy density and grain size leads to the deterioration of the fracture surface. LPS can improve the quality of the fracture surface. Compared with punched holes without LPS, the dimensional accuracy and shape accuracy of punched holes can be improved by LPS. When grain size is close to the thickness of the copper foil, the forming quality of the punched parts becomes uncertain, owing to the difference in the orientation of the initial grains. The instability of laser dynamic flexible micropunching can be reduced by LPS. Especially, the improvement of forming quality of the punched part brought by LPS is significant for the copper foils with coarse grains.

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