IN-SITU OBSERVATIONS OF THE DEFORMATION AND DAMAGE BEHAVIOUR AROUND LASER-DRILLED COOLING HOLES IN INCONEL ALLOY 617 USING THE SCANNING ELECTRON MICROSCOPE

摘要

Subject of the present work is an investigation of short crack behaviour (length approx. <100μm) around laser-drilled cooling holes in a nickel-base-alloy. The investigation of short cracks by light microscopy is impossible due to the very small diameter of laser-drilled cooling holes (approx. 200μm), therefore uniaxial tensile tests with flat tensile specimens were carried out in a scanning electron microscope. A tensile test rig and a heating device specially designed for the SEM were used. The tests were conducted with the nickel-base INCONEL alloy 617. For the description of the deformation and damage behaviour, especially at high temperatures, the experiments were carried out under uniaxial tensile load at 650°C. The formation of a technical crack length (approx. 1mm) in metallic materials will be mainly determined by the crack growth of short cracks. Therefore it seemed to be important to look at the evolution of accumulated fatigue damage in this region, for developing fracture mechanics concepts.