Characterising the Integrity of Machined Surfaces in a Powder Nickel Alloy used in Aircraft Engines

This paper describes methods for evaluating and characterising the integrity of machined surfaces in a powder nickel alloy that is being used for disc applications in aircraft engines. It initially reviews techniques for inspecting the effects of process parameters on surface integrity for hole making and finish turning and then presents the findings of work that has been conducted to understand the influence of machining anomalies on fatigue life. The techniques considered for characterising surface integrity include surface inspection, surface roughness measurement, metallographic assessment of etched surfaces using light microscopy and micro-hardness measurement. More novel techniques are then discussed, exploiting advanced electron microscopy, nano-indentation and x-ray diffraction methods. These are capable of understanding the effects of machining processes on microstructure and quantifying the depth to which machining processes can change the material microstructure.