Microstructural control in Inconel 718 manufactured by laser powder bed fusion

Additive Manufacturing promises intricate and high performance parts to be manufactured with less waste. However, more research is required into defect and temperature control in complex geometries, as well as on the production of functionally graded parts.

This thesis covers the initial concepts of a new method of achieving a homogeneous temperature distribution in a complex part by cutting laser hatch lines in to mini hatches and allowing a different set of laser parameters to be assigned to each hatch. This method should also allow for the generation of parts with consistent quality that contain microstructurally and mechanically distinct regions.

Further to this, a new method of achieving alternate microstructures using the additive manufacturing process has been investigated in Inconel 718. Traditional additive manufacturing produces a microstructure that comprises of long columnar grains. This new method exploits lack of fusion and keyhole defects as well as unmelted powder present in the central region of a printed component in order to generate a wide range of microstructures after hot isostatic pressing. As well as enabling a variation in tensile properties to be achieved in a multi-microstructural part, this method has been shown to be able to produce components using a fraction of the time and energy required in a standard additive manufacturing build.

These findings have implications for the broader field of additive manufacturing, with increased consistency providing a route for simpler part qualification in safety critical industries, and microstructural control providing a higher level of material functionality in complex parts.