Microstructure Development and Different Heat Treatment of Nickel Aluminium Bronze in Wire and Arc Additive Manufacturing Process

Wire and Arc Additive Manufacturing (WAAM) is a promising rapid prototyping process, which can potentially replace the traditional subtraction methods with the benefits of materials, cost and time savings and environment friendliness. It is mainly used to fabricating complex 3-Dimensional large-scale components. This thesis explores the welding process and microstructure development of a Nickel Aluminium Bronze (NAB) alloy and compares the microstructural characteristics with casting samples. As a microstructure control strategy, different heat treatment approaches are used to analyze the redistribution of different phases and changes in mechanical properties. The deposited layers consisted of two dominant phases, α and β, and a variety of precipitates(κⅠ,κⅡ,κⅢ,κⅣ). The β phase retained due to high cooling rate in the WAAM process is harmful for the performance of the construct. The morphology and distribution of the precipitates can be controlled through a heat treatment process, to reduce its detrimental effect on the mechanical properties. The evolution of the microstructure during WAAM processing of NAB is investigated using optical microscopy, electron microscopy and x-ray diffraction. EDS is used to identify different composition distribution. The Differetial Scanning Calorimetry (DSC) is applied to study the microstructure evolution in AM bronze. This technique reveals the temperature ranges where phase transformations occur. The chemical reaction, the appearance of precipitate phases and the retained β phase can be evaluated by DSC. The techniques allows to determine the appropriate heat treatment temperatures. Microhardness test are used to evaluate its mechanical properties. Fatigue properties of NAB by WAAM are analyzed according to its characteristic microstructure and appropriate heat treatments are also predicted for further improving. WAAM can be used in industries to improve fatigue properties as an energy efficient and material efficient alternative of casting way.Materials Science and Engineerin