Microstructure and mechanical properties of Ni-Cu alloys fabricated using wire arc additive manufacturing

Ni-Cu alloys, also known as Monel alloys, are widely used in marine industry due to their high corrosion resistance and good mechanical properties. Submarine propeller shafts, diesel engine piston rods and centrifugal pump shafts are examples of application of these alloys. Despite their good mechanical and corrosion resistant properties, Ni-Cu components may fail in operation via sliding wear, galling and pitting corrosion. Since the Ni-base alloys are expensive, repair is often an economic choice than replacement. A possibility to use wire arc additive manufacturing (WAAM) technology for fabrication of new and repair of used Ni-Cu components was assessed in this thesis. Two Ni-Cu wires with various Ti, Mn, Al and C contents were deposited on a Ni-Cu substrate with a wide range of welding parameters (travel speed, wire feed rate). The solute atom concentrations and particle number density values were modified using various post processing heat treatment schedules. A comprehensive study of the microstructure, mechanical properties, wear and corrosion resistance of the Ni-Cu alloy components fabricated using WAAM has been conducted. Microstructure characterisation, in particular a detailed study of the precipitate’s parameters (size, number density and chemical composition) was carried out using optical, scanning, transmission and atomic resolution electron microscopy. Mechanical properties were assessed using hardness, tensile testing to fracture, wear and corrosion resistance.