Defence Research Establishment Atlantic Dartmouth, Nova Scotia Canada
Recently, the use of high power lasers for surface melting and cladding of nickel aluminum bronze NAB components has stimulated renewed interest in the microstructural development of these alloys. In this study, a laser-clad NAB weldment of nominal composition Cu - 9 wt. Al - 5 wt. Ni - 4 wt. Fe - 1 wt. Mn, provided by DREA was examined using transmission electron microscopy. Significant variations in the microstructure were observed between the weld deposit and heat affected zone of the clad. In the weld deposit, the microstructure predominantly consisted of two phases which are the product of martensitic or possibly bainitic phase transformations. A high density of Fe-rich precipitates, ranging up to 200 nm in size, are also distributed throughout both matrix phases. In the heat affected zone, the microstructure typically contained three major phases a martensitic phase similar to that observed in the deposit region, the fcc alpha phase, and an alpha kappa eutectoid. The small Fe-rich precipitates are retained in the martensitic phase. The observed phase relationship and morphologies will be discussed in terms of the transformation behaviour of the NAB clad.