Solidification microstructure of centrifugally cast Inconel 625

Centrifugal casting is a foundry process allowing the production of near net-shaped axially symmetrical components. The present study focuses on the microstructural characterization of centrifugally cast alloys featuring different chemical compositions for the construction of spheres applied in valves made of alloy IN625 for operation at high pressure. Control of the solidification microstructure is needed to assure the reliability of the castings. Actually, a Ni-base superalloy such as this one should have an outstanding combination of mechanical properties, high temperature stability and corrosion resistance. Alloys such as IN625 are characterised by a large amount of alloying elements and a wide solidification range, so they can be affected by micro-porosity defects, related to the shrinkage difference between the matrix and the secondary reinforcing phases (Nb-rich carbides and Laves phase). In this study, the microstructure characterization was performed as a function of the applied heat treatments and it was coupled with a calorimetric analysis in order to understand the mechanism ruling the formation of micro-porosities that can assure alloy soundness. The obtained results show that the presence of micro-porosities is governed by morphology and by the size of the secondary phases, and the presence of the observed secondary phases is detrimental to corrosion resistance

Microstructure Evolution and Properties of Hastelloy UNS N06200 and UNS N06022 as a Function of the Applied Thermal Treatment

The aim of this study is focused on the mechanical and the microstructural characterization of two Ni-based cast alloys: Hastelloy UNS N06200 and Hastelloy UNS N06022. The analysis has been performed through the observation of different microstructures obtained as a function of different cooling rates performed by the use of test blocks. After solidification, the specimens produced by different cooling rates have been extracted, and UNS N06200 samples have undergone a solution treatment process, while UNS N06022 samples have undergone a solution treatment followed by an ageing process. The mechanical properties have been measured, and some significant and consistent relationships have been pointed out with the heat treatment and the obtained microstructures