Abstract
Nitrogen gas atomised powders of the hardfacing alloy Tristelle 5183 (Fe-21%Cr-10%Ni-7%Nb-5%Si-2%C in wt%) were sieved into different particle size ranges and their microstructures have been investigated. Powder particles larger than approximately 53 μm are composed of dendritic fcc γ-Fe as the principal phase with smaller quantities of: α-Fe, an interdendritic silicide phase isostructural to Fe5Ni3Si2, and Nb(C,N). Particles <53 μm have increasing quantities of either dendritic α-Fe or cellular silicide phase with decreasing amounts of γ-Fe as the particle size decreases, along with ~5% Nb(C,N). Coarse (> 10 μm) sized Nb(C,N) particles, that are seen in all powder size fractions, pre-existed in the melt prior to atomisation, whereas micron-sized Nb(C,N) particles that are found within α-Fe, γ-Fe or silicide are the primary solidification phase. Nanoscale Nb(C,N) also formed interdendritically in the last stages of solidification. Compared with a mould cast sample, a significant difference is the suppression of M7C3 formation in all powder size ranges. The increasing quantities of α-Fe and silicide in smaller sized powder particles is consistent with increased undercooling prior to nucleation permitting metastable phase formation.
Highlights
A laboratory sieve shaker was used to separate the supplied powder into the following size fractions: b20, 20–38, 38–45, 45–53, 53–63, 63–75 and 75–106 μm, with characterisation of these different powder particle size ranges being undertaken in this work
We argue that the MX populations are related to the three Nb(C,N) particle populations observed by SEM/transmission electron microscope (TEM) in the powder, namely (i) the pre-existing Nb(C,N); (ii) the micronsized primary Nb(C,N) and (iii) the nano-scale secondary Nb(C,N)
The current study demonstrates, that the classification of atomised powder should be considered prior to hot isostatic pressing (HIPing) in an effort to avoid the inclusion of particles containing the non-equilibrium microstructures that may degrade the performance of HIPed components
Summary
M.J. Carrington et al / Materials and Design 164 (2019) 107548 weld hardfacing is one which is well established. Weld deposited hardfacings are commonly used when there is the possibility of significant wear and the need for long intervals between refurbishment. Cobaltbased weld hardfacing alloys are currently employed extensively and, the StelliteTM family of alloys has found widespread application because of their excellent performance in minimizing wear, corrosion and oxidation in many environments [1]. The use of cobalt-based hardfacing alloys is not always ideal. In nuclear applications, there is a need to reduce the cobalt content in alloys used to protect components in the primary circuit of a pressurized water reactor (PWR) power plant. The resulting 60Co based radioactive debris has both a high and long-lived nuclear activity which is a hazard for maintenance personnel
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