High compressive loading performance of a complex multi-phase hard-facing alloy explained through a highly elastic silicide phase

Hard-facing alloys in nuclear applications must remain resistant to deformation and wear, whilst also minimising transmutation to problematic elements during service. To this end, the Fe-based alloy RR2450 has been developed to potentially replace Co-based hard-facing alloys. RR2450 is a complex multi-phase stainless steel alloy showing an unusually high strength. To understand the possible root cause for such favourable mechanical behaviour, the phase specific response was recorded in this material during mechanical loading using neutron diffraction and electron microscopy based high-resolution digital image correlation in combination with electron backscatter diffraction (EBSD). The detailed analysis shows that despite the high-volume fraction of hard phases expected to impose constraint on the relatively soft ductile ferrite and austenite phases, the latter still deform plastically first. The in-situ loading experiment using neutron diffraction revealed that the hard π-ferrosilicide phase assumes large elastic strains whilst at the same time showing significant diffraction peak broadening. Additional electron microscopy-based strain mapping on compressed samples confirmed an almost pure elastic response of the π-ferrosilicide phase. The possible effect of lattice cell angular distortion of the π-ferrosilicide phase on diffraction peaks was modelled using crystal structure analysis, demonstrating that small changes (<1°) in angular lattice cell parameters can account for the apparent broadening observed by neutron diffraction. Such reversible elasticity by angular distortion of the unit cell is expected to provide a significant pull-back effect during unloading resulting in improved galling wear resistance, an important performance factor for hard-facing alloys intended for nuclear applications.