Understanding micromechanical deformation in hard-facing alloys for improving galling resistance

Abstract

Three iron-base hard-facing alloys (Nitronic 60, Tristelle 5183 and RR2450) and one cobalt alloy (Stellite 6) are studied to examine their deformation behaviours at the microstructural level. Three-point beam testing is employed to introduce progressive straining and deformation is investigated with high resolution DIC and EBSD to provide quantitative characterization of the deformation mechanisms. A distribution of fine precipitates is found to promote more homogeneously distributed slip, work hardening and potentially better resistance with respect to galling. Crystal plasticity finite element modelling is developed to represent the four differing hard-facing alloys. The general nature of the observed deformations, including spatial strain distributions, influence of hard phases, and frequency distributions of slip magnitude are shown to be consistent with the experimental observations, and to capture the very differing behaviours demonstrated by the four alloys. The models have then been employed to investigate the galling response of the differing alloys. The role of the hard particles, and interfacial decohesion in particular, are investigated as drivers for the onset of galling. Both the experimental and simulation results suggest precipitate decohesion significantly affect the alloys’ galling resistance. Simulations based on characteristic normal load and contact area methods have been carried out. However, cohesive zone CPFE modelling was shown to be necessary for the precipitate alloys, and suggested that a uniform distribution of fine precipitates and harder matrix gives better resistance to decohesion and galling. These findings are potentially important for the design of new hard-facing alloys with enhanced galling resistance.