Microstructural and mechanical properties evolution of 690 nickel-based alloy subjected to severe hand disc grinding conditions

Abstract

This present experimental research paper investigates the effects of severe hand disc grinding conditions on microstructure and mechanical properties evolution of a nickel-based alloy. Hand grinding is an abrasive process widely used in manufacturing industry. This manual process is used for different surface geometries, and it is often applied as the final operation that provides the effective physico-chemical properties of the surface and its sub-layers. To study the effects of manual disc grinding, a prerequisite consists in identifying the manufacturing parameters such as the feed, the normal force and the orientation of the tool with the manufactured surface. Which is neither easy to reproduce from one operator to another knowing the manual aspect of this manufacturing process nor rigorous to carry out a repeatable experimental plan. Therefore, a test bench with independent controlled parameters is required to reproduce the manual grinding process and achieve advanced studies. Mechanical properties and microstructural evolutions of a nickel-based alloy ground under very high thermomechanical loading due to abrasive material removal process were investigated through micro-hardness, XRD, SEM, EDS and EBSD analysis. The typical surface integrity characteristics are presented. Qualitative and quantitative EBSD measurements were performed to evaluate the local strain condition of the material after extreme thermomechanical processing on subsurface integrity of the nickel-based alloy. The microstructure of the material in the modified layer consists of a highly refined grain structure with an enhanced microhardness of up to 75% compared to the bulk material. It is assumed that the first 20 μm of the modified layer also called white layers in nickel-based alloy are formed by severe plastic deformation during material removal process. Keywords: surface integrity, nickel-based alloy, hand disc grinding, severe plastic deformation, grain refinement, SEM, EBSD. • Multi-scale and multi-physic surface characterization approaches to understand severe disc grinding-induced material modifications of nickel-based alloy. • A gradient of material mechanical properties occurred involving changes in its yield strength. • XRD and micro-indentation are complementary techniques to characterize the work-hardened layer induced by disc grinding. • Thermomechanical effects from disc grinding lead to severe plastic deformations of the metal workpieces yielding highly deformed grain structure, severe work hardening resulting in grain refinement under severe cutting conditions. • Presence of disc grinding-induced surface defects such as ductile tearing, material re-deposition (micro-welding) and debris are also concerns which can deteriorate functional performance of components. • SEM and EBSD analyses revealed the presence of a cold-worked layer consisting of a partially nanostructured region generated during grinding by the combination of a severe plastic deformation and high thermal kinetics.