Surface Integrity Analysis of Niobium-Based Cermet Processed by Electrochemical Machining and Hybrid Laser-Electrochemical Machining

Abstract

This study investigates the evolution of surface integrity of a strategically important niobium-based cermet with nickel binder (NbC–Ni), while processing it with electrochemical machining (ECM) and hybrid laser-ECM (LECM) processes for shaping toward molds and cutting tools applications. The results indicate that, while the ECM process can preserve material properties due to its athermal and noncontact nature, it suffers from selective phase dissolution, particle breakout, and passivation issues when processing the cermet. LECM synergistically applies laser and EC process energies to address these challenges, particularly by homogenizing multiphase dissolution and facilitating passivation weakening while using pH-neutral aqueous electrolyte. A combination of metallography techniques were employed to study the surface integrity and correlate it with process mechanisms. Results indicate that ECM selectively dissolves the Ni phase and induces passivation, while LECM mitigates these surface integrity compromising effects by virtue of passivation weakening (lowest O wt % of 33.2) through enhanced transpassive dissolution and escalated reaction kinetics, leading to surface integrity improvement by lowering the roughness (Sa) by 30%, feature slopes (Sdq) by 32%, and increasing the hardness (HV5 738.7) by 55% as compared to ECM. Thus, LECM presents a promising technique for shaping advanced passivating and multiphase materials.