Surface Characteristics of Ni-Based Metallic Glass in Wire Electrochemical Micro Machining

Abstract

Surface characteristics of Ni-based metallic glass in wire electrochemical micro machining (WECMM) process are investigated firstly. Metallic glasses have a unique combination of enhanced mechanical and chemical properties due to the absence of crystalline features. However, their range of application is significantly limited because of the challenges faced when shaping them on a microscale. The technique of nanosecond pulsed electrochemical micro machining with a micro-wire tool electrode is introduced and a specially designed system is developed for micro-shaping metallic glass. Taking a Ni-based metallic glass, Ni72Cr19Si7B2, as an example, polarization and processing characteristics in dilute acid electrolytes are investigated. A significantly more uniform surface is obtained in H2SO4 than in HCl, because of the growth of a passive film during a stable passivation regime. A high current density is beneficial for good surface morphology and roughness. It is demonstrated experimentally that the use of a traveling cathode wire and a traveling anodic workpiece, as well as a carbon nanofiber tool electrode with good surface hydrophilicity, can enhance mass transport significantly in the machining gap. Enhanced surface quality of both front face and side wall is also achieved. Several complex microstructures with good surface quality are fabricated under different conditions.