Micromechanical contributions to material removal and surface finish

Abstract

We study material removal mechanisms of commercially available hard optical materials, with respect to their micromechanical properties, as well as their response to different manufacturing techniques. The materials of interest are heterogeneous materials such as Ni-based (nonmagnetic), Co-based (magnetic), and binderless tungsten carbides, in addition to other hard optical ceramics such as ALON, polycrystalline alumina (PCA), and silicon carbide (SiC). Our experimental work is performed in three stages, emphasizing the contributions of each material’s microstructure to its mechanical response. In the first stage, we identify and characterize material physical properties, such as <i>E</i>-Young's modulus, <i>H_v</i>-Vickers hardness, and <i>K_Ic</i>- fracture toughness (either by microindentation techniques, previously published models, or vendors’ data base). In the second stage, we examine the ability of these materials to be deterministically microground and spotted with magnetorheological finishing (MRF). The evolution of the resulting surface topography is studied using a contact profilometer, white light interferometry, scanning electron microscopy, and atomic force microscopy. In the third stage, we demonstrate that subsurface damage (SSD) depth can be estimated by correlating surface microroughness measurements, specifically, the peakto- valley (p-v) microroughness, to the amount of material removed by an MRF spot.