Ultra-precision grinding of polycrystalline magnesia alumina spinel (MgAl2O4) ceramics based on AE signals monitoring: Surface characteristics and damage mechanisms.

Polycrystalline magnesium aluminate spinel (PMAS) ceramics is a kind of transparent oxide ceramic with the advantages of high hardness, high mechanical strength, thermal stability and chemical corrosion resistance. The optical transmittance and infrared absorption edge of PMAS ceramic are better than that of sapphire and ALON in the mid-infrared band with the wavelengths greater than 4.5 μm, which makes it as an ideal material for manufacturing the optics used in the fields of transparent armor protection, infrared optical window and infrared missile dome. However, the hardness of PMAS ceramics is close to that of sapphire, and the brittleness is greater than that of sapphire, which brings great challenges to ultra-precision ductile grinding. In this paper, the surface characteristics and damage mechanisms in ultra-precision grinding of PMAS ceramics were systematically researched based on AE signals monitoring. Firstly, the effects of grinding depth, feed speed and grain size on the surface characteristics were studied in detail. Secondly, the influences of grinding depth and feed speed on the damage characteristics of PMAS ceramics were researched based on energy spectrum analysis of AE signals. Thirdly, the evolution mechanisms of material removal modes and damage characteristics were revealed based on time-frequency analysis of AE signals. Then, the damage types on ductile surfaces and initiation mechanisms of damage crack were investigated. Ultimately, the crack-free ductile surfaces and surface roughness (Sa) of 3 nm were achieved through ultra-precision grinding. [ABSTRACT FROM AUTHOR]