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ABSTRACT
The nano mechanical properties of brittle materials are the key factors affecting nano machining performance. Lithium niobate (LN) single crystal is the typical anisotropic brittle material. The hardness H and crack length of LN crystals on X-cut wafers were measured through indentation experiments, and the fracture toughness KIC and the critical cutting depth dc along <001> orientations were estimated. A set of fixed-abrasive (FA) lapping pads mixed with diamond grains of different sizes were prepared for lapping on X-cut wafers. The effects of abrasive cutting depth δ and dc on material removal rate (MRR) and surface roughness were discussed. Results indicate that: the surface hardness H of X-cut is about 6 GPa. And the minimum KIC and dc on X-cut are 0.67 MPa.m1/2 and 63.6 nm (along <001> orientation), respectively. Lapping tests show that when the abrasive cutting depth δ exceed the dc, MRR will increase significantly, accompanied with brittle material removal and low surface quality.
Funding
This work is financially supported by Aeronautical Science Foundation of China (2014ZE52055), and National Science Foundation of China (51175260).