Effects of nano mechanical properties on LiNbO₃ fixed abrasive lapping

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 K_IC and the critical cutting depth d_c 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 d_c 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 K_IC and d_c on X-cut are 0.67 MPa^.m^1/2 and 63.6 nm (along <001> orientation), respectively. Lapping tests show that when the abrasive cutting depth δ exceed the d_c, MRR will increase significantly, accompanied with brittle material removal and low surface quality.

KEYWORDS:

• Lithium niobate
• nano-mechanics
• fracture toughness
• critical cutting depth
• material removal rate
• surface roughness

Funding

This work is financially supported by Aeronautical Science Foundation of China (2014ZE52055), and National Science Foundation of China (51175260).