Nanometer-scale chip formation and surface integrity of pure titanium in diamond turning

Titanium is attracting great attentions in aerospace and medical applications where high surface quality plays an important role in improving the product performance. For developing nano-precision machining technology for titanium, clarification of the nanometer-scale chip formation mechanism is essential. In this study, the surface formation mechanism of pure titanium in ultraprecision cutting tests using single-crystal diamond tools was investigated. The results demonstrated that decreasing undeformed chip thickness from the micrometer scale down to the nanometer scale had profound impacts on the shear angle, specific cutting force, and chip morphology. Chip tearing phenomenon occurred when undeformed chip thickness is smaller than a critical value (~ 100 nm), which significantly affected the chip morphology and machined surface integrity. In nanometer-scale cutting, tool feed mark is no longer a major reason of surface roughness; instead, material plucking, debris, scratches, and chip adhesion influenced the surface integrity. The high pressure generated in the nanometer-scale cutting caused a hardness increase in workpiece material and promoted workpiece material adhesion to the tool surface, as well as tool wear.