High pressure phase transformation analysis and molecular dynamics simulations of single point diamond turning of germanium.

摘要

A molecular dynamics (MD) model for single point diamond turning (SPDT) has been developed. Using a nonequilibrium MD simulation of a machining operation the atomistic description of the process is achieved. Germanium was chosen as the primary material of interest due to its brittle-to-ductile transition with decreasing depth of cut. The MD technique was applied to germanium under varying cutting conditions. The original crystalline structure of germanium was found to transform into an apparent amorphous structure during simulated machining. Experimental work confirmed the presence of both an amorphous and a high pressure metallic phase of germanium as being present after and during the machining operation, respectively.; An analysis of the cutting process revealed the existence of sufficient pressure to generate the metallic phase of germanium during machining. The amorphous structure in simulated machining indicates the occurrence of an apparent phase transformation. This supports the assertion that the covalent crystal structure is not stable at the process conditions. The model used does not simulate the metallic form of germanium. Therefore, the model cannot reflect the phase transformation from a covalent phase to a metallic phase.; This work supports previous research in which the depth of cut is the critical parameter in the brittle to ductile transition in machining of germanium, Further, this work establishes pressure as a parameter and the high pressure phase transformation as a necessary mechanism for the transition. The ductile nature of the metallic high pressure phase is believed to provide the machinability of this material.