Abstract
Machining of brittle ceramics is a challenging task because the requirements on the cutting tools are extremely high and the quality of the machined surface strongly depends on the chosen process parameters. Typically, the efficiency of a machining process increases with the depth of cut or the feed rate of the tool. However, for brittle ceramics, this easily results in very rough surfaces or even in crack formation. The transition from a smooth surface obtained for small depths of cut to a rough surface for larger depths of cut is called a brittle-to-ductile transition in machining. In this work, we investigate the mechanisms of this brittle-to-ductile transition for diamond cutting of an intrinsically brittle 3C-SiC ceramic with finite element modeling. The Drucker–Prager model has been used to describe plastic deformation of the material and the material parameters have been determined by an inverse method to match the deformation behavior of the material under nanoindentation, which is a similar loading state as the one occurring during cutting. Furthermore, a damage model has been introduced to describe material separation during the machining process and also crack initiation in subsurface regions. With this model, grooving simulations of 3C-SiC with a diamond tool have been performed and the deformation and damage mechanisms have been analyzed. Our results reveal a distinct transition between ductile and brittle cutting modes as a function of the depth of cut. The critical depth of cut for this transition is found to be independent of rake angle; however, the surface roughness strongly depends on the rake angle of the tool.
Highlights
Owing to the unique electronic and optoelectronic properties, the zinc blende type cubic phase of SiC, i.e., 3C-SiC, is a highly desirable material in the semiconductor, optoelectronic industry [1]
With the advancement of the cutting tool, the stress concentration and the corresponding grooving forces increase at first with very small oscillations, as shown in Figure 7, where the grooving forces resulting from the different rake angles are plotted
This has been accomplished by an iterative process, in which the material parameters have been varied to minimize the differences between simulated and experimentally measured load vs. indentation depth curves for a given maximum indentation depth
Summary
Owing to the unique electronic and optoelectronic properties, the zinc blende type cubic phase of SiC, i.e., 3C-SiC, is a highly desirable material in the semiconductor, optoelectronic industry [1]. The brittle fracture occurs when the material reaches a certain tensile stress, whereas the materials fail in a ductile manner if the shear stress reaches a pre-defined value They characterized the BDT by comparing the experimental undeformed chip thickness and surface morphology to that of numerically obtained values. A material with similar sp 3 bonds, Zhang et al [13] showed that a ductile mode of material removal can be achieved through the consistent choice of machining parameters Their use of a tool with a negative rake angle suppressed the crack propagation, leading to a ductile mode of cutting at low depth. The mechanisms of brittle and ductile cutting of 3C-SiC and their correlation with essential machining parameters like depth of cut and rake angle have not been well understood. Criteria for the brittle or ductile cutting modes are derived
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