Brittle to ductile transition dependence upon the transition pressure value of semiconductors in micromachining
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ulo S. Pizani Departamento de Fisica, Universidade Federal de Sa˜o Carlos, CP 676, 13565-905, Sa˜o Carlos, Sa˜o Paulo, Brazil
Jaime G. Duduch Departamento de Engenharia Mecanica, Escola de Engenharia de Sa˜o Carlos, Universidade de Sa˜o Paulo, CP 359, CEP 13560-970, Sa˜o Carlos, Sa˜o Paulo, Brazil (Received 27 September 1999; accepted 28 April 2000)
Single-point diamond turning tests were carried out in two different [001]-oriented semiconductors, InSb and Si single crystals. The analysis of the conditions in which the machining is in ductile or brittle mode indicates that the plasticity presented by semiconductor crystals during micromachining can be correlated to the value of the transition pressure. It is shown that the ductility presented by different semiconductor single crystals is inversely related to the transition pressure value of the material. I. INTRODUCTION
The elastic and plastic behavior of semiconductors in the submicrometer range is most frequently determined using indentation and scratching tests.1–3 These studies were very useful for modeling the process of material removal in single-point diamond micromachining of brittle materials.4 It is also known that, during indentation,5 when very low loads are used, a diamond-cubic silicon transforms to the denser metallic -tin structure that plastically flows. The same transformation is observed under hydrostatic pressure, at room temperature.6,7 In both cases, upon unloading, this metallic phase transforms into an amorphous semiconductor phase.8–11 In silicon, for example, the critical pressure observed to cause a transformation to a metallic -tin structure is in the range of 11.3–12.5 GPa and the pressure to the transformation into the amorphous semiconductor phase during releasing the load is about 7.5–9.0 GPa. 12 These values of metallic transition are consistent with the hardness value encountered for silicon, which is about 11–12.5 GPa.2 As a result, it was considered that the hardness value of semiconductors crystals is directly proportional to the transition pressure value.13 The ductility of semiconductor crystals during micromachining has always been treated as a function of cutting conditions and tool geometry based on fracture mechanics. Results related to machinability of these materials have not yet reached complete agreement. The amorphous state detected within the indentation impression, as well as in the scratching groove,14,15 enabled a 1688
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J. Mater. Res., Vol. 15, No. 8, Aug 2000 Downloaded: 15 Mar 2015
new approach for analyzing the plasticity in single-point diamond machining.16 –18 Recently, it was proposed20 that the plastic flow of semiconductors during singlepoint diamond turning was constrained to the extension of the transformed layer compressed between the cutting tool edge and the bulk material. It was assumed that the extension of this transformed region is a function of a combination of tool geometry and cutting conditions. This means that the ductile regime could be indirectly estimated
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