I. Zarudi

Towards a deeper understanding of plastic deformation in mono-crystalline silicon

Abstract This paper investigates the plastic deformation in mono-crystalline silicon under complex loading conditions. With the aid of various characterization techniques, it was found that the mechanism of plasticity in silicon is complex and depends on loading conditions, involving dislocations, phase transformations and chemical reactions. In general, plastic deformation in silicon is the coupled result of mechanical deformation controlled by the stress field applied, chemical reaction determined by the external loading environment, and mechanical–chemical interaction governed by both the loading type and environment. Temperature rise accelerates the penetration of oxygen into silicon and reduces the critical stress of plastic yielding. When the chemical effect is avoided, the initiation of plasticity is enabled by octahedral shear stress but the further development of plastic deformation is influenced by hydrostatic stress. Plasticity of silicon in the form of phase transformations, e.g., from the diamond to amorphous or from the amorphous to bcc structures, is determined by loading history.

Microstructures of phases in indented silicon: A high resolution characterization

This letter investigates the structural changes in monocrystalline silicon caused by microindentation with the aid of the high-resolution transmission electron microscopy. It shows that the transformation zone is amorphous when the maximum indentation load, P-max, is low, but a crystalline phase of high-pressure R8/BC8 can appear when P-max increases. The nanodeformation of the pristine silicon outside the transformation zone proceeds with the mechanical bending and distortion of the crystalline planes. Certain extent of plastic deformation took place due to dislocation slipping. The results seem to indicate that the shear stress component played an important role in the deformation of the transformation zone

Effect of ultraprecision grinding on the microstructural change in silicon monocrystals

Abstract The effect of ultraprecision grinding on microstructural change in silicon monocrystals, such as surface roughness and dislocation structure, was investigated both experimentally and theoretically. The study found that there exists an additional concentration of oxygen and carbon in an amorphous layer for all investigated grinding regimes with their distributions dependent on the grinding variables. It showed that two atomic bonding configurations exist in the amorphous layer, i.e. silicon oxide in the surface region followed by amorphous silicon. The research established that the grinding table speed affects the thickness of the dislocation layer in the subsurface. Increase of the table speed leads to a thicker dislocation zone and created microcracks. The paper concludes that the ductile mode of material removal in the grinding of silicon monocrystals is due to the formation of the amorphous phase.

Mechanical property improvement of quenchable steel by grinding

This paper studies a method of surface heat treatment by making use of grinding heat and stress to create favorable microstructures and promote high wear and fatigue resistance. It was found that the thickness of the treated surface layer could be up to 600 μm. The beneficial microstructure of the layer was created by an enhanced martensite transformation, intensive dislocations and a more desirable carbon distribution. It is highly possible that the method can be used to incorporate grinding and surface hardening into a single grinding operation to develop a cost-effective production method.

Behavior of monocrystalline silicon under cyclic microindentations with a spherical indenter

This study discusses the behavior of high-pressure phases of monocrystalline silicon when subjected to cyclic indentations with a spherical indenter. It was found that specific phases form in the second and subsequent indentation cycles under low maximum loads. An increase of the maximum indentation load causes changes of subsequent indentation cycles of the phase transformation events to occur earlier on both loading and unloading. The repeated indentations result in the formation of a multiphase structure in the deformed zone, featuring a nonhysteresis behavior. After a critical stage, the properties of the transformed material are stabilized and further indentations can no longer alter the load–displacement curve. It was also found that the greater the maximum load, the faster the occurence of property stabilization.

Microstructure evolution in monocrystalline silicon in cyclic microindentations

The study presents evidence of the microstructural evolution during cyclic indentation of monocrystalline silicon with a spherical indenter. Transmission electron microscopy examination of microindentation on cross-section view samples showed that the structure change in the transformation zone features a decomposition of the amorphous phase to R8/BC8 crystals. Outside the zone, cyclic loading gives rise to bending of pristine silicon, slip penetration, and radial cracking. The development of the load-displacement curves during consecutive indentations is justified in terms of the phase transformation events observed.

Subsurface damage in single-crystal silicon due to grinding and polishing

Grinding and polishing are widely used surface finish operations for a variety of precision and delicate component of ceramics, such as silicon wafers and gauges. However, the formation and evaluation of the subsurface damage induced have not been investigated, although subsurface damage is extremely important to the quality of the products. Grinding and polishing are usually carried out by a series of steps, beginning with rough grinding with coarse abrasives, followed by fine grinding with fine abrasives and then finished by a final polishing with ultra-fine abrasives. Unfortunately, it is still the manufacturing practice that the thickness of material removal at every step is determined empirically according to a rough examination of the ground/ polished surface. This examination method is not reliable, as has been pointed out recently by the authors [1], and the subsurface damage of a component ean be severe even though its surface may look crack-free. The present work is to evaluate the subsurface damage in single-crystal silicon during grinding and polishing. The treated surface had (1 1 0) orientation. Rough grinding was conducted using coarse loose abrasives (silicon carbide) with a mean diameter of 50 pm and followed by grinding using abrasives of 25 #m. Fine grinding was carried out using loose abrasives (aluminium oxide) with mean diameters 15/~m, 9/~m, 5/~m and 1/~m, respectively. Polishing was arranged as a finishing procedure by ultra-fine particles (0.025/~m) using a matrix such as pitch with a suitable oxide slurry. The detailed grinding and polishing proeedure ean be found in [2]. It is important that at each grinding or polishing step, the depth of subsurface damage be determined such that this damaged layer can be removed in the next step. Subsurface damage was evaluated by means of transmission electron microscopy (TEM). To do this, a specimen after each grinding/polishing was sectioned perpendicular to the ground/polished surface to make cross-section view specimens for TEM. Details of the procedure can be found in [1]. This method of specimen preparation enables the subsurface damage to be investigated thoroughly in the plane perpendicular to the ground or polished

A revisit to some wheel-workpiece interaction problems in surface grinding

Abstract This paper revisited some wheel–workpiece interaction problems in surface grinding including the profile of heat flux and the variation of the wheel’s elastic modulus. A method of using an optical microscope and a CCD camera was applied to capture the depth and width of the heated zone, the details of the temperature field and the stability of the heat flux. It was found that the heat flux in up-grinding can be modeled as a triangle with its apex at the inlet of the wheel–workpiece contact arc. The elastic modulus of the grinding wheel decreases significantly when the grinding temperature is beyond a critical value and can be described by a power law. It was also found that the depth of cut has almost no effect on the partition of the grinding energy.

Effect of temperature and stress on plastic deformation in monocrystalline silicon induced by scratching

Dry air, coolant, and liquid nitrogen were applied, respectively, to study the effect of temperature and stress on plastic deformation in scratching monocrystalline silicon. Phases generated in surface deformation were characterized by means of the transmission electron microscopy. It was shown that the size of the amorphous transformation zone and the depth of slip penetration in sample subsurface were mainly dependent on the stress field applied. The influence of the temperature variation to −196 °C was surprisingly small and the low temperature did not suppress the phase transformation and dislocation activity.

An understanding of the chemical effect on the nano-wear deformation in mono-crystalline silicon components

This paper aims to explain the chemical effect on the wear deformation in mono-crystalline silicon components under nano-sliding. With the aid of various microscopy techniques and theoretical modelling, it shows that two-body and three-body contact sliding processes yield the same mechanism of sub-surface damage. For all the sliding conditions studied with normal loads ranging from 147 mN to 441 mN, no dislocations or micro-cracks were generated. It was found that an amorphous layer always appears and its thickness depends on the sliding load applied and the extent of chemical reaction. Oxygen penetrates into the amorphous layer, changes the atomic bonding of silicon, alters the threshold for amorphous transformation and accelerates wear. However, there still exist a number of problems that need further investigation.