Analysis of onset of dislocation nucleation during nanoindentation and nanoscratching of InP

Nanoindentation and nanoscratching of an indium phosphide (InP) semiconductor surface was investigated via contact mechanics. Plastic deformation in InP is known to be caused by the nucleation, propagation, and multiplication of dislocations. Using selective electrochemical dissolution, which reveals dislocations at the semiconductor surface, the load needed to create the first dislocations in indentation and scratching can be determined. The experimental results showed that the load threshold to generate the first dislocations is twice lower in scratching compared to indentation. By modeling the elastic stress fields using contact mechanics based on Hertz's theory, the results during scratching can be related to the friction between the surface and the tip. Moreover, Hertz's model suggests that dislocations nucleate firstly at the surface and then propagate inside the bulk. The dislocation nucleation process explains the pop-in event which is characterized by a sudden extension of the indenter inside the surface during loadin

Studying grain boundary regions in polycrystalline materials using spherical nano-indentation and orientation imaging microscopy

In this article, we report on the application of our spherical nanoindentation data analysis protocols to study the mechanical response of grain boundary regions in as-cast and 30% deformed polycrystalline Fe-3%Si steel. In particular, we demonstrate that it is possible to investigate the role of grain boundaries in the mechanical deformation of polycrystalline samples by systematically studying the changes in the indentation stress-strain curves as a function of the distance from the grain boundary. Such datasets, when combined with the local crystal lattice orientation information obtained using orientation imaging microscopy, open new avenues for characterizing the mechanical behavior of grain boundaries based on their misorientation angle, dislocation density content near the boundary, and their propensity for dislocation source/sink behavio

Push-out force and impulse measurement of seven types of small arms ammunition with three different surface states

This study analyzes the influence of lubrication treatments on the force absorbed by the breech bolt called push-out force. The results are of high interest for weapon-safety and durability studies, especially when it comes to weapon maintenance. A barrel-ammunition combination represents an expanding vessel under high pressure. The pressure rises from ambient up to 420 MPa in less than a millisecond. During such a highly dynamic process, purely static equations, describing the problem of the casing push-out force, may not be applied. Besides the dynamic behavior, the surface properties and geometry also play an important role. To investigate the push-out force, a measurement system based on a force washer was built. This system was validated using a crusher method and finite element analysis. The impulse was calculated using the data of the measured force to obtain additional information about the force-time properties of the push-out behavior. Untreated ammunition and two lubrication systems: “ice layer” and “oil lubricated,” as well as seven different ammunition sizes ranging from 5.56 to 12.7 mm were considered. The response was the force absorbed by the bolt while the cartridge provides rear obturation to the combustion gases. It was found that both the casing geometry and its treatments have a significant influence on the push-out force

Analysis of onset of dislocation nucleation during nanoindentation and nanoscratching of InP

Nanoindentation and nanoscratching of an indium phosphide (InP) semiconductor surface was investigated via contact mechanics. Plastic deformation in InP is known to be caused by the nucleation, propagation, and multiplication of dislocations. Using selective electrochemical dissolution, which reveals dislocations at the semiconductor surface, the load needed to create the first dislocations in indentation and scratching can be determined. The experimental results showed that the load threshold to generate the first dislocations is twice lower in scratching compared to indentation. By modeling the elastic stress fields using contact mechanics based on Hertz’s theory, the results during scratching can be related to the friction between the surface and the tip. Moreover, Hertz’s model suggests that dislocations nucleate firstly at the surface and then propagate inside the bulk. The dislocation nucleation process explains the pop-in event which is characterized by a sudden extension of the indenter inside the surface during loading

Nanoindentation cracking in gallium arsenide: Part I. In situ SEM nanoindentation

The nanoindentation fracture behavior of gallium arsenide (GaAs) is examined from two perspectives in two parent papers. The first paper (part I) focuses on in situ nanoindentation within a scanning electron microscope (SEM) and on fractographic observations of cleaved cross-sections of indented regions to investigate the crack field under various indenter geometries. In the second parent paper (part II), cathodoluminescence and transmission electron microscopy are used to investigate the relationship between dislocation and crack fields. The combination of instrumented in situ scanning electron microscopy nanoindentations and cleavage cross-sectioning allows us to establish a detailed map of cracking in the indented region and cracking kinetics for conical and wedge indenter shapes. For wedge nanoindentations, the evolution of the half-penny crack size with the indentation load is interpreted using a simple linear elastic fracture model based on weight functions. Fracture toughness estimates obtained by this technique fall within the range of usual values quoted for GaA

Nanoindentation cracking in gallium arsenide: Part II. TEM investigation

The nanoindentation fracture behavior of gallium arsenide (GaAs) is examined from two perspectives in two parent papers. In the first paper (part I), we address the morphology of the crack field induced by different types of indenters by means of in situ nanoindentation inside a scanning electron microscope (SEM) and of cleavage cross-sectioning techniques. In the present paper (part II), we investigate the early stage of crack nucleation under wedge nanoindentation through cathodoluminescence and transmission electron microscopy. We find that the apex angle of the wedge indenter influences the dislocation microstructure and, as a consequence, the mechanism of crack nucleation under nanoindentation. The formation of microtwins depends on both the orientation of the indenter with respect to the orientation of the GaAs crystal and on the apex angle of the indenter. For dicing applications of GaAs wafers, it is desirable to have an opening angle of the indenter smaller than 70° to facilitate the formation of precursor crack

Damping of post-impact vibrations

During the impact of a body on a plate, flexural waves are set which travel circularly outwards from the point of impact. These waves can be used to determine the properties of the impacting body. For accurate measurements, it is advantageous if both the flexural and compression waves pass the sensor just once without being backscattered or reflected from the boundaries. In this paper, various plate shapes are analysed to evaluate the shape which offers the best damping properties against an impact. Experimental analysis indicated that the reflection of the flexural waves can be halved using a plate with star-shaped 60° edges with a damping layer. The damping properties can be further doubled by using a star-shaped plate with power law edges in combination with a damping layer which is attached to the edges. The work reported here offers a possible solution to get significant damping properties. This is achieved by combining a damping layer with edge shaping against a strong single excitation event. The results demonstrate that it is a promising approach for an impact detection systems which could be equally applicable to acoustic damping applications

Cleavage Fracture of Brittle Semiconductors from the Nanometer to the Centimeter Scale

The objective of this paper is to present the fundamental phenomena occurring during the scribing and subsequent fracturing process usually performed when preparing surfaces of brittle semiconductors. In the first part, an overview of nano-scratching experiments of different semiconductor surfaces (InP, Si and GaAs) is given. It is shown how phase transformation can occur in Si under a diamond tip, how single dislocations can be induced in InP wafers and how higher scratching load of GaAs wafer leads to the apparition of a crack network below the surface. A nano-scratching device, inside a scanning electron microscope (SEM), has been used to observe how spalling (crack and detachment of chips) and/or ductile formation of chips may happen at the semiconductor surface. In the second part cleavage experiments are described. The breaking load of thin GaAs (100) wafers is directly related to the presence of initial sharp cracks induced by scratching. By performing finite element modelling (FEM) of samples under specific loading conditions, it is found that the depth of the median crack below the scratch determines quantitatively the onset of crack propagation. By carefully controlling the position and measuring the force during the cleavage, it is demonstrated that crack propagation through a wafer can be controlled. Besides, the influence of the loading configuration on crack propagation and on the cleaved surface quality is explained. © 2005 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

Prediction of creep crack growth in a range of steels

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Prediction of creep crack growth in a range of steels

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