Vicker's Microhardness Studies of L‐arginine Hydrobromide Monohydrate Crystals (LAHBr)
TL;DR: In this article, the microhardness of Larginine hydrobromide monohydrate (LAHBr) has been investigated and the work hardening index n for the three planes is greater than 1.6 which indicates that LAHBr is a soft crystal.
Abstract: Vicker's microhardness study of (100), (010) and (001) faces of a non-linear optical crystal, L-arginine hydrobromide monohydrate (LAHBr)have been reported.(100) plane is found to be the weakest plane. It has been observed that the microhardness decreases with increasing load for the three crystal planes. The microhardness behaviour have been explained successfully with the help of the PSR model proposed by Li and Bradt. Work hardening index n for the three planes are found to be greater than 1.6 which indicates that LAHBr is a soft crystal.
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TL;DR: By exploring the interesting formation and phase‐transition phenomena of soft crystals through interdisciplinary collaboration, new materials having both the characteristics of ordered hard crystals and those of flexible soft matter are expected.
Abstract: A new material concept of soft crystals is proposed. Soft crystals respond to gentle stimuli such as vapor exposure and rubbing but maintain their structural order and exhibit remarkable visual changes in their shape, color, and luminescence. Various interesting examples of soft crystals are introduced in the article. By exploring the interesting formation and phase-transition phenomena of soft crystals through interdisciplinary collaboration, new materials having both the characteristics of ordered hard crystals and those of flexible soft matter are expected.
186 citations
TL;DR: In this article, the authors reviewed the relationship between applied indentation test load P and indentation diagonal length d to analyze the experimentally observed normal and reverse indentation size effect (ISE) in brittle compounds.
Abstract: Indentation size effect, indentation cracks and microhardness measurement of some brittle crystals are reviewed against the background of the existing concepts of indentation deformation of crystalline solids. Several approaches reported in the literature devoted to relationships between applied indentation test load P and indentation diagonal length d are applied to analyze the experimentally observed normal and reverse indentation size effect (ISE) in brittle compounds. Using typical examples of normal and reverse ISE it is shown that the indentation induced cracking model does not give load-independent hardness and the final expression describing the experimental data for various compounds is essentially another form of the Meyer law. Analysis of experiment data on crack lengths and indentation diagonals for different indentation loads suggests that the origin of ISE is associated with the processes of formation of indentation cracks following the general concepts of fracture mechanics. The load-independent hardness H0 may be determined reliably from plots of P /d against d of the proportional resistance model or of HV against 1/d as predicted by strain gradient plasticity theories. It was found that the load-independent hardness of depends on crystal orientation and state of the indented surface. Finally, some comments on determination of fracture toughness and brittle index of crystals are made. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)
119 citations
TL;DR: In this article, single crystals of l -histidine hydrofluoride dihydrate (LHHF), a semiorganic nonlinear optical (NLO) material have been successfully grown by slow evaporation technique.
64 citations
TL;DR: In this article, the microhardness of the wire-bonded balls was investigated with different combinations of electronic-flame-off (EFO) current and firing time settings with forming gas as the inert cover gas.
61 citations
TL;DR: In this paper, single-shot laser-induced surface damage thresholds in the range 3-10GW/cm2 were measured using a 18-ns Q-switched Nd:YAG laser.
Abstract: N-alkyl-2,6-dimethyl-4(1H)-pyridinones, salts of 4-dimethylaminopyridine and 2-amino-5-nitropyridine are considered to be potential candidates for nonlinear optical (NLO) applications, in particular for the generation of blue-green laser radiation. Single crystals were grown following the slow evaporation technique at constant temperature. Single-shot laser-induced surface damage thresholds in the range 3–10 GW/cm2 were measured using a 18 ns Q-switched Nd:YAG laser. The surface morphologies of the damaged crystals were examined under an optical microscope and the nature of damage identified. The Vicker’s microhardness was determined at a load of 98.07 mN. The thermal transport properties, thermal diffusivity (α), thermal effusivity (e), thermal conductivity (K) and heat capacity (Cp), of the grown crystals were measured by an improved photopyroelectric technique at room temperature. All the results are presented and discussed.
54 citations
References
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TL;DR: In this article, the synthesis of 20 other salts of Larginine was attempted and millimeter size crystals of 10 of these were obtained, which were analyzed for crystal structure and chemical composition and the linear and nonlinear optical properties were measured.
332 citations
TL;DR: In this article, a modified version of Kick's Law is used to obtain Knoop hardness numbers independent of the applied load, which is applied to nine specimens of varient hardness and proven valid by graphical methods.
329 citations
TL;DR: In this article, the results of microhardness measurements on flux-grown crystals of (i) single (pure) rare earth aluminates RAlO3 (R = Eu, Gd, Dy, Er) and rare earth orthochromites RCrO3(R = Y, gd, Yb, nodymium, erbium, ytterbium and holmium) are presented.
Abstract: The results of microhardness measurements on flux-grown crystals of (i) single (pure) rare earth aluminates RAlO3 (R = Eu, Gd, Dy, Er) and rare earth orthochromites RCrO3 (R = Y, Gd, Yb), (ii) rare earth aluminates doped with neodymium, erbium, ytterbium and holmium, and (iii) mixed rare earth aluminate crystals of the type (La1−x) Pr(x)AlO3 (x=0, 0.25, 0.75 and 1.00) are presented. The variations in the microhardness value with load are non-linear in all cases. Kick's law fails to explain the observed variations. Instead, they are best explained by the application of the idea of materials resistance pressure in the modified law proposed by Hays and Kendall. The results indicate that the doping does not increase the hardness value of crystals in all cases. The hardness instead depends on the composition of the parent material as well as the dopant entering into the crystal lattice. Mixed rare earth aluminate crystals are shown to be harder than those of single rare earth aluminates.
65 citations
15 Aug 1991-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this article, a normalized Meyer's law was proposed to explain the Knoop microhardness anisotropy by applying the effective resolved shear stress concept advanced by Brookes and coworkers, yielding P 2P c n d d d 0 ∗ η where Pc is a critical test load indicative of the region where hardness is independent of the indentation test load and d 0 is a characteristic indentation dimension.
Abstract: Knoop microhardness profiles were determined for lanthanum hexaboride (LaB6) on the (100), (110) and (111) planes for indentation test loads from 50 to 300 gf. These profiles were analyzed with respect to possible slip systems to explain the Knoop microhardness anisotropy by applying the effective resolved shear stress concept advanced by Brookes and coworkers. As the results of this study, the predicted slip systems for LaB6 are {100}〈011〉,{110}〈111〉 and {111}〈110〉. The load dependence of the microhardness was initially addressed in terms of the classical Meyer's law P = Adn for which the two parameters A and n were observed to be related. The peculiar dimensionality of the classical Meyer's law coefficient A was addressed by applying the concepts of a load-independent “true” microhardness, critical indentation load and characteristic indentation size. Subsequently the development of a normalized Meyer's law was directly demonstrated, yielding P= 2P c n d d 0 ∗ η where Pc is a critical test load indicative of the region where hardness is independent of the indentation test load and d 0 ∗ is a characteristic indentation dimension, below which the indentation size effect is significant. It is suggested that this normalized Meyer's law may have universal applicability to different hardness tests and materials.
62 citations
TL;DR: In this article, the Knoop microhardness of single crystal sulphur was measured as a function of crystallographic orientation and applied test load on the (110) and (111) planes.
Abstract: The Knoop microhardness of single crystal sulphur was measured as a function of crystallographic orientation and applied test load on the (110) and (111) planes. Microhardnesses were determined to be in the range of 25–35 kg mm−2. Anisotropy of the microhardness and a normal indentation size effect (ISE) were observed. The ISE was addressed by the application of the traditional power law and the proportional specimen resistance model (PSR) of Li and Bradt. The load-independent hardness was determined, from which it was concluded that the (111) plane is harder than the (110) plane and also that the (111) plane is more anisotropic in microhardness.
59 citations