Microhardness studies on 4-Dimethylamino-N-methyl 4-Stilbazolium Tosylate (DAST)

The Vickers and Knoop microhardness studies were carried out on the (001) face of 4-Dimethylamino-N-methyl 4-Stilbazolium Tosylate (DAST) crystals grown by the slope nucleation technique. The Vickers microhardness number (H_v) and the Knoop microhardness number (H_k) were found to dwindle with increasing load. The Meyer's index number (n) and hardness were calculated from H_v. The fracture toughness, brittle index and yield strength were calculated. The Young's modulus was calculated using the Knoop hardness value.     

Microhardness studies on nonlinear optical L-alanine single crystals

Vickers and Knoop microhardness tests were carried out on grown L-alanine single crystals by slow evaporation technique over a load range of 10–50 g on selected broad (2 0 3) plane. Vickers (H _v ) and Knoop (H _k ) microhardness for the above loads were found to be in the range of 60–71 kg/mm² and 35–47 kg/mm², respectively. Vickers microhardness number (H _v ) and Knoop microhardness number (H _k ) were found to increase with increasing load. Meyer’s index number (n) calculated from H _v shows that the material belongs to the soft material category. Using Wooster’s empirical relation, the elastic stiffness constant (c ₁₁) was calculated from Vickers hardness values. Young’s modulus was calculated using Knoop hardness values. Hardness anisotropy has been observed in accordance with the orientation of the crystal.     

The Influence of SnO2 Nano-Particles Addition on the Vickers Microhardness of (Bi, Pb)-2223 Superconducting Phase

The Vickers microhardness of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_10+?? superconducting phase with added SnO₂ nano-particles was investigated. The concentration of SnO₂ nano-particles x varied from 0.0 to 2.0 of the sample??s total mass. The experimental data of the Vickers microhardness were analyzed using Meyer??s law, the elastic/plastic deformation model, Hays?CKendall??s approach and the proportional specimen resistance model. The Vickers microhardness number H _v increased as x increased up to 0.4?wt%. The load dependence of H _v exhibited a normal indentation-size effect, H _v increased as the applied load increased. Moreover, this dependence was well fitted with the Hays?CKendall approach rather than the elastic/plastic deformation and proportional specimen resistance models. In addition, we calculated Young modulus, yield strength, fracture toughness and brittleness index as a function of both applied load and SnO₂ nano-particle concentration.     

Microhardness studies in gel-grown ADP and KDP single crystals

Microhardness studies were carried out on (100) faces of gel-grown ADP and KDP single crystals. Slip lines were observed on (100) face of ADP crystal at the corners of the impressions. Microcracks around the indentation were found on (100) face of KDP crystal from 10g load which spread out as the load increased. Vickers hardness numberH _v decreased with increase in load. ΔH _v at 50g load for solution-grown crystals and gel-grown crystals (present case) was determined. Work hardening indexn for both ADP and KDP crystals was less than 2 showing soft-material characteristics. Using Wooster’s empirical relation, values of C₁₁ from hardness were calculated and found to be close to the reported ones. The work was done under a research project sanctioned by the Council of Scientific and Industrial Research (CSIR), New Delhi.     

Significant Change in Mechanical Properties of YBa2Cu3O7−x Bulk Superconductors Diffused with Sn Nanoparticles

Mechanical behavior of YBa₂Cu₃O_7?x (Y123) superconductors exposed to Sn nanoparticles diffusion is determined by the way of Vickers microhardness (H _v ) conducted at different applied loads (0.245N≤F≤2.940 N). Load dependent microhardness, load independent microhardness, elastic modulus, and yield strength values are estimated from the microhardness curves. Unpredictably, the findings of the H _v values reveal that the undiffused sample and Sn diffused sample prepared at 500 ^°C exhibit reverse indentation size effect (RISE) behavior while the other samples obey indentation size effect (ISE) nature. Further, we extract the load independent (true) microhardness using the Meyer’s law, proportional specimen resistance (PSR), elastic/plastic deformation (EPD), Hays–Kendall (HK) approach and indentation-induced cracking (IIC) model, and compare the true hardness with the apparent hardness.     

Some physical properties and Vickers hardness measurements of Fe diffusion-doped Bi<Subscript>1.8</Subscript>Pb<Subscript>0.35</Subscript>Sr<Subscript>1.9</Subscript>Ca<Subscript>2.1</Subscript>Cu<Subscript>3</Subscript>O<Subscript>y</Subscript> superconductors

In this study we have investigated the influence of iron diffusion and diffusion-annealing time on the mechanical and the superconducting properties of bulk Bi_1.8Pb_0.35Sr_1.9Ca_2.1Cu₃O_y superconductors by performing X-ray diffraction (XRD), scanning electron microscopy (SEM), Vickers hardness, dc resistivity (ρ-T) and critical current density (J_c) measurements. The samples are prepared by the conventional solid-state reaction method. Doping of Bi-2223 was carried out by means of iron diffusion during sintering from an evaporated iron film on pellets. Then, the Fe layered superconducting samples were annealed at 830 °C for 10, 30 and 60 h. The mechanical properties of the compounds have been investigated by measuring the Vickers hardness (H_v). The mechanical properties of the samples were found to be load dependent. The load independent Vickers hardness (H₀), Young’s modulus (E), yield strength (Y), and fracture toughness (K_IC) values of the samples are calculated. These all measurements showed that the values of the Vickers hardness, critical current density, and critical transition temperature and lattice parameter c increased with increasing Fe doping and diffusion-annealing time.     

Determination of the hardness and elastic modulus from continuous vickers indentation testing

Continuous Vickers (H _v) indentation tests were performed on different materials (ion crystals, metals, ceramics, silica glass and plastic). Load-indentation depth curves were taken during the loading as well as during the unloading period by a computer controlled hydraulic mechanical testing machine (MTS 810). The indentation work measured both the loading and the unloading periods, and these were used for the evaluation of parameters characterizing the materials. It was found empirically that there were linear connections between the maximum load to the power 3/2 and the indentation work. These connections were used to relate the conventional hardness number, H _v, and Young's modulus, E, with the work performed during loading and unloading. This work can be determined with great accuracy from the measurements. The values of the Young's modulus and the Vickers hardness determined this way agree well with those obtained by conventional methods. On the basis of continuous indentation tests, materials can be easily classified into the isomechanical groups introduced by Ashby. For this classification the H _v/E ratio is generally used. As a substitute for H _v/E another parameter is recommended which can be determined easily from a single measurement.     

Microindentation behavior of CoGaInS4 layered crystals

CoGaInS₄ crystals were grown by iodide vapor transport, and their mechanical properties (load-dependent Vickers microhardness and anisotropic scratch hardness) were studied. The plastic deformation and brittle fracture of the crystals were examined. The physical processes accompanying microindentation were discussed.     

Correlation between hardness and elastic moduli of the covalent crystals

From a statistical manner, we collected and correlated experimental bulk (B), shear (G), Young’s modulus (E), and ductility (G/B) with Vickers hardness (H_v) for a number of covalent materials and fitted quantitative and simple H_v–G and H_v–E relationships. Using these experimental formulas and our first-principles calculations, we further predicted the microhardness of some novel potential hard/superhard covalent compounds (BC₂N, AlMgB₁₄, TiO₂, ReC, and PtN₂). It was found that none of them are superhard materials (H_v ? 40 GPa) except BC₂N. The present empirical formula builds up a bridge between Vickers hardness and first-principles calculations that is useful to evaluate and design promising hard/superhard materials.     

AFM studies of microindented GaN and InGaN

The microhardness characteristics of GaN and GaN/InGaN films epitaxially grown on (0001) sapphire have been investigated using Vickers and Knoop indenters. The variation of H_V and H_K follows a reverse type of indentation size effect (reverse ISE). The microhardness results have also been analyzed using Meyer's law, Hays-Kendall approach and Proportional specimen resistance (PSR) model. The effect of N⁺ implantation on the microhardness of GaN has also been studied. The implanted sample is more resistant to plastic penetration than the unimplanted one and it is found that implantation enhances the surface hardness. Detailed AFM studies around the indented regions of the GaN and GaN/InGaN give the nature and behavior of the deformation on the surface.     

Meßwertstreuung in Abhängigkeit von der Werkstoffhärte bei Kleinlasthärteprüfungen nach Vickers und Knoop

Dispersion of Vickers and Knoop diagonals as a function of workpiece-hardness at low load testing . A statistical analysis of low load hardness test results measured under industrial conditions by the comparative use of Vickers and Knoop indenters was carried out. Accordingly, recommendations can be given for the number of indentations necessary to ensure a constant shape of the distribution of sample means all over the investigated hardness area from approx. 150 up to 950 daN/mm₂.     

Microhardness,chemical etching,SEM, AFM and SHG studies of novel nonlinear optical crystal – l-threonine formate

The crystal l-threonine formate, an organic NLO crystal was synthesized from aqueous solution by slow evaporation technique. The grown crystal surface has been analyzed by scanning electron microscopy (SEM), chemical etching and atomic force microscopy (AFM). SEM analysis reveals pyramidal shaped minute crystallites on the growth surface. The etching study indicates the occurrence of etch pit patterns like striations and step like pattern. The mechanical properties of LTF crystals were evaluated by mechanical testing which reveals certain mechanical characteristics like elastic stiffness constant (C₁₁) and young's modulus (E). The Vickers and Knoop microhardness studies have been carried out on LTF crystals over a range of 10–50 g. Hardness anisotropy has been observed in accordance with the orientation of the crystal. AFM image shows major hillock on growth surface. The second harmonic generation (SHG) efficiency has been tested by the Kurtz powder technique using Nd:YAG laser and found to be about 1.21 times in comparison with standard potassium dihydrogen phosphate (KDP) crystals.     

Wichtige Gesichtspunkte für die Härtemessung nach Vickers und nach Knoop im Bereich der Kleinlast- und Mikrohärte

Important aspects for low load testing of Vickers and Knoop hardness . There are various factors, which can affect the hardness number obtained in low load testing. Both, the Vickers and the Knoop indenter, are widespread applicated for hardness testing at low loads. Subsequently, in respect of these above mentioned hardness testing methods, it is given a summary concerning the most important factors, which, if they are not eliminated, can bring about serious errors in the test results.     

Microhardness studies of SnI2 and SnI4 single crystals

The variation in the microhardness of tin-di-iodide (SnI₂) and tin-tetra-iodide (SnI₄) crystals has been determined using Vicker’s microhardness indentor. It is observed that the microhardness of the crystals depends on the applied load and is independent of the duration of loading. Vickers Hardness Numerals (vhn) for SnI₂ is found to be greater than that of SnI₄ crystals. Mayer’s equation and implications have been discussed.     

Microhardness studies on calcium hydrogen phosphate (brushite) crystals

Vicker's and Knoop microhardness studies were carried out on grown calcium hydrogen phosphate dihydrate (CaHPO₄·2H₂O) crystals over a load range of 10-50 g. The Vickers (H_V) and Knoop (H_K) microhardness numbers for the above loads were found to be in the range of 94-170 kg/mm² and 28-35 kg/mm² respectively. It was also found that these numbers increased with increase in load. The Mayer's index (n) was found to be greater than 1.6 showing soft-material characteristics. The fracture toughness values (K_c), determined from measurements of crack length, were estimated to be 6 ± 0.5 × 10³ kg m^−3/2 and 4.5 ± 0.5 × 10³ kg m^−3/2 at 25 g and 50 g respectively. The brittleness indices (B_i) were found as 2.3 ± 0.1 × 10⁴ m^−1/2 for 25 g and 3.7 ± 0.1 × 10⁴ m^−1/2 for 50 g. Using Wooster's empirical relation, the elastic stiffness coefficient (c₁₁) has been calculated from Vicker's hardness values as 4.8 ± 0.5 × 10¹⁵ Pa for 10 g, 9.7 ± 0.5 × 10¹⁵ Pa for 25 g and 13.3 ± 0.5 × 10¹⁵ Pa for 50 g. The Young's modulus was calculated as 1.5 ± 0.1 × 10¹⁰ N m⁻² from Knoop microhardness values.     

Die wechselseitige Umrechnung von Vickers-und Knoop-Härtewerten im Kleinlastbereich

Interconversion of Vickers and Knoop hardness numbers obtained in low load testing . In the industrial field the Vickers indenter has been largely applicated for hardness testing at low loads; in recent times the Knoop indenter came into use more and more. Consequently the question was raised, whether on the basis of some fundamental assumptions and experimental results equations could be deduced for interconversion of hardness numbers on Vickers and Knoop scales. Subsequently, a set of equations representing the connection between these above mentioned scales is given. The parameters of these equations were computed applying methods of statistical estimation.     

Vickers microhardness studies on cadmium mercury thiocyanate (CMTC) single crystals grown in silica gel

Vickers microhardness study was carried out on the (110) face of the gel-grown cadmium mercury thiocyanate (CMTC) single crystal, subjected to the loads 10, 25 and 50 g. The measurements were made at room temperature with the indentation time as 10 s. Vickers hardness number Hv was calculated and it is found to increase with the applied load. Mayer's index number ‘n’ and elastic stiffness constant were calculated. The anisotropy of the crystal is also studied. The results are discussed in detail.     

A comprehensive study on mechanical properties of Bi1.8Pb0.4Sr2MnxCa2.2Cu3.0Oy superconductors

This study manifests the crucial change in the mechanical performances of Bi_1.8Pb_0.4Sr₂Mn_xCa_2.2Cu_3.0O_y superconductor samples (x = 0, 0.03, 0.06, 0.15, 0.3 and 0.6) prepared by conventional solid-state reaction method by use of Vickers microhardness (H_v) measurements carried out at different applied loads, (0.245 N ≤ F ≤ 2.940 N). Load dependent microhardness, load independent microhardness, Young’s (elastic) modulus and yield strength values being account for the potential technological and industrial applications are evaluated from the hardness curves and compared with each other. It is found that the H_v, elastic modulus and yield strength obtained decrease (increase) with the enhancement of the applied load for the undoped (doped) samples. Surprisingly, the results of the H_v values illustrate that the samples doped with x = 0.03, 0.06, 0.15, 0.3 and 0.6 exhibit reverse indentation size effect (RISE) feature whereas the pure sample obeys indentation size effect (ISE) behavior. Furthermore, the experimental results are examined with the aid of the available methods such as Meyer’s law, proportional sample resistance model (PSR), elastic/plastic deformation (EPD), Hays–Kendall (HK) approach and indentation-induced cracking (IIC) model. The results inferred show that the hardness values calculated by PSR and EPD models are far from the values of the plateau region, meaning that these models are not adequate approaches to determine the real microhardness value of the Mn doped Bi-2223 materials. On the other hand, the HK approach is completely successful for the explanation of the ISE nature for the pure sample while the IIC model is obtained to be the best model to describe the hardness values of the doped materials exhibiting the RISE behavior. Additionally, the bulk porosity analysis for the samples reveals that the porosity increases monotonously with the increment in the Mn inclusions inserted in the Bi-2223 system, presenting the degradation of the grain connectivity.     

The Influence of Na Addition on the Mechanical Properties of Bi-2212 Superconductors

In this work, the effects of Na doping on the mechanical properties of the samples are investigated by Vickers microhardness (H _v) measurements at room temperature. The highest microhardness values were obtained for Bi₂Sr₂Ca₁Cu_1.75Na_0.25O_y sample including x = 0.25 Na content. On the other hand, the experimental results of H _v were compared with true microhardness values (H ₀) calculated by some theoretical approaches such as elastic/plastic deformation (EPD), proportional specimen resistance (PSR), and the Hays-Kendall models. All theoretic calculations also show that the sample with x = 0.25 Na content has the best mechanical properties. In addition, stress-strain curves of samples indicated that all samples protect their elastic properties at all applied loads. Finally, the surface roughness measurements of all the samples were done, indicating that they strongly depend on the content of Na substitution.