Conventional Vickers Hardness Research Articles

Comparison between conventional Vickers hardness and indentation hardness obtained with different instruments

Abstract An extensive comparison between the conventional Vickers hardness at 500 mN and indentation hardness measured with Vickers indenters at 500 mN is presented for up to 20 different materials and for three different instruments. Additionally, the indentation modulus is compared to Young’s modulus, which was measured with alternative methods or taken from the literature. It is shown that the agreement between the results from depth-sensing indentation and the reference values can be improved by additional corrections, for the calculation of the indentation area. With corrections the mean hardness difference to the Vickers hardness reference as average of all investigated materials can be reduced to about 10 % although disturbing pile-up or sink-in effects can still not be considered. For the modulus, the mean difference was only about 6 %.

Comparison of surface and cross-sectional micro-nano mechanical properties of flame sprayed NiCrBSi coating

Nanoindentation was performed on both surface and cross-section of flame sprayed (FS) NiCrBSi coatings to compare the nano-scale mechanical properties of thermal spray coating in different directions. Conventional Vickers hardness measurement was carried out to measure the ‘composite’ properties and compare the possible discrepancies between the micro and the nano methods. Results indicate that at lower penetration depths indentation hardness (HIT), indentation modulus (EIT), and the ratio of elastic to total work of indentation (ηIT) depend on the intralamellar material properties and the values are higher, and H and E profiles come closest to coinciding in shape. At larger indentation depths the characteristics values and they reflect the ‘composite’ properties of coating units including splats, pores and cracks. HIT and EIT values of coating cross-section are superior to the surface. In all cases, the ηIT value of coating surface is higher than that of coating cross-section, probably due to more formations of intergranular and intersplat cracks during coating cross-sectional indentation which leads to more dissipation of the indentation energy.

A finger-like hardness tester based on the contact electromechanical impedance of a piezoelectric bimorph cantilever.

We proposed a finger-like hardness tester based on the electromechanical impedance of a piezoelectric bimorph cantilever. A Vickers indenter was fabricated to the free end of the bimorph to contact the sample. The contact force was monitored by a strain gauge and the contact area was obtained by tracking the bimorph's resonance frequency. The bimorph-sample contact system was modeled by the electromechanical equivalent circuit method. Verification experiments on standard hardness samples were conducted and the measured hardness values agreed well with those given by a conventional Vickers hardness tester. Further hardness measurement on a gear wheel showed that the proposed hardness tester is very adaptive and can be used for inner surface testing or in situ testing, where other hardness testers may not be applicable. The proposed hardness tester can be regarded as an improved ultrasonic hardness tester.

Current Activities for Standardization of Test Method for Interfacial Fracture Toughness of Thermal Spray Coatings in Japan

Collaborative research has been conducted by the Japan Thermal Spray Society (JTSS) to establish a standard test method for evaluating the interfacial fracture toughness of thermal sprayed coatings, including thermal barrier coatings. The test method is based upon the indentation test method utilizing a conventional Vickers hardness test machine. In this committee, round robin tests were performed to check differences in the evaluated results among collaborators. This paper reports on the progress of such activity in Japan.

Hardness determination of bio-ceramics using Laser-Induced Breakdown Spectroscopy

Laser-Induced Breakdown Spectroscopy (LIBS) was applied to the analysis of bio-ceramic samples. The relationship between sample hardness and LIBS plasma properties was investigated, with comparison to conventional Vickers hardness measurements. The plasma excitation temperature T e was determined using the line-to-continuum ratio for the Si (I) 288.16 nm emission line; we have demonstrated a linear relationship between sample surface hardness and plasma temperature. Results indicate that hardness determination based on measurements of T e offers greater reproducibility than Vickers hardness measurements, under the conditions considered here. The validity of spectroscopic diagnostics based on LTE was confirmed.

Conventional Vickers and true instrumented indentation hardness determined by instrumented indentation tests

We evaluate Vickers hardness and true instrumented indentation test (IIT) hardness of 24 metals over a wide range of mechanical properties using just IIT parameters by taking into account the real contact morphology beneath the Vickers indenter. Correlating the conventional Vickers hardness, indentation contact morphology, and IIT parameters for the 24 metals reveals relationships between contact depths and apparent material properties. We report the conventional Vickers and true IIT hardnesses measured only from IIT contact depths; these agree well with directly measured hardnesses within ±6% for Vickers hardness and ±10% for true IIT hardness.

Improvement in depth-sensing indentation to calculate the universal hardness on the entire loading curve

Hardness of materials depend on the applied load and on the shape of the indenter. Various models regarding the indentation size effect have been developed to evaluate this load-dependence which necessitates numerous indentation tests to be valid. The aim of this paper is to reduce substantially the number of tests by calculating the universal hardness on the entire loading curve of a load-depth registration. The use of universal hardness instead of Oliver and Pharr method is required by the comparison with the conventional Vickers hardness. The protocol can be well supported if some improvements in depth-sensing indentation are made like the consideration of the frame compliance of the instrument, the creep displacement calculated as a function of the load and the rounded tip into the indentation depth measurement and consequently into the universal hardness calculation. Additionally, we show that the indentation size effect may be well-represented by the strain gradient plasticity theory whereas significant deviation is observed when only partial depth-corrections are made.

3604 ナノ-メゾ-マクロ強度解析による疲労特性の解析(S13-1 組織因子,S13 実用構造材料の疲労問題と健全性評価)

Fully reversed total-axial-strain-controlled low cycle fatigue (LCF) tests have been conducted in air at room temperature on fine- and coarse-grain low-carbon steels, SUS304 steel and SUS316L steel. Three types of hardness measurements, namely nano-indentation, micro-indentation and conventional Vickers hardness tests, with the indentation size ranging from several tens of nm to several tens of μm, were performed for both virgin and fatigued specimens to evaluate the mechanical behaviour at different scales of the cyclically deformed steel during LCF. OM and TEM observation showed that the microstructural parameters are the dislocation cell size, d_<cell>, slip spacing, w_<slip>, and austenitic grain size, d_γ. Referring 10 d_<cell> and 10w_<slip>. Vickers hardness, HV, corresponding to macro strength was expressed as HV=Hv^*_<base>+Hv^*_<sol>+Hv^*_<cell>+Hv^*_<slip>. Hv^*_<base> is the base hardness, Hv^*_<sol> is the solid solution strengthening hardness, and Hv^*_<cell> and Hv^*_<slip> are the fine grain strengthening hardness due to the dislocation cell and slip band.

Comparison between conventional Vickers hardness and indentation hardness obtained with different instruments

Abstract An extensive comparison between the conventional Vickers hardness at 500 mN and indentation hardness measured with Vickers indenters at 500 mN is presented for up to 20 different eaterials and for three different instruments. Additionally, the indentation modulus is compared to Young's modulus, which was measured with alternative methods or taken from the literature. It is shown that the agreement betweef the results from depth-sensing indentation and the reference values can be improved by additional corrections, for the calculation of the indentation area. With corrections the mean hardness difference to the Vickers hardness reference as average of all investigated materaals can be reduced to about 10% although disturbing pile-up or sink-in effects can still not be considered. For the modulus, the mean difference was only about 6%.

Indentation Testing of MoSi&lt;sub&gt;2&lt;/sub&gt;

Indentation methods have been used for the study of the hardness and deformation characteristics MoSi2. Micro-nanoindentation tests at loads from 10 mN to 2000 mN were carried out using the depth-sensing method. Measurements of the microhardness using conventional Vickers method was carried out at loads of 500 mN, 1000 mN and 2000 mN. The Universal (Martens), Plastic and conventional Vickers hardness values were calculated at different indentation loads. Evident indentation load - size effect was found in both materials. According to the results, the pre-strain reduces the micro-nano hardness values, probably due to the activation of slip systems during the high-temperature deformation.

Indentation Testing of an Al2O3/Al2O3 + ZrO2 Layered Composite

Micro- and macro-hardness of the individual layers of an Al2O3 / Al2O3 + ZrO2 layered composite have been investigated. The indentation load size effect has been studied in a range of indentation load of 25 mN – 100 N using depth sensing indentation technique and conventional Vickers hardness testers. Fracture toughness values of the layers have been measured using indentation fracture method. The effect of residual stresses on the KIC value has been analyzed.

Multi-scale deformation behavior investigation of 18Cr–8Ni austenitic steel subjected to low-cycle fatigue loading

Fully reversed total-axial-strain-controlled low-cycle fatigue (LCF) tests have been conducted in air at room temperature on polycrystalline 18Cr–8Ni austenitic stainless steel samples. The cyclic deformation behavior was determined by analysis of the hysteresis loop associated with cyclic straining. Three types of hardness measurements, namely nano-indentation, micro-indentation and conventional Vickers hardness tests, with the indent size ranging from several tens of nm to several tens of μm, were performed on the cyclically deformed specimens to investigate the characteristics of the deformation resistance at various scales. A linear increasing dependence of the local deformation resistance on the applied strain amplitude was observed at both macro- and meso-scales. This local resistance corresponds with the dependence of the bulk deformation resistance on the imposed strain amplitude; however, no significant change in the deformation resistance at nano-scale was found among various strain amplitudes. Both the slip band and the dislocation structure in specimens cyclically deformed at various strain amplitudes were correlated with the multi-scale deformation resistance.

Measurement of the hardness of hard coatings using a force indentation function

Today the so-called dynamic micro hardness with analysis of the force indentation function is replacing in many cases the conventional Vickers hardness measurement for evaluating the hardness of thin films such as coatings for wear protection with thicknesses in the range of several micrometers. This test procedure requires equipment with a numerically controlled loading unit and a high resolution measurement of the indentation depth. This contribution shows, using various different examples, that the load indentation measurement can solve problems such as the influence of the operator, but the test conditions should be well selected to give comparable and meaningful results. Therefore, this paper analyzes the most important reasons for deviations in practice, and makes suggestions for a standardized test procedure and test documentation.

Microhardness measurement of individual AlMnCr powder particles produced by rapid solidification

Hardness measurement was carried out on powder particles of AlMnCr alloys (Al-5Mn-2.5Cr, Al-5Mn-4Cr-4Cr and Al-5Mn-6Cr), which were produced by ultrasonic helium gas atomization. It has been demonstrated that it is feasible to use conventional Vickers hardness measurement to characterize individual AlMnCr powder particles as small as 10 μm in size by an applied load of 5 g. It has been shown that the hardness is a function of alloy composition, size of powder particles and heat treatment. The hardness increased with the contents of alloying elements, i.e. manganese and chromium, and decreased when the size of powder increased. Decomposition of the supersaturation in the powders was accompanied by a drop in hardness after ageing of the rapidly solidified powders of the Al-5Mn-2.5Cr at 210 °C, 300 °C and 420 °. The results of hardness measurements are consistent with those from the investigations by X-ray diffraction, EDX and TEM.

Load dependence of microhardness of hard coatings

Vickers and Knoop microhardness measurements on hard coatings on WC-Co substrates were studied as a function of indentation load. It is shown that the increase in conventional Vickers hardness with decreasing load, i.e. the indentation size effect, can be derived by considering the elastic recovery in indent length on unloading. It further follows that the large increase in microhardness at light loads (up to 100 gf) depends inversely on the elastic modulus of the hard coating. Microhardness numbers based on Vickers or Knoop diagonal measurements are shown to have varying sensitivity to the elastic recovery effect. Depending on coating thickness, the microhardness- load profiles can indicate the existence of gradient residual stresses in the coatings as well as effects due to the coating-substrate interface and the substrate hardness.