Berkovich Hardness Research Articles

Densification, phase composition, microstructure and properties of spark plasma sintered La0.6Ce0.3Pr0.1B6 bulks

This paper studied the densification, phase composition, microstructure and properties of polycrystalline La0.6Ce0.3Pr0.1B6 bulks prepared by SPS. The dense specimen (98.9 % in relative density) with the average grain size of 15.46 μm has been determined to be a CsCl-type single-phase substitutional solid solution without any impurities or other secondary phases. The homogenous elemental distributions of La, Ce and Pr have been confirmed by both microscale and nanoscale. The room temperature (RT) Vickers hardness (Hv), indentation fracture toughness (KIC) and flexure strength of the dense specimen have been measured to be 23.0 GPa, 2.04 MPa m1/2 and 305.1 MPa, respectively. The Berkovich hardness (HB) and elastic modulus (E) of the dense specimen have been measured to be 30.0 GPa and 376.0 GPa, respectively, by nanoindentation tests at a maximum load of 40 mN. In comparison with the polycrystalline LaB6 bulk, the lower work function Φ of 2.64 eV evaluated by UPS and the larger thermionic emission current densities measured at the same operating condition suggest that the polycrystalline La0.6Ce0.3Pr0.1B6 bulk is a superior-performance thermionic cathode material.

Densification, microstructure, mechanical, and thermionic properties of spark plasma sintered LaB6–HfB2 composite

AbstractLaB6–HfB2 composites with the different HfB2 contents (10 wt.%, 30 wt.%, 50 wt.%, 70 wt.%, and 90 wt.%) were densified by spark plasma sintering (SPS). Results showed that the densification mechanism of the composite transformed from the grain boundary diffusion into the dislocation climbing mechanism as the holding time was extended from 0 to 15 min under temperature range of 1750–1900°C. The HfB2 phase could effectively limit the grain growth of LaB6 phase, and the dynamic growth of the grain was governed by grain boundary diffusion. Both the Berkovich hardness and Vickers hardness obeyed the normal indentation size effect. LaB6–70 wt.% HfB2 composite had the highest fracture toughness of 3.98 ± .43 MPa m.5, whereas the highest current density of 18.34 A/cm2 belonged to LaB6–30 wt.% HfB2 composite. All the results demonstrated that LaB6–HfB2 composite was a promising material with the excellent structural and functional performance.

Directional solidification, nanoindentation and thermionic properties of LaB6(100)-ZrB2 eutectic composite

LaB6 (100)-ZrB2 eutectic composite was directionally solidified by optical floating melting zone at solidification rate V= 100 mm/h. It was shown that the stable eutectic growth can be achieved by periodic diverging and convergent growth, indicating that eutectic spacing was not unique value, but existed a limited range under a given rate. The atoms of the LaB6 (100)/ZrB2 interface were directly bonded. The mechanical property of the individual eutectic phase was evaluated by the nanoindentation. Both average Berkovich hardness and elastic modulus of LaB6/ZrB2 phases was higher than that of LaB6 phase. Thermionic emission of DS LaB6(100)-ZrB2 eutectic obeyed the Longo theory, indicating only the metal ceramic of LaB6 matrix in the composite emitted the electron. The practical work function distribution of DS LaB6(100)-ZrB2 eutectic composite ranged from 2.51 to 3.18 eV, and the lowest work function was located around the LaB6/ZrB2 interface, where had the highest current density

One-step preparation, microstructure and properties of WRe/TZM gradient material for X-ray tube of CT scanner

WRe/TZM gradient material was successfully fabricated simultaneously by spark plasma sintering technique with the gradient die to achieve the one-step bonding. The gradient sintering behavior and the effect of the sintering parameters on microstructure and mechanical properties of WRe/TZM joint were investigated. The results showed that the powders of WRe and TZM alloys could be densified and bonded simultaneously using gradient die to construct different sintering temperatures, and the relative densities of gradient material with WRe and TZM alloys were over 98%. The optimal joint with no pores and cracks was obtained at T = 1600 °C, t = 8 min and P = 30 MPa, under which the joint has the highest shear strength of 279.92 MPa. The Berkovich hardness of interface was mainly affected by the grain size and the solid solution of W and Mo. The resistance to creep at interface was between WRe alloy and TZM alloy. The joint exhibited excellent thermal diffusivity of 44.86 mm2/s. The WRe/TZM gradient material with excellent properties indicates this process is a promising technique route for fabricate the anode target for X-ray tube of CT scanner.

Corrosion Behavior and Mechanical Properties of a Nanocomposite Superhydrophobic Coating

In this work, a mechanically durable anticorrosion superhydrophobic coating is developed using a nanocomposite coating solution composed of silica nanoparticles and epoxy resin. The nanocomposite coating developed was tested for its superhydrophobic behavior using goniometry; surface morphology using scanning electron microscopy and atomic force microscopy; elemental composition using energy dispersive X-ray spectroscopy; corrosion resistance using atomic force microscopy; and potentiodynamic polarization measurements. The nanocomposite coating possesses hierarchical micro/nanostructures, according to the scanning electron microscopy images, and the presence of such structures was further confirmed by the atomic force microscopy images. The developed nanocomposite coating was found to be highly superhydrophobic as well as corrosion resistant, according to the results from static contact angle measurement and potentiodynamic polarization measurement, respectively. The abrasion resistance and mechanical durability of the nanocomposite coating were studied by abrasion tests, and the mechanical properties such as reduced modulus and Berkovich hardness were evaluated with the aid of nanoindentation tests.

Effect of dip-coating process on mechanical behavior of 3Y-TZP using different aging-free coatings

3Y-TZP discs were coated using 5Y-PSZ and 12Ce-TZP suspensions. Samples were evaluated in terms of roughness (Ra, Rq, Rz and Rsk), B3B flexural resistance, hardness, Young's modulus by instrumented indentation and surface damage resistance and Vickers hardness by impress Vickers measurements. Coatings with thickness of ~7 μm were obtained. 3Y-TZP uncoated discs showed similar hardness and Young's modulus when compared to those coated with 5Y-PSZ. Discs coated with 12Ce-TZP had opposite behavior. Vickers and Berkovich hardness showed the same trend, with almost no difference observed between monolithic and the 5Y-PSZ coated samples, and with the 12Ce-TZP coated samples exhibiting lower hardness values. Coated samples presented lower flexural strength than uncoated ones. Correlation between roughness and B3B flexural strength was also performed, showing that surface quality achieved by the coating process is the one that rules the final resistance of the component, instead of the coating material.

Hardening the surface of metals with WC1-x coatings deposited by high-speed plasma spraying

The deposition of protective hardening coatings allows increasing the lifetime of important technical materials and pure metals. This work shows the possibility of depositing protective coatings based on cubic tungsten carbide (WC1-x) on metal substrates using a high-speed (~1 km/s) plasma jet generated by a coaxial magneto-plasma accelerator. In a plasma spraying process, the necessary conditions (high sputtering and crystallization rates) are created for synthesizing the high-temperature WC1-x phase and stabilizing it in the coating structure. The formation of WC1-x phase was confirmed by X-ray diffraction and energy dispersive X-ray spectroscopy. The substrate parameters such as linear dimensions and heat dissipation rate were found to directly affect the phase composition (WC1-x yield) and the structure of the deposited coating. The coatings with a higher WC1-x content are characterized by an increased hardness. The firstly made direct measurements of a Berkovich hardness (H = 33.0 ± 0.9 GPa) and Young's modulus (E = 401 ± 14 GPa) for bulk WC1-x grains, exceeding several micrometers in size, confirmed the suggestion about higher mechanical properties of the metastable WC1-x phase in comparison with hexagonal tungsten carbides WC and W2C.

A comparative study of the influence of the deposition technique (electrodeposition versus sputtering) on the properties of nanostructured Fe70Pd30 films

ABSTRACT Sputtering and electrodeposition are among the most widespread techniques for metallic thin film deposition. Since these techniques operate under different principles, the resulting films typically show different microstructures even when the chemical composition is kept fixed. In this work, films of Fe70Pd30 were produced in a thickness range between 30 and 600 nm, using both electrodeposition and sputtering. The electrodeposited films were deposited under potentiostatic regime from an ammonia sulfosalicylic acid-based aqueous solution. Meanwhile, the sputtered films were deposited from a composite target in radio frequency regime. Both approaches were proven to yield high quality and homogenous films. However, their crystallographic structure was different. Although all films were polycrystalline and Fe and Pd formed a solid solution with a body-centered cubic structure, a palladium hydride phase was additionally detected in the electrodeposited films. The occurrence of this phase induced internal stress in the films, thereby influencing their magnetic properties. In particular, the thickest electrodeposited Fe70Pd30 films showed out-of-plane magnetic anisotropy, whereas the magnetization easy axis lied in the film plane for all the sputtered films. The domain pattern of the electrodeposited films was investigated by magnetic force microscopy. Finally, nanoindentation studies highlighted the high quality of both the sputtered and electrodeposited films, the former exhibiting higher reduced Young’s modulus and Berkovich hardness values.

Investigation of Ti0.54Al0.46/Ti0.54Al0.46N multilayer films deposited by reactive gas pulsing process by nano-indentation and electron energy-loss spectroscopy

Physical vapour deposition technology is well suited to the deposition of advanced TiAlN-based coatings. Among these thin films, multilayer systems consisting of stacked layers of metallic Ti1−xAlx and nitride Ti1−xAlxN with x around 0.5 are expected to have improved mechanical properties with respect to single nitride layers of the same composition. A set of Ti0.54Al0.46/Ti0.54Al0.46N multilayer films with five different periods Λ (from 4 to 50nm) were deposited using the reactive gas pulsing process (RGPP). This RGPP approach allows the deposition of TiAl-based alloy/nitride multilayer films by radio frequency reactive magnetron sputtering with a controlled pulsing flow rate of the nitrogen reactive gas. The coherent growth of the multilayer coatings, depending on the period, is checked by X-ray diffraction and the mechanical properties are determined by Berkovich nano-indentation and friction experiments. A model to describe the dependence of the indentation modulus M and the hardness HB on the penetration depth h, the period Λ, and the film thickness ef is proposed. The indentation modulus of the multilayer films (M at h=0 and for ef~1900nm) is found to be in the range of 340GPa<M<525GPa≈M(Ti0.54Al0.46N). For a fixed penetration depth, M follows a Hall and Petch evolution as a function of the period (4≤Λ≤50nm). The Berkovich hardness, 25GPa<HB<50GPa, also presents the same kind of evolution, and for Λ<16nm (at h=0), HB>HB (Ti0.54Al0.46N)=33GPa. Hence, a superlattice effect is clearly evidenced. Moreover, for the larger periods, the wear behaviour of these multilayered coatings seems to be dominated by the plastic deformation of the metallic layer. The multilayer coating of period Λ=10nm, which exhibits a diffraction pattern typical of superlattices and favourable mechanical properties, is more precisely investigated. Transmission electron microscopy confirms the main growth of the film along the [111] direction, and the evolution of the bonding of nitrogen in the direction normal to the rough interfaces between Ti0.54Al0.46 and Ti0.54Al0.46N layers is specified by electron energy-loss near-edge spectroscopy. Nitride nano-grains are included in the metallic layer, which attests to the mixing of nitrogen into the layers. The structure of these nano-grains presents a progressive evolution into the layer and gradually acquires a TiN-like structure near the interface. For this Λ=10nm period, the indentation modulus and hardness for different penetration depths are weakly sensitive to the multilayer film thickness.

Development of Functionally Graded Tungsten/EUROFER Coating System for First Wall Application

Reduced activation Ferritic/Martensitic (RAFM) steels, e.g. EUROFER are to be used as structural material for the First Wall (FW) of future fusion power plants. The interaction between plasma and FW, especially physical sputtering will limit the FW lifetime under normal operation. Therefore tungsten coating is selected to protect the FW due to its very low sputtering yield and low activation. However, the mismatch in thermo-physical properties between tungsten and EUROFER can lead to large residual thermal stresses and even failure. To overcome the issue of erosion a protective tungsten coating with a functionally graded (FG) tungsten/EUROFER layer (FG tungsten/EUROFER coating system) on EUROFER substrate will be developed and optimized.Non-linear finite element simulations are performed to predict optimal parameters of the coating system. Thereby the potential of the FG-layer in reducing inelastic strains and improving lifetime is demonstrated, and the investigated thickness of FG-layer is suggested. Based on the simulation results samples are fabricated by vacuum plasma spraying (VPS) with three different thicknesses of FG-layer. The microstructural observations revealed that the coating system has fine gradation and variable thickness as designed, low porosity, as well as a sound interface. Berkovich and Vickers hardness identify basic properties of those layers.

Investigation of microstructure and mechanical properties of W–Y and W–Y2O3 materials fabricated by powder metallurgy method

W–2Y, W–1Y2O3 and W–2Y2O3 materials have been fabricated using two different powder metallurgy methods. While W–2Y and W–1Y2O3 have been fabricated using mechanical alloying and hot isostatic pressing (HIPping), W–2Y2O3 has been fabricated by sintering and hot forging method. Transmission electron microscopy observation reveals that W–2Y and W–1Y2O3 materials have nano-structured grains whereas W–2Y2O3 material has μm size grains. In both cases, the particles are distributed in homogeneously inside the grains. Berkovich hardness and 3 point bend tests confirm that in-spite of nano-structured grains, W–2Y, and W–1Y2O3 materials are highly stiff and show no ductility till 1000°C temperature range. In the case of W–2Y2O3, the Berkovich hardness value is found to be 4.9GPa, that is similar to the Berkovich hardness value of pure W and 3-point bend test confirms that W–2Y2O3 is ductile at 400°C and above. Relation between the fabrication techniques, the microstructures and mechanical properties in W–2Y, W–1Y2O3 and W–2Y2O3 materials is reported.

Microstructural and elasto-plastic material parameters identification by inverse finite elements method of Ti(1 − x)AlxN (0 < x < 1) sputtered thin films from Berkovich nano-indentation experiments

The mechanical properties of Ti(1−x)AlxN (0<x<1) films of different thicknesses deposited by r.f. reactive magnetron sputtering on Si <100> and high speed steel substrates have been investigated. The as-deposited coatings have been characterized by X-ray diffraction, atomic force microscopy, four-probe electric resistivity method, mechanical deflection of cantilever beams and Berkovich nano-indentation tests associated with inverse finite elements analysis. The coatings with x<0.58–0.59 present a cubic structure whereas for x>0.7 a hexagonal structure is observed. Between these two compositions cubic and hexagonal structures coexist. The roughness depends on the film thickness and on the Al content and a minimum associated to a very fine microstructure is clearly observed in the two-phase coatings. The electric resistivity sharply increases as soon as the hcp structure appears (x~0.6). The mean residual stresses are compressive, except for the AlN coating, and present a minimum at the neighborhood of x~0.64 where a mixed structure is observed.The indentation modulus M<hkl> and the Berkovich hardness HB<hkl> greatly depend on the Al content and a progressive decreasing has been observed for 0.58<x<0.7. For the M<hkl> evolution, a simple model taking into account the stiffness coefficients of TiN and AlN structures, the mean residual stress level and the variations of the lattice parameters in the two structure domains is proposed.Knowing the elastic properties of these films, inverse finite elements analysis of the indentation curves considering a simple isotropic linear elasto-plastic behavior allows, as a function of the composition, the yield stress σY and the linear hardening coefficient Hp⁎ to be estimated. σY and Hp⁎ are in the ranges 4.2 to 6.8GPa and 60 to 400GPa, respectively. The maximum value of Hp⁎/σY which characterizes the ability of these coatings to exhibit plastic strain hardening is maximum for x=0.5 and 0.6. The quality of the estimation was discussed through a practical identifiability study and quantified using an identifiability index. Tip radius and elasticity of the Berkovich indenter are two very relevant parameters to improve identifiability and correctly extract the plastic parameters of the behavior law. Scratch crack propagation resistance shows an evolution similar to those of Hp⁎/σY.

Investigation of microstructure and microhardness of pure W and W-2Y2O3 materials before and after ion-irradiation

Pure W and W-2Y2O3 materials were fabricated using powder metallurgy method. The microstructures of the materials were investigated by electron back-scattered diffraction and transmission electron microscopy techniques. Both materials contain 1–2μm size W grains. In the case of W-2Y2O3, the material contains yttria particles having sizes between 300 and 900nm. The W matrix in W-2Y2O3 shows stronger texture than that of pure W. Berkovich hardness values are 4.5GPa in pure W and 4.9GPa in W-2Y2O3 for a 10N load. Ion irradiation experiments were performed on both materials at the JANNuS facility (Saclay, France) using Fe and He ions with energies of 24MeV and 2MeV, respectively. Radiation loops are present on the W grains whereas on yttria particles, radiation-induced damages appear as voids. Berkovich hardness values of irradiated materials are slightly higher than the non-irradiated materials. Results of the microstructure and microhardness of irradiated as well as non-irradiated materials are presented in detail.

Deformation and fracture of LLM-105 molecular crystals studied by nanoindentation

Mechanical deformation of crystalline high explosives plays an important role in both the fabrication of polymer-bonded explosives and controlling their sensitivity to mechanically-induced decomposition. Here, we study the deformation behavior of (010)-oriented LLM-105 and β-HMX molecular crystals by nanoindentation with pyramidal (Berkovich) and spherical (19 μm-diameter) indenters. Results reveal indentation elastic moduli of 21 and 18 GPa and Berkovich hardness of 0.73 and 0.65 GPa for LLM-105 and HMX, respectively. For LLM-105 (but not for HMX), indentation stress remains essentially unchanged for spherical indentation strains of ∼10–25%, suggesting that inelastic deformation above a certain strain proceeds via flow at constant stress. Both materials exhibit highly anisotropic surface fracture patterns after Berkovich and spherical indentation, consistent with fracture along (011) cleavage planes. No deformation-induced material decomposition is observed in either material for the indentation conditions used.

Effect of ion-irradiation on the microstructure and microhardness of the W-2Y2O3 composite materials fabricated by sintering and hot forging

A W-2Y2O3 material was developed in collaboration with the Plansee Company (Austria). An ingot of the material having approximate dimension of 95mm×20mm was fabricated by mixing the elemental powders followed by pressing, sintering and hot forging. The microstructure of the W-2Y2O3 composite was investigated using transmission electron microscopy (TEM). The microhardness was studied using nano-indentation technique. We observed that the W-grains having a mean size of about 1μm already formed and these grains contain very low density of dislocations. The size of the yttria particles was between 300nm and 1μm and the Berkovich hardness was about 4.8GPa. The specimens were irradiated/implanted with Fe and He ions at JANNuS facility located at Orsay/Saclay, France. The TEM disks kept were irradiated/implanted at 300 and 700°C using Fe and He ions with an energy of 24 and 2MeV, respectively. The calculated radiation dose was about 5dpa produced by Fe ions and total He content is 75appm at both 300 and 700°C. From the TEM investigation of irradiated samples, few radiation loops are present on the W grains, whereas on yttria particles, the radiation induced damages appear as voids. Berkovich hardness of the irradiated sample is higher than that of the non-irradiated sample. Results on the microstructure and microhardness of the ion-irradiated W-2Y2O3 composites are presented in detail.

Ion-beam modifications of mechanical and dimensional properties of silicon carbide

3C-SiC single crystal epitaxial layers, 6H-SiC single crystal plates and α-SiC Hexoloy sinters were irradiated with 4.0 MeV Xe or 4.0 MeV Au ions at room temperature. Mechanical and dimensional evolutions of silicon carbide are studied by means of nano-indentation and step-height measurements which are correlated with Rutherford backscattering spectrometry and channelling (RBS/C) data in single crystals. Irradiation with Xe ions induces a total lattice disorder related to amorphization for a fluence of 1 × 1015 cm−2 in both polytypes. When complete amorphization is reached, around the same values of Young's modulus (∼350 GPa) and Berkovich hardness (∼27 GPa) are found in both polytypes. The out-of-plane expansion increases with irradiation dose and the saturation value measured in the amorphous layer (normalized to the projected range of the ions) is close to 20–25%. Modifications of macroscopic properties are mainly governed by the disordered fraction of the material in a two-step damage process. A similar behaviour of material evolution is found for the cubic and hexagonal polytypes, either in single crystals or sintered polycrystalline samples. Calculations of Young's modulus and volume swelling are carried out using the analytical (Reuss and Voigt) models of homogenization.

Zirconocene Alkoxides, Promising Precursors for MOCVD of Zirconium Dioxide Thin Films

AbstractSome new volatile bis‐cyclopentadienyl zirconium alkoxides of the type Cp2Zr(OR)(OtBu) (R = iPr, Et, Me) is synthesized by the reaction of the corresponding KOR with the intermediate Cp2ZrCl(OtBu). Moreover, an alternative and convenient synthesis of Cp2Zr(OtBu)2, based on the reaction of Cp2ZrCl2 with an excess of tert‐butanol and triethylamine, is reported. The obtained compounds are identified by chemical analyses, thermogravimetric measurements, infrared (IR), nuclear magnetic resonance (NMR) spectroscopy, and mass spectrometry (MS). Furthermore, a crystallographic study of Cp2ZrCl(OtBu) is also reported. Cp2Zr(OtBu)2 and Cp2Zr(OiPr)(OtBu) are then used for depositing zirconia thin films of high quality and purity on Si(100) and stainless steel AISI 316 substrates by metal‐organic (MO)CVD. The microstructure and composition of the deposits are investigated by X‐ray diffraction (XRD) and secondary ion mass spectrometry (SIMS), while their hardness and elastic recovery on the AISI 316 substrate are measured using load‐depth nano‐indentation tests. The outcomes are consistent with a significant increase in the Berkovich hardness of the coated samples compared to that of bulk AISI 316.

High Hardness BaCb-(BxOy/BN) Composites with 3D Mesh-Like Fine Grain-Boundary Structure by Reactive Spark Plasma Sintering

Boron carbide B4C powders were subject to reactive spark plasma sintering (also known as field assisted sintering, pulsed current sintering or plasma assisted sintering) under nitrogen atmosphere. For an optimum hexagonal BN (h-BN) content estimated from X-ray diffraction measurements at approximately 0.4 wt%, the as-prepared BaCb-(BxOy/BN) ceramic shows values of Berkovich and Vickers hardness of 56.7 +/- 3.1 GPa and 39.3 +/- 7.6 GPa, respectively. These values are higher than for the vacuum SPS processed B4C pristine sample and the h-BN -mechanically-added samples. XRD and electronic microscopy data suggest that in the samples produced by reactive SPS in N2 atmosphere, and containing an estimated amount of 0.3-1.5% h-BN, the crystallite size of the boron carbide grains is decreasing with the increasing amount of N2, while for the newly formed lamellar h-BN the crystallite size is almost constant (approximately 30-50 nm). BN is located at the grain boundaries between the boron carbide grains and it is wrapped and intercalated by a thin layer of boron oxide. BxOy/BN forms a fine and continuous 3D mesh-like structure that is a possible reason for good mechanical properties.

W–2 wt.%Y2O3 composite: Microstructure and mechanical properties

A W-2Y(2)O(3) composite is produced by powder metallurgy, including the pressing of the mixed elemental powders, their sintering and hot forging. The microstructure of the obtained composite is investigated using light microscopy, scanning electron microscopy and transmission electron microscopy. It appears that the material is composed of W grains having a mean size of 1-2 mu m and Y2O3 particles having a mean size of 300 nm to 1 mu m. The W grains contain a high density of dislocations. The mechanical properties of this material are investigated using nanoindentation and 3-point bend test. Berkovich hardness value is found to be 4.9 GPa at 10 N load, which is similar to that of pure W. 3-Point bend test shows that the composite starts to show ductile behavior approximately at 400 degrees C and the bending stress continuously decreases from 200 degrees C to 1000 degrees C. (C) 2012 Elsevier B.V. All rights reserved.

Mechanical properties characterization of c ‐plane (0001) and m ‐plane (10–10) GaN by nanoindentation examination

AbstractThe mechanical properties of m‐plane (10–10) GaN single crystal was measured by nanoindentation examination for the first time. Young's modulus, Berkovich hardness and conical hardness were 284.2 GPa, 15.0 GPa and 15.7 GPa for m‐plane GaN respectively. In contrast, those values in c‐plane (0001) GaN were higher such as 323.8 GPa, 20.0 GPa and 21.2 GPa, respectively. Cathodoluminescence observed dislocation density distribution on m‐plane GaN surface which was gradually decreased following the direction from –c axis edge to +c axis edge. By analyzing the correlation between dislocation density distribution and yield shear stress, we derived a relational equation that reprised the inverse Hall‐Petch relation. This study suggested the possibility for evaluating the reliability for GaN based light emitting device by nanoindentation technique. (© 2010 WILEY‐VCH Verlag GmbH &amp; Co. KGaA, Weinheim)