Microindentation Measurement Research Articles

Structural-phase transformations and changes in the properties of AISI 321 stainless steel induced by liquid carburizing at low temperature

Structural and phase transformations occurring due to the supersaturation of austenite with interstitial atoms (carbon and/or nitrogen) are the key priority in the study of AISI 300 series austenitic steels. It is also very important to achieve a greater hardening depth by nitriding or carburizing. For this purpose, a method of salt bath carburizing at low temperature was proposed. The aim of this work is to perform a detailed analysis of structural-phase transformations and their effect on the properties of AISI 321 austenitic steel subjected to liquid carburizing at a temperature of 780°С. Optical and scanning electron microscopy, optical profilometry, X-ray diffraction analysis, energy-dispersive microanalysis, electron backscatter diffraction analysis, instrumented microindentation and microhardness measurement are used as methods of investigation. It has been discovered that, along with carbon-rich (up to 0.46 wt% C) austenite, chromium carbide Cr23C6, cementite Fe3C, ε-martensite, and α-martensite are formed in the surface layer of the carburized AISI 321 steel. Carbides are present both at the grain boundaries and within the austenite grains. Martensite formed in the carburized AISI 321 steel is induced by deformation, and the martensitic transformation path is γ → ε → α′ (two-stage transformation). In its turn, plastic deformation occurs during cooling that follows carburizing, and this is a relaxation mechanism of high thermal stresses. Liquid carburizing of AISI 321 steel also multiplies the microhardness of the steel surface from 200 ± 7 to 890 ± 110 HV0.025, with the total hardening depth being about 500 μm. The hardened layer is gradient and characterized by increased resistance to elastic-plastic deformation, this being important for increasing the contact endurance and wear resistance of the steel. It has also been found that, due to high carbon concentration, the corrosion resistance of the carburized steel does not deteriorate significantly.

High-throughput characterization of the cyclic response of Ti-6Al-4V using spherical microindentation stress–strain protocols

This paper presents novel high-throughput spherical microindentation measurement and analyses protocols for the cyclic response of metal samples. These protocols are aimed at rapid screening of large design spaces encountered in the development of advanced metal alloys. They involve the measurement of cyclic load-depth hysteresis loops in spherical microindentation, their conversion to cyclic indentation stress–strain hysteresis loops, and the extraction of an indentation cyclic stress–strain curve. The proposed spherical microindentation measurement and analyses protocols are demonstrated on samples of Ti-6Al-4V. The indentation measurements are compared against the measurements obtained on the same material in standard uniaxial stress tests in both monotonic and cyclic loading. The cyclic indentation stress–strain measurements correlated well with the measurements from the standard uniaxial stress tests.

Dual alginate crosslinking for local patterning of biophysical and biochemical properties

Hydrogels with patterned biophysical and biochemical properties have found increasing attention in the biomaterials community. In this work, we explore alginate-based materials with two orthogonal crosslinking mechanisms: the spontaneous Diels-Alder reaction and the ultraviolet light-initiated thiol-ene reaction. Combining these mechanisms in one material and spatially restricting the location of the latter using photomasks, enables the formation of dual-crosslinked hydrogels with patterns in stiffness, biomolecule presentation and degradation, granting local control over cell behavior. Patterns in stiffness are characterized morphologically by confocal microscopy and mechanically by uniaxial compression and microindentation measurement. Mouse embryonic fibroblasts seeded on stiffness-patterned substrates attach preferably and attain a spread morphology on stiff compared to soft regions. Human mesenchymal stem cells demonstrate preferential adipogenic differentiation on soft surfaces and osteogenic differentiation on stiff surfaces. Patterns in biomolecule presentation reveal favored attachment of mouse pre-osteoblasts on stripe regions, where thiolated cell-adhesive biomolecules have been coupled. Patterns in degradation are visualized by microindentation measurement following collagenase exposure. Patterned tissue infiltration into degradable regions on the surface is discernible in n=5/12 samples, when these materials are implanted subcutaneously into the backs of mice. Taken together, these results demonstrate that our hydrogel system with patterns in biophysical and biochemical properties enables the study of how environmental cues affect multiple cell behaviors in vitro and could be applied to guide endogenous tissue growth in diverse healing scenarios in vivo. Statement of SignificanceHydrogels with patterns in biophysical and biochemical properties have been explored in the biomaterials community in order to spatially control or guide cell behavior. In our alginate-based system, we demonstrate the effect of local substrate stiffness and biomolecule presentation on the in vitro cell attachment, morphology, migration and differentiation behavior of two different mouse cell lines and human primary cells. Additionally, the effect of degradation patterns on the in vivo tissue infiltration is analyzed following subcutaneous implantation into a mouse model. The achievement of patterned tissue infiltration following the hydrogel template represents an important step towards guiding endogenous healing responses, thus inviting application in various tissue engineering contexts.

Influencing factor analysis of shale micro-indentation measurement

To address the difficulty in measuring mechanical properties within the reservoir formation during the process of drilling in shale formations, micro-indentation measurement technology is performed to determine the micro elastic modulus and the indentation hardness of a shale outcrop in the Longmaxi Formation in the Sichuan Basin (the Changning Area). Additionally, factors influencing the micro-indentation measurement are analyzed from aspects such as indenter defects, experimental parameter settings, shale surface properties, and shale composition. The results show that the elastic modulus and indentation hardness decrease with increasing indentation depth. The test is less affected by indenter passivation. The area function needs to be calibrated when the tip radius of the indenter is more than 10 μm. It is observed that the test is substantially influenced by the parameter settings, so reasonable parameters should be determined before conducting the test. The Oliver-Pharr method is applicable to shale outcrops of the Longmaxi Formation, which meet the general requirements of the method. The measured values increase with increasing packing density. Moreover, the fitting percentage of the unloading curve has an impact on the result, and the reasonable fitting percentage of the unloading curve for shale samples was determined to be from 45% to 75%.

Hardness, elastic, and electronic properties of chromium monoboride

We report high-pressure synthesis of chromium monoboride (CrB) at 6 GPa and 1400 K. The elastic and plastic behaviors have been investigated by hydrostatic compression experiment and micro-indentation measurement. CrB is elastically incompressible with a high bulk modulus of 269.0 (5.9) GPa and exhibits a high Vickers hardness of 19.6 (0.7) GPa under the load of 1 kg force. Based on first principles calculations, the observed mechanical properties are attributed to the polar covalent Cr-B bonds interconnected with strong zigzag B-B covalent bonding network. The presence of metallic Cr bilayers is presumably responsible for the weakest paths in shear deformation.

Synthesis and Characterization of Ethylene/1‐Octene Copolymer Based Ionomer Nanocomposite

SummaryA new type of ionomeric nanocomposite based on elastomeric ethylene/1‐octene copolymer (EOC) and organophilically modified layered silicate was synthesized through sulfonation of the EOC followed by solution casting. The morphology–mechanical properties correlation of the product was studied with the help of scanning electron microscopy (SEM), atomic force microscopy (AFM), Fourier transform infrared (FTIR) spectroscopy and recording microindentation measurement. The nanocomposite with uniformly distributed filler morphology could be conveniently prepared. It was found that the Martens hardness of ionomer nanocomposite comprising 5 wt.‐% layered silicate is approximately threefold of the neat elastomer.

Robust algorithm for automated microindentation measurement in Vickers hardness testing

Current algorithms for automated processing of Vickers hardness testing images are unsuitable for a broad range of images that are taken in industrial environments because such images show great variations in the Vickers indentation as well as in the specimen surface. The authors present a three-stage multiresolution template matching algorithm that shows excellent results, even for such challenging images. The capabilities of this algorithm are compared to known algorithms from the literature and results are presented. The comparison is conducted on two significant indentation image databases with 150 and 216 highly varying images. The applicability of the proposed algorithm is further illustrated by its competitive runtime performance.

Bone quality and osteonecrosis of the jaw induced by bisphosphonates

Osteonecrosis of the jaw (ONJ) is a complication of long-term bisphosphonates therapy whose etiology and pathogenesis are not fully understood. Our purpose was to assess the quality of bone in the jaws of control subjects, and osteoradionecrosis (ORN) and ONJ patients.Materials and methods: six jaw bone samples were taken from control patients. Eight jaw bone samples in patients with osteonecrosis (2 ORN and 6 ONJ) were also taken during conservative surgery. Histology was used to analyze cellular composition, microarchitecture and static variables of bone formation and resorption. Bone quality was also assessed using Vickers microindentation (measurement of microhardness) and quantitative microradiography [measurement of the mean degree of mineralization of bone (DMB) and of the heterogeneity index (HI) of the distribution of the mineralization].Results: compared to controls, the osteonecrotic bone was hypovascularized, eroded, poor in osteoblasts and contained numerous empty periosteocytic lacunae. DMB (control group 1.14 ± 0.13 g.cm –3 , ORN 1.25 ± 0.14 g.cm –3 and ONJ 1.11 ± 0.12 g.cm –3 ) and HI (control group 0.18 ± 0.08 g.cm –3 , ORN 0.17 ± 0.06 g.cm –3 and ONJ 0.24 ± 0.08 g.cm –3 ) in osteoradionecrosis and ONJ samples were not significantly different from controls. Hypermineralization was never observed in ONJ. Bone microhardness after osteoradionecrosis (50.04 ± 4.34 kg.mm –2 ) and ONJ (47.48 ± 4.10 kg.mm –2 ) was slightly decreased compared to controls (53.52 ± 6.46 kg.mm –2 ).In conclusion, bisphosphonates-induced ONJ was neither associated with modifications of secondary bone mineralization, nor changes in bone microhardness. Bone vessels and cellular changes appeared to play a major role in the development of ONJ.

The Elastic Modulus of β‐HMX Crystals Determined by Nanoindentation

AbstractThis paper presents an investigation on the anisotropic modulus of energetic crystals of β‐HMX by using a Hysitron Triboindenter fitted with a Berkovich tip. High quality single crystals of β‐HMX, whose densities were determined by high precision density gradient tube (DGT), were used in order to extract the moduli of two orthogonal crystal faces: (010), the maximum growth habit face (termed face 1), and the face which is perpendicular to it (termed face 2). Contrary to common expectation, the moduli of face 1 and face 2 were found to be 23.4 and 26.1 GPa, respectively, indicating a negligible crystal anisotropy of the system. Nanoindentation measurement gave even narrower difference, with hardness values of 1.1 GPa for face 1 and 0.95 GPa for face 2, thus further supporting the above conclusion. The result obtained from nanoindentation contradicts with those from the impulse stimulated light scattering (ISLS) and the Brillouin scattering, but was close to the result predicted by molecular dynamics (MDs) simulation. It is also suggested that the modulus value of 31 GPa obtained from previous micro‐indentation measurement may be overestimated.

Influence of friction in material characterization in microindentation measurement

A comprehensive computational study is undertaken to identify the influence of friction in material characterization by indentation measurement based on elasto- plastic solids. The impacts of friction on load versus indentation depth curve, and the values of calculated hardness and Young’s modulus in conical and spherical indentations are shown in this paper. The results clearly demonstrate that, for some elasto-plastic materials, the curves of load versus indentation depth obtained either by spherical or conical indenters with different friction coefficients, cannot be distinguished. However, if utilizing the parameter β (see text for details), to quantify the deformation of piling-up or sinking-in, it is easy to find that the influence of friction on piling-up or sinking-in in indentation is significant. Therefore, the material parameters which are related to the projected area will also have a large error caused by the influence of friction. The maximum differences on hardness and Young’s modulus can reach 14.59% and 6.78%, respectively, for some elastic materials shown in this paper. These results do not agree with those from researchers who stated that the instrumented indentation experiments are not significantly affected by friction.

Nitriding of titanium by using an ion beam delivered by a plasma focus

The room temperature nitriding of titanium is accomplished by utilizing nitrogen ion beams delivered by a 2.3 kJ plasma focus discharge. Titanium samples are exposed to ions at different axial positions (3, 5, 7 and 9 cm from the focus) in order to correlate their surface properties with ion beam parameters such as energy, number density, current density and energy flux (energy deliverance per unit time per unit volume). A BPX65 photodiode detector is employed to measure the ion beam parameters by using the time of flight technique. X-ray diffraction analysis as well as field emission scanning electron microscopy along with the energy dispersive x-ray spectroscopy is carried out to explore the structural, morphological and compositional profiles of the treated samples. The results demonstrate the formation of nanocrystalline TiN thin film with surface features strongly dependent on ion beam energy flux. A Vickers microindentation measurement reveals that the surface hardness is improved 4–5 times for typical nitrided samples.

Shape‐engineered vascular endothelial cells: Nitric oxide production, cell elasticity, and actin cytoskeletal features

Single cell shape determines cellular functions. Therefore, control of cell shape is of considerable importance for the tissue engineering field. This study was designed to assess the effect of surface-induced shaping of vascular endothelial cells (ECs) on the intracellular nitric oxide (NO) production level, the cell elasticity, and cytoskeletal (CSK) features on shape-engineered ECs (round, 90, 120 microm diameter; spindle-shaped, 20, 30, 40 microm width) prepared on a photolithographically microprocessed surface. Intracellular NO production was measured using a microscopic spectrometer with diaminofluorescein diacetate probe. Cell elasticity and actin CSK features were analyzed through microindentation measurement and fluorescence observations with fluorescence and atomic force microscopy. Results showed that spindle-shaped cells exhibited lower NO production, higher cell stiffness, and denser actin stress fibers than the round and nonrestrictedly cultured control cells. Relations between cell shape with NO production, cell elasticity, and actin CSK features were discussed.

A microindentation study of polyethylene composites produced by hot compaction

Microindentation measurements are reported on a range of single polymer polyethylene (PE) composites, which are produced by hot compaction of high modulus PE fibers. It is possible to measure two hardness values, parallel and perpendicular to the fiber direction respectively, from which the microindentation anisotropy is defined. The hardness values relate to the instantaneous elastic recovery of the fibers, and the results show that the microindentation measurement is deforming a material volume below the surface of the sheets comparable to the dimensions of the fibers. It appears that the microindentation anisotropy approaches a limiting value with increasing fiber orientation, i.e., as the Young's modulus of the fibers increases. © 2006 Wiley Periodicals, Inc. J Appl Polym Sci 100: 1659–1663, 2006

65.3: Quantitative Adhesion Analysis of Sputtered Copper Films on Glass Substrate by Microindentation Measurement

Quantitative adhesion testing of copper films on glass substrates was investigated by microindentation measurement. Due to the weak adhesion and inter-diffusion issues between copper (Cu) and glass substrates, we deposited silicon nitride (SiNx) films on glass substrates initially. Optimizing Cu sputtering parameters and introducing ammonia (NH3) plasma treatment onto SiNx, we obtained the superior adhesion strength of Cu/SiNx/glass structures. Based on the values of critical reduced depth (b) with Cu/SiNx/glass (b=1.311) and with Cu/Mo/glass (b=1.005) structures, we inferred that the adhesion strength of these two kinds of structures was almost the same. Furthermore, the etching profiles of Cu/SiNx structures were excellent. The taper angle was approximately 60 degrees, and critical-dimension loss percent was about 7.

06/00003 Microfacies and depositional environment of Tertiary Tanjung Enim low rank coal, South Sumatra Basin, Indonesia: Amijaya, H. and Littke, R. International Journal of Coal Geology, 2005,61, (3–4), 197–221

To address the difficulty in measuring mechanical properties within the reservoir formation during the process of drilling in shale formations, micro-indentation measurement technology is performed to determine the micro elastic modulus and the indentation hardness of a shale outcrop in the Longmaxi Formation in the Sichuan Basin (the Changning Area). Additionally, factors influencing the micro-indentation measurement are analyzed from aspects such as indenter defects, experimental parameter settings, shale surface properties, and shale composition. The results show that the elastic modulus and indentation hardness decrease with increasing indentation depth. The test is less affected by indenter passivation. The area function needs to be calibrated when the tip radius of the indenter is more than 10 μm. It is observed that the test is substantially influenced by the parameter settings, so reasonable parameters should be determined before conducting the test. The Oliver-Pharr method is applicable to shale outcrops of the Longmaxi Formation, which meet the general requirements of the method. The measured values increase with increasing packing density. Moreover, the fitting percentage of the unloading curve has an impact on the result, and the reasonable fitting percentage of the unloading curve for shale samples was determined to be from 45% to 75%.

Processing and mechanical behaviour of TiAl/NiAl intermetallic composites produced by cryogenic mechanical alloying

Cryogenic mechanical alloying of intermetallic powders has been used to produce TiAl/NiAl intermetallic composites. High-energy milling of prealloyed titanium aluminide and nickel aluminide powders at liquid nitrogen temperature results in the stable non-equilibrium mixtures with a fine grain size. Subsequent consolidation by uniaxial hot pressing produces unusual intermetallic composites. Powders and consolidated materials are characterised using microscopy and X-ray diffraction (XRD). Mechanical properties are evaluated by small punch testing and through microindentation measurement. It has been found that no new phase is formed during milling of intermetallic mixtures. Consolidated powders have exhibited exceptionally high hardness. The low fracture toughness of consolidated materials is attributed to the formation of ternary phases during consolidation.

EFFECT OF NITROGEN ON THE RESIDUAL STRESS AND ADHESION OF DIAMOND-LIKE AMORPHOUS CARBON NITRIDE FILMS

Microstructure and adhesion properties of nitrogen-doped diamond-like amorphous carbon (DLC) film deposited by r f plasma-enhanced chemical vapor deposition method is studied by atomic force microscope, Auger electron spectroscopy (AES) and micro-indentation analysis. Results show that, with the increase of nitrogen content, particles of tens of nanometer in size appear in the film. The atomic lateral force microscope and AES analyses show that these nano particles are nitrogen-rich amorphous carbon nitride CNx, where x is larger than 0.126. Micro-indentation measurement shows that this DLC/CNx nano-composite structure reduces the residual stress of the film and improves the adhesion between DLC film and Si substrate.

Fracture toughness determination of dental amalgams through microindentation.

A microindentation technique was used to study and estimate the fracture toughness of six amalgams. A significant difference is observed between fracture toughness at the bulk and the margin of amalgams. All amalgams show significant differences in fracture toughness as a function of distance from the margin. Microindentation measurement of fracture toughness appears to be an effective method of evaluating the localized brittleness of amalgams.