Depth-sensing Indentation Technique Research Articles

Characterization of material property variation across an inertia friction welded CrMoV steel component using the inverse analysis of nanoindentation data

In this study, a new application of the inverse analysis of the depth-sensing indentation technique based on the optimization theory has been satisfactorily demonstrated. The novel approach for determining the mechanical properties from experimental nanoindentation curves has been applied in order to generate the elastic–plastic stress–strain curves of three phases located across the joint of a like-to-like inertia friction weld of a CrMoV steel, i.e. the parent phase of tempered martensite and two child phases formed during the IFW process, martensite in the quenched and over-tempered condition. The inverse analysis carried out in this study consists of an optimization algorithm implemented in MATLAB, which compares an experimental nanoindentation curve with a predicted indentation curve generated by a 3D finite element model developed using the ABAQUS software; the optimization algorithm modifies the predicted curve by changing the material properties until the best fit to the experimental nanoindentation curve is found. The optimized parameters (mechanical properties) have been used to generate the stress–strain relationships in the elastic–plastic regime that can be used to simulate numerically the effects of the variation in material properties arising from phase transformations occurring across the joint during the IFW process of a CrMoV steel.The proposed inverse analysis was capable of fitting experimental load–depth (P–h) curves produced with a Nanoindentation Nanotest NTX unit from three characteristic regions located across the joint where the above mentioned phases are known to exist. The capability of the inverse analysis to build the stress–strain relationship in the elastic–plastic regime using the optimized mechanical properties of the parent metal has been validated using experimental data extracted from the compressive test of an axisymmetric sample of tempered martensite [1]. According to previous experimental studies, the presence of martensite in the quenched and over-tempered condition formed during the IFW of shaft sections of CrMoV steel are responsible of the 1.52:1 harder and 0.75:1 softer regions, compared to the region where the tempered martensite is located [2–4]. These ratios are in very good agreement with the optimized magnitudes of yield stress provided by the inverse analysis, that is, 1.54:1 for the quenched martensite and 0.68:1 for the over-tempered martensite, compared to the optimized value of yield stress of the tempered martensite. Moreover, a relative difference of less than 1.5% between the experimental and predicted maximum depth (hmax) supports the capability of the method for extracting the elastic–plastic mechanical properties defining each of the indented regions.

Characterization of Sputter-Deposited NiTi Thin Film by Nanoindentation

NiTi shape memory alloy thin film sputter-deposited on a large scale silicon wafer was characterized by means of instrumented (depth-sensing) indentation technique. Thickness of deposited thin film was measured by calotest device. Microstructure of thin film was observed using differential interference (Nomarski) contrast. It was shown that the local mechanical properties are different in areas containing different phases (austenite and martensite) according to different deposition conditions (kinetic energy of deposited atoms when impacting the substrate surface).

Cell proliferation on modified DLC thin films prepared by plasma enhanced chemical vapor deposition.

Recently, diamondlike carbon (DLC) thin films have gained interest for biological applications, such as hip and dental prostheses or heart valves and coronary stents, thanks to their high strength and stability. However, the biocompatibility of the DLC is still questionable due to its low wettability and possible mechanical failure (delamination). In this work, DLC:N:O and DLC: SiOx thin films were comparatively investigated with respect to cell proliferation. Thin DLC films with an addition of N, O, and Si were prepared by plasma enhanced CVD from mixtures of methane, hydrogen, and hexamethyldisiloxane. The films were optically characterized by infrared spectroscopy and ellipsometry in UV-visible spectrum. The thickness and the optical properties were obtained from the ellipsometric measurements. Atomic composition of the films was determined by Rutherford backscattering spectroscopy combined with elastic recoil detection analysis and by x-ray photoelectron spectroscopy. The mechanical properties of the films were studied by depth sensing indentation technique. The number of cells that proliferate on the surface of the prepared DLC films and on control culture dishes were compared and correlated with the properties of as-deposited and aged films. The authors found that the level of cell proliferation on the coated dishes was high, comparable to the untreated (control) samples. The prepared DLC films were stable and no decrease of the biocompatibility was observed for the samples aged at ambient conditions.

Diffusion Boride Coatings in CoCrMo Alloy and Some Indentation Properties

Some mechanical properties for cobalt boride (CoB and Co2B) coatings were obtained using the Vickers depth-sensing indentation technique. The coatings were developed on the surface of a CoCrMo alloy using the powder-pack boriding process at temperatures between 1223 and 1273 K using different exposure times for each temperature. Vickers indentations were conducted at constant distances from the surface using loads ranging from 15 to 450 mN. For the entire set of experimental conditions, the behavior of the indentation properties was examined as a function of the indentation loads. Universal expressions were used to determine the apparent or real hardness, the indentation Young’s modulus, and fracture toughness of the CoB and Co2B coatings. The results indicated that the CoB and Co2B coatings exhibited an apparent hardness of 20 and 17 GPa, respectively, in which the fracture toughness of the cobalt boride coatings only varied slightly in the set of experimental conditions proposed in this work.

Analysis of PA 6 nanocomposites — indentation and creep behavior as a function of temperature and load level using different indentation techniques

The short-term performance (Martens hardness and indentation modulus) and the time-dependent creep behavior of polyamide 6 (PA 6) and two PA 6 nanocomposites containing 3.5 wt % montmorillonite (MMT) or 5 wt % halloysite nanotubes (HNT) were analyzed by different depth-sensing indentation techniques in the nano-, microand macro-range of loading as a function of applied load (0.08— 100 N) and temperature (-80—60 °C). Additionally, WAXD and DSC measurements were made to establish the morphology-property relationships of the investigated materials while taking into account the skin-core structure of the injection-moulded samples.

Microstructure-Related Scratch Resistance and Indentation Creep Behavior of PA6 and PA6 Nanocomposites

Instrumented scratch test was carried out to determine the scratch resistance of polyamide 6 (PA 6) nanocomposites, where two kinds of nanofillers were tested, both based on silicates: montmorillonite (MMT) and halloysite nanotubes (HNT). In this work the influence of the sliding velocity, normal applied load and time-dependent recovery on the penetration depth and scratch hardness was investigated. Optical microscopy was utilized to determine the width of the scratch grooves and scanning electron microscopy revealed the damage features of the scratched surfaces. Both MNT and HNT nanofillers improve the scratch resistance of PA 6 considerably. As a result of the microstructure of the polymer nanocomposites MNT gives PA 6 a better residual depth resistance while HNT raises its scratch hardness (i.e. reduces the scratch width). Furthermore, via different depth-sensing indentation techniques in the nano-, micro- and macro-range of loading the short-term performance (Martens hardness and indentation modulus) and the time-dependent creep behavior have been analyzed for PA 6 and the PA 6 nanocomposites as a function of applied load and temperature. Additionally, WAXS (wide-angle X-ray scattering) and DSC (differential scanning calorimetry) measurements to establish morphology–property relationships of the materials investigated considering the skin–core structure of the injection molded samples were made.

Furan resins as replacement of phenolic protective coatings: Structural, mechanical and functional characterization

Phenolic coatings are usually a convenient and economical way to protect metallic materials against wear and corrosion. Furan resins are analogous to phenolics, as they are obtained by replacing formaldehyde by furfural in their formulation. In this work, a furan resin based on furfural and phenol was synthesized and used as an aluminum coating. Thus, toxic emissions of formaldehyde were avoided, while a biobased derivative was used instead. The performance of the proposed resin was compared with the one of a traditional phenolic resin. Physicochemical characteristics including chemical structure, surface polarity and glass transition temperature were evaluated by means of Fourier transform infrared spectroscopy, contact angle measurements and dynamic–mechanical analysis, respectively. Nanomechanical and nanotribological properties were assessed by depth sensing indentation techniques. As well, the corrosion resistance of the furan coating was determined by potentiodynamic polarization tests. The obtained results validate the furan resin as a feasible alternative to phenolics to protect aluminum.

Mechanical Properties of Metal Matrix Nanocomposites Synthesized by Selective Laser Melting Measured by Depth Sensing Indentation Technique

This work presents an investigation of basic mechanical properties (hardness, Young modulus) of metal matrix composites (MMC) reinforced with non-oxide ceramic nanoparticles by means of nanoindentation measurements. The evaluated materials were manufactured by selective laser melting (SLS/M). As a matrix 316L stainless steel and as a reinforcing phase TiC nanoparticles were used. The influence of nanoscale reinforcement on the mechanical properties of MMC manufacturing with SLS/M process was examined. In this case statistical evaluation of hardness and Young modulus based on nanoindentation data was performed.

Mechanical Properties of BSCCO Superconductor by Oliver–Pharr Method and Work of Indentation Approach

Polycrystalline superconducting Bi-Pb-Gd-Sr- Ca-Cu-O bulk samples with nominal composition Bi1.7Pb0.3−xGdxSr2Ca3Cu4O12+y (x = 0.00, 0.01, 0.05) were produced by the melt quenching method. The mechan- ical properties of the samples were characterized by depth sensing indentation technique under different peak loads ranging from 200 to 1800 mN. The experimental data were comparatively analyzed by the Oliver-Pharr method and a work of indentation approach. It was found that the work of indentation approach gave more reliable results because of the reducing pile-up effect. The results implied that both microhardness and reduced elastic modulus increased with increasing Gd substitution.

Towards Quantitative Characterisation of the Small Force Transducer Used in Nanoindentation Instruments

Quantitative characterization of the mechanical properties of materials in micro-/nano-scale using depth-sensing indentation technique demands high performance of nanoindentation instruments in use. In this paper, the efforts to calibrate the capacitive force transducer of a commercial nanoindentation instrument are presented, where the quasi-static characteristic of the force transducer has been calibrated by a precise compensation balance with a resolution of ~1 nN. To investigate the dynamic response of the transducer, an electrostatic MEMS (Micro-Electro-Mechanical System) based on nano-force transfer standard with nano-Newton (10-9 Newton) resolution and a bandwidth up to 6 kHz have been employed. Preliminary experimental results indicate that 1) the force transducer under calibration has a probing force uncertainty less than 300 nN (1σ) in the calibration range of 1 mN; 2) the transient duration at contact points amounts to 10 seconds; 3) the overshoot of engagement is pre-load dependent.

Development of Innovative Algorithm for Nanomechanics and its Applications to the Characterization of Materials

Understanding major mechanisms affecting material strength such as grain size, grain orientation and dislocation mechanism from atomistic viewpoint can empower scientists and engineers with the capability to produce vastly strengthened materials. Computational studies can offer the possibility of carrying out simulations of material properties at both larger length scales and longer times than direct atomistic calculations. The study has conducted theoretical modeling and experimental testing to investigate nanoscale mechanisms related to material strength and interfacial performance. Various computational algorithms in nanomechanics including energy minimization, molecular dynamics and hybrid approaches that mix atomistic and continuum methods to bridge the length and time scales have been used to thoroughly study the deformation and strengthening mechanisms. Our study has also performed experiments including depth-sensing indentation technique andin-situpico-indentation to characterize the nanomechanisms related to material strength and tribological performance. In this project, we have developed the innovative mutil-scale algorithms in the area of nanomechanics. These approaches were used to studies the defect effect on the mechanical properties of thin film, mechanical properties of nanotubes, and tribological phenomena at nanoscale interfaces.

Kinetics of Mechanical Alloying, Mechanical Properties of Micro and Nanostructural Al-C Systems

AbstractA method of mechanical alloying process is described. Carbon transformation to Al4C3 is characterized within the different heat treatment schedules and nine commercial carbon powders are tested. The micromechanism of carbon incorporation into the metallic powder, and its compacting are described. The influence of dispersed carbides on mechanical properties is evaluated together with the influence of deformation on microstructure and properties. It was proved that the transformation efficiency of carbon to Al4C3 by heat treatment of aluminium with the porous furnace black and electrographite is higher than that of the hard cracked graphite. Microstructure changes consisted of the fracture processes and welding of the particles with incorporation of C phase and forming of final granules. The dispersed phase Al4C3 particle size was measured on thin foil structures, and it was constant and as small as 30 nm. The particle size was influenced neither by the carbon type nor by the heat treatment technology applied. Subgrain size measured in the range of 100 grains in thin foils depended on the carbon type, as well. It ranged from 0.3 to 0.7 µm. Using a DSI (depth sensing indentation technique), the Martens hardness, indentation modulus E and deformation work W for Al matrix and Al4C3 particles have been measured. The temperature dependence of ductility, and reduction of area in the temperature range of 623–723 K and strain rate of 10−1 s−1, indicated a considerable increase of these properties. In a case when the volume fraction of Al4C3 changes from lower to higher, the grain rotation mechanism dominates instead of the grain boundary sliding. The comparison of the tensile test results and changes in fracture for the Al-Al4C3 system at two temperatures and two strain rates is summarized. The dependence of the minimum deflection rate on the applied force as well as the dependence of the time to fracture on the applied force for two temperature levels (623 and 723 K) by small punch testing are depicted. The composite was tested in two different states: a) as received by mechanical alloying with hot extrusion (HE) as the final operation and b) ECAPed (mean grain size of 100–200 nm). The dependence of the minimum deflection rate on the applied force as well as the dependence of the time to fracture on the applied force for two temperature levels are evaluated. The anisotropy of the creep properties and fracture using small punch tests for the Al-Al4C3 system produced by ECAP were analysed.

Fabrication of in situ Ni(W)–WC nano composites via mechanical alloying and spark plasma sintering

Microstructural and mechanical properties of spark plasma sintered Ni-30wt% W powders fabricated via mechanical alloying (MA) for 48h were reported in the present study. Due to the intensive WC contamination during MA, the synthesized powders are termed as Ni(W)–WC nanocomposites. The MA’d powders were sintered at temperatures between 800 and 1000°C via spark plasma sintering (SPS) technique and high density (∼97%) Ni(W)–WC composite compacts having high micro hardness values (∼4.30GPa) and high elastic modulus (∼270GPa) were obtained. The effects of sintering temperature, duration and hBN spraying of the graphite die on the phase compositions, i.e. WC content, microstructure and mechanical properties were investigated systematically by using X-ray diffractometer (XRD), Rietveld analyses, scanning electron microscopy (SEM), microhardness and depth-sensing indentation techniques. The crystallite sizes of both the Ni(W) solid solution and the WC phases increased with increasing sintering temperature and durations: An average crystallite size of 39nm for the Ni(W) solid solution phase in the SPS-800 sample increased to 86nm for the SPS-1000-5min sample, likewise, about 14nm crystallite size of WC phase in the SPS-800 sample increased to 78nm for the SPS-1000-5min sample. The SPS-1000-hBN sample had the highest relative density and microhardness values of 97.33% and 4.35GPa, respectively.

Determination of the Drucker–Prager parameters of polymers exhibiting pressure-sensitive plastic behaviour by depth-sensing indentation

This paper presents a method to determine the Drucker–Prager parameters of pressure-dependant elastic-perfectly plastic polymeric materials by means of the depth-sensing indentation technique. This is achieved via an inverse analysis of the load–displacement data resulting from two tests performed with Berkovich and spherical tips. The well-posedness and the effective range of application of the proposed method are carefully assessed first. Then the method is tested for two elasto-plastic materials with mild initial strain-hardening (HDPE and PMMA), and the results are compared to those measured using conventional tensile and compression tests. It is found that the pressure-sensitivity indices can be accurately predicted, while the yield stress predictions in tension and compression fall within the non-linear portion of the uniaxial stress–strain curves, i.e., inside the region where plastic deformation begins.

Correlating the adhesion of an acrylic coating to the physico-mechanical behavior of a polypropylene substrate

In this study, the adhesion strength of an acrylic coating onto a polypropylene (PP) based substrate was studied. The adhesion strength of the PP containing various wt% of oxidized wax was found to be dependent on the surface free energy of the substrate. To this end, the geometric mean and the acid–base approaches were used to estimate the surface free energy, both of which shown to exist a direct relation between surface hydrophilicity and the content of the oxidized wax. The viscoelastic behavior of the adherend also contributed to the coating adhesion. The viscoelastic response of the blends was investigated using dynamic mechanical thermal analysis (DMTA) and universal testing machine (UTM) for the bulk properties of the substrate and a depth sensing indentation technique for its near-surface, respectively. Bulk and near-surface moduli were decreased as a result of incorporation of wax additive into PP matrix. These were attributed to the homogeneous distribution of low molecular weight wax chains in the polymeric matrix and hence their impact on substrate integrity. The DMTA analysis showed a single phase matrix for all blends. Using a linear trend line, the adhesion test results revealed a good correlation to surface free energy calculations compared with the substrate modulus. The weaker effect of substrate modulus on surface adhesion was ascribed to the substrate plasticity and/or development of internal stresses in the coating layer. However, the glass transition temperature of the coating suggested that the internal stresses in coating layer were responsible to relax prior to conducting adhesion measurement.

Local mechanical properties of materials based on matrix-particles system

In this study, the local mechanical properties: indentation modulus E IT and indentation hardness H IT were experimentally investigated on two matrix – particle systems using depth-sensing indentation technique with a sharp Vickers and Berkovich indenter. The continuous stiffness measurement (CSM) technique was used to obtain the depth profiles of both measured values, which allowed separation of some effects that could affect the results. The investigated materials were interstitial free steel sheet and an Al-Al 4 C 3 alloy prepared by mechanical alloying. Indentation curves obtained on individual particles were analysed in detail with respect to particle fracturing and/or penetrating of the particle into the matrix as a secondary indenter. Due to sample preparation the measured hardness can be affected up to 2.5 times, while the modulus value remains unaffected. The H IT and E IT values as well the deformation work for matrix and for the particles are included in the article.

Interaction of silver nanopowder with copper substrate

Addition of lead into tin based solders represents a serious health risk and environmental problem. Lead-free solders represent one of the ways to remove pollution of lead into environment, nevertheless, new advanced joining methods have to be considered. Aggregation effect of nanoparticles studied in this work seems to be an interesting alternative. It was found experimentally that Ag nanopowder annealed at temperatures above silver oxide decomposition forms continuous Ag layer and yields a firm junction between copper plates. Oxide layer is observed at the Cu-Ag interface. The oxide interlayer thickness reflects the temperature and annealing time. Microstructure of prepared experimental joints, composition profiles and local mechanical properties were studied on cross-sectional samples by analytical electron microscopy and depth-sensing indentation technique.

Investigation of mechanical and creep properties of polypyrrole by depth-sensing indentation

In this study, we used depth-sensing indentation (DSI) technique to investigate some mechanical properties (reduced elastic modulus, indentation hardness, and creep) of polypyrrole (PPy) conducting polymer obtained with different support electrolyte concentration. The influence of support electrolyte concentration on these parameters was also determined. The order of doping degree of the samples was determined by cyclic voltammetry. The indentation load–displacement curves of the samples were obtained under different peak load levels with a 70 s holding time at maximum load. Reduced elastic modulus and hardness values were determined by analysis of these curves using the Feng–Ngan (F–N) and Tang–Ngan (T–N) methods, respectively. Both reduced elastic modulus (E r) and indentation hardness (H) exhibited significant peak load dependence, i.e., indentation size effect (ISE). It was found that both E r and H values decreased as the support electrolyte concentration was increased. This was explained by an increase in the free volume as the doping degree was raised. The creep behavior of the samples was monitored from the load holding segment of the load–unload curves. It was found that creep increases with the increasing support electrolyte concentration.

Deposition of hard thin films from HMDSO in atmospheric pressure dielectric barrier discharge

An atmospheric pressure dielectric barrier discharge burning in nitrogen with a small admixture of hexamethyldisiloxane (HMDSO) was used for the deposition of thin organosilicon films. The thin films were deposited on glass, silicon and polycarbonate substrates, and the substrate temperature during the deposition process was increased up to values within the range 25–150 °C in order to obtain hard SiOx-like thin films. The properties of the discharge were studied by means of optical emission spectroscopy and electrical measurements. The deposited films were characterized by the Rutherford backscattering and elastic recoil detection methods, x-ray photoelectron spectroscopy, infrared spectroscopy measurements, ellipsometry and the depth sensing indentation technique. It was found that the films' properties depend significantly on the substrate temperature at deposition. An increase in substrate temperature from 25 to 150 °C led to an increase in film hardness from 0.4 to 7 GPa and the film chemical composition changed from CHxSiyOz to SiOxHy. The films were transparent in the visible range.

Structural and defect changes of hydrogenated SiGe films due to annealing up to 600°C

AbstractIn order to better understand the effects of the hydrogen incorporation on the defects and the disorder in the undoped nano/microcrystalline SiGe:H, we performed a comparative study on samples deposited under different plasma conditions. With variation of the pressure, we were able to change the structure of SiGe:H films. We have used the combination of the infrared spectroscopy, CPM, PDS and thermal desorption measurements to study the thermal dependence of defect density, disorder, as well as hydrogen concentration. The film mechanical properties were tested by depth sensing indentation technique. The results showing a different hydrogen bonding with the change of deposition conditions are interpreted as a whole by terms of the specific local hydrogen bonding environment, related to different growth mechanism. (© 2010 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)