Instrumented Nanoindentation Tests Research Articles

Micro-mechanisms of deformation and strengthening during high pressure torsion of CoCuFeMnNi high entropy alloy

The equiatomic FCC CoCuFeMnNi HEA subjected to high pressure torsion (HPT) till 5 turns, showed a fourfold increase in hardness and three orders of magnitude decrease in grain size with an insignificant change in strain rate sensitivity and activation volume. There is a gradual transition from planar slip at low strain to twinning followed by shear banding at high strain accompanied by conversion of low angle to high angle grain boundaries, resulting in average grain size of 55 ± 33 nm at the periphery of 5 turn HPT sample. Atom probe tomography revealed that nano-clusters present in FCC matrix in the homogenized sample underwent partial dissolution during HPT to increase the copper concentration from 8.24 ± 3.29 to 17.02 ± 1.51 atomic%, contributing to significant solid solution strengthening in addition to dislocation and grain size strengthening, leading to tremendous increase in hardness (539 to 1941 MPa). Transient instrumented micro and nano-indentation tests yield activation volume between 12 and 17 b3 for the homogenized and HPT processed samples with three orders of magnitude difference in grain size and dislocation density. This indicates that the dislocation–solute environment interaction is the rate controlling mechanism during the deformation of the investigated HEA. The present work provides a unique pathway to design high entropy alloys that can explore and utilize non-equilibrium solid solution strengthening as a major strengthening mechanism to achieve high strength.

A systematic study on microstructure evolution, mechanical stability and the micro-mechanical response of tensile deformed medium manganese steel through interrupted tensile test

In the current work, the microstructure evolution, mechanical stability of austenite and the micro-mechanical response of tensile deformed Fe-0.18C-4Al-7Mn (Wt%) steel are investigated. Interrupted tensile tests on the annealed samples (750 °C, 1 h) were performed at a tensile elongation of 5, 10, 20, 30, 40 and 60% to understand the deformation behavior and transformation-induced plasticity (TRIP) effect. Strain-induced martensitic transformation (SIMT) of reverted austenite is explored using X-ray diffraction (XRD), transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) analysis. The coefficient of mechanical stability of austenite (k-parameter) is quantified through the interrupted tensile tests using XRD analysis. Instrumented nanoindentation test was conducted on individual phases of the interrupted tensile-tested samples to determine their hardness and modulus values. The scanning electron microscopy (SEM) analysis reveals the gradual decrease in width and increase in length of austenite-martensite islands with an increase in the percentage of elongation. Evolution of dislocation lines, dislocation tangles and dislocation accumulations occur at ferrite grain boundaries and martensite lath boundaries during tensile deformation. The volume fraction of austenite decreases, and the transformation of austenite to martensite and dislocation density of austenite increase with the increase in the tensile elongation. Austenite is found to be mechanically more stable at 30% of tensile elongation due to the low austenite transformation ratio. Nanoindentation results show that the hardness increases with an increasing percentage of deformation. Multiple pop-ins are observed in load (P)–indentation depth (h) curves due to dislocation interaction at the interphase boundary.

Size effect and anisotropy in cold rolled Zr-base bulk metallic glasses during nanoindentation

A series of instrumented nanoindentation tests have been performed in control loading rate mode on Zr52.5Cu18Ni14.5Al10Ti5 (VIT105) and Zr58.5Cu15.6Ni12.8Al10.3Nb2.8 (VIT106A) as-cast and various cold rolled samples to investigate the indentation size effect (ISE) in three perpendicular planes i.e., rolling-width (RW), normal-rolling (NR) and normal-width (NW) planes at peak loads in the range of 50 mN - 500 mN. The hardness, reduced modulus and dynamic hardness have reduced with the increase of indentation depth in NR, RW and NW planes. The as-cast and cold rolled BMGs exhibit normal ISE for NR, RW and NW planes. The size effect has been analyzed using power law, Nix-Gao model, and proportional specimen resistance model suggesting that dynamic mechanical softening and the friction between the indenter and specimen are the underlying reasons behind the observed ISE.

Multi-cycling nanoindentation in additively manufactured Inconel 625 before and after laser peening

In this research, a room temperature multicycle nanoindentation technique was implemented to evaluate the effects of the laser peening (LP) process on the surface mechanical behavior of additively manufactured (AM) Inconel 625. Repetitive deformation was introduced by loading-unloading during an instrumented nanoindentation test on the as-built (No LP), 1-layer, and 4-layer laser peened (1LP and 4LP) conditions. It was observed that laser-peened specimens had a significantly higher resistance to penetration of the indenter and lower permanent deformation. This is attributed to the pre-existing dislocation density induced by LP in the material which affects the dislocation interactions during the cyclic indentation. Moreover, high levels of compressive stresses, which are greater in the 4LP specimen than the 1LP specimen, lead to more effective improvement of surface fatigue properties. The transition of the material response from elastic-plastic to almost purely elastic in 4LP specimens was initiated much earlier than it did in the No LP, and 1LP specimens. In addition to the surface fatigue properties, hardness and elastic modulus were also evaluated and compared.

Instrumented Nanoindentation Tests Applied to Bulk Metallic Materials: From Calibration Issue to Pile-Up Phenomena.

Instrumented nanoindentation tests have reached an effective level of theoretical and practical knowledge to become an interesting and useful tool for determining hardness, H, and local elasticity (reduced Young’s modulus), Er, of a variety of materials, from coatings and thin films to bulk metallic materials. Nanoindentation instruments are equipped with analysis software for raw data for hardness and reduced Young’s modulus evaluation, generally based on the Oliver and Pharr analysis method. On the other hand, it is widely known and recognized that prior data acquisition, a tip-dependent calibration procedure of compliance, and area function are needed. With this in view, an accurate and sound calibration protocol is here reported. Hardness and local elastic modulus is measured on different bulk metallic materials, showing the distinctive strengths of using nanoindentation. Finally, a local elastic-plastic phenomenon mostly induced by the nanoindentation tip on ductile metallic material (i.e., pile-up) is also reported and modelled. This manuscript is thus intended to favor and account for the importance of using the instrumented nanoindentation tests for H and Er measurements of metallic materials.

Eight-year Microtensile Bond Strength to Dentin and Interfacial Nanomechanical Properties of a One-step Adhesive.

To evaluate the microtensile bond strength (µTBS) of a one-step self-etch adhesive (1-SEA) to dentin and its interfacial nanomechanical properties after 8 years of water storage. Flat coronal dentin surfaces of extracted human third molars were bonded with a 1-SEA (Clearfil S3 Bond Plus, CS3+) and built up with a hybrid resin composite (Clearfil AP-X). After storage in water for 24 h or 8 years, non-trimmed stick-shaped specimens were fabricated from the central part of each bonded tooth and subjected to the µTBS test at a crosshead speed of 1.0 mm/min. Failure modes and the morphology of debonded interfaces were analyzed using a scanning electron microscope (SEM). In addition, the elastic modulus (E) and hardness (H) of the adhesive layer and the resin composite were determined by an instrumented nanoindentation test. The acquired µTBS, E, and H data were statistically analyzed using t-tests to examine the effect of storage time (α = 0.05). The 8-year µTBS was slightly lower than that after 24 h, but the difference was not significant (p = 0.123). The SEM observation of debonded surfaces after 8 years revealed extrusions and lacunas. E and H of the adhesive layer and the resin composite significantly decreased over the 8-year water storage (p < 0.001). Although 8 years of water storage did not decrease the µTBS of CS3+ significantly, the observed failure mode patterns and significantly decreased nanomechanical properties indicated resin degradation of the adhesive and the resin composite.

Development of deposition beam current dependent microstructure and nanomechanical properties in ZrO2-8wt%Y2O3 thermal barrier coatings produced by electron beam-physical vapor deposition technique

8 wt% yttria stabilized zirconia (8YSZ) coatings have been produced by changing the beam currents of electron beam-physical vapor deposition. The phase composition, microstructure, roughness, nanomechanical properties and residual stress were characterized and analyzed. The as-deposited 8YSZ coating was mainly composed of the metastable tetragonal phase. The enhancement of deposition beam current caused larger crystallite sizes and root mean square roughness, which confirmed by microscopic observations and atomic force microscopy technique. The nanomechanical properties were evaluated by an instrumented nanoindentation test. It was found that Young's modulus and hardness increase with the improvement of deposition beam current, which is due to the lower porosity. The thermal residual stresses generated in the deposition process was measured by two-dimension X-ray diffraction using sin2ψ technique. The measurement result indicated that residual stresses were dependent on the coating process.

Experimental Correlation of Mechanical Properties of the Ti-6Al-4V Alloy at Different Length Scales

This article focuses on a systematic study of a Ti-6Al-4V alloy in order to extensively characterize the main mechanical properties at the macro-, micro- and submicrometric length scale under different stress fields. Hardness, elastic modulus, true stress–strain curves and strain-hardening exponent are correlated with the intrinsic properties of the α- and β-phases that constitute this alloy. A systematic characterization process followed, considering the anisotropic effect on both orthogonal crystallographic directions, as well as determining the intrinsic properties for the α-phase. An analytical relationship was established between the flow stress determined under different stress fields, testing geometries and length scales, highlighting that it is possible to estimate flow stress under compression and/or tensile loading from the composite hardness value obtained by instrumented nanoindentation testing.

Characterization of W-Cr Metal Matrix Composite Coatings Reinforced with WC Particles Produced on Low-Carbon Steel Using Laser Processing of Precoat.

The paper presents the study results of laser processing of precoat applied on C30 steel. The precoat consisted of powder mixtures with a binder in the form of water glass. Tungsten powder, chromium, and tungsten carbide (WC) were used to produce the precoat. The laser processing was carried out using a Yb:YAG disc laser with a rated power of 1 kW. Constant producing parameters (power of laser beam, 600 W; laser beam scanning rate, 400 mm/min) were applied. Chemical composition of the precoat was a variable parameter in coating production. A mixture consisting of 50% W and 50% Cr as a metal matrix was prepared. Subsequently, WC particles in weight ratios of 25%, 50%, and 75% were added to matrix. As a result, W–Cr metal matrix composite coatings reinforced with WC particles were formed. This study focused on investigation of microstructure, microhardness, phase, and chemical composition as well as corrosion and wear resistance, of the newly formed W–Cr/WC coatings. An instrumented nanoindentation test was also used in this study. As a result of laser beam action, the newly formed coatings had an interesting microstructure and good properties which were improved in comparison to substrate material. It is anticipated that the resulting coatings, depending on the treatment parameters (e.g., W–Cr/WC powder mixture) used, can be successfully applied to metal forming or foundry tools.

Quantitative mapping of high modulus materials at the nanoscale: comparative study between atomic force microscopy and nanoindentation.

Local mechanical properties of submicron features are of particular interest due to their influence on macroscopic material performance and behaviour. This study is focused on local nanomechanical measurements, based on the latest Atomic Force Microscopy (AFM) mode, where the peak force set point is finely controlled at each pixel. After probe calibration, we evaluate the impact of spring constant of two AFM hand-crafted natural full diamond tips with steel cantilevers, used for mapping. Based on the fast capture of the cantilever deflection at each pixel and real time force curve analysis in the elastic region, AFM local measured contact moduli mappings of the silica beads (>50GPa) incorporated in an epoxy resin matrix, are compared with those determined using classical instrumented nanoindentation tests. Our analyses show that with the two AFM probes, without local residual deformation, the high moduli of the silica beads measured with this advanced AFM mode are within the standard deviation of the values determined by classical nanoindentation. LAY DESCRIPTION: The knowledge of material properties at the nanometer scale is a key parameter for well understanding and determining the behavior of material at macroscopic scale. In this paper, we compare two methods (an advanced mode and a classical one) based on the analysis of probes in interaction with the surface of studied material. We focus on a latest developed mode for determining local mechanical properties with a very high spatial resolution. For the advanced mode, we also consider two different hand-crafted probes. Our analyses show that with the high spatial resolution advanced mode, local mechanical properties are well determined. We also highlight the impact of the properties of the used probes for this advanced mode. In a final step, the power of the presented investigation lies in the fact that it does not modify the topography of the surface.

Effect of microstructure inhomogeneity on mechanical properties of different zones in TA15 electron beam welded joints

Abstract The effects of microstructure inhomogeneity on the mechanical properties of different zones in TA15 electron beam welded joints were investigated using a micromechanics-based finite element method. Considering the indentation size effect, the mechanical properties for constituent phases of the base metal (BM) and heat affected zone (HAZ) were determined by the instrumented nano-indentation test. The macroscopic mechanical properties of BM and HAZ obtained from the tensile test agree well with the numerical results. The incompatible deformation between the constituent phases tends to localize along the softer primary phase α where failure usually initiates in form of localized plastic strain. Compared with the BM, the mechanical properties of constituent phases in the HAZ differ substantially, leading to more serious strain localization behavior.

Improved microstructure heterogeneity and low-temperature fracture toughness of C–Mn weld metal through post weld heat treatment

The Crack Tip Opening Displacement (CTOD) test was used to investigate the effect of post-weld heat treatment (PWHT) on the low-temperature fracture toughness of C–Mn weld metal. The microstructure observations, instrumented nano-indentation test and microstructure-based finite element simulation were conducted to analyze the toughening mechanisms. The study found that the CTOD value increased significantly from 0.241 mm to 1.754 mm after PWHT. The hardness and strength between acicular ferrite (AF) and proeutectoid ferrite (PF) both get closer, which improves the extent of microstructure heterogeneity. The simulation indicated that the distributions of the strain and stress on AF and PF are homogenized with the improvement of microstructure coordination after PWHT, making the level of plastic strain localization within PF decreased and the stress concentration on the interphase of AF and PF lessened. As a result, the resistance of crack initiation and propagation increases, and the low-temperature fracture toughness is improved. Moreover, the dislocation densities in AF and PF both decrease, the dislocation morphology evolves from dislocation tangles into movable dislocation lines, and amounts of fine carbides precipitate and spheroidize, which also contribute to the toughening of microstructures.

Modification of physical-mechanical properties of NiTi alloy by electron beam in surface melting mode

This paper presents a research data on investigation of physical-mechanical properties of the surface of NiTi shape memory alloy after low-energy high-current pulsed electron beam (LEHCPEB) treatment in surface melting mode. Investigation of physical-mechanical and functional properties (Young’s modulus EIT, dynamic hardness HIT, plasticity characteristic δH, and parameter of shape recovery ratio η) was held by method of instrumented nanoindentation test. Our data suggest that after LEHCPEB treatment physical-mechanical properties of the surface layers of ~500 nm thickness change in depth from the surface without critical influence to the pseudoelastic properties of NiTi alloy.

Effect of hydrogen addition on the mechanical properties of Zr-based metallic glass

In this study, correlation between the softening phenomenon and free volume content in hydrogenated Zr57Al10Cu15.4Ni12.6Nb5 amorphous metal through instrumented nanoindentation tests and differential scanning calorimetry (DSC) analysis is reported. X-ray diffraction analyses revealed that hydrogen addition gives rise to the development of large void structures that facilitate the local atomic displacement. The mechanical characterization using nanoindentation showed that hydrogen addition may induce the softening of Zr-based metallic glasses even for high Zr content. The shear softening of Zr57Al10Cu15.4Ni12.6Nb5 ribbons is attributed to the weakness of atomic cohesion due to the squeezing and mobility of hydrogen atoms. The resistance to hydrogen embrittlement combined with high thermal stability may increases the possibilities of potential use of Zr57Al10Cu15.4Ni12.6Nb5 amorphous alloy as good metal membrane.

Multi-cycling instrumented nanoindentation of a Ti-23Nb-0.7Ta-2Zr-1.2O alloy in annealed condition

In this study, depth-dependent mechanical properties (i.e. hardness, elastic modulus, and indentation size effect) as well as strain rate sensitivity of a new class of titanium based alloys, Ti-23Nb-0.7Ta-2Zr-1.2O, are considered. To this end, local deformation micro-mechanisms of this alloy are investigated systematically through a constant-strain rate (CSR) instrumented nanoindentation testing technique. The CSR nanoindentation tests were performed at ambient (room) temperature with nominal indentation depths of 100–2000nm and strain rates of 0.005, 0.05, and 0.5s−1 using a Berkovich pyramidal indenter. Nanoindentation is a particularly reliable tool for studying elastic/plastic behavior of metallic alloys. Large strain gradients around the indenter should reveal and help clarify the thermally activated mechanisms contributing to the plastic deformation processes which can quantitatively be interpreted by examining the rate sensitivity index, m, and activation volume. Indentation results show that the strain rate sensitivity and activation volume, Burger’s vector times activation area, are depth-dependent phenomena revealing different controlling plastic deformation mechanisms.

Biological and Mechanical Effects of Micro-Nanostructured Titanium Surface on an Osteoblastic Cell Line In vitro and Osteointegration In vivo.

Hybrid micro-nanostructure implant surface was produced on titanium (Ti) surface by acid etching and anodic oxidation to improve the biological and mechanical properties. The biological properties of the micro-nanostructure were investigated by simulated body fluid (SBF) soaking test and MC3T3-E1 cell co-culture experiment. The cell proliferation, spreading, and bone sialoprotein (BSP) gene expression were examined by MTT, SEM, and reverse transcription-polymerase chain reaction (RT-PCR), respectively. In addition, the mechanical properties were evaluated by instrumented nanoindentation test and friction-wear test. Furthermore, the effect of the micro-nanostructure surface on implant osteointegration was examined by in vivo experiment. The results showed that the formation of bone-like apatite was accelerated on the micro-nanostructured Ti surface after immersion in simulated body fluid, and the proliferation, spreading, and BSP gene expression of the MC3T3-E1 cells were also upregulated on the modified surface. The micro-nanostructured Ti surface displayed decreased friction coefficient, stiffness value, and Young's modulus which were much closer to those of the cortical bone, compared to the polished Ti surface. This suggested much better mechanical match to the surrounding bone tissue of the micro-nanostructured Ti surface. Furthermore, the in vivo animal experiment showed that after implantation in the rat femora, the micro-nanostructure surface displayed higher bonding strength between bone tissues and implant; hematoxylin and eosin (H&E) staining suggested that much compact osteoid tissue was observed at the interface of Micro-nano-Ti-bone than polished Ti-bone interface after implantation. Based on these results mentioned above, it was concluded that the improved biological and mechanical properties of the micro-nanostructure endowed Ti surface with good biocompatibility and better osteointegration, implying the enlarged application of the micro-nanostructure surface Ti implants in future.

Computational prediction of mechanical properties of a C-Mn weld metal based on the microstructures and micromechanical properties

The effects of the mechanical properties and microstructure of grain boundary ferrite (GF) and acicular ferrite (AF) on the tensile properties of C-Mn steel weld metal were investigated using a micromechanics-based finite element method. Considering indentation size effect, the uniaxial elastic-plastic properties for the constituent phases were determined by the instrumented nano-indentation test. Actual microstructures of the weld deposited metal obtained by optical microscopy were used as the representative volume elements (RVEs) in the modelling. Periodic boundary condition was used in the simulation to quantitatively evaluate the strain distribution due to the microstructure-level heterogeneity in terms of the mechanical properties and the distribution of the individual grain boundary ferrite and acicular ferrite. The macroscopic mechanical properties of the weld metal obtained from the tensile test were predicted well by the numerical results. It is found that the incompatible deformation between the harder acicular ferrite and the softer grain boundary ferrite tends to localize along grain boundary ferrite where failure usually initiate in the form of localized plastic strain as observed in the experiment.

Improvement of biological and mechanical properties of titanium surface byanodicoxidation.

A homogeneous and uniform array of nanotubes with a diameter of about 70nm was produced on titanium (Ti) surface by anodic oxidation. The wall thickness of the nanotubes was around 20nm, and the depth was about 200nm. The biological properties of the anodized Ti surface were investigated by simulated body fluid (SBF) soaking test and in vitro cell culture test. The mechanical properties were evaluated by instrumented nanoindentation test and friction-wear test. The results showed that the anodized Ti surface can induce the formation of bone-like apatite after immersion in SBF for four weeks, enhance cell adhesion, proliferation and gene expression, it also showed decreased friction coefficient, similar stiffness and Young's modulus to those of the cortical bone. Based on these results, it can be concluded that anodic oxidation endowed the Ti surface with improved biological and mechanical properties, which was attributed to the formation of nanostructured surface.

Infrared spectroscopy, nano-mechanical properties, and scratch resistance of esthetic orthodontic coated archwires

To evaluate the material composition, mechanical properties (hardness and elastic modulus), and scratch resistance of the coating of four commercialized esthetic orthodontic archwires. The coating composition of esthetic archwires was assessed by Fourier-transform infrared spectroscopy (FTIR). Coating hardness and elastic modulus were analyzed with instrumented nano-indentation tests. Scratch resistance of coatings was evaluated by scratch test. Coating micromorphologic characteristics after scratch tests were observed in a scanning electron microscope. Statistical differences were investigated using analysis of variance and Tukey post hoc test. The FTIR results indicate that all analyzed coatings were markedly characterized by the benzene peak at about 1500 cm(-1). The coating hardness and elastic modulus average values ranged from 0.17 to 0.23 GPa and from 5.0 to 7.6 GPa, respectively. Scratch test showed a high coating elasticity after load removal with elastic recoveries >60%, but different failure features could be observed along the scratches. The coatings of esthetic archwires evaluated are probably a composite of polyester and polytetrafluoroethylene. Delamination, crack propagation, and debris generation could be observed along the coating scratches and could influence its durability in the oral environment.

A review of recent research on nanoindentation of polymer composites and their constituents

Abstract Although instrumented nanoindentation testing has been used to characterize the mechanical properties of materials since the 1970s, the vast majority of the research involving nanoindentation of polymer composite materials and their constituents has been done since the early 2000s. The objective of this article is to review recent archival journal publications dealing with nanoindentation of polymer composites and their constituents, with emphasis on publications that have appeared since 2000. Developments in experimental nanoindentation, numerical simulation of nanoindentation and combined experimental/numerical nanoindentation techniques will be discussed. The review will show that nanoindentation has been particularly useful in the characterization of polymer matrix materials, fibers, particles and other constituent materials in polymer composites. Studies of both indirect and direct measurement of elastic, viscoelastic and dynamic mechanical properties of constituents by nanoindentation are reviewed, along with nanomechanical characterization of composite interface and interphase regions and comparisons of bulk and in situ properties measured by nanoindentation. Finally, some general conclusions and recommendations for future studies are offered.