Series Of Nanoindentation Tests Research Articles

Stochastic nature of incipient plasticity in a body-centered cubic medium-entropy alloy

The stochastic nature of the small-scale incipient plasticity (i.e., “pop-in” behavior manifested as a sudden displacement excursion in the load-displacement curves) in a single grain of the body-centered cubic NbTiZr medium-entropy alloy is explored through a series of nanoindentation tests with three spherical tips having different radii (1.8, 3.4, and 8.2 μm). The maximum shear stress underneath the indenter shows distinct distributions depending on the tip radius, wherein both a narrow high-stress regime and a broad low-stress regime are observed. By recourse to deconvolution of the data and detailed statistical analysis, the two regimes were found to be dominated by homogeneous and heterogeneous yielding mechanisms, respectively. Upon hydrogen charging, the tip radius dependence is sustained, but the fraction of heterogeneous yielding is enhanced, which is due to the hydrogen's effect in assisting defect formation. The suggested scenarios for how the mechanisms are affected by the stressed volume (or tip radius) and hydrogen-induced structural changes were confirmed by direct observations of the deformation behavior underneath the indenter with cross-sectional transmission electron microscopy made on post-pop-in samples.

Impacts of E-Beam Irradiation on Polycrystalline Metals in Both Bulk and Thin Film Forms

This study aims to explore the impact of e-beam irradiation on the mechanical and structural characteristics of four different polycrystalline metals (Ni, Cr, V, and Ti), in both bulk and thin film forms. Thin metal films are fabricated using magnetron sputtering. The primary goal is to identify suitable metal candidates for growing thin films, which could serve as exit windows for e-beam accelerators. This selection is based on their properties, power dissipation capabilities, and the effects of irradiation on mechanical attributes such as hardness, ductility, defect density, and strength.For the bulk polycrystalline metal samples, a series of nanoindentation tests has been conducted before and after e-beam irradiation to investigate changes in hardness and elastic modulus. Additionally, to compare performance with the bulk samples, thin metal films are subjected to the same procedure before and after irradiation, allowing for the evaluation of film hardness, moduli, and creep properties. Results indicate that irradiated bulk samples of Ni, Cr, and V become harder, whereas Ti experiences softening. There is no significant irradiation effect on modulus for all for polycrystalline metal samples. To understand the underlying reasons behind these effects, both the fabricated metal films and bulk metal samples undergo comprehensive characterization tests for their microstructural properties, elastic behavior, and chemical composition. This involves the utilization of SEM with EDS, FESEM and AFM to analyze microstructure and surface attributes of the films, followed by X-ray diffraction to gain insight into film morphology and lattice orientation.

Experimental study of micromechanical properties alterations of shale matrix treated by ScCO2-Water saturation using nanoindentation tests

Supercritical CO2 (ScCO2) fracturing is a preferred alternative to water-based fracturing for stimulation of the shale gas reservoirs, and also promotes CO2 geological sequestration. The injected ScCO2 will interact with shale minerals and then induce changes in rock matrix micromechanics. In this study, a series of nanoindentation tests was conducted on the shale sample to investigate the effects of ScCO2-water treatment on shale matrix micromechanics. X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy-dispersive spectroscopy (EDS) were used to analyze the changing mechanisms of micromechanical properties. The dispersion of grid nanoindentation data of different minerals indicates the strong heterogeneity of shale’ micromechanical properties. After ScCO2-water treatment, different shale minerals experienced different reductions of Er and H because of the dissolution induced the alterations in crystal structures, and their contents also altered in varying degrees. The values of hf/hm and Wp/Wt can be combined with the hysteresis loops enclosed by the P-h curves to determine the dominant work and irreversible deformation that produced in the process of indentation. According to the observation of indentation morphology, unlike other minerals, considerable micro-fractures were generated in clay minerals, which is correlated to the significant plastic deformation and the layered crystal structure.

Antagonist softening and hardening effects of hydrogen investigated using nanoindentation on cyclically pre-strained nickel single crystal

Since hydrogen-plasticity interaction is a key feature in the study of hydrogen embrittlement, a series of nanoindentation tests were carried out to evaluate the possible impact of hydrogen on the dislocation structures formed during cyclic pre-straining of nickel single crystal. Ex-situ nanoindentation and in-situ electrochemical nanoindentation tests were performed on cyclically pre-strained nickel single crystal and nickel-hydrogen systems to characterise the change in the reduced modulus and hardness. Although the reduced modulus was less affected by the conditions explored, the change in hardness highlights the competition between the hardening and softening processes associated with hydrogen. When hydrogen was pre-charged before the cyclic tests, the dislocation microstructures were softer than those induced by cyclic tests in hydrogen-free metals. In contrast, when in-situ electrochemical nanoindentation tests were performed, the hydrogen ingress on cyclically strained nickel single crystal induced a hardening of the microstructure. This effect was due to a pinning effect by the solute on the dislocations. The competition between these processes is discussed in terms of hydrogen and vacancy concentrations.

Continuous multi-cycle nanoindentation behavior of a gradient nanostructured metastable β titanium alloy fabricated by rotationally accelerated shot peening

A novel gradient nanostructured structure fabricated by rotationally accelerated shot peening (RASP) has been proven useful in the enhancement of strength and ductility. In this study, a series of nanoindentation tests using continuous multi-cycle (CMC) mode are first used to characterize the nanoindentation behavior of the RASP-processed metastable β titanium alloy with a gradient nanostructured structure. The experimental results indicate that indentation depth and grain size paly a dominant role in the nanoindentation behavior. Inverse indentation size effect (ISE) on the hardness occurs at shallow indentation depth (<50 nm), which is due to the hardening behavior caused by the effect of grain boundaries. While ISE occurs at the indentation depth ranging from 50 nm to 225 nm, then ISE disappears in deep indentation depth (>225 nm), which is dominated by the known strain gradient mechanism. The hardness, reduced module and back stress decrease from the treated surface with a nanostructured grain size of 20 nm to the center zone with a coarse grain size of 216 μm. For the RASP-processed sample, the fine grain zone exhibits a more pronounced inverse and normal ISEs than these of the coarse grain zone. In addition, the Bauschinger effect and back stress strengthening mechanism are also firstly used to explain the variation of gradient micro-mechanical properties.

Deformation mechanics of sputtered copper layers during nanoindentation tests

The mechanical properties of the thin sputtered copper layer on the SiO2-coated silicon substrate is needed as part of the requirements in quantifying the reliability of the Through-Silicon Via (TSV) interconnects. In this respect, two different Cu coating layers, each from the different sputtering process, are examined. A series of nanoindentation tests are performed on the Cu coating layer samples with indenter speeds ranging from 80 to 400 nm/s, and the indentation depths of 320 nm. The properties of elastic modulus, hardness and the hardening behavior of the Cu coating layers have been quantified. Results show that the coating with higher contamination of C at 8.41 wt. % displays a significant hardening and a peak load level, as reflected in the measured nanoindentation load-displacement curves. However, insignificant effect of the applied probe displacement speeds up to 400 nm/s on the resulting properties of the coating is registered. The Johnson-Cook constitutive equation adequately describes the strain rate-dependent hardening behavior of the Cu coating layer.

Identifying the origin of strain rate sensitivity in a high entropy bulk metallic glass

A series of nanoindentation tests were performed on a high entropy bulk metallic glass (HE-BMG). At low peak-loads, high positive strain rate sensitivity was found. But increasing the peak-load, the sensitivity of hardness to strain rate decreased dramatically. At low peak-loads, sluggish diffusion in HE-BMG significantly impedes atomic arrangement in the shear yielding events, whereas at high peak-loads, the shear-band deformation is dominated by the shear front triggered events. The work showed the origin of strain rate sensitivity in HE-BMGs and might help for tailoring the mechanical properties.

Characterization of the ageing of an epoxy resin using high temperature nanoindentation

This article aims to understand better the mechanical properties and behavior of organic matrix composite materials under elevated temperature conditions. Two specific specimens of cured RTM6 epoxy resin are tested with DMA analysis: one being unaged and the other one aged for 5000 h at 130 °C under ambient air. Anti-plasticization effects seem to occur on aged resin. Series of nano-indentation tests are carried out from the surface to the core of the sample so as to measure gradient properties of the resin, at temperatures up to 150 °C using a high temperature indentation machine prototype. Thermo-oxidation phenomena involve oxidized layer formation during thermal ageing of the epoxy resin which is characterized through measurements of indentation Young’s modulus. After aged treatment, the variation of Young’s modulus of the oxidized layer at the surface of the sample is not clearly affected by the increasing test temperature whereas Young’s modulus of the core of the sample is decreasing significantly with the temperature test as on unaged epoxy resin. Thus, asymptotic growing of the oxidized layer is then confirmed.

Indentation hardness and modulus of electrochemically deposited triple protective-decorative Cu-Ni-Cr system

With respect to the corrosion-protective and decorative characteristics of the Cu-Ni-Cr systems the advance of the technology resulted in products covering the required technical and economic norms and indicators. However, the knowledge about the mechanical characteristics such as elastic and plastic properties of the individual layers and the whole multilayered system is still sparse. The objective of this study is to obtain by means of nanoindentation experiments the mechanical characteristics of standard triple Cu-Ni-Cr coating system whose morphology, structure, texture, composition, and the copper-, nickel- and chrome-layer thickness are predefined. A series of nanoindentation tests in vertical direction to the layered coating and in the lateral direction (along a vertical cut) is analyzed to assess the changes of the mechanical properties of the investigated system in depth and along the layer as well as at layer-to-layer and layer-to-substrate interfaces.

Testing effects on hardness of a Zr-based metallic glass under nanoindentation

A series of nanoindentation tests were performed on a Zr-based bulk metallic glass at different peak-loads and strain rates. It is observed that the strain rate sensitivity index gradually decreases from positive to almost zero with increasing peak-load. Furthermore, at a fixed strain rate, the indentation hardness firstly shows a dramatic reduction and then becomes stable with increasing peak-load. These observations can be well understood in the framework of the activation and the accumulation of free volume via shear transformation zones. The current work may provide a practical way to tailor the hardness of the metallic glass.

Indentation recovery in GdPO4 and observation of deformation twinning

A series of nanoindentation tests on both single and polycrystalline specimens of a monazite rare-earth orthophosphate, GdPO4, revealed frequent observation of anomalous unloading behavior with a large degree of recovery, where previously this behavior had only been observed in xenotime-structure rare-earth orthophosphates. An indentation site in the polycrystalline sample was examined using TEM to identify the deformation mechanism responsible for recovery. The presence of a twin along the (100) orientation, along with a series of stacking faults contained within the deformation site, provide evidence that the mechanism of recovery in GdPO4 is the collapse of deformation twins during unloading.

Experimental investigation and FE simulation of nano-indentation on Al–Al2O3 nanocomposites

The main purpose of this paper is to investigate the nano-indentation test method and validation of its finite element simulation (FE). In the first stage, a series of nano-indentation tests were performed on the Al–Al2O3 nanocomposites by using Triboscope system and Berkovich indenter to obtain its hardness. To prepare the Al–Al2O3 nanocomposites, a pre-alloyed powder was milled in a planetary ball mill followed by cold compaction and sintering. Then in the second stage, the nano-indentation process on Al–Al2O3 nanocomposites was simulated by a 2D axisymmetric finite element (FE) model. Using the same projected area to depth function as the standard Berkovich indenter, a conical indenter with half angle 70.3° was considered in simulations. The results showed that, a homogenous distribution of the nano-sized Al2O3 particles in the Al matrix was achieved after 20h milling. The young’s modulus, yield strength, and hardness of the produced nanocomposite were increased than the pure aluminum. The results of load–displacement curve obtained from the finite element simulation of non-sharp indenter showed a good agreement with that obtained from the nano-indentation experiment. The scatter of the FE results than the experimental results in the pure aluminum is smaller than that observed for the nanocomposite.

Determination of Stress-Strain Constitutive Relation of Echelle Grating Al Film by Nanoindentation Test and Simulation

For the research on elastic-plastic deformation characteristics of the echelle grating in the mechanical ruling depth range, a series of nanoindentation tests are completed about the deposited Al film of available echelle grating with a Berkovich indenter on a CSM nanoindentation instrument. Then a finite element analysis of the nanoindentation process is studied with an orthogonal experiment method for a series of given parameters containing the yield stress and strain-hardening exponent. The optimum combinations of yield stress and strain-hardening exponent are 200MPa and 0.1, which are got by the objective of the least absolute value of maximum loads deviation between the indentation test and the finite element analysis. Finally the elastic-plastic stress-strain curve of power function of the Al film is represented with the difference analysis from the orthogonal simulations.

Fabrication and mechanical property prediction of carbon nanotube reinforced Aluminum nanocomposites

The use of carbon nanotubes (CNTs) in nanotechnology and leading industries is of extreme importance due to its various applications. One such application is producing Aluminum reinforced nanocomposites which may find applications in the aerospace and automobile industries. Scientists and engineers have, recently, concentrated increasing attention on the manufacturing and modeling of such materials. This paper deals with preparing Carbon Nanotube Reinforced Aluminum Nanocomposite (CNRAN) and predicting its mechanical and surface properties using the finite element method (FEM). To prepare the reinforced nanocomposite, a pre-alloyed powder was milled in a planetary ball mill under the argon atmosphere. Multi-wall carbon nanotubes (MWCNTs) were then added to the powder in a particular procedure. Next, a finite element model consisting of MWCNTs as the fibers and Aluminum as the matrix was constructed. A series of nano-indentation tests were carried out to obtain the mechanical and surface properties of the constructed material. The finite element models were then used to predict the results obtained from real indentation tests. The predicted hardness and elastic modulus from the FE model show good agreement with experimental findings.

Nanoindentation of TiO2 thin films with different microstructures

A series of nanoindentation tests has been carried out with TiO2 films produced by physical vapour deposition (PVD) under different conditions. Films with different microstructures and crystallographic structures have been prepared by changing experimental parameters such as the temperature of the substrate, the deposition angle (by the so-called glancing angle physical vapour deposition, GAPVD) or by exposing the growing film to a beam of accelerated ions. The obtained results of hardness and Young's modulus depict interesting correlations with the microstructure and structure of the films providing a general picture for the relationships between these characteristics and their mechanical properties. Different models have been used to extract Young's modulus and hardness parameters from the experimental nanoindentation curves. The obtained results are critically discussed to ascertain the ranges of validity of each procedure according to the type of sample investigated.

Mechanical Characterization of Cellulosic Thecal Plates in Dinoflagellates by Nanoindentation

Dinoflagellates constitute an important group of microorganisms. Symbiotic dinoflagellates are responsible for the primary production of coral reef ecosystems and the phenomenon of their demise is known as "coral bleaching." Blooming of the planktonic dinoflagellates is the major cause of "red tides." Many dinoflagellates have prominent membrane-bound thecal plates at their cell cortices. These thecal plates have high cellulose content and are biologically fabricated into various shapes. However, the mechanical properties of theca have not previously been characterized; understanding these properties, including hardness and elastic modulus, will give insights into the ecological significance and biotechnological potential of bio-fabricated structures. A series of nanoindentation tests were performed on various locations of cellulosic thecal plates isolated from the dinoflagellates Alexandrium catenella and Lingulodinium polyedrum. Despite having transparent properties, thecal plates possess mechanical properties comparable to softwood cell walls, implicating their role as a protective cell covering. Consistent measurements were obtained when indentation was performed at various locations, which contrasts with the high variability of cellulose microfibers from plant sources. The present study demonstrated the novel properties of this potential new source of cellulose.

Mechanical Characterization of Cellulosic Thecal Plates in Dinoflagellates by Nanoindentation

Dinoflagellates constitute an important group of microorganisms. Symbiotic dinoflagellates are responsible for the primary production of coral reef ecosystems and the phenomenon of their demise is known as "coral bleaching." Blooming of the planktonic dinoflagellates is the major cause of "red tides." Many dinoflagellates have prominent membrane-bound thecal plates at their cell cortices. These thecal plates have high cellulose content and are biologically fabricated into various shapes. However, the mechanical properties of theca have not previously been characterized; understanding these properties, including hardness and elastic modulus, will give insights into the ecological significance and biotechnological potential of bio-fabricated structures. A series of nanoindentation tests were performed on various locations of cellulosic thecal plates isolated from the dinoflagellates Alexandrium catenella and Lingulodinium polyedrum.2 Despite having transparent properties, thecal plates possess mechanical properties comparable to softwood cell walls, implicating their role as a protective cell covering. Consistent measurements were obtained when indentation was performed at various locations, which contrasts with the high variability of cellulose microfibers from plant sources. The present study demonstrated the novel properties of this potential new source of cellulose.

The influence of machining induced residual stress and phase transformation on the measurement of subsurface mechanical behavior using nanoindentation

Surface integrity of machined components is critical for product performance in service. Due to the very small scale of the subsurface, nanoindentation can be used to determine the surface/subsurface mechanical properties. However, the test data may be significantly influenced by machining induced residual stresses, strain hardening, size effect, and microstructures. A fundamental relationship between these factors and mechanical behavior in the subsurface is yet to be understood. Furthermore, it is not clear if residual stress in the subsurface can be determined from nanoindentation data. This study focuses on the basic relationships between nanohardness, residual stress, and microstructure. A series of nanoindentation tests were conducted on the cross-sections of the machined samples with distinct surface integrity induced by hard turning, grinding, and honing. It was found that white layer increases nanohardness and dark layer decreases nanohardness in subsurface, while strain hardening only slightly increases subsurface hardness. The research results indicate that residual stress nature can be qualitatively determined by the shape of a load–displacement curve and the characteristic parameters such as slope at initial loading, total depth, residual depth, and the ratio of residual depth to total depth. Residual stress affects the load–displacement curve shape at the onset of material yielding. Microstructure changes make a significant difference on the characteristics of a load–displacement curve, while strain hardening exerts slight influence. The effect of residual stress influence on indentation depth can be explained based on the Mohr's circle.

Investigation of Mechanical Properties of Diatom Frustules Using Nanoindentation

Diatom frustules have been identified as potential candidate materials for nanotechnology applications. However, for successful engineering applications, their mechanical properties must be fully determined. Toward this end, indentation hardness and elastic properties frustules of the centric diatom Coscinodiscus concinnus were evaluated using nanoindentation. A series of nanoindentation tests were performed on the outer surfaces of frustules at various locations. Analysis of the indentations revealed that the Young's modulus and hardness values appear to be strongly dependent on the location of the indentation. The modulus varied from 0.591 to 2.768 GPa in the center and 0.347 to 2.446 GPa at locations away from the center. Similarly, frustule hardness varied between 0.033 and 0.116 GPa in the center and between 0.076 and 0.12 GPa away from the center. Another series of nanoindentation tests were performed on the frustules (positioned in both concave and convex orientations) at various locations to analyze the failure mode. It was found that the failure modes in each of the orientations were also drastically different. In convex orientation, cracks initiated along the sharp edges of the indentation were followed by circular ring cracks, whereas in concave orientation only cracks along the sharp edges (corresponding to the three edges of the indenter) were revealed. The porosity and the nonplanar nature of the frustules make it difficult to extract the mechanical properties accurately at each location.