Results Of Nanoindentation Experiments Research Articles

Effect of the structure and volume fraction of nanophase on the mechanical properties of (FeNi)86B14 amorphous nanocrystalline alloys

The influence of precipitated nanophases on the mechanical properties of Fe-based amorphous nanocrystalline alloys is an urgent issue to be explored. Two amorphous nanocrystalline alloys, i.e., (Fe0.9Ni0.1)86B14 and (Fe0.7Ni0.3)86B14 containing nanophase of the body-centered cubic and face-centered cubic structures, respectively, were selected to investigate the effect of the structure and volume fraction of nanophase on their mechanical properties. The results of nanoindentation experiments and the calculation of the volume and size of the shear transition zone reveal that the two alloys show different mechanical properties. When the volume fraction of the nanophase in (Fe0.9Ni0.1)86B14 is larger than 50%, the elastic modulus is increased suddenly and the volume and size of the shear transition zone is decreased dramatically, while no dramatic change occurs in (Fe0.7Ni0.3)86B14. Moreover, it was found by using molecular dynamics simulations that the main reason for these abnormal mechanical properties is the change of cluster type in the system due to the incorporation of nanophases with different structures.

Nano-indentation deformation behavior of heavy ion irradiated reduced activation ferritic/martensitic (RAFM) steels

The Nano-indentation deformation behavior of the heavy ion irradiated RAFMs is investigated in the present work. Specimens of the CLF-1 steel were irradiated with 123.4 MeV 20Ne ion at both -50 °C and 400 °C, respectively, to achieve a mean displacement damage level of 0.15 dpa. A quasi-uniform distribution of the displacement damage was produced in the specimens by utilizing an energy degrader at the irradiation chamber. The results of nano-indentation experiments indicate that during the loading stage, the irradiated materials exhibit a lower strain rate, but during the holding stage after reaching the maximum load, the irradiated materials show a higher strain rate than the un-irradiated material. Transmission electron microscopy observation showed that the low-temperature irradiation produced a high density of irradiation-induced dislocation loops, which impeded the glide of dislocation lines during the loading stage. However, as the load increases gradually to the holding stage, the dislocation lines can overcome the pinning by the dislocation loops. The strain that did not occur due to the pinned effect of the dislocation loops in the loading stage was released during the holding stage, resulting in a higher strain rate in the irradiated specimen during the holding stage. Based on the Peierls mechanism, a quantitative relationship between the number density of the irradiation-induced dislocation loops and the strain rate during the holding stage was established. The calculated results agree well with the experimentally obtained strain rate during the holding stage.

Microstructure and properties of SLM-Hastelloy X alloy after different hot isostatic pressing + heat treatment

In this paper, the microstructure and mechanical properties of SLM-Hastelloy X alloy treated by hot isostatic pressing and heat treatment (HIP + HT) were studied. The microscopic characteristics show that the grains are transformed into equiaxed grains after different HIP + HT. The precipitates of M23C6 carbide are distributed in grains and grains boundaries. The number of precipitates in grains decreased during the increase of the temperature of the heat treatment. The results of nano-indentation experiments show that the average elastic modulus first increases and decreases with the growth of heat treatment temperature, and the average hardness fluctuates significantly in increasing the temperature of post-treatment. When the heat treatment temperature reaches the maximum value, the minimum value of average hardness is obtained of 2.46 GPa. The Vickers hardness decreases from 204HV0.5 to 188HV0.5 with the increase of heat treatment temperature. According to tensile tests, a good combination of strength and plastic properties of SLM-Hastelloy X alloy after HIP + HT treatment is obtained except for HIP+1150 °C/h.

Quantitative micro mechanical and pore structural characterisation of coal before and after freezing

Altering the coal pore spaces and mechanical properties is of great significance in increasing the production of coalbed methane. Freezing has been used to change the pore structure in coal beds. This study uses micro computed tomography (μCT) and nanoindentation experiments to study the microstructure of coal samples before and after being frozen by liquid nitrogen. The change of porosity is analysed layer-by-layer. The change of volume fraction and quantity of pores with different diameters are counted and analysed. Pore network model is used to analyse the pores structural connectivity and permeability. In addition, the changes of elastic modulus and hardness are analysed based on nanoindentation experiments, and the relationship between the two is studied. The μCT results showed that the porosity of coal samples increases to varying degrees after freezing, with the maximum value being 41.23% and the minimum value being 17.93%. After coal is frozen, the volume fraction of large pores (>10 μm) increases, and the number of pores with the diameter less than 5 μm decreases. The results of nanoindentation experiments showed that elastic modulus of three coal samples increases after freezing, while one decreases. In addition, there is a positive correlation between the elastic modulus and hardness of coal samples.

Interrelationship between hydrogen and α′-martensite of SUS 304 austenitic stainless steel revealed by tensile tests

The hydrogen embrittlement (HE) behavior of SUS 304 austenitic stainless steel (ASS) was investigated by in-situ scanning electron microscope（SEM）observations combined with electron backscatter diffraction (EBSD), slow strain rate tensile (SSRT) tests and nanoindentation techniques. The specimens for in-situ tensile tests were cathodic pre-charged with hydrogen for 0 and 96 hours. The in-situ EBSD analysis and SEM observation indicated that α′-martensite was generated along the twin boundaries during the tensile process of 304 ASS, and the pre-charged hydrogen promoted the α′-martensite transformation. In turn, the tensile sample was first stretched by 20% to produce α′-martensite and then hydrogen charged, and the SSRT tests showed that the pre-existing α′-martensite increased the hydrogen diffusion depth and HE sensitivity of the experimental steels. The results of nanoindentation experiments showed that hydrogen was captured by the grain boundary as hydrogen trap, which slightly reduced the average hardness of the material owing to the “elastic shielding effect” of hydrogen, but because of the general solid solution hardening mechanisms and the martensitic transformation promoted by hydrogen, the role of hydrogen in hardness reducing cannot be overestimated. The presence of α′-martensite in 304 ASS determined the fracture mechanism during the subsequent tensile process. If the sample had no α′-martensite at the time of hydrogen charging, the fracture mode was transgranular fracture with the cracks initiating and propagating along the twin boundaries. But if the sample contained a certain amount of α′-martensite when hydrogen charging was carried out, the fracture mode was intergranular fracture with cracks initiating along the twin boundaries but propagating along the grain boundaries.

The Effects of Substrate Bias on the Properties of HfC Coatings Deposited by RF Magnetron Sputtering

In the paper, by using radio frequency (RF) magnetron sputter technology, the HfC coating grew on a 316L stainless steel substrate in an Ar atmosphere at various substrate bias voltages from 0 to −200 V. From the X-ray diffraction (XRD) and transmission electron microscopy (TEM) experiments, the HfC coatings were well crystallized and (111) preferential growth had been successfully obtained by controlling bias voltage at −200 V. Nanoindentation experimental results for the prepared HfC coatings indicated that they possessed the maximum nanohardness due to the formation of the (111) orientation. The results of electrochemical measurements displayed that 316L stainless steel (316L) coated with the HfC coatings had better corrosion resistance than bare 316L. With the bias voltage increasing to −200 V, adhesion of the 316L substrate with the HfC coating could be greatly improved, as well as corrosion resistance. The antithrombogenicity of the HfC coatings was identified by platelet adhesive and hemolytic ratio assay in vitro. It was shown that the hemocompatibility of coated 316L had been improved greatly compared with bare 316L and the HfC coatings possessed better antithrombogenicity with the bias voltage elevating above −150 V.

Effect of Indentation Load on Raman Spectra of the InP Crystal

In this study, the Raman spectroscopy method was used for examination of structural changes made on the (001) surface of InP crystal using nanoindentation with a maximum load up to 100 mN. The presence of the metallic, high-pressure B1 phase of InP was not confirmed. Consequently, this result indicates a dislocation-governed mechanism of nanoindentation induced incipient plasticity of InP crystal. An increase in the maximum load caused a decrease in the width as well as a shift in the main Raman bands (LO, TO) into lower frequencies. Our findings were explained under assumption that an increase in the maximum load causes a decrease in both the dislocation density and the stresses in the vicinity of residual impressions. This unexpected relationship was confirmed by results of nanoindentation experiments.

Effect of doping on nanoindentation induced incipient plasticity in InP crystal

This article is concerned with incipient plasticity in an InP crystal studied by nanoindentation experiments and ab initio simulations. We consider dislocation-nucleation phenomena and pressure-induced phase transformation to be the alternative mechanisms that govern the elastic-plastic transition displayed by the InP crystal. The ab initio calculations have shown that S- and Zn-doping of the low-pressure zinc blende structure of InP decreases the pressure of phase transformation of the rock-salt structure. The nanoindentation examination of undoped as well as S- and Zn-doped crystals of (001) and (111) orientation revealed an increase in contact pressure at the onset of plastic behavior (pop-in) for doped specimens. As they are contrary to the outcomes of the ab initio simulations, the results of nanoindentation experiments point toward dislocation nucleation as an origin of InP incipient plasticity. Additional investigations were performed on an undoped as well as Si-doped GaAs crystal, which showed that the contact pressure at the pop-in event takes a lower value for the Si-doped sample than the undoped sample. This result is in contrast to the case of the InP crystal displaying phase transformation-steered incipient plasticity of GaAs. Our investigations exhibit the complexity of the semiconductor’s nanodeformation simultaneously providing a convenient way to identify its incipient plasticity mechanism.

Yield Strength Improvement of an Al-6063 Alloy by Applying a Novel Combination of Cold Working and Heat Treatments for Die Casting of Plastic Parts

In this work, a novel combination of designed heat treatments and cold work performed on Al-6063 alloy was proposed. The consumption of aluminium and its alloys in the automotive and aeronautic industries has increased over the past few years, in the same way, as the consumption of material for manufacturing moulds for casting of plastic parts and dies for plastics and metals. Then, it is important to find a low-cost alternative to maximise the mechanical properties of aluminium, with a negligible effect on the ductility of the alloy, which is important due to thermal and mechanical fatigue on mould and dies. It is well known that precipitation hardening increases the mechanical and yield strength of aluminium alloys with a major ductility loss. However, the developed methodology consists of a solution heat treatment, followed by cold working (strain hardening), and lastly a heat treatment (precipitation hardening and stress reliever) to produce Al 6063 aluminium alloys with enhanced mechanical strength and with a negligible ductility loss. The proposed methodology increases around 23.45% of the tensile and yield strength, with a ductility reduction of less than 1.5% in the elastic materials region. The experimental tensile testing results are correlated with nanoindentation experimental results in order to confirm that the level of cold working is directly proportional to mechanical strength levels by two different characterisation techniques at a macro- and nanoscales, respectively.

Geomechanical Upscaling Methods: Comparison and Verification via 3D Printing

Understanding geomechanical properties of rocks at multiple scales is critical and relevant in various disciplines including civil, mining, petroleum and geological engineering. Several upscaling frameworks were proposed to model elastic properties of common rock types from micro to macroscale, considering the heterogeneity and anisotropy in the samples. However, direct comparison of the results from different upscaling methods remains limited, which can question their accuracy in laboratory experiments. Extreme heterogeneity of natural rocks that arises from various existing components in them adds complexity to verifying the accuracy of these upscaling methods. Therefore, experimental validation of various upscaling methods is performed by creating simple component materials, which is, in this study, examining the predicted macroscale geomechanical properties of 3D printed rocks. Nanoindentation data were first captured from 3D printed gypsum powder and binder rock fragments followed by, triaxial compression tests on similar cylindrical core plugs to acquire modulus values in micro and macroscale respectively. Mori-Tanaka (MT) scheme, Self-Consistent Scheme (SCS) method and Differential Effective Medium (DEM) theory were used to estimate Young’s modulus in macroscale based on the results of nanoindentation experiments. The comparison demonstrated that M-T and SCS methods would provide us with more comparable results than DEM method. In addition, the potential applications of 3D printed rocks were also discussed regarding rock physics and the geomechanics area in petroleum engineering and geosciences.

Effect of topology and material properties on the imprint quality of the femtosecond-laser-induced surface structures

Femtosecond laser surface processing (FLSP) is a technique that can be used to modify surfaces imparting many desirable properties, such as an improved wettability, heat transfer, and drag reduction. The morphology of the FLSP surface along with surface chemistry is critical factors that strongly influences the wetting behavior of surfaces produced. Reproducing the FLSP original surface over a large area in an economic manner is a challenge. In this paper, imprinting the FLSP surface on oxygen-free copper is investigated. Based on the topology of an FLSP titanium surface, a model has been established to investigate the topology of the mounds, which is defined by the roughness and period between the self-organized structures. This topology affects the imprint quality indicated by the plastic deformation in the blank and is defined as the target material specimen. Both oxygen-free copper and stainless steel 304 were used as blank target material in this study and represent both soft and hard material specimens. The stress–displacement relationship was used to determine the sensitivity of imprint parameters. The imprint model was verified by comparing an equivalent imprint model with nanoindentation experimental results. The model results showed that the die’s morphology, in particular the die roughness-to-period ratio (referring to the peak-to-valley height and the peak-to-peak distance), had greater influence than the blank material itself.

Materials characterization part I: contact area of the Berkovich indenter for nanoindentation tests

This is the first of two papers associated with materials characterization methods based on hardness testing. This paper presents a method to determine the area function of the Berkovich indenter used in nanoindentation hardness tests. The geometry and hence projected area of the indenter is known to affect the force-displacement response of a material during the loading and unloading stages. It is therefore important that the projected area is accurately defined to ensure determination of correct material hardness values. It is shown that values for the projected area determined from numerical methods applied to experimental data differ from values predicted inversely from theory based on the assumption of perfect tip geometry. This difference is attributed principally to a blunting of the tip, presenting as a tip radius. A simulation of the nanoindentation hardness test system is developed using finite element modelling (FEM) methods. Solutions for a range of load indentation curves obtained from experiment with fused silica are determined from best fit analyses using the root mean square error objective function (RMSE). A linear regression method is subsequently developed and used to estimate the area function. A parametric study of simulation and experimental results has been completed to verify the FEM and to assess the influence of varying tip curvature on force-displacement response during the loading and unloading stages and is summarily reported. A new method of analysis for determination of area function is proposed for use with numerical-based simulations, which for the first time, accommodates variation in tip geometry and which is shown to deliver improved agreement with nanoindentation experimental results. The second paper will focus on the study of the tip geometry of the Vickers microindenter.

Controlled tip wear on high roughness surfaces yields gradual broadening and rounding of cantilever tips.

Tip size in atomic force microscopy (AFM) has a major impact on the resolution of images and on the results of nanoindentation experiments. Tip wear is therefore a key limitation in the application of AFM. Here we show, however, how wear can be turned into an advantage as it allows for directed tip shaping. We studied tip wear on high roughness polycrystalline titanium and diamond surfaces and show that tip wear on these surfaces leads to an increased tip size with a rounded shape of the apex. Next, we fitted single peaks from AFM images in order to track the changes in tip radius over time. This method is in excellent agreement with the conventional blind tip reconstruction method with the additional advantage that we could use it to demonstrate that the increase in tip size is gradual. Moreover, with our approach we can shape and control the tip size, while retaining identical chemical and cantilever properties. This significantly expands the reproducibility of AFM force spectroscopy data and is therefore expected to find a wide applicability.

Nanomechanical Analysis of Polydimethylglutarimide Based Lift Off Resist Used for Temporary Bonding and Film Transfers

Temporary bonding has attracted renewed interest for the integration of dissimilar materials in device structures, which cannot be achieved by epitaxial growth techniques alone when the lattice mismatch between the dissimilar materials is too large. In this quest polydimethylglutarimide (PMGI) based lift-off (LOR) resist has been found suitable to serve as a temporary sacrificial adhesive for clean film exfoliation, layer transfer and temporary bonding applications [1]. Furthermore polydimethylglutarimide (PMGI) lends itself easily for temporary bonding purposes, because subsequent complete de-bonding can be readily achieved using an n-methyl-2-pyrrolidone (NMP)-based solvent. In this study we focus on the nanomechanical analysis of PMGI using the Nanoindenter XP by Agilent with continuous stiffness measurement (CSM) attachment. This investigation is aiming to elucidate the relationship between bonding parameters, bond strength and the nanomechanical properties of Young’s modulus and hardness of polydimethylglutarimide (PMGI) as a function of prebake temperature and PMGI resist film thickness. The influence of the spin-on process and the pre-bake treatment on the structure and properties of the PMGI adhesive layers is discussed and correlated to the resulting hardness, modulus and final bond strength and the corresponding Thermal Gravimetric Analysis (TGA) tracking the mass loss of the resist as a function of temperature. . For this experiment Si wafers were first cleaned with standard clean 1 (H2O:NH4OH:H2O2=5:1:1). Afterwards the wafers were spin coated at 2000 rpm with LOR 5A (from MicroChem), which is based on PMGI, and subsequently pre-baked in order to partially evaporate the solvent in the resist. The spin speeds were optimized to achieve 1.00 μm and 500 nm resist thickness for this investigation. Thicker lift-off resist thickness is not practical for a load-depth analysis with a Berkovich tip, because the nanoindenter is depth limited. The solvent, which is used with PMGI lift-off resist is cyclopentanone with a boiling point of 131ºC. With a glass transition point (Tg) of 180-190 ºC, we have chosen to conduct a series of prebakes at 50 °C, 70 °C, 90 °C, 110 °C and 130 °C, 150 °C & 160 °C each for 5 min and to benchmark the results against the hardness and bond strength achieved after thermal compression bonding of Silicon wafer pairs via adhesive PMGI layers at 250 C. This series of different thermal treatments influenced the resist mechanical properties, hardness and modulus. Our nanoindentation experimental results are indicated in Figure 1. As expected, the 500 nm films exhibited high hardness values as compared to the 1 µm thick films. Both PMGI lift-off resist films hardness approach the Si substrate hardness.

Residual stress in low temperature carburised layer of austenitic stainless steel

Microstructure, elements concentration and residual stress of a low temperature carburised layer on 316L austenitic stainless steel were investigated by optical microscopy, electron probe microanalysis, nanoindentation and X-ray diffraction (XRD). The results show that surface carbon concentration and nanohardness increase significantly after low temperature carburisation in the mixture gas of 30 vol.-% CO–30 vol.-% H2–40 vol.-%N2 at 743 K for 20 h, while Young’s modulus keeps unchanged. A finite element model was proposed to simulate the nanoindentation of unstressed carburised layer based on the results of nanoindentation experiments. Combined with the experimental and simulation results, the residual stress was calculated based on Suresh model, which agrees well with the corrected data by XRD method. The surface displacement around indenter was discussed.

Effect of pH on the structural, optical and nanomechanical properties of CdS thin films grown by chemical bath deposition

CdS nano-structured thin films were prepared on glass substrates with chemical bath deposition technique for different pH values. The effects of pH and annealing on the structural, optical and nanomechanical properties of CdS films were studied using X-ray diffraction (XRD), scanning electron microscopy (SEM), UV–vis spectrophotometer and nanoindentation techniques. The results of XRD analysis and SEM investigation reveal that both different pH values of the bath solution and annealing affect the crystal structure and the surface morphology of the films markedly. Also, the results of the optical absorption show that the Eg values of the films decrease with increasing pH values. In this kind of study the mechanical properties of the CdS thin films determined using nanoindentation tests are being reported here for the first time. Nanoindentation experimental results show that nanohardness and elastic modulus values exhibit a peak load dependence. Our results reveal that, the annealing of CdS films at 300°C results in slow and normal grain coarsening. The slow grain growth also influences the lattice strain (microstrain) which effects nanohardness and elastic modulus. The results also indicate that there is a direct dependence of the physical and optical properties of the CdS films on pH and annealing process.

Temperature Dependence of Mechanical Properties in Molecular Crystals

Quantitative evaluation of the mechanical behavior of molecular materials by a nanoindentation technique has gained prominence recently. However, all the reported data have been on room-temperature properties despite many interesting phenomena observed in them with variations in temperature. In this paper, we report the results of nanoindentation experiments conducted as a function of temperature, T, between 283 and 343 K, on the major faces of three organic crystals: saccharin, sulfathiazole (form 2), and l-alanine, which are distinct in terms of the number and strength of intermolecular interactions in them. Results show that elastic modulus, E, and hardness, H, decrease markedly with increasing T. While E decreases linearly with T, the variations in H with T are not so, and were observed to drop by ∼50% over the range of T investigated. The slope of the linear fits to E vs T for the organic crystals was found to be around 1, which is considerably higher than the values of 0.3–0.5 reported in the litera...

Grain Boundary Nanohardness of Coarse Grain Alumina

Here, we present the results of nanoindentation experiments conducted at ultralow peak loads of, for example, 1000, 5000, and 10,000 μN on a dense (~99.5%), coarse grain (~10 μm) alumina ceramic. The results showed that the nanohardness values of alumina were sensitive to the applied loads as well as to the locations of measurements, for example, the center of the grain, away from the center of the grain and at the vicinity of the grain boundary. The location sensitivity of nanohardness was linked to compositional variations of the different locations and to the presence of an amorphous phase.

Nanoindentation experiments with different loading rate distinguish the mechanism of incipient plasticity

Recent findings in nanodeformation of semiconductors posed a dilemma whether the nanoscale plasticity starts with phase transformation or nucleation of dislocations in a stressed nanovolume. In this letter we demonstrate the results of nanoindentation experiments with different loading rate, which enable us to conclude on a mechanism of incipient plasticity. The recorded nanodeformation response of GaAs and Si contrasts that observed for either GaN or metallic Fe crystal, which supports the phase transformation nature of the GaAs incipient plasticity. The derived relationship between the energy barrier for defect nucleation and applied stress served as a verification of the obtained results.

Fatigue Induced Alteration of the Superficial Strength Properties of 2024 Aluminum Alloy

Aircraft aluminum alloy 2024 T3 specimens have been subjected to constant amplitude fatigue loading at R=0.1. During fatigue, an appreciable increase of the surface hardness of the material at the meso-scale can be observed and captured by means of nanoindentations. Surface hardness increases with increasing fatigue stress amplitude and advancing number of applied fatigue cycles. Observed increase of specimen surface hardening degree during fatigue causes an evolution of superficial mechanical strength properties of the alloy. Stress-strain curves associated with the evoluting superficial mechanical properties are derived, employing a developed finite element method (FEM)-supported evaluation procedure of nanoindentation experimental results.