Nanoindentation Test Results Research Articles

Microstructure-Based Multiscale Analysis of Hot Rolling of Duplex Stainless Steel Using Various Simulation Software

We proposed a microstructure-based multiscale simulation framework using various commercial simulation software and applied it to analyze the hot rolling of duplex stainless steel. According to the Integrated Computational Material Engineering (ICME) concept, we established a procedure to bridge various simulation software from nano- to macroscopic length scales. Using our framework, first, microstructure evolutions by multiphase field (MPF) simulations coupled with the Calculation of Phase Diagrams (CALPHAD) database were performed. In our application, we simulated the columnar and equiaxed solidification during the continuous casting of duplex stainless steel. In the MPF simulations, the temperature field in the slab was calculated by heat conduction analysis using a finite element method (FEM). Then, the macroscopic elastic and plastic mechanical properties of the microstructure obtained by the MPF simulations were estimated by the virtual material test using a nonlinear FEM based on the homogenization method. Because the elastic constants of single δ-ferrite and γ phases in the microstructure are necessary for the virtual material test, they were calculated by molecular dynamics and first principle calculations. Furthermore, the plastic stress–strain properties of the single phases were estimated on the basis of the results of nano-indentation and uniaxial tensile tests. Subsequently, the hot rolling of the slab was simulated using an elastoplastic FEM with the mechanical properties obtained by the virtual material test. Finally, the static recrystallization in the rolled slab was again simulated by the MPF method.

Performance evaluation of polybenzimidazole coating for aerospace application

Abstract In Present study, characteristic behavior of PBI as a protective coating for aircraft application is presented. Performance of PBI coating is evaluated after exposure to hot wet environment and liquid immersion. Critical properties including hardness, scratch resistance and adhesion of PBI coating are assessed and results are presented. M21 epoxy based carbon fiber composite is used as substrate material. Atmospheric pressure plasma treatment (APPT) is performed to prepare the surface of substrate prior to application of PBI coating. Lap shear tests demonstrate that APPT has improved the adhesion strength of PBI bonded joints to about 250%. SEM analysis shows that strong composite/coating interface resulted in cohesive failure of the bonded joints. Lap shear test results on conditioned samples reveal that composite bonded joints has depicted about 15% decrease in strength after exposure to hot/wet environment under the conditions of 80 °C and 95% relative humidity (RH). However, mode of failure of bonded joints has not changed even after 1000 h of conditioning. PBI coated samples were also immersed in water and Skydrol to evaluate the effect on hardness and scratch resistance of PBI coating. Scratch tests on conditioned samples reveal that the visco-elastic recovery has increased from 58% (unexposed sample) to 71% with PBI coated panel immersed in skydrol. However, no major effect on visco-elastic recovery is observed with the samples immersed in water and the sample conditioned in hot/wet environment. Nano-indentation test results indicate that PBI coated panel immersed in skydrol has not depicted any decrease in elastic modulus ad hardness; whereas coated panel immersed in water for 1000 h has shown a minor decrease in both modulus and hardness. All these results indicate that PBI coating has great potential to retain its properties under harsh environment and it can be used as protective coating for aerospace application.

Effect of Heavy Ion Irradiation Dosage on the Hardness of SA508-IV Reactor Pressure Vessel Steel

Specimens of the SA508-IV reactor pressure vessel (RPV) steel, containing 3.26 wt. % Ni and just 0.041 wt. % Cu, were irradiated at 290 °C to different displacement per atom (dpa) with 3.5 MeV Fe ions (Fe2+). Microstructure observation and nano-indentation hardness measurements were carried out. The Continuous Stiffness Measurement (CSM) of nano-indentation was used to obtain the indentation depth profile of nano-hardness. The curves showed a maximum nano-hardness and a plateau damage near the surface of the irradiated samples, attributed to different hardening mechanisms. The Nix-Gao model was employed to analyze the nano-indentation test results. It was found that the curves of nano-hardness versus the reciprocal of indentation depth are bilinear. The nano-hardness value corresponding to the inflection point of the bilinear curve may be used as a parameter to describe the ion irradiation effect. The obvious entanglement of the dislocations was observed in the 30 dpa sample. The maximum nano-hardness values show a good linear relationship with the square root of the dpa.

Improvement of environmental stress cracking resistance of polycarbonate by silicone coating

To explore the possibility of using surface coating to reduce environmental stress cracking (ESC) of transparent polycarbonate (PC) parts, silicone coated and SiO2 coated PC were tested in a self-made three-point bending apparatus in the presence of ethanol. The variation of stress with time was recorded, and the surface cracking was observed to evaluate the ESC resistance of samples. Slower stress relaxation rates and fewer surface cracks indicated that silicone coating improved the ESC resistance of PC, but SiO2 coated PC was found to be no better than that of uncoated PC. Silicone coating reduced the absorption of ethanol in PC, weakening the surface plasticization, thus hindering the formation and development of cracks in PC. Nanoindentation test results showed that the mechanical properties such as hardness and elastic modulus of silicone coating are a better match for PC than SiO2 coating. This allows the silicone coating to have a favorable effect in providing continuous protection for PC under the combined action of ethanol and stress.

Bone Formation is Affected by Matrix Advanced Glycation End Products (AGEs) In Vivo.

Advanced glycation end products (AGEs) accumulate in bone extracellular matrix as people age. Although previous evidence shows that the accumulation of AGEs in bone matrix may impose significant effects on bone cells, the effect of matrix AGEs on bone formation in vivo is still poorly understood. To address this issue, this study used a unique rat model with autograft implant to investigate the in vivo response of bone formation to matrix AGEs. Fluorochrome biomarkers were sequentially injected into rats to label the dynamic bone formation in the presence of elevated levels of matrix AGEs. After sacrificing animals, dynamic histomorphometry was performed to determine mineral apposition rate (MAR), mineralized surface per bone surface (MS/BS), and bone formation rate (BFR). Finally, nanoindentation tests were performed to assess mechanical properties of newly formed bone tissues. The results showed that MAR, MS/BS, and BFR were significantly reduced in the vicinity of implant cores with high concentration of matrix AGEs, suggesting that bone formation activities by osteoblasts were suppressed in the presence of elevated matrix AGEs. In addition, MAR and BFR were found to be dependent on the surrounding environment of implant cores (i.e., cortical or trabecular tissues). Moreover, MS/BS and BFR were also dependent on how far the implant cores were away from the growth plate. These observations suggest that the effect of matrix AGEs on bone formation is dependent on the biological milieu around the implants. Finally, nanoindentation test results indicated that the indentation modulus and hardness of newly formed bone tissues were not affected by the presence of elevated matrix AGEs. In summary, high concentration of matrix AGEs may slow down the bone formation process in vivo, while imposing little effects on bone mineralization.

The Furfurylation of Wood: A Nanomechanical Study of Modified Wood Cells

Furfurylation of wood is of interest worldwide as an environmentally friendly modification process. It is widely assumed that low-molecular weight furfuryl alcohol (FA) can penetrate into wood cells and polymerize in-situ during the process, resulting in substantial improvement in the physical-mechanical properties and durability of wood. In this study, confocal laser scanning microscopy (CLSM) was used to visualize the microscopic distribution of polymerized FA resin in the Masson pine wood cavities, and a Nanoindenter was used to probe the mechanical properties of modified wood cells. The effects of catalysts (maleic anhydride and a mixed organic acid catalyst), FA concentration, curing time, and curing temperature on the nanomechanical properties of wood cell walls were investigated. An improvement in the indentation modulus and hardness of modified wood cells demonstrated indirectly but strongly that FA indeed penetrated wood cells during the modification process. Based on the results of the cell wall nanoindentation test, a combination of 50% furfuryl alcohol, 8 h curing time, and 95 °C curing temperature were proposed as the starting processing parameters for the development of a more practical and effective wood furfurylation process using a mixed organic acid catalyst.

Multi-Level Assessment of Fracture Calluses in Rats Subjected to Low-Magnitude High-Frequency Vibration with Different Rest Periods.

The aim of this study was to investigate the influences of low-magnitude high-frequency vibration (LMHFV) with different rest period regimes (vibrational loading per day [with or without the loading divided into bouts]; or vibrational loading for 7day followed by 7day rest [with or without the loading divided into bouts]) on bone healing at multi-levels. Transverse fractures of rat bilateral tibias were established using a Kirschner wire inserted for fixation. The animals were randomly assigned to five groups (n=7 for each group): four for vibrational groups by LMHFV with different rest period regimes and one for fractured model without mechanical loading. The macromechanical properties of the fractured tibias and the nanomechanical properties of the calluses were investigated through three-point bending and nanoindentation tests, respectively. Atomic force microscopy (AFM) was performed to analyze the nanostructure of the calluses. Micro-computed tomography (micro-CT) scanning was conducted to evaluate the microarchitecture of the calluses. The serum concentration of osteocalcin (OG) and tartrate-resistant acid phosphatase 5b (TRAP5b) were measured to assess the bone formation and resorption rates, respectively. Significantly higher values of failure load and elastic modulus were observed in DL (vibrational loading for 15min per day) and DLR (vibrational loading per day in which three bouts of 5min of vibration were separated by 4h) than FBC (fractured model without mechanical loading) at macro-level (P<0.05). The results of nanoindentation test showed the highest values of indentation modulus and hardness in DLR (significantly higher than FBC; P<0.05); besides, higher value of hardness was also observed in DL (significantly higher than FBC; P<0.05). Though AFM imaging showed no significant differences in grain sizes between the vibrational groups and FBC, roughness of DLR showed the highest value, i.e. it was significantly higher than that in FBC (P<0.05). For microarchitectural parameters obtained from micro-CT imaging, tissue mineral density (TMD) of DLR and VL7 (vibrational loading for 7day followed by a 7-day rest, 15min per day during vibrational periods) were significantly higher than that in FBC (P<0.05), but no significant differences in other parameters were observed between vibrational groups and FBC. There were no significant differences of OG between vibrational groups and FBC; however, FBC showed significantly higher TRAP5b concentration than all vibrational groups (P<0.05). The results show that LMHFV with different rest period regimes not only altered the macro- and nano-level bone mechanical properties but also influenced the TMD of calluses and nano-level spatial arrangement (roughness) significantly. The most significant effect of LMHFV with different rest period regimes was observed in DLR, which indicated that both osteogenic accumulation and cellular resensitization can be satisfied under this regimen. Hence, the DLR group demonstrated a great potential in clinical applications.

Optimal design of process parameters, experimental fabrication and characterisation of a novel hybrid polymer nanocomposite

The aim of the work was to fabricate and characterise a novel nanocomposite material that is a multiphase hybrid polymer composite with MWCNT filler. The optimisation of process parameters on tensile strength of epoxy/polyester/MWCNT nanocomposites using the Taguchi method was performed. The contribution of each process parameter on the output response was then analysed using analysis of variance (ANOVA). Experimental specimens were then made to confirm optimum values for each process parameter. The results indicated that the tensile strength of the optimal nanocomposites was improved to 86.3% with the addition of MWCNTs at a ratio of 1%. The results of nanoindentation tests exhibited the enhancement of Young's modulus and hardness by 71% and 27.5%, respectively, at 1% of MWCNTs. Morphologies of the fracture surface of resulting nanocomposites observed by a field emission scanning electron microscope (FESEM) showed good adhesion between the fillers and the resin.

Phase structure development as preheating UHMWPE powder temperature changes in the micro-UPM process

In this study, using high-speed mechanical drilling on printed circuit boards (PCBs) with two micro carbide drill bits with diameters of 0.15 mm and 0.20 mm, two different PCB micro-cylinder array inserts are fabricated using the micro-ultrasonic powder moulding (micro-UPM) process. According to the temperature curves recorded by a measurement module, when viscoelastic heating dominated, the temperature increasing rate was about three times the rate when interfacial friction heating dominated. From the differential scanning calorimetry and nanoindentation test results, if the ultra-high molecule weight polyethylene (UHMWPE) powder was not preheated, then the micro-cylinder array polymer parts generally consisted of nascent and melt-recrystallised phases as a whole. However, when the micro-cavity and compressed UHMWPE powder grew from room temperature of 28 °C to 85 °C, the two-phase structure gradually developed into a single melt-recrystallised phase. According to single-crystal x-ray diffraction test results, the crystallinity of the base region of the micro-UPM cylinder array part is higher than that of the micro-cylinder region, whereas the grain size of the (1 1 0) crystal surface is larger than that of the (2 0 0) crystal surface.

The Effect of Adding Selected Nanoparticles on the Mechanical Properties of the Cement Matrix of Self-Compacting Concrete

The interest in nanomaterials as an addition that improves the properties of concrete has been growing for more than a decade. One of the principal ways of evaluating concretes is the testing of their micro- and nanohardness by means of nanoindentation. This paper presents the results of nanoindentation tests of hardened self-compacting concrete modified with different amounts of nanoparticles. The investigations covered a reference series of self-compacting concrete without any nanoparticle addition and ten concrete series modified with different amounts of SiO2, TiO2and Al2O3powder nanoparticles. An analysis of the test results is carried out and conclusions are drawn.

Novel biodegradable calcium phosphate/polymer composite coating with adjustable mechanical properties formed by hydrothermal process for corrosion protection of magnesium substrate.

Ceramic type coatings on metallic implants, such as calcium phosphate (Ca-P), are generally stiff and brittle, potentially leading to the early failure of the bone-implant interface. To reduce material brittleness, polyacrylic acid and carboxymethyl cellulose were used in this study to deposit two types of novel Ca-P/polymer composite coatings on AZ31 magnesium alloy using a one-step hydrothermal process. X-ray diffraction and scanning electron microscopy showed that the deposited Ca-P crystal phase and morphology could be controlled by the type and concentration of polymer used. Incorporation of polymer in the Ca-P coatings reduced the coating elastic modulus bringing it close to that of magnesium and that of human bone. Nanoindentation test results revealed significantly decreased cracking tendency with the incorporation of polymer in the Ca-P coating. Apart from mechanical improvements, the protective composite layers had also enhanced the corrosion resistance of the substrate by a factor of 1000 which is sufficient for implant application. Cell proliferation studies indicated that the composite coatings induced better cell attachment compared with the purely inorganic Ca-P coating, confirming that the obtained composite materials could be promising candidates for surface protection of magnesium for implant application with the multiple functions of corrosion protection, interfacial stress reduction, and cell attachment/cell growth promotion. © 2015 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 104B: 1643-1657, 2016.

Wear characteristics of functionally graded nanocrystalline Ni–P coatings

In this study, functionally graded Ni–P coatings with a gradual change of phosphorus content were deposited using a single electroless bath. For comparing tribological and mechanical properties, three types of single layer coatings were deposited. According to the results among the single layer coatings, medium P coating had the minimum wear resistance, while its hardness was not minimum. The main reason may be that the medium P coating had the minimum H/E ratio, and this ratio is a more appropriate parameter than hardness for predicting wear resistance. Results of nanoindentation test showed gradual changes in hardness profile in the cross-section of FGCs due to the gradual changes of phosphorus content in the thickness of the coatings and, consequently, gradual changes in structures. In addition, functionally graded coatings indicated much better wear resistance than single layer coatings because during the wear process cracks were effectively prevented through the thickness as a result of gradual composition and structures.

An investigation of the characteristics of Al2O3/TiO2 PEO nanocomposite coating

Plasma electrolytic oxidation (PEO) was employed to obtain Al2O3/TiO2 nano-composite coatings. The process was carried out in a silicate base electrolyte in the presence of 0–4gL−1 TiO2 nanoparticles. A DC power supply was used to apply 150mAcm−2 current density for 60min on aluminum samples. XRD analysis on the coated samples revealed that γ-alumina and Mullite were formed in all cases, while TiO2 detected just by the incorporation of TiO2 nanoparticles. Surface and cross-section elemental maps of composite coatings implied that the nanoparticles were uniformly distributed in coatings upper parts. Coatings possessed about 25 and 10% porosity in the absence and presence of nanoparticles, respectively. This showed that the denser coating was formed in the presence of nanoparticles. Electrochemical measurements also revealed that adding nanoparticles increased the corrosion resistance of the coatings by decreasing the corrosion current density to about 3 times. Nano-indentation test results showed the increase of Hardness, Young's modulus, Stiffness and Fracture toughness of Al2O3/TiO2 nano-composite coatings.

Novel Investigation on Nanostructured Multilayer and Functionally Graded Ni-P Electroless Coatings on Stainless Steel

In this study, step-wise multilayer and functionally graded Ni-P coatings were deposited with electroless in which the content of phosphorus and nickel would be changed gradually and step-wise through the thickness of the coatings, respectively. To compare the properties of these coatings with Ni-P single-layer coatings, three types of coatings with different phosphorus contents were deposited. Heat treatment of coatings was performed at 400 °C for 1 h. The microstructure and phase transformation of coatings were characterized by SEM/EDS, TEM, and XRD. The mechanical properties of coatings were studied by nanoindentation test. According to the results of the single-layer coatings, low P coating had the maximum hardness and also the ratio of hardness (H) to elasticity modulus (E) for the mentioned coating was maximum. In addition, low and medium P coatings had crystalline and semi-crystalline structure, respectively. The mentioned coatings had 〈111〉 texture and after heat treatment their texture didn’t change. While high P coating had amorphous structure, after heat treatment it changed to crystalline structure with 〈100〉 texture for nickel grains. Furthermore, the results showed that functionally graded and step-wise multilayer coatings were deposited successfully by using the same initial bath and changing the temperature and pH during deposition. Nanoindentation test results showed that the hardness of the mentioned coatings changed from 670 Hv near the substrate to 860 Hv near the top surface of coatings. For functionally graded coating the hardness profile had gradual changes, while step-wise multilayer coating had step-wise hardness profile. After heat treatment trend of hardness profiles was changed, so that near the substrate, hardness was measured 1400 Hv and changed to 1090 Hv at the top coat.

Effect of starting materials on the wear performance of NiTi-based composites

NiTi alloys have exhibited significant potential as a matrix of wear resistant composites. In this study, in order to examine the effect of starting materials on the wear performance of NiTi-based composites, both elemental Ni/Ti and prealloyed NiTi powders were used to fabricate NiTi–6wt% nano-Al2O3 composites using hot isostatic pressing (HIP). Nanoindentation and microhardness test results indicate that the composite samples produced from the elemental Ni/Ti powders exhibited higher hardness and lower pseudoelasticity properties than those of the samples fabricated from the prealloyed NiTi powders; this is attributed to the higher amount of Ni3Ti/NiTi2 phases in the samples from the elemental powders. The wear test results also confirm the superior performance of the composite samples produced from the elemental powders. The high-resolution transmission electron microscopy studies of the wear debris demonstrate that the heavy local plastic deformation induced during the wear test appeared to inhibit the pseudoelasticity during the wear process. Hence, it can be deduced that the role of the hardness enhancement is more pronounced than that of the pseudoelasticity reduction in the wear performance of NiTi-based composite samples.

Investigation of Tungsten/Steel Brazing Using Nb Interlayer

Due to its excellent thermal physical properties, tungsten is used as structural material in divertor components of fusion reactors. With the rapid development of the technology, the joining of W to reduced activation ferritic/martensitic steel is required for use as a component according to the design of helium cooled high performance divertors. However, W and steel have remarkable differences in their coefficients of thermal expansion, which results in a large residual stress in the joints during the manufacturing and service and consequently leads to failure of the joint. In order to obtain a sound W/steel joint, an appropriate interlayer material inserted between tungsten and steel is necessary to solve the above-mentioned problem. A brazing process, using a Ni–based foil–type filler and a Nb slice as intermediate materials, was carried out in vacuum at 1150 °C for 30 min to investigate the joining of tungsten and steel. The microstructures, chemical composition, hardness and strength of the joint were investigated by scanning electron microscopy (SEM), electron probe microanalysis (EPMA), nanoindentation and tensile strength measurement, respectively. The results show that brazing of W and steel was successfully carried out using a Nb interlayer. The bonding interfaces were bonded well. The average tensile strength of 284 MPa was obtained and all specimens fractured in W near the joining seam, in a brittle fracture mode. The nanoindentation test results indicated that the high hardness of 23 GPa were produced at the W/Ni–based filler brazed seams due to the formation of the Boron–riched phase.

Non-ideal assembly of the driving unit affecting shape of load-displacement curves

The results of nanoindentation testing strongly rely on load-displacement curves, but an abnormal load-displacement curve with obvious inflection in the unloading portion was commonly observed in previously published papers and the reason is not clear. In this paper, possible reasons involved in a custom-made indentation instrument, such as sensors, control and assembly issues, are analyzed and discussed step by step. Experimental results indicate that non-ideal assembly of the precision driving unit strongly affects the shape of the load-displacement curve and its affecting mechanism is studied by theoretical analysis and finite element simulations. This paper reveals the reason leading to the abnormal load-displacement curve, which is helpful for debugging of indentation instruments and can enhance comparability of indentation results.

Micro scale laser shock forming of pure copper and titanium sheet with forming/blanking compound die

A new process fabricating micro parts of thin metal foils by laser shock waves with forming/blanking compound die is reported in this article, in which flexible rubber material was used as the soft punch to act on the thin metal sheet. Systematic studies were carried out experimentally on the process with different laser energies and materials. The formed parts were examined in terms of their morphology, surface roughness, forming depth and mechanical properties (including nanohardness, plasticity and elastic modulus) characterized by nanoindentation test. According to the results, the ablation states of confinement medium and the surface roughness of the different regions change with energies. Additionally, the proper energies are necessary to form complex parts and the forming process can be applied to manufacture parts with good surface quality. What׳s more, the nanoindentation test results showed that the nanohardness, plasticity and elastic modulus of material were increased after impact. The increase in nanohardness and plasticity can attribute to higher stiffness of the parts. The enhanced elastic modulus indicates an increased stiffness of the parts, providing an evidence for the reduced spring back of copper during laser shocking.

Overview of Enhanced Continuum Theories for Thermal and Mechanical Responses of the Microsystems in the Fast-Transient Process

The recently growing demand for production and applications of microscale devices and systems has motivated research on the behavior of small volume materials. The computational models have become one of great interests in order to advance the manufacturing of microdevices and to reduce the time to insert new product in applications. Among the various numerical and computational techniques, still the approaches in the context of continuum theories are more preferable due to their minimum computational cost to simulation on realistic time and material structures. This paper reviews the methods to address the thermal and mechanical responses of microsystems. The focus is on the recent developments on the enhanced continuum theories to address the phenomena such as size and boundary effects as well as microscale heat transfer. The thermodynamic consistency of the theories is discussed and microstructural mechanisms are taken into account as physical justification of the framework. The presented constitutive model is calibrated using an extensive set of microscale experimental measurements of thin metal films over a wide range of size and temperature of the samples. An energy based approach is presented to extract the first estimate of the interface model parameters from results of nanoindentation test.

Characterization and nanomechanical properties of novel dental implant coatings containing copper decorated-carbon nanotubes

Fluorapatite–titania coated Ti-based implants are promising for using in dental surgery for restoring teeth. One of the challenges in implantology is to achieve a bioactive coating with appropriate mechanical properties. In this research, simple sol–gel method was developed for synthesis of fluorapatite–titania–carbon nanotube decorated with antibacterial agent. Triethyl phosphate [PO4(C2H5)3], calcium nitrate [Ca(NO3)2] and ammonium fluoride (NH4F) were used as precursors under an ethanol–water based solution for fluorapatite (FA) production. Titanium isopropoxide and isopropanol were used as starting materials for making TiO2 sol–gels. Also, Copper acetate [Cu(C2H3O2)2·H2O] was used as precursor for decoration of multi walled carbon nanotubes (MWCNTs) with wet chemical method. The decorated MWCNTs (CNT(Cu)) were evaluated by transmission electron microscopy (TEM). The phase identification of the FA–TiO2–CNT(Cu) coating was carried out by XRD analysis. Morphology of coated samples was investigated by SEM observations. The surface elastic modulus and hardness of coatings were studied using nanoindentation technique. The results indicate that novel dental implant coating containing FA, TiO2 and copper decorated MWCNTs have proper morphological features. The results of nanoindentation test show that incorporation of CNT(Cu) in FA–TiO2 matrix can improve the nanomechanical properties of composite coating.