Continuous Stiffness Method Research Articles

Comparison of the mechanical properties of Mo films by different nanoindentation techniques

Nanocrystalline Mo films were prepared by magnetron sputtering. Indentation size effect (ISE) on hardness (H) was both studied by constant strain rate method (CSR) and continuous stiffness method (CSM). Inverse ISE appears and H from CSR is higher than that from CSM. Significant dislocation motion barrier effect of increased grain boundary (GB) induces strengthening. Each step of CSM promotes the generation of heterogeneous GBs and enhances GB-emitting dislocations ability, leading to softening.

Investigation on nanoindentation and TOF-SIMS applications in the hydrogen and oxygen absorption behavior of Zr-Sn-Nb alloys

This paper focuses on nanoindentation and TOF-SIMS (time-of-flight secondary ion mass spectrometry) small-scale test methods in the study of hydrogen absorption and oxygenation behavior analysis of Zr-Sn-Nb oxidized at 650°C −1200 °C. The CSM (Continuous Stiffness Method) test demonstrates the hardness fluctuations caused by element proliferation in post-high temperature oxidation microstructures. The deformation resistance ability of typical microstructures is as follows: β-Zr layer > α-Zr(O) layer > ZrO2 layer. In addition, hydrogen-induced softening occurred in steam-containing hydrogen conditions (HIT=2～3Gpa), compared to steam (HIT=5～16Gpa). The 1200℃ load-displacement curve demonstrates that the pop-in (or pop-out) effect exists in the Zr-Sn-Nb alloy, related to the influence of hydrogen charge, essentially to dislocation nucleation, winding, and movement. TOF-SIMS provides an effective method for small molecular chemical elements, such as H and O, while ZrO, ZrO2, ZrO2H, ZrO3H, OH, and O2 ions also be found. Based on these results, this study also hypothesizes the OH- dominated oxidation reaction equation.

Elastic properties of the non-mixing copper donor assisted material in friction stir welding of aluminum alloys using nanoindentation

Friction stir welding of high-strength materials such as steels is the impeded by the lack of the vast heat input needed to start the process. Contact friction is considered the most dominant source of heat generation for FSW steels which tends to cause severe wear conditions of the tool hear. To relieve the extreme wear conditions that occur on the tool heads because of FSW steels, we introduce the non-mixing Cu donor stir material to friction stir welding of aluminum alloys. The elastic properties of the Cu donor assisted friction stir welded aluminum alloys are measured using nanoindentation. The hardness and elastic modulus were measured for two regions, the base metal (BM) and the stir zone (SZ). The measurements were conducted for 20% and 60% Cu non-heat treated (NHT) and heat-treated (HT) samples. The nanomechanical properties were measured using nanoindentation with the continuous stiffness method (CSM) in depth control. The HT samples are softer than the NHT samples as expected. However, the 20% Cu NHT and HT samples depicted the same hardness at the SZ. Similar results were observed for the 60% Cu donor stir samples. It therefore concluded that the SZ is softer than the BM for the 20% and 60% Cu donor stir material as expected. The hardness of the weld at the SZ is similar to the hardness of the Al6061-T6 plate, suggesting that the Cu donor stir material did not impact the hardness properties of the Al6061-T6 plate due to the depletion of the Cu donor stir material during the welding process, an important result of the concept of the donor material. The elastic moduli of the Cu donor stir welded samples vary between 75~85 GPa at a depth of indentation of ~4600 nm, which are different from the elastic moduli of Cu 110 (117.2 GPa) and similar to the elastic modulus of aluminum alloys (68.9 GPa), an important outcome.

High-dose ion irradiation damage in Fe28Ni28Mn26Cr18 characterised by TEM and depth-sensing nanoindentation

One of the key challenges for the development of high-performance fusion materials is to design materials capable of maintaining mechanical and structural integrity under the extreme levels of displacement damage, high temperature and transmutation rates. High-entropy alloys (HEAs) and other concentrated alloys have attracted attention with regards to their performance under fusion conditions. In recent years, a number of investigations of the irradiation responses of HEAs have peaked the community’s interest in them, such as the work of Kumar et al. (2016), who examined Fe27Ni28Mn27Cr18 at doses as high as 10 dpa. In this work, we study Fe28Ni28Mn26Cr18 concentrated multicomponent alloy with irradiation doses as high as 20 dpa. We find the presence of Cr rich bcc precipitates in both the un-irradiated and in the irradiated condition, and the presence of dislocation loops only in the irradiated state. We correlate the features found with irradiation hardening by the continuous stiffness method (CSM) depth-sensing nanoindentation technique and see that the change in the bulk hardness increases significantly at 20 dpa for temperatures 450 °C. These results indicate that the alloy is neither stable as a single phase after annealing at 900 °C, nor particularly resistant to irradiation hardening.

Small-scale high-cycle fatigue testing by dynamic microcantilever bending

The lifetime of cyclically loaded devices is often limited by the fatigue resistance of their individual phases. An advanced method is presented for measuring the high-cycle fatigue behavior of materials at the micrometer scale using a nanoindenter. It is based on the cyclic deflection of focused ion beam-fabricated microcantilevers using the continuous stiffness method (CSM). In line with experimental data on bulk nanocrystalline copper, the specimens exhibit grain coarsening followed by the formation of extrusions and a fatigue strength exponent of −0.10. The method is suitable for characterizing single phases and individual components of further complex systems

Dislocation loop evolution and radiation hardening in nickel-based concentrated solid solution alloys

Effects of chemical composition, ion irradiation dose and temperature on unfaulting of irradiation induced Frank dislocation loops to perfect loops in two nickel based single-phase solid solution alloys, Ni–20Fe and NiFe–20Cr, have been studied. The fraction of Frank loops decreases with irradiation dose from 7.2 to 38.4 dpa at 500°C, but with more Frank loops remaining in the ternary alloy. However, perfect loops and dislocation networks become the dominant features of defects at 580°C in both alloys. The results indicate a thermally assisted loop unfaulting process that may be hindered by more sluggish defect motion in the alloy with more chemical components. Nano-indentation with both continuous stiffness method and single indentation method are used to measure radiation hardening. Loop unfaulting in both alloys irradiated at 580°C reduced radiation hardening while significant hardening is observed after irradiation at 500°C. The quasi-static single indentation method exhibits lower hardness results compared to continuous stiffness method, because dislocations induced from the cyclic loading in the latter method get relaxed and stabilized, resulting in higher resistance to the indenter.

Fracture toughness of amorphus SiC thin films using nanoindentation and simulation

Fracture toughness of SiC on Si thin films of thicknesses of 150, 750, and 1500 nm were measured using Agilent XP nanoindenter equipped with a Dynamic Control Module (DCM) in Load Control (LC) and Continuous Stiffness Method (CSM) protocols. The fracture toughness of the Si substrate is also measured. Nanovision images implied that indentations into the films and well deep into the Si caused cracks to initiate at the Si substrate and propagate upward to the films. The composite fracture toughness of the SiC/Si was measured and the fracture toughness of the SiC films was determined based on models that estimate film properties from substrate properties. The composite hardness and modulus of the SiC films were measured as well. For the DCM, the hardness decreases from an average of 35 GPa to an average of 13 GPa as the film thick increases from 150 nm to 1500 nm. The hardness and moduli of the films depict the hardness and modulus of Si at deep indents of 12 and 200 GPa respectively, which correlate well with literature hardness and modulus values of Si. The fracture toughness values of the films were reported as 3.2 MPa√m.

Microscale High-Cycle Fatigue Testing by Dynamic Micropillar Compression Using Continuous Stiffness Measurement

The continuous stiffness method (CSM) is used for fatigue testing FIB-fabricated micropillars up to the high cycle fatigue (HCF) range on a commercial nanoindentation platform. The frequency of ~ 40 Hz allows reaching several million (106) cycles within hours under constant nominal stress amplitude testing conditions. It is shown that both the evolution of the strain and plastic strain amplitudes can be evaluated from the harmonic measurements provided by the lock-in amplifier. Defining a custom threshold on strain amplitude decrease as failure criterion further enables the determination of S-N curves. The new method was validated by tests on ECAP copper, which is shown to exhibit the same cyclic softening during micropillar testing as observed macroscopically. The calculated plastic strain amplitude is also well in line with literature data. Generally, the new method has a great potential for studying the local cyclic behavior of individual layers and phases of complex systems and would also be of great advantage for studying local fatigue effects at interfaces.

Mechanical properties of RF-sputtering MoS2 thin films

We present an evaluation of the hardness and Young’s modulus properties of medium pressure sputtered molybdenum disulfide (MoS2) thin films by applying nano-indentation with continuous stiffness method combined with microstructure analysis using small angle x-ray diffraction, Raman, and an electron microscope in scanning and transmission mode. Our results indicate a vertical growth of MoS2 crystallites with stacking values of 7-laminates along the [0 0 1] direction and an average height of 105 nm, principal Raman vibrations at at 378 cm−1 and A1g at 407 cm−1 and an interplanar distance of ~0.62 nm as confirmed by high-resolution transmission electron microscopy. An average hardness of H = 10.5 ± 0.1 GPa and elastic modulus of E = 136 ± 2 GPa from 0 to 90 nm of indenter penetration were found in these investigations.

Global and local strain rate sensitivity of bimodal Al-laminates produced by accumulative roll bonding

Laminated metallic composites of 5 mm thickness, with a bimodal grain size distribution and alternating layers of commercial purity aluminum (Al99.5) and high purity aluminum (Al99.999) were successfully processed by accumulative roll bonding at room temperature up to 8 cycles. With increasing number of ARB cycles the layers of commercial purity aluminum become ultrafine-grained, whereas the grain size in the high purity aluminum remains clearly above 1 μm. The mechanical properties of the laminates were investigated by compression testing with strain rate jumps and by nanoindentation using continuous stiffness method and nanoindentation strain rate jump tests. Thereby the strain rate sensitivity was determined both globally, proving the bulk laminate material, and locally, proving the single layers of the laminate. It was found that the local strain rate sensitivity of the ultrafine-grained Al99.5-layers is increasing up to 4 ARB cycles, while the local strain rate sensitivity of the coarse grained Al99.999-layers remains rather constant independently of the number of cycles. In contrast to that, the global strain rate sensitivity of the bulk laminate increases up to 8 cycles without saturation. Thermally activated annihilation of dislocations at the grain boundaries and interfaces between the coarse grained and ultrafine-grained layers is proposed in order to interpret the findings.

Superconducting niobium nitride thin films by reactive pulsed laser deposition

The structural, electronic, and nanomechanical properties of cubic niobium nitride thin films were investigated. The films were deposited on Si(100) under different background nitrogen gas pressures (26.7-66.7Pa) at constant substrate temperature of 800°C by reactive pulsed laser deposition. Our results reveal that the NbNx films exhibit a cubic δ-NbN with strong (111) orientation and highly-oriented textured structures. We find nitrogen background pressure to be an important factor in determining the structure of the NbNx films. The dependence of the electronic structure as well as that of the superconducting transition temperature (Tc) on the nitrogen gas background pressure is studied. A correlation between surface morphology, electronic and superconducting properties is found for the deposited NbNx thin films. The highly-textured δ-NbN films have a Tc up to 15.07K. Nanoindentation with continuous stiffness method is used to evaluate the hardness and modulus of the NbNx thin films as a function of depth. The film deposited at nitrogen background pressure of 66.7Pa exhibits improved superconducting properties and shows higher hardness values as compared to films deposited at lower nitrogen pressures.

Effect of double ion implantation and irradiation by Ar and He ions on nano-indentation hardness of metallic alloys

In this study, the authors have investigated the combined effect of a double layer of implantation on four different metallic alloys, ODS steel MA957, Zircaloy-4, Ti–6Al–4V titanium alloy and stainless steel 316, by ions of two different species – He and Ar – on the hardening of the surface as measured by nano-indentation. The data was collected for a large number of indentations using the Continuous Stiffness Method or “CSM” mode, applying the indents on the implanted surface. Careful analysis of the data in the present investigations show that the relative hardening due to individual implantation layers can be used to obtain an estimate of the relative hardening effect of a combination of two separate implanted layers of two different species. This combined hardness was found to lie between the square root of the sum of the squares of individual hardening effects, (ΔHA2+ΔHB2)0.5 as the lower limit and the sum of the individual hardening effects, (ΔHA+ΔHB) as the upper limit, within errors, for all depths measured.

Enhancing the Ductility of Sn-Ag-Cu Lead-Free Solder Joints by Addition of Compliant Intermetallics

Tin (Sn)-rich lead (Pb)-free solders containing rare-earth (RE) elements have been shown to exhibit desirable attributes of microstructural refinement and enhanced ductility relative to conventional Sn-3.9Ag-0.7Cu lead-free solder, due to the unique mechanical properties of RE-Sn intermetallics. However, the roles of soft intermetallic phase in the enhanced ductility of Pb-free solder still need to be further investigated. In this paper, Ca and Mn were selected as doping elements for Sn-Ag-Cu solder. The mechanical properties of Ca-Sn and Mn-Sn intermetallics as a function of indentation depth were measured by nanoindentation using the continuous stiffness method (CSM). The microstructure and mechanical properties of as-reflowed Ca- and Mn-containing Sn-Ag-Cu solder joints were studied and compared with those of conventional Sn-Ag-Cu and RE-containing solder joints. It is shown that soft intermetallics result in higher ductility in Pb-free solders.

Nanomechanical properties of NbN films prepared by pulsed laser deposition using nanoindendation

Structural and mechanical properties of niobium nitride thin films deposited by pulsed laser deposition were investigated using X-ray diffraction, atomic force microscopy, and nanoindentation. Niobium nitride was deposited on Si(100) by pulsed laser deposition (PLD) of Nb in nitrogen background. A Nanoindenter XP equipped with a dynamic contact module (DCM II) head was used in conjunction with the continuous stiffness method (CSM) in depth and load control modes to measure the hardness and modulus of the NbN thin films. NbN film reveals simple cubic δ-NbN structure with the corresponding reflections of (111), (200), and (220) planes. Highly textured NbN film shows a strong (111) preferred orientation. The NbN thin films depict polycrystalline structure, with a wide range of grain sizes that range from 15 to 40nm with an average surface roughness of 6nm. The average modulus of the film is 420±60GPa, whereas for the substrate the average modulus is 180GPa, which is considered higher than the average modulus for Si reported in the literature due to pile-up. The hardness of the film increases monotonically from an average of 12GPa for deep indents (Si substrate) measured using XP CSM and load control (LC) modes to an average of 25GPa measured using the DCM II head in CSM and LC modules. The average hardness of the Si substrate is 12GPa.

Mechanical and structural characterization of atomic layer deposition-based ZnO films

Zinc oxide thin films were deposited by atomic layer deposition (ALD). The structural and mechanical properties of the thin films were investigated by x-ray diffraction, transmission electron microscopy, atomic force microscopy, and nanoindentation. Diethyl zinc was used as the chemical precursor for zinc and water vapor was used as the oxidation agent. The samples were deposited at 150 °C and at a pressure of 2.1 × 10−1 Torr in the ALD reactor. A growth rate of 2 Å per cycle was calculated in the ALD process window. The Nano Indenter XP was used in conjunction with the continuous stiffness method in depth control mode in order to measure and to analyze the mechanical properties of hardness and modulus of ALD ZnO thin film samples. For comparison, we benchmarked the mechanical properties of single crystal bulk ZnO samples against those of our ALD ZnO thin films.

A new paradigm in thin film indentation

A new method to accurately and reliably extract the actual Young's modulus of a thin film on a substrate by indentation was developed. The method involved modifying the discontinuous elastic interface transfer model to account for substrate effects that were found to influence behavior a few nanometers into a film several hundred nanometers thick. The method was shown to work exceptionally well for all 25 different combinations of five films on five substrates that encompassed a wide range of compliant films on stiff substrates to stiff films on compliant substrates. A predictive formula was determined that enables the film modulus to be calculated as long as one knows the film thickness, substrate modulus, and bulk Poisson's ratio of the film and the substrate. The calculated values of the film modulus were verified with prior results that used the membrane deflection experiment and resonance-based methods. The greatest advantages of the method are that the standard Oliver and Pharr analysis can be used, and that it does not require the continuous stiffness method, enabling any indenter to be used. The film modulus then can be accurately determined by simply averaging a handful of indents on a film/substrate composite.

Evaluation of mechanical characteristics of the plate-type polymer hyperfine pit pattern by the nanoindentation process

It’s important to measure quantitative properties about the thermal-nano behavior of polymers in order to produce high quality components using the nanoimprint lithography process. Nanoscale indentation can be used to make the cells for molecular electronics, drug delivery, slots for integration into nanodevices and defects for tailoring both the structure and properties. In this study, the formability of polymethylmetacrylate (PMMA) and polycarbonate (PC) were characterized. Thermo-mechanical properties during formation at a high temperature. Polymers become softer at elevated temperature due to heating. In this case it is particularly important to study the high temperature-induced mechanical properties of the polymer. Nanoindentation was used to measure the thermo-mechanical properties of both PMMA and PC. The polymer was heated with the heating stage on a NanoXP. For a CSM (Continuous Stiffness Method) mode test, the heating temperature was 110°C, 120°C, 130°C, 140°C and 150°C for the PMMA, and 140°C, 150°C, 160°C, 170°C and 180°C for the PC. The maximum indentation depth for this test was 2000 nm. For the basic mode test, the heating temperature was 90°C and 110°C for the PMMA, and 140°C and 160°C for the PC. The maximum loads for this test were 10 mN, 20 mN and 40 mN. An indented pattern was also observed by using AFM. The pile-up phenomenon was mitigated due to the indentation at elevated temperature but the sink-in phenomenon occurred in this instance. When patterning at a high temperature, one should consider the variation in the indentation profile and depth after unloading when designing a structure. It was thought that the mechanical properties decrease when the working temperature increases because PMMA and PC are thermoplastics which soften or melt by heating. Further research in this area is required about the molecular weight and molecular movement at elevated temperature when the free volume of molecules increases.

Nanoindentation behaviour of aluminium based hybrid composites with graphite nanofiber/alumina short fiber

Nanoindentation was performed on Al based hybrid composites containing graphite nanofiber/alumina short fiber. Measurement of hardness and elastic modulus were carried out using the continuous stiffness method (CSM) with an indentation depth of about 2000 nm. To find out the hardness and moduli of the composites at various local regions, nanoindentation tests were carried out in different locations of the sample. In all cases, the measured values for hardness and modulus are a mixture of the effects of the presence of the graphite nanofiber (GNF) and alumina short fiber (Al 2O 3sf) and of the precipitation phases in the Al matrix. Moreover, the large number of dislocations in the plastic zone formed in the indented region of the GNF contributes to an increase in values of both modulus and hardness. The enhancement of indentation properties of the Al matrix is attributed to the possible indentation on the Al 4C 3 phase or MgAl 2O 4 precipitate. The hardness values and material pile-up are also shown to depend significantly on the mismatch between the moduli of the Al matrix and reinforcements.

Nanoindentation of rare earth–Sn intermetallics in Pb-free solders

Incorporating rare earth (RE) elements into Sn-rich solder often results in the formation of RE–Sn intermetallics, which affect the deformation behavior of the solder. Little information is available on these constituent phases, and even less on their mechanical properties. In this paper, we report on Young's modulus and hardness of LaSn 3, CeSn 3 and YSn 3 intermetallic compounds formed in a Sn–Ag–Cu–2RE alloy, determined using nanoindentation. Nanoindentation on pure Sn was also performed for comparison. The Continuous Stiffness Method (CSM) was used during indentation to obtain the instantaneous Young's modulus as a function of depth. Scanning electron microscopy (SEM) was used to analyze the indentations after testing. The measured values of Young's modulus for LaSn 3, CeSn 3 and YSn 3 were 64 ± 3, 69 ± 3 and 98 ± 4 GPa, respectively. Values of hardness for LaSn 3, CeSn 3 and YSn 3 were 1.04 ± 0.16, 1.03 ± 0.03 and 3.47 ± 0.27, respectively. Comparison of these values with limited data in the literature was conducted and is discussed.

열간나노압입공정을 이용한 극미세 점구조체 제작을 위한 플라스틱소재 판의 기계적 특성 조사

It's important to measure quantitative properties about thermal-nano behavior of polymer for producing high quality components using Nanoimprint lithography process. Nanoscale indents can be used to make the cells for molecular electronics and drug delivery, slots for integration into nanodevices, and defects for tailoring the structure and properties. In this study, formability of polymethylmetacrylate(PMMA) and polycarbonate(PC) were characterized Polymer has extreme variation in thermo mechanical variation during forming high temperature. Because of heating the polymer, it becomes softer than at room temperature. In this case it is particularly important to study high temperature-induced mechanical properties of polymer. Nanoindenter XP(MTS) was used to measure thermo mechanical properties of PMMA and PC. Polymer was heated by using the heating stage on NanoXP. At CSM(Continuous Stiffness Method) mode test, heating temperature was <TEX>$110^{\circ}C,120^{\circ}C,130^{\circ}C,140^{\circ}C$</TEX> and <TEX>$150^{\circ}C$</TEX> for PMMA, <TEX>$140^{\circ}C,150^{\circ}C,160^{\circ}C,170^{\circ}C$</TEX> and <TEX>$180^{\circ}C$</TEX> for PC, respectively. Maximum indentation depth was 2000nm. At basic mode test, heating temperature was <TEX>$90^{\circ}C$</TEX> and <TEX>$110^{\circ}C$</TEX> for PMMA, <TEX>$140^{\circ}C,160^{\circ}C$</TEX> for PC. Maximum load was 10mN, 20mN and 40mN. Also indented pattern was observed by using SEM and AFM. Mechanical properties of PMMA and PC decreased when temperature increased. Decrease of mechanical properties from PMMA went down rapidly than that of PC.