High Temperature Nanoindentation Research Articles

A direct comparison of high temperature nanoindentation creep and uniaxial creep measurements for commercial purity aluminum

Measuring the uniaxial creep response from nanoindentation has been of great interest to the small scale mechanics community. However, several experimental and modeling challenges pose obstacles to direct comparison of indentation and uniaxial results. In this work, new experimental procedures are developed to improve the precision and accuracy of high temperature nanoindentation tests. Indentation creep experiments are performed on commercial purity aluminum alloy at a number of temperatures up to 550 °C. The activation energy for creep was found to be 140.2KJ/mol/K, matching the value determined with high temperature uniaxial creep experiments extremely well. Uniaxial power-law creep parameters (stress exponent and pre-exponential term) are calculated from the indentation data for direct comparison of results to the uniaxial data. The results are in good agreement with the literature values for uniaxial compression/torsion tests over a wide range of strain rates and temperatures demonstrating the capabilities of high temperature indentation creep experiments. The relative contributions and interplay of indentation size effect, strain rate and temperature on the creep response is also explored.

Preparation and optical, nanomechanical, negative thermal expansion properties of Sc2W3O12 thin film grown by pulsed laser deposition

Negative thermal expansion Sc2W3O12 thin films have been grown on silicon and quartz substrates by pulsed laser deposition (PLD). The effects of oxygen pressure, substrate temperature and annealing temperature on the morphologies and phase composition of the Sc2W3O12 thin films were systematically investigated using X-ray diffraction (XRD), atomic force microscopy (AFM) and field emission scanning electron microscopy (FESEM). The negative thermal expansion, optical and nanomechanical properties of the Sc2W3O12 thin films were characterized by high temperature X-ray diffraction, spectrophotometry and nanoindentation. The results indicate as-deposited Sc2W3O12 thin films to be amorphous. Orthorhombic Sc2W3O12 thin films were observed to form by heating at 1000°C for 7min in air. The Sc2W3O12 thin film deposited at 500°C under an oxygen pressure of 20Pa has the lowest root mean square (RMS) roughness value. Meanwhile it also shows the optimum optical performance with an average transmission of over 85%. The Young's modulus (E) of the Sc2W3O12 thin film is 153.40GPa and the hardness (H) is 8.62GPa. The orthorhombic Sc2W3O12 thin film exhibits an anisotropic negative thermal expansion with an average linear thermal expansion coefficient was calculated to be −3.0×10−6K−1 in the temperature range from 25°C to 600°C.

Temperature-dependent mechanical properties of wood-adhesive bondline evaluated by nanoindentation

ABSTRACTPhenol formaldehyde (PF) and urea formaldehyde (UF) were used to prepare wood-adhesive bonds, respectively. The reduced elastic modulus (Er) and hardness (H) of the control wood cell wall, the adhesive, and the cell wall penetrated with an adhesive (CW-adhesive) at the wood-adhesive bondline were measured within a certain temperature range from 20 to 160°C using high-temperature nanoindentation (NI). The results indicated that the wood-PF bondline showed a strong dependence on elevated temperatures, while the wood-UF bondline presented better mechanical stability. A reduction of carbohydrates and increment of lignin in wood resulting from heat treatment at a temperature above 140°C were beneficial to increase the micromechanics of wood cell walls at the bondline. Furthermore, the possible post cross-linking reactions between the wood cell walls and PF adhesive molecules during the long heating period at high temperature made a major contribution to a significant increase in Er and H of the bondline. However, the significant difference in the mechanics of the PF adhesive and CW-PF in bondline after heat treatment negatively affects the interfacial adhesion properties of wood panels.

Advanced characterization methods for wear resistant hard coatings: A review on recent progress

Abstract Due to economical demands to further increase the efficiency of production processes, it is essential to exploit the full potential of wear resistant hard coatings. This is, however, possible only if the coating microstructure and properties are well characterized. Thus, in the present work, recently suggested advanced characterization techniques for coatings are reviewed. The application of atom probe tomography, electron backscatter diffraction and synchrotron X-ray nanodiffraction enables previously unrevealed insights in their chemical composition, microstructure and crystallographic structure. For the determination of mechanical and tribological properties at elevated temperatures, high-temperature nanoindentation and high-temperature ball-on-disk tests in combination with in-situ measurement techniques are discussed. Utilization of micromechanical tests for coatings provides information about their fracture toughness and rupture strength. High-temperature X-ray diffraction and biaxial stress temperature measurements for the determination of the coefficient of thermal expansion are compared. The thermal conductivity as well as the specific heat capacity of coatings can be studied using the 3- ω technique, time domain thermoreflectance and differential scanning calorimetry. The introduced portfolio of characterization techniques enables the determination of a complementary microstructural, mechanical and thermo-physical fingerprint of wear resistant hard coatings, which allows to understand the complex structure–property relations in these materials and subsequently to further improve their performance.

Thermally Activated Deformation Behavior of ufg-Au: Environmental Issues During Long-Term and High-Temperature Nanoindentation Testing.

For testing time-dependent material properties by nanoindentation, in particular for long-term creep or relaxation experiments, thermal drift influences on the displacement signal are of prime concern. To address this at room and elevated temperatures, we tested fused quartz at various contact depths at room temperature and ultra-fine grained (ufg) Au at various temperatures. We found that the raw data for fused quartz are strongly affected by thermal drift, but corrected by use of dynamic stiffness measurements all the datasets collapse. The situation for the ufg Au shows again that the data are only useful with drift correction, but with this applied it turns out that there is a significant change of elastic and plastic properties when exceeding 200°C, which is also reflected by an increasing strain rate sensitivity.

A high temperature nanoindentation study of Al–Cu wrought alloy

Aluminum–copper alloys are widely used because of their low density and good mechanical strength accomplished with precipitation hardening. The alloy Al–Cu–Mg–Pb (AA2030) has been investigated before and after aging, at room temperature and at high temperatures. The mechanical properties at room temperature have been studied by Brinell hardness tests. T4 and T6 stages of the alloy have been investigated by differential scanning calorimetry up to 450°C, showing the precipitation of different clusters. High temperature nanoindentation has been used to characterize the mechanical properties up to 460°C in order to obtain a better understanding of the local dominating deformation mechanism in the material. A continuous decrease in the hardness and Young's modulus was found with the increasing temperature. The strain rate sensitivity of the alloy increased with the temperature from 0.022 at RT, up to 0.16 at 460°C. The activation volume was constant (around 31–41b3) up to 240°C, beyond this point a large increase was observed up to 178b3. The results were comparable with similar materials, and indicate thermally activated processes.

Investigating the nanomechanical behavior of thermosetting polymers using high-temperature nanoindentation

High-temperature nanoindentation to investigate the temperature-dependent mechanical behavior of thermosetting polymers is introduced. Both the elastic modulus and hardness of three widely used adhesive polymers (phenol formaldehyde, urea formaldehyde, and polymeric isocyanate) in the pure phase and in the individual phase in wood-based composites were determined within a certain temperature range (from room temperature to 160°C). The results indicated that Loblolly pine accelerated the curing of urea formaldehyde, whereas negatively affected the curing of phenol formaldehyde. The different cure states resulted in significantly different indentation responses between the pure polymer and the polymer within composite. Temperature exerted a positive effect on the mechanical properties of adhesive polymers. The adhesive polymers showed higher reduced elastic modulus (Er) and hardness (H) at elevated temperatures as compared to room temperature, possibly due to the positive contributions of the removal of moisture and post-polymerization. Irregular particles and micropores observed on the surface of polymer within wood-adhesive composite seem to provide evidence for the post-polymerization of the adhesive during the heating test.

Mechanical Characterization of PM2000 Oxide‐Dispersion‐Strengthened Alloy by High Temperature Nanoindentation

AbstractNanoindentation measurements with a commercial Hysitron xSol 800 up to temperatures of 700 °C have been applied to study mechanical properties of PM2000 ODS steel. Beside the temperature dependence of hardness H and indentation modulus E, a careful analysis of time‐dependent features such as creep and stress exponent was performed. The H/E is dominated by a transition from small hardness variations at low temperatures to a strong hardness decrease starting at about 400 °C. The two different deformation regimes have been attributed to modifications in dislocation pinning at temperatures up to 400 °C and thermal activation over obstacles, when fine oxide nanoparticles of diameter 5–20 nm are present.

Temperature-dependent mechanical deformation of silicon at the nanoscale: Phase transformation versus defect propagation

This study uses high-temperature nanoindentation coupled with in situ electrical measurements to investigate the temperature dependence (25–200 °C) of the phase transformation behavior of diamond cubic (dc) silicon at the nanoscale. Along with in situ indentation and electrical data, ex situ characterizations, such as Raman and cross-sectional transmission electron microscopy, have been used to reveal the indentation-induced deformation mechanisms. We find that phase transformation and defect propagation within the crystal lattice are not mutually exclusive deformation processes at elevated temperature. Both can occur at temperatures up to 150 °C but to different extents, depending on the temperature and loading conditions. For nanoindentation, we observe that phase transformation is dominant below 100 °C but that deformation by twinning along {111} planes dominates at 150 °C and 200 °C. This work, therefore, provides clear insight into the temperature dependent deformation mechanisms in dc-Si at the nanoscale and helps to clarify previous inconsistencies in the literature.

High Temperature Nanoindentation Response of RTM6 Epoxy Resin at Different Strain Rates

This paper explores the feasibility of characterizing the mechanical response of the commercial aerospace grade epoxy resin RTM6 by nanoindentation tests at varying temperatures and strain rates. Since glassy polymers exhibit time-dependent mechanical properties, a dynamic nanoindentation technique was used. This method consists on superimposing a small sinusoidal force oscillation on the applied force. Viscoelastic properties are then characterized by their storage and loss moduli, whereas the visco-plastic response of the material can be associated to its hardness. In such experiments, thermal stability of the measuring technique is critical to achieve a low thermal drift and it becomes increasingly important as the measuring temperature increases. Our results show that conventional methods applied for drift correction in nanoindentation of inorganic materials are not applicable to glassy polymers leading to physically inconsistent results. We propose a method for drift correction based on the hypothesis that viscoelastic modulus should be a function of the applied load and frequency but independent of the global strain rate. Using this method, it was possible to determine the viscoplastic properties of RTM6 between RT and 200 °C.

Structural relaxation driven increase in elastic modulus for a bulk metallic glass

The change in elastic modulus as a function of temperature was investigated for a zirconium-based bulk metallic glass. High temperature nano-indentation was done over a wide temperature range from room temperature to the glass-transition. At higher temperature, there was a transition from inhomogeneous to homogeneous deformation, with a decrease in serrated flow and an increase in creep displacement. Hardness was found to decrease, whereas elastic modulus was found to increase with temperature. The increase in elastic modulus for metallic glass at higher temperature was explained by diffusive rearrangement of atoms resulting in free volume annihilation. This is in contrast to elastic modulus increase with temperature for silicate glasses due to compaction of its open three dimensional coordinated structure without any atomic diffusion.

Towards Simulation of Dislocation-Based Creep Mechanisms: Application to Oxide Dispersion Strengthening Steels

This paper presents an experimental study on the micro-creep response of a model Oxide Dispersion Strengthening (ODS) ferritic steel, using high temperature nano-indentation testing. The results are interpreted using a theoretical approach based on different dislocation climb mechanisms, accounting for the present testing conditions: high stress and high dislocation density. This work is regarded as a first step towards implementation of dislocation-based creep mechanisms in advanced dislocation dynamics simulations.

Elevated temperature mechanical properties of novel ultra-fine grained Cu–Nb composites

Ultra-fine grained materials exhibit outstanding properties and are therefore favorable for prospective applications. One of these promising systems is the composite assembled by the body centered cubic niobium and the face centered cubic copper. Cu–Nb composites show a high hardness and good thermal stability, as well as a high radiation damage tolerance. These properties make the material interesting for use in nuclear reactors. The aim of this work was to create a polycrystalline ultra-fine grained composite for high temperature applications. The samples were manufactured via a powder metallurgical route using high pressure torsion, exhibiting a randomly distributed oriented grain size between 100 and 200nm. The mechanical properties and the governing plastic deformation behavior as a function of temperature were determined by high temperature nanoindentation up to 500°C. It was found that in the lower temperature regions up to 300°C the plastic deformation is mainly governed by dislocation interactions, such as dislocation glide and the nucleation of kink pairs. For higher temperatures, thermally activated processes at grain boundaries are proposed to be the main mechanism governing plastic deformation. This mechanistic view is supported by temperature dependent changes in hardness, strain rate sensitivity, activation volume, and activation energy.

Tip shape effect on hot nanoindentation hardness and modulus measurements

This paper focuses on tip shape and degradation of diamond indenters upon high temperature nanoindentation tests. Accurate indenter area functions (IAFs) are essential for the correct measurement of mechanical properties by instrumented indentation techniques (IIT), particularly during high temperature (HT) nanoindentation. However, being a relatively new technique, sufficient information is lacking. This paper examines the shape and degradation of a Berkovich indenter tip after HT nanoindentation testing of 1 mm-thick SiC and Al thin films at room temperature and at T=100°C, 200°C and 300°C. IAFs were determined by the reference method and by atomic force microscopy (AFM), with the latter giving higher contact areas, although tip defect values extracted from both methods were in good agreement. Examination of the tip by AFM after HT nanoindentation on SiC reveals a blunt tip and the need for a new IAF. The work emphasizes the importance of carrying out indenter tip shape calibrations on a regular basis, especially when indenting and scanning hard samples and metals that readily oxidise at T>200°C, where the tip gets easily contaminated.

Temperature dependent deformation mechanisms in pure amorphous silicon

High temperature nanoindentation has been performed on pure ion-implanted amorphous silicon (unrelaxed a-Si) and structurally relaxed a-Si to investigate the temperature dependence of mechanical deformation, including pressure-induced phase transformations. Along with the indentation load-depth curves, ex situ measurements such as Raman micro-spectroscopy and cross-sectional transmission electron microscopy analysis on the residual indents reveal the mode of deformation under the indenter. While unrelaxed a-Si deforms entirely via plastic flow up to 200 °C, a clear transition in the mode of deformation is observed in relaxed a-Si with increasing temperature. Up to 100 °C, pressure-induced phase transformation and the observation of either crystalline (r8/bc8) end phases or pressure-induced a-Si occurs in relaxed a-Si. However, with further increase of temperature, plastic flow rather than phase transformation is the dominant mode of deformation. It is believed that the elevated temperature and pressure together induce bond softening and “defect” formation in structurally relaxed a-Si, leading to the inhibition of phase transformation due to pressure-releasing plastic flow under the indenter.

Progress in high temperature nanomechanical testing of coatings for optimising their performance in high speed machining

Frictional heating results in very high operating temperatures in high speed machining but the nanoindentation tests used to evaluate novel PVD coating systems for improved cutting performance are invariably performed at room temperature. If nanomechanical measurements are to be used reliably in the optimisation of coatings for high speed machining then it is much better that the measurements are performed at the relevant temperature. High temperature nanoindentation data are reviewed for a wide range of nitride-based hard coatings on cemented carbide and design rules suggested for coating optimisation for different machining applications. The importance of high temperature mechanical properties and microstructure on the adaptive and multifunctional behaviour in improving tool life is investigated. The coatings studied show large differences in how their hardness, modulus and H/E vary with increasing temperature which have a significant influence on their behaviour in high temperature mechanical contact applications which have differing requirements in terms of hot hardness and plasticity. In continuous high-speed turning operations the high temperature hardness is paramount and coatings with high hot hardness display longer tool life. In interrupted cutting conditions toughness and plasticity are at least as important, and in end milling of hardened steels for example, high hot hardness should be combined with improved plasticity for longer tool life. Multilayer AlTiCrSiYN/AlTiCrN coatings have shown improved performance compared to the state of the art monolayer coatings. The reasons for this improved performance are discussed. Overall, the high temperature nanoindentation data show excellent correlation to coating life in high speed machining applications.

The Role of Innovative Nanomechanical Test Techniques in Designing More Durable, Adaptive and Multifunctional Coatings

For applications involving high temperature contact the mechanical properties at the operating temperature are more relevant than those measured at room temperature. High temperature nanoindentation and nano-impact data are reviewed for a wide range of nitride-based hard coatings on cemented carbide and design rules suggested for coating optimisation for different machining applications.

Optimum high temperature strength of two-dimensional nanocomposites

High-temperature nanoindentation was used to reveal nano-layer size effects on the hardness of two-dimensional metallic nanocomposites. We report the existence of a critical layer thickness at which strength achieves optimal thermal stability. Transmission electron microscopy and theoretical bicrystal calculations show that this optimum arises due to a transition from thermally activated glide within the layers to dislocation transmission across the layers. We demonstrate experimentally that the atomic-scale properties of the interfaces profoundly affect this critical transition. The strong implications are that interfaces can be tuned to achieve an optimum in high temperature strength in layered nanocomposite structures.

Variations in nanomechanical properties of back-end Zr–2.5Nb pressure tube material

The Zr–2.5Nb pressure tube alloy used in Canada Deuterium Uranium (CANDU) nuclear reactors consists of a dual-phase microstructure produced by a multi-step manufacturing process. The metallurgical characteristics of the pressure tubes influence their in-reactor behavior, especially with respect to reactor life-limiting properties such as diametral creep. In order to predict the in-reactor behavior of pressure tubes, a greater understanding of the influence of tube-to-tube variations in metallurgical factors such as texture, grain size, and β-phase percentage would be greatly beneficial. In this paper, a testing method combining high temperature nanoindentation with subsequent electron channeling contrast imaging (ECCI) in the scanning electron microscope (SEM) is presented to compare two back end pressure tube off-cuts. Nanoindentation was used to measure local mechanical properties such as hardness, modulus, and strain rate sensitivity. Post-examination of residual indents with ECCI allowed for the correlation of microstructural characteristics to nanomechanical properties. A difference in hardness was observed between the two tubes in the axial normal plane, which was correlated to differences in β-phase area percentage and/or morphology.

Mechanical Characterization of Lead-Free Sn-Ag-Cu Solder Joints by High-Temperature Nanoindentation

The reliability of Pb-free solder joints is controlled by their microstructural constituents. Therefore, knowledge of the solder microconstituents’ mechanical properties as a function of temperature is required. Sn-Ag-Cu lead-free solder alloy contains three phases: a Sn-rich phase, and the intermetallic compounds (IMCs) Cu6Sn5 and Ag3Sn. Typically, the Sn-rich phase is surrounded by a eutectic mixture of β-Sn, Cu6Sn5, and Ag3Sn. In this paper, we report on the Young’s modulus and hardness of the Cu6Sn5 and Cu3Sn IMCs, the β-Sn phase, and the eutectic compound, as measured by nanoindentation at elevated temperatures. For both the β-Sn phase and the eutectic compound, the hardness and Young’s modulus exhibited strong temperature dependence. In the case of the intermetallics, this temperature dependence is observed for Cu6Sn5, but the mechanical properties of Cu3Sn are more stable up to 200°C.