The Basics of Nanoindentation Method SHIMIZU, Satoshi
Journal of the Japan Society for Precision Engineering,
2021/04/05, Letnik:
87, Številka:
4
Journal Article
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•The creep behavior of ceramic-organic supercrystalline nanocomposites is assessed for the first time, via nanoindentation.•The organic phase, even though less than 10 wt%, plays a ...dominant role in the nanocomposites’ deformation.•Partial recovery of creep after unloading reveals that supercrystals feature both viscoelasticity and viscoplasticity.•Ligands-facilitated rearrangement of the ceramic nanoparticles is proposed as dominating creep mechanism of supercrystals.•The applicability of nanoindentation methodologies, single loading and continuous stiffness measurement, is analyzed.
Supercrystalline nanocomposites (SCNCs) are inorganic-organic hybrid materials with a unique periodic nanostructure, and thus they have been gaining growing attention for their intriguing functional properties and parallelisms with hierarchical biomaterials. Their mechanical behavior remains, however, poorly understood, even though its understanding and control are important to allow SCNCs’ implementation into devices. An important aspect that has not been tackled yet is their time-dependent deformation behavior, which is nevertheless expected to play an important role in materials containing such a distribution of organic phase. Hereby, we report on the creep of ceramic-organic SCNCs with varying degrees of organic crosslinking, as assessed via nanoindentation. Creep strains and their partial recoverability are observed, hinting at the co-presence of viscoelasticity and viscoplasticity, and a clear effect of crosslinking in decreasing the overall material deformability emerges. We rationalize our experimental observations with the analysis of stress exponent and activation volume, resulting in a power-law breakdown behavior and governing deformation mechanisms occurring at the organic sub-nm interfaces scale, as rearrangement of organic ligands. The set of results is reinforced by the evaluation of the strain rate sensitivity via strain rate jump tests, and the assessment of the effect of oscillations during continuous stiffness measurement mode.
•Micromechanical properties of coals of different coal grades were explored.•The evolutionary characteristics of the nanocarbon structure of coals are investigated.•The relationship between ...nanocarbon structure and micromechanical properties is discussed.
The micromechanical properties of coals are key parameters affecting the development of coalbed methane (CBM). In order to understand the relationship between the micromechanical properties and the nanocarbon structure of coals, high resolution transmission electron microscopy (HRTEM) and nanoindentation were used to investigate the micromechanical properties of vitrinite in different coals and the response to changes in nanocarbon structure. Coals with higher coal rank have greater elastic modulus and hardness. The end-of-loading displacement and creep displacement decrease with the increase of coal rank, both of which have a good negative correlation with the elastic modulus and hardness. Fringe length, degree of orientation, proportion of straight fringes, and proportion of stacks all increase with increasing coal rank. The curvature of the fringes decreases with increasing coal rank. The variation of the nanocarbon structure has an important effect on the micromechanical properties. The nanocarbon structure parameters of fringe length, proportion of straight fringes, degree of orientation, and proportion of stacks have good linear relationships with the micromechanical parameters of elastic modulus and hardness. In addition, this study analyzes the effect of the micromechanical properties of coal on the effectiveness of the proppant. Therefore, the evolution of the nanocarbon structure should be emphasized in future studies on the micromechanical properties of coal.
•The elastic modulus, hardness and creep stress exponents of 3 (U,Ce)O2 compounds were measured up to 800 °C.•The creep stress exponents indicate that the (U,Ce)O2 compounds were deforming by ...dislocation glide at 800 °C.•Cost-effective small scale mechanical testing techniques can used to measure mechanical properties on nuclear materials.
Continuing to refine our knowledge of the evolving mechanical properties of nuclear fuel over the entire fuel service cycle is necessary to understand the pellet-clad mechanical interaction that occurs in the fuel rods during the operation. A challenge with measuring the mechanical properties of irradiated fuels is their high levels of radioactivity that usually require the use of hot cells making testing time consuming and expensive. Nanoindentation based techniques can be employed on minute volumes of material to measure mechanical properties, including Young’s modulus, hardness, and creep stress exponents. Increasing the mixed oxide fuels mechanical properties database through a variety of testing techniques should enhance modelers’ abilities to predict failure mechanisms in the fuel/clad interface. A current challenge to testing mixed oxide fuels is the plutonium component in the fuel. Mixed fluorite type oxides with ceria (CeO2) can be used as a surrogate for mixed oxide fuels. In this study, (U,Ce)O2 solid solutions samples are used to develop elevated temperature nanoindentation and nanoindentation creep testing methods for use on mixed oxide fuels. Nanoindentation testing was performed on 3 separate (Ux-1,Cex)O2 compounds ranging from x equals 0.1 to 0.3 in equal steps at temperatures up to 800 °C: their Young’s modulus, hardness, and creep stress exponents were evaluated. The Young’s modulus decreases in the expected linear manner while the hardness decreases in the expected exponential manner. The nanoindentation creep experiments at 800 °C give stress exponent values, n = 4.7–6.9, that suggests dislocation motion as the deformation mechanism.
Small scale mechanical deformations have gained a significant interest over the past few decades, driven by the advances in integrated circuits and microelectromechanical systems. One of the most ...powerful and versatile characterization methods is the nanoindentation technique. The capabilities of these depth-sensing instruments have been improved considerably. They can perform experiments in vacuum and at high temperatures, such as in-situ SEM and TEM nanoindenters. This allows researchers to visualize mechanical deformations and dislocations motion in real time. Time-dependent behavior of soft materials has also been studied in recent research works. This Special Issue on "Small Scale Deformation using Advanced Nanoindentation Techniques"; will provide a forum for researchers from the academic and industrial communities to present advances in the field of small scale contact mechanics. Materials of interest include metals, glass, and ceramics. Manuscripts related to deformations of biomaterials and biological related specimens are also welcome. Topics of interest include, but are not limited to: Small scale facture Nanoscale plasticity and creep Size-dependent deformation phenomena Deformation of biological cells Mechanical properties of cellular and sub-cellular components Novel mechanical properties characterization techniques New modeling methods Environmentally controlled nanoindentation In-situ SEM and TEM indentation
Most oxide ceramics are known to be brittle macroscopically at room temperature with little or no dislocation‐based plasticity prior to crack propagation. Here, we demonstrate the size‐dependent ...brittle to ductile transition in SrTiO3 at room temperature using nanoindentation pop‐in events visible as a sudden increase in displacement at nominally constant load. We identify that the indentation pop‐in event in SrTiO3 at room temperature, below a critical indenter tip radius, is dominated by dislocation‐mediated plasticity. When the tip radius increases to a critical size, concurrent dislocation activation and crack formation, with the latter being the dominating process, occur during the pop‐in event. Beyond the experimental examination and theoretical justification presented on SrTiO3 as a model system, further validation on α‐Al2O3, BaTiO3, and TiO2 are briefly presented and discussed. A new indentation size effect, mainly for brittle ceramics, is suggested by the competition between the dislocation‐based plasticity and crack formation at small scale. Our finding complements the deformation mechanism in the nano‐/microscale deformation regime involving plasticity and cracking in ceramics at room temperature to pave the road for dislocation‐based mechanics and functionalities study in these materials.
The complex metallic phase γ-Mg17Al12 is found in most Mg-Al alloys, however, its mechanical properties are largely unknown. Here, its deformation at 25–278 °C is studied using several instrumented ...indentation methods (quasi-static, rate jump and stress relaxation) in conjunction with atomic force and electron microscopy. Two distinct deformation regimes with a transition around 150 °C are identified by all techniques. Serrated flow, slip steps and weak thermal activation characterise the low temperature regime, while homogeneous flow in terms of both load-displacement data and distribution of dislocations is seen above 150 °C. The results are discussed in terms of the underlying deformation mechanisms and the role of thermal activation. The transition from lattice or solute diffusion controlled, serrated flow to homogeneous flow is consistent with the onset of dislocation climb. Preliminary observations by TEM are in agreement with expectations based on gamma surface calculations in the literature. The comprehensive use of different instrumented indentation and microscopy techniques facilitates a complementary and consistent characterisation and has allowed us to extend the insights from previous studies at high temperatures across the transition to the low temperature deformation regime. This is essential to unravel the role of Mg17Al12 as a load-bearing phase in technical alloys and the effect of its complex crystal structure on plasticity.
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