On Extracting Mechanical Properties from Nanoindentation at Temperatures up to 1000∘^{\circ}C

Alloyed MCrAlY bond coats, where M is usually cobalt and/or nickel, are essential parts of modern turbine blades, imparting environmental resistance while mediating thermal expansivity differences. Nanoindentation allows the determination of their properties without the complexities of traditional mechanical tests, but was not previously possible near turbine operating temperatures. Here, we determine the hardness and modulus of CMSX-4 and an Amdry-386 bond coat by nanoindentation up to 1000$^{\circ}$C. Both materials exhibit a constant hardness until 400$^{\circ}$C followed by considerable softening, which in CMSX-4 is attributed to the multiple slip systems operating underneath a Berkovich indenter. The creep behaviour has been investigated via the nanoindentation hold segments. Above 700$^{\circ}$C, the observed creep exponents match the temperature-dependence of literature values in CMSX-4. In Amdry-386, nanoindentation produces creep exponents very close to literature data, implying high-temperature nanoindentation may be powerful in characterising these coatings and providing inputs for material, model and process optimisations

Apparatus and process for determining the susceptibility of microorganisms to antibiotics

A process for determining the susceptibility of microorganisms to antibiotics involves introducing a diluted specimen into discrete quantities of a selective culture medium which favors a specific microorganism in that the microorganism is sustained by the medium and when so sustained will change the optical characteristics of the medium. Only the specific microorganism will alter the optical characteristics. Some of the discrete quantities are blended with known antibiotics, while at least one is not. If the specimen contains the microorganisms favored by the selective medium, the optical characteristics of the discrete quantity of pure selective medium, that is the one without antibiotics, will change. If the antibiotics in any of the other discrete quantities are ineffective against the favored microorganisms, the optical characteristics of those quantities will likewise change. No change in the optical characteristics of a discrete quantity indicates that the favored microorganism is susceptible to the antibiotic in the quantity

Numerical study of critical properties and hidden orders in dimerized spin ladders

Dimerized antiferromagnetic spin-1/2 ladders are known to exhibit a quantum critical phase transition in the ground state, the existence or absence of which is dependent on the dimerization pattern of the ladder. The gapped phases cannot be distinguished by the conventional Landau long-range order parameter. However, they possess a non-local (hidden) string order parameter, which is non-zero in one phase and vanishes in the other. We use an exact diagonalization technique to calculate ground state energies, energy gaps and string order parameters of dimerized two- and three-leg Heisenberg ladders, as well as a critical scaling analysis to yield estimates of the critical exponents nu and beta.Comment: 7 pages, 14 figures. V.2: Extended version to appear in PR

Investigation of a high angle grain boundary in Fe2.4wt.%Si BCC micropillars

Iron-silicon sheet steel is the most widely used material for the iron cores of electrical machines like generators, motors or transformers. Although already ubiquitous, the demand will nevertheless rise in the future since electro-mobility is spreading rapidly. For this reason, even small improvements of efficiency have a huge energy saving potential. Currently, hysteresis losses are one of the main limiting factors for efficiency, resulting from the movement of domain walls, which may be pinned by dislocations. Even though electrical sheet steel is generally used in a fully recrystallized state, it is the final stages of production involving cutting that introduce large plastic strains, and hence high local dislocation densities. These have been shown to cause significant loss in performance. The aim of this work is to understand the evolution of deformation structures on a fundamental basis taking grain boundaries, size effects and different strain-rates into account. To this end, single- and bi-crystalline-micropillars of 1, 2 und 4 µm in diameter were investigated. 158 micropillars were deformed in order to provide a statistically-relevant dataset. In addition, macroscopic single- and bi-crystal-samples with a diameter of 2.5 mm were deformed as a reference for the size effect. The considered grain boundary has an angle of about 50° and a very high geometrical transmission factor (m’=0.89). Regarding the strain-rate-sensitivity three different strain rates were used for the deformation of the micro-/macroscopic single- and bi-crystals, with strain rate jump tests additionally conducted for the single-crystals. To visualize the deformation structure, selected micropillars were lifted out of the sample, thinned to the middle and analyzed utilizing EBSD. For most micropillars a clear slip system could be determined. Regarding one orientation the active slip system changed from the single- to the bi-crystal, likely because the newly-activated slip system was better aligned relative to the slip system of the other half-crystal. The bi-crystal-micropillars showed a higher resolved shear stress despite direct slip transmission across the grain boundary. Furthermore, a pronounced strain-rate sensitivity and size effect was found

The influence of temperature on the development and swimming performance of flatfish

Growth and development were studied in turbot {Scophthalmus maximus L.) reared at 12° and 16° until 26 days after hatching. Muscle growth occurred by fibre hypertrophy and hyperplasia and was faster at 16°. In larvae, the sequence of organogenesis was altered by temperature. The influence of temperature on the swimming performance of settled stages of turbot and plaice (Pleuronectes platessa) was studied. Maximum swimming speed (Umax), elicited following an escape response, scaled similarly between 13 and 23°, for turbot, and could be fitted by the model: A comparison of Umax between wild caught and laboratory reared turbot showed that Umax for farmed turbot was lower than for wild fish filmed within 2 weeks of capture. 3 months after capture the average differences in escape performance were no longer significant, suggesting they were due to an acclimation. Standardised Umax for eighteen wild juvenile turbot was determined at 18° and over a temperature change. Repeatability of ranking of the experimental Umax of individuals was maintained over a 6 week period, and through temperature change. For plaice Umax scaled in proportion to TL0.65 between 5° and 13°. Umax did not increase at temperatures above 9°. There was no difference in Umax or tail beat frequency (f) between laboratory reared and wild caught plaice. Umax and f decreased after an acute temperature reduction from 9° to 5° and showed no compensation for the reduction temperature after a 29 days acclimation period. Stride length (X) was independent of temperature. After the 29 day period at 5°, raising the temperature to 9° resulted in an increase in Umax without a corresponding increase in f, although tail beat amplitude (A) was higher. The effects of temperature change during early development on locomotory performance and phenotype are discussed

Towards nanoindentation at application-relevant temperatures – A study on CMSX-4 alloy and amdry-386 bond coat

With nickel-based superalloys reaching their fundamental limit in high-temperature applications, new alloys are required with improved mechanical properties. Small-scale mechanical testing – particularly nanoindentation – is of great benefit to alloy development, allowing hardness and modulus to be measured on small volumes of newly-developed materials. We show that it is now possible to carry out such tests in vacuum up to 1000˚C, paving the way for candidate alloys and coatings to be tested at operation-relevant conditions. In this work, a \u3c001\u3e oriented single-crystal CMSX4 sample and a 200 µm Amdry-386 bond coat were tested using a modified MicroMaterials NanoTest indenter. 1 µm indents were placed at 50 µm spacings from the bulk into the coating, allowing local mechanical properties to be determined. The data show a room-temperature hardness of CMSX4 of 4 GPa and modulus of 110 GPa, close to that found in the literature. The Amdry-386 at this temperature has a hardness and modulus of 4 GPa and 95 GPa, respectively. The CMSX4 shows a hardness peak at 400˚C and 5.5 GPa, after which the hardness rapidly decreases to around 2 GPa at the highest temperatures. The bond coat matches this behaviour closely. At both room and elevated temperatures, almost 100% of the indents show a thermal drift of \u3c0.3 nm/s, corresponding to a depth uncertainty of \u3c5%. This unparalleled drift performance allows future investigations of creep behaviour that were not possible until now

(Nano-)Mechanical properties and deformation mechanisms of the topologically closed packed Fe-55Mo µ-phase at room temperature

Topologically close-packed (TCP) intermetallic phase precipitates in nickel-base superalloys are assumed to cause a deterioration of the mechanical properties of the γ - γ‘matrix. Although these intermetallic phases are well studied in terms of their structure, their mechanical properties have not yet been investigated in detail due to their large and complex crystal structures and pronounced brittleness. In this study we have chosen the Fe-Mo system as a model system in order to investigate the plastic deformation behavior of these phases. A special focus is placed on the hexagonal μ-phase. To this aim we apply nano-mechanical testing methods: nano-indentation and micropillar-compression to enable plastic deformation of these brittle phases. This is due to the confining pressure in nano-indentation and the reduction in specimen size in micro-compression experiments. Indentation experiments at room temperature show a hardness of ~11 GPa and a Young’s modulus of ~270 GPa. Electron backscatter diffraction (EBSD) assisted slip trace analysis reveals dominant dislocation activity on basal planes at room temperature. Micro-compression experiments on well-oriented single-crystalline micro-pillars reveal the structure related anisotropy of the critical shear stresses (CRSS) of different slip systems. Finally, transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HR-TEM) investigations of specimens target-prepared from nano-indents and deformed micro-pillars reveal the dislocation and defect structures of the µ-phase

Numerical study of the influence of surface reaction probabilities on reactive species in an rf atmospheric pressure plasma containing humidity

International audienceThe quantification and control of reactive species (RS) in atmospheric pressure plasmas (APPs) is of great interest for their technological applications, in particular in biomedicine. Of key importance in simulating the densities of these species are fundamental data on their production and destruction. In particular, data concerning particle-surface reaction probabilities in APPs are scarce, with most of these probabilities measured in low-pressure systems. In this work, the role of surface reaction probabilities, gamma, of reactive neutral species (H, O and OH) on neutral particle densities in a He-H2O radio-frequency micro APP jet (COST-mu APPJ) are investigated using a global model. It is found that the choice of gamma, particularly for low-mass species having large diffusivities, such as H, can change computed species densities significantly. The importance of gamma even at elevated pressures offers potential for tailoring the RS composition of atmospheric pressure microplasmas by choosing different wall materials or plasma geometries

Microcompression experiments on glasses ‐ strain rate sensitive cracking behavior

Figure 11 – microcompression experiments on glasses showing stable crack growth (a) and reversible deformation (b) It is well known that the mechanical properties of glasses are closely related to their atomic structure. The exact structure-property-relationship, however, is only poorly understood even for fundamental mechanisms like shear and densification. Nanomechanical test methods like micropillar compression and nano indentation can help fill this gap. In this study a sodium-boro-silicate glass is quenched from different temperatures to induce changes in the atomic structure. Micropillar compression was used to introduce plastic deformation into these glasses at room temperature under a uniaxial stress state. By changing the strain rate it is shown that deformation shifts from completely reversible deformation, to stable crack growth, and finally brittle failure. It is shown that by changing the glass structure, the strain rates corresponding to these deformation regimes are shifted. Finally, the occurrence of shear and densification is discussed. These findings are analysed against the background of the glass structure. Please click Additional Files below to see the full abstract

Deformation of micrometer and mm-sized Fe2.4wt.%Si single- and bi-crystals with a high angle grain boundary at room temperature

Plasticity in body-centred cubic (BCC) metals, including dislocation interactions at grain boundaries, is much less understood than in face-centred cubic (FCC) metals. At low temperatures additional resistance to dislocation motion due to the Peierls barrier becomes important, which increases the complexity of plasticity. Iron-silicon steel is an interesting, model BCC material since the evolution of the dislocation structure in specifically-oriented grains and at particular grain boundaries have far-reaching effects not only on the deformation behaviour but also on the magnetic properties, which are important in its final application as electrical steel. In this study, two different orientations of micropillars (1, 2, 4 microns in diameter) and macropillars (2500 microns) and their corresponding bi crystals are analysed after compression experiments with respect to the effect of size on strength and dislocation structures. Using different experimental methods, such as slip trace analysis, plane tilt analysis and cross-sectional EBSD, we show that direct slip transmission occurs, and different slip systems are active in the bi-crystals compared to their single-crystal counterparts. However, in spite of direct transmission and a very high transmission factor, dislocation pile-up at the grain boundary is also observed at early stages of deformation. Moreover, an effect of size scaling with the pillar size in single crystals and the grain size in bi-crystals is found, which is consistent with investigations elsewhere in FCC metals