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Tantalum thin films may be deposited in two phases. The stable bulk alpha phase is well known, but the metastable tetragonal beta phase is relatively poorly understood. We reported previously on a series of 100% β -Ta films deposited under varying sputter pressures in a low-oxygen environment, and discussed texture, stresses, and phase selection. Here, we discuss microstructure, morphology, and properties of these same β -Ta films. Grain size increases with sputter pressure, which can be explained by the energies of incident species at the growing film. Mechanical properties were measured by nanoindentation. Hardness decreases with grain size in accordance with the Hall-Petch relation while comparison of indentation modulus with biaxial modulus measurements indicates that the β phase is elastically anisotropic, and much stiffer in the [001] direction than in others. Finally, a canonical resistivity value for virtually oxygen-free, 100% β -Ta films of 169 ± 5 µΩcm is reported for the first time. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Large magnetostriction with low saturation magnetic field was recently reported in Fe-Pd ferromagnetic strain glass alloys. Such behaviour is highly desirable for miniaturized sensor and actuator applications. The origin of high performance magnetostriction in Fe-Pd ferromagnetic strain glass is suggested to stem from its martensitic nanodomains. However, the atomic formation mechanism underlying these nanodomains and their associated local crystal symmetry breaking have not been well revealed. Moreover, accumulating experimental results indicate that the nano-structure can lead to a small saturation field but cannot guarantee large magnetostriction. Consequently, the necessary conditions for low field triggered large magnetostriction of Fe-Pd ferromagnetic strain glass alloys still remain unclear. In this paper, the chemistry, structure and transformation properties of the Fe 98- x Cu 2 Pd x (x = 28.5 ∼ 31) system are systematically explored to discover the origin of the high performance magnetostriction of ferromagnetic strain glass alloys. We found that the structure of ferromagnetic strain glass consists of local chemical order. This leads to tetragonal martensitic nanodomains with the local crystal symmetry breaking. The local chemical order also induces strong local phonon softening and a low modulus during the strain glass transition. Further investigation shows that the combination of martensitic nanodomains and low modulus are the necessary conditions to achieve both large magnetostriction and a low saturation field, because they can result in small energy barriers for the rotation of nanodomains. These findings provide an effective guideline to design high performance magnetostrictive materials and devices. [Display omitted] [ABSTRACT FROM AUTHOR]

Abstract: One of the crucial characteristics of a porous medium is its relative density ρ *, i.e. the volume fraction of the solid. For example, in low density foams (ρ * <0.1) the macroscopic material properties depend on the foam geometry only through the relative density. The relative density of nanoporous (NP) metal foams synthesized by dealloying is typically in the range ρ * ⩾0.4. This places NP metal foams in a previously unexplored parameter regime and necessitates reexamination of scaling laws derived for low density foams. In this work we demonstrate that the modulus of NP metal foams does not exhibit a clear correlation with the relative density. We trace this apparent disagreement with existing scaling laws to the agglomeration of mass in the junctions. We then derive and verify a new scaling relationship for the dependence of relative density and relative modulus on the geometric parameters such as strut thickness, length and junction size. We find good agreement between our model and experimental measurements for single crystal gold NP foams with large junction sizes. In contrast, polycrystalline NP platinum with nanosized grains within the struts shows an enhancement in the modulus that cannot be attributed to the foam geometry only. Based on this analysis, we infer a more than an order of magnitude enhancement of the modulus of the nanograined Pt struts compared to bulk platinum. [Copyright &y& Elsevier]

Abstract: This paper scrutinizes the reliability of indentation-based damage quantification, frequently used by many industrial and academic researchers. In this methodology, damage evolution parameters for continuum damage models are experimentally measured by probing the deformation-induced degradation of either hardness or indentation modulus. In this critical assessment the damage evolution in different sheet metals was investigated using this indentation approach, whereby the obtained results were verified by other experimental techniques (scanning electron microscopy, X-ray microtomography and highly sensitive density measurements), and by finite element simulations. This extensive experimental–numerical assessment reveals that the damage-induced degradation of both hardness and modulus is at least partially, but most likely completely, masked by other deformation-induced microstructural mechanisms (e.g. grain shape change, strain hardening, texture development, residual stresses and indentation pile-up). It is therefore concluded that hardness-based or modulus-based damage quantification methods are intrinsically flawed and should not be used for the determination of a damage parameter. [Copyright &y& Elsevier]

A new correlation between ultrasonic shear wave velocity and Poisson’s ratio has been established for isotropic solid materials, based on the data generated experimentally and collected from the literature. Poisson’s ratio has been found to decrease with increasing ultrasonic velocity in various solid materials such as metals and alloys, ceramics and glasses, intermetallics and polymers. The slope of the plot of the ultrasonic velocity against Poisson’s ratio is found to be almost constant for any given alloy system with different microstructures associated with various heat treatments, alloying elements, grain size, temperature effect, etc. Further, it has been demonstrated that ultrasonic shear wave velocity is a better parameter for materials characterization as compared to longitudinal wave velocity. [Copyright &y& Elsevier]