Giant pop-ins and amorphization in germanium during indentation

Sudden excursions of unusually large magnitude (>1 μm), “giant pop-ins,” have been observed in the force-displacement curve for high load indentation of crystalline germanium(Ge). A range of techniques including Raman microspectroscopy, focused ion-beam cross sectioning, and transmission electron microscopy, are applied to study this phenomenon. Amorphous material is observed in residual indents following the giant pop-in. The giant pop-in is shown to be a material removal event, triggered by the development of shallow lateral cracks adjacent to the indent. Enhanced depth recovery, or “elbowing,” observed in the force-displacement curve following the giant pop-in is explained in terms of a compliant response of plates of material around the indent detached by lateral cracking. The possible causes of amorphization are discussed, and the implications in light of earlier indentation studies of Ge are considered

Effect of processing condition and composition on the microhardness of Cu-(2.5-10)vol.%Al₂O₃ nanocomposite powder particles produced by high energy mechanical milling

Nanostructured Cu-(2.5-10vol.%)Al₂O₃ nanocomposites were produced using high energy mechanical milling. For the as-milled Cu- Al₂O₃ composite powder particles having Al₂O₃ volume fractions of 2.5% and 5%, the increase in average microhardness is significant with the increase of milling time from 12 hours to 24 hours. With the increase of the content of Al₂O₃ nanoparticles the microhardness increases and in the range of 255HV-270HV. The milled nanocomposite powders were heat treated at 150, 300, 400 and 500°C for 1 hour, respectively, to determine the thermal stability of the powder particles as a function of annealing temperature. The average microhardness increased/decreased for the Cu- Al₂O₃ composites after annealing at 150°C due to the dislocation density, while increasing the annealing temperature to 300°C and 400°C the average microhardness almost remained mostly unchanged. Further increasing the annealing temperature to 500°C causes significant decrease in average microhardness due to reduction in dislocation density and coarsening of Cu grains of the Cu- Al₂O₃ composite powders produced after 24 hours of milling. This paper is to report and discuss the changes of the microhardness of the material, caused by the compositions and processing conditions, used to fabricate the Cu-(2.5-10)vol.% Al₂O₃ nanocomposite powders

Phase transformations in (111) Si after spherical indentation

Phase transformations in (111) Si after spherical indentation have been investigated by cross-sectional transmission electron microscopy. Even at an indentation load of 20 mN,a phase transformation zone including the high-pressure crystalline Si phases was observed within the residual imprints. The volume of the transformation zone, as well as that of the crystalline phases increased with the indentation load. Below the transformation zone, slip was found to occur on {311} planes rather than on {111}planes, usually observed on indentation of (100) Si. The distribution of defects was asymmetric, and for indentation loads up to 80 mN, their density was significantly lower than that reported for (100) Si. The experimental observations correlated well with modeling of the applied stress through ELASTICA

An Architecture for Provenance Systems

This document covers the logical and process architectures of provenance systems. The logical architecture identifies key roles and their interactions, whereas the process architecture discusses distribution and security. A fundamental aspect of our presentation is its technology-independent nature, which makes it reusable: the principles that are exposed in this document may be applied to different technologies

Sandwich-structured, damage-resistant TiN/graded TiSiN/TiSiN film

The development of hard, multi-layer coatings is an effective strategy to enhance the wear resistance of cutting tools and so extend their service life. In the present study, a sandwich structured TiN/g-TiSiN/TiSiN film (where a graded (g-) TiSiN layer with an increasing Si content from 0 to 10 at% was inserted as a transitional layer between the TiN layer and the TiSiN layer with a fixed silicon content of 10 at%) was prepared on to a M42 tool steel substrate. Its mechanical properties were compared to both a dual-layered TiN/g-TiSiN film and a monolithic TiN film. Nanoindentation testing, assisted by focused-ion-beam (FIB) microscopy, was employed to evaluate contact-induced deformation and the mode of fracture of these films. Indented regions created on samples by a 5 μm radius indenter were examined by transmission electron microscopy (TEM). Finite element analysis was used to model the stress distributions within these films and predict the regions where crack initiation and growth may occur. The deformation of the monolithic TiN film was found to be predominantly accommodated by shear sliding along columnar grain boundaries, leading to a lower resistance to deformation. For the bilayer TiN/g-TiSiN film, the g-TiSiN layer hindered the propagation of columnar cracks, however, this bilayer film exhibited a stress concentration together with radial cracks at the bottom of the film. Compared with the former two films, the sandwich-structured film that contained the graded TiSiN interlayer exhibited the highest resistance to contact damage. This is because the graded TiSiN interlayer altered the stress distribution in the film and lowered the overall stress concentration level

Migration of dissolved organic carbon in biochars and biochar‑mineral complexes

The objective of this work was to determine the contribution of dissolved organic carbon (DOC) from a biochar mineral complex (BMC), so as to better understand the interactions between DOC, biochar, clay, and minerals during thermal treatment, and the effects of BMC on amended soils. The BMC was prepared by heating a mixture of a H3PO4‑treated saligna biochar from Acacia saligna, clays, other minerals, and chicken manure. The BMC was applied to a sandy loam soil in Western Australia, where wheat was grown. Liquid chromatography‑organic carbon detection (LC‑OCD) tests were carried out on water extracts from the untreated biochar, the BMC, the BMC‑amended soil, and on a control soil to measure the DOC concentration. LC‑OCD tests provide a fingerprint of the DOC, which allows the fractions of DOC to be determined. Thermal processing enhanced the reaction of the A. saligna biochar with manure, clays and minerals, and affected the distribution of the DOC fractions. Notably, the process leads to immobilization of hydrophobic DOC and to an increase in the concentration of low‑molecular‑weight neutrals in the BMC. The application of the BMC to soil increases the DOC in the amended soil, especially the biopolymer fraction.The objective of this work was to determine the contribution of dissolved organic carbon (DOC) from a biochar mineral complex (BMC), so as to better understand the interactions between DOC, biochar, clay, and minerals during thermal treatment, and the effects of BMC on amended soils. The BMC was prepared by heating a mixture of a H3PO4‑treated saligna biochar from Acacia saligna, clays, other minerals, and chicken manure. The BMC was applied to a sandy loam soil in Western Australia, where wheat was grown. Liquid chromatography‑organic carbon detection (LC‑OCD) tests were carried out on water extracts from the untreated biochar, the BMC, the BMC‑amended soil, and on a control soil to measure the DOC concentration. LC‑OCD tests provide a fingerprint of the DOC, which allows the fractions of DOC to be determined. Thermal processing enhanced the reaction of the A. saligna biochar with manure, clays and minerals, and affected the distribution of the DOC fractions. Notably, the process leads to immobilization of hydrophobic DOC and to an increase in the concentration of low‑molecular‑weight neutrals in the BMC. The application of the BMC to soil increases the DOC in the amended soil, especially the biopolymer fraction

Synergistic toughening of hard, nacre-mimetic MoSi2 coatings by self-assembled hierarchical structure

Like many other intermetallic materials, MoSi2 coatings are typically hard, but prone to catastrophic failure due to their low toughness at ambient temperature. In this paper, a self-assembled hierarchical structure that closely resembles that of nacre (i.e., mother of pearl) was developed in a MoSi2 -based coating through a simple, yet cost-effective, depostion technique. The newly formed coating is tough and can withstand multiple indentations at high loads. Key design features responsible for this remarkable outcome were identified. They include a functionally graded multilayer featuring elastic modulus oscillation, varying sublayer thickness and a columnar structure that are able to attenuate stress concentrations; interlocking boundaries between adjacent sublayers that improve the bonding and arrest the cracks; a transitional layer that bridges the coating and substrate and facilitates load transfer. Moreover, the contributions of six important structural characteristics to damage resistance are quantified using finite elemnet analysis and in an additive manner (i.e., from low- to high-level complexity). The in-situ toughened coating is envisaged to enhance the mechanical performance and extend the lifespan of metal components used in safety-critical applications

Transport critical current density in Fe-sheathed nano-SiC doped MgB2 wires

The nano-SiC doped MgB2/Fe wires were fabricated using a powder-in-tube method and an in-situ reaction process. The depression of Tc with increasing SiC doping level remained rather small due to the counterbalanced effect of Si and C co-doping. The high level SiC co-doping allowed creation of the intra-grain defects and nano-inclusions, which act as effective pinning centers, resulting in a substantial enhancement in the Jc(H) performance. The transport Jc for all the wires is comparable to the magnetic Jc at higher fields despite the low density of the samples and percolative nature of current. The transport Ic for the 10wt% SiC doped MgB2/Fe reached 660A at 5K and 4.5T (Jc = 133,000A/cm2) and 540A at 20K and 2T (Jc = 108,000A/cm2). The transport Jc for the 10wt% SiC doped MgB2 wire is more than an order of magnitude higher than for the state-the-art Fe-sheathed MgB2 wire reported to date at 5K and 10T and 20K and 5T respectively. There is a plenty of room for further improvement in Jc as the density of the current samples is only 50%.Comment: 4 pages, 7 figures, presented at ASC 2002, Housto

Phase transformation pathways in amorphous germanium under indentation pressure

Nanoindentation-induced phase transformations have been studied in amorphous Ge thin films. These films initially tend to deform via plastic flow of the amorphous phase under load but at a critical pressure a sudden phase transformation occurs. This transformation, to a soft metallic (β-Sn-like)-Ge phase confined under the indenter, is signified by a "pop-in" event on loading. Following "pop-in," the indentation tests fall into two distinct types of behavior. In one case, the rate of deformation with increasing load after "pop-in" increases, and the observed end-phase following complete unloading is observed to be predominately diamond-cubic Ge. In the other case, the deformation rate (slope of the loading curve) remains the same as that before "pop-in," and the end phases following unloading are found to contain predominantly unstable r8 and more stable hexagonal Ge phases. The different transformation pathways for these two cases are shown to be related to the probability that the soft (β-Sn-like)-Ge phase volume, which suddenly forms at the transformation pressure, is either unconstrained by the indenter tip (the first case) or totally constrained under the indenter tip (in the latter case)

Indentation-Induced Damage Mechanisms in Germanium

The response of crystalline Ge to indentation has been studied over a range of maximum loads. At a certain load, an unusual 'giant pop-in' event occurs, in which a discontinuous extension of >1 μm is observed in the force-displacement curve. In such cas