Nm Everitt

High temperature nanoindentation – the importance of isothermal contact

The suitability of high temperature techniques was investigated by finite element analysis modelling to give a qualitative view of how the thermal picture develops under a diamond indenter without controlled heating of the diamond. In the case of a low-conductivity sample such as fused silica, the thermal gradient below the indenter tip is relatively diffuse, whereas with a high-conductivity sample such as gold, most of the sample is able to equilibrate at the set temperature, leading to a very steep thermal gradient in the volume of material that must accommodate the deformation. However, in both cases indentation is occurring in material that is at a lower, and unknown, temperature than the bulk sample. The results of the model are validated by comparing results obtained by heating the indenter either indirectly by contact with the sample or utilising a separate heater for the indenter (an isothermal contact method). Nanoindentation results are presented for experiments using a cubic boron nitride Berkovich indenter on both fused silica, at temperatures up to 600°C, and annealed gold at temperatures up to 300°C. Indentation without separate indenter heating tended to produce unacceptable thermal perturbation in the system, whereas the isothermal contact method maintained acceptable thermal drift and produced values of modulus and hardness that compared well with those in the literature.

On the Precipitation Hardening of Selective Laser Melted AlSi10Mg

Precipitation hardening of selective laser melted AlSi10Mg was investigated in terms of solution heat treatment and aging duration. The influence on the microstructure and hardness was established, as was the effect on the size and density of Si particles. Although the hardness changes according to the treatment duration, the maximum hardening effect falls short of the hardness of the as-built parts with their characteristic fine microstructure. This is due to the difference in strengthening mechanisms.

CVD diamond wires and tubes

Abstract Diamond has been uniformly deposited onto the surface of thin metal wires using hot filament CVD. The diamond-coated wires are stronger and stiffer than the uncoated wires. Subsequent etching of the metal core in a suitable chemical reagent allows free-standing diamond tubes to be made, the typical dimensions being 1 cm long with an internal diameter of 10–150 μm. The formation of a thick, chemical-resistant carbide layer at the metal-diamond interface when using Ti and W wires is investigated.

In-situ mass spectrometric study of the gas phase species involved in CVD of diamond as a function of filament temperature

Abstract We have used a molecular beam mass spectrometer to obtain quantitative measurements of the composition of the gas-phase species during the chemical vapour deposition (CVD) of diamond films as a function of filament temperature for a variety of different hydrocarbon precursor gases. For filament temperatures near to, and above, the optimum for diamond growth (ca. 2400 K), we find that the relative concentrations of the various stable hydrocarbon species (CH 4 , C 2 H 2 and C 2 H 4 ) present in the gas mixture, and the way that these concentrations vary with temperature, are remarkably insensitive to the particular choice of hydrocarbon feedstock gas.

CVD diamond coated fibres

Abstract Diamond-coated fibres have been fabricated using hot filament chemical vapour deposition (CVD) and tested for mechanical stiffness. The fibres coated include small (

Microhardness anisotropy of lamellar bone

The Knoop microhardness test has been utilised to observe in-plane microhardness anisotropy of rat tibiae. The elongated rhombohedral geometry of the Knoop indenter enables the Knoop microhardness (HK) to be calculated for a given indenter orientation. Two indenter orientations were used: the major axis of the indenter was aligned along the length of, and across the mid-sagittal section. The statistical analysis demonstrated that the variation in HK was primarily due to the orientation of the Knoop indenter (p < 0.001). HK was consistently greater when the indenter was aligned with the major diagonal radial on the mid-sagittal section.

Young's modulus of diamond-coated fibres and wires

Abstract Diamond-coated fibres and wires were produced by hot filament chemical vapour deposition (HFCVD) of diamond on a variety of core materials including tungsten(W) and silicon carbide (SiC). Fibres with a diamond volume fraction exceeding 95% have been produced. Three different methods of measuring the fibre Youngs modulus(a resonance method, a bend test and a tensile test) are presented, together with recent results. Possible applications for such fibres include reinforcements in metal matrix composites (MMCs).

A biomechanical model of anther opening reveals the roles of dehydration and secondary thickening.

Summary Understanding the processes that underlie pollen release is a prime target for controlling fertility to enable selective breeding and the efficient production of hybrid crops. Pollen release requires anther opening, which involves changes in the biomechanical properties of the anther wall. In this research, we develop and use a mathematical model to understand how these biomechanical processes lead to anther opening. Our mathematical model describing the biomechanics of anther opening incorporates the bilayer structure of the mature anther wall, which comprises the outer epidermal cell layer, whose turgor pressure is related to its hydration, and the endothecial layer, whose walls contain helical secondary thickening, which resists stretching and bending. The model describes how epidermal dehydration, in association with the thickened endothecial layer, creates forces within the anther wall causing it to bend outwards, resulting in anther opening and pollen release. The model demonstrates that epidermal dehydration can drive anther opening, and suggests why endothecial secondary thickening is essential for this process (explaining the phenotypes presented in the myb26 and nst1nst2 mutants). The research hypothesizes and demonstrates a biomechanical mechanism for anther opening, which appears to be conserved in many other biological situations where tissue movement occurs.

Preparation of solid and hollow diamond fibres and the potential for diamond fibre metal matrix composites

The development of techniques to grow diamond thin films using chemical vapour deposition (CVD) is now an area of active world-wide research [1, 2] and the unique physical and chemical properties of diamond promise many potential applications in optical components, semiconducting devices and hard wear-resistant coatings [3, 4]. Previous work has focused primarily on planar silicon on molybdenum substrates, but some preliminary results have recently been reported for coatings on wires [5, 6]. This paper describes a technique for producing uniform diamond coatings on the surface of metallic wires or ceramic fibres and the production of free-standing diamond tubes. The factors that affect the quality of the diamond fibres are discussed and their potential use in reinforced composites is considered. In the present experiments, diamond-coating was carried out in a standard hot filament CVD reactor [1, 2], in which CH 4 and H2 in a ratio of 1:100 were passed into a vacuum chamber at a total flow rate of 200 standard cm 3 min -I and a pressure of about 4000 Pa. A Ta filament held at 2000 °C dissociated the gases allowing carbon to deposit on to the surface of the wires and fibres in the form of a polycrystalline diamond film at a rate of about 0.5/xmh -1. If the wire was placed parallel to, and a few millimetres from, the filament (as for planar substrates) the uniformity of the diamond-coating was limited by the thickness of the wire, since diamond grew fastest on the side of the wire facing the filament. This effect became noticeable for wires and fibres with diameter > 250/zm, placing an upper limit upon the thickness of wires or fibres that can be uniformly coated by this method of around 300/zm. Alternatively, if the wire was positioned centrally and coaxially within the coils of the filament, uniform coatings on wires and fibres with a wide range of diameters were achieved. In this case, for thicker wires or fibres (even up to a few millimetres diameter), the diameter of the filament coils was simply increased to maintain an optimum distance of about 4-5 mm between the surface of the wire and the filament. This ensured that the wire was heated to a sufficient temperature to favour diamond deposition (typically about 900 °C), and also that the

Knoop microhardness anisotropy of the ovine radius

The Knoop indenter has been used to characterise fully the Knoop microhardness (H(K)) anisotropy of compact bone. 2120 indentations were performed on mature ovine radii and a linear relationship was found between H(K) and the angle between the major diagonal of the indenter and the lamella boundaries (p<<0.001). H(K) increased significantly with ash fraction (p<0.001), but decreased with atmospheric vapour pressure (p<0.05). A significant interaction was found between ash fraction and atmospheric vapour pressure (p<0.01). H(K) significantly varied with indentation position along the diaphysis and around the cortex (both p<<0.001), however radial variation in H(K) was not statistically significant. The variation of ash fraction showed similar trends. These data show that H(K) varies similarly to Vickers microhardness, but in addition, can provide clear information on the anisotropy of Haversian bone without the need for excising many different indentation planes. A large number of indentations are required to obtain low type I and type II errors in the statistical analysis.