Biomedical subjects

V Randle

Publications and source records attributed to V Randle.

8 recordsLinked to original sources

PubMed2005

Time evolution of sigma 3 annealing twins in secondary recrystallized nickel.

Samples of commercially pure nickel have been annealed in air at 0.68T(m) (900 degrees C) for 1, 2 and 3 h in order to study the relationship between the grain growth characteristics and grain boundary misorientation, particularly annealing twins (Sigma 3). Orientation mapping by electron backscatter diffraction was used to obtain the experimental data. Anomalous grain growth was observed in commercially pure nickel after each of the anneals. The main findings are as follows. The texture was mainly {100}<001> and {112}<111> and it was more pronounced in coarse-grained areas than in fine-grained areas. The length fraction of Sigma 3s (annealing twins) increased with annealing time and therefore with the level of anomalous grain growth. Two to three twins per grain were sited in coarse-grained regions whereas less than one twin per grain was sited in fine-grained regions. It is suggested that the nucleation and growth of twinning is mechanistically linked to anomalous grain growth.

Crystallization↗

PubMed2004

The role of misorientation and phosphorus content on grain growth and intergranular fracture in iron-carbon-phosphorus alloys.

The relationship between the crystallography of intergranular fracture and phosphorus segregation has been investigated in a Fe-0.06wt%P-0.002wt%C alloy aged for 1 h at temperatures between 600 degrees C and 1000 degrees C. Two novel techniques were devised for the investigation: first, electron back-scatter diffraction (EBSD) across the reconstructed fracture surface and, second, a combination of Auger electron spectroscopy, stereophotogrammetry and microscopy to measure phosphorus and carbon on fracture facets combined with EBSD measurements direct from the fracture surface. In total, 700 misorientations were measured from across the reconstructed fracture surface and in 'control' areas away from the fracture. It was found that Sigma 3s were in general more resistant to brittle fracture than were random boundaries, and it was suggested that alloys of this type could be grain boundary engineered to improve fracture resistance by a short anneal in the austenite region to increase the final proportion of Sigma 3s. Sixteen fracture facets yielded combined Auger/EBSD data. The combined Auger/EBSD methodology to acquire joint crystallographic and segregation information from facets was shown to be feasible, although laborious. There were significantly more [110] planes than any other type in the sample population of facets from which combined segregation/crystallography data had been collected. The data suggested that there was on average lower phosphorus segregation on fracture facets that were near [110] than on other intergranular fracture facets.

Alloys↗

PubMed2002

Single-section plane assessment in grain boundary engineered brass.

The present paper reports a comparative analysis of sigma 3 (in the coincidence site lattice notation) grain boundary types, in two grain boundary engineered brass specimens, by use of electron backscatter diffraction (EBSD) data coupled to the measurement of boundary traces in a single section. Although most of the data were analysed using the new single-section technique, an analysis of boundary plane orientations in three dimensions was made in a subset of the data in order to validate the single section methodology. The single-section trace analysis procedure. coupled with EBSD, is a viable and robust tool for analysis of sigma 3 grain boundary planes. The procedure provides data which suggest that part of the enhanced strain-to-failure in specimen B compared to specimen A is the result of an increased proportion of mobile sigma3 boundaries, i.e. those which are displaced from the [111] symmetrical tilt configuration.

Journal Article↗

PubMed2002

Application of electron backscatter diffraction (EBSD) to fracture studies of ferritic steels.

The application of electron backscatter diffraction (EBSD) to fracture studies has provided a new method for investigating the crystallography of fracture surfaces. The crystallographic indices of cleavage planes can be measured both directly from the fracture surface and indirectly from metallographic sections perpendicular to the plane of the adjoining fracture surfaces. The results of direct individual cleavage facet plane orientation measurements are presented for carbon-manganese (C-Mn) and low-alloy Mn-Mo-Ni (similar to ASTM A553 type-B). Pressure vessel steel weld metals, obtained from fracture surfaces of Charpy impact test specimens fractured at various test temperatures and for an ultra-low carbon steel (Fe-0.002C- 0.058P) fractured at -196 degrees C by impact. In addition to the direct measurement from the fracture surface, cleavage facet orientation measurements for the ultra-low carbon steel were complemented by the results obtained from the metallographic sections. Fractographic observations revealed that cleavage fracture is accommodated by a microvoid coalescence fracture micromechanism, which was induced by decohesion of second phase particles (inclusions). The correlation between the direct and indirect methodologies shows that the cleavage facet planes are dominated by the [001] plane orientations, and indicated that even when information concerning the full five degrees of freedom is inaccessible, the cleavage facet plane could still be determined. Finally, the advantages and disadvantages of direct orientation measurements from the fracture surface and indirectly by a destructive sectioning technique are discussed.

Journal Article↗

PubMed2001

A comparison between three-dimensional and two-dimensional grain boundary plane analysis.

An EBSD-based methodology for assessment of grain boundary planes, in particular sigma3 boundaries in face-centred cubic materials, has recently been devised. The method is based on trace analysis in a single, two-dimensional section rather than the more arduous three-dimensional method. The paper reports a data set of grain boundary planes in alpha-brass. mainly sigma3s, which have been analysed using both methods so that they can be compared and a recommendation made about the usefulness of the new method. It is shown that the new, two-dimensional method is a valuable tool in the analysis of grain boundary geometry, especially when used in conjunction with v/v(m), a parameter for assessing the proximity to the misorientation reference structure.

Journal Article↗

PubMed2001

Combined application of electron backscatter diffraction and stereo-photogrammetry in fractography studies.

The main aim of this paper is to report on recent experimental developments that have succeeded in combining electron back-scatter diffraction (EBSD) with stereo-photogrammetry, compared with two other methods for study of fracture surfaces, namely visual fractography analysis in the scanning electron microscope (SEM) and EBSD directly from facets. These approaches will be illustrated with data relating to the cleavage plane orientation analysis in a ferritic and C-Mn steel. It is demonstrated that the combined use of EBSD and stereo-photogrammetry represents a significant advance in the methodology for facet crystallography analysis. The results of point counting from fractograph characterization determined that the proportions of intergranular fracture in C-Mn and ferritic steels were 10.4% and 9.4%, respectively. The crystallographic orientation was determined directly from the fracture surface of a ferritic steel sample and produced an orientation distribution with a clear trend towards the [001] plane. A stereo-photogrammetry technique was validated using the known geometry of a Vickers hardness indent. The technique was then successfully employed to measure the macroscopic orientation of individual cleavage facets in the same reference frame as the EBSD measurements. Correlating the results of these measurements indicated that the actual crystallographic orientation of every cleavage facet identified in the steel specimens is [001].

Journal Article↗

PubMed1999

Crystallographic analysis of facets using electron backscatter diffraction.

Applications of electron backscatter diffraction (EBSD), also known as backscatter Kikuchi diffraction in the scanning electron microscope (SEM) are first and foremost microtexture and grain boundary misorientation analysis on a single polished section in the specimen. A more subtle and revealing approach to analysis of these data is to use EBSD to probe the orientations of planar surfaces, i.e. facets, which bound crystals. These surfaces include: * grain or phase boundaries * fractures * cracks It is of great interest to know the crystallography of such facets since it provides a key to understanding the physical properties of them. As far as investigation methodology is concerned, surfaces or facets associated with polycrystals are of two types: exposed or unexposed. Exposed facets, such as a fracture surface, can be viewed directly in the SEM, whereas unexposed facets, such as a grain boundary, are usually revealed as an etched trace on a polished surface. Photogrammetric methods can be used to obtain the positional orientation of an exposed facet, and the crystallographic orientation is obtained either directly from the surface or by indirect sectioning. Calibrated sectioning is required to obtain the equivalent parameters for an internal surface. The present paper compares the methods for obtaining and interpreting the crystallography of facets, with illustrations from several materials.

Journal Article↗

PubMed1989

Measurement of lattice parameter and strain using convergent beam electron diffraction.

A brief review is presented of the methods of measuring lattice parameters and strain using diffraction techniques. The presence of strain leads to broadening of diffraction maxima, which is normally separable from any broadening caused by size. The special advantages of the convergent beam electron diffraction (CBED) technique is the local nature from which the data are derived. Examples of the use of CBED techniques in measuring lattice parameters and strain are given from studies of precipitation (including misfit measurements) and from investigations of partially recrystallised microstructures. These examples are used to illustrate the advantages and limitations of the CBED technique.

Crystallography↗