Optimization of an oxide dispersion strengthened Ni-Cr-Al alloy for gas turbine engine vanes

The investigation was carried out to determine the optimum alloy within the Ni-16Cr-Al-Y2O3 system for use as a vane material in advanced aircraft gas turbine engines. Six alloys containing nominally 4%, 5% and 6% Al with Y2O3 levels of 0.8% and 1.2% were prepared by mechanical attrition. Six small-scale, rectangular extrusions were produced from each powder lot for property evaluation. The approximate temperatures for incipient melting were found to be 1658 K (2525 F), 1644 K (2500 F) and 1630 K (2475 F) for the 4%, 5% and 6% aluminum levels, respectively. With the exception of longitudinal crystallographic texture, the eight extrusions selected for extensive evaluation either exceeded or were close to mechanical property goals. Major differences between the alloys became apparent during dynamic oxidation testing, and in particular during the 1366 K (2000 F)/500 hour Mach 1 tests carried out by NASA-Lewis. An aluminum level of 4.75% was subsequently judged to be optimum based on considerations of dynamic oxidation resistance, susceptibility to thermal fatigue cracking and melting point

Foliar micro-morphology of Gasteria bicolour haw. (Asphodelaceae) from South Africa

Background: The succulent genus, Gasteria, which comprises 16 species, is endemic to South Africa and has its main centre of distribution in theSavanna Region of the Eastern Cape. Whereas G. bicolor has been investigated phyto-chemically and pharmacologically, not much data  concerning the anatomical and micro-morphological features can be found in literature.Materials and Methods: This study was undertaken, using light and scanning electron microscopy to obtain information on the micro-morphological features of this important medicinal plant to facilitate itsidentification and authentication. The elemental composition of the leaf was determined by energy dispersive X-ray spectroscopy (EDXS).Results: The epidermal cells are either hexagonal or pentagonal in form, and are compactly arranged with undulate anti-clinal cell walls. Theepidermal cell width was approximately 50 µm. Stomata apertures are elliptical and the upper epidermis of the leaf has paracytic stomata which are slightly raised above the epidermal surface with 4 to 5 subsidiary cells surrounding each stoma. Based on the EDXS microanalysis, the mineralcrystals present at the level of the mesophyll of G. bicolor were probably mixtures of calcium oxalate, calcium sulphate and silica.Conclusion: The co-occurrence of aluminum suggests the potential role of the crystals in detoxification of aluminum and heavy metals, as reportedpreviously.Key words: Foliar micro-morphology, Gasteria bicolor, light microscopy, scanning electron microscop

Basic studies on dispersion hardening

Transmission electron microscopy and X-ray diffraction observations of substructure and elastic strains in cold worked and annealed dispersion strengthened alloy

A novel systematic method to evaluate computer supported collaborative design technologies

Selection of suitable computer-supported collaborative design (CSCD) technologies is crucial to facilitate successful projects. This paper presents the first systematic method for engineering design teams to evaluate and select the most suitable CSCD technologies comparing technology functionality and project requirements established in peer-reviewed literature. The paper first presents 220 factors that influence successful CSCD. These factors were then systematically mapped and categorised to create CSCD requirement statements. The novel evaluation and selection method incorporates these requirement statements within a matrix and develops a discourse analysis text processing algorithm with data from collaborative projects to automate the population of how technologies impact the success of CSCD in engineering design teams. This method was validated using data collected across 3 years of a student global design project. The impact of this method is the potential to change the way engineering design teams consider the technology they use and how the selection of appropriate tools impacts the success of their CSCD projects. The development of the CSCD evaluation matrix is the first of its kind enabling a systematic and justifiable comparison and technology selection, with the aim of best supporting the engineering designers collaborative design activity

Modelling the relationship between design activity and computer-supported collaborative design factors

Computer-Supported Collaborative Design (CSCD) technologies can enable teams to collaborate across boundaries. Emerging research documents the potential of CSCD technologies to contribute towards successful collaborative design, however, no model exists to define the relationship between a successful design activity and CSCD factors which influence its success. This paper utilises a systematic literature review to categorise known CSCD factors, categorise and characterise them, and applies this knowledge towards developing an established design activity model to include CSCD factors