A European consortium is evaluating materials for the construction of a new supersonic transport aircraft that may replace Concorde. Current designs propose to use an aluminium alloy for the fuselage which is required to have superior creep resistance and damage tolerance to the Concorde alloy 2618A. Promising results have been obtained with extruded Al-Cu alloys containing minor additions of magnesium and silver which stimulate hardening by the relatively stable V precipitate. Data is presented which shows that these alloys have tensile and accelerated creep properties which are better than those of competing commercial alloys of the 2000 series, together with satisfactory levels of fracture toughness. Of the four experimental alloys studied, the optimal composition is Al-5·6Cu-0·45Mg-0·45Ag-0·30Mn-0·18Zr (wt-%).
A Cu-Al alloy has been used as bond coat between a carbon steel substrate and a final coating deposit obtained by applying the twin wire electric arc spraying coating technique. The presence of a copperbased material in the composite system can change the overall temperature profile during deposition because copper exhibits a thermal conductivity several times higher than that of the normally recommended bond coat materials (such as nickel-aluminum alloys or nickel-chromium alloys). The microstructures of 420 and 304 stainless steels deposited by the electric arc spray process have been investigated, focusing attention on the deposit homogeneity, porosity, lamellar structure, and microhardness. The nature of the local temperature gradient during deposition can strongly influence the formation of the final coating deposit. This study presents a preliminary study, undertaken to investigate the changes in the temperature profile which occur when a Cu-Al alloy is used as bond coat, and the possible consequences of these changes on the microstructure and adhesion of the final coating deposit. The influence of the thickness of the bond layer on the top coating temperature has also been also evaluated.
In the present work, sand cast Al alloy A356 was laser alloyed with tungsten using a two stage technique of laser alloying. A continuous wave, fibre optically delivered, Nd-YAG laser was employed for alloying the tungsten powder, and the coatings were produced by varying beam interaction with the substrate by altering the traverse laser velocity. Characterisation of the laser treated alloy was performed by various techniques. Optical (OM) and scanning electron microscopy (SEM) were used to examine the morphology and microstructure of the specimen surfaces and cross-sections. Surface layers alloyed with tungsten contained relatively large amounts of intermetallic compounds such as Ti5Si4, Mg2Si, Al5 W, Al12W, and Al3·21Si0·47 identified by X-ray diffraction. Friction and wear tests were carried out on all specimens by using a ball on disc tribometer under dry conditions. The static partners were balls of 6 mm diameter made of WC + 6%Co. It was determined that the laser treated surfaces presented an increase in wear resistance between 40% and nearly 110% when compared to the wear resistance of the untreated Al alloy, and the improvement was proportional with the laser beam- substrate interaction time.
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