Serrated yielding in Cu-1 wt-%Cd alloy

Abstract

The influence of grain size and temperature on the serration patterns of the Portevin-Le Chatelier (PLC) effect and on the yield and flow stresses in a Cu-1 wt-%Cd alloy was investigated in the temperature range 150 to 360 ° C. Two kinds of serration patterns were observed in this alloy. Type I occurred at lower temperatures and its yield points are moderately spaced. Type II consists of regular jerky flow observed athigher temperatures. The Hall-Petch equation is obeyed over the temperature range in which jerky flow occurs. The Hall-Petch parameter k (?) is observed to show a local maximum in the temperature range where serrated flow is first observed. The PLC effect is associated with the solute- dislocation interactions, implying that k (?) contains a component associated with grain size dependent dislocation storage.     

Effect of vapour phase hydrogen peroxide,as a decontaminant for civil aviation applications,on microstructure,tensile properties and corrosion resistance of 2024 and 7075 age hardenable aluminium alloys and 304 austenitic stainless steel

Abstract

A response to the chemical or biological contamination of aircraft requires the use of a suitable decontaminant. Among possible chemical decontaminants, vapour phase hydrogen peroxide appears to be a likely candidate in terms of a combination of efficacy, low environmental impact and potential for materials compatibility. The present paper examines the effect of hydrogen peroxide, both in the vapour phase and as a liquid concentrate on two common structural materials used in aviation, namely 2024 and 7075 age hardenable aluminium alloys and on 304 austenitic stainless steel, the latter as employed in galley and lavatory surfaces. The present paper characterises both the effects of hydrogen peroxide on the microstructure of the materials and the impact that decontamination has on the tensile properties and corrosion resistance of these materials. Microstructural effects are both relatively small in magnitude and confined to a region immediately beside the exposed surface. No systematic effect is found on either the tensile properties or the post-exposure corrosion resistance of the three alloys examined. These observations are encouraging in terms of the use of vapour phase hydrogen peroxide for decontamination applications.     

Tensile creep behaviour of NiAl-Cr(Zr) multiphase intermetallic alloy

Abstract

The microstructure of a multiphase NiAl-33.5Cr-0.5Zr intermetallic alloy was examined by SEM with energy dispersive spectroscopy and TEM. The tensile creep behaviour of the hot isostatically pressed NiAl-33.5Cr-0.5Zr alloy was studied. The results of the creep test indicated that all of the creep curves under the present test have similar characteristics: a short primary creep stage, a dominant tertiary creep stage, and nearly identical creep strains (~45%). The apparent stress exponent and the apparent activation energy were analysed and discussed. The mechanism of the creep deformation was also analysed by the observation of TEM.     

Effects of heat treatment processes on microstructure and properties of 2·25Cr–1Mo–0·25V HSLA steels

Abstract

In the present paper, the effects of the heat treatment processes with two conditioning treatments and four quenching–tempering processes on the mechanical properties of 2·25Cr–1Mo–0·25V high strength low alloyed (HSLA) steel are investigated. The results show that the conditioning treatments have obvious effects on the low temperature impact energy but little effect on the tensile strength. The elevation of the final austenitising temperature increases the strength, whereas it results in the decrease in the low temperature impact energy due to the coarse microstructure. The results of the fracture surfaces analysis further make sure that the fracture surfaces of tensile specimens all exhibit ductile characters with a lot of dimples. However, the fracture surfaces of impact specimens exhibit two typical fracture characters, i.e. the ductile and brittle fracture surface corresponding to the fine and coarse microstructures respectively. In addition, the elongation and reduction in area seem to be insensitive to the heat treatments. Meanwhile, the impact fracture mode is more sensitive to the grain size and not to the low temperature impact energy.     

Process and compressive properties of porous nickel materials

Abstract

Compressive properties are investigated for the porous Ni materials processing by innovated powder metallurgical (PM) method. The porous Ni materials first show a short elastic region, then a long and oblique stress yield region within the strain range of about 10–50%, and finally, a densification region where the stress increases rapidly.     

Synthesis and wear of Al based,free standing functionally gradient materials: effects of different reinforcements

Abstract

In the present study, three aluminium based functionally gradient materials (FGMs), reinforced with different ceramic particulates (silicon carbide, aluminium oxide, and titanium carbide), were successfully synthesised using the innovative gradient slurry disintegration and deposition (GSDD) technique. The results for Al/SiC and Al/Al₂O₃ revealed, in common, an increase in the weight percentage of reinforcement along the direction of deposition, to result in an increase in porosity and microhardness. However, for Al/TiC, the reverse trend was observed, with porosity and microhardness decreasing with increasing distance from the base of the ingot. The porosity levels for Al/TiC were also found to be significantly lower than those ofthe other two FGMs. Thermomechanical analysis of the FGMs showed thatthe average coefficient of thermal expansion of the high reinforcement end was reduced, as compared to the high aluminium end. Sliding wear test results also revealed that the high reinforcement end was more wear resistant than the high aluminium end, except for the case of Al/Al₂O₃. An attempt is made to interrelate the effects of different types of particulates, with microstructural development, microhardness and wear rate results obtained in the present study.     

European Union Policy: update New Chemicals

Abstract

In a previous article the EU New Chemicals Policy was introduced. With publication of draft legislation expected Spring 2003, more detail is provided about the policy and its likely effect on the PM industry; some technical and commercial issues underlying its implementation are discussed.     

Microstructure and properties of carbide free bainite railway wheels produced by programmed quenching

Abstract

A kind of carbide free bainite steel was used to produce railway wheels. The alloy design, manufacture process, microstructure and behaviours are summarised. The novel steel is distinctively superior in excellent combination of strength and toughness compared with the traditional pearlite type wheel steels. The details of the microstructure of novel steel have been investigated in nanoscale.     

Development of precipitate size and volume fraction of niobium carbonitrides in stabilised stainless steel

Abstract

Niobium carbonitride (NbX) precipitates have been studied in a niobium stabilised austenitic stainless steel AISI type 347 with approximate nominal composition Fe–0.06C–17.5Cr–11.4Ni–0.8Nb. The steel was extruded to seamless tube, solution annealed at 1100°C for 3 min, water quenched, and subsequently isothermally aged at 700°C for times up to 70 000 h. Size distribution and volume fraction of the coarse distribution (1–10 µm) of NbX particles were measured using scanning electron microscopy (SEM). The fine distribution (～30 nm) was investigated using energy filtered transmission electron microscopy (EFTEM). Size distribution and volume fraction were determined using jump ratio images. Coarse NbX (～0.3% volume fraction) precipitates were formed during solidification and extrusion, and were little affected by solution annealing and isothermal aging. Fine NbX (～0.5% volume fraction) precipitates formed during solution annealing and grew during the first 800 h of aging. Precipitate size determination using EFTEM appears to give accurate results, while volume fraction determination requires homogeneous material for good results.     

Development of laminated composite materials based on orthorhombic aluminide/titanium alloy and their tensile mechanical properties

Abstract

Laminated composite materials consisting of an orthorhombic Ti₂AlNb based alloy and an (α+β) titanium alloy have been fabricated at a laboratory scale using a two-step process involving diffusion bonding and hot rolling. The feasibility of fabrication of two and three layered materials with high quality bonding between layers was demonstrated. Preliminary assessment of the tensile mechanical properties of the obtained composite materials showed that they were superior to those of the titanium alloy and slightly inferior to the orthorhombic alloy.