Review of effect of P and Sr on modification and porosity development in Al–Si alloys

Abstract

The benefits of Sr additions to Al–Si alloys to modify the eutectic are often impaired by the development of porosity, sometimes to the degree that benefits are negated. Experimental reports are reviewed in this paper, suggesting an explanation in terms of the oxide population in the melt. The unmodified silicon particles are nucleated by AlP, which has in turn nucleated on oxide bifilms. The oxide bifilms, which are essentially cracks, are straightened by the crystalline growth of Si particles, leading to increased crack size and consequently reduced mechanical properties. The addition of Sr improves properties by suppressing the formation of Si on bifilms and thereby preventing the straightening of the pre-existing cracks. Si is now forced to precipitate at a lower temperature as a coral-like eutectic. Unfortunately, the bifilms are now freed (the primary Si particles no longer exist to grow around and sequester the bifilms), remaining in suspension in the liquid metal, allowing them to act to block interdendritic flow and aid the initiation of the formation of pores, countering the benefits of the improved structure.     

Grain boundary engineering: an overview after 25 years

Abstract

In 1984, 'grain boundary design', later known as 'grain boundary engineering (GBE)', was proposed. The central premise of GBE is that specific thermomechanical treatments, mainly on face centred cubic materials which readily form annealing twins, can be used to improve resistance to various forms of intergranular degradation such as corrosion, cracking or embrittlement. Engagement with the concept has accelerated in recent years. This overview charts the progress of GBE from its inception 25 years ago to the present day, including suggestions of key topics for ongoing or future research. These topics comprise confirmation of which boundaries are 'special' in terms of crystallography and properties, optimisation of processing regimes, new approaches to GBE in systems without annealing twinning and incorporation of connectivity metrics, especially in three dimensions.     

Evaluation of semiphysical phase transformation model for engineering steels using measured continuous cooling transformation diagrams

Abstract

A semiphysical model has recently been constructed by Parker that calculates the phase transformation behaviour of engineering steels as a function of time for an arbitrary cooling path. To compare the model with measured diagrams from the literature for linear cooling, a large number of continuous cooling transformation (CCT) diagrams have been calculated. The quantified comparison has been used to construct heuristics that indicate the accuracy of the model as a function of the steel composition. For 10 alloying elements the domain for which the model is valid has been established.     

Highly porous metals and ceramics

Abstract

Cellular solids are a class of highly porous materials that covers a wide range of structures, such as foamed materials, replicated porous or additive manufactured structures, honeycombs, lattice structures, interconnected fibres or hollow spheres and syntactic foams. The pores can be more or less closed or completely open. Depending on their morphology and composition, these materials possess unique properties and are used as components in special and advanced engineering applications. These include filtering liquids and particles in gas streams, porous burners, biomedical devices, lightweight stiff structures, impact absorbers, sound damping modules, thermal management components, etc. The present paper gives an overview on the main fabrication methods and the resulting architectures, in relation to applications of metals and ceramics with >50 vol.-% porosity.     

2001年《中国粮油学报》学术论文的评述

本文综述了 2 0 0 1年《中国粮油学报》刊载的重要科研成果 ,对指导本学科发展 ,推动科技创新和粮油深加工具有参考价值。     

Some views on 2 year review/revision cycle of IAEA regulations for safe transport of radioactive material

Abstract

In the past the International Atomic Energy Agency (IAEA) transport regulations have normally been reviewed or revised within a 10 year cycle to support changes in transport operations arising from administrative and technical developments and new knowledge in fields concerning the transport of radioactive material. Beginning in 2003, consistent with the time schedules of the United Nations (UN) Sub-Committee of Experts on the Transport of Dangerous Goods and of the relevant international modal organisations, a regular 2 year review of the IAEA transport regulations was established, with a view to issuing a revised or amended edition as necessary. This paper describes the process of the review/revision itself, the transfer to the regulations of the UN and the modal organisations as well as implementation within the legislation of the member states. The advantages and disadvantages of the more frequent process are analysed: on the one hand harmonisation with the UN and the modal organisations, on the other hand a possible lack of sufficient stability in the regulations themselves. The need for the 'Schedules of requirements for the transport of specified types of radioactive material consignment', which are an integral part of the IAEA transport regulations TS-R-1 but which from 1 January 2005 are no longer a part of the international modal regulations, is discussed.     

Meeting tribological challenges with surface engineered materials

Abstract

Tribological applications in the automotive, cutting tool and biomedical implant sectors continue to raise challenges for engineering materials. A brief review of these sectors indicates opportunities to improve surface durability through the application of innovative coating materials. Specific devices that might be improved in this way are engine piston rings, roller bearings, cams, cam followers, cutting tools and total joint replacements. This is the first time that the impact of thin hard coatings on tribological function has been assessed in three distinct engineering sectors.     

A review of advances in processing and metallurgy of titanium alloys

Abstract

Titanium and its alloys exhibit excellent mechanical properties, unrivalled corrosion resistance and outstanding biocompatibility; however, annual global titanium production is dwarfed by commodity metals. This is in part due to the current primary production method (Kroll process), which requires a complex and discontinuous reduction route in addition to several costly downstream processing steps to convert titanium sponge to usable product forms. Alternative extraction processes are reviewed in the present paper with emphasis on the electrochemical reduction routes, such as the Fray–Farthing–Chen (FFC) Cambridge process. Improvements in thermomechanical processing including the use of modelling are briefly examined. Alloy development is also discussed with particular regard to superelastic and shape memory alloys.