An Investigation into the Effects of Different Oxy-Nitrocarburizing Conditions on Hardness Profiles and Corrosion Behavior of 16MnCr5 Steels

This work is aimed to develop and optimize a gas ferritic oxynitrocarburizing treatment applied to an industrial 16MnCr5 component. The main effort has been to reduce the treatment time and the gas consumption by using a nitriding atmosphere that comprises nitrous oxide and ammonia. Special attention has been paid to improve the salt spray corrosion resistance with respect to the hardness requirements and the whole compound zone depth. Several changes have been applied to a base treatment by modifying the time and the temperature of each process phase, as well as the gas mixture and the flow of the nitrocarburizing atmosphere. Microhardness investigations and measurements of the compound layer's depth have been carried out on the treated specimens in order to evaluate the influences due to the variations of the process variables during the nitrocarburizing process. The introduction of nitrous oxide and ammonia allows reducing the nitriding time from 3 to 2 hours, and the purge time can be significantly reduced. Moreover, the increase of the nitrocarburizing temperature from 550 to 580°C allowed reducing the time of this phase from 4 to 3 hours. The post-oxidation time was moved from 3 to 4 hours in order to increase the thickness of the surface oxide layer and to improve the corrosion resistance

Lanthanides: a focused review of eutectic modification in hypoeutectic Al–Si alloys

A modified fibrous-like eutectic structure strongly improves the final mechanical properties of Al–Si foundry alloys, especially ductility. Beside widely used commercial eutectic modifiers such as Sr and Na, lanthanides appear to be a possible alternative in the eutectic Si modification process for hypoeutectic Al–Si casting alloys. All lanthanides have similar physical and chemical properties, such as density, melting point, and fading phenomena, which have been compared in the present review. They also show atomic radii close to the optimal atomic radius for a modifying agent. However, the microstructural evolution of eutectic Si is strictly related to the specific element and content of lanthanides, whose abundance, reserve, mining, production and market situations have been preliminary evaluated in this paper. The eutectic modification mechanisms induced by lanthanides are not well-discussed and clarified yet. The advantages and disadvantages of individual addition of lanthanides for chemical modification of hypoeutectic Al–Si alloys have been here critically reviewed. The use of lanthanides for eutectic Si modification in Al–Si alloys has been discussed from both effectiveness and economical point of views. Nowadays, the actual cost and their efficiency seem to make lanthanides still far to be used in foundry industry for commercial and large-scale applications

Optimizing the Heat Treatment Process of Cast Aluminium Alloys

The influence of heat treatment process on the microstructure and mechanical properties, and the distortion of a low-pressure die-cast AlSi7Mg0.3 alloy is reported. This work is aimed at optimizing the whole heat treatment process, including solution heat treatment, quenching and artificial ageing, of A356 alloy wheels, produced by low pressure die casting. In particular, the optimization process is focused on reducing time and temperature of solution and ageing heat treatments, and on selecting the right quenching medium, reducing the distortion of A356 alloy 17-in and 18-in wheels and obtaining the required mechanical properties. The time and temperature of solution treatment are normally chosen to dissolve coarse \u3b2-Mg2Si phase coming from the solidification process, especially where the solidification rate is slow as in the thickest zones of wheel, e.g. the hub and the spoke regions. Generally, the time required is about 45 minutes at the temperature of 540\ub0C, which is the typical solution temperature used for A356-type alloy. More time is however required at this temperature to change the morphology of eutectic silicon particles. This is aimed to improve the mechanical properties, especially ductility and fatigue properties, of wheels after further artificial ageing. The solutionising temperature is here selected to reduce the time of the heat treatment and to avoid any type of incipient melting of the material within an industrial tunnel furnace. The quenching is the most critical step in the sequence of heat-treating operations. The objective of quenching is to preserve the solid solution formed at the solution heat-treating temperature, by rapidly cooling to some lower temperature, usually near the room temperature. The most rapid quench rate, giving the best mechanical properties, can also cause unacceptable amounts of distortion or cracking in components. This is particularly true for aluminium wheels where the different thickness throughout the casting can produce distortion higher than 2-3 mm, critics for subsequent machining operations. The optimization process is here focused on the quenching rate, which is varied by changing the temperature of the quenchant, in order to reduce the wheels\u2019 distortion and to guarantee the appropriated supersaturation level of atoms for subsequent ageing treatment. Therefore, the temperature of forced water, used as quenchant, has been varied in the range of 50 to 95\ub0C, and the distortion level and the hardness of the wheels systematically measured. A temperature of 95\ub0C is observed to be the optimum solution, but useless from an industrial point of view. The extreme vapour produced by the boiling water can compromise the automatism for handling of wheels and delay too much the cooling of the wheels after solutioning. Therefore, the best compromise between distortion and mechanical properties and productivity has been revealed to be at a temperature of 75\ub0C. The time and temperature of ageing are considered in the present work in order to reach an underageing temper of the material, which is typical for the manufacture of wheels to improve impact and fatigue properties. The influence of the different painting processes, generally carried out at a temperature of 180\uf7190\ub0C for several minutes after ageing and subsequent machining operations, have to be considered to determine the final mechanical properties. These temperatures are typical temperature for ageing treatment of cast aluminium alloys, such as the A356-type alloys. Therefore, the present study takes into account the painting temperatures and times to optimize the ageing treatment of the wheels, reaching the desired mechanical properties. This study develop an optimization approach of the whole heat treatment process of cast aluminium alloy wheels. The work evidences the typical problems and targets of wheels\u2019 producers, suggesting an integrated approach to improve the productivity and the quality of castings. Metallographic and image analysis techniques have been used to quantitatively examine the microstructural changes occurring during heat treatment; while hardness and tensile testing measurements have been carried out to monitor the evolution of the mechanical properties after each step of T6 heat treatment

Enhanced heterogeneous nucleation on oxides in Al alloys by intensive shearing

Oxides, in liquid aluminium alloys, can cause severe difficulties during casting, contribute to the formation of cast defects and degrade the mechanical properties of cast components. In this paper, microstructural characteristics of naturally occurring oxides in the melts of commercial purity aluminium and Al-Mg binary alloys have been investigated. They are characterised by densely populated oxide particles within liquid oxide films. With intensive shearing, the particle agglomerates are dispersed into uniformly distributed individual particles. It was found that with intensive melt shearing, grain refinement of α-Al can be achieved by the dispersed oxide particles. The smaller lattice misfit between the oxide particles and the α-Al phase is characterised by a well defined crystallographic orientation relationship. And the mechanisms of grain refinement are discussed.The EPSR

Constitutive and stochastic models to predict the effect of casting defects on the mechanical properties of High Pressure Die Cast AlSi9Cu3(Fe) alloys

The effect of casting defects on mechanicalproperties of a high-pressure die-castAlSi9Cu3(Fe) alloy is reported. A series of Ushapedstructural components are cast usinga combination of injection parameters andpouring temperatures in order to generatedifferent types and amount of casting defectsthroughout the casting. It has been found thatcastings contain defects, primarily pores andoxides, and that the presence and distributionof these defects are highly sensitive to theprocess conditions. Moreover, significantvariations of the defect distribution have,however, been found in castings producedunder the same conditions, indicating thestochastic nature of defects in die castings.The tensile properties are affected by theamount and distribution of defects and aredetermined by the defect area fraction. Theinfluence of casting defects on mechanicalproperties are investigated through atheoretical verification based on constitutiveand stochastic models. The analyticalapproach, based on the Ghosh constitutivemodel of tension instability, correctly indicatesthe trends of the experimental results, whilethe Weibull statistics evidences how the scaleparameter and the Weibull modulus arestrongly affected by the casting conditions.An integrated stochastic-analytical approachis then proposed and it appears to beapplicable to describe the tensile properties interms of fractographic defects and cumulativefailure probability Pi

Serge Lusignan, L’università di Parigi e la cultura letteraria in lingua francese (xiii-xiv secolo)

L’histoire de la langue en une perspective sociolinguistique apporte parfois des lumières importantes sur les études littéraires. Tel est le cas pour cette contribution de Serge Lusignan, spécialiste du rapport entre latin et langue vulgaire au Moyen Âge, qui reprend ici la question de la diglossie latin-français au sein de l’université de Paris entre xiiie et xive siècle. L’affirmation fréquente et presque banale selon laquelle le latin était à cette époque la seule langue admise dans les co..

Le “Sermon d’Amiens” anonyme du xiiie siècle en langue vernaculaire, édition et traduction par Annette Brasseur

Décrié par la critique jusqu’au xixe siècle, ce Sermon anonyme n’était connu jusqu’ici que grâce aux pages que lui avait consacrées Michel Zink dans sa Prédication en langue romane avant 1300 (1982) et à une édition anglaise par Stephen Murray (Berkeley, 2004), historien de l’art spécialiste de l’architecture romane et gothique, qui a consacré entre autres un ouvrage important à la cathédrale d’Amiens. Annette Brasseur offre ici la première édition critique d’un ouvrage aussi court que comple..

“Cleriadus et Meliadice” entre manuscrits et imprimés: ‘miroir du prince’ ou roman d’amour?

Dans un bel article de 1974, Roger Dubuis s’interrogeait sur l’«indifférence du genre narratif aux problèmes politiques du xve siècle»: une fine analyse de quelques romans (Comte d’Artois, Jehan de Saintré, Jehan de Paris) et de deux des CNN caractérisées par des allusions précises à la réalité contemporaine, lui permettait de nuancer son titre pour conclure que «le genre narratif, au xve siècle, s’il n’est jamais un prétexte à engager la lutte sur le terrain politique, n’est pas cependant fe..

L’Histoire d’Alexandre le Grand dans les tapisseries au xve siècle. Fortune iconographique dans les tapisseries et les manuscrits conservés. La tenture d’Alexandre de la collection Doria Pamphilij à Gênes, sous la direction de Françoise Barbe, Laura Stagno et Elisabetta Villari

Ce très beau volume est consacré aux deux tapisseries illustrant la Jeunesse et l’Épopée d’Alexandre le Grand conservées et exposées dans la Sala dei Giganti du Palazzo Doria Pamphilij à Gênes; il réunit une quinzaine de contributions dues à des spécialistes de domaines divers, histoire de la tenture, histoire de l’art, histoire du goût, issues d’un colloque qui s’est tenu à Gênes en 2008: il en ressort un panoramique qui permet de situer cette tapisserie dans le cadre bien plus vaste de la r..

Corinne Denoyelle, Poétique du dialogue médiéval

Cet ouvrage repose sur deux prémisses: le constat d’une présence abondante du dialogue dans les œuvres narratives du Moyen Âge et l’existence d’une logique et d’une écriture qui lui sont propres. C.D. se propose donc d’offrir une description précise du dialogue en tant que «production écrite et inscrite dans un contexte littéraire donné» dont on puisse dégager une sorte de «grammaire» (p. 11). Le corpus – dont malheureusement ne sont nulle part explicités les critères de sélection – comprend ..