A B S T R A C TThe possibility to reuse the metal powder wasted in Laser Material Deposition (LMD) process has been evaluated and a simple procedure developed. LMD uses metal powder which is fed through a nozzle into the focal point of a laser, where it melts the powder and the substrate material. During the process, a high ratio of particles hits against an unmelted area and directly bounces off the deposited area. The efficiency ratio of deposition can drop to 40% depending on the configuration and spot size. This work deals with the design of a procedure to recollect and reuse the wasted powder of a nickel based superalloy IN718. After usage, powder is recollected, undesired fractions are magnetically segregated and aggregates are removed by sieving. The particles are mixed again and ready for reuse. In order to study the effectiveness of the process, no new powder has been added to the recovered fraction, and this procedure has been repeated five times. Experimental tests show that deposited material present similar properties than those obtained with new powder grains. But, after 3 reuses, the porosity content increases consequently and the rupture strain decreases strongly. The implementation of this process allows the improvement of the final efficiency, reducing costs and decreasing the hazardous powder amount.

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Please cite this article as: Barcena, J., de Cortazar, M.G., Seddon, R., Lloyd, J.C., Torregaray, A., Coleto, J., Effect of the incorporation of interfacial elements on the thermophysical properties of Cu/VGCNFs composites, Composites Science and Technology (2010), doi: 10.1016/j.compscitech.2010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. and addition of metal nanoparticles (Ti) to Cu matrix deposited by electroless plating. The effect of the incorporation of these metallic elements on the microstructure and thermophysical properties is discussed. B and Ti lead to higher interaction at the Cu/C interface over Ni and Co. ACCEPTED MANUSCRIPTThis allows the reduction of the coefficient of thermal expansion but regarding the thermal conductivity it was not possible to obtain a value higher than that of copper.

Titanium diboride (TiB 2 ) particles have traditionally been added to aluminium melts incorporated into Al-Ti-B master alloys for grain-refining purposes. The addition of only 0.15 wt% is enough to have a significant influence on the grain refinement. Moreover, the addition of TiB 2 particles provides further advantages, since the average size of the pores gets lower and the remaining porosity is more evenly distributed. However, TiB 2 particles that have not participated in nucleation events tend to be pushed by the solidification front and lie at grain boundaries where they create aggregates that may impair the properties of the alloys. Due to its inertness and good wetting behaviour with aluminium, TiB 2 can also be used as a reinforcing phase in metal matrix composites (MMCs). [1][2][3][4][5][6] When the amount of TiB 2 incorporated is increased in order to reinforce the materials, other solidification-related phenomena appear. In particular, TiB 2 particles are insoluble in aluminium and do not react chemically with it, but it has been observed that some solidification characteristics of the alloy are affected by the addition of TiB 2 : solidification events start earlier due to the lower undercooling required and the solidification time is reduced. [4] These phenomena have also been reported in other MMC systems. SiC-reinforced composites have been the most studied, but, in the case of TiB 2 -reinforced alloys, not much data on solidification aspects are available: some studies have focused on Al/TiB 2 composite alloys, [1,3,4] and Youssef et al. [4] recorded a reduction of the latent heat and solidification time, which was related to microstructural aspects of the materials.The present study deals with the analysis of the cooling curves of two aluminium alloys reinforced with 6 wt% of TiB 2 particles and produced by plaster casting. This lost wax variant used to produce the different samples is characterized by a low solidification rate due to the low thermal conductivity of the plaster that is used to build the moulds. Notice that the amount of 6 wt% of TiB 2 greatly exceeds the level necessary for grain refining. The aim was that the particles improve the properties of the alloys following the patterns shown by other particle-reinforced aluminium matrix composites (AMCs): mainly wear resistance, Young's modulus and high-temperature strength.The solidification curves of the reinforced and nonreinforced materials are studied and the effect of the presence of TiB 2 particles on the main solidification parameters, such as the maximum temperature of primary a-aluminum growth, the temperature and time difference between the maximum and minimum of the liquidus recalescence and the precipita-COMMUNICATION [*] Dr. A. Veille`re, Dr.Two aluminium alloys with 6 wt% TiB 2 particles are studied for applications where increased wear resistance and mechanical strength at high temperature are required. The incorporation of hard ceramic particles has a strong influence on the microstructure and properties of the alloys. T...

The present work deals with aspects related to the solidification and properties of an Al-Si10Mg/SiC 20p alloy cast in plaster moulds. Several strategies were followed to shorten its solidification time such as embedding copper tubes into the mould to make circulate cooling fluids immediately after the casting step. The analysis of cooling curves provided valuable information on the effect of the particles on solidification events. The precipitation of different phases of the MMC takes place at higher temperatures and earlier than in the case of the non reinforced alloy. Particles affect the solidification pattern of the alloy and play a noticeable role in the precipitation of the phases. This fact should be taken into account to design the filling and feeding systems correctly and for modelling and processing parameters as well as in thermal treatments. Eventually samples were obtained under the highest solidification rate conditions to analyse the microstructure and tensile properties of the MMC material.Keywords: F3S.20S, MMCs, lost wax, plaster casting, solidification Praca przedstawia aspekty związane z krzepnięciem i właściwościami stopów Al-Si10Mg/SiC20p odlewanych w formach gipsowych. Aby skrócić czas krzepnięcia stopu testowano kilka strategii, takich jak osadzanie rur miedzianych w formie aby umożliwić obieg cieczy chłodzących natychmiast po odlaniu stopu. Analiza krzywych chłodzenia dostarczyłacennych informacji na temat wpływu cząstek na proces krzepnięcia. Wydzielanie różnych faz w kompozytach metalowo-ceramicznych odbywa się w wyższych temperaturach i wcześniej, niż w przypadku nieumacnianego stopu. Cząstki wpływają na schemat krzepnięcia stopu i odgrywają zauważalną rolę w wydzielaniu faz. Fakt ten powinien być brany pod uwagę przy projektowaniu prawidło-wego systemu zalewania formy, modelowaniu parametrów procesu, jak również obróbki cieplnej. Na koniec pobrano próbki otrzymane przy najwyższej szybkości krzepnięcia do analizy mikrostruktury i właściwości wytrzymałościowych kompozytu metalowo-ceramicznego.

The Al-Cu5MgTi alloy is a heat treatable alloy that presents good machining properties. It is mainly used in aircraft parts when better mechanical properties than those provided by Al-Si alloys such as Al-Si7Mg0.3 are required. Nevertheless it is not so extensively applied as the latter due to its lower castability. Its solidification range is very large and this makes it prone to hot tearing related problems. The Al-Cu5MgTi alloy is mainly applied when high mechanical properties are needed at high temperatures. Magnesium alloying increases the strength and hardness of this alloy through thermal treatment and titanium is used as a grain refiner so that the insoluble constituents can be better dispersed as well as the porosity and defect distribution decrease.The use of grain refiners in these alloys is highly recommended due to the clear benefits they provide. The hot tearing related problems become reduced, mechanical properties get improved, and surface quality and the response to thermal treatments is better. Al-Ti-B type grain refiners have been used with this alloy in different foundry processes. Their use is even more essential in the case of low cooling rate processes like sand casting or lost wax processes as the large solidification intervals of the alloy (450-650 8C) [1] tends to create problems related to hot tearing and poor mechanical properties.TiB 2 particles incorporated in Al-Ti-B grain refiners are extensively used by aluminum foundries to promote heterogeneous nucleation and formation of equiaxed microstructure thus to improve the mechanical properties of the castings. The addition of only 0.15 wt% TiB 2 is enough to get a significant refinement of the grains. [2,3] Even though the main effect of the addition of TiB 2 particles into aluminum alloys is the refinement of the aluminum grains, there are other additional microstructural changes such as an increase in the modulus and ductility of the base alloy as well as a change in the thermal properties that can also be explained by the presence of these particles. The alloy studied in this work contains up to 5 wt% of TiB 2 particles. This amount largely exceeds the levelThe paper describes the influence of 5 wt % titanium diboride (TiB 2 ) particles on the microstructure of an Al-Cu alloy produced by plaster casting process. The elaboration route leads to a composite material with 1% of in situ TiB 2 particles and 4% ex situ of TiB 2 particles. The comparison of the reinforced alloy with the corresponding non-reinforced counterpart makes clear that the presence of TiB 2 particles has a large influence in the observed microstructure. The presence of TiB 2 particles decreases the grain sizes and the porosity level. It is also found that TiB 2 particles play an important role in the precipitation events of Al 2 Cu precipitates that are formed during solidification at the TiB 2 /aluminum matrix interfaces.504

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ResumenUna de las vías desarrolladas, en los últimos años, para la mejora de las propiedades mecánicas de las aleaciones de aluminio es la de la incorporación de refuerzos cerámicos en forma de partículas cerámicas. El objetivo principal del trabajo ha sido desarrollar el proceso de fabricación de una aleación de aluminio 6061 reforzada con partículas de diboruro de titanio, TiB 2 , y analizar las propiedades del material obtenido. Se ha observado que el proceso de fabricación planteado, consistente en la fabricación de las partículas por medio del proceso de síntesis autopropagada a alta temperatura SHS (Self propagating high temperature synthesis) y su posterior incorporación a la aleación 6061, es un proceso viable para la fabricación de aleaciones reforzadas adecuadas para la realización de procesos subsiguientes de extrusión o forja. El resultado final es la obtención de un material adecuado para la fabricación de componentes extruidos y que presenta una mejora de sus propiedades de tracción y fatiga, en comparación a la aleación base. Palabras claveMateriales compuestos de matriz metálica (MCMM); Síntesis autopropagada a alta temperatura (SHS); Extrusión; Aluminio 6061; Partículas TiB 2 . Development and characterization of a metal matrix composite of aluminium 6061 and TiB 2 particulates AbstractThe incorporation of ceramic particles has been one of the ways developed to improve the mechanical properties of aluminium alloys during the last years. The main objective of this work has been to develop the manufacturing process of the reinforced aluminium alloy and analyse its mechanical properties and microstructure. Details about an innovative MMC manufacturing process and the results obtained in the development of a new family of TiB 2 -reinforced aluminium alloys for forging and extrusion applications are presented. It has been observed that the considered manufacturing process, consisting in the fabrication of particles by SHS and their incorporation into the selected alloy, is a feasible process to manufacture reinforced alloys that can be subsequently extruded or forged. The final result is the development of a material suitable for extrusion and forging applications and that presents an improvement of fatigue and tensile properties of the matrix alloy. KeywordsMetal matrix composites (MMC); Self propagating high temperature synthesis (SHS); Extrusion; Aluminium 6061; TiB 2 particles. INTRODUCCIÓNEl interés del sector del transporte, en los materiales compuestos de matriz metálica, MCMM, se debe a las posibilidades que ofrecen de sustitución de materiales y diseños con mayor peso y de contribución a la reducción del consumo de combustible mediante el aligeramiento de materiales. El sector aeronáutico está especialmente interesado en el desarrollo de materiales reforzados con partículas debido a su buen balance de propiedades/coste [1] .En los últimos años, gran parte de la investigación en MCMM se ha centrado en el desarrollo de nuevos procesos de fabricación de materiales reforzados con partículas. Ell...