Phase change materials and thermosensitive painting: Application on smart thermal protection systems

In order to promote new ideas and assess novel alternatives for TPS concepts, ESA has launched an exploratory study on Smart TPS for future re-entry vehicles. Within this context, the objectives of the present work have been achieved within two phases: (1) definition of Smart TPS concepts, study and selection of the most promising ones and (2) demonstration of their feasibility. After a trade-off approach, where the smart concepts have been evaluated versus system aspects, the two most promising were selected for proof-of-concept. The first one, based on Phase Change Materials (PCMs), provides increased safety by preventing the formation of hot spots in the primary structure. The second one is a thermosensitive painting able to retrieve information of the thermal history of the TPS after re-entry, enabling easier maintenance. Both concepts have been tested under simulated re-entry conditions at high temperature. It has been demonstrated that the use of PCM restricts the temperature achieved in critical zones of the primary structure notably lower than that achieved without PCM. In addition, outstanding accuracy of the thermal paints has been confirmed by comparison with thermocouples measurements. Excellent adherence with the substrate has been also confirmed under thermal cycling and plasma conditions.Peer reviewe

Production of Ti/Tib master alloy by SHS process for the obtention Ti/Tib composites for the automotive industry

High technology transport sectors are looking for higher performance materials, competitive in terms of cost, lighter than conventional titanium alloys and recyclable, which could improve efficiency of several components and reduce fuel consumption through weight reduction. This work has been carried out in the framework of Growth NEWTIRAL project (Contract N°G5RD-CT01-00529) financially supported by the European Commission, which investigates the production of in situ Ti/TiB master alloy (with a high volume fraction of reinforcing phase) that is further melted together with titanium ingots. This way a composite with controlled TiB reinforcement volume fraction can be obtained via conventional casting route. This study focuses in the investigation of the production technique of the Ti/TiB master alloy, which is produce by SHS (Self Propagating High temperature Synthesis). This technique is a self-sustaining combustion process of any chemical compound that results in the formation of valuable condensed products. The SHS is based on the principle of maximum utilization of chemical energy of reacting substances (exothermicity) for obtaining inorganic compounds, materials, and items of various application purposes and also for organizing highly efficient technological processes. The obtained product is characterised using different techniques: XRD, SEM, and mechanical properties.Peer reviewe

Production of γ-TiAl based alloy by combustion synthesis + compaction route, characterization and application

Synthesis and densification of γ-TiAl alloy with nominal chemical composition Ti-48A1-2Cr-2Nb (at.%) have been investigated. The alloy is prepared in one step using a combustion synthesis + compaction process, where the synthesis and the shaping take place at the same time. Two different combustion routes are used: Forced Self-propagating High-temperature Synthesis + Compaction (FSHS + C) and Thermal Explosion + Compaction (TE + C). The optimal synthesis parameters such as ignition point, load application delay time, load value, load holding time, heating and cooling rates are determined. After the processing, the density of the samples was measured to be of about 99 % of the theoretical value. It is shown that the oxygen content can be controlled during the processing and products with the same or lower oxygen content than that in the original raw material can be obtained. Analysis of chemical composition and microstructure shows that a complete chemical homogenization, required phase composition, desired lamellar microstructure and relaxation of possible internal stresses require additional thermal treatment of samples prepared by both FSHS + C and TE + C processes.Peer reviewe

Development of new aluminium alloys for semisolid processing

Semisolid metallurgy (SSM) or semisolid forming is an emerging technology that enables the forming of complicated shapes and the processing of materials increasing their mechanical properties compared with conventional methods. In the present article the advantages of SSM process are described in terms of fundamentals of the forming process and the microstructural characteristics of the product. An overview of the main casting methods in the semisolid state are also shown: Thixocasting and New Rheocasting (NRC). Each process is briefly analysed, their advantages/disadvantages identified and an attempt made to suggest that the latter one finds the optimal performance.Peer reviewe

Structural and microstructural behaviour of SnO2 dense ceramics doped with ZnO and WO3

SnO2-based varistors doped with ZnO and WO3 were prepared by mixed oxide method. Experimental evidence shows that the increase in ZnO amount increases the volume and microstrain of unit cell while the WO3 promotes a decrease. The effect of ZnO and WO3 additives could be explained by the substitution of Sn4+ by Zn2+ and W6+. The addition of WO3 inhibits the grain growth due to the segregation in the grain boundary without influence in the densification of the samples. Besides that, an increase in the electrical resistance of the SnO2-ZnO-WO3 system was observed independent of the WO3 concentration. (c) 2005 Elsevier B.V. All rights reserved

Microstructure and mechanical properties of gamma TiAl based alloys produced by combustion synthesis + compaction route

Microstructure and mechanical properties of γ-TiAl alloy with the chemical composition Ti-48Al-2Cr-2Nb (at.%) have been investigated. The alloy was prepared in one step using a combustion synthesis + compaction process, where the synthesis and the shaping take place at the same time. Two different combustion routes were used: forced self-propagating high-temperature synthesis + compaction (FSHS + C) and thermal explosion + compaction (TE + C). Fully lamellar microstructure was obtained in both processing routes after the appropriate homogenisation thermal treatment. Nevertheless, TE + C route showed coarser lamellar colonies. A remarkable oxygen content reduction was achieved in samples synthesised by FSHS + C route. Tensile properties (especially UTS) were found to be in the same range as other alloys obtained by conventional processing routes, however, low ductility was achieved. Good creep and fatigue properties were obtained. All fracture surfaces showed a brittle fracture mechanism. Finally, it was found out that the studied processing routes showed promising results as an alternative manufacturing technology for γ-TiAl based alloys.This work was carried out within the frame work of the project with reference 18955/05/NL/CP, entitled “High Temperature Complex Parts Based on Intermetallics” supported by ESA (European Space Agency).Peer reviewe