Challenges in Additive Manufacturing of space parts: Powder feedstock cross-contamination and its impact on end products

This work studies the tensile properties of Ti-6Al-4V samples produced by laser powder bed based Additive Manufacturing (AM), for different build orientations. The results showed high scattering of the yield and tensile strength and low fracture elongation. The subsequent fractographic investigation revealed the presence of tungsten particles on the fracture surface. Hence, its detection and impact on tensile properties of AM Ti-6Al-4V were investigated. X-ray Computed Tomography (X-ray CT) scanning indicated that these inclusions were evenly distributed throughout the samples, however the inclusions area was shown to be larger in the load-bearing plane for the vertical specimens. A microstructural study proved that the mostly spherical tungsten particles were embedded in the fully martensitic Ti-6Al-4V AM material. The particle size distribution, the flowability and the morphology of the powder feedstock were investigated and appeared to be in line with observations from other studies. X-ray CT scanning of the powder however made the high density particles visible, where various techniques, commonly used in the certification of powder feedstock, failed to detect the contaminant. As the detection of cross contamination in the powder feedstock proves to be challenging, the use of only one type of powder per AM equipment is recommended for critical applications such as Space parts. 2017 by the authors

SURFACE ENGINEERING FOR PARTS MADE BY ADDITIVE MANUFACTURING

peer reviewedthe surface preparation of metal parts made by additive manufacturing (AM). AM is a technology of choice for manufacturing of parts with complex shapes (heat exchangers, RF supports, optical parts…) and integrated functions such as conformal cooling channels, clips, hinges, etc. This opens the door for lightweight parts which are of prime importance for space applications. The potential of the AM technologies is however impeded by the quite rough surface finish that is observed on the as-manufactured parts. It is known that such a finish is likely to impact the performance of the parts. Several post-treatment techniques can be applied to improve the surface condition of the AM parts. However, so far, the influence of the successive post-processing steps on the final properties is not well established. Therefore, a better understanding of the impact of surface characteristics on the material behaviour is needed to expand the use of AM for high performance parts. The objective of this study, supported by ESA, is to propose and evaluate various surface finishing techniques for parts made by the AM technologies, in order to check their compatibility, evaluate their properties and derive guidelines for future applications. CRM is the prime proposer of this study and is in charge of the surface treatment and characterisations. Sirris additive manufacturing facilities are used to produce the parts. Thales Alenia Space and Walopt are included into the industrial team to provide concrete application cases. The study focuses on metals. Two metals under study are presented here: AlSi10Mg and Ti6Al4V. This paper is devoted to the early results of the first steps of surface preparation, namely material removal from the surface of the produced parts in order to improve their surface properties. As a first phase, tribo-finishing (TF) is tested on prototype parts to check its capabilities. Surface and volume parameters are analyzed, namely achieved roughness, material removal rate, location of removed material. The limitations in terms of geometry and applicability are discussed as well. These first observations should serve as guidelines for further application of AM for the design of parts used in space industry

Fibre strength selection and the mechanical resistance of fibre-reinforced metal matrix composites

For predicting the strength of fibre-reinforced metal matrix composites, the in situ fibre strength value has to be introduced in the calculations. Tension tests series have been conducted on SiC fibres (SCSO and SCS2 TEXTRON) before and after chemical interaction with a pure liquid aluminium bath and the reacted fibres have been tested before and after dissolution of the aluminium coating simulating the metallic matrix around the fibres. The results obtained for the different fibre batches show that the in situ fibre resistance may differ significantly from the strength of as-received or extracted fibres that is usually adopted in the models

DEVELOPMENT OF COMPOSITE MATERIALS BASED ON A CARBON NANOTUBES NETWORK FOR SPACE APPLICATIONS

For few years, carbon nanotubes (CNTs) are added to in various materials. As CNTs have high mechanical, thermal and electrical properties, it is expected to boost by adding CNTs the performances of the matrix material. Usually carbon nanotubes are used as additive to an organic matrix and in small quantities, below 1 wt%. In this work we develop composite materials with high amount of CNT, based on a carbon nanotubes network. The main type of CNT network manufactured and tested is buckypaper obtained by filtration of CNTs dispersed in a liquid solution. Other CNT networks like 3D preformed shape and CNT arrays have been also investigated. The potential improvement brought by adding CNT network to conventional materials has been evaluated using the engineering rules established for composites. Hence, the maximal achievable material properties have been estimated. Using the previously described analysis, the potential of CNT reinforced composite for different space applications have been ranked. The mechanical (mainly for CNT fibre) and thermal driven applications seem the most promising ones, especially if specific properties are considered (due to the low density of CNTs). On the basis of this evaluation and manufacturing technologies available in our consortium, experimental efforts have been put on the optimization of the CNT network mainly for improving its thermal performances. Influence of the CNTs characteristics on the macroscopic buckypaper properties has been evaluated with CNTs of different morphology (MWNT, DWNT), length and functionalization. Several processes for manufacturing the buckypaper have been tried, using different solutions for CNTs dispersion (surfactant, water or ethanol), or applying alternative method like in-situ growth of CNTs on buckypapers. Among different CNT network post-treatment also tried, thermal treatment up to 2800°C has given the greatest improvement on the specific thermal conductivity. Eventually the CNT network is infiltrated by an organic (epoxy) or inorganic (aluminium) matrix to make the composite. 3D shape CNT network gives highly reinforced composite with 30wt% of CNTs. Even if current properties of CNT reinforced composite materials are not yet competitive with reference aerospace materials, improvement potential is large and manufacturing technologies are growing.NON CONVENTIONAL MATRIX / CARBON NANOTUBES REINFORCED COMPOSITE FOR APPLICATIONS IN SPAC

ADVANCED MANUFACTURING METHODS FOR SYSTEMS OF MICROSYSTEM NANOSPACECRAFT – STATUS OF THE PROJECT

In the frame of an ESA TRP project, CSL, SIRRIS, ALMASpace and TAS-F associated to evaluate advanced manufacturing methods for application to space hardware. The state of the art of the new manufacturing methods, including additive manufacturing but also advanced bonding, joining and shaping techniques has been reviewed. Then three types of case studies have been developed successively. The first type was a re- manufacture of an existing piece of hardware using advanced techniques to evaluate if there is some potential improvement to be achieved (cost, production time, complexity reduction). The second level was to design and manufacture a part based on the application requirements. The last level was to design and manufacture a part taking into account the subsystem to which it belongs. All case studies have been tested in terms of achieved performances and resistance to the mechanical and thermal environment

New applications of Advanced Manufacturing Methods for space instrumentation and Systems of Nanospacecraft

In the frame of an ESA TRP project, our consortium has investigated the possibility to use advanced manufacturing methods for application to space hardware. After a review of the state of the art of the new manufacturing methods, including additive manufacturing but also advanced bonding, joining and shaping techniques, several case studies have been realized. These new techniques imply a different approach already at the design phase since the manufacturing constraints can be completely different. The goal of the project was to evaluate the different technologies from the design to the realization and learn how the classical design and development of such parts shall be adapted to take into account the different specificities of the new techniques. Three types of case studies have been developed successively. The first type was a re-manufacture of an existing piece of hardware using advanced techniques to evaluate if there is some potential improvement to be achieved (cost, production time, complexity reduction). The second level was to design and manufacture a part based on the application requirements. The last level was to design and manufacture a part taking into account in addition the subsystem to which it belongs. All case studies have been tested in terms of achieved performances and resistance to the mechanical and thermal environment. For each level, several case studies were proposed by ALMASpace and TAS-F and a pre-selection was performed to verify the feasibility and the interest of the proposed part for the project. For the first 2 levels, the 2 selected case studies have been designed, built and tested. A single case study was built for last level. The cases studies of level one were an aluminium inertial wheel housing (using electron beam welding to connect simple machined parts) and a mechanism housing fully made by additive manufacturing (electron beam melting of Titanium). The ones of level two were an aluminium tray for nanosatellite structure (assembled by salt dip brazing) and an antenna support bracket (designed by topological optimization and manufactured by laser beam melting of aluminium). The third level case study is a Sun Sensor for nanosatellite designed by topological optimization and including electronic circuit (optical detector and proximity electronic) deposited by aerosol jet printing directly on the aluminium structure. All case studies have been manufactured and tested and all part manufactured, despite including some imperfections, fulfilled all performance requirements