1、Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 1,ESA SME Initiative Course D:Materials,Dr. Ton de Rooij Head of Materials Mechanics and Processes Section Materials and Processes Division Product Assurance and Safety Department,Material properties requirements, for metallic materials,Materi
2、als and Processes Division ESA/ESTEC/TOS-QM,Sheet: 2,Constraints on materials,Temperature Vacuum Thermal cycling Chemical (corrosion) Galvanic compatibility Atomic oxygen Moisture absorption/desorption Fluid compatibility,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 3,Constraints on mate
3、rials, cont,Temperature The range of temperatures experienced will play a large part in the materials selection. Extremes are illustrated by the examples of cryogenic tanks and thermal protection systems for re-entry applications. Temperatures below room temperature generally cause an increase in st
4、rength properties, however the ductility decreases. Ductility and strength may increase or decrease at temperatures above room temperature. This change depends on many factors, such as temperature and time of exposure.Materials shall be compatible with the thermal environment to which they are expos
5、ed.Passage through transition temperatures (e.g., brittle-ductile transitions or glass transition temperatures including the effects of moisture or other phase transitions) shall be taken into account.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 4,Constraints on materials, cont,Thermal
6、cycling Thermal cycling can induce thermal stresses and due to the difference in coefficient of thermal expansion between fibres and matrix for composites and between base metal and coating micro-cracks can form which could jeopardise long-term properties. Materials subject to thermal cycling shall
7、be assessed to ensure their capability to withstand the induced thermal stresses and shall be tested according to ECSS- Q- 70- 04.Chemical (corrosion) The chemical environment to which a material is subjected in its life span may cause changes in the material properties. Corrosion is the reaction of
8、 the engineering material with its environment with a consequent deterioration in properties of the material. Corrosion will include the reaction of metals, glasses, ionic solids, polymeric solids and composites with environments that embrace liquid metal, gases, non-aqueous electrolytes and other n
9、on-aqueous solutions, coating systems and adhesion systems.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 5,Constraints on materials, cont,Galvanic compatibility If two or more dissimilar materials are in direct electrical contact in a corrosive solution or atmosphere galvanic corrosion m
10、ight occur. The less resistant material becomes the anode and the more resistant the cathode. The cathodic material corrodes very little or not at all, while the corrosion of the anodic material is greatly enhanced. Material compatibilities shall be selected in accordance with ECSS- Q-70-71, Maximum
11、 potential differences shall be in accordance with ECSS- Q-70-71, In the construction of a satellite, two metals that form a compatible couple may have to be placed in close proximity to one another. Although this may not cause anomalies or malfunctions in the space environment, it has to be borne i
12、n mind that spacecraft often have to be stored on earth for considerable periods of time and that during storage they may inadvertently be exposed to environments where galvanic corrosion can take place. In fact, this is known to have taken place on several occasions and it is for this reason that t
13、he Agency has been studying the dangers involved.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 6,Constraints on materials, cont,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 7,Constraints on materials, cont,Atomic oxygen Spacecraft in low earth orbit (LEO) at altitudes of betw
14、een 200 km and 700 km are exposed to a flux of atomic oxygen. The flux level varies with altitude, velocity vector and solar activity. The fluence levels vary with the duration of exposure.Moisture absorption/desorption The properties of composite materials are susceptible to changes induced by the
15、take-up of moisture. Moisture absorption occurs during production of components and launch of the spacecraft, desorption occurs in the space vacuum.Fluid compatibility In some occasions materials are in contact with liquid oxygen, gaseous oxygen or other reactive fluids or could come into contact wi
16、th such a fluid during an emergency situation.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 8,Metallic Materials used in space,Light metals, such as beryllium, magnesium, aluminium and titanium and their alloysSteels, such as low-alloy, tool, corrosion resistant, precipitation hardable,
17、and maragingNickel and nickel base alloys, including pure nickel, Monel alloys, Inconel alloys, and other nickel- and cobald-base superalloysRefractory metals, principally niobium and molybdenumCopper-base alloys, including pure coppers, beryllium coppers, bronzes and brassesPrecious metalsWelding,
18、brazing and soldering alloysVarious plating alloys,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 9,Aluminium and its alloys,Aluminium alloys are some of the basic building materials of existing spacecraft and appear in many subsystems.,Light alloys based on aluminium are used in: primary
19、and secondary structures; plumbing; plating in many applications (electronics, thermal control, corrosion protection etc); aluminised layers on other materials (see adhesive tapes and plastic films); fillers in other materials to provide electrical or thermal conductivity.In addition to standard all
20、oys, more recent alloy developments include: additions of lithium to increase mechanical performance and decrease density. Li-additions are often lower than other conventional alloying elements, so Al-Li alloys may appear within different alloy groups (2000-, 7000- and 8000-series wrought products).
21、 reinforced alloys (metal matrix composites - MMC) consisting of aluminium alloys reinforced with whiskers, metal wires, boron fibres or carbon fibres. thin Al-alloy sheets with layers of fibre-reinforced polymer composite in between (Fibre Metal Laminates - FML).,Materials and Processes Division ES
22、A/ESTEC/TOS-QM,Sheet: 10,Aluminium and its alloys, cont,Main categories A large number of commercial, wrought and cast, alloys are available. A similarly large number of mechanical and thermal tempers are used to optimise certain properties, often at the expense of others (e.g. higher strength, but
23、poorer corrosion resistance). Not all of these alloys or tempers are suitable for aerospace engineering, from the point of view of either mechanical performance or environmental resistance. Many aluminium alloys exhibit excellent corrosion resistance in all standard tempers. However, the higher-stre
24、ngth alloys, which are of primary interest in aerospace applications, must be approached cautiously. In structural applications preference should be given to alloys, heat treatments and coatings which minimise susceptibility to general corrosion, pitting, intergranular and stress-corrosion cracking.
25、 Some alloys are clad with thin layers of pure aluminium to improve corrosion performance.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 11,Aluminium and its alloys, cont,Processing/Assembly All classical methods find a use: shaping and forming processes (wrought products produced by roll
26、ing, extrusion, forging; cast products); joining by welding, brazing, riveting, bolting, adhesive bonding etc. Not all alloys are weldable . Most high-strength alloys cannot be brazed.Space use does not raise special problems in this respect; except that processes must be extremely reliable. Aircraf
27、t industry standards are normally followed.Processing of metals gives rise to residual stresses that may cumulatively reach design-stress levels, particularly as regards fatigue phenomena.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 12,Aluminium and its alloys, cont,Residual stresses fr
28、om processing (forming and heat-treatments), machining, assembly (improper tolerances during fit-up, over-torqueing, press-fits, high-interference fasteners and welding), operational use, storage and transportation need evaluation Corrosion must be considered during the whole manufacture and prelaun
29、ch phase; electrolytic couples should be avoided and all metals should be suitably protected against external damage by the use of plating, conversion coatings, paints and strippable coatings. This is particularly important in special operating environments (fuel tanks for example).,Precautions The
30、properties of aluminium alloys are strongly dependent on their previous thermal and/or mechanical history.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 13,Aluminium and its alloys, cont,Stress CorrosionThe metallic components proposed for use in most spacecraft must be screened to preven
31、t failures resulting from SCC.Such metal-alloy selection must in particular be applied during the design phases of all spacecraft making use of the:,Space Shuttleitems intended for long-term storage prior to launchhighly stresses structuresall parts used or associated with the fabrication of launch
32、vehicles, etc.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 14,Aluminium and its alloys, cont,Stress Corrosion, contStress corrosion cracking (SCC), defined as the combined action of sustained tensile stress and corrosion, can cause premature failure of aluminium alloys.Because metallurg
33、ical processing of aluminium alloys usually results in a pronounced elongation of grains, the variation of susceptibility with grain orientation is more extensive than for other metals (see ECSS-Q-70-36).Because conventional processing are designed to optimise strength, residual stresses - especiall
34、y in thick sections - are usually greater in aluminium products than in wrought forms of other metals. Both the residual stress distribution and the grain orientation shall be carefully considered in designing a part to be machined from wrought aluminium.Wrought heat-treatable aluminium products sho
35、uld be mechanically stress-relieved (TX5X or TX5XX temper designations) whenever possible.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 15,Aluminium and its alloys, cont,Mechanical stress relieved (TX5X or TX5XX) where possible. Including weldments of the weldable alloys.The former desig
36、nation is shown in parenthesis when significantly different.High magnesium content alloys 5456, 5083 and 5086 should be used only in controlled tempers (H111, H112, H116, H117, H323, H343) for resistance to stress-corrosion cracking and exfoliation.Alloys with magnesium content greater than 3.0% are
37、 not recommended for high-temperature application, 66C (150F) and above.Excluding weldments. (E)ESA classification - not in NASA MSFC-SPEC-522A.,Stress Corrosion (table I), cont,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 16,Aluminium and its alloys, cont,Hazardous/precludedCertain allo
38、ys and tempers are unsuitable for structural applications in long-term, manned structures, such as International Space Station (ISS):Some 5000-series alloys and tempers are limited to a maximum use temperature of 66C in ISS.Some 5000-series alloys with a high magnesium content require specific tempe
39、rs to provide resistance to stress-corrosion cracking and exfoliation.Porous platings (corrosion protection) and aluminised layers are not permitted, because they fail to provide adequate protection and can act as sources for contamination (See also: Tapes and films).Electrolytic couples must be avo
40、ided or corrected by a suitable insulation between the metals concerned. Bare metal-to-metal contact is to be avoided in any moveable part.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 17,Aluminium and its alloys, cont,Effects of space environment In general, metals do not suffer from sp
41、ace-environment conditions.Vacuum does not affect aluminium alloys. All metals in contact under vacuum conditions or in inert gas have a tendency to cold weld. This phenomenon is enhanced by mechanical rubbing or any other process which can remove oxide layers. Radiation at the level existing in spa
42、ce does not modify the properties of metals.Temperature problems are analogous to those encountered in technologies other than space, except for a complication arising from the difficulty of achieving good thermal contact in vacuum and due to the absence of any convective cooling. Aluminium alloys w
43、ith magnesium contents greater than 3% are not recommended for applications where temperatures may exceed 66C.Atomic oxygen in low earth orbit (LEO) does not degrade aluminium alloys.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 18,Copper and its alloys,General Copper and copper-based al
44、loys are established materials in electrical, electronic and also in more general engineering applications (such as bearing assemblies, etc). Not all are acceptable for space, so discussion is limited to those alloys which have been evaluated and to specific comments relating to their use in space.U
45、se in spacecraft The main applications for copper are in electrical/electronic subsystems (wiring, terminals in soldered assemblies) and plating (electronics, thermal control, corrosion protection etc). Copper is also used as a metallising coating -see Plastic Films - and as an additive in other mat
46、erials -see Lubricants.,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 19,Copper and its alloys, cont,Main categories Copper materials are generally grouped as: commercially pure grades, of which there are many different named varieties that indicate the manufacturing method and the level
47、of control of impurities, including oxygen; alloys in which the alloying additions affect the metallurgical microstructure and consequently their characteristics (mechanical, electrical and thermal properties, environmental resistance). The main alloying addition generally provides the named classif
48、ications: brass: copper - zinc alloys, often containing other alloying elements, such as lead which acts as a lubricant for machining operations - so-called free-machining; bronze: copper - tin alloys, often containing other alloying elements. Electronic assemblies use wires made of high-purity copp
49、er or copper alloy and terminals of copper alloy.,Beryllium-copper (also known as copper-beryllium) is a copper alloy with small additions of Be. These alloys are used for electrical/electronic applications (spring contacts); for low temperature applications; for high-strength corrosion resistant components and in safety applications in hazardous environments (no sparks produced when impacted).Copper is also used as a matrix phase in some reinforced metals,Materials and Processes Division ESA/ESTEC/TOS-QM,Sheet: 20,Copper and its alloys, cont,
