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|PRODUCT DATA of 08: Miscellaneous Alloys|
|Material||08: Miscellaneous Alloys|
|General Information||A metal is classed as miscellaneous if it does not fall within another declared materials list (DML) category in ECSS-Q-70. Also included in this section are comments on metal-based materials that are either prohibited or should be approached with caution for space applications.|
|Use in Spacecraft||Light alloys based on magnesium and beryllium are used in some primary and secondary structures.
Plating appears in many applications (e.g. electronics, thermal control and corrosion protection) and calls mainly for silver and gold.
"Memory alloys" based on titanium and nickel can find uses as actuators:
In addition to standard conventional alloys, more recent material developments include:
|Main Categories||Miscellaneous metals include, but are not limited to:
NOTE This chapter also includes comments on metal-based materials that are either prohibited or can be used cautiously for space applications.
|Processing and Assembly||Magnesium alloys are available as wrought forms or for casting. Care shall be taken in storing magnesium alloys due to their tendency to corrode. Machining shall be performed with special precautions to prevent ignition and burning of swarf.
Sophisticated techniques and rigorous safety procedures shall be applied during processing of beryllium to avoid the formation and release of beryllium oxide,
Superalloys are processed following recognized aerospace procedures or other appropriate industry standards.
Specialist methods for processing refractory metals and alloys are applied.
During processes when metals with known or suspected toxicity problems are involved, appropriate safety equipment shall be used for operatives and appropriate procedures followed for collection and disposal of waste.
|Precautions||The metallic components proposed for use inmost spacecraft shall be screened to prevent failures resulting from SCC. Three alloy ratings were derived: high-resistance, moderate-resistance and low-resistance to SCC (these are listed in Tables 1, 2 and 3 respectively of ECSS-Q-ST-70-36C). The alloys listed in Table 1 should be used for space applications. For alloys listed in Table 2 or 3 a detailed justification for space use shall be provided, demonstrating that SCC testing according to the standard method detailed in ECSS-Q-ST-70-37C took place (method incorporates constant load and alternate immersion in 3,5 % NaCl solution).
Beryllium and Beryllium oxide dust and vapours are toxic: special precautions shall be taken when work is done on this material.
NOTE Cadmium in NiCd batteries is acceptable.
|Hazardous and Precluded||Mercury and mercury-containing compounds can cause accelerated cracking of aluminium and titanium alloys. It is therefore a prohibited substance for the manufacture of aerospace structures and subsystems.
Specialized safety equipment and procedures for the collection and disposal of dust and debris shall be used for operatives working with toxic materials, such as beryllium and osmium, and for materials with a risk of ignition and burning, such as magnesium.
In electronic assemblies, tin-, silver- and gold-plating on terminals of PCBs is removed in order to achieve an approved tin-lead finish. Soldering directly to gold finishes is unacceptable and de-golding processes are used. In unavoidable use of gold-finishes, such as in RF circuitry, selective plating processes are used for soldered connections.
|Effects of Space environment||Vacuum affects volatile metals, such as cadmium and zinc. These metals sublime readily at temperatures over 100 ºC and 150 ºC respectively, and can form conductive deposits on insulators or opaque deposits on optical components. Oxide layers slow down the process of evaporation when they are thick enough and not cracked. 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 or disrupt oxide layers. It is particularly intense for pairs of cubic-lattice metals which alloy readily.
|Some Representative Products||European sources of beryllium are: SAGEM (F), Royal Ordnance Factory (UK), Heraeus (D), Brush Wellman (UK and D); Superalloys: Aubert and Duval (F)
Magnesium alloys: Magnesium Elektron (UK).
Procurement to internationally recognized specifications isrecommended, such as ISO,MIL Specs, B.S., SAE., DIN or AFNOR specifications.
The materials listed in Table A-9 (from ECSS-Q-ST-70-36), can be considered.