Material Properties Requirements for Metallic Materials.ppt

Dr. Ton de Rooij
Processes Section
Material properties requirements, for metallic materials

Temperature
The range of temperatures experienced ill play a large part in the materials selection.
!xtremes are illustrated "y the examples of cryogenic tan#s and thermal protection systems
for re$entry applications. Temperatures belo room temperature generally cause an
increase in strength properties% hoever the ductility decreases. Ductility and strength may
increase or decrease at temperatures a"ove room temperature. This change depends on
many factors% such as temperature and time of exposure.
Materials shall "e compati"le ith the thermal environment to hich they are exposed.
Passage through transition temperatures &e.g.% "rittle$ductile transitions or glass transition
temperatures including the effects of moisture or other phase transitions' shall "e ta#en into
account.
Thermal cycling
Thermal cycling can induce thermal stresses and due to the difference in coefficient of
thermal expansion "eteen fi"res and matrix for composites and "eteen "ase metal and
coating micro$crac#s can form hich could jeopardise long$term properties.
Materials su"ject to thermal cycling shall "e assessed to ensure their capa"ility to
+,.
Chemical (corrosion)
The chemical environment to hich a material is su"jected in its life span may cause
changes in the material properties. (orrosion is the reaction of the engineering material
ith its environment ith a conse-uent deterioration in properties of the material. (orrosion
ill include the reaction of metals% glasses% ionic solids% polymeric solids and composites
ith environments that em"race li-uid metal% gases% non$a-ueous electrolytes and other
non$a-ueous solutions% coating systems and adhesion systems.

Galvanic compatibility
f to or more dissimilar materials are in direct electrical contact in a corrosive solution or
atmosphere galvanic corrosion might occur. The less resistant material "ecomes the
anode and the more resistant the cathode. The cathodic material corrodes very little or not
at all% hile the corrosion of the anodic material is greatly enhanced.
/ Material compati"ilities shall "e selected in accordance ith !(SS$ )$*+$*0%
/ Maximum potential differences shall "e in accordance ith !(SS$ )$*+$*0%
n the construction of a satellite% to metals that form a compati"le couple may have to "e
placed in close proximity to one another. Although this may not cause anomalies or
malfunctions in the space environment% it has to "e "orne in mind that spacecraft often
have to "e stored on earth for considerable periods o! time and that during storage
they may inadvertently "e exposed to environments here galvanic corrosion can ta#e
place. n fact% this is #non to have ta#en place on several occasions and it is for this

Atomic oxygen
Spacecraft in lo earth orbit ("#$' at altitudes of "eteen 1++ #m and *++ #m are
exposed to a flux of atomic oxygen. The flux level varies ith altitude% velocity vector and
solar activity. The fluence levels vary ith the duration of exposure.
Moisture absorption/desorption
The properties of composite materials are suscepti"le to changes induced "y the ta#e$up
of moisture. Moisture a"sorption occurs during production of components and launch of the
spacecraft% desorption occurs in the space vacuum.
Fluid compatibility

Metallic Materials used in space
2ight metals% such as "eryllium% magnesium% aluminium and titanium and their alloys
Steels% such as lo$alloy% tool% corrosion resistant% precipitation harda"le% and
maraging
3ic#el and nic#el "ase alloys% including pure nic#el% Monel alloys% nconel alloys% and
other nic#el$ and co"ald$"ase superalloys
Refractory metals% principally nio"ium and moly"denum
(opper$"ase alloys% including pure coppers% "eryllium coppers% "ron4es and "rasses
Precious metals
6arious plating alloys
Aluminium and its alloys
Aluminium alloys are some o! the basic building materials o! existing spacecra!t and
appear in many subsystems'
2ight alloys "ased on aluminium are used in7 primary and secondary structures8 plum"ing8 plating in many applications &electronics% thermal control% corrosion protection etc'8 aluminised

n addition to standard alloys% more recent alloy developments include7 additions of lithium to increase mechanical performance and decrease density. 2i$additions
are often loer than other 9conventional9 alloying elements% so Al$2i alloys may appear ithin
different alloy groups &1+++$% *+++$ and :+++$series rought products'. reinforced alloys &metal matrix composites $ MM(' consisting of aluminium alloys reinforced
ith his#ers% metal ires% "oron fi"res or car"on fi"res. thin Al$alloy sheets ith layers of fi"re$reinforced polymer composite in "eteen &;i"re Metal
2aminates $ ;M2'.
Main categories
A large num"er of commercial% rought and cast% alloys are availa"le. A similarly large num"er
of mechanical and thermal tempers are used to optimise certain properties% often at the
expense of others &e.g. higher strength% "ut poorer corrosion resistance'. 3ot all of these alloys
or tempers are suita"le for aerospace engineering% from the point of vie of either mechanical
performance or environmental resistance.
Many aluminium alloys exhi"it excellent corrosion resistance in all standard tempers. Hoever%
the higher$strength alloys% hich are of primary interest in aerospace applications% must "e
approached cautiously. n structural applications preference should "e given to alloys% heat
treatments and coatings hich minimise suscepti"ility to general corrosion% pitting% intergranular
and stress$corrosion crac#ing. Some alloys are clad ith thin layers of pure aluminium to
improve corrosion performance.
rocessing/Assembly
All classical methods find a use7 shaping and forming processes &rought products
produced "y rolling% extrusion% forging8 cast products'8 joining "y elding% "ra4ing% riveting%
"olting% adhesive "onding etc.
3ot all alloys are elda"le . Most high$strength alloys cannot "e "ra4ed.
Space use does not raise special pro"lems in this respect8 except that processes must "e
extremely relia"le. Aircraft industry standards are normally folloed.
Processing of metals gives rise to residual stresses that may cumulatively reach design$
stress levels% particularly as regards fatigue phenomena.

Residual stresses from processing &forming and heat$treatments'% machining% assem"ly
&improper tolerances during fit$up% over$tor-ueing% press$fits% high$interference fasteners
and elding'% operational use% storage and transportation need evaluation
(orrosion must "e considered during the hole manufacture and prelaunch phase8
electrolytic couples should "e avoided and all metals should "e suita"ly protected against
external damage "y the use of plating% conversion coatings% paints and strippa"le
coatings.
This is particularly important in special operating environments &fuel tan#s for example'.
recautions
The properties of aluminium alloys are strongly dependent on their previous thermal and<or
mechanical history.
tress Corrosion
The metallic components proposed for use in most spacecraft must "e screened to prevent
failures resulting from S((.
Such metal$alloy selection must in particular "e applied during the design phases of all
spacecraft ma#ing use of the7
Space Shuttle
highly stresses structures

tress Corrosion& cont*
Stress corrosion crac#ing &S(('% defined as the com"ined action of sustained tensile stress
and corrosion% can cause premature failure of aluminium alloys.
=ecause metallurgical processing of aluminium alloys usually results in a pronounced
elongation of grains% the variation of suscepti"ility ith grain orientation is more extensive
than for other metals &see !(SS$)$*+$>?'.
=ecause conventional processing are designed to optimise strength% residual stresses $
especially in thic# sections $ are usually greater in aluminium products than in rought forms
of other metals.
=oth the residual stress distri"ution and the grain orientation shall "e carefully considered in
designing a part to "e machined from rought aluminium.
5rought heat$treata"le aluminium products should "e mechanically stress$relieved &T@@
or T@@@ temper designations' henever possi"le.

+rought ,& - Cast
1+1,% rod "ar T: >*.+ All
110B T?% T: =>:.+ &Tens$+' All
&!' 1,0B T: >B.+ All
?+++ series All >.+ &Almag >' As cast
&!' *+1+ T? ? A*01.+% (*01.+ As cast
*+,B T*>
*0,B T*>
T@@@' here possi"le.
alloys.
parenthesis hen significantly different.
,. High magnesium content alloys ,?%
controlled tempers &H000% H001% H00?%
H00*% H>1>% H>,>' for resistance to
stress$corrosion crac#ing and exfoliation.
. Alloys ith magnesium content greater
than >.+C are not recommended for
high$temperature application% ??(
MS;($SP!($11A.
a0ardous/precluded
(ertain alloys and tempers are unsuita"le for structural applications in long$term% manned
structures% such as nternational Space Station &SS'7
Some +++$series alloys and tempers are limited to a maximum use temperature of ??°( in
SS.
Some +++$series alloys ith a high magnesium content re-uire specific tempers to provide
resistance to stress$corrosion crac#ing and exfoliation.
Porous platings &corrosion protection' and aluminised layers are not permitted% "ecause they
fail to provide ade-uate protection and can act as sources for contamination &See also7 Tapes
and films'.
!lectrolytic couples must "e avoided or corrected "y a suita"le insulation "eteen the metals
concerned.

#!!ects o! space environment
n general% metals do not suffer from space$environment conditions.
Vacuum does not affect aluminium alloys. All metals in contact under vacuum conditions or in
inert gas have a tendency to cold eld. This phenomenon is enhanced "y mechanical
ru""ing or any other process hich can remove oxide layers.
1adiation at the level existing in space does not modify the properties of metals.
Temperature pro"lems 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 a"sence of any convective cooling. Aluminium alloys ith
magnesium contents greater than >C are not recommended for applications here
temperatures may exceed ??E(.

(opper and copper$"ased alloys are esta"lished materials in electrical% electronic and also in
more general engineering applications &such as "earing assem"lies% etc'. 3ot all are accepta"le
for space% so discussion is limited to those alloys hich have "een evaluated and to specific
comments relating to their use in space.

2se in spacecra!t
The main applications for copper are in electrical<electronic su"systems &iring% terminals in
soldered assem"lies' and plating &electronics% thermal control% corrosion protection etc'. (opper
is also used as a metallising coating $see Plastic ;ilms $ and as an additive in other materials
$see 2u"ricants.
Main categories
(opper materials are generally grouped as7
commercially pure grades% of hich there are many different 9named9 varieties that
indicate the manufacturing method and the level of control of impurities% including oxygen8 alloys in hich the alloying additions affect the metallurgical microstructure and
conse-uently their characteristics &mechanical% electrical and thermal properties%
environmental resistance'. The main alloying addition generally provides the named
classifications7 / brass3 copper $ 4inc alloys% often containing other alloying elements% such as lead
hich acts as a 9lu"ricant9 for machining operations $ so$called 9free$machining98 / bron0e3 copper $ tin alloys% often containing other alloying elements.
!lectronic assem"lies use ires made of high$purity copper or copper alloy and terminals of
copper alloy.
=eryllium$copper &also #non as copper$"eryllium' is a copper alloy ith small additions of =e.
These alloys are used for electrical<electronic applications &spring contacts'8 for lo temperature
applications8 for high$strength corrosion resistant components and in safety applications in
ha4ardous environments &no spar#s produced hen impacted'.

rocessing/Assembly n electronic assem"ly operations% copper ires are soldered to terminals &either manually
or automatically'. The correct selection and use of process materials &approved solders and
fluxes for space hardare% solvents% etc' is a controlling factor in ma#ing relia"le soldered
connections
=eryllium$copper alloys are heat treated to optimise mechanical performance. ;a"rication
processes &forming% machining% joining% etc' are generally performed in a softened condition
and the material su"se-uently solution treated and aged.
a0ardous/precluded =eryllium and "eryllium oxide are toxic. Processing methods hich may release "eryllium
from the alloy or produce "eryllium oxide &heat treatment% elding% machining% etc' re-uire
appropriate safety e-uipment for operatives and proper facilities for the collection and
disposal of dust and de"ris.

recautions
Heating "rass in an oxidising atmosphere or under corrosive conditions can cause
de4incification of the alloy &loss of 4inc from the exposed surface layer'.
(old or#ed "rass alloys are sensitive to stress$corrosion crac#ing. Annealing heat
treatments are used to remove the cold or#.
Atmospheres containing sulphur dioxide% oxides of nitrogen and ammonia can cause S(( of
some copper alloys. (hlorides in marine atmospheres may cause stress corrosion
pro"lems% "ut to a lesser extent than the a"ove pollutants.
Many copper alloys containing over 1+C 4inc are suscepti"le to S((.
n electronic assem"lies% terminals fa"ricated from "ron4e are preferred. =rass terminals
re-uire a "arrier layer &plating'% to prevent diffusion and surface oxidation of 4inc% prior to
applying a tin$lead coating.
Some constituents of potting compounds and sealants &catalysts' are corrosive to copper%
and other metals.
alloys are generally plated $ see Miscellaneous metals.
All metals in contact under vacuum conditions or in inert gas have a tendency to cold eld.
This phenomenon is enhanced "y mechanical ru""ing or any other process hich removes
or disrupts surface oxide layers.
1adiation at the level existing in space does not modify the properties of copper alloys.
Temperature pro"lems are similar to those encountered in technologies other than space%
"ut are complicated "y the difficulty of achieving good thermal contact in vacuum and the
a"sence of any convective cooling.
Atomic oxygen in lo earth or"it attac#s copper.

C4A no' , Condition (5 cold rolled) -
00+ >*
1. Maximum per cent cold rolled for hich stress$
corrosion$crac#ing data are availa"le.
>. AT $ annealed and precipitation hardened.
,. HT $ or# hardened and precipitation
hardened.
Nickel and its alloys
Some alloys are used in electrical applications &such as heating elements'.
The magnetic characteristics of certain alloys are utilised in transformer components.
A fe alloys have controlled$expansion and constant$modulus properties &"imetals%
thermostats% glass sealing% precision e-uipment'.
Fthers have "een developed for specific applications &hydrogen storage' or to exploit a
particular peculiarity &shape$memory effect'.
There are also a num"er of alloys used as elding and "ra4ing filler materials. Some 3i$
"ased materials are applied as coatings or hard facings to other materials to provide ear or
corrosion resistance.
General
As a family% the 3i$"ased alloys are used in many engineering fields for their corrosion
resistance and high$temperature performance.

2se in spacecra!t
etc'.
3i$alloys are applied to su"systems re-uiring corrosion resistance &storage and delivery
systems'8 high$temperature performance% often com"ined ith oxidation resistance &propulsion
units $ gas tur"ines and roc#et motors% poer generation% heat$exchangers and tur"ines'8 high$
relia"ility% high$strength fasteners.

Main categories
The main use of commercially pure nic#el is in platings &"y electro$ or electroless
deposition' to provide corrosion protection to the underlying su"strate materials.
#lectroless nic7el can "e hardened to provide a"rasion resistance hilst retaining
corrosion resistance.
3ic#el provides elevated$temperature corrosion resistance to many acids.
As it is !erromagnetic% care is needed in its use in some applications &electronics% some
science missions'.
3ic#el$"ased materials can "e grouped "y principal alloying additions. Hoever% alloys ithin

Nickel and its alloys, cont…
The resistance of 3i$alloys to a particular corrosive media largely depends on the composition.
3i$Mo$;e alloys% often ith additions of (r7 resistance to high acid concentrations% retained
at high$temperatures. &also used in high$temperature structural applications. '
3i$(r$Mo$(u alloys7 resistance to strong mineral acids% many fluorine compounds% sea
ater $ often used as castings.
3i$;e$(r7 nconel ?1 $ resistance to inorganic and organic acid solutions% al#aline
solutions% chloride ion stress$corrosion% especially sea$ater8 nconel :1 $ resistance to
strong mineral acids% reducing and oxidising% sulphuric and phosphoric acids at all
concentrations to "oiling point.

Heat$resistant alloys tend to form to% not entirely independent% groups. Those developed to7
resist corrosive attac# imposed "y the service conditions $ hot corrosion8
resist deformation and fracture under the imposed service stresses and temperatures $
creep resistant or 9super alloys9.
Almost all heat$resistant 3i alloys are developments of the "asic :+3i $ 1+(r composition.
Modifications to this include variations in the (r content and the addition of other alloying
elements.
3i$;e$(r &usually ith 0$1C (r' alloys are used at service temperatures up to a"out
00++( in oxidising% car"urising% sulphidising environments and also are resistant to other
forms of chemical attac#.

(reep$resistant alloys &nic#el$"ased superalloys' pro"a"ly have the most complex compositions
of any engineering alloys and have similarly complex microstructures. Alloying increases the
strength and temperature capa"ility "ut reduces the processa"ility. This limits the product forms
availa"le. Sheet and complex forgings can only "e made in loer$alloy variants and their
temperature resistance is correspondingly loer.
turbine blades3 Alloy selection is normally made on creep and corrosion<oxidation
re-uirements% "ut toughness and fatigue resistance are also important factors.
discs3 Alloy selection is "ased on com"ined mechanical performance &creep and high$cycle
fatigue% crac# propagation and fracture toughness' at the service temperature. Alloys ith
high iron contents tend to have loer service temperatures% "ut conventional 3i$"ased
superalloys can operate at higher temperatures.
sheet alloys3 Mechanical performance at service temperature &and conditions' is
determined "y composition and the strengthening mechanism used. (ommercially availa"le
alloys may "e solid solution strengthened% precipitation hardened or oxide dispersion
strengthened &FDS'. Sheet alloys are readily elda"le% ith the exception of FDS alloys
and Rene ,0
6ic7el8based superalloys possess good com"inations of high$temperature mechanical
properties and oxidation resistance up to approximately +(. Many of these alloys also
have excellent cryogenic temperature properties.
Magnetic alloys generally have a high magnetic permea"ility in lo or moderate strength
magnetising fields% or exhi"it particular magnetic hysterisis characteristics.
They are mainly used in telecommunications or for electronic transformer
components. Pure nic#el and some high nic#el content$(o alloys have
magnetorestrictive characteristics used in transducers.
5ith careful control of composition and processing techni-ues% the thermal expansion
coefficient of some 3i$;e alloys can "e lo or "e matched to the (T! of non$metallic
materials such as glasses and ceramics. Some alloys can% "y composition modifications%
"e strengthened ma#ing them suita"le for load$"earing applications.
Gses include vacuum e-uipment% metrology and chronometry.

Some 3i$;e alloys exhi"it positive temperature coe!!icients o! elastic modulus
&most other metallic materials have negative values'.
These materials find specialist uses in springs and vi"rating devices.
3i$Ti memory alloys are "ased around the +7+ composition. They can "e
deformed "elo a specific temperature% then% on heating a"ove a higher temperature
&these systems sho some thermal hysterisis'% ill return to the original shape.
Applications include temperature sensitive actuators% fixing and gripping
devices &often in inaccessi"le locations'.

rocessing/Assembly
The chemical composition largely dictates the processing methods applica"le to a
particular alloy.
n addition to casting% normally under vacuum% and forging% poder metallurgy
techni-ues are used to produce highly$alloyed or dispersion$strengthened materials
from metal poders.
Similar processes% i.e. hot isostatic pressing% can "e used for the consolidation &porosity
elimination' of cast components.
All processes re-uire strict control and the specifications applied to aircraft and other
critical industry applications &poer generation' are used.

recautions
n electronic assem"lies% "rass terminals may "e plated ith a "arrier layer of nic#el
provided that its magnetic properties are accepta"le in the final assem"ly. &3ic#el may have
poor soldera"ility compared ith copper platings'.
Thermal cycling can affect oxidation and hot$corrosion resistance "y affecting the surface
composition of alloys. Spalling of the protective layer increases attac# "y corrosive media.
The selection and use of coatings for oxidation<corrosion resistance re-uires full evaluation
of service conditions and interfacial effects &thermal mismatch% diffusion% etc'. =arrier%
ceramic$type coatings can crac# and spall during thermal cycling and elements of metal

As a class% alloys ith a high nic#el content are
resistant to stress corrosion crac#ing.
>. ncluding eldments
Vacuum presents no special pro"lems. All metals in contact under vacuum conditions or in
ru""ing or any other process hich can remove or disrupt oxide layers.

Titanium and Ti$alloys are generally chosen for their mechanical properties% temperature
resistance and<or chemical resistance. The specific points of special interest for the spacecraft
designer are considered here% since the "asic aspects of titanium alloy assem"lies are similar to
those for aeronautic design.
(onventional Ti$alloys are used for primary and secondary structures8 fasteners8 in plum"ing
systems &standard tu"e alloy grades and commercially pure (P$grades' and in areas here
operating temperatures preclude the use of aluminium alloys. 9Memory alloys9 "ased on titanium
may find specialised uses as actuators.

Main categories
The characteristics of titanium alloys are generally grouped according to their metallurgical
structure hich is% in turn% controlled "y the chemical composition and heat$treatment history.
(ommercially pure &(P Ti' products are normally selected for chemical resistance.
mpurities in (P Titanium can increase strength "ut ith a loss in corrosion resistance.
Titanium alloys are normally selected for their strength properties% hich depend on a
num"er of specific heat$treatments &age hardening% -uench and temper'. The most
commonly used titanium alloy is Ti?Al,6 for hich extensive mechanical and corrosion
property data is availa"le.
rocessing/Assembly
All classical methods of shaping and forming processes can "e used% ith rought products
"eing produced "y rolling% extrusion% forging8 cast products. Fing to titanium9s high$affinity
for oxygen and other gases% melting and casting processes are carried out under vacuum to
prevent contamination and su"se-uent property degradation.
Titanium alloys can generally "e joined "y elding% "ra4ing% riveting% "olting and adhesive
"onding% although only certain alloys can "e "ra4ed. 3ot all alloys are elda"le and a
protective atmosphere is re-uired &inert$gas or vacuum' to avoid pic#$up of F% 3 and H
hich degrade properties.
Some metals and processing chemicals can degrade the properties of titanium alloys "y

recautions
The properties of titanium alloys are strongly dependent on their previous thermal
and<or mechanical history.
Some alloys have a limit on the section dimensions that can "e successfully hardened
"y heat$treatment.
The fatigue life of titanium alloys is reduced "y fretting at interfaces &either "eteen Ti$

itanium and its alloys, cont…
The corrosion and chemical resistance of titanium alloys relies on the adherent%
protective oxide layer hich is sta"le "elo >(. A"ove this temperature% the oxide film
"rea#s don and small atoms &such as (% F% 3 and H' em"rittle the metal. (onse-uently
high$temperature processing methods are done under vacuum or in an inert$gas
atmosphere.
During production% the selection of appropriate processes and avoidance of surface
contamination are vital to avoid property degradation. (ontamination 4ones formed
during processing can "e removed "y su"se-uent machining or "y chemical milling of the
surfaces of titanium parts.
(orrosion must "e considered during the hole manufacture and prelaunch phase8
electrolytic couples should "e avoided and all metals should "e suita"ly protected against
external damage "y the use of plating% conversion coatings% paints and strippa"le
coatings. This is particularly important in special operating environments &fuel tan#s for
example'.
Miscellaneous Alloy (rought)
tress corrosion (table .) a0ardous/precluded
em"rittlement and are generally unsuita"le for
hydrogen$containing atmospheres.
detrimental to performance.
corrosion% hydrogen em"rittlement% or reduce
fracture toughness include7 hydrochloric acid%
cadmium% silver% chlorinated cutting oils and
solvents% methyl alcohol% fluorinated hydrocar"ons%
mercury and compounds containing mercury.

Vacuum poses no special pro"lems. All metals in contact under vacuum conditions or in
ru""ing or any other process hich can remove or disrupt oxide layers. ;retting is a
particular concern for titanium alloys.

Steels
General
Steels% as a family of materials% offer a ide range of characteristics that find uses in many and
varied applications. This section concentrates on those materials% normally aircraft grades%

2se in spacecra!t
Steels are used in structural items &e.g. roc#et motor casings' and ithin engineering

SME Initiative
Steels, cont…
Main categories
Steels are "ased on alloys of iron and car"on &"eteen +.+C and 1C('. All contain some level of other elements% i.e. even plain car"on steels &up to 0.*C (' contain manganese up to a"out 0CMn.
mpurity levels &e.g. phosphorus and sulphur' depend mainly on the smelting and melting processes used
Alloy steels contain one or more additional alloying elements to improve properties and or#a"ility.

SME Initiative
Steels, cont…
Alloying additions to plain car"on steels produce a ide range of alloy steels ith improved performance.
The tensile strengths attaina"le from alloy steels depend on the composition% mechanical or#ing and heat$treatment processes.
;or engineering uses &i.e. materials having a com"ination of useful properties such as strength% toughness% processa"ility etc.' strengths rarely exceed 01+MPa.
The exceptions "eing some cold$or#ed products% e.g. ires% some hardened and tempered items such as "all "earings and some spring steels and 9maraging9 steels. 5here the GTS
exceeds 01+MPa% stress$corrosion "ecomes an issue.

melting
Most conventional processing techni-ues are applied to steels &machining% elding%
fastening% etc'.
Heat treatments may "e applied to the "ul# of the material or used to selectively harden the
surface. A ide range of compositional and mechanical surface treatments are availa"le to
selectively improve surface properties &e.g. car"urising% nitriding% shot peening% thread
rolling'.
High$strength martensitic steels &GTS IJ 011 MPa' re-uire careful machining using
car"ide$tipped tools and other techni-ues to ensure that the formation of an untempered
martensitic structure does not occur on surfaces.

SME Initiative
Steels, cont…
recautions (ar"on and lo$alloy steels ith ultimate tensile strengths "elo 011 MPa &0:+#si' are
generally resistant to stress$corrosion crac#ing.
Some steels have a ductile$"rittle transformation hich% depending on the alloy composition% can occur ithin the normal service conditions for some space components.
Depending on the alloy% some steels exhi"it poor elda"ility. This is lin#ed to the car"on content &or car"on$e-uivalent value' and can produce "rittleness in the eld affected 4one.
Steels are prone to corrosion in atmospheric and acidic a-ueous solutions.
2o$alloy steels% depending on the composition% tend to have "etter resistance to atmospheric corrosion.
High$alloy steels ith nic#el contents I>C sho improved resistance to atmospheric and marine environments.

Platings on steels commonly used in terrestrial applications for improved corrosion
resistance may not "e suita"le for space. These include 4inc% cadmium or other volatile
metals $ see Miscellaneous Metals.
6acuum poses no special pro"lems. All metals in contact under vacuum conditions or in
Radiation at the level existing in space does not modify the properties of metals.

(ar"on steel &0+++ series' =elo 011 MPa &0:+ #si' GTS
2o alloy steel &,0>+% ,>,+% etc.'
=elo 011 MPa &0:+ #si' GTS0
&!' D?A(% H$00 =elo 0,+ MPa &10+ #si' GTS
Music ire &ASTM 11:' (old dran
HK$:+ steel )uenched and tempered
HK$0>+ steel )uenched and tempered
HK$0,+ steel )uenched and tempered
0+B spring steel )uenched and tempered
3itronic >>> All
!uropean suppliers provide a ide range of steels% all of hich are denoted "y national and
international specifications and standards% including series specifically for aerospace grade
materials.
shon to have a high resistance to stress$
corrosion crac#ing are listed in the ta"le
&from !(SS$)$*+$>?'.
0. A small num"er of la"oratory failures of specimens cut
from plate more than cm thic# have "een o"served at
*C yield% even ithin this ultimate strength range. The
use of thic# plate should therefore "e avoided in a
corrosive environment hen sustained tensile stress in
the short transverse direction is expected.
>. ncluding eldments.

General
Stainless steels $ also #non as corrosion$resistant steels $ have alloying additions
specifically to provide a continuous% adherent% self$healing oxide film and so reduce the attac#
of corrosive media.
n addition to corrosion resistance% they also exhi"it a num"er of other properties ma#ing them
useful engineering materials &oxidation resistance% creep resistance% toughness at lo
temperature% magnetic or thermal characteristics'.
This section concentrates on those materials% normally aircraft grades% hich may "e
considered for use in space and discusses precautions re-uired for their application.
2se in spacecra!t
Gse of stainless steels in spacecraft centre on applications re-uiring corrosion resistance
&e.g. storage and handling of li-uids and aste'% components ithin some thermal protection
systems and fasteners such as high$relia"ility% high$strength "olts.

Main categories
Stainless steels contain chromium &at least 01C' hich provides the protective oxide film%
plus a num"er of other alloying elements to ena"le a range of characteristics.
austenitic $ derived from the "asic 0:(r<:3i compositions &>++$series'% or higher strength
versions in hich some of the 3i$content has "een replaced "y nitrogen and manganese
&1++$series'. Strength is increased "y cold$or#ing and properties are retained at lo
temperatures. ! erritic $ ,++$series materials contain "eteen 00$>+C(r and a maximum of +.0C(.
Fften used in the annealed or cold$or#ed condition% increased strength can "e o"tained
"y heat$treatment. martensitic $ also fall ithin the ,++$series% normally have chromium contents "eteen 00
and 0:C. Some can "e heat$treated to give high tensile strengths &I0,++MPa'. duplex L mixed ferritic<austenitic microstructures. High (r and Mo contents provide pitting
corrosion resistance and reasona"le resistance to S(( in chloride environments% &i.e.
"etter than some austenitic grades'. precipitation hardened $ "ased on martensitic or duplex grades ith additions of copper
and aluminium for precipitation hardening. They can "e heat$treated to give high strengths
com"ined ith high corrosion resistance.

Most conventional processing techni-ues are applied to steels &machining% elding%
fastening% etc'.
(are is re-uired ith some alloys that the processing does not degrade the
microstructure% hence properties.
5elding can affect the corrosion resistance of the eld and heat$affected 4one &localised
reduction of (r$content' and produce heat distortion of the assem"ly. (orrect choice of
filler rod is important.

recautions
(hromium ithin the alloy may react ith car"on and form localised (r$depleted areas and
"rittle compounds% normally at grain "oundaries. This effect is #non as 9sensitisation9 and
can have serious conse-uences for corrosion resistance% especially stress$corrosion crac#ing.
9Sta"ilised9 stainless steels have alloying additions &Ti% Mo% 3"' specifically to 9tie$up9 car"on
as car"ides and so prevent sensitisation &also #non as eld decay'.
Gnsta"ilised% austenitic steels have a service temperature limit of >*+(.
5ith the exception of sta"ilised or lo$car"on grades &such as >10% >,*% >0?2% >+,2'% elded
assem"lies re-uire solution treating and -uenching after elding.

recautions& cont*
Austenitic stainless of the >++$series and the and !erritic steels of the ,++ series are
generally resistant to stress$corrosion crac#ing.
Martensitic stainless steels of the ,++$series are more or less suscepti"le% depending
on composition and heat treatment.
recipitation hardening stainless steels vary in suscepti"ility from extremely high to
extremely lo% depending on composition and heat treatment. The suscepti"ility of these
materials is particularly sensitive to heat treatment% and special vigilance is re-uired to
avoid pro"lems due to S((.
Stainless steel parts and fa"rications normally re-uire careful cleaning prior to operation
in service. (leaning processes are normally chemical pic#ling using various com"inations
of acids% the residues of hich also have to "e removed thoroughly. Some grades may "e
suscepti"le to hydrogen embrittlement resulting from hydrogen pic#$up during pic#ling
processes.
characteristics and service at elevated temperatures.

Vacuum poses no special pro"lems. All metals in contact under vacuum conditions or in

A1:? stainless steel All
(ustom , stainless steel H0+++ and a"ove
0$ PH stainless steel H0+++ and a"ove
PH 0,$: Mo stainless steel (HB++ and SRHB+ and a"ove?%*.
PH 0$* Mo stainless steel (HB++
0*$* PH stainless steel (HB++
!uropean suppliers provide a ide range of stainless steels% all of hich are denoted "y
national and international specifications and standards% including series specifically for
aerospace grade materials.
evaluated and shon to have a high
resistance to stress$corrosion crac#ing
are listed ta"le&from !(SS$)$*+$>?'.
1. ncluding eldments of >+,2% >0?2% >10 and
>,*.
>:( &0+++;'.
&B++;'.
0+( &B+;'.
General
;usion joining techni-ues produce permanent joints. Soldered joints and some "ra4ed joints
can "e disassem"led ith care.

2se in spacecra!t
5elding is a common fa"rication method for metals used in spacecraft.
=ra4ing usually refers to joining ith alloys of copper% silver and 4inc and is preferred to
soldering hen stronger joints and an increase in temperature resistance is re-uired.
Soldered joints are used for electrical and thermal conducting paths and for lo mechanical
strength joints. Soldering is commonly referred to as 9soft$soldering9 in hich lo$melting point
alloys% such as tin$lead or indium$"ased materials are used.

Main categories
Filler materials& elding procedures and post8eld processes are detailed in aerospace
standards and specifications
(omments on eld filler materials also apply to bra0e metals and processes. An added
complication is that "ra4e fillers are generally very different from the parent eld materials
and so galvanic couples and other corrosion effects also need consideration.
older alloys that are accepta"le for use in electronic assem"lies in space% and their
associated fluxes and process chemicals &solvents8 cleaning "aths% etc'% have "een su"ject to
intense evaluation% see the ta"les 9Guide to choice o! solder8types !or space use: and
91epresentative products: ta"le &from !(SS$)$*+$+:'.
older alloys consist of the tin$lead and indium$lead alloys defined in !(SS$)$*+$+: and
!(SS$)$*+$>:. They are procured according to these specifications% hich define purity
levels and% here necessary% fluxes of suita"le formulation for the assem"ly of spacecraft
electronics.
Solder Type Solidus 2i-uidus Gse
?> tin solder &eutectic'
0:> 0:> Soldering P(=s here temperature limitations are critical and in applications here an extremely short melting range is re-uired.
?1 tin silver loaded
0* 0:B Soldering of components having silver$plated or 9paint9 finish% i.e. ceramic capacitor. This solder composition is saturated ith silver and prevents the scavenging of silver surfaces.
?+ tin solder 0:> 0:: Soldering electrical ire<ca"le harnesses or terminal connections and for coating or pre$tinning metals.
B? tin silver &eutectic'
110 110 May "e used for special applications such as soldering terminal posts.
Guide to choice o! solder8types !or space use

Composition ;< tin solder (eutectic)
;- tin silver8 loaded solder
MinC ?1. ?0. B.
2ead &P"' MaxC remainder remainder remainder +.0+
Antimony &S"' MaxC +.+ +.+ +.+ +.01
(opper &(u' MaxC +.+ +.+ +.+ +.+
Arsenic &As' MaxC +.+> +.+> +.+> +.+>
Fthers MaxC +.+: +.+: +.+: +.+:

rocessing/Assembly
&nuclear% poer$generation% etc' may offer guidance on specialist materials.
;usion joining processes are s#illed operations and personnel must have appropriate training
and certification to produce the re-uired high$-uality% relia"le joints.
recautions
3ot all metals and alloys can "e joined "y elding or "ra4ing.
3ot only the eld itself &fusion 4one'% "ut the heat$affected 4one and the unaffected parent
&"ase' metals must "e considered.
3ot all 9industrial9 elding techni-ues can "e used on all materials.
The correct selection of parent materials and eld methods re-uires consideration of all
factors that affect operational capa"ility of the parts concerned

recautions& cont*
=ra4ing is normally restricted to joints in structural parts that experience shear loading
rather than tensile loading.
;luxes used to produce elded% "ra4ed or soldered joints may "e corrosive and need to
"e removed thoroughly prior to post$joining processes &heat$treatment' and operation in
service.
Residues of chemicals or processes used for flux removal must also "e cleaned from
*+$+:.
a0ardous/precluded
(orrosive acid fluxes availa"le for the pre$tinning of soldered joints can provo#e stress$
corrosion crac#ing and general surface corrosion of component leads or terminal posts. Their
general use is therefore restricted and precise control of the flux$removal processes is
re-uired
General
A metal is classed as miscellaneous if it does not fall ithin another Declared Materials 2ist
&DM2' category in !(SS$)*+=. Also included in this section are comments on metal$"ased
materials that are either prohi"ited or should "e approached ith caution for space
applications.
2se in spacecra!t
2ight alloys "ased on magnesium and "eryllium are used in some primary and secondary
structures. Plating appears in many applications &electronics% thermal control% corrosion protection
etc' and calls mainly for silver and gold. 9Memory alloys9 "ased on titanium and nic#el may find uses as actuators n addition to standard conventional alloys% more recent material developments include7
/ reinforced alloys &metal matrix composites $ MM(' consisting of magnesium alloys
reinforced ith car"on fi"res8 / lithium additions to conventional magnesium alloys8 / reinforced silver alloys.

Miscellaneous metals include% "ut are not limited to7
magnesium alloys8 "eryllium and =e$alloys. &See7 9(opper and (u$alloys9 for =e$(u alloys'8 refractory alloys8 superalloys% hich as a group include co"alt$% iron$ or nic#el$"ased alloys. &See7 93ic#el
and 3i$alloys9 for 3i$"ased superalloys'8 mercury8 plating materials7 cadmium% 4inc% tin% gold% silver% osmium etc.
This section also includes comments on metal$
"ased materials that are either prohi"ited or
should "e approached ith caution for space
applications.
rocessing/Assembly
Magnesium alloys are availa"le as rought forms or for casting. (are is needed in storing
magnesium alloys due to their tendency to corrode.
Processing of "eryllium re-uires sophisticated techni-ues and rigorous safety procedures
to avoid the formation and release of "eryllium oxide% metal particles and compounds
hich are toxic.
Superalloys are processed folloing recognised aerospace procedures or other
appropriate industry standards.

Magnesium alloys
Dusts of magnesium and its alloys are flamma"le8 re-uiring special safety measures. Some
magnesium alloys &ith thorium' may have a slight residual radioactivity.
?eryllium and ?e8alloys
This metal is produced "y poder metallurgy involving hot isostatic processing and it is
recommended that component parts are initially rough machined% heat treated to remove major
residual stresses and then fine machined.
A final chemical etching treatment is strongly recommended to remove +.0mm from the surface
of machined parts. This ill generally remove mechanical damage such as su"surface
microcrac#s and deformation tins.

Miscellaneous Refractory alloys are generally selected for extreme high$temperature applications here
other metals cannot "e used. Hoever% engineering data on refractory alloys are limited%
especially under the extreme environments encountered on spacecraft.
3ic#el$"ased and (o"alt$"ased superalloys possess various com"inations of high$
temperature mechanical properties and oxidation resistance up to approximately +(.
Many of these alloys also have excellent cryogenic temperature properties.
Some metals% such as cadmium and 0inc% are rather volatile and should not appear in
space hardare. Platings of these metals% as ell as tin% are #non to gro his#ers "oth in
air and under vacuum. They should "e excluded from all spacecraft and ground$support
e-uipment.
Porous platings are potential sources of danger and this occurs fre-uently ith gold plate
over silver.

Mercury and mercury8containing compounds can cause accelerated crac#ing of
aluminium and titanium alloys. t is therefore a prohi"ited su"stance for the manufacture of
aerospace structures and su"systems.
Specialised safety e-uipment and procedures for the collection and disposal of dust and
de"ris are re-uired for operatives or#ing ith toxic materials% such as beryllium and
osmium& and !or materials ith a ris7 o! ignition and burning& such as magnesium.
n electronic assem"lies% tin8& silver8 and gold8plating on terminals of P(=s is removed in
order to achieve an approved tin$lead finish.
oldering directly to gold !inishes is unacceptable and de$golding processes are used.
n unavoida"le use of gold$finishes% such as in R; circuitry% selective plating processes are
used for soldered connections.
Miscellaneous metallic materials, cont…
Vacuum affects volatile metals% such as cadmium and 4inc. These metals su"lime readily
at temperatures over 0++°( and 0+°( respectively% and may form conductive deposits on
insulators or opa-ue deposits on optical components.
Atomic oxygen in lo earth or"it attac#s some metals% such as silver &solar$cell
interconnectors' and osmium &extreme$G6 mirrors'.

Magnesium% 2AB>> All
!uropean sources of "eryllium are7 SAN!M &;'% Royal Frdnance ;actory &G..'% Heraeus &D'%
=rush 5ellman &G.. and D'8 Superalloys7 Au"ert and Duval &;'
Magnesium alloys7 Magnesium !le#tron &G'
Procurement to internationally recognised specifications is recommended% such as SF% M2
Specs% =.S.% SA!.% D3 or A;3FR specifications.
The materials listed in the ta"le &from !(SS$)$*+$>?'% can "e
considered

Documents

Material Properties Requirements for Metallic Materials.ppt