design manual wha (2)
TRANSCRIPT
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TUNGSTEN HEAVY ALLOY
Design Manual
S. G. Caldwell, Ph.D.
1!" C#un$% Line adMadis#n, AL '("()***+""*+!"!***+*+!1! -awww.$ungs$en/0#d.#2
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Table of Contents
1. The Metallurgy of Tungsten Heavy Alloys... 3
2. Alloy Selection Criteria .... 5
Why use WHAs?ensity
Mechanical !ro"erties
Ther#al an$ %lectrical !ro"erties
&Mag& 'ersus &(on)Mag& Alloys
3. esign Consi$erations ...... *
The (ature an$ A$vantages of !+M
Monolithic or Multi)!art?&,a$iation -oints&
!reserving Mai#u# Mechanical Strength
/. Machining 0ui$elines ...
11Saing
0rin$ing
Milling
Turning acing an$ 4oringrilling
Ta""ing%MTher#al Contouring
5. -oining .... 1/Mechanical
4raing
Wel$ing
Sinter 4on$ing
6. inishing . 15
Corrosion 4ehaviorCoatings
7. Ty"ical A""lications ... 16
,a$iation Shiel$ing
Aircraft Counter8alances
Well 9ogging,acing Weights
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4oring 4ars
:r$nance A""lications
Conclu$ing ,e#ar;s
1. The Metallurgy of Tungsten Heavy Alloys
The na#e &tungsten& is $erive$ fro# the Se$ish ter# #eaning &heavy stone&.
Tungsten has 8een assigne$ the che#ical sy#8ol W after its 0er#an na#e wolfram.While so#eti#es regar$e$ as a scarce or eotic #etal its a8un$ance in nature is actually
a8out the sa#e as that of co""er. The largest ;non tungsten reserves are in #ainlan$
China though "lentiful reserves also eist in (orth A#erica.
Tungsten has the highest #elting "oint of all #etals. The
etre#ely high #elting "oint of "ure tungsten #a;es all the co##on #anufacturing
techniues use$ for #etals such as iron i#"ractical. S"ecialie$ #etho$s #a;e "ossi8le
the "rocessing of "ure tungsten into ro$ sheet an$ ire for a i$e variety of highte#"erature a""lications inclu$ing incan$escent la#" ire T@0 el$ing electro$es an$
high te#"erature heat shiel$ing.
Another i#"ortant in$ustrial "ro"erty of tungsten is its high $ensity of 1.3 g+cc
. @n a$$ition to high gravi#etric $ensity its high ra$iogra"hic $ensity #a;es
it an i$eal #aterial for shiel$ing or colli#ating energetic ) an$ )ra$iation. or such
a""lications tungsten is co##only alloye$ in or$er to circu#vent the etre#ely high"rocessing te#"eratures that oul$ otherise 8e reuire$ to #elt an$ cast the "ure #etal.
Tungsten heavy alloys are i$eally suite$ to a i$e range of $ensity
a""lications offering a $ensity a""roaching that of "ure tungsten 8ut ithout the verycostly "rocessing an$ inherent sie an$ sha"e li#itations of the for#er. WHAs are
"ro$uce$ 8y a "o$er #etallurgy techniue ;non as liui$ "hase sintering in hich co#"letely $ense fully alloye$ "arts are for#e$ fro# "resse$ #etal "o$ers at a
te#"erature less than half the #elting "oint of "ure tungsten. While sintere$ steel an$
co""er alloy "arts co##only contain significant resi$ual "orosity that #ay reuire"oly#eric infiltrants to seal sintere$ WHAs have a non"orous surface.
WHA "arts are #anufacture$ fro# very fine high "urity #etal "o$ers B ty"ically
tungsten nic;el an$ iron. The 8len$e$ #etal "o$er is co#"acte$ un$er high "ressure
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"hase any re#aining $ensification occurs very uic;ly as the alloy assu#es a
&s"heroi$ie$& #icrostructure 8y a #echanis# ;no as :stal$ ,i"ening. The sintere$
structure of a co##on co##ercial WHA is to)"hase consisting of a lin;e$ netor; oftungsten s"heroi$s containe$ in the $uctile #atri "hase.
The s"heroi$ie$ #icrostructure shon 8elo is ty"ical for #ost co##ercial WHA
"ro$ucts. The roun$e$ "hase is essentially "ure tungsten hichis surroun$e$ 8y a #etallic nic;el)iron 8in$er "hase containing so#e $issolve$ tungsten.
This structure "rovi$es the #ai#u# #echanical "ro"erties for a given alloy co#"osition.
Through the "rocess of "ressing an$ 9!S #etal "o$ers are transfor#e$ into fully $ensesha"es that are very close to the $i#ensions of the finishe$ "arts.
WHAs can su8seuently 8e su8ecte$ to "ost sinter heat treat#ent an$ #echanical$efor#ation to increase tensile "ro"erties an$ create $irectional #icrostructures. While
such o"erations are co##only reuire$ for #ilitary a""lications co##ercial WHAs
generally $o not reuire this a$$itional "rocessing an$ are su""lie$ in the as)sintere$ statefor #ai#u# econo#y.
WHAs are a s"ecial class of #aterials $iffering fro# "ure tungsten. They shareal#ost no co##on characteristics ith &tungsten steels&
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2. Alloy Selection Criteria
Why Use WHAs?
WHAs "rovi$e a uniue co#8ination of $ensity #echanical strength #achina8ilitycorrosion resistance an$ econo#y. Conseuently WHAs are i$ely use$ for
countereights inertial #asses ra$iation shiel$ing s"orting goo$s an$ or$nance
"ro$ucts. These versatile #aterials "rovi$e $istinct a$vantages hen co#"are$ toalternate high $ensity #aterials as seen in the ta8le 8elo.
Material ensity
!g"cc#
Tensile
Strength
Stiffness Machin-
ability
To$icity %adio-
acti&ity
'ost
W() *+,-*., moderate high e$cellent lo/ none moderate
Lead **,0 ma$, &ery lo/ &ery lo/ &ery lo/ high none lo/
1ranium *2,+-*2,. moderate medium special high present high
As can 8e seen fro# these $ata WHA overco#es the toicity $efor#a8ility an$ inferior
$ensity of lea$ an$ its alloys. 9i;eise it can "rovi$e euivalent $ensity to $e"lete$
uraniu# 8ut ithout the s"ecial #achining consi$erations an$ licensing reuire#ents for a ra$ioactive su8stance. WHA is truly the#aterial of choice for high $ensity a""lications. These uniue alloys "rovi$e the $esigner
ith #any ne free$o#s.
There is one s"ecial category of $ensity a""lications in hich WHAs shoul$ not 8e
use$. or a""lications in hich the service te#"erature ill ecee$ E3==C slight surface
oi$ation ill occur in air. @t is i#"ortant to note that at service te#"eratures ecee$ing
E5==C WHA strength ill fall off ra"i$ly even in a "rotective at#os"here. or these
s"ecial cases "ure tungsten #ay "rovi$e a 8etter o"tion. @f reactive at#os"heres are
"resent in co#8ination ith elevate$ te#"erature the 8est choice for very $ense #aterials
ill 8e the "latinu# grou" #etals B 8ut at etre#ely high cost.
Density
ensity is the single #ost i#"ortant "ro"erty that #a;es a WHA the #aterial ofchoice for a given a""lication. The selection of a s"ecific co#"osition for a given $ensity
a""lication #ay ulti#ately 8e #a$e on the 8asis of concurrent #echanical "ro"erty
reuire#ents or sintering consi$erations unless a s"ecific value of $ensity is critical.WHAs can a""roach the $ensity of "ure tungsten an$ G ithout the high cost of the
for#er or the licensing an$ s"ecial han$ling reuire#ents of the latter.
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As is true ith #ost #echanical $esigns the o"ti#u# $esign is the one that
a$euately a$$resses all critical "ara#eters an$ offers the 8est co#"ro#ise of the
re#aining o"tions. As the $ensity of a WHA is increase$ the availa8le $uctility $ecreases.Alloy $ensity varies accor$ing to tungsten content as can 8e seen in the folloing ta8le of
Tungsten !ro$ucts stan$ar$ alloys.
TP)lloy3
'omposition!Wt, 4#
M5L-T-6**0'lassification
Typical ensity!g"cc# !lbs"in6#
Magnetic
Permeability !#
S*+ .W-!7Ni"Fe# 'lass * *+,*0 ,8*. >8,
ens6* .W-!+Ni"Fe# 'lass * *+,6 ,866 *,6-*,9
S*+9 .6,9W-!7Ni"Fe# 'lass 6 *+,86 ,87+ 0,9-9,
ens67 .6,9W-!+Ni"Fe# 'lass 6 *+,88 ,872 *,6-*,9
S*2 .9W-!7Ni"Fe# 'lass 7 *2,*7 ,899 0,-0,9
ens69 .9W-!+Ni"Fe# 'lass 7 *2,*8 ,898 *,*-*,6
S*29 .+W-!7Ni"Fe# 'lass 0 *2,9+ ,8+* 6,9-7,
@n a$$ition to these stan$ar$ co#"ositions Tungsten !ro$ucts can also #anufacturecusto# alloys. !lease inuire ith any s"ecial a""lications you #ay have.
Mechanical ro!erties
Mechanical "ro"erties of #o$ern WHAs far sur"ass those availa8le fro# WHAs
even a fe $eca$es ago. Three factors "ri#arily contri8ute to this a$vanceF higher
"urity ra #aterials cleaner an$ #ore "recisely controlle$ "rocess environ#ents an$ the use of #o$ern tungsten)nic;el)iron co#"ositions rather than the ol$er
alloys containing co""er.
@t is also i#"ortant to note as a general consi$eration that #ai#u# attaina8le"ro"erties for these alloys varies ith the sie of the 8lan;. This is a $irect conseuence of
the nature of the sintering o"eration use$ to #a;e the "arts. A nu#8er of gra$ients Bther#al che#ical an$ gravitational B eist $uring sintering. As the #ai#u# section
thic;ness of a given "art is increase$ ther#oche#ical re#oval of i#"urities fro# the
center of the "resse$ "art "rior to surface "ore closure 8eco#es #ore $ifficult. Therefore
s#all "arts ill alays ten$ to have higher #echanical "ro"erties than larger ones.
Tungsten !ro$ucts offers a stan$ar$ set of co##ercial alloys that confor# to M@9)T)
21=1/ ASTM 4777)*7 an$ AMS)77254 reuire#ents for #echanical "ro"erties. Asseen in the ta8le 8elo the no#inal "ro"erties liste$ #eet or ecee$ these s"ecification
reuire#ents. All values shon are for #aterial in the as)sintere$ state as this is the #ostco##only su""lie$ con$ition of the #aterial for co##ercial a""lications.
TP )lloy3 Wt,4 W 1TS !:si# ,64 ;S !:si#
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ens67 .6,9 ** 2 6 02 6+
S*2 .9 *6 +9 0 9 62
ens69 .9 **. +9 7 9 62
S*29 .+ ** +9 7 96 62
All WHAs are susce"ti8le to hy$rogen e#8rittle#ent hich loers the $uctility ofthe alloy. Tungsten !ro$ucts can "rovi$e alloys in a hy$rogen outgasse$ con$ition hich in so#e cases #ay $ou8le the tensile elongation. urther
"ro"erty enhance#ents are "ossi8le through a$$itional "ost)sinter "rocessing. or
structural a""lications it is reco##en$e$ that #aterial 8e use$ in the #ost
$uctile con$ition feasi8le for the given "art.
Ther"al an# $lectrical ro!erties
The "ro"erties of WHA are governe$ 8y the "ro"erties of its "rinci"al constituent
tungsten. While "ro"erties ill vary slightly ith tungsten content 8in$er co#"osition
an$ #icrostructure several "ro"erties ill 8e cite$ for a ty"ical alloy such as S175. This#aterial ill have a ther#al con$uctivity of E12= W+#) an$ a corres"on$ing electrical
con$uctivity of E13D @ACS. The ther#al e"ansion is very lo ith a CT% of
E5.=%)6+C at 2=C. The s"ecific heat of S175 is E=.36 cal+g+C. While the #elting
"oint of "ure tungsten is etre#ely high WHAs ill 8egin to for# a liui$ "hase hen
heate$ in ecess of E1/5=C . WHAs are not suita8le for high te#"erature
a""lications.
%Mag% versus %&on'Mag%
@t is unfortunate that in$ustry literature has $escri8e$ fa#ilies of agnetic& an$
&non)#agnetic& WHAs thus i#"lying significant #agnetiation of the for#er.&Magnetic& $enotes a reasona8le attraction to a #agnet B not that the WHA itself 8ehaves
as a "er#anent #agnet in the con$ition su""lie$. The #agnetic res"onse of WHAs is #ost
co##only #easure$ ith an instru#ent such as the Low Mu Permeability Indicator
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ag& gra$es. Therefore unless s"ecifically reuire$ 8y a given a""lication stan$ar$
agnetic& alloys are the 8etter choice.
(. Design Consi#erations
!o$er #etallurgy offers to o"tions for WHA #anufacturing B near netsha"e 8lan;s or net sha"e "arts. These consi$erations a""ly as ell to !+M "arts of
#aterials such as co""er an$ steel as ell. urther the s"ecific nature of WHA "resents
a$$itional consi$erations that #ust ta;en into account in the $esign "rocess.
The &ature an# A#vantages of )M
!+M is a very useful #o$ern #anufacturing "rocess that "rovi$es a #eans of
"ro$ucing "arts fro# 8len$e$ #etal "o$ers that circu#vents the nee$ to start ith larger
than nee$e$ #ill sha"es an$ then s"en$ #oney an$ ti#e re#oving ecess stoc;. Through
!+M in$ivi$ual "arts can so#eti#es 8e #a$e
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uring high te#"erature 9!S gravity ten$s to $istort or &slu#"& "arts. This
8ehavior 8eco#es #ore "ro#inent the greater the "art height is ith res"ect to the 8asalarea. Higher DW alloys shoul$ 8e use$ for greater slu#" resistance. or #any
a""lications $ue to these !+M consi$erations a 2.5DW alloy ill 8e a goo$ choice.
Single iece or Multi'art?
While conventional is$o# hol$s that there is econo#y in sie this "hiloso"hy has a
li#it hen a""lie$ to !+M. As "art sie increases attaina8le #echanical "ro"erties
$ecrease slightly. 9arge "arts also invite the for#ation of a front to 8ac; $ensity gra$ient
es"ecially in loer DW alloys. Also as "art sie increases #achining alloances #ustalso 8e increase$ to guarantee clean u" of the 8lan; to the finishe$ geo#etry. 'ery tall
"arts oul$ "rove i#"ractical to #a;e as a single "iece 8ecause of furnace height
li#itations an$ ten$ency for gravitation colla"se $uring 9!S.
The solution for large or s"ecial geo#etry "arts is to fa8ricate the# as s#aller
&8uil$ing 8loc;s& hich can either 8e #echanically fastene$ to su""orting structures or
furnace 8rae$ into a large #onolithic co#"onent an$ then #achine$. The 8uil$ing 8loc;a""roach also #a;es "ossi8le the creation of functionally gra$ient #aterials hen utilie$
in furnace 8rae$ or sinter 8on$e$ asse#8lies.
:riginal reuire#ent 4etter o"tion
Ma;ing a large eight co#"onent as a series of s#aller #echanically attache$ ones
overco#es #anufacturing sie li#itations an$ can result in 8etter #echanical "ro"ertiesan$ #ore econo#ical "arts that if $a#age$ in service can 8e re"lace$ 8y section as nee$e$
rather than as a hole.
esire$ "art too
large+tall for
$e"en$a8le 9!S
!art asse#8le$ fro# 3
&8uil$ing 8loc;s&
for #achining
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Tungsten !ro$ucts currently offers 7 stan$ar$ gra$es of WHA in a variety of 8loc;
flat an$ roun$ sha"es B or custo# #achine$ to final for#. Sies can range fro# gra#
eight to #any hun$re$s of ;ilogra#s. Sheet is availa8le in thic;nesses $on to =.=25&.
%*a#iation +oints%
Many cylin$rical sha"e$ ra$ioisoto"e containers having noncircular ra$ial in$os
oul$ 8e virtually i#"ossi8le to #anufacture as a single "iece as it oul$ 8e etre#ely
$ifficult to $evise a #etho$ to %M the a"erture an$ "reserve any shar" angular $efinition.The solution is to e#"loy Tungsten !ro$ucts &ra$iation oint& construction hich "revents
any "ossi8ility of straight line of sight ra$iation lea;age 8y #eans of geo#etric offsets in
the #ating halves. As seen in the transverse cross sectional $iagra#s 8elo even very
carefully #achine$ flat oints can allo so#e ra$iation "enetration. 4y use of a si#"leste" the ris; of $irect line lea;age fro# the containe$ source is eli#inate$. A #ore
ela8orate oint ith larger offsets that further re$uces ra$ial features #ay 8e ustifie$ in
so#e a""lications. Securing har$are such as 8olts can 8e also #a$e of WHA to "reserve
"rotection level.
!oor 0oo$ 4etter
reserving Ma,i"u" Mechanical Strength
0oo$ #echanical $esigns avoi$ unnecessary stress concentration. This is es"eciallyi#"ortant consi$ering the notch sensitivity of all WHAs. Attention to $etails such as the
shar"ness of internal corners root ra$ii of notches grooves an$ threa$s an$ the "roi#ity
of holes or other cutouts to "art e$ges hel" "reserve the #ai#u# attaina8le strength fro#
a WHA "art. Concave ra$ii shoul$ 8e li#ite$ to =.=2=& or greater henever "ossi8le.Holes shoul$ not 8e locate$ closer than 1.5 ti#es hole $ia#eter fro# the e$ge of a "art.
While #ost eights are reuire$ to su""ort only lo acceleration centrifugal or inertial
loa$s these strength of #aterials consi$erations 8eco#e even #ore i#"ortant in "arts thatalso serve a structural function or are utilie$ in high s"ee$ a""lications.
!oor
"ractice
1=
source
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0oo$
"ractice
-. Machining ui#elines
A "rinci"al a$vantage of WHAs over "ure tungsten for $ensity a""lications is theira8ility to 8e rea$ily #achine$ into co#"le geo#etries using co##on #etalcutting tools
an$ techniues. While it is generally sai$ that WHAs #achine si#ilar to gray cast iron
this $escri"tion can 8e #islea$ing. 9oer DW alloys ith high $uctility ten$ to #achine
#ore li;e a stainless steel of co#"ara8le har$ness. ue to the high elastic stiffness ofWHAs cutting forces ill 8e higher than for #ost #etals. ,igi$ tooling an$ a$euate
s"in$le torue are #an$atory for goo$ results. Coolant+lu8ricants if e#"loye$ shoul$ 8ethe non)al;aline ater solu8le ty"e.
Sa/ing
4lan;s of WHA #ay 8e rea$ily cut using a heavy $uty sho" 8an$sa eui""e$ ith either
a 8i)#etal 8la$e ith hoo; "rofile teeth or a seg#ente$ e$ge car8i$e 8la$e at lo s"ee$
. Coolant is not reuire$ for 8an$sa sectioning. WHAs #ay also 8e cut onan a8rasive sa using alu#ina or silicon car8i$e 8la$es ith coolant.
rin#ing
WHAs are ca"a8le of ecellent surface finishes hen centerless or surface groun$.
'itrifie$ 8on$ alu#ina or silicon car8i$e heels of #e$iu# har$ness are reco##en$e$. A
ater solu8le coolant shoul$ 8e use$. ia#on$ heels shoul$ not 8e use$ $ue to ra"i$loa$ing. Surface grin$ing of very thin stoc; shoul$ 8e "erfor#e$ carefully so as to avoi$
8oing fro# intro$uce$ resi$ual stress.
Milling
'irtually all co##ercial WHAs easily for# short chi"s hen #achine$. Theece"tion to this rule is lo DW alloys su""lie$ in a very $uctile state in hich case
chi"8rea;ing #ust 8e a$$resse$ in tooling selection. Milling of WHAs is 8est "erfor#e$
using #ulti)insert cutter hea$s. The use of coolant+lu8ricant is o"tional.
Roughing
5S= 'arbide>rade
%a:e
!#
'learance
!#
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?*9 or ?6 -+to > ,9-,*9 ,7-,*69 6-0
Finishing
5S= 'arbide>rade
%a:e
!#
'learance
!#
rade
%a:e
!#
'learance
!#
rade
%a:e
!#
'learance
!#
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Ta""ing can 8e the #ost challenging o"eration for WHAs $ue to the high resultant
torue on the ta" shan;. or this reason 2 or 3 flute "ositive ra;e s"iral "oint high
clearance ta"s shoul$ 8e use$. !re#iu# co8alt steel ta"s "erfor# 8est for this a""lication.The use of ta""ing co#"oun$ is essential. Choose the
coarsest threa$ "ossi8le for a given $ia#eter an$ a""lication. Holes shoul$ 8e ta""e$ to
co#"letion ithout 8ac; trea$ing to avoi$ 8in$ing. With care threa$s as fine as 2)56 can8e successfully ta""e$. @t is generally 8est to ta" large holes ith a single "oint tool. or
other $ifficult to ta" situations the use of a slightly larger "ilot hole #ay solve the "ro8le#
8ut ith re$uce$ threa$ engage#ent area.
$DM Sha!ing
%M 8oth ire an$ sin;er ty"es are routinely use$ to sha"e WHA 8lan;s. %Mshoul$ hoever 8e a &last resort& techniue for several reasons. irst it is inefficient
co#"are$ to #etalcutting alternatives. WHAs have high arc erosion resistance an$ are
occasionally use$ as %M tools. %M sha"ing is therefore very slo. Also even at
loer s"ar; energy settings %M can still intro$uce surface layer $a#age that can inso#e a""lications "rove $etri#ental. Gsing %M to sha"e highly $uctile WHAs can
so#eti#es e#8rittle the# through reintro$uction of hy$rogen into the #etal. Still %Mre#ains the only "ractical sha"ing techniue in so#e s"ecific a""lications. An ea#"le is
the #achining of 8lin$ non)circular holes ith relatively shar" corners an$ ta"er.
Ther"al Contouring
Techniues such as oyfuel "las#a et an$ laser cutting are not reco##en$e$ for
WHAs. These #etho$s ty"ically "ro$uce unacce"ta8le levels of oi$ation an$ ty"ically"ro$uce localie$ ther#al crac;ing.
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. +oining
WHA can rea$ily 8e oine$ to itself or other #aterials. Whenever feasi8le#echanical #etho$s of attach#ent are "referre$ as they avoi$ "ossi8le ther#oche#ical
alteration an$ its effect on local #echanical "ro"erties.
Mechanical
-oining is #ost co##only "erfor#e$ using stan$ar$ fasteners such as 8olts an$ "ins.WHA "arts can 8e li;eise 8e threa$e$ to "erfor# as fasteners . @n choosing a #echanical oining #etho$ it is i#"ortant to ;ee" in
#in$ the notch sensitivity i#"act sensitivity an$ lo CT% of WHAs. Threa$s shoul$
have as generous a root ra$ius as "ossi8le for #ai#u# strength. @#"act fasteningtechniues such as riveting are not reco##en$e$. Shrin; fitting is "ossi8le "rovi$e$ the
WHA "art is the inner #e#8er. or shrin; fitting an interference fit of E=.==5& "er si$e is
"re"are$ an$ the WHA "art coole$ in $ry ice or 9(2hile the outer #e#8er is heate$ toseveral hun$re$ $egrees 8efore fit u".
ra3ing
1/
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4raing is 8est "erfor#e$ in a hy$rogen furnace to "rotect the WHA "art fro#
oi$ation. A variety of filler #etals such as "ure co""er #onel an$ stan$ar$ 8raing
alloys 8ase$ on co""er silver an$+or nic;el can 8e use$. 4raing te#"erature constraintsan$ the en$ a""lication generally $eter#ine the filler #etal choice. 9arge co#"onents can
8e asse#8le$ fro# a nu#8er of s#aller "ieces using this a""roach. As ith any 8raing
o"eration goo$ oint "re"aration is essential for "ro$ucing fully 8on$e$ interfaces.Clearances of E=.==2& or less are ty"ical. 4raing can alter the che#istry ithin the
i##e$iate vicinity of the oint. !oints of attach#ent shoul$ not 8e locate$ along such
ones. Manual torch 8raing using a flu is also "ossi8le 8ut ill result in oi$ation an$ isli#ite$ to oining s#aller co#"onents. 9o te#"erature sol$ers ill not et WHAs.
Wel#ing
Wel$ing is generally not "erfor#e$ on WHAs $ue to the vast $ifference in #elting
"oint 8eteen the W "hase an$ 8in$er "hase. A T@0 torch can hoever 8e use$ as
a very intense heat source to flo fillers such as #onel "ure nic;el or nic;el)8ase$
su"eralloys into a oint for a &uasi)el$&. This techniue reuires #uch e"erience forgoo$ results.
Sinter on#ing
This is a techniue that is ty"ically li#ite$ to oining "arts at the ti#e of #anufactureto for# larger asse#8lies. !erfor#e$ in a hy$rogen furnace at the 9!S te#"erature sinter
8on$ing results in an invisi8le interface ith no local $egra$ation in #echanical "ro"erties.
4. 0inishing
WHAs are reasona8ly resistant to corrosion an$ are not susce"ti8le to stresscorrosion crac;ing as is a co#"etitive high $ensity #aterial G. or so#e $ensity
a""lications such as aircraft counter8alance eights long ter# corrosion resistance
8eco#es a concern $ue to "ersistent e"osure to harsh environ#ents. @n such cases a
variety of "rotective finishes can 8e a""lie$. While relatively resistant to corrosion un$era#8ient con$itions etre#e hu#i$ity salt s"ray an$ the "resence of strong electrolytes
can "ro#"t surface corrosion. This is $ue to the electroche#ical $ifference 8eteen the
#atri an$ the tungsten "hases hich sets u" #icro)scale galvanic cells on the e"ose$surface. The #atri "hase is #ost rea$ily attac;e$ 8y aci$ic solutions hereas the
tungsten "hase is #ost ra"i$ly $issolve$ 8y al;aline solutions. WHAs are not generally
use$ in #arine a""lications 8ut shoul$ have a "rotective coating for any such use.
@t is i#"ortant to note that certain conversion coatings though in i$es"rea$ in$ustrial use are not suita8le for WHAs. As anea#"le the che#istry of 8lac; oi$e "rocesses for steels is 8ase$ on the "resence of an
iron)rich surface hich is $efinitely not the case for any co##ercial WHA. Therefore if
such a techniue is utilie$ the e"ecte$ a""earance an$ $ura8ility of oi$e coating on
WHA ill not 8e achieve$. Si#ilarly ano$iing "rocesses hich are i$ely use$ for
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alu#inu# an$ reactive #etals are not a""ro"riate for WHAs hich 8y nature $o not for#
the sa#e ty"e of coherent surface oi$e layer.
Conversely hen a unifor# che#ical attac; is $esira8le the sa#e electroche#ical $ifferences 8eteen
the to "hases co#"rising WHA "revents consistency of $issolution res"onse. While8asic #ar;ing can 8e $one che#ically it ill not 8e unifor# on a #icrosco"ic scale. @f
high $efinition solvent resistant "atterns or @ #ar;ings are reuire$ on WHA "arts it is
reco##en$e$ that either vi8ratory scri8e or laser #ar;ing syste#s 8e e#"loye$.
Metallic
Ca$#iu# "lating ith a chro#ate overcoat is co##only use$ for aircraft eights.This ty"e of "lating is i$eal shoul$ the coating nee$ to 8e "erio$ically stri""e$. or #ore
$ura8le an$ less toic "rotective coatings nic;el is an ecellent choice. Al;aline "lating
solutions shoul$ 8e use$ to avoi$ hy$rogen intro$uction into highly $uctile "arts.
5rganic
A variety of "oly#eric finishes inclu$ing e"oy an$ acrylic 8ase$ #ay 8e
effectively use$. :rganic coatings are "ro8a8ly the 8est choice in #ost a""lications.
!aints a$$itionally allo convenient color co$ing an$ @ #ar;ing of co#"onents henreuire$. :rganic coatings also "rovi$e a $ielectric layer useful in "reventing the
for#ation of a galvanic cou"le hen WHA eights are fastene$ to $issi#ilar #etals such
as alu#inu# alloys. or o"ti#u# $ura8ility organic coatings shoul$ 8e $rie$ 8y 8a;ing
at the reco##en$e$ te#"erature to ensure the full set of curing reactions occur.
6. Ty!ical A!!lications
*a#iation Shiel#ing
Mo$ern in$ustrial ra$iogra"hy an$ oncology syste#s currently utilie 8ea# energiesthat can ecee$ 2 Me' fro# isoto"ic sources an$ ell over 2= Me' fro# s#all
accelerators. The a8sor"tion 8ehavior of WHAs for high energy electro#agnetic ra$iation
is $erive$ fro# the high linear a8sor"tion coefficient of the "rinci"al tungsten "hase.
These alloys are ecellent #aterials for the shiel$ing an$ colli#ation of )an$ )ra$iation
$ue to their co#8ination of ra$iogra"hic $ensity #achina8ility strength an$ lo toicity.
WHAs offer a su"erior "rotection level to lea$ in an euivalent thic;ness. 4ut unli;e lea$WHAs resist $efor#ation an$ can 8e accurately fastene$ B i#"ortant factors in the
construction of #ulti)leaf ra$iation colli#ators. WHA can 8e su""lie$ in the for# of thin
rolle$ an$ #achine$ sheet for such a""lications. or 8ul; shiel$ing a""lications Tungsten!ro$ucts has #anufacture$ #any shiel$ing co#"onents in the 1==)1=== ;g sie range.
9arge isoto"e containers can 8e fa8ricate$ ith co#"le geo#etry ra$ial 8ea# "orts using
&ra$iation oint& construction. Class 2 3 or / WHAs are ty"ically use$ for shiel$ing.
Aircraft Counterbalances
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anneale$ an$ resolutionie$+uenche$ for #ai#u# $uctility