Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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BACKGROUND OF l'HE tNVENTION
This invention relates to wear-resistant composite materLa]s.
The wear resistance of materials normally increases with l1ard-
ness but it is also strongly affected by their microstructural character-
iatics, especially by the presence oE a second phase. It is known thatabrasion resistance of steels lncreases when they contain hard second
phases like carbides. ~lowever, the abrasive wear of steels containlng a
large proportion of carbides depends fitrongly on the cohesion of these
carbidea with the matrix, as well as on tlle si~e, shape and brittleness
of the carbides. The highest abrasion resistances are generally found in
alloys havlng hard second phases coherently bonded to the matrix and not
distributed as a brittle contim1ous network in it. Many works have been
done to attain this objective using powder meT~allurgy techniques, especi-
ally in the production of rnetallic articles containing a disperslon of
hard particles which consist of intermetallic or ceramic (usually carhide
particles). There are two drawbacks for this kind of material. First,
these intermetallic or ceramic particles are brittle and can fracture
under high stress abrasive condition~s, and secondly, they cannot be
easily or properly bonded to the matrix. Under such condLtions, the hard
phase tends to be dislodged, thus giving rise to acceLerated wear.
It has been proposed in United States Patent No. 3,790,353, to
provide a wear resistant pad by uti1i~ing cemented metal carbide parti-
cles in a metal matrix wherein the metal matrix is melted to form the
wear pad. The above ment:Lolled patent specTLEies the pad thickrless Ln
terms of partlcle size which places a slgn-LEicant restrictlon on tlle
product geometry particularly witrl regard to product thickness. It wL1L
be apparent that wlth melting oTE the matrix the hLgher density cermet
partLcles ~ill tend to settle, and therefore, thickness cannot be
increased as desired unless a suEficiently hLgh proportion oE cerlTIet
partLcLes are used in order that tlle partLcles contact one another all(l
cannot aettle. Such high proportions of cermet parttc]es, namely greater
than about 50% by volume, provide a rLaterlal with less toughness than
obtninable with lower proportions. Also, tlle higll temperatures required
Eor melting cause a reaction wLth the cermet produclllg a brittle carbide
at the cermet-matrix interface, further reducing toughness.
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It has been found tllflt the limitation~s of prior n~tllods an he
overcome, and specifically, that a wkle range o~ thiclcness, sllape or com-
positions of tougll wear-resistant cl~mpo6ites call he rrovided by tlle use
of cermet partlcles, a steel powder matrix, an-l consolidating hy sublect-
lng to lleat in the solld state. Slncc? tlle n~trix Ls not melted in tbepresent lnventlon, the aforesaid .settllnr prohlem does not ~rise an(l the
composltlon in terms of cermet particle si~e, p;trticle-to-matrix propor-
tlon, can be chosen to provide tlle clcs~recl wenr- resistant prorertles nncl
toughl1es~ characterlstics without tlle previous restrictlons of product
thickness, etc.
In accordance with tlle prese!lt invention, a wear-resistallt com-
posite ls provided wltll a composite comrrisillg cermet particles dispersed
ln a iron-base matrix that i8 consolidsted in the so1lcl state.
The wear-resistant materia] of tlle ~resent invelltion is made by
forming a mixture of cermet particles 3nd all iron-bAse n~3trlx powdc~r, and
consolidating the mixture by subjecting to lleat at a temperature below
the melting polnt of the matrix.
In accordance Witll one specific embodiment oE tl-e inveTItiorl,
consolidation co~prises slntering tlle mlxture nlld in~iltratLng witll a
metal having a relatlvely low melting point.
BP~IEF DESCI'IPTION ()F Tlll URAWINGS
Figure 1 is a micrograph fillOW~, tlle mi crostructure of an
examrle of a com~osite made in accord;lllte with one elllbodiment of the
invention.
Fig~re 2 is a baclcscatterecl e~ectroll micrograph sllowillg the
microstructure of a wear-reslstant composite materlal mflde by the metllod
describecl in Example l.
DESCRIPTION OF PRIFI.RPNiD E~ ()DI~IENTS
The prodnceion oE cermet particle~s as usecl in the preseot
inventlon, iæ known. One metlloci involves agglooleratlng WC and ~etal
binder powders (0.2 to lO ~m) and consoli(lating by vacuum sintering. Tlle
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most commonly used and preferred cermet is tun~sten carbide with cohalt
as blnder. Nickel, or nickel or cobalt alloys, may also be used as hind-
er. For the present invention, the preEerred size range of the cermet
particles is 0.1 to 5 mm, and pre~eral)ly from 0.5 to 2 mm. Preferably
the cermet particles are generally spllerical, since these are less
susceptlble to breakap,e.
The matrix ~aterial ~y comprtse var~ou~q iron-ba~se powders and,
preferably, carbon steel9 alloy steel ~r sta-lnless steel. The ma~rix
materlal may be prepared by known techn~ques.
Productlon of the composite ll~volves mi~inK the cermet parti-
cles with the steel ~tr~x powder. The cllolce of the ~Itrix and the pro-
portions will depend on the particul~r propertles, such a~s wear-resist-
ance and tougllness, desired. It appears that suitable compof,~tes can be
provided with volume proportlons oF the cermet partlcles up to nbout 6()%,
and preferably, in the range of 20 tn 40~.
The mixture is then consolid.~ted by subject~ng to heat at a
temperature below the melting pOi[lt of the matrix. Prior to consolida-
tion, the mixture may ~e compacted or mnlded to the desired shape. The
mlsture may also be formed by slip~casting.
Consolidation involves, sintering and subsequent infiltrating,
or simultaneous sintering and infiltrating, with metals such as copper,
copper alloys or nickel alloys.
The micrograph of Figure 1 shows the resulting microstructure
in a composite consolidated with sintering and infiltration. It can be
seen that the ~C~Co cermet particles are distributed in a copper infil-
trated steel matrix and that the particles are surrounded by a layer of
steel. There is little or no copper film immediately around the cemented
particles. The steel matrix deforms plastically during cold pressing and
bonds to cermet particles preventing massive copper penetration to the
surface of these particles. ~xamination of fracture surfaces oE green
compacts has shown that a steel layer is present on the surface of
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cemented particles. It was observed tllat the porosity in the composite
-ieces before consolidation tends to concentrnte nround cemented c<qrbLde
particles. Tbis local poroslty is detrimelltal to the collesion betwr-~>n
tlle cermet particles and the ~ trix nn(l to the strengtl1 of ti~e non infil-
trated sintered specimens. In SllCh nOn~ fi1trated SpeC:LlnerlS, Celllentedpartlcles are easily pulled out oi tl1e materi.ll whicl1 doe6 not occllr
wlth material lnf1Ltrated in accord.lllce wlth the preser1t invention. Sim-
ilarly the alternate n~thods of consolidatior1 by subjecting to heat ancl
pressure referred to hereinbefore involve plastlc deEormation of tlle0 rnatrix to remove porosity and achieve a similar result.
EXAMPLI~' I
Mearly spherical (0.4 to 0.7 mm in diameter) cementecl tun~sten
carbide particles were used in the wenr-resistarlt composite material~s.
The cornposition o~ the cemented cnrbide particles were 907O by weight of
WC and 10% by welght of cobalt. ~n atomized low alloy s~eel powder known
by the trademark "Ancorsteel 2000" was used to form the steel matrlx.
Graphite was added to the steel powder to give a steel matrix containing
0.5% by weight of carbon.
Various amounts o~ cernented carbide particles and steel powders
were wet miY~ed with water and alcoh()l. The volr1me proportion of cemented
carbide particles was between 7 to 35%. A binder known by tlle trademark
"Superloid" was added to the water to increase the strength o~ future
green compacts. Preforms were then molded fro1n these mixtures. Afl:er
drying at about 80C the preEorms were cornpacted at 55() ~l'a to a rlel-)s;ty
of abol1t 80% of thr theoretical lens~ty.
The green compacts were sinterecl and Ln~iltratecl at ll2()C
durtng 1800 seconds wlth a copper alloy contair1lng 1% by wt. o~ cl)romJum.
'Che lnfiltrated pieces were subsequently oil quenclled and tllen tempere(l
at 5U0C ~or 3600 seconds. A typical microgr.1pl1 oi the cermet coltalning
3~ wear-resistant material obtained by tllis metho(l is ShOWII ln F'Lgllre 2.
Abrasive wear mensuren)ents were made by tl)e higl) stress A~.TM
B611/76 metllod. In this method a steel lisk turrls in an abrasive-wlLer
oll~ture ~ile tlle tested spec:imen is pressed a~nLrlst it. Arl nbr-l-;ive~
water Eilm is pulled between the specimell and tlle steel disk c~usin~
abrasiorl of tlle specimen. In tlle plrsent work 30 mesl1 Ottawa si]Lca
abrasive particles were used with the FoLlowlng water to grit ratLo:
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0.4 cm3 ~ /g of gri.t. Volurne 10sses and re1atlve llfe spa-ls n~ selected
iron base alloys arld oE the cermet coll~aining wear-resistallt l~terlals
are presented ln 'rable I.
TA~I~F. I
Volume 106ses and relatlve llfe sparls of selected iron b,~se
alloys and oE tlle cermet cont.lLIlillg wear-resistal1t m;ltertals
prodllced by sinterin~ an~l subseql1ellt Lnfiltration
Vo.lume l.osses Rel.ative
~aterials ~cm3/10()() wllr.~cl l.ife Spr
revolutLons~
ASTM A36 steel C.30 1*
Austeni.tic rnangallese steel 0.198 1.52
112.1% (wt.) Mrl]
High ~lromlum cast iron U.227 1.32
125-30% (wt,) Cr]
Cermet containing wear-resistant materla1
Volume proportion of
cemented carbide particles
(%)
7 O.In9 2.75
1~ ().068 4.41
22 0.0525 5.71.
o.n373 ~.04
0.0198 15.15
* A value of 1 was glven to the ASTM ~36 steel
