CA1256126A - Dense ceramics containing a solid solution and method for making the same - Google Patents
Dense ceramics containing a solid solution and method for making the sameInfo
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- CA1256126A CA1256126A CA000518683A CA518683A CA1256126A CA 1256126 A CA1256126 A CA 1256126A CA 000518683 A CA000518683 A CA 000518683A CA 518683 A CA518683 A CA 518683A CA 1256126 A CA1256126 A CA 1256126A
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- Prior art keywords
- sic
- process defined
- ceramic
- solid solution
- aln
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/58—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides
- C04B35/581—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on borides, nitrides, i.e. nitrides, oxynitrides, carbonitrides or oxycarbonitrides or silicides based on aluminium nitride
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/515—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics
- C04B35/56—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides
- C04B35/565—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products based on non-oxide ceramics based on carbides or oxycarbides based on silicon carbide
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- C—CHEMISTRY; METALLURGY
- C04—CEMENTS; CONCRETE; ARTIFICIAL STONE; CERAMICS; REFRACTORIES
- C04B—LIME, MAGNESIA; SLAG; CEMENTS; COMPOSITIONS THEREOF, e.g. MORTARS, CONCRETE OR LIKE BUILDING MATERIALS; ARTIFICIAL STONE; CERAMICS; REFRACTORIES; TREATMENT OF NATURAL STONE
- C04B35/00—Shaped ceramic products characterised by their composition; Ceramics compositions; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/622—Forming processes; Processing powders of inorganic compounds preparatory to the manufacturing of ceramic products
- C04B35/64—Burning or sintering processes
- C04B35/65—Reaction sintering of free metal- or free silicon-containing compositions
Abstract
Abstract of the Disclosure Dense ceramic composites comprising a mixture of a solid solution containing the elements Si, C, Al, O, and N (referred to by the acronym SiCAlON) and a high temperature refractory phase have desirable physical properties and can be formed by pressureless sintering techniques. The refractory phase can be SiC, AlN, Al2O3, or AlON and constitutes between 1 and 99% of the volume of the ceramic. The method for pressureless sintering may also be used for densification of SiCAlON ceramics, or composites containing SiCAlON, allowing fabrication of the same into complex shapes economically.
Description
~Z561Z6 T)T~NS~3 C131~MIC.5 COMT~INJNG ~ SOL:[D SOLUTION
AND M13TE~OI) FOR M~KING THe SAME
B _ ground_o _the Irlvel!-tion Fie _ : This invention relates to the field of ceralnics and particularly to ceramics contailling solid soLutions containing the elements Si, C, Al, O, and N
(reEerred to by the acronym SiCAlON), and a method for densiEying such ceramics.
Description of the Prior Art: Silicon b~sed I() cerarnics are leading candidates for applications in high temperature environmellts including energy conversion devices due to their high strength to temperatures on the , order of 15U0C. .5iC and Si3N4 ceramics also find use in I applications, over a wide temperature range, where wear and/or chelllical resistance is required.
Pressureless sintering of SiC has been accom-plished using either B and C (or B4C) or Al (or A12O3) as sintering aids to obtain nearly single phase SiC with densities greater than 97% of theoretical. Very active
AND M13TE~OI) FOR M~KING THe SAME
B _ ground_o _the Irlvel!-tion Fie _ : This invention relates to the field of ceralnics and particularly to ceramics contailling solid soLutions containing the elements Si, C, Al, O, and N
(reEerred to by the acronym SiCAlON), and a method for densiEying such ceramics.
Description of the Prior Art: Silicon b~sed I() cerarnics are leading candidates for applications in high temperature environmellts including energy conversion devices due to their high strength to temperatures on the , order of 15U0C. .5iC and Si3N4 ceramics also find use in I applications, over a wide temperature range, where wear and/or chelllical resistance is required.
Pressureless sintering of SiC has been accom-plished using either B and C (or B4C) or Al (or A12O3) as sintering aids to obtain nearly single phase SiC with densities greater than 97% of theoretical. Very active
2() powders having high surface area (mean particle si æ is ! less than 0.5 micrometers) are required to provide the driving force for sintering. Very little densiEication !. occurs by pressureless sintering with SiC particle sizes greater thall 1 micrometer. Since pressureless sintering al]ows fabrication oE complex shapes economically, it would thereEore be an improvement in the art if SiC
particles in the 1-10 micrometer range could be densified without pressure.
Similarly, several metllods have recently been 7~1) develc)~ed Eor the pressureless sintering of Si3N4. One oE tlle most successEul methods for pressureless sintering involves the Eormatioll oE a solid solution of aluminum ~25~26 oxynitride itl silicon nitride to form SiAlON (a coined term consistillg oE the chemical abbreviatioIls for the elemellts pre~ent in the :~olid solutioll). l'llis family of mater;als sinter via a traIlsient liquid pllase an~1 has r, proven successful in malcing cuttirlg tools.
lrl allalogy with the Si7~10Ns, CutLer et al.
(U.S. Patent 4,14L,740 issued Fl3B. 27, 1979 for SOT~ID
soLu~rro~ ANI) PROCESS FOR PROI)UClNG ~ SOLlD SOLUTIOM) (1iscovered t~lal: a complete solid soLution exists between 1() alpha pllase SiC (2~ polykype), ~lN, and ~l20C. This Eamily o~ new materials was named usirlg the acronym SiC7~l0~, analogous to the SiAlON system. Tllese compounds exhihit tlle same hexagonal wurkzite structure and have similar lattice parameters.
Subsequellt studies on the SiC-AlN system indicated that the system had mecharlical properties similar to silicon carbide. The main advantage of the solid solutions was that by changillg composition, one could control properties (i.e., density, hardness, 2() fracture toughlless, Young's modulus and thermaL expansion co-eEficient) of the den~e cerarnic. This family of materia]s thus appears to have tlle potential to broaden the appIications of SiC. It would also appear that the sol;d solubility rallge in the SiC-~lM-~I20C system is IllUCh greater l:hall that found in the si1~LoN system, thus broadening the physical property range where engineering of properties ls possible.
'r~e Illajor limitation of tlle prior SiCAlON work was that attempts to pressureless sinter tlle composites
particles in the 1-10 micrometer range could be densified without pressure.
Similarly, several metllods have recently been 7~1) develc)~ed Eor the pressureless sintering of Si3N4. One oE tlle most successEul methods for pressureless sintering involves the Eormatioll oE a solid solution of aluminum ~25~26 oxynitride itl silicon nitride to form SiAlON (a coined term consistillg oE the chemical abbreviatioIls for the elemellts pre~ent in the :~olid solutioll). l'llis family of mater;als sinter via a traIlsient liquid pllase an~1 has r, proven successful in malcing cuttirlg tools.
lrl allalogy with the Si7~10Ns, CutLer et al.
(U.S. Patent 4,14L,740 issued Fl3B. 27, 1979 for SOT~ID
soLu~rro~ ANI) PROCESS FOR PROI)UClNG ~ SOLlD SOLUTIOM) (1iscovered t~lal: a complete solid soLution exists between 1() alpha pllase SiC (2~ polykype), ~lN, and ~l20C. This Eamily o~ new materials was named usirlg the acronym SiC7~l0~, analogous to the SiAlON system. Tllese compounds exhihit tlle same hexagonal wurkzite structure and have similar lattice parameters.
Subsequellt studies on the SiC-AlN system indicated that the system had mecharlical properties similar to silicon carbide. The main advantage of the solid solutions was that by changillg composition, one could control properties (i.e., density, hardness, 2() fracture toughlless, Young's modulus and thermaL expansion co-eEficient) of the den~e cerarnic. This family of materia]s thus appears to have tlle potential to broaden the appIications of SiC. It would also appear that the sol;d solubility rallge in the SiC-~lM-~I20C system is IllUCh greater l:hall that found in the si1~LoN system, thus broadening the physical property range where engineering of properties ls possible.
'r~e Illajor limitation of tlle prior SiCAlON work was that attempts to pressureless sinter tlle composites
3() were ullsuccess~ul and processing was expensive, requiring hot pressillg. WlliLe hot pressing resuLted in dense polycrystalline ceramics, in or~ler to make complicated shapes econolllic~IIy in large volullles, one must prefoml the material to a shape simi]ar to that desired for tlle ,, 1~6~
final colnpol1ent and sinter without pressure. As an exarllp]e of the utility oE sucl1 a tecllniyue, one is referred to the work of cutler (U.S. Patent 3,960,581, issued Jul1e 1, 1976, for PROCESS OF PROI~UCING A SOLII) .', ~SOr.UTTON OF Al.[IMl:N[JM ox:rl)~3 IN Sl:LlCON NITE~ 3 ) where Si~L()N materials were pressureless sintered. No techrliqlles heretofore have been reported ti~at allow sintering (wi~l1out hot-pressing) o compounds in the Si~ L~ 0C pllase field into a sub~starltially c1ense 1() polycrystaLIir1e ceramic.
In recognitior1 oE the interest in high-strer1gth ceramic materials havil1g specific physical properties, it would be an adval1tage in the art to provide an inexpen-sive metl1od Eor fabricating complex shapes of a solid solution consisting of silicon carbide, aluminum oxycar-bide and aLuminull1 nitride.
Sumn!ary of the Ir1verltiorl ~ process for pressureless sintering (i.e., sinteril1g in tlle absence oE applied pressure) SiCAlON
2() ceranlics has been invented. In addition, this process allows mixtures of the solid solution witl1 other materials to be formed. Specifically, mixtures oE the soLid so]ution Witl1 SiC and AlN allow improved tilermaL
conductivity as compared to the complete solid solutions, while retaining the desirable aspects of pressureless sintering and engineering of properties.
~ metl1od is disclosed for densifying solid solutions of at least alumir1um oxycarbide and silicon carbide and/or a]uminum l1itride (i.e., SiC~lON ceramics).
3() ~1aterials can be made whic11 consist of an intirllate mixture oE SiCA]ON solid solution witll a distil1ct second pllase oE either Si( or ~lM.
i6~'26 ~ tec1~ni.que for pressureless sintering oE
ox;(les, carbi(les and n.itrides of si.licon an~ alun1i1lun1 in tt1e prese1lce oE a.L-1min~ 1 ancl carbon or alu111;111lm carbide or alumi1l~l111 oxycarbi.de to for111 a substa11tial:1.y dense pol.ycrysta1:1.ine body oE virtually any sl1ape has been discovered.
r1hese ceramic bodies can comprise about 1 to 99~ by vo:1.u111e of a so:1id so.lution consisti11g of aluminu1n oxycarhi-.~e a11d s;..1.ico11 cArl~i.de a11d/or a1u111i11um nitride 1~) a11d at .Least: one reEractory phase of SiC and/or ~I.N.
Descri~ rl of tlle_)_awi~
FlG. :L is an x-ray diffraction pattern of a pressure1.ess sinterecl SiC~l()N ceramic described in ~xample 2.
FIG. 2 is an optical micrograph oE the SiCAlON
ceran1ic in F]:G. 1, taker1 at 15~0 magnifications, showing the existence of two distinct phases. 11he so].id solution i5 tllerefOre illhOlllOyelleOUS.
Fl(;. 3 is an x-ray diEEraction patter11 illus-2() trating pea1cs due to t:he solid soLutio1l and SiC.
FIG. ~ is a graphical representat.ion oE the strengt11 data from pressure:~ess sintered bars of SiC~lON
(contai11i11y a reEractory pl1ase of Si.C) in co1nparison to pressure:Less sintered SiC (without the solid solutio1l).
FIG. 5 is a graphical representation of the fracture toug11r1ess data Erom SiC~lON (contai1li1-g a refractory phase of SiC) in compariso1l to SiC without the solid solution.
FIG. 6 is a graphical representatiorl of the 3() sinteri1lg behavior of SiC-A12OC without containme1lt when sinterecl at 2()1)()C in N2 for 5 minutes.
FT~. 7 is a graphica:1. represer1tatio1l of the sinteri1lg behavi.or of Si.C and SiC~lON (containi1lg a .s'~ ' L ~
~2~i;6~26 refractory phase of SiC) as a unctioll of tlle starting SiC partic]e size.
Oescrl~tion of tlle Invention tn contrast to previou~s work whicl1 required intimate mi~ctu~es oE reactant.s to form a solid solution and hot pressing to densify SiCAlON materials, tl)e present ;nvel1t;on relies upon convelltiollal ceramic peocessillg. I)ellse polycryst:allille SiCAlON ceramlc bodies ~or mixtures of Si('AlON witll SiC and/or ~IN) can 1() be made according to tlle instant inventioll by mixillg certain compoullds containillg the elemel1ts Si, C, Al, (), and N in tlle proper proportions and malll-er, formillg sllaped bodies (;ncllldillg complex sllapes) by convel-tional pres.sing techniques, slip casting, injection molding, and tlle like, and sinterillg without applied pressure in a furnace. 'rllere are a nulnber of compoullds which can be used, some of w~lich are illustrated by the following reactions:
x(SiC) + z(4~1 + Al203 ~ 3C )~ [xSiC-3z(Al20C)]
2() x(SiC) + z(Al203 ~ Al4C3) --~ [xSiC 3z(Al20C~
x[a SiC. bAlN] + z(Al203 -1- Al4C3) ---~ [xaSiC 3z(Al20C) xbAlN]
(n-l)SiC ~- SiO2 ~ Al4C3 ---~ [nSiC 2Al20C]
Si -~ SiO2 ~ 4Al ~4C --~ 2~SiC-Al20C]
'I'he bracket [ ] is meant to imply that a solid solution of tlle indicated chemical composition can be formed.
Ilowever, a complete solid solution is not necessarily formed in the densified ceramic. Several types of solid , .. .
. . ~
;126 soluti.ons may exist as discrete particles witlli.rl tlle cerami.c- bc~(ly that mlght be ricll or deficient ill certain el.emellts. Tlowever, the overall. or averaged composition oE the resu.l.tillg body would be es.sentially that of the brackete(l compoulld.
Cut:Ler and Mi.l.ler (US. Patent 4,l4l,740) cl.aime~l tllat a complete so:Lid solution e~ists between ~L2~(, S.iC and ~J.M indicatillg tllat tlle variables a, b, n, x, all(l z vary over tlle entire stoichiometry range.
l~) RaEaniel.. l.o alld Vi.rlcar Eound that the solid so:Lution betweerl Si.C and AIM varied between 5 and l.()0 weight perCellt alllllli.llUIII nitri.(3e at 21()()C. Since the forlllatior of the sol.id solution is aiEfusion limited, the wide rarlge Eor the solid solution is dependellt on partic.Le l.S si.ze, .sinterillg temperature and tinle. Since the present inventioll does not rely on the formatiorl oE a complete so:Lid so].ution, the only li.mitation on x and z is that t:llere be enough l.iquid pllase to allow sinterillg. Since mirlor liquid amounts allow actival:ed sinterirlg to occur, 2() the ratio oE x to z can be as great as 99:1. SiC, ~lN or otller compounds (i.e., 13eSiN2, MgSiN2, beta ~14SiC4, beta ~lsC3N, Si3~].4N4C3, and tlle like) havil-lg the wurtzite structure are needed to stabilize ~12OC so ratios oE x to z are preferably not less than 2:98.
Z5 ~rhe urlique t:echnique oE the present invention comprises perEorming tlle sinterirlg in sucll a n~nr-er as to substantially limit decomposition or volatilization of the powder compact prior to densification. ~ensification occurs rapidly over a narrow temperature range (between 3(~ :l800 and 2000C). It is tllereEore believed tllat densifi-cation ta~es place primarily vi.a a liquid phase or tran-sient liquid pllase mecllallism. ~ liquid pllase is knowrl to be present at temperatures i.n excess of 1840C in the ~1203-~l4C3 system due to a eutectic reaction between '126 ~1203 arld 7~14C~4C. Microstructural evidence of solutiorl-precipitatioll confirllls tllat: a liquid phase is present duritlg tlle reaction. Iiquid pllase sinterillg tllereEore competes witl~ decomposi tion of some of tlle reaction constituerlts due to their lligl~ vapor pressure.
necOmpOsitiOrl may be limited by a llumber of d; fferellt teclln;ques incl ud;rlg 1) using a c]osed c~ucible corlta;llilly tlle green body (i.e., a grapllite or boron n; tride crucible ) 2 ) by embedmerlt of tlle green body in a I 0 loose]y paclced mass of ceramic particles of a substan-tially simi]ar cllemical composi tion; 3 ) by controlling the ~eating rate and sintering ti ll~ to limit decomposi-ti on and promote sinterillg; and 4 ) by controlling the sinterillg atmosphere so as to suppress the decomposition J 5 and subsequent volati zation of reaction componerlts . By suppressillg decompositiorl, sintering to lligll aensities is possible. Ihere is a minimum temperature at whicll tlle above reactions take place. ~t temperature extremes in excess of the mirlimulll temperature required for densif ica-2~J tion, tllere is evidence of decomposition of tlle reaction products. Tl~e range of acceptable sinterillg telllperatures is obviously deperlderlt oll tl~e volume oE tlle liquid pllase, but ternperatures between l 750 and 2200 C llave been found to be acceptable.
Ille tecJ~nique is not limited to speciali ty cllemicals but ratller can utilize commercially available raw materials witll starting purities preferably greater thall 98.5%. Starting particle size determines the extent of tlle solid solution formed. Substantial densificatiorl ~() llas been obtained from starting materials with powders in the 1-10 micron particle size range. ~rl~e finer the starting particle size, tlle greater tlle amoullt of soLid s o L ut i Oll f o rmed .
t~'~
1n eacb oE t11e examples citecl be1ow a met1~od Eor controLLi11g decomposition and volatiLization is d; sclosed 1n tl~e absence of controlliny tl~e vapor pressure of the reaction little or no densiEication 'i takes p1ace.
7~9 Ci. ted abo~1e previou .5 work was limited to ma1ci11g powders wl~icl~ were colnpLete solid solutions (ll.S.
Patent 4 141 740). The present inve1ltlon in co11trast per11~ 3 mi xt11re.s oE tlle so1i(l SOllltiOII alld Otller ll.igll 1~ telnF)-?ra1-11rf? re~rac1()ry p~1ases Wl1;CI1 l1ave qnod El1ysica properties to be made. '1'1~e pressureless sintering tecl111ique l1erei1 discLosed can be applied to eitl1er l1o111oge11e~ s soJid soLutions in11o111Oge11eou~s solid so1utions or mixtures of SiC?~ N and other pl1ases.
IS ~X~MPL13 M~'1'130D F(~ I)r'N~IFYING 1~ E10MOGENEOUS SOLID SOI.UTION
SiC (0.615 grams) made by tlle carbotl1erlllal reduc-tion o ~ ().255 grams ~1203 (Meller 1).3 micrometers) and 1).36() gra111s A14C3 made by tl1e ca rbotl1ermic red1lctio11 2(1 Oe 7~12()3 were n1ixed in an agate mortar and pestle ~or 15 mi1-utes. 1~pproxi111ate]y 3 wt. % po LyvinyL pyrrolidone (PVP) was added as a binder duriny the mixir1g operation ~n(l the powder was r111iaxially pressed at 7() MPa to forln a J8 m111 cliameter dis1c. '1'he binder was pyrolyzed by slowly 2!; l1eatillg to 900C under N2. Tlle compacted powder was the placed in a 20 m1n diameter by 20 m1n deep cavity withir1 a der1se grapllite (Poco graphite) crucible 9 an in diameter and 1() cm high. The crucible was closed using a graphite foil seal whic11 mated the crucib1e to a threaded graphite 3() lid. 'l'1~e crucible was tl1en placed in a yraphite resis-tance heated furnace and heated at a rate of approxi-mately 75C/mi11ute to 2015C under flowiny N2 and heLd for 15 minutes. 'l'he disk sintered (16% linear shrir1kaye .
~S61:26 g in diameter) to closed porosity and a density of 3.1 g/cc (greater t~lan 99~ of t~leoretical density). The micro-structure indicated tl~e presence of a single phase wllen viewed optically at 1500X rnagnification. X-ray diffrac-tion also indicated that a homogeneous solid solution had formed (see 'L'able 1) and conEirmed that the samples had reacted to form a solid solution consisting of 70 mole percent SiC and 30 mole percent ~12OC. Since sintering was dolle in a nitrogen envirollment tllere is no doubt that Il) tlle solid solutio~l contaills some ~lN.
~rable 1 XRD PFIl~K POSITIONS FOR CU Kd~ RADlATlON
(lC)MPOtlND 2e AT PtlANE
(100) (002) (101) t102) (110) (103) (200) (112) I_ SiC (2~) 33.5 35.6 38.1 49.8 60.0 65.2 70.~ 72.0 ~lN (411) 33.1 36.0 37.9 49.8 59.3 66.0 69.7 71.4 ~120C (4EI) 32.5 35.3 37.1 48.6 58.4 64.2 67.9 70.8 ~5iC-~20C~ 33.0 35.3 37.6 49.2 59.2 65.2 69.6 71.( *~xperimentally n~asured value.s for solid solution com-%() posed of 70 mole percent SiC and 30 mole percent ~120C.
EK~MPLE 2 METI101) FOR VENSIFYING AN INEIOMOG~N~OUS SOLlV SOLU'rION
SiC (150 grams of Starclc BD-10 beta SiC, 17 m2/g containirlg s and C additions), ~1203 (58.19 grams of Bialcow91ci CR-30), and ~14C3 (87.81 grams, Cerac) were milled for 10 hours in a poLyetllylene ball milL with 425 ml of 2-propanol and 1 kg. of nigll purity alumilla milling media to make a uniforlll mixture of tlle powders. ~fter air drying the 5 gram disk of tlle powders was formed by uniaxial pressing at 34.5 MPa, followed by isostatic ~S~i~Z6 pressing at 207 MPa. ~rhe pressed dislc was loaded into t}le grap}lite cylinder described in example 1 and heated in N2 at a rate oE approximately 60C per minute to 2000C and lleld there for 1 hour. Upon cooli~lg, it was ~1etermilled that the linear shrinkage was 13.6~ and the density was 2.93 g/cc or 95% of tlleoretical. X-ray diffraction s}lowed tllat the SiC 3() mole % A12oC material was a complete solid solution (F1G. 1). Optical Inicro-scopy sllowed two d;stinct phases (F:rG~ 2), wllicll were 1() aE~parent:ly Si and ~1 rich SiCAlON so:Lid solutiolls.
~'X~MPTJES 3-7 Fo~MA~l~roN OF A MIXTURL~ OF SiCAlON
Al`11) SiC l~rJD ME'I'IIOD FOR l)RNSIFlCATl(:)N
Commercial grades of SiC (tbiden beta SiC, 17 m2/g arld contains no boron), A12o3 (Biakowski CR-3()), and ~14C3 (Cerac), with weights as givell in Table 2, were vibratory milLe(l for 15 hours in 1~5~ cc of cyclohexalle alld 6 kg ~12O3. Tlle powders were air dried and screened throug)l a ~0 Ine.qtl screen before ulliaxial pressing at 35 2(1 MPa, followed hy isostatic pressing at 2()7 MPa. Tlle parts were contailled in a graphite crucible as described in ~xample :I and sintered at the conditions listed in q~able 3. 'I'he powders sintered to closed porosity with sllrilll~ages and densities as indicated in 'rable 3. X-ray diffraction (F'~G. 3) showed that invariably the sintered samples consisted of SiC and the solid solution (SiCAlON).
nptical microscopy revealed three phases, indicating tllat tlle solid solution was l~ot holllogelleous. Bar samples were tested in four poillt belldillg ~FIG. 4) and tlle strengtlls 3~) were comparable witll ~sic. Fracture toughlless of tlle new materials as determilled ~)y the indelltatiollllletllod was superior to SiC (Fl(,. 5). Similar results were obtained with a a wide variety of SiC materials illcluding Starck .'~
~6~26 BV-10 (beta SiC with B and C additions), Starck B-10 (beta SiC without B and C additions~, Starck AD-10 (alpha SiC wittl B and C additions), and Starck A-10 (alplla SiC
without B and C additions).
'l'able 2 Composition of ~xan~les 3-7 Example Composition (grams) % SiC in SiC.A12OC
_ SiC ~ ~l~O~ ~laC~ (mole percent), 32~0.0 26.4 37.3 90.0 l() 4240.0 51.0 72.0 80.0 5~.50.0 58.2 87.8 70.0 6120.() 68.0 96.0 60.0 7. 1 ~0.0 ~ 6~.0 96.0 50.0 Table 3 Sintering Conditions and Densification of Examples 3-7 Example Sintering coiiditLons Shrinkage Density Temp(C) ¦Time a-t Temp(min) I (%) (g/cc) 3 1925 60 14.8 3.12
final colnpol1ent and sinter without pressure. As an exarllp]e of the utility oE sucl1 a tecllniyue, one is referred to the work of cutler (U.S. Patent 3,960,581, issued Jul1e 1, 1976, for PROCESS OF PROI~UCING A SOLII) .', ~SOr.UTTON OF Al.[IMl:N[JM ox:rl)~3 IN Sl:LlCON NITE~ 3 ) where Si~L()N materials were pressureless sintered. No techrliqlles heretofore have been reported ti~at allow sintering (wi~l1out hot-pressing) o compounds in the Si~ L~ 0C pllase field into a sub~starltially c1ense 1() polycrystaLIir1e ceramic.
In recognitior1 oE the interest in high-strer1gth ceramic materials havil1g specific physical properties, it would be an adval1tage in the art to provide an inexpen-sive metl1od Eor fabricating complex shapes of a solid solution consisting of silicon carbide, aluminum oxycar-bide and aLuminull1 nitride.
Sumn!ary of the Ir1verltiorl ~ process for pressureless sintering (i.e., sinteril1g in tlle absence oE applied pressure) SiCAlON
2() ceranlics has been invented. In addition, this process allows mixtures of the solid solution witl1 other materials to be formed. Specifically, mixtures oE the soLid so]ution Witl1 SiC and AlN allow improved tilermaL
conductivity as compared to the complete solid solutions, while retaining the desirable aspects of pressureless sintering and engineering of properties.
~ metl1od is disclosed for densifying solid solutions of at least alumir1um oxycarbide and silicon carbide and/or a]uminum l1itride (i.e., SiC~lON ceramics).
3() ~1aterials can be made whic11 consist of an intirllate mixture oE SiCA]ON solid solution witll a distil1ct second pllase oE either Si( or ~lM.
i6~'26 ~ tec1~ni.que for pressureless sintering oE
ox;(les, carbi(les and n.itrides of si.licon an~ alun1i1lun1 in tt1e prese1lce oE a.L-1min~ 1 ancl carbon or alu111;111lm carbide or alumi1l~l111 oxycarbi.de to for111 a substa11tial:1.y dense pol.ycrysta1:1.ine body oE virtually any sl1ape has been discovered.
r1hese ceramic bodies can comprise about 1 to 99~ by vo:1.u111e of a so:1id so.lution consisti11g of aluminu1n oxycarhi-.~e a11d s;..1.ico11 cArl~i.de a11d/or a1u111i11um nitride 1~) a11d at .Least: one reEractory phase of SiC and/or ~I.N.
Descri~ rl of tlle_)_awi~
FlG. :L is an x-ray diffraction pattern of a pressure1.ess sinterecl SiC~l()N ceramic described in ~xample 2.
FIG. 2 is an optical micrograph oE the SiCAlON
ceran1ic in F]:G. 1, taker1 at 15~0 magnifications, showing the existence of two distinct phases. 11he so].id solution i5 tllerefOre illhOlllOyelleOUS.
Fl(;. 3 is an x-ray diEEraction patter11 illus-2() trating pea1cs due to t:he solid soLutio1l and SiC.
FIG. ~ is a graphical representat.ion oE the strengt11 data from pressure:~ess sintered bars of SiC~lON
(contai11i11y a reEractory pl1ase of Si.C) in co1nparison to pressure:Less sintered SiC (without the solid solutio1l).
FIG. 5 is a graphical representation of the fracture toug11r1ess data Erom SiC~lON (contai1li1-g a refractory phase of SiC) in compariso1l to SiC without the solid solution.
FIG. 6 is a graphical representatiorl of the 3() sinteri1lg behavior of SiC-A12OC without containme1lt when sinterecl at 2()1)()C in N2 for 5 minutes.
FT~. 7 is a graphica:1. represer1tatio1l of the sinteri1lg behavi.or of Si.C and SiC~lON (containi1lg a .s'~ ' L ~
~2~i;6~26 refractory phase of SiC) as a unctioll of tlle starting SiC partic]e size.
Oescrl~tion of tlle Invention tn contrast to previou~s work whicl1 required intimate mi~ctu~es oE reactant.s to form a solid solution and hot pressing to densify SiCAlON materials, tl)e present ;nvel1t;on relies upon convelltiollal ceramic peocessillg. I)ellse polycryst:allille SiCAlON ceramlc bodies ~or mixtures of Si('AlON witll SiC and/or ~IN) can 1() be made according to tlle instant inventioll by mixillg certain compoullds containillg the elemel1ts Si, C, Al, (), and N in tlle proper proportions and malll-er, formillg sllaped bodies (;ncllldillg complex sllapes) by convel-tional pres.sing techniques, slip casting, injection molding, and tlle like, and sinterillg without applied pressure in a furnace. 'rllere are a nulnber of compoullds which can be used, some of w~lich are illustrated by the following reactions:
x(SiC) + z(4~1 + Al203 ~ 3C )~ [xSiC-3z(Al20C)]
2() x(SiC) + z(Al203 ~ Al4C3) --~ [xSiC 3z(Al20C~
x[a SiC. bAlN] + z(Al203 -1- Al4C3) ---~ [xaSiC 3z(Al20C) xbAlN]
(n-l)SiC ~- SiO2 ~ Al4C3 ---~ [nSiC 2Al20C]
Si -~ SiO2 ~ 4Al ~4C --~ 2~SiC-Al20C]
'I'he bracket [ ] is meant to imply that a solid solution of tlle indicated chemical composition can be formed.
Ilowever, a complete solid solution is not necessarily formed in the densified ceramic. Several types of solid , .. .
. . ~
;126 soluti.ons may exist as discrete particles witlli.rl tlle cerami.c- bc~(ly that mlght be ricll or deficient ill certain el.emellts. Tlowever, the overall. or averaged composition oE the resu.l.tillg body would be es.sentially that of the brackete(l compoulld.
Cut:Ler and Mi.l.ler (US. Patent 4,l4l,740) cl.aime~l tllat a complete so:Lid solution e~ists between ~L2~(, S.iC and ~J.M indicatillg tllat tlle variables a, b, n, x, all(l z vary over tlle entire stoichiometry range.
l~) RaEaniel.. l.o alld Vi.rlcar Eound that the solid so:Lution betweerl Si.C and AIM varied between 5 and l.()0 weight perCellt alllllli.llUIII nitri.(3e at 21()()C. Since the forlllatior of the sol.id solution is aiEfusion limited, the wide rarlge Eor the solid solution is dependellt on partic.Le l.S si.ze, .sinterillg temperature and tinle. Since the present inventioll does not rely on the formatiorl oE a complete so:Lid so].ution, the only li.mitation on x and z is that t:llere be enough l.iquid pllase to allow sinterillg. Since mirlor liquid amounts allow actival:ed sinterirlg to occur, 2() the ratio oE x to z can be as great as 99:1. SiC, ~lN or otller compounds (i.e., 13eSiN2, MgSiN2, beta ~14SiC4, beta ~lsC3N, Si3~].4N4C3, and tlle like) havil-lg the wurtzite structure are needed to stabilize ~12OC so ratios oE x to z are preferably not less than 2:98.
Z5 ~rhe urlique t:echnique oE the present invention comprises perEorming tlle sinterirlg in sucll a n~nr-er as to substantially limit decomposition or volatilization of the powder compact prior to densification. ~ensification occurs rapidly over a narrow temperature range (between 3(~ :l800 and 2000C). It is tllereEore believed tllat densifi-cation ta~es place primarily vi.a a liquid phase or tran-sient liquid pllase mecllallism. ~ liquid pllase is knowrl to be present at temperatures i.n excess of 1840C in the ~1203-~l4C3 system due to a eutectic reaction between '126 ~1203 arld 7~14C~4C. Microstructural evidence of solutiorl-precipitatioll confirllls tllat: a liquid phase is present duritlg tlle reaction. Iiquid pllase sinterillg tllereEore competes witl~ decomposi tion of some of tlle reaction constituerlts due to their lligl~ vapor pressure.
necOmpOsitiOrl may be limited by a llumber of d; fferellt teclln;ques incl ud;rlg 1) using a c]osed c~ucible corlta;llilly tlle green body (i.e., a grapllite or boron n; tride crucible ) 2 ) by embedmerlt of tlle green body in a I 0 loose]y paclced mass of ceramic particles of a substan-tially simi]ar cllemical composi tion; 3 ) by controlling the ~eating rate and sintering ti ll~ to limit decomposi-ti on and promote sinterillg; and 4 ) by controlling the sinterillg atmosphere so as to suppress the decomposition J 5 and subsequent volati zation of reaction componerlts . By suppressillg decompositiorl, sintering to lligll aensities is possible. Ihere is a minimum temperature at whicll tlle above reactions take place. ~t temperature extremes in excess of the mirlimulll temperature required for densif ica-2~J tion, tllere is evidence of decomposition of tlle reaction products. Tl~e range of acceptable sinterillg telllperatures is obviously deperlderlt oll tl~e volume oE tlle liquid pllase, but ternperatures between l 750 and 2200 C llave been found to be acceptable.
Ille tecJ~nique is not limited to speciali ty cllemicals but ratller can utilize commercially available raw materials witll starting purities preferably greater thall 98.5%. Starting particle size determines the extent of tlle solid solution formed. Substantial densificatiorl ~() llas been obtained from starting materials with powders in the 1-10 micron particle size range. ~rl~e finer the starting particle size, tlle greater tlle amoullt of soLid s o L ut i Oll f o rmed .
t~'~
1n eacb oE t11e examples citecl be1ow a met1~od Eor controLLi11g decomposition and volatiLization is d; sclosed 1n tl~e absence of controlliny tl~e vapor pressure of the reaction little or no densiEication 'i takes p1ace.
7~9 Ci. ted abo~1e previou .5 work was limited to ma1ci11g powders wl~icl~ were colnpLete solid solutions (ll.S.
Patent 4 141 740). The present inve1ltlon in co11trast per11~ 3 mi xt11re.s oE tlle so1i(l SOllltiOII alld Otller ll.igll 1~ telnF)-?ra1-11rf? re~rac1()ry p~1ases Wl1;CI1 l1ave qnod El1ysica properties to be made. '1'1~e pressureless sintering tecl111ique l1erei1 discLosed can be applied to eitl1er l1o111oge11e~ s soJid soLutions in11o111Oge11eou~s solid so1utions or mixtures of SiC?~ N and other pl1ases.
IS ~X~MPL13 M~'1'130D F(~ I)r'N~IFYING 1~ E10MOGENEOUS SOLID SOI.UTION
SiC (0.615 grams) made by tlle carbotl1erlllal reduc-tion o ~ ().255 grams ~1203 (Meller 1).3 micrometers) and 1).36() gra111s A14C3 made by tl1e ca rbotl1ermic red1lctio11 2(1 Oe 7~12()3 were n1ixed in an agate mortar and pestle ~or 15 mi1-utes. 1~pproxi111ate]y 3 wt. % po LyvinyL pyrrolidone (PVP) was added as a binder duriny the mixir1g operation ~n(l the powder was r111iaxially pressed at 7() MPa to forln a J8 m111 cliameter dis1c. '1'he binder was pyrolyzed by slowly 2!; l1eatillg to 900C under N2. Tlle compacted powder was the placed in a 20 m1n diameter by 20 m1n deep cavity withir1 a der1se grapllite (Poco graphite) crucible 9 an in diameter and 1() cm high. The crucible was closed using a graphite foil seal whic11 mated the crucib1e to a threaded graphite 3() lid. 'l'1~e crucible was tl1en placed in a yraphite resis-tance heated furnace and heated at a rate of approxi-mately 75C/mi11ute to 2015C under flowiny N2 and heLd for 15 minutes. 'l'he disk sintered (16% linear shrir1kaye .
~S61:26 g in diameter) to closed porosity and a density of 3.1 g/cc (greater t~lan 99~ of t~leoretical density). The micro-structure indicated tl~e presence of a single phase wllen viewed optically at 1500X rnagnification. X-ray diffrac-tion also indicated that a homogeneous solid solution had formed (see 'L'able 1) and conEirmed that the samples had reacted to form a solid solution consisting of 70 mole percent SiC and 30 mole percent ~12OC. Since sintering was dolle in a nitrogen envirollment tllere is no doubt that Il) tlle solid solutio~l contaills some ~lN.
~rable 1 XRD PFIl~K POSITIONS FOR CU Kd~ RADlATlON
(lC)MPOtlND 2e AT PtlANE
(100) (002) (101) t102) (110) (103) (200) (112) I_ SiC (2~) 33.5 35.6 38.1 49.8 60.0 65.2 70.~ 72.0 ~lN (411) 33.1 36.0 37.9 49.8 59.3 66.0 69.7 71.4 ~120C (4EI) 32.5 35.3 37.1 48.6 58.4 64.2 67.9 70.8 ~5iC-~20C~ 33.0 35.3 37.6 49.2 59.2 65.2 69.6 71.( *~xperimentally n~asured value.s for solid solution com-%() posed of 70 mole percent SiC and 30 mole percent ~120C.
EK~MPLE 2 METI101) FOR VENSIFYING AN INEIOMOG~N~OUS SOLlV SOLU'rION
SiC (150 grams of Starclc BD-10 beta SiC, 17 m2/g containirlg s and C additions), ~1203 (58.19 grams of Bialcow91ci CR-30), and ~14C3 (87.81 grams, Cerac) were milled for 10 hours in a poLyetllylene ball milL with 425 ml of 2-propanol and 1 kg. of nigll purity alumilla milling media to make a uniforlll mixture of tlle powders. ~fter air drying the 5 gram disk of tlle powders was formed by uniaxial pressing at 34.5 MPa, followed by isostatic ~S~i~Z6 pressing at 207 MPa. ~rhe pressed dislc was loaded into t}le grap}lite cylinder described in example 1 and heated in N2 at a rate oE approximately 60C per minute to 2000C and lleld there for 1 hour. Upon cooli~lg, it was ~1etermilled that the linear shrinkage was 13.6~ and the density was 2.93 g/cc or 95% of tlleoretical. X-ray diffraction s}lowed tllat the SiC 3() mole % A12oC material was a complete solid solution (F1G. 1). Optical Inicro-scopy sllowed two d;stinct phases (F:rG~ 2), wllicll were 1() aE~parent:ly Si and ~1 rich SiCAlON so:Lid solutiolls.
~'X~MPTJES 3-7 Fo~MA~l~roN OF A MIXTURL~ OF SiCAlON
Al`11) SiC l~rJD ME'I'IIOD FOR l)RNSIFlCATl(:)N
Commercial grades of SiC (tbiden beta SiC, 17 m2/g arld contains no boron), A12o3 (Biakowski CR-3()), and ~14C3 (Cerac), with weights as givell in Table 2, were vibratory milLe(l for 15 hours in 1~5~ cc of cyclohexalle alld 6 kg ~12O3. Tlle powders were air dried and screened throug)l a ~0 Ine.qtl screen before ulliaxial pressing at 35 2(1 MPa, followed hy isostatic pressing at 2()7 MPa. Tlle parts were contailled in a graphite crucible as described in ~xample :I and sintered at the conditions listed in q~able 3. 'I'he powders sintered to closed porosity with sllrilll~ages and densities as indicated in 'rable 3. X-ray diffraction (F'~G. 3) showed that invariably the sintered samples consisted of SiC and the solid solution (SiCAlON).
nptical microscopy revealed three phases, indicating tllat tlle solid solution was l~ot holllogelleous. Bar samples were tested in four poillt belldillg ~FIG. 4) and tlle strengtlls 3~) were comparable witll ~sic. Fracture toughlless of tlle new materials as determilled ~)y the indelltatiollllletllod was superior to SiC (Fl(,. 5). Similar results were obtained with a a wide variety of SiC materials illcluding Starck .'~
~6~26 BV-10 (beta SiC with B and C additions), Starck B-10 (beta SiC without B and C additions~, Starck AD-10 (alpha SiC wittl B and C additions), and Starck A-10 (alplla SiC
without B and C additions).
'l'able 2 Composition of ~xan~les 3-7 Example Composition (grams) % SiC in SiC.A12OC
_ SiC ~ ~l~O~ ~laC~ (mole percent), 32~0.0 26.4 37.3 90.0 l() 4240.0 51.0 72.0 80.0 5~.50.0 58.2 87.8 70.0 6120.() 68.0 96.0 60.0 7. 1 ~0.0 ~ 6~.0 96.0 50.0 Table 3 Sintering Conditions and Densification of Examples 3-7 Example Sintering coiiditLons Shrinkage Density Temp(C) ¦Time a-t Temp(min) I (%) (g/cc) 3 1925 60 14.8 3.12
4 2050 5 14.2 3.15 2() 5 2050 5 14.2 3.15 6 2~50 5 16.3 3.14 7 _ 1925 60 13.0 3.07 ~AMPLE 8 j MET~OD FOR SINT~RING SiC-AlN TO FO~ SiCAlON
¦ 25 giC (made by carbotllermal reduction of silica, j 3.0 grams), AlN-15SiC (made by Cutler process (U.S. Pat.
! 4,141,74U), 3.0 grams), A:l2O3 (Meller, 0.8293 grams), C
i (carboll black, 0.2928 grams), and ~ 325 mesh, 0.8778 ! grams) were mixed in a mortar and pestal for 30 minutes and processed and sintered as in ~xample 1. The sample sintered to a density near 80~ of theoretical.
~Z5fi~
i ~X ~MP LE 9 Ml~lllOI) FOR PR~SSUR~I E.5S SINTF:RING SiCAlON VI~ MBEDMENT
SiC (Stark 7~D-10, 90 grams~, ~1203 ~Reynolds ~lP-DBM, 51 grarns ), Al (Cerac, 54 gralns ), and C (Cabot ', Mogul L, 18 grams) were ball milled with 1500 grarns of l~igl~ purity alumina media in a plastic mill with 500 ml isopropanol for 12 hours. The powder was pressed into a pellet as in T~xample 2 and subsequently embedded in its own powder. The embedded sample was heated to 2000C in I () 10 rmillutes and l~eld for 5 minutes . Tlle embedded disk sintered to greater tharl 95% of tlleoretica l density and ~ad an x-ray diEfraction pattern of a mixture of SiC~lOM
and SiC.
FX ~MPLE 1 () METHOD FOR PRESSURELESS SINTERING
WITIIOUT CONTAINMENT
I he pressed pellets prepared as in Example 2 were sintered uncontailled in W2 by heatillg from 1()00C in le.s.s tharl 5 millutes (Fl(~. 6). Tlle SiC- 30 mole ~ ~12OC
disks silltered to closed porosity, being greater tllan 9596 of tl~eoretical density. Tl~e densification occurs quicker tllan decompo.9iti.0Jl and contai.llment is not necessary.
Since C O is tlle ma jor product of tlle decomE)ositioll process, control of CO partial pressure will allow tlle pressureless sinterillg of SiC~lON ceramics at low heating ra te s wi t llou t con ta i nllle n t .
F.X~MPLE 11 S l:NTER r NG 1- 5 M [ CRON Si C USING Si C~l ON
SiC (( arborulldulll 1500 grit alpha SiC Witllollt 8 3() or C additions, 152.04 grams), A12O3 (Reynold's TIP-I~BM, 58.98 grams), and ~14C3 ((erac, 89.0() grams) were mixed or 2 hours in llexalle. Tl~e powder was compacted and . :~
~.~5~
sinte~ed as described in ~xample 2. Considerable shrink-age and densification occurred (FIG. 7) whereas little or no densification occurred when the powder was sintered in tl~e absence of SiC~lON. Sintering of larger particle size powders is possible due to the presence of the liquid phase.
SIN'rEl~ING SiCAlON USING sio2 AS TH~: OXYGl~:N SOVRCE
SiO2 (M5 Cab-O-Sil, 30 grams), ~1 (Alcoa 123, 1() 54 grams), Si (~tlantic ~quipment, 13.5 grams), and C
(Gulf ~cetylene Black, 24 grams) were ball milled in 600 ml 2-propanol for 10 hours with 1 kg high purity alumina media. The parts compacted as in Exarnple 2 and sintered at 1925~C in N2. The disk sintered (13.3% linear shrink-age) and X-ray diffraction showed SiC~lON and SiC phases.
The present invention is unique in the following respects:
1. Starting materials may be conventional ceramic powders in terms of composition (e.g., SiC, A12O3, and the like), which are of a conventional particle size (i.e., less than 10 microns in diameter). The starting particle sizes are preferably 1-5 microns if inhomoge-neous solid solutions or mixtures of the solid solution and a refractory phase are desired, or preferably less than 0.5 microns if a complete solid solution is desired.
2. Complex shapes may be formed in the green state (using conventional binders) and sintered without the application of external pressure to form a dense, strong ceramic body havil)g propertles equivalent to tllose of ,~
¦ 25 giC (made by carbotllermal reduction of silica, j 3.0 grams), AlN-15SiC (made by Cutler process (U.S. Pat.
! 4,141,74U), 3.0 grams), A:l2O3 (Meller, 0.8293 grams), C
i (carboll black, 0.2928 grams), and ~ 325 mesh, 0.8778 ! grams) were mixed in a mortar and pestal for 30 minutes and processed and sintered as in ~xample 1. The sample sintered to a density near 80~ of theoretical.
~Z5fi~
i ~X ~MP LE 9 Ml~lllOI) FOR PR~SSUR~I E.5S SINTF:RING SiCAlON VI~ MBEDMENT
SiC (Stark 7~D-10, 90 grams~, ~1203 ~Reynolds ~lP-DBM, 51 grarns ), Al (Cerac, 54 gralns ), and C (Cabot ', Mogul L, 18 grams) were ball milled with 1500 grarns of l~igl~ purity alumina media in a plastic mill with 500 ml isopropanol for 12 hours. The powder was pressed into a pellet as in T~xample 2 and subsequently embedded in its own powder. The embedded sample was heated to 2000C in I () 10 rmillutes and l~eld for 5 minutes . Tlle embedded disk sintered to greater tharl 95% of tlleoretica l density and ~ad an x-ray diEfraction pattern of a mixture of SiC~lOM
and SiC.
FX ~MPLE 1 () METHOD FOR PRESSURELESS SINTERING
WITIIOUT CONTAINMENT
I he pressed pellets prepared as in Example 2 were sintered uncontailled in W2 by heatillg from 1()00C in le.s.s tharl 5 millutes (Fl(~. 6). Tlle SiC- 30 mole ~ ~12OC
disks silltered to closed porosity, being greater tllan 9596 of tl~eoretical density. Tl~e densification occurs quicker tllan decompo.9iti.0Jl and contai.llment is not necessary.
Since C O is tlle ma jor product of tlle decomE)ositioll process, control of CO partial pressure will allow tlle pressureless sinterillg of SiC~lON ceramics at low heating ra te s wi t llou t con ta i nllle n t .
F.X~MPLE 11 S l:NTER r NG 1- 5 M [ CRON Si C USING Si C~l ON
SiC (( arborulldulll 1500 grit alpha SiC Witllollt 8 3() or C additions, 152.04 grams), A12O3 (Reynold's TIP-I~BM, 58.98 grams), and ~14C3 ((erac, 89.0() grams) were mixed or 2 hours in llexalle. Tl~e powder was compacted and . :~
~.~5~
sinte~ed as described in ~xample 2. Considerable shrink-age and densification occurred (FIG. 7) whereas little or no densification occurred when the powder was sintered in tl~e absence of SiC~lON. Sintering of larger particle size powders is possible due to the presence of the liquid phase.
SIN'rEl~ING SiCAlON USING sio2 AS TH~: OXYGl~:N SOVRCE
SiO2 (M5 Cab-O-Sil, 30 grams), ~1 (Alcoa 123, 1() 54 grams), Si (~tlantic ~quipment, 13.5 grams), and C
(Gulf ~cetylene Black, 24 grams) were ball milled in 600 ml 2-propanol for 10 hours with 1 kg high purity alumina media. The parts compacted as in Exarnple 2 and sintered at 1925~C in N2. The disk sintered (13.3% linear shrink-age) and X-ray diffraction showed SiC~lON and SiC phases.
The present invention is unique in the following respects:
1. Starting materials may be conventional ceramic powders in terms of composition (e.g., SiC, A12O3, and the like), which are of a conventional particle size (i.e., less than 10 microns in diameter). The starting particle sizes are preferably 1-5 microns if inhomoge-neous solid solutions or mixtures of the solid solution and a refractory phase are desired, or preferably less than 0.5 microns if a complete solid solution is desired.
2. Complex shapes may be formed in the green state (using conventional binders) and sintered without the application of external pressure to form a dense, strong ceramic body havil)g propertles equivalent to tllose of ,~
Claims (24)
1. A ceramic comprising: 1 to 99 volume % of a solid solution (SiCAlON) comprised of at least aluminum oxycarbide and silicon carbide and/or aluminum nitride with at least one secondary phase comprised of SiC AlN, Al2O3, or AlON.
2. The ceramic described in Claim 1 where the secondary phase is either alpha or beta phase SiC.
3. The ceramic described in Claim 1 where the secondary phase is AlN.
4. The ceramic described in Claim 1 where the secondary phase is Al2O3.
5. The ceramic described in Claim 1 where the secondary phase is AlON.
6. The ceramic described in Claim 1 where the secondary phases are any combination of SiC AlN, Al2O3, and AlON.
7. The ceramic described in Claim 1 where the secondary phase is SiC and the starting SiC particle size is greater than 1 micron prior to pressureless sintering.
8. A process for reactive sintering SiCAlON
or SiCAlON - refractory phase ceramics in the absence of applied pressure comprising:
mixing elements or compounds containing the elements Al O, C, Si, and optionally N;
forming a shape of said reaction mixture using ceramic processing techniques; and sintering the reactant mixture while limiting the volatilization oh species from the reaction mixture,
or SiCAlON - refractory phase ceramics in the absence of applied pressure comprising:
mixing elements or compounds containing the elements Al O, C, Si, and optionally N;
forming a shape of said reaction mixture using ceramic processing techniques; and sintering the reactant mixture while limiting the volatilization oh species from the reaction mixture,
9. The process defined in Claim 8 where a highly impervious container is used to control the vapor pressure.
10. The process defined in Claim 8 where embedment is used to control the vapor pressure.
11. The process defined in Claim 8 where heating rates greater than 200°C/minute above 1000°C are used to limit volatilization.
12. The process defined in Claim 8 where atmospheric control is used to establish an equilibrium partial pressure of carbon monoxide.
13. The process defined in Claim 8 where the pressureless sintered ceramic is a homogeneous solid solution.
14. The process defined in Claim 8 where the pressureless sintered ceramic is an inhomogeneous solid solution.
15. The process defined in Claim 8 where the pressureless sintered ceramic is a mixture of the solid solution, either homogeneous or inhomogeneous, and a refractory phase.
16. The process defined in Claim 8 where the starting materials are SiC, Al2O3, and Al4C3.
SiCAlON ceramics heretofore only attainable using applied pressure while hot pressing.
3. By selecting the appropriate particle size, the compositions of the ceramic body can be controlled while still allowing densification to occur. The processing technique allows for the densification of complete solid solutions or mixtures of the solid solution with another refractory phase. The solid solution can therefore be used as a sintering aid to promote the densification of ceramics which are otherwise difficult to sinter.
Numerous variations and modifications can be made without departing from the invention. For example, AlN could be the primary secondary phase instead of SiC.
Accordingly, it should be clearly understood that the form of the invention described above is illustrative only and is not intended to limit its scope.
SiCAlON ceramics heretofore only attainable using applied pressure while hot pressing.
3. By selecting the appropriate particle size, the compositions of the ceramic body can be controlled while still allowing densification to occur. The processing technique allows for the densification of complete solid solutions or mixtures of the solid solution with another refractory phase. The solid solution can therefore be used as a sintering aid to promote the densification of ceramics which are otherwise difficult to sinter.
Numerous variations and modifications can be made without departing from the invention. For example, AlN could be the primary secondary phase instead of SiC.
Accordingly, it should be clearly understood that the form of the invention described above is illustrative only and is not intended to limit its scope.
17. The process defined in Claim 8 where the starting materials are SiC, Al2O3, AlN, and C.
18. The process defined in Claim 8 where the starting materials are AlN?SiC, Al2O3, and Al4C3 (or Al and C).
19. The process defined in Claim 8 where the starting materials are AlN, Al2O3, and Al4C3 (or Al and C).
20. The process defined in Claim 8 where the starting materials are SiO2, Si, and Al4C3 (or Al and C).
21. The process defined in Claim 8 where the starting materials are SiO2, SiC, and Al4C3 (or Al and C).
22. The process defined in Claim 8 where the SiC contains no B and/or C additions.
23. The process defined in Claim 8 where the SiC is greater than 1 micrometer in particle size prior to pressureless sintering.
24. The process defined in Claim 8 where the SiC (or SiC-AlN) powders have been prepared by carbother-mal reduction, resulting in starting powders with surface area greater than 20 m2/g, so that the pressureless sintered material is single phase when viewed optically at 1500 magnifications.
Applications Claiming Priority (2)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US77825185A | 1985-09-20 | 1985-09-20 | |
| US778,251 | 1985-09-20 |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1256126A true CA1256126A (en) | 1989-06-20 |
Family
ID=25112746
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000518683A Expired CA1256126A (en) | 1985-09-20 | 1986-09-19 | Dense ceramics containing a solid solution and method for making the same |
Country Status (3)
| Country | Link |
|---|---|
| EP (1) | EP0241514A4 (en) |
| CA (1) | CA1256126A (en) |
| WO (1) | WO1987001693A1 (en) |
Families Citing this family (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| FR2737489B1 (en) * | 1995-08-04 | 1997-09-12 | Centre Nat Rech Scient | PROCESS FOR THE PREPARATION OF DENSIFIED CERAMIC PRODUCTS AND CERAMIC PRODUCTS THUS OBTAINED |
| CN113024261B (en) * | 2021-04-23 | 2022-05-31 | 北京科技大学 | Method for preparing high-purity AlON ceramic powder and hot-pressing sintering method thereof |
| CN114149269B (en) * | 2021-12-02 | 2022-11-04 | 北京科技大学 | AlN-SiC solid solution combined SiC composite refractory material for side wall of aluminum electrolytic cell and preparation method thereof |
Family Cites Families (8)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US3890250A (en) * | 1973-03-14 | 1975-06-17 | Norton Co | Hot pressed silicon nitride containing finely dispersed silicon carbide or silicon aluminum oxynitride |
| US3895219A (en) * | 1973-11-23 | 1975-07-15 | Norton Co | Composite ceramic heating element |
| US3960581A (en) * | 1974-04-29 | 1976-06-01 | The University Of Utah | Process for producing a solid solution of aluminum oxide in silicon nitride |
| US3974106A (en) * | 1974-05-22 | 1976-08-10 | Norton Company | Ceramic electrical resistance igniter |
| US4053303A (en) * | 1976-12-06 | 1977-10-11 | Aluminum Company Of America | Method of carbothermically producing aluminum-silicon alloys |
| US4141740A (en) * | 1978-02-23 | 1979-02-27 | University Of Utah | Solid solution and process for producing a solid solution |
| JPS59107975A (en) * | 1982-12-08 | 1984-06-22 | 旭硝子株式会社 | Silicon carbide sintered body |
| JPS59190268A (en) * | 1983-12-16 | 1984-10-29 | 旭硝子株式会社 | Silicon carbide sintered body |
-
1986
- 1986-09-19 CA CA000518683A patent/CA1256126A/en not_active Expired
- 1986-09-19 EP EP19860906120 patent/EP0241514A4/en not_active Ceased
- 1986-09-19 WO PCT/US1986/001957 patent/WO1987001693A1/en not_active Application Discontinuation
Also Published As
| Publication number | Publication date |
|---|---|
| EP0241514A1 (en) | 1987-10-21 |
| WO1987001693A1 (en) | 1987-03-26 |
| EP0241514A4 (en) | 1988-09-28 |
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