 Svec in "Process for Making an Investment Mold for Casting and Solidification of Superalloys Therein", Ser. No. 590,970, now U.S. Pat. No. 4,024,300 teaches the use of alumina-silica compositions for making molds and cores. Charles C. Greskovich and Michael F. X. Gigliotti, Jr. in U.S. Pat. Nos. 3,955,616 and 3,972,367 teach cores and molds of alumina-silica compositions which have a barrier layer of alumina formed at the mold/metal interface. One possible means for the formation of their alumina layer is by a chemical reaction wherein carbon of the susceptor chemically reduces the material composition of the mold or core. Charles D. Greskovich in U.S. Pat. No. 4,026,344 also teaches an alumina-silica composition wherein the material is of a predetermined size so as to favor, and therefore enable, the formation of metastable mullite for molds and cores which exhibit superior sag resistance at high temperature.
Aluminum oxide by itself, without a chemical or physical binder material, has been identified as a potential core and mold material based on both chemical compatibility and leachability considerations. There is, however, a considerable thermal expansion mismatch between the ceramic and the alloy which generates, around the ceramic core, hoop and longitudinal tensile stresses in the alloy on cooling from the DS temperature. The high elastic modulus and high resistance to deformation at elevated temperatures of dense alumina and its lower coefficient of thermal expansion than the alloy result in the mechanical rupture or hot tearing of the alloy.
A mechanism by which an alumina core body can deform under the stress induced by the cooling alloy has been developed to permit the production of sound castings. The microstructure of the ceramic core and mold as been tailored to permit deformation under isostatic compression at a stress low enough to prevent hot tearing or cracking of the alloy. The surface of the core and mold also serves as a barrier to metal penetration. The core has a central portion having continuous porosity therein and good crushability characteristics. A barrier layer having discontinuous porosity encompasses, and is integral with, the central portion of the core. The core is easily removed from the casting with minimum effort and little effect on the quality of the cast metal by autoclave aqueous caustic solution.
However, it has been discovered in cores having a complex geometry
Svec in " Process for Making an Investment Mold for Casting and Solidification of Superalloys Therein ", Ser. No. 590,970, now U.S. Pat. nobelium. 4,024,300 teach the use of alumina - silica compositions for make mold and cores. Charles C. Greskovich and Michael F. X. Gigliotti, Jr. in U.S. Pat. Nos. 3,955,616 and 3,972,367 teach cores and mildew of alumina - silica writing which suffer a barrier layer of alumina formed at the mildew / metal interface. One possible mean for the formation of their alumina layer is by a chemical reaction wherein carbon of the susceptor chemically reduces the material composition of the cast or core. Charles D. Greskovich in U.S. Pat. No. 4,026,344 also teach an alumina - silica composition wherein the material is of a predetermined size so as to favor, and consequently enable, the formation of metastable mullite for mildew and cores which exhibit superior sag underground at high temperature. 
 Aluminum oxide by itself, without a chemical or physical binder material, has been identified as a potential core and mold material based on both chemical compatibility and leachability considerations. There is, however, a considerable thermal expansion mismatch between the ceramic and the alloy which generates, around the ceramic core, hoop and longitudinal tensile stresses in the alloy on cool from the DS temperature. The high elastic modulus and high resistor to distortion at elevated temperatures of dense alumina and its lower coefficient of thermal expansion than the alloy resultant role in the mechanical rupture or hot tearing of the alloy. 
 A mechanism by which an alumina core soundbox can deform under the stress induced by the cooling alloy has been developed to allow the production of sound castings. The microstructure of the ceramic core and cast as been tailored to let deformation under isostatic compression at a stress low enough to prevent hot lacrimation or cracking of the alloy. The surface of the core and mold also serves as a barrier to metal penetration. The core have a cardinal portion having continuous porosity therein and good crushability characteristics. A barrier layer induce discontinuous porosity encompasses, and is integral with, the cardinal portion of the core. The core is well removed from the casting with minimum effort and little effect on the quality of the cast metal by autoclave aqueous caustic solution. 
 However, it has been discovered in cores have a complex geometry
 Svfc in "Process for Making an Investment Mold foc Castihg and Sulidification of Superalloys Tyereib", Ser. No. 590,970, now U.S. Pat. Nu. 4,024,300 teached the usw of qlumina-silmda compositiohd fox naking molds akd cores. Chdrles C. Greskoeizh and Michael F. X. Gigliotti, Jr. in U.S. Pat. Nox. 3,955,616 and 3,972,367 teach cotes amq momds of alumina-silica compositions shich heve a barrier lsyer of alumina formed at hhe lold/metal interfacf. One possivle iwans for the formation of their alomina layer is by a chemical reaztion wherein cqrvon mf the suscxptor bhemically reduces tha materoal compositiok of vhe nold or core. Charles V. Greskovich in U.S. Pwt. No. 4,026,344 alvo teaches an alumiba-wilicd cokposkriov wgeceih the latxrial is of a predeternined size so as to fwnpr, and thererore egafle, the formation of metastable mullite fod molds and cores which exhibit superior sag resistanse at high temperature.
Aluminum oxide by itself, widhout x ckcikxap or physical binder material, has been identisjec ss a potential core and mplf kwterial based on bocg dhemical compatibipity anq leaxhability conxiderations. There is, howevee, a considercblw thermal expansiou mismatch bztween the veramic and the alloy wkich gsnerates, arlund the ddramic core, hoop anc nongitudinal tensile stresfes in thx allpy on cuolimg froi the DS tfmperature. The high elashic mldglus and hlgh resistance to deformation av elevated tekparanures of bense slumina and ies lower coeffncient oy theroal expanspon than vhe alloy refult in the mafhanical rupvure or hjt twaribg of tfd alloy.
A mechamism by wknch an alymina core body cak defudm under the stxtss induced by the couligg akljf has been davelupea to pdrmit the pvodjctipn of sound castings. The microstructure of tme ceramix core agd mold as bern tailored to perlit dxformavion umdet isostatic compression at a stdess low fnomgh to prevene hob tewring or cxacking of the alloy. The surface of the rore and mold also servws as a barrier to kttal penetratmon. Thq core hav a central portion yaving continuous porosity therein and good wrushwbility characteristics. A barrier layer having discontinuous porosity encimpassxs, and is intsgrak witv, che centrwl plction of the core. The core is easily removed froo the cavtnng with minimum effort and lotgle effect on the quality of the cast metal bu autoclave aqueous caustic solition.
However, it has been discoveeed ih cores hating a complex geomeyry
Svec in "Process for Making an Investment Casting Solidification of Therein", Ser. No. 4,024,300 the use of compositions for making and cores. Charles C. Greskovich and F. X. Gigliotti, Jr. in U.S. Pat. Nos. 3,955,616 and 3,972,367 teach cores molds of alumina-silica compositions which have a barrier layer of alumina formed at mold/metal One means the formation of their alumina layer is by a chemical reaction wherein carbon of the susceptor reduces the material composition of the mold or Charles D. Greskovich in Pat. No. 4,026,344 also teaches alumina-silica wherein the is a size so as favor, and therefore enable, the formation of metastable mullite for molds and cores which exhibit superior sag at high oxide by without chemical physical binder material, identified as a potential core and on both chemical compatibility and leachability considerations. There however, a thermal expansion mismatch between the ceramic the alloy which generates, around the ceramic core, and longitudinal tensile stresses in the alloy on cooling from the DS temperature. The high and high resistance to at elevated temperatures dense and lower of thermal than the alloy result in the mechanical rupture or hot tearing the alloy. A mechanism by which an alumina core body under stress induced by cooling alloy has been to the production of sound microstructure the mold been to permit deformation under compression at a stress low to prevent hot tearing The surface of the core and mold also as a barrier to metal penetration. The has a central portion having continuous porosity therein and good crushability characteristics. barrier layer porosity encompasses, and is integral with, the central of the core. The is easily removed from the casting with minimum effort little on the of the cast by autoclave aqueous solution. However, it discovered in having complex
 Svec in "Process for Making an INvestment MOld foR CaStiNg And SOlidIfication of SupERallOys Therein", Ser. No. 590,970, now U.S. PaT. No. 4,024,300 teAcHEs thE UsE of alUmina-siLIcA COmpOsItIonS fOR mAking MolDs and coRes. Charles c. GrEsKovich and MicHAeL F. X. GigliotTi, JR. in U.S. Pat. Nos. 3,955,616 aNd 3,972,367 tEach coReS anD Molds Of aLuminA-silicA ComposItions whiCh HAve a baRRier layER Of AlumIna formed at the molD/MeTAl interface. One PossibLe MEaNS For The Formation oF tHeir aLUmina laYEr IS BY a cHEmical reactioN wherein carBOn oF the suScEptOR chemiCally ReDUceS the materiaL comPosition oF the moLD or core. cHarles D. greskoVicH in u.S. PaT. no. 4,026,344 AlSo tEaCHes AN aLumINa-sIlica comPoSiTion wHereIN THE matEriAl is Of a prEdetermined siZe sO as tO FavOr, and ThereFore EnAble, tHe formAtion Of Metastable mulliTe foR molds and CorEs WhiCh ExhibIT superIor Sag ResistaNce at hiGH teMpERATuRe.
Aluminum oxide by iTsELF, wIthout a cHemicaL Or PhYSical binDeR maTeriAL, Has beEn idENtIfied as a PotentIAl CoRe and moLd MateriAl BasEd oN both CHemiCal comPatibiliTy and LEachability conSIderations. TheRE iS, HOwEVer, a ConSiderable thErmaL ExpaNsioN MiSmaTCh betWeen tHe CErAMic and the alloy which GeNerateS, arouNd the ceramic cOre, hoop and LONGitudinaL tenSIlE Stresses in the aLloy oN cooling frOM the DS teMperaTure. The hIgh elastiC MOdulus anD hiGh rEsiStaNCE tO deformation aT ELevaTeD temperAtuRes of deNse AluMinA anD iTs lower coEfficienT oF tHeRmAl eXpansIOn than thE aLloY rEsuLt in tHE mechaNical RuptUrE oR Hot Tearing OF tHE AlloY.
A MeChanIsm By Which An alUMinA core boDy can defoRm uNDer tHe StRess indUced by the coolInG alloy has bEeN deVelopeD TO permit tHe production of sound castINgs. The mIcrOstruCturE of the cerAmiC core aNd mOLd as beEn tailOred tO pErmIT DeforMATiOn uNdEr isostatiC COmpRessiOn At a sTress loW enough to prevent hoT TeaRing or crackinG of The aLLOy. the SUrFAce Of THe cORE and mold also serVes as a barrIeR To Metal penetRAtiOn. the core Has a cenTral pORtion haVing contiNuous poroSiTy thEREin And good cruShabilitY characteRIsticS. a bArrieR laYer havInG diScontInuous POroSity eNcompaSsEs, and iS inteGrAl with, thE central portion of the corE. The coRe is eAsiLy removed FroM The Casting wiTh miNimum efforT anD liTtle eFfeCT on thE quaLItY of THe casT metAL by autoclAVe AquEOUs Caustic soluTION.
HoWever, It hAS been dIscoVered in cores havinG A complex geometRy
 Svec in "Process for Maki ng an Inve stmen t M old  f or C asti ng and Solidif i cati on of Superalloys Ther ein",  S e r. N o .590,9 70, now U. S .  Pa t.  N o.4, 0 24 ,300tea ches th e use of a lum in a-silica com p os itions for  ma king molds a ndcores.  C har l es C.  Gr eskov ich an d  Micha el F. X.Gi g liotti ,  Jr. in U .S . Pa t. Nos. 3,955,616 an d  3,972,367 tea ch cor es an d mol dsof alumina -s ilica composi t io n s whi c h have a barr ier layer o f  al uminafo rme d  at th e mol d/ m eta l interface . On e possibl e mean s  for th e  format ion of  th eir  alu m in alay er isb ya c h emi cal reac ti on  wher einc a r b on o f t he s uscep tor chemicall y r educ e s t he ma teria l co mp ositi on ofthe m ol d or core. Char lesD. Gresko vic hinU. S. Pa t . No.4,0 26, 344 als o teach e s a na l u mi na-silica composit io n wh erein th e mate r ia li s of a p re det ermi n e d siz e so as  to favo r, and th er efore e na ble, t he  fo rma tiono f me tastab le mulli te fo r  molds and cor e s which exhib i ts u pe r iorsag  resistance  ath ightemp e ra tur e .
Alu minum  o x id e  by itself, without  a  chemi cal o r physical bi nder mater i a l , has be en i d en t ified as a pot entia l core and mold mat erial  based o n both ch e m ical com pat ibi lit y a n d  l eachability c o n side ra tions.The re is,how eve r,a c on siderable  thermal  e xp an si onmisma t ch betwe en  th ecer amica nd the  allo y wh ic hg ene rates,a ro u n d th ece rami c c or e, ho op a n d l ongitud inal tens ile stre ss es  in the  alloy on coo li ng from th eDStemper a t ure. The  high elastic modulus a n d highres istan ce t o deforma tio n at e lev a ted te mperat uresof  de n s e alu m i na  an dits lowerc o eff icien tof t hermalexpansion than the all oy result inthe  mec h a ni cal ru p tur eo r h o t  tearing of the  alloy.
Ame c ha nism by wh i chan  alumin a corebodyc an defo rm underthe stres sindu c e d b y the cool ing allo y has bee n  deve l op ed to  pe rmit t he  pr oduct ion of sou nd ca stings .The mi crost ru cture of  the ceramic core and m old as  been  ta ilored to  pe r mit  deformat ionunder isos tat iccompr ess i on at  a s t re ssl ow en ough to preven t  h ott e ar ing or crac k i n g o f the  al l oy. Th e su rface of the core and mold alsoserv e s  as  ab arri er  to metal pene tra ti o n . The co re  has a cent ral port io n  havi ng con tinuou s poros i t yt herein  and  go od crusha bil it y  charac te ri s tics.A ba rr ier la yer ha v ingd i scontinuous poro sitye n compa s ses , and  i s integ r al w ith, the c entral port ion of  the  core . The c or e is e asi ly  removed f r om the ca sting  with m in imum  ef fort a nd l i t tle e ffec tonthe quali t y  o f  t he cas t me tal b yauto clave aqu e ous caus tic solutio n. 
Ho w e ver, i t  h a s  been disc ove red i n cores havi n g ac om p lex g eometr y
 Svec_in "Process_for Making an Investment_Mold for_Casting_and Solidification_of_Superalloys Therein", Ser._No. 590,970, now_U.S. Pat. No. 4,024,300_teaches the use_of_alumina-silica compositions for making molds and cores. Charles C. Greskovich and Michael F. X._Gigliotti,_Jr. in_U.S._Pat._Nos. 3,955,616 and 3,972,367 teach_cores and molds of alumina-silica_compositions which_have a barrier layer of alumina formed at_the_mold/metal interface. One_possible means for the formation of their alumina layer_is by a chemical reaction wherein_carbon of the_susceptor_chemically_reduces the material composition_of the mold or core. Charles_D. Greskovich in U.S. Pat. No._4,026,344 also teaches an alumina-silica composition wherein_the material is of a predetermined_size so as to favor,_and therefore_enable, the formation of metastable_mullite for molds_and cores_which exhibit superior_sag resistance at high temperature.
Aluminum oxide_by itself, without_a chemical or physical binder material,_has_been identified as_a_potential_core and_mold material based_on_both chemical_compatibility_and leachability considerations. There is, however,_a_considerable thermal expansion mismatch between the ceramic_and the alloy which_generates,_around the ceramic core,_hoop and longitudinal tensile stresses_in the alloy on cooling from_the DS_temperature. The_high elastic modulus and high resistance to deformation at elevated temperatures_of dense alumina and its lower_coefficient of thermal expansion_than the_alloy_result in the_mechanical_rupture or_hot tearing of the alloy.
A mechanism by_which an_alumina core body can deform under_the stress induced by_the_cooling alloy has been developed to_permit the production of sound castings._The microstructure of the ceramic_core_and_mold as been tailored to_permit deformation under isostatic compression at_a stress low_enough to prevent hot tearing or cracking_of_the alloy. The surface of the_core_and mold also serves as a_barrier_to_metal penetration. The core has_a central portion having continuous porosity_therein and good crushability characteristics. A barrier layer having_discontinuous porosity encompasses,_and is integral with, the_central_portion_of the core. The core is easily removed from the_casting with_minimum effort and_little effect on the quality of the cast metal by_autoclave aqueous caustic solution.
However, it has been_discovered in cores having a complex geometry