PHYSICAL METALLURGY OF ALLOY 718 - DTIC
Alm--------DMIC Ilepori 217June 1, 1965ENOPHYSICAL METALLURGY OF ALLOY 718id965JUL 2)rh,OTtAC1- lInsttut1J
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\VDMIC Report 217PHYSICAL METALLURGY OF ALLOY 718byH. J. Wagner and A. M. HalltoOFFICE OF THE DIRECTOR OF DEFENSERESEARCH AND ENGINEERINGDEFENSE METALS INFORMATION CENTERBattelle Memorial InstituteColumbus, Ohio 43201IEIII[
TABLE OF CONTENTSPageeSUMMARY .INTRODUCTION.i.EFFECT OF COMPOSITION AND HEAT TREATMENTON MECHANICAL PROPERTIES .TRENDS IN SPECIFICATIONS .1.15.8.8MICROSTRUCTURE AND MICROCONSTITUENTS . . . . . .Freckles .Other Phases in Cast Alloy 718 .Cast Alloy .Wrought Alloy .Microstructures Obtained from Typical Heat Treatments. .and Service Conditions .STRENGTHENING MECHANISM .REFERENCES .8141419zzZ3I
PHYSICAL METALLURGY OF ALLOY 718byH. J.Wagner and A. M. Hall*SUMMARYWrought, weldable nickel-chromium-baseAlloy 718 was introduced about 5 years ago forservice at medium temperatures, i.e., to about1300 F. Though not as strong as the nickel-basesuperalloys in the 1500 to 1800 F range, its cornbination of good mechanical and fabricationproperties at both high and low temperatures hasearned it an important role in a number of aerosuace systems. It has been used for its goodcryogenic properties in cryogenic tankage forrockets; its short-time strength at temperaturesto 1200 r has permitted its use in liquid-fueledrocket -,ngines; its creep-rupture properties attemperatures up to 1300 F have enabled it to beused in fabricated parts of various aircraftturbine engines,The chemical composition and heat treatment of Alloy 718 act together in producing theproperties desired. In particular, it has beenfound that the columbium, aluminum, titanium,and carbon content have important influences.Recent information indicates that for optimumcreep-rupture properties, it is desirable tomaintain aluminum on the high side, and titanium*Associate Chief and Chief, Ferrous and HighAlloy Metallurgy Research Division, BattelleMemorial Institute, Columbus, Ohio,on the low side, at the same time using 17501'annealing temperatures.For optirniu- short-timetensile properties at cryogenic or medium ternperatures, the trend has been towards loweraluminum content, higher titanium content, andan annealing temperature of 1950 F. In all typesof applications the--e has been a tendency towardreducing the range of allowable composition.Microstructtre and rnicrocollstituents are,as expected, profoundly influenced by compositionand heat treatment. The report describes microstructure's and conditions for the formation andsolution of Laves phase (freckles), 1'i 3 Cb, gammaprime strengthening phase, and other rnicroconstituents. The nature of the Y' strengthening phaseis indicated to be a n.aetastable phase based on theNi 3 Cb composition, but w th a body-centeredtetragonal Ni 3 V structure. After overaging thistransforms to the stable orthorhornbic Ni 3 Cb.Though much has been learned concerningAlloy 718, this reortindicates that rrauch moreunderstanding needs to be obtained in order thatthe full potentialities of the alloy may be realized.
tINTRODUCTIONSome 5 years ago a wrought, weldable nickelchromium-base alloy was introduced. (1)* Primarily, it was intended for use at medium temperatures, 1300 F at most, its main applications beingin lightweight welded frames and other assembliesin aircraft turbojet engines. It filled a need for a.weldable, wrought material which the nickel-basesuperalloys were not fully capable of satisfying.Though the nickel-base superalloys have outstanding strength at higher temperatures - between 1500and 1800 F - they are quite difficult to weld.The nominal composition of Alloy 718, contrasted with Reng 41, is as follcws:Co Cr Fe Mo TiAlloy 53 -718Reng 55 1141191919 --3AlGb0.8 0.6 5.210 31.5--CEFFECT OF COMPOSITIOINAND HEATTREATMENT ON MECHANICALPROPERTIES(I-)The composition range for Alloy 718 givenin Specification AMS 5596A is as follows:Since Alloy 718 was first introduced, it hasbroadened its areas of application into thecryogenic-temperature field. Its good propertiesin the range of temperature from -423 to 1300 Fmake it especially suitable for use in the LOXL14 2 rocket engines. In these applications,Alloy 718 is used for the fuel/oxidizer injectorplates, forged rings, thrust chamber jackets,turbine wheels, bellows, and tubing.Nicomposition. This report discusses these influences, and to the extent that information hasbeen found, illustrates their interrelationships.However, no attempt has been made to present acomplete compilation of design properties in thisreport.B0.05 0.0040.09 0. 005This illustrates how Alloy 718 differs from thenickel-base superalloys: (1) substitution of columbium for much of t.e aluminum and titanium, (2) theintroduction of almost 20 percent iron, and (3) reduction of the amounts of cobalt and molybdenum,The effect of these differences is to reducethe high-temperature capabilities of Alloy 718, butin return for this loss Alloy 718 has gained weldability.The improved weldability of Alloy 718 derivesmainly from a change in composition of the principal strengthening phase, y'Igamma prime). Whilethe nickel-base superalloys are strengthene.d bya Y' phase corresponding to Ni 3 (Al, Ti), the y'in Alloy 718 is mainly Ni 3 (Al, Ti, Cb), or perhapsNi 3 (Al, Ti, Cb, Mo). Some disagreement existsas to the exact composition of the phase. In mostgeneral terms, it is described as a metastablestructure, rich in columbium, and initially precipitatinrg sAt'h.atitiS coherent with the fcc (facecentered cubic) matrix. Because the rate ofprecipitation of the Y' is relatively low, in cornparison with the rate in the nickel-base superalloys,precipitation hardening does not occur during thewelding cycles. It is this fact that accounts for thegood weldability of Alloy 718.The properties and microstructure of Alloy718 are strongly influenced by heat treatment and*References are given on pages 23 and 24.Cr17.00-21.00Ni Co50.00-55.00Mo2.80-3.30Cb Ta5.00-5.50Ti0.65-1.15Al0.40-0.80B0.0020-0. 0060FeBalanceC0.03-0.10MnSiPSCoCu0. 35 maximum0.35 maximum0. 015 maximum0.015 maximum1.00 maximum0.10 maximumVarious companies have issued specifications for Alloy 718 with chemical compositiondiffering from that shown above. These specifications are discussed later.Heat treatment of Alloy 718 to developtensile properties, stress-rupture properties,or good notch-tensile properties have andergoneconsiderable change since 1960. For background,some of the changes that have occurred arediscussed below.Characteristically, high strength in Alloy718 is developed by a high-temperature annealingtreatment followed by a lower temperature agingtreatment. The specific annealing and agingtemperature and times, as well as the rates ofcooling from these temperatures, have been altered steadily over the past 5 years.In 1960 the International Nickel Company, (2)who had developed the alloy, recommendF-d thathot-rolled or annealed (mill annealed) productsbe aged at 1325 F for 16 hours. An optimumaging temperature of 1275 F for 16 hours wasrecommended for cold-rolled sheet.Annealing temperatures of about 1750 Fwere recommended, and users were cautionednot to use annealing temperatures exceeding1800 F. Figure 1 illustrates some of the datasupporzing the recommendations.Subsequently, it was found that improvedmechanical properties could be obtained bymodifying the aging treatment. (1,3,4) Barker(l, 3)reported that aging at 1200 F for 200 hours(following the 1700 F to 1325 F treatment) couldraise the room-temperature tensile strength from180,000 to 240,000 psi. Also, a double-agingprocedure has been found to be beneficial. The
"%-May, 1961, data report of the International Nickel.()edhe -othe yield and tensile strengths without decreasingthe ductility or stress-rupture properties:(1) Anneal, age at 1325 Ffor 8 hours,furnace cool at the rate of 20*/hr to1150 F, air cool(2) Anneal, age at 1325 F for 8 hours,furnace cool at the rate of 100*/hr to1150 F, hold at 1150 F for 8 hours,air cool.200In addition, a change was made in the. rocedure. ,,.fr.properties, annealing at 1700 to 1800 F wasrecommended, but for best stress-ruptureproperties 1900 F was preferred.,s-In the course of the past few years, considerable data have been accumulated showing theeffects of annealing temperature, aging temperature and times, and chemical composition.Nevertheless, the present situation is that thematter is still unsettled. One reason is,undoubtedly, that the data have not always beenconsistent. One reason for the lack of consistencyseems to have been that the optimum heat treatment depends on the chemical composition,particularly the aluminum content. This isillustrated in Figure 2, which is plotted from datain a Iatrobe Steel Company report. (5)190"180nieStrength170190160 10Annealedand Aged-.-'r 8150CL.140.-.l.'o. 0.2 Yield-o 170,0-srer'gth120C160C1S1100na2-L Annealed at I700F,I hr,air c9oled; aged0at 1325F,B hr,cool at 100 /hr to 1150F;150-age atll5OF,8hr,aircool.oO Annealed oa1750F, aged as above0j3 Annealed at 1800F,aged as above0908140e-0e70 1306020.%Yield50Srnt0.240FIGURE 2.30200.30.40.50.60.7Aluminum Content, percent0.8YIELD STRENGTH OF ALLOY718AS A FUNCTION OF ALUMINUMCONTENT5Latrobe Steel Company data( )10j70160017001800190020002100Annealing Temperature, FFIGURE 1. EFFECT OF ANNEALING TEMPERATURE ON THE ROOM-TEMPERATURETENSILE PROPERTIES OF ALLOY718 - ADAPTED FROM A 1960BROCHURE( 2 )Annealed for 15 min; aged at 1325 F for 16 hr.Eiselstein(b) made a systematic study, ofthe effects of changes in the titanium, aluminum,boron, and columbium .content on the mechanicalproperties of Alloy 718. He found, as expected,that the effects of chemical composition weredependent on the heat treatment. The effect ofaluminum content on the room-temperatureyield strength was a function of both the annealingtemperature and the aging temperature. Whenthe alloy was heat treated as follows:
Anneal: 1750 F, 1 hr, air coolAge: 1325 F, 8 hr, furnace cool atrupture properties are needed. If the aluminumcontent is not low, howvei, th-e 1750 F annea.-20 * /hrto 11 50F, air cool.20/rt10,arco.mentin combination w ith a 1325 to 1350 F aging treatseems preferable.the titanium andit was found that increasingcolumbium content within the specification rangeincreased the yield and tensile strengths at roomtemperature and at 1200 F. The elongation wascorrespondingly decreased. Increasing alumninurn,on the other hand, seems to have lowered thetensile and yield strengths, without affecting theelongation. Boron had a slight adverse effect onroom-temperature tensile strength but increasedthe elongation.At 1300 F, increasing the titanium contenthnczeased the tensile and yield strengths, whiledecreasing the elongation. Increasing thealumninum content over 0.7 percent resulted in aslight increase in tensile strength, accompaniedby a decrease in the elongation,The effect of columbium content on thetensile properties is shown in Figure 5. Often,when speaking of colbmnbium, the term columbium tantalum is used. In such a case, the tantalumcontent can be considered to be 10 percent of thecolumbium content. The figure shows a regularincrease in yield strength as the columbiuni tantalum is increased from 2 to 6 pfrcent, forthe annealed and aged material. As annealed(not aged), an increase in tensile and yieldstrengths %as also observed, which is indicativeof some solution strengthening.Although Figure 5 shows some advantage incolumbium. contents above 5 percent with respectto tensile strength, the ductility drops noticeably.Therefore, composition limitations were first setat nominally 5 percent columbium. Exdstingspecifications allow up to 5.50 percent columbium.Table 1 summarizes the results c" someof Eiselstein's experiments on the effects ofaluminum and titanium.Figures 3 and 4(7) show the effect ofaluminum content on the room-teraperature tensile properties of Alloy 718 annealed at 1750 or1950 F, and then aged at 13Z5, 1350, 1375, or1400 F, followed by aging at 1200 F. Thesefigures show how intimately related are the heattreatment and composition. For the highestyield strength, the optimum combination wouldbe: low aluminum, 1950 F anneal, and a 1325 or1350 F aging treatment. However, in rupturetesting, specimens with this chemical compositionand heat treatment are notch brittle,The combination of low aluminum content,high annealing temperature, and relatively lowaging temperature is also good with respect tofatigue life and short transverse properties butis not desirable when optimum long-time stress-Carbon in amounts between 0. 01 and 1percent was found to reduce the yield and tensilestrengths at 1300 F. Presumably, this decreaseis the result of reduction in the effective amountof columbium, which is tied up by the carbon.Smnooth-bar rupture life appears to dependmore on the annealing temperature than on thechemical composition. In investigating the effectsof boron, titanium, aluminum, carbon, andannealing temperature ( 1325 F age, 8 hr, furnacecooled to 1150 F, air cooled), Eiselstein( 6 ) foundthat increasing the annealing temperatures from1750 or 1800 F to 1900 F increased the rupturelife more than did compositional changes whilethe annealing temperature was held at 1750-1800F. With the 1900 F anneal, compositioaial variation was more important than when the lowerannealing temperature was used, In general, itTABLE 1. SUMMARY(a) OF THE EFFECT OF VARIATION OF THE TITANIUM AND ALUMINUMCONTENT OF ALLOY 718(6)ElementRange ofVariation,percentTensile StrengthRoom12001300TempFFTitanium0.6-1.3 Aluminum0.4-0.9--00.1-0.8 (Over0. 7%)Yield StrengthRoomIZ001300TempFF RoomTemp--0(a) , increase; -, decrease; 0, no change.Heat treatment: 1750 F, 1 hr, AC 1325 F, 8 hr, FC at ZO0/hr to 1150 F, AC.Elongation1200F1300FI-
40.2% Yield Strengtho 17008Annealed o! 1750 F/lhr,AC,and aged as follows:hcA- 1325 F/8 hr, FC,100*/hr0 1350 F/a hr, FC,100 */hr00 -1375 F/8 hr, FC,100*/.NrV -l4O00F/10 tvrFC, 00*/ hr160ototototo1200 F/S1200 F/81200 F/S1200 F /8hr,AChrAChr, AChr, ACElongation1325 IF00150-20* 14N -0g;1400 FI13011350j2-W35 F00040.203040506070.809Aluminum Content, per centEFFECT OF ALUMINUM CONTENT ON THE ROOM-TEMPERATURE YIELD STRENGTH OFALLOY 718 HOT-ROLLED BAR STOCKFIGURE 3.19040010.0OAnnealed at 1950F/Ihr,AC,and aged as followstA- 135 0*h1616 0C-20/rC31350 F/8 hr, FC,100 */hr to 1200 F /8 hr, ACO3-1375 F/8 hr, FC,100 V/hr to 1200 F /8hr. ACV -1400 F/tIhr,FC,100 */hr to 1200 F /8 hr, ACOpElongation150,7,Qr200014010C1300.1FIGURE 4.0.20.30.40.50.6Aluminum Content, per cent0.70.80.9EFFECT OF ALUMINUM CONTENT ON THE ROOMV-TEMPERATURE 0.2% YIELD STRENGTHOF ALLOY 718, HOT-ROLLED BAR STOCK
of the relationships, and suggests why more daaare needed. Meanwhile, specifications forchemical composition and heat treatment haveundergone many changes since the alloy was firstdeveloped. These specifications are discussedin the next section.220200Tensile StrengthS180TRENDS IN SPECIFICATIONS-160(D)Specifications for Alloy 718 have beenissued by a number of companies,( 8 - 15 ) who140-intend.120using the alloy in different kinds of service.In the main, the service for which the alloy isintended can be grouped into the following categories:Q02% YieldStrength-100108(1) High temperature, requiring good shorttensile properties-timeW 80CLSReduction" 400.2-20(3)tiIIS0Q:(2) High temperature, requiring good creeprupture propertiesCryogenic, requiring good tensile properties and toughness.The major application for the material in0I2345678Cb To Content, per centFIGURE 5.ROOM-TEMPERATURE TENSILEPROPERTIES OF ALLOY 718 AS AFUNCTION OF COLUMBIUM ANDTANTALUM6 CONTENT (AfterEiselstein)( )the first category is in the hot parts of liquidfueled rocket engines. Aircraft turbine enginesare the main applications for the second category.In Category (3) fall such missile hardware ascryogenic tankage and piping. These applicationsare sometimes called out in the specificationsthemselves, as indicated in the following quotations from some of the specifications:8AMS 5596A( )"2.was found that in 1300 T, 75,000-psi rupturetests(1) Titanium had little or no effect on thesm
PHYSICAL METALLURGY OF ALLOY 718 by H. J. Wagner and A. M. Hall* SUMMARY Wrought, weldable nickel-chromium-base on the low side, at the same time using 1750 1' Alloy 718 was
HAYNES HR-224 alloy HAYNES HR-235 alloy HAYNES NS-163 alloy HAYNES R-41 alloy HAYNES Waspaloy alloy HAYNES X-750 alloy STELLITE 6B alloy HAYNES 25 alloy HAYNES 75 alloy HAYNES 80A alloy HAYNES 188 alloy HAYNES 214 alloy HAYNES 230 alloy HAYNES 242 alloy HAYNES 244 alloy HAYNES 263 alloy HAYNES .
HASTELLOY G-3 alloy 0.935 HASTELLOY X alloy 0.925 HAYNES HR-160alloy 0.910 HAYNES 214 alloy 0.906 HAYNES 230 alloy 1.010 HAYNES 242 alloy 1.019 HAYNES 263 alloy 0.941 HAYNES 625 alloy 0.950 HAYNES 718 alloy 0.925 HAYNES 188 alloy 1.009 HAYNES 25 alloy 1.028
Inconel 718 alloy is estimated to increase from -100 o C to a specific temperature below -100 o C. Therefore, Inconel 718 alloy is considered a pertinent material fo r the production of Lox Pi pe under cryogenic conditions. Key words INCONEL 718 alloy , cryogenic tensile test, rocket engine, of lox pipe, high strength alloy, gas tungsten arc .
Metallurgy is the art or science of separating metals from their ores, making and compounding alloys, and working or heat-treating metals to give them certain desired shapes or properties. Metallurgy has been broken down into three branches—chemical metallurgy, physical metallurgy, and mechanical metallurgy
Keywords: Alloy 718, Oilfield Equipment, Stress-corrosion Cracking, Microstructure . Abstract . Alloy 718 (UNS N07718) was developed for use in the aircraft gas turbine engine, but its unique . drilling (MWD) tools in which sophisticated electronic instruments are contained by an alloy tube that must be both strong and non-magnetic.
718. They found that both solution annealed and fully heat treated 718 began to melt when heated to the alloy's NST. Initial liquation was observed both *Also known as Inconel 718. intragranularly and intergranularly adja cent to niobium-rich MC-type carbides. Welding hot cracks in Inconel 718 have been studied by R. Vincent (Ref. 27) using
Chemical metallurgy The scientific approach to metallurgy involves chemical and physical metallurgy. Chemical metallurgy deals with the domain of the reduction and oxidation of metals. It is the science of obtaining metals from their ores, and of the consideration of the
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