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'ENGINEERING RESEARCH iNSTITUT.E I fr UNIVERSITY OF MICHIGAN __ ___ ' PR1 &3carESS BE.POPT TI: NATIONAL ADVT7.SOi:Y COmMIEE- FOP AERONAUTICS, ON TELXT IN TaCT TM JPEALOIWW OF TALANDALLOY FB USE IN TEiE fIGC T f IE CO,Nr' T ENGWK, GAS 7$ JITNS BY The Enr iering Eesearch T"ti ttte of.Te University of M ichi'an Jtnel.. 1'9)0 tuLti- o aec t e o. t, -Of t of. I,. j- tto establish.he influence of prior tre'tnent can 2'emica.l cmpocition on th high-tefer-" ature strength of wrought heatsrc iBi no alioge on a fnoaucxtal basis. Clarifj. cat ion of the princif: ivoled out Zo that producers fabricators, dweilsoo a:nd opci at w ti derrtaad the t pricncipal effects of the various fact-rA invo.lved in the nprc:u. ctlox an u e of ch al alloys for aircraft prop usi n ryr te, ccesful cC) n..tt o-t cf 0the O 'pri should lead to: (1) fundarme.;ta&ll4:cord short-tkim:,e etho.es of et.ima t i n propertie a4t l: 'i emp.av 'c:; (2) unl..foritv aid ordi ctab l.ty of properties; (2)) clarify the oxfacte of coanditicona o rf uproduction and fn alI treatmaent BO that. ar cpft,' uptw rpe, a...t poss, ile w1"ill be I nsured for eca llo'y a ( ') cm Vc trflence al lI.Utfttine of chemca.al

ENGINEERING RESEARCH INSTITUTE Pae Pags 2 UNIVERSITY OF MICHIGAN composition so that the eost efficient use can be made of the scarce and expensive alloys involved. The procedure being used is to: (1) Obtain systematic data on the relation of prior processing, final treatment, and variable chemical composition to strength properties at high temperatures. (2) Determine the frundaiental srystalline structural conditions resulting from these variables which control properties at high temperatures. (3) Determine th.e fundamental structural changes occurrin during testing. (4) Concentrate at first on one alloy, low carbon N1l5. The fnldamental principles involved are then being checked against four other typical alloys; Inconel-X, Tinken 16-2 —6, 816l and 19-9DL. (5) Guide all experimentation by the most recent theories and techniques of the solid state physics of metals as related to properties of alloys at high temperatures. Effort is devoted to the development of techniques required to apply suLch principles to ongineering alloys. The various actual experimental inavestigations are briefly described in the following sections.

ENGINEERING RESEARCH INSTITUTE p UNIVERSITY OF M ICHI.GAN I tELATION OF kEAT TREATMENT.AH) HOT-COLD WORK TO HIGHEI E4PATJP ROPE TIS, OF LOQW-CABBON N155 ALLOY (1) One report was previously submitted showing the influence of conditions of solution treating, aging and hot-cold working on the rupture properties of low-carbon N155 alloy at 12000F. A second report of this type, entitled "Properties of Low-Crbon N155 Bar Stock from 1200 to 1800OF" will be submitted about June 1, 19'0. (2) The first report showed the results of systematically varying the treatment conditions on the rupture properties at 1200~F. The second report extends rupture data for five typical treatments to 1800~F and gives creep and stress-time for total deformation data at 12000 to 1500DF. (3) Conclusions were that general trends for various types of treatments can be established by this procedure; but absolute values are variable between different lots of stock. It appeared that differences in hot-working conditions may be respuonsible for variation of properties after similar treatments and that thi effect is not minimized until a high temperature solution treatment is used. Sigma phase formation controlled by hotworking conditions may be the cause of the variations. Further work of this type is not contemplated because the amount of testing required for significant results is impractically large. Effort should be concentrated on fundamental structural studies which should provide short-time methods of estimating effects.

ENGINEERING RESEARCH INSTITUTE U_________ UNIVERSITY OF MICHIGAN jPe II. FUNDAMENTAL EFFECTS OF EAT TREATMENT AND HOT-COID WORK ON TBE PROPERTIES OF HEAT-RESISTANT ALLOYS (1) Reports have been issued which relate internal lattice strains and microstructures in solution treated and aged low-carbon N155 and InconelX alloys to short-time creep and repture properties at 12000F. X-ray diffraction line width and intensity measurements combined with electron and optical microscopic methods were utilized. (2) This approach has been extended to include cold work and hot-cold work effects in low-carbon N155 alloy. A report entitled, "The Fundamental Effects of Cold Working on the Creep Properties of Low-carbon N155 Alloy" will be issued about June 1, 1950. The results showed a good correlation between internal strain from cold work and creep resistance, except for samples worked in the temperature range from 1600~ to 20500F. Abnormally low creep strength for the observed internal stress, as measured by X-ray diffraction line widths, was observed for the latter samples. Indications were that the introduction of internal stress to the lattice by cold work is' opposed by relief of stress by relaxation at high temperatures. The tendency for relaxation is increased by increasing amounts of reduction. Increasing the temperature of working increases the amount of strain relief during the working process. Aging after cold working reduces creep etrength primarily by relaxation of internal strain,

ENGINEERING RESEARCH INSTIT'UTE UNIVERSITY OF MICHIGAN 3 Thus, there is an optimum amount of cold work of about 20 per cent reduction for creep strength at 1200~F and probably an optimum at smaller reductions for creep resistance at higher temperatures. Temperature of reduction apparently has little effect up to about 150OOFo Above this temperature relaxation occurs rapidly during working and the material is not effectively cold worked. Very little relaxation takes place at 1200~F with reductions up to 40 per cent at room temperature. Thus, cold work effectively improves the creep resistance of low-carbon N155 at 12000F. Relaxation does occur during aging at 1400F and occurs rapidly at higher temperatures. Thus, strengthening from cold working will not be maintained for long time periods at 1400I F (or at temperatures above 1200~F). The length of time strengthening from cold work will be maintained at temperatures above 12000F is a function of the rate of relaxation of cold-work stresses. This in turn is a function of the inherent resistance of the matrix to reiaxation, the degree of reduction, and apparently the treatment prior to cold work. (3) The work in the report on the fundamental effects of aging on low-carbon N155 alloy has beern extended in answer to several questions which were raised. in regard to the original report. (a) Long time creep tests were carried out and the conclusions in regard to the effect of aging were unchanged over those from short time test originally reported. (b) The stability of prior formed precipitate configurations at 1200"F under stress was checked and found to be very high. Thus, whatever precipitate configuration is formed in low-carbon N15 by prior aging at temperatures above 1200~F can be assumed to be that configuration which holds during creep at 1200~F1

ENGINEERING RESEARCH iNSTIT'TE T -; ____________ UNIVERSITY OF MItCHlGAN l 6 (c) X-ray diffraction line extinct ion rneas remente were made on various aged low-cerbon N155 samples to obtain the depenece of extinction upon aging conditions. Th'i inforrat ion is felt to be more undamental tlan the pre silou.sly reported diffract ion line heigtits from the sseae set of samples. The conclepl ions reached to date 'a that aging apparertly increases e,salc size of tie lattce at the same te it s reducing he creep resistance. It is possible that this is the fndazaenral reason why aging of low-carbon N155 lowere the creep resistaence and furtaier, that the incongrous atoms are not in rendomn solid ecltt ion but are congregated along mosaic block surfaces. (4) The data In the report entitled "The Fundeamental Aging Effects Influencing the High Temperature froperties of Solution Treated Inconel-X Alloy" re being extended to inclitse study of double aging effecte and aging during testing. (5) Generality of the results of the study of the fundamental effects of aging on the creep properttie of low-carbon N155 alloy Is being checked by applying the sas e techniques to other tp ical alloys. The results of a Similar investigationi of the strongly age-hardenable alloy Inconel-X have been reported. At the present time a similar program is In protgess on Tnlken 16-25-6, S816 is being procured, and 19-)1L will be included later. The objectives of the progra. is to determine if aging improves strength at high temperatures by introducing precipitation stresses or if the precipitation process is such that it merely removes strengthening atoms from solution. Inconel-X was of the former type and low-carbon N3l35 of the latter. Timrken alloy is a. lower alloyed material than low-carbon Nl15, allo y. Sol6 is more highly alloyed and aay be i:termediate to Nl55

ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN Pa 7 and Inconel-X in its behavior. 19-9DL is a low alloy material involving a border line austenitic-ferritic matrix. (6) All of the fundamental studies point to the ability of an alloy to resist strain relief (strain from mechanical cold work, aging precipitates, or from odd size atoms in oolution)as one of the most important factors in the creep resistance of alloys of the type being considered. This was particularly evident in the results of the fundamental studies on cold worked N155 alloy. The effectiveness of cold vork in improving creep resistance appeared to be dependent on the rate at which broadened X-ray diffraction lines were sharpened at elevated temperatures. This can be interpreted to mean that the rate of internal stress relaxation at elevated temperatures is important to creep resistance, inasmuch as most of the c-eep data correlated with line broadness. A program is therefore in progress to study the relationship of internal stress relief characteristics to creep resistance. Alloys made by adding tungsten in 2 per cent increments up to 8 per cent to a 0.12C - 1.7 n- 0.5 Si - 20 Cr -20 Ni - 20 Co - 0.1li - balance Fe base are being used. X-ray diffraction line broadness as a function of various conditions of rolling and line sharpening as a function of annealing conditions will be related to creep resistance. In addition, relaxation creep tests on anealed stock will be made to determine if this characteristic can be related to creep resistance and the effectiveneso of cold work for a given temperature of service. (7) Identification of excess constituents has been limited to development of radio-active isotope tectnitqgues for high resolution autoradiographs. Early promise of this type of an approach has been complicated by chemical precipitation of silver from the emulsions by the metals in the

ENGINEERING RESEARCH INSTITUTE t ___~___________ |UNIVERSITY OF MICHIGANi Pge 3 alloys. At the present time, it appears that these difficulties have been overcome and that it will be possible to apply the method to alloys of interest to this program in the near future,.

ENGINEERING RESEARCH INSTITUTE UNIVERSITY OF MICHIGAN Page Ii. INFLUFNOE OF I'ONS IAL T T TME..mt.N.ERT~s'is OF S'.J143t,!.T.TGH '11111'C,'.ttwiR /' S uroegtht alloye t o )have te qute va,able properties I the hostworked comrlitton. Thisa viabiltv io carr:icd over after a fanal treatment tnliess t.hat final treatment c.si s Lo a sot t ion treatsent at a. sufficlently high $tempersat;ure to IVL.s..ie the effecfts. of xariabe.le p>rior processi ing. In practice, etuch alloys nare nt u ^..eod in, te as-hot worked condition, or are finally tr-eated t tecrat too ioe to tbe tfree of variability from. hot workiing Tnese sfactorse ba Lcelreved to be the major reaaons for the scatter-bands for any o.n al.. io: with a sin;l.e treatment. A. progrm s t.hV.'ereffore, ui.tertake1tn tO ectabl the relationship between h ot-working condrl titeons and roertiee in t.e hot w(or)oed condition and after subseq;.Uenxt hot-cold 1work anrd/or heat treatment.t, In view of tlhe variation between e the, t a thats of lw- carbon N15 a:loy in t rep-ol~t eA tilod "Prpcertiee of Lotw-Carbon 11 55 Bar Stock f ro 1200" to i,800"F0', F t atrpeare rnrccea. y to Ktain b: itc i Sfrmation of th is tyype before r e ia ble t. i ca, d tall cn be ectab iW o sluc &ll oyI, Furthermore, a q2ulck meth.icx of estimating: thte condit ontLs of alloys ought to be poos ible once t. f',da:en. ' tal etru.ctxztral. eaLns are cl ar:ified e The resuit of t le OBfxn t Q rle eo tLe4: ea' fef t oef tefcT tfre of wo zking low-carbon N1i5 alloy in th'e rep orti te F'iln::iarltal Eff.ecte of Coald eWorkin on the Creeo Propertieo- of Locr-Coar bon, U15 Al.o" -poluIts to the eddte necessity for s>~a r purog':ram in viea w of the abnotc.rial ly Jhigh reo. rates of.stochk rolled 1 oper cen1t hetwee 'On 1O"" a O ~F e exerint pgrao m Is e bel; cve h lpCeCd to ahow the rl.ation': 'tw:,en reia. of

ENGINEERING RESEARCH INSTITUTE - P.Ige i0 ___UTNIVERSI'TY OF.MICHIGAN. I reduction, amount of reduction, and the effect of reduction over a range of temperatures. The stock being used is 7/8 inch square low-carbon N155 bar stock from previous programs. t 18 being solution-treated 1 hour at 2200'F prior to hot-working to mIninize effects from prior hot work. (1) Samples of the solution-treated stock arc being rolled under the following cronditions: (a) Twenty-five per cent at 1300o, 2000, ard 2200F in two passes. (b) Forty per cent reduction at 1800", 0000~ and 2200~F obtained by first reducing 15 per cent in two pasces, reheating and reducing 25 per cent more in two passes. (c) Partial simultation ofg ove a ranige of temperature by reducing 15 per cent at 2200"F, allowing stock t to cool to l800~F in a furnace and then reducing 25 per cent more. (2) High-temperature strength is now being evaluated by: (a) Bupture tests at 1200~ and 15000 out to 1000 hours, inasmuch as prior experience indicates that the effect of hot-working conditions on rupture properties can best be shown by the slopes of stressrupture time curves. (b) Creep resistance in the rupture test is being measured and creep tests will be made at lover stresses. (c) Room temperature tensile and hardness properties are being established. (3) Testing has been limited tc the as-rolled condition and after a solution treatment at 2200"F plis 24 hour age at 1400F,. It is expected that these will be extcncd to inc lude an intermediate temperature of solution treatment aad an intered lte temperature of solution treatment

ENG;INEERING RESEARCH IN"STITU. T, ___ ______''______....____. _____UNIVERSIrY O' iCH! AN plus hot-cold work, The data are as yet too incomplete to show trends. The as-rolled material should show the greatest variability in properties of any treatment except subsequent hot-cold working. Solution treating at 2200~F and aging serves to check the assrmption that a 2200F treatment minimizes variability in prior processing as well as a base line for evaluating the influence of the hot-working conditions, If further testing demonstrates that the 2200~F treatment can be relied upon to be free of the influence of prior processing conditions, it will be omitted from the program. (4) X-ray diffraction and microscopic studies will be made to establish the fundamental causes for the influence of hot-working conditionse

ENGINEERING RESEARCH INSTITUTE Page 12 UNIVERSITY OF MICHIGAN IV. FUNDAMNTAL STRUCTURAL CHANGES DURING CREEP AND RUPTURE ESTING This entire investigation has been confined to the r6lationship of structural conditions prior to testing to the creep and rupture test data. Studies of the structural changes induced by testing conditions have not been made to any large extent. Consequently, questions have existed regarding certain aspects of the results: (1) Interpretation of the data has been based on current theories of the mechanisms of creep. These theories have largely been based on socalled pure metals or simple alloys..Little information of this type is available for complex engineering alloys, like those used in this investigation. Analysis will therefore be made of the types of lattice distortion occurring in the creep and rupture specimens during testing. Priqr treatment and chemical composition will also be varied. Particular attention will be given to determining if the prior internal structural conditions of the alloys should be related to the type of mechanism associated with primary or secondary creep and the effects of the structural changes during primary creep on the subsequent secondary creep. (2) Precipation effects during testing have been somewhat superficially studied by metallographic examinations and limited X-ray analysis of the aging of solution treated and aged low-carbon N155 alloy during testing at 1200~F. The development of a structure resembling sigma phase during testing of low-carbon N155 alloy at 13500 and 1500~F from one heat and not from another, the two heats differing only in finishing temperature of hot-rollingstrongly suggests that further work should be done on precipation effects during testing at temperatures of 13500F or above. This was supported by the results obtained by working N155 at various

ENGINEERING RESEARCH i.N3ST1MTTE I P UNIVERSITY OF MITCHIQAN - I ' v temperatures and finding that creep resistance was abnormally low after working in the temperature reang fro 1600 to 2050 F. It is therefore planned to stuidy siima phase formationr during testing by more thorough microscopic mrethods, and by X-ray diffraction techniques and to consider other possible method.s of obtaining information of this type.

ENGINEERING RESEARCH INSTITUTE. e. UNIVERSITY OF,MICHlIAN Ii V. INFLUENCE OF COMPOSITION ON PROPERTIES AT HIG TEMPERATURES (1) One report entitled "An Investigation of the Influence of Chemical Composition on Wrought Cr-Ni-Co-Fe-Mo-W-Cb Alloys in the Solution Treated and Aged Condition as Related to Rupture Properties at 1200'F" was submitted under date of October 26, 1949. The NACA has approved this report for a Technical Note. (2) A similar report on the 100-hour rupture properties at 15000~ is being prepared and should be submitted during June 1950. (3) Tests are in progress to extend the stress-rupture data for all of the variable composition alloys to 1000 hours at both 12000 and 1500F. (4) A program has been started to determine the fundamental internal crystalline conditions associated with modification of high temperature strength by the addition of alloying elements. The initial approach to the problem consists of makinls in te intensity measuements of Xray diffraction lines from which mosaic block sizes and random atomic displacement of tChehmatrix, if a as influened by chemical composition (can be evaluated Lattice parameter and hardness measurements together with electron and optical microscopic studies.will be used to evaluate precipitation effects. Creep and rupture tests at 1200~ and 1500F will be correlated with the structural measurements. The type.alloys in the initial program include: Chemical Composition (Weight Percent) C Mn Si Cr Ni Co Mo W Cb N.12 1.7 0.5 20 20 20 0 0 0 0.12.t tlt it tl ft I tt 1 r tt tt tl t~ ~ T* tt It It 2k tt f it tt IT It it tt t ft. tt t t t tt li 4 t4 it It it it t it It t It It It It, f1 2 O tI l t.t it t tt 4 ti I tl It. ' II It tI it 3 1 tt

ENGINEERING RESEARCH INSTITUTE E UNIVERSITY OF MICHIGAN Page The alloys are being prepared as II pound induction furnace heats and forged using procedures developed in the first part of the program. This program has been initiated because the work completed under Items 1 and 2 did not show the fundamental reasons for the pronounced influence of the elements being considered on the rupture strengths beyond the indication that the primary effect of columbium was to increase deformation prior to fracture and the other elements increased creep resistance, The latest theories of the physics of the solid state and plastic flow indicate that mozaic block size and random atomic displacement effects from alloying elements might be fundamental properties of metallic lattices through which it might be possible to systematize high temperature creep data. (5) A report entitled "The Rupture Properties of Low-Carbon N155 Alloy Made With A Columbium-Tnntalum Ferro-Alloy" was submitted under date of April 14, 1950, showing that no significant effect was found for the substitution of a columbium-tantalum ferro-alloy for ferro-columbium when the alloys were solution treated at 2200'F and aged at 1400OF.

UNIVERSITY OF MICHIGAN 3 9015 02652 8045