Journa l of R esearch of the Nati onal Bureau of Standa rds Vol. 53, No.6, December 1954 Research Paper 2551 Creep of High-Purity Nickel William D. Jenkins, Thomas G. Digges, and Carl R. Johnson study wa s mad e of the creep behavior in tensio n at 300 0 700 0 900 0 and 1 200 0 F of initi, !I y annealed high-purit y nickeL Di sco ntinuou s flow was in of' the three st ages of creep , and . it was affected by s train rate , and prior-s train hi sto ry. Th e phenomenon of st ra m aglllg was especially promlll ent at 300 0 F as manifested by t he attain- ment of an appreciable creep life in s pecimens stressed in excess of the te ns il e st reno-th at thi s Th e experimentall'e s ult s are analyzed in terms of the past and t theor ies of deformat IOn of metal s. Stralll hard enlllg, recovery , and t he initiation , propagation , and types of fr act ur es obtamed dunng creep are further evaluated by mean s of true-st ress- tru e- st rain and hardness data obtained at room tempe ratur e and by metallograph ic examinat ion of th e fractured specim ens . I. Introduction Numerous equalic,.ls hlwe been proposed by ana- lysts of creep daLa .·,S descriptive of the extension- time relationship i.n the ereep of m etallic mat erials. Th e equations arc mod ified and new ones R ]' e pro- posed as expel'imenL" 1 results are accumulated. To da te , however, no LheoretieRl Lreatment of the com- pl ete extension-time "elation is uuivel' sRlly Rc ceptecl, and there is st ill need for Rdditional precise data from experiments ealTied ou 1.. und er aCCUl'Rtely controllecl conditions. Th e int err elation of s train hard ening, recovery, and recr ystallizaLion are not fully under- s Lood, and the import ant role of the th ermal-me- chanical his tory on creep behavior ha s not be en gen- erally recognized. Any adeq uale pbysical Lheory of the mechanism of plasLic now in creep mu st acco un t for Lhe influence of all Lhese 1'acto1's . Th e present tests on high-purity nickel were made as one phase of a proj cct to st udy Lhe mechanism of creep in polycrys Lalline metals a nd to evaluate the creep bel HtVior of these metals in com- paris on with binary alloys of such metal s. Th e com- prehensive program mclucles a st udy of th e creep charRcteristics of high -puri ty copper, high-purity nickel , and allo ys of these two metals. As pre- viollsly point ed out [1]/ the relatively low tempera- tures at which creep may occur in each of these metals, the unlimi ted solid sol ubilitv of the two metals in each other , thp availabili ty 'of co mmercial metal of high purity , and the wide industrial applica- tions of both the metals and Rlloys made the binary system an attractive one for use in the present iH- vestiga tion. The present pRper is concerned with the results of creep tests made on high-puri ty nickel Rt 300°, 700°, 900° , and 1,200° F, the influence of rat e of lo ading to selected creep stresses on creep be havior , and the eff ect of prior-s tra in h i st ory on the tensile properties at room temper ature of Lhe n ickel. Contoul' and hardne ss sUlTeys were also mad e on specimens frac- tured in creep an d on spe cimens fra ct ur ed in tension at room temperature, and the microstructur es were correlated with ereep and tensile behavior. 1 Fig ures in br ackets indicate the li terature references at t he end of this paper. 2. Previous Investigations Th e re sults of cr ee p and other tesLs mad c at the KaLional Bur eau of Standards on high -purity copper, both initially as annealed and as co ld-worked to vario Ll s amount s, and on annealed high-puriLY nickel arc pre sented in several publicat ions [1, 2, 3, 4] . The results of Lension tests mad e at tempcrature s rang ing from - 32 0° Lo + 1,500° F on the same l ot of high-pu r ity nickel [3] as th at used in th e pr es ent creep te sts showed irr egularities in some of the tensile properties at teniperatu l' es of abouL 80° to 30 0° F and 500° to 700° F; s train aging occurred in the rango 80 ° to 300° F; rccovery and ]'ecryst Rlliza- Lio n predomin ated in specimens fra ctured at 1,200° or 1,500° F . Several comprehen sive summari es and appraisals of existing th eories of creep have been recently publIshed [ 5, 6] . Hazlett [mel Parker [7] included the r es ults of some constR nt-s tr ess creep tests on Iligh-p uri ty nickel ill Lheir disc ll ssion of Lll e na ture of th e croep curve. No attempt will be made, there- for e, to complet ely rev iew lh e abunrlant literature on Lhe deformation of m eLal s, but refe ren ce will be mRcl e to selected pub li cat ions that arc closely related to the resu lt s gi \T en in subseq uenl sections of III is pap er. 3. Material, Apparat us , and Pro cedures Th e n ickel wa s pr epared by indu ction melting, and all bars were processed from one 14- by 14- by 60-in. ingot. This ingot was milled, then forged to 8- by 8-in. blooms, and hot-rolled to 2 %-in. s quare billets. The billets were then hot-rolled to %-in.-diametel' bars and annealed ] 6 h I' at 1,100° F , followed by 8 hI' at 1,000 ° F . The av erage grain diameter was 0.045 mm in Lhe above con.dition as supplied by the manufa cture!'. All the specimens used in the creep test s excep t two were prepared from the SRme bar , desig nat ed as .A in tab l es], 2, and 3 i the two specimens prepared from bar E were used for check purposes. Chemical, spectrochemical, and vacuum- fusion analyses were made on specimens prepared from bar A, and the results (percentage by weigh t) were as follows: 99.85 Ni , 0.009 Cu, 0.04 F e, 0.03 Mn , 0.11 Si, 0.007 C, 0.002 S, < 0.01 Co, 0.001 O2, 0.001 N 2, and 0.0002 H 2• 329
Creep of High-Purity Nickel
May 28, 2023
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