the process of growing, so that recrystallization goes on being repeated in the ... s 1m , DynamIC recrystallizatIOn occurs In metals In which dynamic recovery 's.
Dynamic Recrystallization of Aluminium
l'~
a highdenmy· of stable phase (ZrNb)C precipitates which arise near "Nb,C particles aft o . . . , . er treatment at 1200-1300 C. The IDcreased toughness of the gram body of precIpItation of those panicles could be due, not .only to the suppressIOn of the localization of slip, but also to the higher stress re qUIre: . d f or . . ' propagatIon of a mtcrocrack [3,4] interacting with (ZrNb)C particles. REFERENCES f
1. A . D. Korotayev, A. N. Tyumentsev. M. G. Glazunov et al., (Nature of the secondary phases and rupture mechanism in aHoy Nb-Zr-C), Fiz . metal . mtlalloved., 52, 2, 377-385 (981). 2. L. M. Brown and W. M. Stobbs, The work·b,ardening of coppcr-siJica, r. A model based on imcrnal stresses wilh. no plastic rClaxation, Phil. Mag., 23, 1185-1195 (1971). 3. A . G. Evans. The strength of britrle materials, containing second phase dispersions, Phil . .~fag., 26 , D27- 1344 (1972) • .... C. A. Atkinson, Simple approxjrnation for calculating the effect of inclll'iions on fracture, Scripta Met ., S, 64)~~O (1971).
Ph)'1. Met. Metall. Vol. 52, No. J, pp. 143-1.52, 1981 Printed in Poland
00] 1- 9 18Xl81 /CflOl 4l-I OS07.50)O :0 1982 Periamon Prc.u Ltd.
UDC 669.7 1:539.37:548.53
DYNAMIC RECRYSTALLIZATION OF ALUMINIUM" •
S, P. BELYAYEV, V. A. LIKHACHEV, :\1. M. MYSHLYAYEV and O. N. SEN'KOV lnstitute of Solid State Physics, Academy of Sciences. U .S.S .R.
(Reail;ed 3J March 1980, /inal version 23 June 1980) The structure investigated is that formed during hot deformation o f aluminium by twisting in the range l00-630 c C. At temperatures below 350 0 it is round that dynamic recrystallization occurs at high level s or deformation, and appears to be the process governing piasIic deformation.
High-temperature treatment of metals and alloys is widely used in industry because it can achieve large degrees of reduction at low stresses without intermediate annealing treatment. The fact that the high levels of plasticity reached in the process of hot deformation are not accompaniect" by appreciable work hardening [1-4] is an indication that dynamic sol'{ening processes must develop rapidly during bot deformation. There are two possible mechanisms of softening [4-7], dynamic recovery and recrystallization. In dynamic recovery, dislocations are liberated from tangles by cross-slip and climb in the course of deformation, with subsequent annibilati on and fOlutation of a substructure. Dynamic recrystalhzatton during deformation involves the nucleation and growth of new grains, which become deformed !O the process of growing, so that recrystallization goes on being repeated in the new grains. DynamIC reCovery takes place in both old and new grains in the course of dynamic recrystallization. • • Fiz. ""'laJ. melal/qved., 52, No.3, 61.7-626, 1981. ,
144 "
,•
Dynam ic Recrystallization of Aluminium
The investigation of dynamic recovery and dynamic recrystallization processes on difl: ,and alloys [5-12] have shown that the tendency to dynamic recovery during h t d e , erent metal, .h h " a e,ormahon d'm' , h WIt t e energy of stacking faults, whIch characterizes the capacity of disloc t' f 'n,s e, .. " a Ions or cross·sli , b . I s 1m , DynamIC recrystallizatIOn occurs In metals In which dynamic recovery 's k P and . I wea and the e sufficIent for the onset of recrystallization builds up in the course of deforma!' It' f ' nergy . Ion . IS, Or Instan b o served In metals such as copper [6-8], nickel [I, 9] and in many alloys (5 10 12] h' h ce, ' . ' , , W . Ie are all ch acterlzed by a low stacking fault energy at large degrees of deformation and is the ' f at0 . . . ' major actor i the process of softening dUring deformation, On the other hand In aluminium [1 - 7] , [4 n , , . ~ Iron 1 and refractory metals with a b.c,c. lattice [4], in which the stacking fault energy reaches high val ' . . . ues, recov. ery processes 10 the course of deformatIon are so rapId that dynamic recrystallization is not obs . h'Ig hI eve Is ultimately leading to fracture, ' erved even at qUIte However, the improved conditions for dynamic recovery achieved, for instance, by lowering the n.
On the basi s of the above experimental results we ca n describe the development of a dislocation structure and plastic deformation under conditi ons providing for uynamic recrys tallization in aluminium, as foll ows. At tbe stage of strengthening a la rge quantity of dislocations is nuclea ted, subsequently to move in their own slip planes. T he number of act ive planes gradually inc reases and so does the dislocation density inside them, as a result of which interaction sta rts bct\veen dislocations and the n~wly formed tangles. Deformati on inside the grain is ve ry hetero gcn~ou s, with high densities of on e kind in local regions, and the appeara nce of mac roscopic strain bands with 13ltice misorientati ons of seve ral tl!n s of degrees. As they increase in dens ity the d islocation s a re redi slributl.:u. \\ ith format:\)n of a substructure and partial annihilation. But the defo rmat ion rate is too high :.lI1d the t ernper~Hu rt!s too modera l~ fo r these processes to be rap id eno ugh to co mpens" te th ose elrect s and the density ot pinned dislocati ons gro ws con tinuously . So resistance to ddo rmatio n is il1 c rca ~illg the \\ hole timc. finall y, jl a ce rtain moment of time, the den si ty o f defects or, more accurately, the das tic stn:sS nellis in dcf0rtnari o n bands and .n ea r boundaries, reach th e level needed fo r tht! o n ~c t of rccrystallization. Once sla rted , recrysta lliza li on must relieve Jocal stresses clearing ou t the defeclS from the local \'ol ume thro ugh which it passes . T he re will be fu rther slrengthening of neighbouri ng micro regio ns and also defo rmation of the ne w grains, which become greater in q uantity a nd smaller in size in the process. The equ ilib rium between the processes of softening (mai [lJy due to dynamic recr ystallization) in microregiQus
Dynam ic Rccrys{allil:llion of Alummium
15 1
in v..l1ich defo rmatio n has been co nsiuerJbk. ::l nu th e processes o f str ength cn in g in the ncighbouring h:55 strained reg io ns, prov ides fo r a cons tant macroscopic fl ow stress, which appears On the stress-stra in ~' urvc as a st3g(: of steady n ov..·.
CO:\CI.US IONS Dynam il.: rec rys tallization ma y occ ur in al um inium in the co u rse o f hot defo rmation under ce rtai n conditions \I.:hich hinder dynami c recove r y. T he defor matio n is hete rogeneous and ca uses bl!nding Bnd local macrosco pic la tt ice ro tatio ns (strains ban d s). Rec rystallizat io n cent rc:s arc formed in th e regio ns o f maximum latt ice di sto rtion whi ch nrc slightly misaligned re lative to neighbouring re gions. The process o f stead y Row is apparently co ntro lled by dynamic recrystallization. Th at hypothesis is based o n the fact s tha t steady flow a nd rec rystalli za tion start at th e same po int and the activa ti o n .energies of the stead y-s tate stage a nd rec rys talli zatio n o f alumi nium are very si milar. The authors a re ve ry grat efu l to A. N . Orlov fo r his interest in tbis wo rk and useful d iscussio ns.
REF E R ENCES 1. 1. J. J onas, C. M . Se llars and W . J . T egan, Slfcngth a tld slfuct ure dur ing hot wo rk ing, lvfctal/urgical Rev. , 1-&, 130, 1- 24 ( 1969). :2. J . P. Immarigcon and H . 1. McQueen, Dynamic rccovery of alumin ium dur ing hot rolli ng, Cat/ad .•\fe l. Quart., 8 , I , 25-34 (1969). 3. Y u. M . Vaynblat and I. P. Rod ina, (St ructure of aluminium alloy D I6 at the s teady stage of hot de formation), Fiz. metal, metallaved., 35,4, 838- 841 ( 1973). 4. H . 1. McQueen and J , J . J onas, R~co vc ry and rccr is talliz:llion during high temperature deform:lI ion, In: Treatise on .Material Science alld Technology, 6, Plastic Deformat ion of Materials , Ed. R. J. Arsenault, N .Y. Acad. Press, 393-493 (1975 ). 5. T . l'akamura, Steady s tale d efor mation and dynamic restora tion processes d ur ing hi gh stra in rate and high tempe rat ure defo rm a tion in metals and all oys, Higtt Ve/o c:.ity Dejormat. Solids Symp. T okyo , 1977, 108- 119 (197 8) . 6. V, Sedlacek. D ynarni sc hc Erholung und Rl!c rystall isa lion , Neue /fii((e, 22 , 9 , 465--469 (19 77) , 7. V. O(;cnasc k and V, Sedlacek, Rek.rys!aliz;1Cc a zotaveni u hliniku a mcdi bcham a po deformaci za le pta I, KOL'ol:e moter. , IS , J, 269 - 2S0 ( 19 77); 1 . K udrman, M , Mora vec and V. St!dl;:i.~ek , Rckrys ta lizace a zota veni u hliniku a nl!.!di bcham a po deforrnaci za tcp b II, K or;oL'e matcr. , 15 , J, 28 1-292 (1977). S. H. J. \fcQue~n and S, Bt! rgerson , Dynamic rccrysta ll iz.:uion of copper dur ing hot torsion, Mat er. Sci. J., 6, I, '1.
10. J
I.
J~. 13.
14. i5 .
16 .
J i.
25 - 29 (1972). \1. 1. LUl on and C. M. Sdlar
