effects on dynamic and metadynamic recrystallization on microstructures of wrought in-718 due to hot...

E L S E V I E R Materials Science and Engineering A196 (1995) 89-95

MATERIALS SCIENCE &

ENGINEERING

A

Effects of dynamic and metadynamic recrystallization on microstructures of wrought IN-718 due to hot deformation

L.X. Zhou, T.N. Baker

Department of Metallurgy and Engineering Materials, University of Strathelyde, Glasgow G1 IXN, UK

Received 24 January 1994, in revised form 30 August 1994

Abstract

The recrystallized grain size of IN-718 under hot-working conditions is related to the deformation parameters. The high temperature deformation of IN-718 in compression has been studied at temperatures of 950-1100 °C over a range of constant strain rates of 0.1, 5 x 10 -2 and 5 x 10 -3 s -~ using a 200 tonf press. After deformation the material was water quenched. The time interval between the termination of deformation and water quenching was a critical factor in this work. It was found that the dynamically recrystallized grain size increased with increasing temperature and decreasing strain rate under steady state conditions. Metadynamic recrystallization was observed at temperatures of 1050 °C and higher with strain rates of 0.1 and 5 x 10 -2 s- ~. The fraction of metadynamic recrystallization increased with increasing strain rate and temperature. An increase in metadynamic recrystallization leads to a relative increase in the recrystallized grain size. This study clarified some of the disputed areas involving the effect of strain rate on the final grain size.

Keywords: Dynamic recrystallization; Metadynamic recrystallization; Microstructure; Hot deformation

1. Introduction

The microstructures o f alloys during and after hot deformat ion are affected by hot working variables as shown by the extensive work which has been carried out on austenitic steel and nickel alloys [1-7]. For the nucleat ion o f dynamic recrystallization to take place during deformat ion, it is necessary for a critical dislocation density difference to exist across the interface between the nucleus and the surrounding material. Dynamic recrystallization ( D R X ) and dynamic struc- tural changes occur during hot working and result in a microstructure in an unstable state and also provide the driving force for me tadynamic or for static recrystallization after hot deformat ion is complete. However , differences o f opinion have been expressed regarding the grain size resulting f rom hot deformat ion o f IN-718 after different strain rates [8-10].

The aim of the present research was to investigate strain rate and temperature effects on the recrystallized grain size and, by compar ing the results with published data [8-10] , to clarify the dependence o f recrystallized grain size according to the part icular range o f strain rate employed.

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2. Experimental materials and procedure

The chemical composi t ion o f IN-718 used in this investigation is given in Table 1. Compared with an earlier study [5], a relatively large size o f compression sample was chosen in order to simulate industrial prac- tice. Cylindrical samples for the compression test, 34 m m in diameter and 45 m m in height, were prepared f rom an extruded billet o f 200 m m diameter. The mi-

Table 1 Chemical composition of the material tested

Element Content (wt.%)

AI 0.O6 B 0.004 C 0.037 Co 0.16 Cr 18.35 Fe 17.64 Mo 2.98 Nb 5.11 Ni 53.88 Ti 0.96

90 L.X. Zhou, T.N. Baker / Materials Science and Engineering A 196 (1995) 89 95

Fig. 1. Microstructure of the starting material, showing uniform and equaxied grains.

i i00 *C 20 r~L~.

1 oso *c c~

Heating tO00 *C

I 3 . , ~ I / 9s°*c

Compression

WQ 50% Deformation

Fig. 2. Procedures of the compression tests.

crostructures of the starting material showed that it was uniform with an initial grain size of 114 ~tm (ASTM 3), as shown in Fig. 1, and free of 8 phase when examined by transmission electron microscopy (TEM). The high temperature compression tests were carried out on a 200 tonf press which is designed for constant-strain-rate compression under high temperature conditions. This testing equipment consists of a microprocessor control system, an induction heating system, load cell and data-recording facilities [11].

Fig. 2 is a schematic diagram showing that the specimens were heated to the testing temperatures and soaked at temperature for 20 min before compression. Tests were conducted over a temperature range 950 l l 0 0 ° C at true strain rates of 0.1, 5 x 1 0 -2 and 5 x 10-3 s-~, followed by water quenching, to preserve the hot-deformed structures. The time interval between completed deformation to the quenching is 2 s. During this time the specimens were taken from the coil, and the insulation removed, before water quenching. The data of t ime- load-d i sp lacement were recorded by the microprocessor system, at intervals of 0.1 s-1.

The recrystallized grain size drx was measured on specimens taken from the central region of the com- pressed material by the "linear intercept" procedure using an optical microscope; the minimum number of grains counted was 300 per specimen.

The specimens for TEM were cut into slices on a diamond saw, and discs produced by spark machining. The last step in the preparation of specimens for TEM was that the discs, of about 25 ~tm thickness, were jet polished at between - 35 and - 40 °C in a 10% perchlo- ric ac id-30% n-bu tanol -60% ethanol solution. The polishing voltage and current were 25-30 V and 60 - 65 mA respectively. It was necessary for the polishing temperature to be strictly controlled.

3. Results

The relationship between mean recrystallized grain size and finishing stress a0. 7 at three strain rates is shown in Fig. 3. For a given strain rate, the log log relationship between drx and a07 shows that the slopes at the various strain rates are different and increase with increasing strain rate (Fig. 3).

For a given strain rate, the mean recrystallized grain size increased with increasing temperature, as shown in Fig. 4. However, the effect of strain rate on the recrystallized grain size differs, according to the temperature range. For a temperature lower than 1050 °C, the recrystallized grain size increased only slightly with decreasing strain rate but, when the temperature was above 1050 °C, the grain size increased rapidly with increasing strain rate.

The percentage of recrystallized grains was found to increase with temperature and the strain rate, as listed in Table 2. Fully recrystallized microstructures were obtained at temperatures of 1050 °C and above. The main feature of recrystallized microstructures produced at 1050 °C and an k of 5 x 10-3S 1 and viewed opti-

50 ' I

40

30

"•20 -,_.,

t~

o

10

0 0 . l s -1 -2 -1 [] 5 x l 0 s

zx 5x10"3 s -1

i t i i i I i i i 50 100 150 200 250 300

True Stress (MPa)

Fig. 3. The relationship between the finishing stress o-0. 7 and the mean recrystallized grain size drx at various strain rates.

L.X. Zhou, T.N. Baker / Materials Science and Engineering A 196 (1995) 89-95 91

40 I I I

-r"..~ 30

¢)

c/3 r"

• .~ 20

10 0 0.1 s d [ ] 5 X 1 0 2 S "1

A 5 X 1 0 3 S 1

1000 1050 1100 1150

Temperatur e o C

Fig. 4. Dependence of mean recrystallized grain size and testing temperature for specimens deformed at various strain rates to a strain of 0.7.

cally appears to be irregular grain boundaries E (Fig. 5), which is regarded as one indication of dynamically recrystallized grains [12].

The microstructures after a strain of 0.7 at 1050 °C using strain rates of 0.1, 5 x 10 : and 5 x 10-3s - l respectively were examined by TEM. Dynamically recrystallized microstructures were observed in all the specimens. The microstructures were heterogeneous from region to region. Typical microstructures are pre- sented in Figs. 6(a) and 6(b), in which can be seen the range of different dislocation densities commonly observed under these conditions and associated with critically worked (C), partly worked (P), as well as nearly dislocation-free regions (F).

For a given temperature of 1050 °C, a difference in the microstructures produced between material tested at strain rates of 0.1 and 5 × 10 3 s ~ was found. The size of almost dislocation-free grains is larger after a strain

Table 2 Recrystallization percentage in deformed samples

Temperature (°C)

Recrystallization C/,) for the following ~)

0 .1s ~ 5 x 1 0 2s ~ 5 x 1 0 -~s -~

950 76 63 1000 94 88 85 1050 100 100 100 1075 100 100 1100 100

Fig. 5. Optical micrograph of microstructure deformed at 1050 °C and strain rate of 5 x 10 3 s - ~, showing irregular grain boundar ies at E.

rate o f 0 . 1 s ~ than after a strain rate of 5 x 10 3 s - l . There are no grains with a diameter larger than 5 lam after deformation at a strain rate of 5 x 10 3 s - l . How- ever, some recrystallized grains, which were dislocation free and with a grain diameter greater than 10 gm (although most grains were dynamically recrystallized) were observed in microstructures produced after a strain rate of 5 x 10-2s ~. The fraction and size of dislocation-free grains increased as the strain rate increased from 5 x 10 2 to 0.1 s ~. On the contrary, the fraction and size of critical work-hardened grains increased with decreasing strain rate in the range between 0.1 and 5 x 10 -3 S 1. The dislocation density of critical work-hardened grains, however, increased with increasing strain rate, within the test range.

4. Discussion

4.1. Recrystallized microstructure

The features of dynamically recrystallized microstructures are different from those of statically recrystallized microstructures and are heterogenous from region to region. Dynamically recrystallized microstructures can be classified into three regions: (i) dynamically recrystallized nuclei with almost dislocation-free grains, (ii) growing dynamically recrystallized grains containing dislocations, (iii) critically work-hardened dynamically recrystallized grains, in which the dislocation density is the critical dislocation density for D R X [13].

Grains almost free of dislocations were found in the microstructures produced at all strain rates used in the present tests. The fraction and grain size of these grains increased with increasing strain rate. At a strain rate of 5 x 10 3s-1, the size of the almost dislocation-free

92 L.X. Zhou, T.N. Baker / Materials Science and Engineering A196 (1995) 89 95

grains was less than 5 gm in diameter, a size which can be classified as dynamically recrystallized nuclei [4,7,13], with little growth by metadynamic recrystallization after hot deformation. However, at strain rates of 0.1 and 5 x 10-2s ~, microstructures with some metadynamic recrystallization effects were observed, i.e. the size of the grains with a low dislocation density was greater than 10 jam (Fig. 7), and these grains were believed to be the result of dynamically recrystallized nuclei, or growing grains with a low dislocation density during metadynamic recrystallization.

Metadynamic recrystallization is defined as a static recrystallization (SRX) process without an incubation time, and the nuclei are formed in the prior D R X process [13]. Because there is no grain growth restric- tion by concurrent deformation in the metadynamic recrystallization process, the recrystallized grains pro- Fig. 7. A large dislocation-free grain F was developed at a tempera-

ture of 1050°C and a strain rate of 0.1 s ~.

(o )

{b ) Fig. 6. Typical microstructures developed at 1050 °C, for a strain rate of 5x 10 -3s ~ and strain of 0.7, in which can be seen the range of different dislocation densities commonly observed under these conditions, and associated with critically worked (C), partly worked (P) as well as nearly dislocation-free regions (F).

duced by this process are larger than those found after DRX. Furthermore, the features of the metadynamically recrystallized microstructures are similar to those found after SRX.

In the present study, the microstructures underwent metadynamic recrystallization during the time interval (2 s) between the completion of the hot-deformation process and water quenching. Within this time interval, the temperature of the centre of the sample cooled to 1010 °C for the sample deformed at 1050 °C, as shown in Fig. 8. The temperature of 1010 °C is still sufficiently high for metadynamic recrystallization to take place. The time interval in present study can be compared with a holding time in previous investigations [5,13].

Microstructural changes due to metadynamic recrystallization and recovery, during the time interval, are classified with reference to the same three regimes de- scribed above.

1 2 0 ( } r I I i ' I '

[ .w S I X )

d

6 ( l f l

i =E

E-~ 4 0 0

0 • . f . _ ~ I I , I , I ,

I 2 3 4 5

Time. s

Fig. 8. Cooling curve of the specimen after deformation at 1050 °C.


(i) Metadynamic recrystallization takes place from the dynamically recrystallized nuclei which are formed during the prior DRX. The nuclei grow rapidly because concurrent deormation is terminated. This is indicated by the increase in dr~ and the decrease in the fraction of dynamically recrystallized grains.

(ii) Concurrently, growing dynamically recrystallized grains (containing a dislocation density gradient) un- dergo metadynamic recovery or grain growth, according to the local dislocation density gradient. In the case of growing grains surrounded by nuclei, metadynamic recovery takes place; this mechanism does not lead to nucleation or growth and so does not contribute to changes in the microstructure. However, in the cases in which growing grains are adjacent to a fully work-hardened region which has a higher dislocation density, the growing grains continue to grow during the holding period. In this case, because there is no concurrent deformation, the rate of growth is higher and therefore results in larger grains [14,15].

(iii) Fully work-hardened grains are consumed by growth of adjacent grains, and metadynamic or static recovery takes place in these grains. With a prolonged holding time, SRX could occur in the fully work-hardened grains.

An examination of the recrystallized grains by TEM indicated that about 70% of grains observed after deformation at 5 × 10 2 s - ' are dynamically recrystallized grains. For a strain rate of 0.1 s - ~, the fraction of dynamically recrystallized grains is less than 50%, and more than half the microstructures are metadynamically (statically) recrystallized grains. However, at a strain rate of 5 x 1073 s 1, grains were fully dynamically recrystallized. The difference in the nature of the recrystallized grains accounts for the larger grain size observed for a given finishing stress in tests at the higher strain rate (Fig. 3), because it has been shown previously [15] that statically recrystallized grains are larger than dynamically recrystallized grains produced by the same deformation conditions.

The time interval between the completion of the hot-deformation process and quenching is therefore critical for the achievement of a dynamically recrystallized grain microstructure.

4.2. Effect of strain rate on final grain size

Table 3 Measurement of mean recrystallized grain size in deformed samples

Temperature d~x(tam) for the following (°C)

0.1s - l 5 x 1 0 2 s - t 5 x 1 0 - 3 s - t

1000 9.0 ± 0.4 10.2 + 0.5 11.3 + 0.6 1050 17.2 ± 0.4 17.8 + 0.4 18.8 + 0.4 1075 26.5 ±0 .6 24.1 +0 .4 1100 38.0 ± 0.5

result is in good agreement with work published by Howson and Couts [10], but in contradiction with that published by Camus et al. [8]. The difference can be understood by the following explanation.

(1) The strain rate ranges employed in the two sets of experiments were different, the present work being carried out in the strain range from 0.1 to 5 x 10 - 3 S - 1

while the work of Camus et al. used the comparatively higher range from 4 to 4 × 10 - 2 s - 1 .

(2) The strain rates employed in processing affect the metadynamic recrystallization process, which occurs after the hot-deformation process has finished.

4.2.1. Dynamically recrystallized grain size The recrystallized grain size increased with decreasing

strain rate for temperatures of 1050 °C or below, at strain rates of 5 x 10 2and 5× 10 - 3 s - ' , as shown in Fig. 4 and Table 3. The microstructures under these conditions were examined by TEM and are illustrated in Fig. 6 which shows that the majority of grains are dynamically recrystallized at a strain rate of 5 x 10 -3 s -~. For a strain rate of 0.1 s ~, metadynamically recrystallized grains were found. Because the testing temperatures are relatively low, the increase in grain size is small as a result of metadynamic recrystallization. The compensation in grain size at this test condition is insufficient to reverse the relationship between the final grain size and the strain rate. Therefore, as the strain rate decreases at a constant temperature, the dynamically recrystallized grain size increases. This result is in good agreement with work published by Howson and Couts [10]. It is suggested that decreasing the strain rate promotes dynamic recovery and reduces the number of nucleation sites [4,16-18].

From the above analysis of the microstructure, it is obvious that the final microstructures are influenced by DRX and metadynamic recrystallization. However, generally the effect of strain rate from 0.1 to 5 × 10 3s-~ on the final grain size is not very strong, an observation which is in good agreement with conclusions reported previously [8,9]. The mean recrystallized grain size drx slightly increased with increasing strain rate ~ for temperatures of 1050 °C and below. This

4.2.2. Grain growth during metadynamic recrystallization

From an analysis of the microstructural change during metadynamic recrystallization, the driving force for grain growth comes from the local dislocation density gradient, which is related to the critical dislocation density P0c of DRX [13]. According to the analysis by Roberts [19], DRX occurs at a critical value of dislocation density, which is expressed as

94 L.X. Zhou, T.N. Baker / Materials Science and Engineering A 196 (1995) 89-95

( )1. Po ~> constant \bd~bmr2 j = Poc (1)

where P0 is the dislocation density in unrecrystallized material, P0c the critical dislocation density for DRX, s the grain boundary energy, b the magnitude of Burgers vector, r the dislocation line energy, dsb the subgrain diameter, rn the grain boundary mobility and ~ the strain rate.

From the above equation, P0c increases with increasing strain rate. P0~ is related to the peak strain ep of the flow stress-strain curve [18,20] and increases with increasing peak strain ep. At a given temperature, the peak strain increases with increasing strain rate for IN-718 [11].

A higher P0~ leads to an increase in the gradient of the dislocation density between a critically work-hardened region and a dynamically recrystallized nuclei region or a critically work-hardened region and the growing dynamically recrystallized grains with a low dislocation density and surrounded by fully work-hardened regions. Both situations result in an increase in grain growth. Therefore increasing the strain rate accelerates metadynamic recrystallization and also increases the extent of metadynamic recrystallization and the grain size.

It is evident that the final microstructures depend not only on the deformation parameters, temperature, strain and strain rate but also on the time interval or holding time at the deformation temperature. For a given holding time, metadynamic recrystallization increases with increasing strain rate [14, 21-23].

In the work published by Camus et al. of the strain rates they employed (4, 4 x 10 1 and 4 x 1 0 - 2 s i), 4 and 4 x 10-~s 1 were sufficiently high to produce a large fraction of metadynamically recrystallized grains at temperatures of 1050 °C and lower, in the time interval between the completion of hot deformation and quenching, although the time interval was claimed to be less than 1 s. Dynamically recrystallized microstructures were obtained by using the lowest strain rate of 4 x 10-2s 1.

In the work carried out by Barker et al. [9], the strain rate range used was f r o m 4 x 10 2 t o 2 x 10 -2s 1. The microstructures produced in this strain rate range at a temperature of 980 °C were similar. It is considered by the present authors that the effect of strain rate in this very narrow range, on recrystallized grain size, was too small to identify. Even for the much wider range of strain rates used in present work (Fig. 4), the recrystallized grain size (final grain size) was only slightly affected by strain rate at a similar temperature to that used by Barker et al. [9].

For temperatures higher than 1050 °C, the recrystallized grain size increased rapidly with increasing strain rate, as shown in Fig. 3. These results are in agreement with the work published by Camus et al. [8]. It is

considered that increasing the temperature enhances metadynamic recrystallization. The slopes of the curves at the three strain rates increased with increasing strain rate. This is not consistent with the relationship d = E"a 3,,4 found for many metals and minerals for DRX [1,2,12,19,24-27]. The observations of the TEM examination confirmed that microstructures with many dislocation-free grains were present, and the fraction of these grains increased with increasing deformation temperature.

It is clear that increasing the strain rate accelerates DRX and metadynamic recrystallization and leads to a decrease in the grain size. For the case of the final grain size, whether it increases or decreases depends on whether the dynamically recrystallized grains can be preserved by quenching. The final recrystallized grain size decreases with increasing strain rate if the dynamically recrystallized grains can be preserved. This is the case when using a range of low strain rates, such as a strain rate of 5 x 10 3 s i used in the present work on IN-718. Using higher strain rates, as in work by Camus et al. or in the present work, 0.1 and 5 x 10 2s-1 at temperatures of 1050 °C and higher, it was found that the final recrystallized grain size increased with increasing strain rate. This condition produced a finer dynamically recrystallized microstructure at the end of the deformation, which is very difficult to preserve by im- mediate quenching and finally results in microstructures with a high proportion of metadynamically recrystallized grains. In the final microstructures, which are a combination of dynamically and metadynamically recrystallized grains, the average size of the grains could be larger than those formed with lower strain rates.

The work of Barker et al. [9] showed that the final grain size was almost independent of the strain rate range that they employed. It is therefore expected that in this work [9] the final grains were almost all dynamically recrystallized grains, produced using the lowest strain rate in the range. In the present work, however, microstructures such as those seen in Fig. 7, produced under the highest strain rate (0.1 s l), are likely to contain a certain fraction of metadynamically recrystallized grains. This suggests that the grain growth, as a result of metadynamic recrystallization, compensated for the difference in the dynamically recrystallized grain size caused by using a higher strain rate during DRX. Therefore there is almost no difference in the final grain size produced by this range of strain rates.

5. Conclusions

(1) In high temperature compression tests carried out on specimens of IN-718 using a microprocessor controlled 200 tonf press, for temperatures above 1050 °C, the recrystallized grain size (final grain size) increased


with increasing strain rate and, for temperatures below 1050 °C, the grain size increased slightly with decreasing strain rate.

(2) The grain size after DRX increases with decreasing strain rate. However, a fine microstructure could be subjected to metadynamic changes, unless the material is cooled very rapidly after deformation.

(3) A cooling experiment undertaken to simulate the cooling rates achieved in the time interval after deformation but before water quenching indicated that the temperature change at the specimen centre was such that metadynamic recrystallization could occur.

(4) Metadynamically recrystallized microstructures were produced under conditions of high strain rate and high temperature and lead to a relative increase in the recrystallized grain size.

(5) An increase in strain rate accelerates both DRX and metadynamic recrystallization.

(6) The final microstructure is influenced by the time interval or holding time between the temperature at the finish of the deformation process and the critical temperature for the softening process prior to quenching.

Acknowledgements

Cooper-Cameron Forged Products of Livingstone are thanked for financial support and Committee of Vice-Chancellors and Principals of the Universities of the United Kingdom for the ORS award to one of the authors (L.X.Z.). The authors would also like to thank Professor C.M. Sellars for helpful advice.

References

[1] M.J. Luton and C.M. Sellars, Acta Metall., 17 (1969) 1033. [2] C.M. Sellars, in C.M. Sellars and G.J. Davies (eds.), Hot Working

and Forming Processes, Metal Society, London, 1980, p. 3. [3] W. Roberts and B. Ahlblom, Proc. 4th Int. Conf on the Strength

of Metals and Alloys, Vol. 2, Ecole Nationale Superi6ure de la M6tallurgie et de l'Industrie des Mines, Nancy, 1976, p. 400.

[4] T. Sakai and M. Ohashi, Mater. Sci. Technol., 6 (1990) 1251. [5] A.A. Guimaraes and J.J. Jonas, Metall. Trans. A, 12 (1981) 1655. [6] F.J. Humphreys, Mater. Sci. Technol., 15 (1991) 371. [7] J.J. Jonas, Proc. 4th Int. Conj. on the Strength of Metals and

Alloys, Vol. 2, Ecole Nationale Superi6ure de la M6tallurgie et de l'lndustrie des Mines, Nancy, 1976, p. 976.

[8] G. Camus, B. Pieraggi and F. Chevet, in A.K. Sachdev and J.D. Embury (eds.), Formability and Metallurgical Structure, TMS Inc., Warrendale, PA, 1986, p. 305.

[9] J.F. Barker, D.D. Krueger and D.R. Chang, Proc. Conf. on Advanced High Temperature Alloys, American Society for Metals, Metals Park, OH, 1984, p. 125.

[10] T.E. Howson and W.H. Couts, Jr., in E.A. Loria (ed.), Superalloy 718 Metallurgy and Applications, Minerals, Metals and Materi- als Society, New York, 1989, p. 685.

[11] L.X. Zhou and T.N. Baker, Mater. Sci. andEng., A177(1994) 1. [12] D.W. Livesey and C.M. Sellars, Mater. Sci. Technol., 1 (1985)

136. [13] T. Sakai, M. Ohashi, K. Chiba and J.J. Jonas, Acta Metall., 36

(1988) 1781. [14] H.J. McQueen and J.J. Jonas, J. Appl. Met. Work., 3 (1985) 410. [15] H.J. McQueen and S. Bergerson, Met. Sei. J., 6 (1972) 25. [16] C.M. Sellars, Philos. Trans. R. Soc. London, Set. A, 288 (1978)

147. [17] N.D. Ryan, H.J. McQueen and E. Evangelista, in N. Hansen,

D.J. Jensen, T. Leffers and B. Ralph (eds.), Annealing Pro- cesses--Recovery Recrystallization and Grain Growth, Proc. 7th Riso Int. Symp. on Metallurgy and Materials" Science, 1986, Riso National Laboratory, Riso, 1986, p. 527.

[18] H.J. McQueen, Mater. Sci. Eng., AIOI (1988) 149. [19] W. Roberts, in G. Krauss (ed.), DeJormation, Processing and

Structure, American Society for Metals, Metal Park, OH, 1984, p. 109.

[20] J.J. Jonas, C.M. Sellars and W.J. McG. Tegart, Metall. Rev., 14 (1969) 1.

[21] H.J. McQueen and J.J. Jonas, Treatise Mater. Sci. Technol., 6 (1975) 393.

[22] R.A. Petkovic, M.J. Luton and J.J. Jonas, Can. Metall. Q., 14 (1975) 137.

[23] R.A. Petkovic, M.J. Luton and J.J. Jonas, Acta Metall., 28 (1980) 729.

[24] T. Sakai and J.J. Jonas, Acta Metall., 32 (1989) 189. [25] L. Blaz, T. Sakai and J.J. Jonas, Met. Sci., 17 (1983) 609. [26] G. Glover and C.M. Sellars, Metall. Trans., 4 (1973) 765. [27] I.S. Servi and N.J. Grant, Trans Am. Inst. Min. Eng., 191 (1951)

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effects on dynamic and metadynamic recrystallization on microstructures of wrought in-718 due to hot...

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