REPORT DOCUMENTATION PAGE Form Approved OMB No

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1 REPORT DOCUMENTATION PAGE Form Approved OMB No Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instructions, searching existing data sources, gathering and maintaining the data needed, and completing and reviewing the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, including suggestions for reducing the burden, to Department of Defense, Washington Headquarters Services, Directorate for Information Operations and Reports ( ), 11 Jefferson Davis Highway, Suite 4, Arlington, VA Respondents should be aware that notwithstanding any other provision of law, no person shall be subject to any penalty for failing to comply with a collection of information if it does not display a currently valid OMB control number. PLEASE DO NOT RETURN YOUR FORM TO THE ABOVE ADDRESS.. REPORT TYPE 1. REPORT DATE (DD-MM-YYYY) TITLE AND SUBTITLE Mechanisms of Recrystallization in Superalloys Final Report. DATES COVERED (From To) 1 January Jul-07 a. CONTRACT NUMBER FA86-06-M-4001 b. GRANT NUMBER c. PROGRAM ELEMENT NUMBER 6. AUTHOR(S) Dr. Frank J Montheillet d. PROJECT NUMBER d. TASK NUMBER e. WORK UNIT NUMBER 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) Ecole des Mines de Saint-Etienne (ENSM-SE) 18, cours Fauriel Saint-Etienne Cedex 40 France 8. PERFORMING ORGANIZATION REPORT NUMBER N/A 9. SPONSORING/MONITORING AGENCY NAME(S) AND ADDRESS(ES) EOARD PSC 81 BOX 14 FPO AE SPONSOR/MONITOR S ACRONYM(S) 11. SPONSOR/MONITOR S REPORT NUMBER(S) SPC DISTRIBUTION/AVAILABILITY STATEMENT Approved for public release; distribution is unlimited. 1. SUPPLEMENTARY NOTES 14. ABSTRACT This report results from a contract tasking Ecole des Mines de Saint-Etienne (ENSM-SE) as follows: The project will study the effects and influence of very low (0 - ppm) and very high (-1%) niobium content in solid solution. Quantitative analysis of the stress-strain relationship will be conducted to determine stress-strain curves (up to large strains) at various temperatures and strain rates (typical ranges: 800 to 0 C, 0.01 to 1 s-1). Beyond the overall strain rate sensitivity (m) and apparent activation energy (Q), strain hardening (h) and dynamic recovery (r) parameters will be extracted from the data using one of the available physical equations. Evolutions of the above rheological parameters with Nb content for given straining conditions will therefore be deduced and compared with that of industrial grades. Electron Backscattering Diffraction imaging will be used to determine the Dynamic Recrystallization mechanisms operating in the various cases. Deformation microstructures will be characterized quantitatively (grain or crystallite size distributions, misorientation distributions, crystallographic texture). Such data will be put into correlation with the associated hot deformation flow stress (Derby diagrams). Two or three different states likely to be associated with precipitation of NiNb will first be selected from the stress-strain curve shapes and microhardness measurements. Transmission Electron Microscopy will then be used to determine the nature, size, morphology and localization of the intermetallic (NiNb) particles after straining followed by quench. In particular, their possible interactions with dislocations and grain boundaries will be analyzed. 1. SUBJECT TERMS Microstructure, Superalloy, Metallic Materials 16. SECURITY CLASSIFICATION OF: 17. LIMITATION OF 18, NUMBER 19a. NAME OF RESPONSIBLE PERSON ABSTRACT OF PAGES WYNN SANDERS, Maj (S), USAF a. REPORT b. ABSTRACT c. THIS PAGE UL UNCLAS UNCLAS UNCLAS 19b. TELEPHONE NUMBER (Include area code) +44 (0) Standard Form 98 (Rev. 8/98) Prescribed by ANSI Std. Z9-18

2 MECHANISMS OF RECRYSTALLIZATION IN SUPERALLOYS!"##$%"$ $&%%' ( )*+ *,%%-

3 !"#$%&&'%('' )* )* + )!, # ) * *- * #". / # " )) 0#" ) "#$%&&'%(''!0!!1 ) * * 1 ) * * *! 4)- * * * ) * )* #". /0!!1 )! (4-6 7 *)! " 4 / /

4 CONTENTS I. INTRODUCTION II. PREPARATION OF MODEL HIGH PURITY BASE Ni-Nb ALLOYS III. RHEOLOGICAL BEHAVIOUR OF THE Ni-0.01Nb, Ni-Nb, and Ni-1Nb ALLOYS IV. QUANTITATIVE ANALYSIS OF THE STRESS-STRAIN CURVES OF Ni-Nb ALLOYS V. STEADY STATE STRESS VS. GRAIN SIZE RELATIONSHIP VI. DISCUSSION VII. CONCLUSIONS AND FUTURE DEVELOPMENTS! " #!#

5 $../0/. # # %#%%!%!& # # #"!! "% % % % %!%% % "% '% ()*+, -'*./001$11/4 "% # % # 4 6 /7!!" 4% 849 #!!-"-1 4-"8-14-"9!#4-" 8-14-"9 40-" "9! ":: 1! -14-" -14-" #"! ##% # #! " ;! " %!-140-" % #"! #"! &"!! #! % 8:::9 : :< 1-1-"! #4444-"8-14-"-14-"-1 4-" -14-"!9!& # =1 1 >?, "!?"! # # & # %%!< '!" % <:../. 1../4$! # %# " 6 &4@@0A 7 % "! %# #! #1! #% "% % % "! % " %! # % 8 %!: 1 )(9 # #":

6 Table I. Chemical analyses of the alloys *! -"89 8%9 8%9 )8%9-8% " B / 0 $ $ B -140-" B :# " 44# # 40C 8 % 9! " % 4/%% "! ## % % % 4D%%4$ %###D%% % /%% % %" /1 $%%' $'% $'# ' % # %% #"::E " 8 :::$9 * % % "& 8 40%9 # % % # %%! % 0!! Table II. Temperature and strain rate conditions of the torsion tests carried out on pure Ni, Ni-0.01Nb, Ni-0.1Nb, Ni-1Nb, and Ni-Nb % 4 $ $ " %! %.@4C #! 4 4 #!

7 0?# #?!% = Γ F - %E % - #%E%% 8 % 9!8 % 9#! #!% # # #'BG $ Γ σ = ( $ + % + ) 849 $ π+ + %:" %?# #? # % = ΓF- % % Γ - #%#...'$%%' 1!-14-"! # % '# 4 $4$ 4! % 6/7" #!# # % " -: " " " ## &:! # & #! %!%!&## &!" #" '!! # % "%!%!&! % % %.@ 4C " 8% = σf ε 9! 8% = σf ε9 %# σ # ε '#, "::: % #! % # % H4D$% H4$8!?# #? % %!9: % #! % #! %! % 8I 9! 8I % σ 4F '# $*! -!-14-" -14-" " % "! # # % 6 /7 σf84f9 = %IF+ +#%%I % J#" #% % # "GI H0$>F%I H$4>F%

8 / Table III. Strain rate sensitivity values of the Ni-0.01Nb alloy % 8C 9 % 8 9 % 8! 9. 4/$ 4@ 4 4 4/0 40 * # 4D$ 4$

9 D 00 Ni-0.01Nb 0.0 s -1 Flow Stress (MPa) C 0 C Strain Ni-0.01Nb 0.1 s -1 Flow Stress (MPa) 0 80 C 900 C 90 C 0 C Strain Ni-0.01Nb 0. s -1 Flow Stress (MPa) C 0 C Strain Figure 1. Torsion stress-strain curves of alloy Ni-0.01Nb

10 . Ni-0.01 Nb Stress (MPa) C 0 C Strain Rate (s -1 ) Figure. Strain rate dependence of the flow stress of alloy Ni-0.01Nb (triangles: peak stress; circles: steady state stress) 0 Ni-0.01Nb 0.1 s -1 Flow Stress (MPa) 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T Figure.Temperature dependence of the flow stress of alloy Ni-0.01Nb (triangles: peak stress; circles: steady state stress)

11 @...,$'% * # -1-" # % 8'# D9 "% %!#% #*E %# -14-"8'# 9'.C 4 4 σ H "0./ $ 4 #!"!1# 8 % " 9 J #! " # % 1 '# 0! % % 8 9% 8! 9 ":<: % #!% % " σ 4F ε =4 4 '# / % "!# " σ σ %# % I % I 8% 9* I #! #% 8":<9 Table IV. Strain rate sensitivity and apparent activation energy (at 0.1 s 1 ) values for the peak stress (m M, Q M ) and the steady state flow stress (m S, Q S ) of the Ni-Nb alloy % % I F+ I % 8C 9 % I F+ I % 8K9 8>F%9 8K9 8>F% D 4D $.0 0/@ 44. $0D 4 4D@ D$ 444 $.

12 Ni-Nb 0.0 s -1 Flow Stress (MPa) C 0 C Strain Ni-Nb 0.1 s -1 Flow Stress (MPa) C 90 C 0 C Strain 700 Ni-Nb 0. s Flow Stress (MPa) C 0 C Strain Figure 4. Torsion stress-strain curves of alloy Ni-Nb (crosses mean fracture)

13 Ni-Nb 7 6 Stress (MPa) C 0 C Strain Rate (s -1 ) Figure. Strain rate dependence of the flow stress of alloy Ni-Nb (triangles: peak stress; circles: steady state stress) 0 Ni-Nb 0.1 s -1 Flow Stress (MPa) 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T Figure 6. Temperature dependence of the flow stress of alloy Ni-Nb (triangles: peak stress; circles: steady state stress)

14 4...6$'#!-140-"! % "% % % 8- $ -"9 #" % "% 4 # %'# D! 8 9" 4C # 40% 40C % % % % 89 4% # %% %# # A 89 # - $ -" 8 %! <:$9 J! # 1#% %" εh0"! 8'#.9 ' " " % # %!; #!"% %" 8!9! #@C 4 4C 14 4 G L 1;% % I $D>F% "! " " 8<:9 % %!% %M1! %!" Nb-wt% Temperature ( C) Ni Nb 600 Ni (atom per cent) Figure 7. Ni rich part of the Ni-Nb phase diagram

15 4$ 1 Ni-1Nb Torque (Nm) s -1 0 C s C s N (rev) Figure 8. Torque-twist curves of alloy Ni-1Nb (the star means fracture).70/.//.. /1 /$/. 0 $ : #!-1 4-"-14-"-14-"-14-"!& # =1 1> 8=>9 6=4@.DA >4@@47 #!%! # %% G ρ = ρ ε 89 ρ! # %!%! % :# 89 %" σ = αµ " ρ α 4µ %" B # %G { } 4F 8 9E [ 8 9 ] σ = σ σ σ ε ε 8$9 ; ε σ! σ = α µ " F 8 9! " "!%!& ' 1! 8ε σ 9 % %!*% %! σ ##"8$9!%!& E % " 8 ε = ε 9!

16 4 ε < 80F/9 ε E% -14-" %4 4 : # %"=># 00 Ni-0.01Nb 0.1 s -1 Flow Stress (MPa) 0 80 C 900 C 90 C 0 C Figure 9.Example showing how the YLJ equation (broken lines) fits the first part (i.e., before the onset of DRX) of the experimental stress-strain curves (dotted lines).'σ Strain : σ % % # % * # % # 67E" %G % % I B E σ = ε + 89 % %I = ε E % % I I #σ!+# '# 41!-14-"-14-" -14-"-14-"

17 40 0 Pure Ni 0 Ni-0.01Nb C 0 C Strain Rate (s -1 ) Ni-0.1Nb C 0 C Strain Rate (s -1 ) Ni-1Nb C 0 C Strain Rate (s -1 ) Ni-Nb 900 C 0 C Strain Rate (s -1 ) Figure a. Strain rate dependence of σ for pure nickel and the four alloys Ni-0.01Nb, Ni-0.1Nb, Ni-1Nb, Ni-Nb 900 C 0 C Strain Rate (s -1 )

18 4/ Pure Ni 0 C Ni-0.01Nb 900 C r r Strain Rate (s -1 ) Ni-0.1Nb Strain Rate (s -1 ) Ni-1Nb r r r Strain Rate (s -1 ) Ni-Nb Strain Rate (s -1 ) Figure b. Strain rate dependence of r for pure nickel and the four alloys Ni- 0.01Nb, Ni-0.1Nb, Ni-1Nb, Ni-Nb Strain Rate (s -1 )

19 4D 0 Pure Ni 0 Ni-0.01Nb 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T 0 Ni-0.1Nb 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T 0 0. s s s -1 Ni-1Nb 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T 0 Ni-Nb 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T Figure c. Temperature dependence of σ for pure nickel and the four alloys Ni- 0.01Nb, Ni-0.1Nb, Ni-1Nb, Ni-Nb 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T

20 4. Pure Ni Ni-0.01Nb r r 1 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T Ni-0.1Nb 0. s E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T 0.0 s s -1 Ni-1Nb r r r 1 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T Ni-Nb 1 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T Figure d. Temperature dependence of r for pure nickel and the four alloys Ni- 0.01Nb, Ni-0.1Nb, Ni-1Nb, Ni-Nb 7.E-4 8.0E-4 8.E-4 9.0E-4 9.E-4 1/T %% #G

21 G'# 4 % σ 6897 #% "< #% "%' % #8'# 4"9; % % #"%A -14-"-14-"!%!4C Table V. Strain rate sensitivities m and m r associated with σ and r, respectively (brackets indicate estimated values) 8C 9 % %. $ /$$ $@ /@ 44D 4 4$ $ $. // / 1 4 4D@

22 G ' σ % "! # 8'# 49 * %89 % I F+ # I "<: ; % # % # % # I *$4 4 "% %#! I ; $ 4 "1# #' #% " %I 8 % #% 9#"!! # "% "% & # -14-" -14-"8'# 49' % %!: % H"!I %! #%% I E89 '!-14-" %I % #% #I %.,) # % % % G σ = αµ " F 8/9 α%!"h@x4 4 %8 9 %µ %% % #6' *"!4@.7G $ µ = µ 4 + η 8D9 E% µ HD.@x4 8 -$K9 H4D/K 8-9ηH /!'# 441 # % % % #: # ## #!" 4!% 84-"9" % 0! %!$ 6 47!!! # #!% B! -14-"!% # 1 ;! %!%!!"!# "! #!'# 44 # % "% 4 " #! -14-"-14-"

23 4 Table VI. Temperature dependence parameters associated with σ and r (brackets indicate estimated values) 4 ε 8 9 % I F+ 8K9 I 8>F%9 %I F+ 8K9 $ I 8>F%9-4 //0 647.D/ 44 $ D$ 647 $. $ $@ -14-" 4 $4 $./4 D4 $ 0 $D.@. / $.0 $/.D $D -14-" 4 $.$/ D 4/ 4/ $ $.4/ D 4./ $D $ /$@ " 4 04D $@/ 1 1 $ $0 $0$ 4D. 40 $ /@4 / -14-" 4 0@D0 $@/ $/ 1

24 80 60 Ni Ni- 0.01Nb Ni- 0.1Nb Ni- 1Nb Ni-Nb r h Figure 11. Diagram showing the h and r values of the five materials investigated.////..8/.1. *%" "! #!# 8!9&G σ = KF, 8.9 E#! ##"/.6, "!4@@7 # " # "-14-"-14-" % 08!9 %.@@C ε =4 4 # % % # $N%! # %#8 9*! %% % 8(,9# " ## &!'# 4# %(B, "!8 # &% " % # # 40#9 E "<::' -!-1 4-" -14-" #!! H4$0-14-" 8%!9 % # ; (B, H0. %! % "% " JE! # % ## & # "%## #"% "! # %'! 8)9 # % # 8" 9

25 $ $$% ""!, Steady State Flow Stress (MPa) 0 Ni-Nb Alloys 0.1 s -1 OM EBSD Ni-1 %Nb Ni-0.1 %Nb 1 0 Average Grain Size (µm) Figure 1. Diagram showing the relationship between steady state flow stress and average grain size. Optical microscopy (OM) and EBSD data. The broken line fits the whole set of OM data. Table VII. Exponent a of the steady state flow stress vs. grain size relationship (OM: optical microscopy) Ni-0.01 %Nb Ni -8)9-14-"8)9-14-"8)9-14-"8)9-14-"8(B,9 *) 0$ /. 4$0 0. $$

26 ..0. ## "!"6 7"% % "!&.') B σ! σ!! "% "!'# 4$ -1-"!: ## %G σ = σ + E 8@9 E89 # %$D$ # %! 8 # 9 %% :"% % σ σ!" "!# &!# &!B E #E " #: " #"! "%# %.,(()9 '# 4 "% %I # % %I! %I!# # %E%% "% " # -14-" B! % I % # # "%! # E! % -14-" "% #" "% % # 4" ## %% # %8O49 #8 49"%

27 0 0.1 s -1 σ M - σ M Ni Nb Content (wt%) 0.1 s -1 σ S - σ S Ni Nb Content (wt%) Figure 1. Influence of niobium content on the peak and steady state flow stresses of pure nickel and the Ni-Nb alloys at various temperatures and a strain rate of 0.1 s 1

28 / 00 S 0.1 s M mq/r (K) Nb Content (wt%) C Strain Rate Sensitivity m m M m S Apparent Activation Energy Q (kj/mol) Nb Content (wt%) Q S 0.1 s Nb Content (wt%) Figure 14. Influence of the solute niobium content on mq, m and Q (M: peak stress; S: steady state stress) Q M.0.0

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30 . Pure nickel - L/Lo (%) Temperature ( C) Time (s) Ni-1Nb - 0 C Ni-1Nb C L/Lo (%) Time (s) Ni-1Nb - Temperature ( C) L/Lo (%) Time (s) Ni-1Nb C Temperature ( C) L/Lo (%) Time (s) Temperature ( C) Figure 1. Dilatometry measurements carried out on pure nickel at and on alloy Ni-1Nb at 0, 900, 800, and 700 C L/Lo (%) Time (s) Temperature ( C)

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