PhD project: Effect of Aluminum on deformation mechanisms and ductility in Ti-alloys

Transcription

1 PhD project: Effect of Aluminum on deformation mechanisms and ductility in Ti-alloys Light Metals Division Strategy meeting 12 th December 213 Dipl. Ing. Arnas Fitzner Michael Preuss, Joao Quinta da Fonseca, Matthew Thomas

2 Project aims! Improve formability, machinability and in service properties of Ti alloys with a fundamental approach! Understand why CP-Ti twins profusely, but Ti6Al4V does not! Study the effect of specific alloying elements on deformation % 1.7% compression 3.7% strain % 5 5!m LD 45 RD ND Slip 8.7% Twin Strain maps from DIC 12/12/213 Arnas Fitzner 2

3 Theory on Deformation Twinning! Twinning influenced by: Strain rate Temperature Microstructure: Texture, grain size! Alloying effects: & morphology Constant in this study Critical resolved shear stress increase CRSS [Williams 22] " Relative change in deformation system activity Lattice spacing, c/a-ratio [Yoo 1981] " Twin shear is geometrical function of atom shuffle Stacking fault energy γ reduction " Twinning easier with alloying in fcc [Meyers 22] Precipitation of Ti 3 Al [Crossley 197, Loretto 213] " Shearing APB more difficult " Less twinning 12/12/213 Arnas Fitzner 3

4 Processing of binary model alloys!"#$"%&'(%").)/,%") +)%,--) # α β +)&1-)!!!"! 2!m!*#") 12/12/213 Arnas Fitzner 4

5 Ti-Al Phase diagram & SRO formation Al Atomic Fraction Ti Ti Temperature [ C] " / / / /' I / / i/ i / / ~+~!!+! 2 Experiments 5hrs cooling 1K/hr 5 days Ti Al at 2 K at 15 K at 1 K Phase modeling & experimental assessment of short range ordering SRO strengthening highly effective 5 1/nm 4 I Al concentration [at%] Ti 3 Al Ti-Al phase diagram with Ti 3 Al in DO 19 structure (Adapted from [Ghosh 28, Namboodhiri; Leyens and Peters 23; Mishin 2, Massalski 199] 12/12/213 Arnas Fitzner 5

6 Mechanical behaviour More than linear solid solution strengthening until 1at% Al with SRO Ageing decreases work hardenability, no strength increase!.2 [MPa] RX Aged Ti Al concentration [at%] 12/12/213 Arnas Fitzner 6

7 II NDI NDII EBSD microstructures and textures2!m!"#$%&$'%!"#$%&"'(")"*+,-".$'+/'!12*' Ti-Al, RX NDI NDII! Ti-Al ~9% compression NDII NDI Twin fraction TT1 2!m Ti-Al ~9% compression 5 4! 1 4 RX Aged 3 Ti-7Al ~9% compression Series Ti-7Al 2~9% compression compression 5 Ti-1Al ~9% Ti 1 15 Alcontent concentration alloys in at% [at%] Series1 Ti-1Al ~9% compression Poly. (Series9) Ti-13Al ~9% compression Linear (Series1) Automated EBSD map analysis Ti-13Al ~9% compression Aluminium Twin fraction [%] NDI!!!"!!!!"! /12/213 Arnas Fitzner 7

8 Lattice strain measurement at ISIS, EnginX Transverse µ! {2} transverse [!m/m] !!!!!"!!"!!! 3 6 9! [%] Sample Neutron counts /!s Twin initiation strain!!!"! Time of flight in!s 12/12/213 Arnas Fitzner 8 "I {2} axial [!A] {13} Axial {11} {12}! 3 6 9! [%] {11} {2}! Twin rate {1}

9 Neutron Results #I/#! true ["A]!" {2} ["m"m] RX Aged ! Easy access of intergranular strains! Twinning rate! Equivalent to axial {2}- pole intensity development due to texture change! Elastic lattice strain for twin initiation! Elastic strain in parent grains when twinning becomes obvious in axial detector and strain relaxation starts # Twinning rate and initiation strain related Ti Al concentration [at%] 12/12/213 Arnas Fitzner 9

10 IMPORTANCE OF TWINNING Nano-indentation 12/12/213 Arnas Fitzner 1

11 Nanoindentation Characterization of anisotropy Relate hardness to crystal orientation pre- and post-deformation 1 cm!!!"! 2!m 12/12/213 Arnas Fitzner 11

12 Nanoindentation Strong orientation effect on hardness Dislocation structure has minor effect Work hardening dominated by twinning Tensile twin!!!!!!!!!!!!!!!" Nanohardnes [GPa] 2.8 unstrained s3-7 Twin 2.2 s8-7 Parent basal & prismatic s8-7 Twin 2. strain free 1.8 Poly. (unstrained)!!!! Poly. (s3-7 Parent) 3% 1 2!!!!! 35 "!!!!!!!!!!!!!!!!!!" TT2!!!!!!"! basal & prismatic pyramidal Tensile Twins Slip Dislocation hardening!!!! by slip Poly. (s8-7 Parent) Poly. (s8-7 Twin)!!!!!!!!!!!!! 1.2!"!!!!"! Poly. (s3-7 Twin) 9% 1.4! TT1 s3-7 Parent 1.6 LD 85!!!!!!! Angle of c-axis [ ] /12/213 Arnas Fitzner 12!!!!!!!

13 Summary true stress [MPa] True stress [MPa] -12 ('4&'< I2 ;&&,$#(/) I2 ;&&,$#(/) )$7 ) <$')/&$ "# I2 ;&&,$#(/) <$')/&$ )(#47$D!&=)%'77(# I2"# ;&&,$#(/) ('4&' Ti-6Al aged < '# -'&'77$7 H! <$')/&$ "# '# -'&'77$7 %""#)(#47$D : 'G <$')/&$ I2 ;&&,$#(/) <$')/&$<$#% <$')/&$<$#%) I2 ;&&,$#(/) ('4&'< %"< ) '#?\B -'&'77$7 (# #"<(# Ti8Al_s22_RD '# -'&'77$7-6 I <$')/&$ "# 8("/ )$7$!%$ I2 ;&&,$#(/) <$')/&$ "# )(#47$D!&=)%'77 <$')/&$<$# H"%%$ 7(#$L2 )$7$!%$ I2 ;&&,$#(/) ('4&'< )$7 )$7$!%$ )$7$!%$ :;7 <$')/&$ "# '# -'&'77$7 %"-'&'77$7 :<$ ') H )$7$!%$ %/&$ () :;7 <$')/&$ "# )(#47$D!&=)%'77( H"%%$ )$7$!%$ I2 ;&&,$#(/) ('4&' I2 ;&&,$ :;7 H! <$')/&$<$# :;7-4 '# -'&'77$7 <$')/&$<$#%)?\B (# #"< :;7 '# -'&'77$7 %" :%/& 'G! :;7 <$')/&$ "# )(#47$ )$7$!%$ I2 ;&&,$# :;7 Ti-8Al_Neutron )$7$!%$ H"%%$ <$')/&$<$#% 9 )$7$!%$ <$')/&$<$#%)?\B (#7(#$L2 #"<(# '# -'&'77$7 %" Ti-3Al '# -'&' :;7 :;7 )$7$!%$ )$7$!%$ I )$7$!%$ %/&$ () (# :;7 H"%%$ 7(#$L2 9, )$7$!%$ <$')/&$<$#%)?\B <$')/& 3@2 Ti-Al :;7 -'&'7 :;7 '# )$7$!%$ :;7 )$7$!%$ Ti-1Al :;7 %/&$ () (#(! :;7 )$7$!%$ Ti-6Al aged Ti-6Al )$7$!%$ :;7 <$')/&$ Ti-13Al ' :;7 Ti-6Al aged@2 %/&! :;7 )$7$!%$ )$7$!%$ :;7 )$7$!%$!" :;7 Ti4Al aged Ti4Al :; Ti-7Al Aged Ti-1Al Aged 6 work hardening rate [MPa] Ti-2Al Ti-4Al -8-2 "=#$true/#%true [MPa] ! Initial SFE reduction promotes twinning! SRO towards Ti Al with Al addition or upon ageing causes slip localisation # Negative for work hardening, creep and Ti-Al Ti-Al ductility 5 5 Ti-6Al Ti-6Al Research only possible by linking 4! 4 diffractionand imaging-techniques Ti-2Al Ti-2Al 3 3 Excellent communication and availability Ti8Al_s22_RD Ti8Al_s22_RD 2! 2 of techniques and advanced analysis Ti-4Al Ti-4Al 1 1 programs required for quality research true strain [%] Ti-7Al Ti-1Al Ti-3Al 2 Ti-7Al aged Ti-13Al 1 Ti-1Al aged "min Ti-Al true strain [%] -2] True strain [1! per. per. Mov. Mov. 1 Avg. (Ti-6Al (Ti-6Al Avg. aged) aged) 12/12/213 Arnas Fitzner 13

14 Discussion? 1!m 12/12/213 Arnas Fitzner 14