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Fracture mechanism maps for titanium
Scripta METALLURGICA
Vol. 13, pp. 851-856, 1979 Printed in the U.S.A.
Pergamon Press Ltd. All rights reserved.
FRACTURE MECHANISM MAPS FOR TITANIUM Y. Krishna Mohan Rao, V.Kutumba Rao and P.Rama Rao Department of Netallurgical Englneering,Banaras Hindu University, Varanasi 221005, India (Received June 8, 1979)
Introduction The fracture mechanism map, first developed by Ashby (I), is a binary plot which identifies the fields of stress and temperature in which a particular mechanism of fracture is dominant. The Ashby procedure for constucring such a map consists in plotting the normalized tensile stress, ~n/E (where ~n is the nominal applied stress in creep tests and the ultimate tensile strength in tensile tests and E is the elastic modulus at the test temperature), versus the homologous temperature, T/Tm (where T m is the melting point in K). Each datum in the map is labelled with the logarithm of time to fracture, loglo tf (tf in seconds). A mode of failure is assigned to each datum point based primarily on fractographic observations and using indirect evidence where such observations are not available. Boundaries are then drawn separating blocks of data with one mode of failure from those with another. Fracture maps have also been drawn taking ~n/E as y-axis and loglo tf as x-axis. The standard stress-rupture plots showing the variation of loglo tf with ~n/E at different temperatures can be superposed on this kind of fracture map. Both these types of fracture mechanism maps (referred to henceforth in this paper as the Ashby maps) have been constructed by Ashby and coworkers (2-5) for fcc materials (Ni and its alloys, AI and its alloys, Pb and its alloys, and austenltic steels), bcc materials (Fe and steels) and several ceramics. The present report is concerned with construction of fracture mechanism maps of the typ@ outlined above for Ti. which is hop (alpha form) upto 1185 K and bcc (beta form) beyond, on the basis of data obtained from published literature as well as our own experiments. Further, we have found that a method of representing the fracture data in which loglo tf is plotted against T/Tm gives rise to features which in some ways may be more desirable when compared to the two Ashby techniques. Modes of Tensile Fracture in Titanium Of the large amount of publlshed data on the tensile behavlour of various grades of commercial purity (CP) Ti, we have considered only such investigations in which obs%rvations on fracture have been made. Amateau et al (6) have p@rformed tensile tests on large grained (~ I mm grain size) alpha Ti (99.6 wt% pure) using sheet specimens in the
851 0036- 9748/79/090851- 05502.00/0 Copyright (c) 1979 Pergamon Press Ltd.
852
FRACTURE MECHANISM MAPS
Vol. 13, No. 9
temperature range 77 to 300 K. Pure cleavage fracture was observed in tests below 89 K, a mixture of cleavage and ductile modes between 89 and 117 I{ and only ductile fracture above 117 K. In a recent investigetion on Ti of different purities (99.8 and 99.5 %~%) and grain sizes (I and 20j/m) Conrad et al (7) found ductile fracture in all cases at temperatures upto 650 K. Beevers and Edmonds (~) have also found ductile fracture in Ti of circa 99.8 ~ Durlty bet~reen 77 and 573 K. R o s i and P e r k i n s ( 9 ) have f o u n d t h e f r a c t u r e mode o f CP Ti ( 9 9 . 7 ~ ( pure) to be ductile in tensile tests on round bar specimens (~hA~m grain size) over the temperature range 77 to 925 K with the exception of the tests at 77 K and 925 K. The specimen tested ~[ 77 K failed in a brittle fashion (cleavage mode of failure) and the one tested at 925 K necked down to a point (rupture). High temperature creep fracture data on CP Ti were gathered mainly from the work of Grant and coworkers (lO~ll). In the temperature range 644 to 1033 K, uuff and Grant (!0) observed sharp breaks in stress rupture plots for 99.6 ~ % pure Ti which were attributed to a change in fracture mode from transgranular to intergranular. Above 1155 K (beta form) fracture of 99.3 ~ % pure Ti was reported to be transcrystalline by Richardson and Grant (ii). In view of the high temperatures and large ductilities reported by these authors as well as present experimental observations outlined in the following section~ these fractures can be deemed to belong to the category of rupture. From the above observations one can conclude that CP Ti (purity in the range 99.3 to 99.8 wt% but mostly around 99.7 %~%) fractures during monotonic tensile loading in any of the following ways: by cleavage , by ductile transgranular fracture, by intergranular creep fracture and by rupture. Ashby and coworkers (2-$) have dra~m a distinction between ductile transgranular fracture and transgranular creep fracture on the basis of a difference in the dominant deformation mechanism during the gro~.~h of voids leading to eventual fracture. In the published literature on fracture of Ti, referred to above, no such distinction has been made. However, the deformation mechanism map for Ti developed by Okazaki et al (12) indicates that the dominant deformation mechanism above about O.PI T m (485 K) is dislocation creep rather than dislocation glide. On this basis it should be possible to d l s t i n g u l s h b e t w e e n ductile transgranular fracture and transgranular creep fracture in Ti. In order to be assured of this distinction and to fill certain of the gaps in the available information experiments were undertaken by us. Experimental Titanium of 99.8 wt% purity and 35~um grain size was used. Tensile tests were conducted on round specimens using an Instron over the temperature range 300 to 1023 K. F r a c t u r e surfaces were examined in a Phillps PSEM 500 scanning electron microscope. The results are given in Table I. Specimens tested at temperatures from 300 to ~ 5 0 0 K failed by the ductile mode. The dimples were characteristically flat-bottomed and had sharp and angular edges. Above 500 K and upto about 970 K fracture surfaces still showed dimples. However, the latter dimples were deeper with sizes much larger and edges much smoother and less angular than those observed at l o w e r temperatures. Recalling also that Okazakl et al (12) have noted a transition from dislocation glide to dislocation creep above about 485 K, we have designated (Table I) the fracture mode above ~ 5 0 0 K as transgranular creep and have distinguished the same from ductile transgranular fracture below this temperature. As the temperature of testing was further raised to above 970 K the specimens failed by necking down to almost zero cross section~ i.e., by rupture.
Vol. 13, No. 9
FRACTURE MECHANISM MAPS
853
Construction of the Fracture Map~ The three types of fracture maps constructed for CP Ti are sho~Tn in Figs.l, 2 and 3. For this purpose test temperatures were normalized by dividing with the melting p6int of Ti (1941 K) and nominal tensile stresses were normalized by dividing with the elastic modulus (E) at the test temperature using the data of Armstrong and Brovm (13) for variation of E with temperature. The delineation of fracture fields in the stress-temperature (Fig.l) and stress-fracture time (Fig.2) diagrams follows closely the Ashby procedure. Ashby et al (4) utilize the variation of ultimate tensile strength (UTS) ~ t h temperature for positioning the boundary between ductile transgranular fracture and transgranular creep fracture in the stress-tempersture diagrams. We have adopted this principle in Fig.l. The temperature above which this changeover occurs was taken in Figs.! and 2 to be about 0.~5 T m on the basis of the deformation mechanism map for Ti (12). The lower time boundary for this transition in the stress-time diagram has been taken at about 10 2 seconds (4). Additionally, we have drawn a dashed vertical llne at 0.25 T m in Fig.l to indicate the unlikelihood of the occurrence of creep fracture below this temperature. The boundary between the transgranular and intergranular fracture fields was fixed following the breaks in stress-rupture plots obtained by Cuff and Grant (II). Based on the present experiments, as also the work of Grant and coworkers (i0, ii)~ a demarcation at about 0.5 Tm has been made to delineate the rupture field. The alpha (hcp) form of Ti is known to be prone to cleavage fracture~ however~ within a limited stress and temperature regime arising out of the grain size dependence of strength and ductility. Consequently the cleavage fracture field appears as indicated in Figs.l and 2. Bands on the maps indicate either a gradual transition from one mode of failure to another or a mixed mode of fracture. A plot between time to fracture and homologous temperature constitutes an as yet unexplored possibility for representing fracture data. Fig.3 is such a plot for CP Ti. The data points in this diagram are labelled with the logarithm of normalized tensile stress. This map gives the stresstemperature-time regimes of the various fracture modes with an accuracy no different from that of Figs.l and 2 and at the same time displays some additional features. For instance~ the fracture maps as drawn by Ashby et al (2-5)~ particularly the stress-temperature diagrams (such as Fig. l) contain large ill-deflned areas to which one cannot easily assign a fracture mode. In comparison, Fig.3 does not suffer in a major way from such ambiguities because it is more faithful to practical test conditions and data. Further~ the fracture fields in Fig.3 are more reasonably proportionate. As an example note that in Ashby maps (Figs.l and 2) the transgranular fracture field appears very narrow compared to the intergranular field. This does not reflect the fact that transgranular creep fracture and rupture~ and not intergranular creep fracture, dominate the high temperature fracture behaviour of Ti. Fig.8 does not give rise to such an erroneous impression. Moreover~ the Ashby maps of Figs.! and 2 show a sharp transition from ductile transgranular fracture to intergranular creep fracture even at low temperatures. The map of the third type shows more realistically that such a transition cannot take place~ at least not over the range of fracture times for which data are available. Thus a systematic progression as the test temperature is raised~ from cleavage~ through ductile transgranular fracture~ transgranular creep fracture and intergranular creep fracture to rupture is clearly brought out in Fig.S. Similar fracture mechanism maps for a variety of Ti alloys, namely an ~ alloy (Ti-SAI-2.5 Sn), a near- ~ alloy (IMI 688)~ an ~ + ~ alloy (Ti-6AI-4V) and a ~ alloy (Ti-15 Mo) are under preparation.
854
FRACTURE MECHANISM MAPS
Vol. 13, No. 9
Acknowledgements The authors are thankful to Professor S.L.Malhotra for extension of facilities, Professor M.F.Ashby for encouragement and the Aeronautics Research and Development Board of the Ministry of Defence, Government of India for financial support. References i. 2.
M.F.Ashby~ 'Fracture 1977 Advances in Research on the Strength and Fracture of Materials~J' Ed. D.M.R. Taplin, Vol. l, Pergamon Press, Oxford (1978). M,F Ashby,~ C. Gandhi, and D.M.R. Taplin, Acta ~ t 27, 699
(1977). 3. 4. 8. 6. 7. 8. 9. I0. ii. 12. 13.
C.Gandhi, M.F.Ashby, Cambridge University Engg.Dept. Report CUED/C/MATS/TR.48 (1978). M.F.Ashby, R.J.Fields and T.Weerasoorlya, Cambridge University Engg. Dept. Report CUED/C/MATS/TR.47 (1978). R.J.Fields and M.F.Ashby, Cambridge University Engg.Dept.Report, Fracture Mechanism Maps for Pure Iron (1978). M.F.Amateau~ H.I.Burrier~ Jr. and L.J.Ebert, Trans. ASM~ 59, 921(1966). H.Conrad~ M.K.Keshavan and G.A.Sargent, Proc. 2nd Intl. Conf. on Mechanical Behaviour of Materials~ Massachusetts, Boston~ August,(1976) 538. C.J.Beevers and D.V.Edmonds, Trans AIME, 248, 2391 (1969). F.D.Rosi and F.C.Perklns, Trans ASM, 48. 972 (1953). F.B.Cuff and N.J.Grant, Iron Age~ Nov.20, 134 (1952). L.S.Richardson and N.J.Grant, Trans AIME. 216. 18 (1969). K. Okazaki~ T.Odawara and H.Conrad, Scripta Met~ ii, 437 (1977). P.E.Armstrong and L.H.Brown, Trans AIME~ 230, 962 (1964). TABLE
1
Experimental Details and Results of the Present Work Test No. 1 2
Temperature K 300 300
~ominal strain rate ~ec -1 4.2 x I0 -2 4.2 x lO -4
UTS MPa 549 506
3 4
300 483
4.2 x 10 -6 4.2 x lO -2
434 226
8 6 7 8 9
583 679 679 679 873
4.2 8.3 4.2 4.2 4.2
x x x x x
193 165 163 151 115
I0
971
4.2
x 10 -2
ii 12
971 1023
i0 -4 10 -4 10 -4 10 -5 10 -2
4.2 x 10 -4 4.2 x 10 -4
% Elonga- % HeducFracture mode tion tion in area 47 Ductile 35 71 Ductile 40 92 Ductile 46 Ductile 9 35 19 14 14.5 13 16.5
65 63 73 60 69
86
42
79
47 21
52 65
i00 i00
Trans granular creep Trans granular creep Transgranular creep Transgrsnular creep Ductile Trans granular creep Rupture Rupture
Vol.
13, No.
9
FRACTURE
MECHANISM
16'
MAPS
855
I C P TITANIUM LL Pt'*A DYNAMIC FRACTURE
OUCTILI[ TRANSGRANULAN
v Ul Ul UJ /=. U)
~, 16'
IN TE RGRAI~IL A III
Z
|
4-4 S|
',
N
?i ,.'°"°"
I
:[ nO
le
~
r.ror,r.
Z
02
0
O'
HOMOLOGOUS
O.S
0.8
1"0
(T/Tin)
TEMPERATURE,
FIG.I.Fracture mechanism map of the first type for CP Ti. Various shadings used for data points indicate different fracture modes. Open symbols indicate unidentified fracture mode. Points are marked with the logarithm of time to fracture (in seconds).
CLEA~G[ "+ .
,-el .
'" '.
DUCTILE TRANS~qANUi.AR F RACI~It[ O.I(,TI
~
o-4|'r. RUPTURE
iJlm • 4 A~
1~, 0
O.4ST.
,.d6VpU aT ,u ¢le61) mm~neoN * eaANT ( m ~ ) CUFF• e m i t (~1|) a I i 10 s
TIME TO FRACTURE
I 10'
; tr
:!L ' @UTm
10 e
10*
(SECONOS)
FIG. 2. Fracture mechanism map of the second type for CP Ti. Symbol shadings have the same meaning as in Fig.1. Superposed straight lines are isothermal stress-rupture lines.
856
FRACTURE MECHANISM MAPS
108! TRANSGRANU°AR - - 5
INTERCdRtANULAR
ICR,,~RAC,~E! CRE,~.ACTURE I I1¢~ , ~
"
Ul
I I
Q Z
I t ~
• l
/
~ ~-~'"
.
~
0
~.11~. E~;;][,1
':?.".T'~ -3~ec:.':
Vol. 15, No. 9
I CP
!,,., ..... o" ,.~,
J. . . . . . . ,..L.o°o,
TITANIUM
1 YEAR
...
...
ImC.*.O,ON, am*NT(~S°) Z. ;.o., • psnx,~ (~0s3) v v v
lO(~w
. -°.so
lo1' ~
ICUFF • GRANT'I~52)
AA~
,1 ° FRACTURE
27
M.I
V
•
V
. . . . :; " • ". A A ~::.:. - ~ 6
I B, I ~
%
"-.-~,
,o ,,
'-
,i~:I[,t~.- ~.o~ ,,,-llr, zw-~, o
i.~
0
% t
~ : i. ~ , . _.-,~6~k
-~"~"~.,..,
%
,
0"2
, ]z
,
0"4
0'6
HOMOLOGOUS TEMPERATURE,
0"8
1"0
( T / Tin)
FIG.3. Fracture mechanism map of the third type for CP Ti. Symbol shadings have the same meanings as in Fig.l. Points are marked with the logarithm of normalized tensile stress. Note that the stress within each fracture field varies only a little while showing a much larger variation with temperature.
Vol. 13, pp. 851-856, 1979 Printed in the U.S.A.
Pergamon Press Ltd. All rights reserved.
FRACTURE MECHANISM MAPS FOR TITANIUM Y. Krishna Mohan Rao, V.Kutumba Rao and P.Rama Rao Department of Netallurgical Englneering,Banaras Hindu University, Varanasi 221005, India (Received June 8, 1979)
Introduction The fracture mechanism map, first developed by Ashby (I), is a binary plot which identifies the fields of stress and temperature in which a particular mechanism of fracture is dominant. The Ashby procedure for constucring such a map consists in plotting the normalized tensile stress, ~n/E (where ~n is the nominal applied stress in creep tests and the ultimate tensile strength in tensile tests and E is the elastic modulus at the test temperature), versus the homologous temperature, T/Tm (where T m is the melting point in K). Each datum in the map is labelled with the logarithm of time to fracture, loglo tf (tf in seconds). A mode of failure is assigned to each datum point based primarily on fractographic observations and using indirect evidence where such observations are not available. Boundaries are then drawn separating blocks of data with one mode of failure from those with another. Fracture maps have also been drawn taking ~n/E as y-axis and loglo tf as x-axis. The standard stress-rupture plots showing the variation of loglo tf with ~n/E at different temperatures can be superposed on this kind of fracture map. Both these types of fracture mechanism maps (referred to henceforth in this paper as the Ashby maps) have been constructed by Ashby and coworkers (2-5) for fcc materials (Ni and its alloys, AI and its alloys, Pb and its alloys, and austenltic steels), bcc materials (Fe and steels) and several ceramics. The present report is concerned with construction of fracture mechanism maps of the typ@ outlined above for Ti. which is hop (alpha form) upto 1185 K and bcc (beta form) beyond, on the basis of data obtained from published literature as well as our own experiments. Further, we have found that a method of representing the fracture data in which loglo tf is plotted against T/Tm gives rise to features which in some ways may be more desirable when compared to the two Ashby techniques. Modes of Tensile Fracture in Titanium Of the large amount of publlshed data on the tensile behavlour of various grades of commercial purity (CP) Ti, we have considered only such investigations in which obs%rvations on fracture have been made. Amateau et al (6) have p@rformed tensile tests on large grained (~ I mm grain size) alpha Ti (99.6 wt% pure) using sheet specimens in the
851 0036- 9748/79/090851- 05502.00/0 Copyright (c) 1979 Pergamon Press Ltd.
852
FRACTURE MECHANISM MAPS
Vol. 13, No. 9
temperature range 77 to 300 K. Pure cleavage fracture was observed in tests below 89 K, a mixture of cleavage and ductile modes between 89 and 117 I{ and only ductile fracture above 117 K. In a recent investigetion on Ti of different purities (99.8 and 99.5 %~%) and grain sizes (I and 20j/m) Conrad et al (7) found ductile fracture in all cases at temperatures upto 650 K. Beevers and Edmonds (~) have also found ductile fracture in Ti of circa 99.8 ~ Durlty bet~reen 77 and 573 K. R o s i and P e r k i n s ( 9 ) have f o u n d t h e f r a c t u r e mode o f CP Ti ( 9 9 . 7 ~ ( pure) to be ductile in tensile tests on round bar specimens (~hA~m grain size) over the temperature range 77 to 925 K with the exception of the tests at 77 K and 925 K. The specimen tested ~[ 77 K failed in a brittle fashion (cleavage mode of failure) and the one tested at 925 K necked down to a point (rupture). High temperature creep fracture data on CP Ti were gathered mainly from the work of Grant and coworkers (lO~ll). In the temperature range 644 to 1033 K, uuff and Grant (!0) observed sharp breaks in stress rupture plots for 99.6 ~ % pure Ti which were attributed to a change in fracture mode from transgranular to intergranular. Above 1155 K (beta form) fracture of 99.3 ~ % pure Ti was reported to be transcrystalline by Richardson and Grant (ii). In view of the high temperatures and large ductilities reported by these authors as well as present experimental observations outlined in the following section~ these fractures can be deemed to belong to the category of rupture. From the above observations one can conclude that CP Ti (purity in the range 99.3 to 99.8 wt% but mostly around 99.7 %~%) fractures during monotonic tensile loading in any of the following ways: by cleavage , by ductile transgranular fracture, by intergranular creep fracture and by rupture. Ashby and coworkers (2-$) have dra~m a distinction between ductile transgranular fracture and transgranular creep fracture on the basis of a difference in the dominant deformation mechanism during the gro~.~h of voids leading to eventual fracture. In the published literature on fracture of Ti, referred to above, no such distinction has been made. However, the deformation mechanism map for Ti developed by Okazaki et al (12) indicates that the dominant deformation mechanism above about O.PI T m (485 K) is dislocation creep rather than dislocation glide. On this basis it should be possible to d l s t i n g u l s h b e t w e e n ductile transgranular fracture and transgranular creep fracture in Ti. In order to be assured of this distinction and to fill certain of the gaps in the available information experiments were undertaken by us. Experimental Titanium of 99.8 wt% purity and 35~um grain size was used. Tensile tests were conducted on round specimens using an Instron over the temperature range 300 to 1023 K. F r a c t u r e surfaces were examined in a Phillps PSEM 500 scanning electron microscope. The results are given in Table I. Specimens tested at temperatures from 300 to ~ 5 0 0 K failed by the ductile mode. The dimples were characteristically flat-bottomed and had sharp and angular edges. Above 500 K and upto about 970 K fracture surfaces still showed dimples. However, the latter dimples were deeper with sizes much larger and edges much smoother and less angular than those observed at l o w e r temperatures. Recalling also that Okazakl et al (12) have noted a transition from dislocation glide to dislocation creep above about 485 K, we have designated (Table I) the fracture mode above ~ 5 0 0 K as transgranular creep and have distinguished the same from ductile transgranular fracture below this temperature. As the temperature of testing was further raised to above 970 K the specimens failed by necking down to almost zero cross section~ i.e., by rupture.
Vol. 13, No. 9
FRACTURE MECHANISM MAPS
853
Construction of the Fracture Map~ The three types of fracture maps constructed for CP Ti are sho~Tn in Figs.l, 2 and 3. For this purpose test temperatures were normalized by dividing with the melting p6int of Ti (1941 K) and nominal tensile stresses were normalized by dividing with the elastic modulus (E) at the test temperature using the data of Armstrong and Brovm (13) for variation of E with temperature. The delineation of fracture fields in the stress-temperature (Fig.l) and stress-fracture time (Fig.2) diagrams follows closely the Ashby procedure. Ashby et al (4) utilize the variation of ultimate tensile strength (UTS) ~ t h temperature for positioning the boundary between ductile transgranular fracture and transgranular creep fracture in the stress-tempersture diagrams. We have adopted this principle in Fig.l. The temperature above which this changeover occurs was taken in Figs.! and 2 to be about 0.~5 T m on the basis of the deformation mechanism map for Ti (12). The lower time boundary for this transition in the stress-time diagram has been taken at about 10 2 seconds (4). Additionally, we have drawn a dashed vertical llne at 0.25 T m in Fig.l to indicate the unlikelihood of the occurrence of creep fracture below this temperature. The boundary between the transgranular and intergranular fracture fields was fixed following the breaks in stress-rupture plots obtained by Cuff and Grant (II). Based on the present experiments, as also the work of Grant and coworkers (i0, ii)~ a demarcation at about 0.5 Tm has been made to delineate the rupture field. The alpha (hcp) form of Ti is known to be prone to cleavage fracture~ however~ within a limited stress and temperature regime arising out of the grain size dependence of strength and ductility. Consequently the cleavage fracture field appears as indicated in Figs.l and 2. Bands on the maps indicate either a gradual transition from one mode of failure to another or a mixed mode of fracture. A plot between time to fracture and homologous temperature constitutes an as yet unexplored possibility for representing fracture data. Fig.3 is such a plot for CP Ti. The data points in this diagram are labelled with the logarithm of normalized tensile stress. This map gives the stresstemperature-time regimes of the various fracture modes with an accuracy no different from that of Figs.l and 2 and at the same time displays some additional features. For instance~ the fracture maps as drawn by Ashby et al (2-5)~ particularly the stress-temperature diagrams (such as Fig. l) contain large ill-deflned areas to which one cannot easily assign a fracture mode. In comparison, Fig.3 does not suffer in a major way from such ambiguities because it is more faithful to practical test conditions and data. Further~ the fracture fields in Fig.3 are more reasonably proportionate. As an example note that in Ashby maps (Figs.l and 2) the transgranular fracture field appears very narrow compared to the intergranular field. This does not reflect the fact that transgranular creep fracture and rupture~ and not intergranular creep fracture, dominate the high temperature fracture behaviour of Ti. Fig.8 does not give rise to such an erroneous impression. Moreover~ the Ashby maps of Figs.! and 2 show a sharp transition from ductile transgranular fracture to intergranular creep fracture even at low temperatures. The map of the third type shows more realistically that such a transition cannot take place~ at least not over the range of fracture times for which data are available. Thus a systematic progression as the test temperature is raised~ from cleavage~ through ductile transgranular fracture~ transgranular creep fracture and intergranular creep fracture to rupture is clearly brought out in Fig.S. Similar fracture mechanism maps for a variety of Ti alloys, namely an ~ alloy (Ti-SAI-2.5 Sn), a near- ~ alloy (IMI 688)~ an ~ + ~ alloy (Ti-6AI-4V) and a ~ alloy (Ti-15 Mo) are under preparation.
854
FRACTURE MECHANISM MAPS
Vol. 13, No. 9
Acknowledgements The authors are thankful to Professor S.L.Malhotra for extension of facilities, Professor M.F.Ashby for encouragement and the Aeronautics Research and Development Board of the Ministry of Defence, Government of India for financial support. References i. 2.
M.F.Ashby~ 'Fracture 1977 Advances in Research on the Strength and Fracture of Materials~J' Ed. D.M.R. Taplin, Vol. l, Pergamon Press, Oxford (1978). M,F Ashby,~ C. Gandhi, and D.M.R. Taplin, Acta ~ t 27, 699
(1977). 3. 4. 8. 6. 7. 8. 9. I0. ii. 12. 13.
C.Gandhi, M.F.Ashby, Cambridge University Engg.Dept. Report CUED/C/MATS/TR.48 (1978). M.F.Ashby, R.J.Fields and T.Weerasoorlya, Cambridge University Engg. Dept. Report CUED/C/MATS/TR.47 (1978). R.J.Fields and M.F.Ashby, Cambridge University Engg.Dept.Report, Fracture Mechanism Maps for Pure Iron (1978). M.F.Amateau~ H.I.Burrier~ Jr. and L.J.Ebert, Trans. ASM~ 59, 921(1966). H.Conrad~ M.K.Keshavan and G.A.Sargent, Proc. 2nd Intl. Conf. on Mechanical Behaviour of Materials~ Massachusetts, Boston~ August,(1976) 538. C.J.Beevers and D.V.Edmonds, Trans AIME, 248, 2391 (1969). F.D.Rosi and F.C.Perklns, Trans ASM, 48. 972 (1953). F.B.Cuff and N.J.Grant, Iron Age~ Nov.20, 134 (1952). L.S.Richardson and N.J.Grant, Trans AIME. 216. 18 (1969). K. Okazaki~ T.Odawara and H.Conrad, Scripta Met~ ii, 437 (1977). P.E.Armstrong and L.H.Brown, Trans AIME~ 230, 962 (1964). TABLE
1
Experimental Details and Results of the Present Work Test No. 1 2
Temperature K 300 300
~ominal strain rate ~ec -1 4.2 x I0 -2 4.2 x lO -4
UTS MPa 549 506
3 4
300 483
4.2 x 10 -6 4.2 x lO -2
434 226
8 6 7 8 9
583 679 679 679 873
4.2 8.3 4.2 4.2 4.2
x x x x x
193 165 163 151 115
I0
971
4.2
x 10 -2
ii 12
971 1023
i0 -4 10 -4 10 -4 10 -5 10 -2
4.2 x 10 -4 4.2 x 10 -4
% Elonga- % HeducFracture mode tion tion in area 47 Ductile 35 71 Ductile 40 92 Ductile 46 Ductile 9 35 19 14 14.5 13 16.5
65 63 73 60 69
86
42
79
47 21
52 65
i00 i00
Trans granular creep Trans granular creep Transgranular creep Transgrsnular creep Ductile Trans granular creep Rupture Rupture
Vol.
13, No.
9
FRACTURE
MECHANISM
16'
MAPS
855
I C P TITANIUM LL Pt'*A DYNAMIC FRACTURE
OUCTILI[ TRANSGRANULAN
v Ul Ul UJ /=. U)
~, 16'
IN TE RGRAI~IL A III
Z
|
4-4 S|
',
N
?i ,.'°"°"
I
:[ nO
le
~
r.ror,r.
Z
02
0
O'
HOMOLOGOUS
O.S
0.8
1"0
(T/Tin)
TEMPERATURE,
FIG.I.Fracture mechanism map of the first type for CP Ti. Various shadings used for data points indicate different fracture modes. Open symbols indicate unidentified fracture mode. Points are marked with the logarithm of time to fracture (in seconds).
CLEA~G[ "+ .
,-el .
'" '.
DUCTILE TRANS~qANUi.AR F RACI~It[ O.I(,TI
~
o-4|'r. RUPTURE
iJlm • 4 A~
1~, 0
O.4ST.
,.d6VpU aT ,u ¢le61) mm~neoN * eaANT ( m ~ ) CUFF• e m i t (~1|) a I i 10 s
TIME TO FRACTURE
I 10'
; tr
:!L ' @UTm
10 e
10*
(SECONOS)
FIG. 2. Fracture mechanism map of the second type for CP Ti. Symbol shadings have the same meaning as in Fig.1. Superposed straight lines are isothermal stress-rupture lines.
856
FRACTURE MECHANISM MAPS
108! TRANSGRANU°AR - - 5
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Vol. 15, No. 9
I CP
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HOMOLOGOUS TEMPERATURE,
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( T / Tin)
FIG.3. Fracture mechanism map of the third type for CP Ti. Symbol shadings have the same meanings as in Fig.l. Points are marked with the logarithm of normalized tensile stress. Note that the stress within each fracture field varies only a little while showing a much larger variation with temperature.