Compressive creep of Fe3Al-type iron aluminide with Zr additions
High-temperature creep ofa Fe3Al-type iron aluminide alloyed by zirconium was studied in the temperature range 873-1073 K. The alloy contained (wt.%) 31.5% Al, 3.5% Cr, 0.25% Zr, 0.19% C (Fe balance). It was tested in two states: (i) as received after hot rolling and (ii) heat treated (1423 K/ 2 h/a...
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Інститут проблем міцності ім. Г.С. Писаренко НАН України
2008
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| Цитувати: | Compressive creep of Fe3Al-type iron aluminide with Zr additions / F. Dobes, P. Kratochvil, K. Milicka // Проблемы прочности. — 2008. — № 1. — С.117-120. — Бібліогр.: 8 назв. — англ. |
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irk-123456789-484392013-08-19T18:31:47Z Compressive creep of Fe3Al-type iron aluminide with Zr additions Dobes, F. Kratochvil, P. Milicka, K. Научно-технический раздел High-temperature creep ofa Fe3Al-type iron aluminide alloyed by zirconium was studied in the temperature range 873-1073 K. The alloy contained (wt.%) 31.5% Al, 3.5% Cr, 0.25% Zr, 0.19% C (Fe balance). It was tested in two states: (i) as received after hot rolling and (ii) heat treated (1423 K/ 2 h/air). Creep tests were performed in compression at constant load with stepwise loading: in each step, the load was changed to a new value after steady state creep rate had been established. Stress exponent and activation energy of the creep rate were determined and possible creep mechanisms were discussed in terms ofthe threshold stress concept. A rapidfall ofthe stress exponent and ofthe threshold stress with the increasing temperature indicates that creep is impeded by the presence of precipitates only at temperature 873 K. The results were compared with the results oflong-term creep tests in tension performed recently on the same alloy. Изучена высокотемпературная ползучесть Изучена высокотемпературная ползучесть алюминида железа типа Fe3Al, легированного цирконием в диапазоне температур 873...1073 К. Сплав содержал (ат.%) 31,5 Al, 3,5 Сг, 0,25 Zг, 0,19 С (остальное Fе). Испытания проводили в двух состояниях: в состоянии поставки после горячей прокатки и после термообработки (1423 К/2 ч/воздух). Испытания на ползучесть выполняли при постоянной сжимающей нагрузке при ступенчатом нагружении: на каждой ступени использовали нагрузку другой величины после того, как наступала стадия установившейся скорости ползучести. Определена экспонента напряжения и энергия активации для скорости ползучести, обсуждены возможные механизмы ползучести с позиций концепции порогового напряжения. Резкое уменьшение экспоненты напряжения и порогового напряжения при увеличении температуры свидетельствует о том, что наличие вторичных фаз снижает скорость ползучести только при температуре 873 К. Полученные результаты сравнивали с данными длительных испытаний на ползучесть при растяжении, выполненных на том же сплаве. 2008 Article Compressive creep of Fe3Al-type iron aluminide with Zr additions / F. Dobes, P. Kratochvil, K. Milicka // Проблемы прочности. — 2008. — № 1. — С.117-120. — Бібліогр.: 8 назв. — англ. 0556-171X http://dspace.nbuv.gov.ua/handle/123456789/48439 539.4 en Проблемы прочности Інститут проблем міцності ім. Г.С. Писаренко НАН України |
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Научно-технический раздел Научно-технический раздел |
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Научно-технический раздел Научно-технический раздел Dobes, F. Kratochvil, P. Milicka, K. Compressive creep of Fe3Al-type iron aluminide with Zr additions Проблемы прочности |
| description |
High-temperature creep ofa Fe3Al-type iron aluminide alloyed by zirconium was studied in the temperature range 873-1073 K. The alloy contained (wt.%) 31.5% Al, 3.5% Cr, 0.25% Zr, 0.19% C (Fe balance). It was tested in two states: (i) as received after hot rolling and (ii) heat treated (1423 K/ 2 h/air). Creep tests were performed in compression at constant load with stepwise loading: in each step, the load was changed to a new value after steady state creep rate had been established. Stress exponent and activation energy of the creep rate were determined and possible creep mechanisms were discussed in terms ofthe threshold stress concept. A rapidfall ofthe stress exponent and ofthe threshold stress with the increasing temperature indicates that creep is impeded by the presence of precipitates only at temperature 873 K. The results were compared with the results oflong-term creep tests in tension performed recently on the same alloy.
Изучена высокотемпературная ползучесть |
| format |
Article |
| author |
Dobes, F. Kratochvil, P. Milicka, K. |
| author_facet |
Dobes, F. Kratochvil, P. Milicka, K. |
| author_sort |
Dobes, F. |
| title |
Compressive creep of Fe3Al-type iron aluminide with Zr additions |
| title_short |
Compressive creep of Fe3Al-type iron aluminide with Zr additions |
| title_full |
Compressive creep of Fe3Al-type iron aluminide with Zr additions |
| title_fullStr |
Compressive creep of Fe3Al-type iron aluminide with Zr additions |
| title_full_unstemmed |
Compressive creep of Fe3Al-type iron aluminide with Zr additions |
| title_sort |
compressive creep of fe3al-type iron aluminide with zr additions |
| publisher |
Інститут проблем міцності ім. Г.С. Писаренко НАН України |
| publishDate |
2008 |
| topic_facet |
Научно-технический раздел |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/48439 |
| citation_txt |
Compressive creep of Fe3Al-type iron aluminide with Zr additions / F. Dobes, P. Kratochvil, K. Milicka // Проблемы прочности. — 2008. — № 1. — С.117-120. — Бібліогр.: 8 назв. — англ. |
| series |
Проблемы прочности |
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| first_indexed |
2025-07-04T08:56:48Z |
| last_indexed |
2025-07-04T08:56:48Z |
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1836706076805824512 |
| fulltext |
UDC 539. 4
C o m p r e s s iv e C r e e p o f F e 3A l- t y p e I r o n A li im in id e w ith Z r A d d it io n s
F. D o b es,1a P . K ratoch vfl,2b and K . M ilick a 1c
1 Institute o f Physics o f Materials, Academy o f Sciences o f the Czech Republic, Brno, Czech
Republic
2 Department o f Metal Physics, Charles University, Prague, Czech Republic
a dobes@ipm.cz, b pekrat@met.mff.cuni.cz, c milicka@ipm.cz
High-temperature creep o f a Fe3Al-type iron aluminide alloyed by zirconium was studied in the
temperature range 873-1073 K. The alloy contained (wt.%) 31.5% Al, 3.5% Cr, 0.25% Zr, 0.19% C
(Fe balance). It was tested in two states: (i) as received after hot rolling and (ii) heat treated (1423 K /
2 h/air). Creep tests were performed in compression at constant load with stepwise loading: in each
step, the load was changed to a new value after steady state creep rate had been established. Stress
exponent and activation energy o f the creep rate were determined and possible creep mechanisms
were discussed in terms o f the threshold stress concept. A rapid fa ll o f the stress exponent and o f the
threshold stress with the increasing temperature indicates that creep is impeded by the presence o f
precipitates only at temperature 873 K. The results were compared with the results o f long-term
creep tests in tension performed recently on the same alloy.
K eyw o rd s : iron alum inides, creep, threshold stress.
In troduction . Iron-alum inides-based alloys are prom ising candidates for many
industrial applications since they have excellent resistance to oxidation and sulfidation.
One o f their drawbacks is the insufficient high-temperature strength. This can be
im proved either through solid solution hardening or through precipitation hardening. The
alloying b y additions o f zirconium is expected to be effective in the precipitation
hardening due to low solubility and formation o f phases (Fe, A l)2Zr and (Fe, A l)12Zr [1,
2]. This is in agreem ent w ith the review o f existing studies o f h igh temperature
m echanical properties o f iron alum inides [3, 4], w hich docum ented that the addition o f Zr
brings the best results. This fact initiated an investigation o f quaternary a lloy on Fe3A l
base w ith chrom ium and zirconium . The results o f microstructural observations and o f
tensile creep tests at 873 K were published elsew here [5]. The aim o f the present paper is
to report additional results o f com pressive creep tests o f the sam e alloy perform ed in more
extensive range o f temperatures and to start d iscussion o f the potential rate-controlling
m echanism s.
E xp erim en ta l. The com position o f the a lloy used for the experim ent w as as fo llow s
(wt.%): A l = 31.5; Cr = 3.5; Zr = 0.25; C = 0.19; Fe - balance. The alloy w as prepared in
the vacuum furnace and cast under argon in the Research Institute for M etals in PanenskM
Brehany, C zech Republic. The casting (dim ensions 400X 120X 38 m m ) w as hot-rolled to
the final thickness o f 13 m m at 1473 K in several steps w ith 20% reductions for each pass.
The rolled p iece w as heated after each second pass and the temperature did not decrease
under 1273 K during the total rolling period. A fter the final pass, the slab w as quenched
from the temperature at least 1273 K into oil. One set o f sam ples w as additionally
annealed at 1423 K /2 h and air cooled.
The specim ens for com pressive creep tests w ere prepared with the axis
perpendicular to the rolling plane. The dim ensions o f sam ples were: diameter 4 mm,
height 12 mm. Constant load com pressive creep tests o f the alloy w ere perform ed at
temperatures from 873 to 1073 K. A stepw ise loading w as used: in each step, the load was
changed to a new value after steady-state creep rate had been established. The terminal
values o f the true stress and the true strain rate w ere evaluated for the respective step.
© F. DO B ES, P. KRATOCHVIL, K. MILICKA, 2008
ISSN 0556-171X. Проблемы прочности, 2008, N 1 117
mailto:dobes@ipm.cz
mailto:pekrat@met.mff.cuni.cz
mailto:milicka@ipm.cz
F. Dobes, P. Kratochvtt, and K. Milicka
Protective atmosphere o f dried and purified argon w as used. During the test, temperature
w as kept constant w ithin ± 1 K. Creep curves were PC recorded by m eans o f special
software. The sensitivity o f elongation m easurem ents w as better than 10_ 5 .
R esu lts. The applied stress dependence o f the m inim um creep rate in the rolled
material is g iven in Fig. 1. The dependence can be described at a g iven temperature by the
pow er function
£ = A o n , (1)
where A is a temperature dependent factor and n is exponent. The values o f exponent n
are decreasing w ith increasing temperature: n = 12.2 at 873 K, 5.4 at 923 K, 4 .9 at 973 K,
4.7 at 1023 K, and 4.6 at 1073 K. The apparent activation energy o f creep can be obtained
from the A rrhenius-type p lot (Fig. 2). It is about 433 kJ/m ol at 50 M Pa, 407 kJ/m ol at 80
MPa, and 375 kJ/m ol at 100 M Pa at temperatures from 923 to 1073 K, respectively, but it
can be very h igh (greater than 700 kJ/m ol) at low er temperatures.
APPLIED STRESS [MPa]
Fig. 1 Fig. 2
Fig. 1. Applied stress dependence o f creep rate at different temperatures.
Fig. 2. Dependence o f creep rate on reciprocal absolute temperature.
A n exam ple o f creep results obtained on sam ples after heat treatment is g iven in
Fig. 3. The heat treatment has positive effect on the creep resistance. The observed
deceleration o f the creep rate is less than one order o f magnitude. The results o f previous
research o f creep o f the sam e alloy are also g iven in Fig. 3. A good coincidence o f tensile
and com pressive creep data can be admitted.
D iscussion . The values o f stress exponent n in Eq. (1) are usually taken as an
indication o f potential creep controlling m echanism s. W hen dislocation m otion controls
creep deform ation o f pure m etals and single phase solid solutions, the exponent n o f
about 3 to 5 is expected. The values o f n can be substantially greater in alloys reinforced
w ith particles o f secondary phases. The creep behavior is then rationalized b y m eans o f
the threshold stress concept: the stress dependence o f the creep rate is rewritten as
£ = A , ( o ~ o th f , (2 )
w here o th is the threshold stress. The value o f exponent n should be close to the value
o f n observed in pure m etals and single phase solid solutions. The value o f the threshold
stress can be determ ined in tw o different w ays:
118 ISSN 0556-171X. npoÖÄeubi npounocmu, 2008, № 1
Compressive Creep o f Fe^Al-type Iron Aluminide
(i) The m ethod based on the additivity rule [6 ]. It is necessary to know the behaviour
o f corresponding single phase material.
(ii) The second m ethod m akes use o f linearized p lot o f (£ )1/n vs. applied stress.
The m ethod is sensitive to the choice o f stress exponent n.
i
Tension
♦ rolled
£> heat treated
►
i
>
►
o
|
!
j i
A
-
♦
- -
~ * y 8 7 3 K
1 1
200 300
APPLIED STRESS [MPa]
Fig. 3 Fig. 4
Fig. 3. Comparison of results o f creep tests in tension and in compression.
Fig. 4. Dependence o f threshold stress on temperature.
Fig. 5
APPLIED STRESS [MPa]
Stress dependence o f creep rate in present alloy and in two similar alloys from [8].
To enable a com parison w ith the previous application o f the m ethod to the results o f
creep in F e -A l alloys - and also the alloy w ith Zr addition from [8 ], w e have used the
second m ethod w ith the sam e value o f n , i.e ., n = 4. The results are g iven in Fig. 4. Very
good agreem ent is obtained at temperature 873 K. The values o f the threshold stress in the
present a lloy are very rapidly decreasing w ith the increasing temperature and at
temperature 923 K and above they are substantially low er than the values reported in [8].
This fact, together w ith the above g iven values o f stress exponent n, indicates that creep is
im peded by the presence o f precipitates on ly at temperature 873 K. A t temperatures
greater than 923 K it could be expected that either the precipitates have on ly minor
influence on the creep resistance o f the investigated alloy or that they are dissolved. This
can be further docum ented by comparing present data w ith the data published in [8] for
ISSN 0556-171X. npo6n.eubi npounocmu, 2008, N 1 119
F. Dobes, P. Kratochvtt, and K. Milicka
temperature 973 K (Fig. 5). The slope o f the stress dependence o f present alloy is lower
than that o f the alloy F e-20A l-C r-Z r . Creep rates at lo w applied stresses are substantially
slow er in F e-2 0 A l-C r-Z r than in the present alloy. On the other hand, creep properties o f
the present a lloy are comparable w ith the properties o f the binary alloy F e -3 0 A l without
second-phase precipitation.
C O N C L U S I O N S
1. The uniaxial com pressive tests o f F e -3 1 .5 A l-3 .5 C r alloy w ith 0.25 wt.% o f Zr at
temperatures from 873 to 1023 K give the results comparable w ell w ith those o f tensile
creep tests.
2. The values o f stress exponent n, activation energy Q , and threshold stress indicate
a change o f deform ation m echanism w ithin the above range o f temperatures.
3. The applied amount o f zirconium does not im prove creep resistance efficiently at
temperatures above 873 K.
Acknowledgments. The paper is based on work supported by the Grant Agency o f the Czech
Republic within the project 106/05/0409.
1. M. Palm, Intermetallics, 13, 1286 (2005).
2. F. Stein, M. Palm, and G. Sauthoff, Intermetallics, 13, 1275 (2005).
3. D. G. Morris, M. A. Munoz-Morris, and J. Chao, Intermetallics, 12, 821 (2004).
4. D. G. Morris, M. A. Munoz-Morris, and C. Baudin, Acta Mater., 52, 2827 (2004).
5. P. Kratochvil, P. Malek, M. Cieslar, et al., Intermetallics, 15, 333 (2007).
6. R. Lagneborg and B. Bergman, Metal Sci., 10, 20 (1976).
7. R. W. Lund and W. D. Nix, Acta Metall., 24, 469 (1976).
8. D. G. Morris, M. A. Munoz-Morris, and L. M. Requejo, Acta Mater., 54, 2335 (2006).
Received 28. 06. 2007
120 ISSN 0556-171X. npo6neMbi npouHocmu, 2008, № 1
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