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Influence of coatings and hot corrosion on the fatigue behaviour of nickel-based superalloys
Thin SolidFilms, 84 (1981) 29-36 METALLURGICAL
AND PROTECTIVE
29
COATINGS
INFLUENCE OF COATINGS AND HOT CORROSION ON THE FATIGUE BEHAVIOUR OF NICKEL-BASED SUPERALLOYS * K. SCHNEIDER,
H. VON ARNIM AND H. W. GRtiNLING
Brown, Boveri & Cie, Mannheim (F.R.G.) (Received
March 23,198l;
accepted
April 10, 1981)
The fatigue behaviour of materials and components is strongly affected by the surface conditions, i.e. the surface finish and the materials properties in the nearsurface region. Therefore any change in these conditions during fabrication or service may change the fatigue properties. It is common practice to coat turbine blades with materials that are resistant to hot corrosion. However, this treatment involves chemical and mechanical changes in the materials surface properties which could also change the fatigue properties of these components. The recommended heat treatment for the coating normally differs from that which produces the best mechanical or creep properties of the base metal and hence may cause additional changes in the fatigue properties. Chemical and mechanical changes in the surface conditions of an uncoated component may also take place during operation. Additionally, a large amount of notching may occur since oxidation and hot corrosion are not homogeneously distributed but take place preferentially at sites such as grain boundaries. In this work we investigate the effect of Pt-Al coatings on the high cycle fatigue (HCF) behaviour of the cast nickel-based alloys IN 738LC and IN 939 which are commonly used in large industrial gas turbines. A reduction in the fatigue life due to the coating was observed. However, the simultaneous occurrence of hot corrosion attack and cyclic loading was much more detrimental. Fractographic and metallographic investigations showed that, in the as-coated condition, the crack initiation sites in the Pt-Al-coated alloys were internal pores situated just below the surface of the substrate. After aging or hot corrosion cracks initiate at the surface probably as a result of notch development by the attack. When HCF and hot corrosion are acting concurrently the coatings are expected to give a beneficial effect by protecting the surface from accelerated crack initiation.
1. INTRODUCTION
Coatings on gas turbine buckets are applied to reduce oxidation, erosion and hot corrosion. Owing to the presence of the coating material, both the composition *Paper presented U.S.A.,
at the International April 6-10, 1981.
0040-6090/S
I/0000-0000/~02.50
Conference
on Metallurgical
Coatings,
0 Elsevier Sequoia/Printed
San Francisco,
CA,
in The Netherlands
30
K. SCHNEIDER, H. v. ARNIM, H. W. GRijNLING
and the mechanical properties of the surface are changed. Thus the deformation behaviour of both the coating and the coating-substrate system must be considered. Even though the coating is not designed to enhance the strength of the component in most cases, its strain behaviour and toughness are important with respect to its ability to protect the surface and to prevent crack initiation under mechanical loading. Coatings on gas turbine blades develop a protective oxide scale and hence change their composition during service; the same considerations apply to the scalecoating system. Apart from the changes produced in the surface properties, some coating procedures require heat treatments different from those normally recommended to achieve the required substrate metal properties. This paper deals with the interaction between the coating and the substrate with respect to the high cycle fatigue (HCF) behaviour of a coated component. A material subjected to cyclic loading at high temperatures can endure a certain number of cycles without showing any signs of damage. However, when a certain amount of damage has accumulated locally in the material or at the surface a crack initiates and further damage is determined by the propagation of this crack. In the early stages crack initiation occurs preferentially on sites where stress concentrations are found, e.g. machining notches at the surface, local corrosion attack, inclusions and pores. The microstructural elements determining crack initiation, the effect of the PtAl coating LDC 2 (Fig. 1) on crack initiation and the effect ‘of long-term exposure and hot corrosion attack (Table I) on the HCF behaviour are investigated for the nickel-based cast alloys IN 738LC and IN 939.
Fig. 1. LDC 2 coating on IN 738LC.
1
31
FATIGUEBEHAVIOUR OFNi-BASEDSUPERALLOYS TABLEI HOT CORROSION
CONDITIONS
Complete immersion in a mixture preheated for 24h at 850°C; the mixture contained 4.3 wt.% Na,SO,, 22.7 wt.% CaS0,.2H,O, 22.3 wt.% Fe,O,, 20.6 wt.% ZnSO,.H,O, 10.4wt.%K,SO,, 2.8wt.%MgO,6.5wt.%AI,O, and 10.4
Salt
Atmosphere Temperature
wt.%SiOz Aircontaining0.015vol.%SO, and 0.015vol.%SO,; flowrate, 601h-’ 850“C
2. TESTSANDRESULTS Tension-tension tests were chosen to compare the effects of the surface, the coatings, the inclusions and the pores because every part of a test specimen should experience an identical stress. The test frequency was 156 Hz and the test temperature was 850 “C. The uncoated and coated specimens were tested in the asmachined and the as-coated conditions respectively. Both types of specimen were retested after corrosion attack in the as-corroded condition without any further machining. The results of HCF tests carried out on IN 738LC at a temperature of 850 “C with a stress ratio R of zero where R is the ratio of the minimum load to the maximum load are given in Fig. 2. The specimens tested were uncoated, as coated with LDC 2 or coated with LDC 2 and exposed either to air or to corrosive slag at 850°C for a lengthy period. The specimens exposed to the hot slag continued to corrode during testing because the hot corrosion persisted owing to the presence of slag deposits on the specimen surface and internal sulphide precipitation during precorrosion. A large variation in the specimen lifetimes was found. The lifetimes of the specimens coated with LDC 2 were within the scatter band of the lifetimes of the stress amplitude
f = 156Hzin air 105
l@
107
cycles to failure --)
Fig. 2. Resultsof HCF tests of IN 738LCat 850“C (f = 156 Hz in air; R = 0):-o-, -.-m-.-, LDC2 coated; LDC 2 coated and pre-corroded
--V --, LDC2 coated for 1000 h at 850 “C in slag.
and aged 5000 hat
uncoated; 850”C;-P-x--,
32
K. SCHNEIDER,
H. v. ARNIM, H. W. GRtiNLING
uncoated IN 738LC. The lifetimes at lower stress levels appear to be reduced by long-term exposure (5000 h at 850 “C) and by combined long-term exposure and hot corrosion. In contrast with these results, coating IN 939 with LDC 2 produces an identical effect to that of the corrosive slag during HCF testing (Fig. 3). The reduction in the lifetime after exposure to corrosive slag for 1000 h at 850 “C is also more pronounced. stress amplitude 200 n
(N/mm2)
1.
150.
..\.F
50.
-_.--X--+
tension-tension test f=156Hzinair ebBssmtioR-0 08 IV
10s
10’
10’
cycles to failure ----)
Fig. 3. Results of HCF tests of IN 939 at 850°C (f = 156 Hz in air; R = 0):-O--, uncoated; -. -m-, LDC 2 coated; - - ‘I ~ -, in corrosive slag; ~ x - - -, pre-corroded for 1000 h at 850 “C in slag.
3. DISCUSSION In both uncoated alloys the cracks initiated in areas containing pores or other inhomogeneities in all the HCF tests (Fig. 4). The cracks all run for a long distance on a transgranular plane at a particular angle (similar to the stage I mode) and show almost no striations until they change direction and become normal to the applied stress. The more homogeneous material IN 939 shows a smaller scatter band than that of IN 738LC. The application of an LDC 2 coating sometimes produces a shift in the crack initiation sites towards the coating-substrate interface (Fig. 5). In the case of IN 939 a test under hot corrosion conditions gives similar results to those obtained for the specimen coated with LDC 2. Even in the short testing times used in this work the hot corrosion attack shifts the crack initiation sites towards the surface (Fig. 6). The fatigue cracks remain intergranular and straight for long distances normal to the stress axis. Long-term annealing (5000 h at 850 “C) reduces the lifetime of LDC 2 coated IN 738LC. In this case the cracks start at the surface either in the diffusion zone or at the surface of the coating (Fig. 7). The most severe testing conditions were found to exist for uncoated IN 939 and for LDC 2 coated IN 738LC after exposure to corrosive slag for 1000 h at 850 “C. The corrosive attack produces notches in the surface which are more critical than the internal pores. Cracks start at grain boundaries (Fig. 8) and are rapidly
FATIGUE BEHAVIOUR
OF b&BASED
33
SUPERALLOYS
Fig. 4. The appearance of fractures in an IN 939 specimen mm-* after 1.99 x 10s cycles; f = 156 Hz).
after HCF testing at 850 “C (R=O;o=139N
100 pm -
Fig. 5. The appearance of fractures in an LDC 2 coated IN 738LC specimen after HCF testing at 850 “C (R = 0; o = 132 N mm-’ after 9.5 x lo6 cycles; f = 156 Hz).
34
K. SCHNEIDER,
H. v. ARNIM, H. W. GRtiNLING
Imm -
Fig. 6. The appearance of fractures in an IN 939 specimen after HCF testing in corrosive (R = 0; IJ= 118 N mm-’ after 7 x 10’ cycles;f = 156 Hz).
slag at 850 “C
130 pm -
Fig. 7. Crack initiation in LDC 2 coated IN 738LC after long-term annealing HCF testing at 850 “C (R = 0; 0 = 96.9 N mm-’ after 1.89 x 10’ cycles).
(5000 h at 850 “C) and
FATIGUE BEHAVIOUR
OF Ni-BASED
SUPERALLOYS
35
accelerated by corrosion due to slag deposits on the specimen surfaces at the freshly opened crack sites. There may also be an interaction between mechanical stresses and hot corrosion similar to that found for creep testing’. The amount of corrosive attack on the fracture surfaces of IN 939 and IN 738LC (Fig. 9) compared with that observed in a crucible test (Fig. 20 in ref. 2) is very surprising. These results appear to confirm reports3 that the HCF behaviour of cast alloys based on nickel is primarily governed by crack propagation. Therefore the heat
Fig. 8. Scanning electron micrograph of crack initiation in an IN 939 specimen after HCF testing in corrosive slag at 850°C (R = 0; o’= 40 N mm-’ after 2.96 x 10’ cycles (not broken); f = 156 Hz (a) corroded surface zone; (b) unattacked base metal.
Fig. 9. Comparison
of corrosive
attack
on fatigue cracks in IN 939 and in IN 738LC.
36
K. SCHNEIDER,
H. v. ARNIM, H. W. GRUNLING
treatment of the coating may negate its protective effect by introducing more sources of stress. This behaviour was observed in the present work only when long-term annealing changed the composition or the structure of the LDC 2 coating. Our investigations have shown that the HCF properties of cast alloys based on nickel can be improved by hot isostatic pressing (HIP) provided that the cracks initiate at internal pores4. However, if the alloys are coated or are exposed to severe corrosion, the effect of HIP is beneficial only if the crack propagation rate is reduced by the coating procedure. Crack propagation appears to be rapidly accelerated by hot corrosion attack. The following model may explain this phenomenon. Hot corrosion attack, which is usually sulphidation, ahead of the crack tip dissolves the material and leaves mainly low alloyed nickel to be tested. Therefore a very much lower fatigue limit is achieved. 4.
CONCLUSIONS
The cast alloys IN 939 and IN 738LC behave differently under HCF testing because of their different porosities?. Coating with Pt-Al produces a larger decrease in the HCF lifetimes for IN 939 than for IN 738LC because acicular phases which act as crack initiation sites are produced6. Completely different results are obtained after hot corrosion because crack initiation is at the surface and crack propagation is accelerated by the corrosion. It is expected that under hot corrosion conditions coated specimens will have better HCF properties because corrosion notches cannot be produced when the coating has developed a smooth surface scale. The coating itself does not have a grain structure which could give rise to a preferential attack. Therefore coatings can improve cyclic properties if they satisfy certain requirements for deformation and for adhesion to the substrate metal. ACKNOWLEDGMENTS
Part of the work described here was funded by the German Federal Ministry for Science and Technology. REFERENCES 1
2 3
4 5
6
W. Hartnagel, R. Bauer and H. W. Griinling. Constant strain rate creep tests with gas turbine blade materials under hot corrosion environmental conditions, in V. Giittmann and M. Merz (eds.), Proc. Eur. Symp. on the Interuction between Corrosion and Mechanical Stress at High Temperatures, Petten, The Netherlands, May 1980, Applied Science, London, 1981. Ch. Just, P. Huber and R. Bauer, Evaluation of a new corrosion resistant alloy for gas turbine blades, CIMAC Publ. GT34. Vienna, 1979. W. Hoffelner and M. 0. Speidel, in 1. Kirman et ul. (eds.), Proc. Int. Conf. on the Behavior ofHigh Temperature Alloys in Aggressive Environments, Petten, The Netherlands, 1979, Metals Society, London, 1980. G. M. McColvin, High cycle fatigue of nickel-base alloys, in D. Coutsouradis et al. (eds.), High Temperature Alloysfor Gas Turbines, Applied Science, London, 1979. H. W. Griinling, K. Schneider and H. v. Arnim, Influence ofcoatings on high cycle fatigue properties of cast nickel base alloys, Finul Rep., 1981 (COST 50 programme, round 2, D2) (available from Directorate Genera1 for Research, Science and Education, Commission of the European Communities, Brussels). A. Strang, The effect of corrosion resistant coatings on the structure and properties of advanced gas turbine blading alloys, CIMAC Pub/. GT34. Vienna, 1979.
AND PROTECTIVE
29
COATINGS
INFLUENCE OF COATINGS AND HOT CORROSION ON THE FATIGUE BEHAVIOUR OF NICKEL-BASED SUPERALLOYS * K. SCHNEIDER,
H. VON ARNIM AND H. W. GRtiNLING
Brown, Boveri & Cie, Mannheim (F.R.G.) (Received
March 23,198l;
accepted
April 10, 1981)
The fatigue behaviour of materials and components is strongly affected by the surface conditions, i.e. the surface finish and the materials properties in the nearsurface region. Therefore any change in these conditions during fabrication or service may change the fatigue properties. It is common practice to coat turbine blades with materials that are resistant to hot corrosion. However, this treatment involves chemical and mechanical changes in the materials surface properties which could also change the fatigue properties of these components. The recommended heat treatment for the coating normally differs from that which produces the best mechanical or creep properties of the base metal and hence may cause additional changes in the fatigue properties. Chemical and mechanical changes in the surface conditions of an uncoated component may also take place during operation. Additionally, a large amount of notching may occur since oxidation and hot corrosion are not homogeneously distributed but take place preferentially at sites such as grain boundaries. In this work we investigate the effect of Pt-Al coatings on the high cycle fatigue (HCF) behaviour of the cast nickel-based alloys IN 738LC and IN 939 which are commonly used in large industrial gas turbines. A reduction in the fatigue life due to the coating was observed. However, the simultaneous occurrence of hot corrosion attack and cyclic loading was much more detrimental. Fractographic and metallographic investigations showed that, in the as-coated condition, the crack initiation sites in the Pt-Al-coated alloys were internal pores situated just below the surface of the substrate. After aging or hot corrosion cracks initiate at the surface probably as a result of notch development by the attack. When HCF and hot corrosion are acting concurrently the coatings are expected to give a beneficial effect by protecting the surface from accelerated crack initiation.
1. INTRODUCTION
Coatings on gas turbine buckets are applied to reduce oxidation, erosion and hot corrosion. Owing to the presence of the coating material, both the composition *Paper presented U.S.A.,
at the International April 6-10, 1981.
0040-6090/S
I/0000-0000/~02.50
Conference
on Metallurgical
Coatings,
0 Elsevier Sequoia/Printed
San Francisco,
CA,
in The Netherlands
30
K. SCHNEIDER, H. v. ARNIM, H. W. GRijNLING
and the mechanical properties of the surface are changed. Thus the deformation behaviour of both the coating and the coating-substrate system must be considered. Even though the coating is not designed to enhance the strength of the component in most cases, its strain behaviour and toughness are important with respect to its ability to protect the surface and to prevent crack initiation under mechanical loading. Coatings on gas turbine blades develop a protective oxide scale and hence change their composition during service; the same considerations apply to the scalecoating system. Apart from the changes produced in the surface properties, some coating procedures require heat treatments different from those normally recommended to achieve the required substrate metal properties. This paper deals with the interaction between the coating and the substrate with respect to the high cycle fatigue (HCF) behaviour of a coated component. A material subjected to cyclic loading at high temperatures can endure a certain number of cycles without showing any signs of damage. However, when a certain amount of damage has accumulated locally in the material or at the surface a crack initiates and further damage is determined by the propagation of this crack. In the early stages crack initiation occurs preferentially on sites where stress concentrations are found, e.g. machining notches at the surface, local corrosion attack, inclusions and pores. The microstructural elements determining crack initiation, the effect of the PtAl coating LDC 2 (Fig. 1) on crack initiation and the effect ‘of long-term exposure and hot corrosion attack (Table I) on the HCF behaviour are investigated for the nickel-based cast alloys IN 738LC and IN 939.
Fig. 1. LDC 2 coating on IN 738LC.
1
31
FATIGUEBEHAVIOUR OFNi-BASEDSUPERALLOYS TABLEI HOT CORROSION
CONDITIONS
Complete immersion in a mixture preheated for 24h at 850°C; the mixture contained 4.3 wt.% Na,SO,, 22.7 wt.% CaS0,.2H,O, 22.3 wt.% Fe,O,, 20.6 wt.% ZnSO,.H,O, 10.4wt.%K,SO,, 2.8wt.%MgO,6.5wt.%AI,O, and 10.4
Salt
Atmosphere Temperature
wt.%SiOz Aircontaining0.015vol.%SO, and 0.015vol.%SO,; flowrate, 601h-’ 850“C
2. TESTSANDRESULTS Tension-tension tests were chosen to compare the effects of the surface, the coatings, the inclusions and the pores because every part of a test specimen should experience an identical stress. The test frequency was 156 Hz and the test temperature was 850 “C. The uncoated and coated specimens were tested in the asmachined and the as-coated conditions respectively. Both types of specimen were retested after corrosion attack in the as-corroded condition without any further machining. The results of HCF tests carried out on IN 738LC at a temperature of 850 “C with a stress ratio R of zero where R is the ratio of the minimum load to the maximum load are given in Fig. 2. The specimens tested were uncoated, as coated with LDC 2 or coated with LDC 2 and exposed either to air or to corrosive slag at 850°C for a lengthy period. The specimens exposed to the hot slag continued to corrode during testing because the hot corrosion persisted owing to the presence of slag deposits on the specimen surface and internal sulphide precipitation during precorrosion. A large variation in the specimen lifetimes was found. The lifetimes of the specimens coated with LDC 2 were within the scatter band of the lifetimes of the stress amplitude
f = 156Hzin air 105
l@
107
cycles to failure --)
Fig. 2. Resultsof HCF tests of IN 738LCat 850“C (f = 156 Hz in air; R = 0):-o-, -.-m-.-, LDC2 coated; LDC 2 coated and pre-corroded
--V --, LDC2 coated for 1000 h at 850 “C in slag.
and aged 5000 hat
uncoated; 850”C;-P-x--,
32
K. SCHNEIDER,
H. v. ARNIM, H. W. GRtiNLING
uncoated IN 738LC. The lifetimes at lower stress levels appear to be reduced by long-term exposure (5000 h at 850 “C) and by combined long-term exposure and hot corrosion. In contrast with these results, coating IN 939 with LDC 2 produces an identical effect to that of the corrosive slag during HCF testing (Fig. 3). The reduction in the lifetime after exposure to corrosive slag for 1000 h at 850 “C is also more pronounced. stress amplitude 200 n
(N/mm2)
1.
150.
..\.F
50.
-_.--X--+
tension-tension test f=156Hzinair ebBssmtioR-0 08 IV
10s
10’
10’
cycles to failure ----)
Fig. 3. Results of HCF tests of IN 939 at 850°C (f = 156 Hz in air; R = 0):-O--, uncoated; -. -m-, LDC 2 coated; - - ‘I ~ -, in corrosive slag; ~ x - - -, pre-corroded for 1000 h at 850 “C in slag.
3. DISCUSSION In both uncoated alloys the cracks initiated in areas containing pores or other inhomogeneities in all the HCF tests (Fig. 4). The cracks all run for a long distance on a transgranular plane at a particular angle (similar to the stage I mode) and show almost no striations until they change direction and become normal to the applied stress. The more homogeneous material IN 939 shows a smaller scatter band than that of IN 738LC. The application of an LDC 2 coating sometimes produces a shift in the crack initiation sites towards the coating-substrate interface (Fig. 5). In the case of IN 939 a test under hot corrosion conditions gives similar results to those obtained for the specimen coated with LDC 2. Even in the short testing times used in this work the hot corrosion attack shifts the crack initiation sites towards the surface (Fig. 6). The fatigue cracks remain intergranular and straight for long distances normal to the stress axis. Long-term annealing (5000 h at 850 “C) reduces the lifetime of LDC 2 coated IN 738LC. In this case the cracks start at the surface either in the diffusion zone or at the surface of the coating (Fig. 7). The most severe testing conditions were found to exist for uncoated IN 939 and for LDC 2 coated IN 738LC after exposure to corrosive slag for 1000 h at 850 “C. The corrosive attack produces notches in the surface which are more critical than the internal pores. Cracks start at grain boundaries (Fig. 8) and are rapidly
FATIGUE BEHAVIOUR
OF b&BASED
33
SUPERALLOYS
Fig. 4. The appearance of fractures in an IN 939 specimen mm-* after 1.99 x 10s cycles; f = 156 Hz).
after HCF testing at 850 “C (R=O;o=139N
100 pm -
Fig. 5. The appearance of fractures in an LDC 2 coated IN 738LC specimen after HCF testing at 850 “C (R = 0; o = 132 N mm-’ after 9.5 x lo6 cycles; f = 156 Hz).
34
K. SCHNEIDER,
H. v. ARNIM, H. W. GRtiNLING
Imm -
Fig. 6. The appearance of fractures in an IN 939 specimen after HCF testing in corrosive (R = 0; IJ= 118 N mm-’ after 7 x 10’ cycles;f = 156 Hz).
slag at 850 “C
130 pm -
Fig. 7. Crack initiation in LDC 2 coated IN 738LC after long-term annealing HCF testing at 850 “C (R = 0; 0 = 96.9 N mm-’ after 1.89 x 10’ cycles).
(5000 h at 850 “C) and
FATIGUE BEHAVIOUR
OF Ni-BASED
SUPERALLOYS
35
accelerated by corrosion due to slag deposits on the specimen surfaces at the freshly opened crack sites. There may also be an interaction between mechanical stresses and hot corrosion similar to that found for creep testing’. The amount of corrosive attack on the fracture surfaces of IN 939 and IN 738LC (Fig. 9) compared with that observed in a crucible test (Fig. 20 in ref. 2) is very surprising. These results appear to confirm reports3 that the HCF behaviour of cast alloys based on nickel is primarily governed by crack propagation. Therefore the heat
Fig. 8. Scanning electron micrograph of crack initiation in an IN 939 specimen after HCF testing in corrosive slag at 850°C (R = 0; o’= 40 N mm-’ after 2.96 x 10’ cycles (not broken); f = 156 Hz (a) corroded surface zone; (b) unattacked base metal.
Fig. 9. Comparison
of corrosive
attack
on fatigue cracks in IN 939 and in IN 738LC.
36
K. SCHNEIDER,
H. v. ARNIM, H. W. GRUNLING
treatment of the coating may negate its protective effect by introducing more sources of stress. This behaviour was observed in the present work only when long-term annealing changed the composition or the structure of the LDC 2 coating. Our investigations have shown that the HCF properties of cast alloys based on nickel can be improved by hot isostatic pressing (HIP) provided that the cracks initiate at internal pores4. However, if the alloys are coated or are exposed to severe corrosion, the effect of HIP is beneficial only if the crack propagation rate is reduced by the coating procedure. Crack propagation appears to be rapidly accelerated by hot corrosion attack. The following model may explain this phenomenon. Hot corrosion attack, which is usually sulphidation, ahead of the crack tip dissolves the material and leaves mainly low alloyed nickel to be tested. Therefore a very much lower fatigue limit is achieved. 4.
CONCLUSIONS
The cast alloys IN 939 and IN 738LC behave differently under HCF testing because of their different porosities?. Coating with Pt-Al produces a larger decrease in the HCF lifetimes for IN 939 than for IN 738LC because acicular phases which act as crack initiation sites are produced6. Completely different results are obtained after hot corrosion because crack initiation is at the surface and crack propagation is accelerated by the corrosion. It is expected that under hot corrosion conditions coated specimens will have better HCF properties because corrosion notches cannot be produced when the coating has developed a smooth surface scale. The coating itself does not have a grain structure which could give rise to a preferential attack. Therefore coatings can improve cyclic properties if they satisfy certain requirements for deformation and for adhesion to the substrate metal. ACKNOWLEDGMENTS
Part of the work described here was funded by the German Federal Ministry for Science and Technology. REFERENCES 1
2 3
4 5
6
W. Hartnagel, R. Bauer and H. W. Griinling. Constant strain rate creep tests with gas turbine blade materials under hot corrosion environmental conditions, in V. Giittmann and M. Merz (eds.), Proc. Eur. Symp. on the Interuction between Corrosion and Mechanical Stress at High Temperatures, Petten, The Netherlands, May 1980, Applied Science, London, 1981. Ch. Just, P. Huber and R. Bauer, Evaluation of a new corrosion resistant alloy for gas turbine blades, CIMAC Publ. GT34. Vienna, 1979. W. Hoffelner and M. 0. Speidel, in 1. Kirman et ul. (eds.), Proc. Int. Conf. on the Behavior ofHigh Temperature Alloys in Aggressive Environments, Petten, The Netherlands, 1979, Metals Society, London, 1980. G. M. McColvin, High cycle fatigue of nickel-base alloys, in D. Coutsouradis et al. (eds.), High Temperature Alloysfor Gas Turbines, Applied Science, London, 1979. H. W. Griinling, K. Schneider and H. v. Arnim, Influence ofcoatings on high cycle fatigue properties of cast nickel base alloys, Finul Rep., 1981 (COST 50 programme, round 2, D2) (available from Directorate Genera1 for Research, Science and Education, Commission of the European Communities, Brussels). A. Strang, The effect of corrosion resistant coatings on the structure and properties of advanced gas turbine blading alloys, CIMAC Pub/. GT34. Vienna, 1979.