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The influence of orientation, temperature and frequency on fatigue crack growth
Effect o f intmstltlel c o n t e n t on high t e m l m r a t u r a fatigue crack prOlm~,ation and l o w cycle fatigue o f A l l o y 720. Bashir, S. sad Thomas, M.
Prec. Conf. Superalloys 1992, Champion, Pennsylvania, USA, 20-24 Sept. 1992, (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h Dr, Warrendale, PA 15086, USA) 1992 pp 747-755 Alloy 720 is a high-strength cast and wrought turbine disc alloy now in use for up to approx 1200°F (650~C) in Allison's Ta00, T406, GMA 2100 and GMA 3007 engines. In the original composition intended for use as turbine blades, large carbide and beride stringers formed and acted es preferred crack initiators. The stringering was attributed to relstively higher boron and carbon levels. These interstitiels are known to affect creep and ductility of superalloys, but the effects on low-cycle fatigue and fatigue crack propagation have not been studied. Recent emphasis on the totel-life approach in the design of turbine discs necessitates better understanding of the interaction fatigue crack propagation and low-cycle fatigue beheviour at high temperatures. The objective was to improve the damage tolerance of Alloy 720 by systematically modifying 8 and C levels in the master melt, without altering the low-cycle fatigue and strength characteristics of the original composition. Improvement in strain-controlled low-cycle fatigue life was achieved by fragmenting the continuous stringers via composition modification. The fatigue crack propagation rate was reduced by a concurrent reduction of both C and R levels to optimally low levels at which the frequency of brittle second phases was minimal. The changes in composition have been incorporated for production disc forgings. ue.n(m. of high t e m p e r a t u r e elastic-plastic m a l l r o c k g r o w t h evmr m s nickel-base superelloy on t h e life prediction of structural components. Rosenberger, A. H., Ghonem, H. snd Andrieu, E.
Proc. Conf. Superalloys 1992, Champion, Pennsylvania, USA, 20-24
Sept. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h Dr, Warrendale, PA 15086, USA) 1992 pp 737-746
The role of small crack behaviour in life predictions Js addressed with particular reference to cracks growing in the notch plastic zones of geometric stress concentrations. An experimental study of the elastic-plastic fatigue beheviour of small surface cracks in Alloy 718 at 650°C was conducted under global strain control. Ouring cycling, crack lengths were continuously measured using the direct current potential drop technique, while the near field crack mouth opening displacement was measured using a laser interferomatry technique. Crack tip plastic zones were measured by a post-test metallogrephic technique. The anomalous growth heheviour discovered at short crack lengths has been analysed using several driving force parameters in an attempt to consolidate its growth rate with that of long cracks. This analysis has demonstrated that the anomalous growth rate is a transient phenomenon and not an intrinsic feature of the material. The conclusion is that in turbo-machinery, accurate residual life predictions for components of Alloy 718 can he based on the integration of long crack growth rate data for this alloy. Fatigue crack propagation in single crystal CMSX-2 at elevated temperatufa. Antolovich, B. F., Saxena, A. and Antolovich, S. D.
reOpC.Conf. Superalloys 1992, Champion, Pennsylvania, USA, 20-24 t. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h
Dr, Warrendale, PA 15086, USA) 1992 pp 727-736 The fatigue crack propagation beheviour of the Ni-bess superalloy CMSX-2 in single crystal form was investigated. Tests were conducted for two temperatures (25 and 700"C), two orientations ([001][110] end 1001][010]), and in two environments (laboratory air and ultra-high vacuum, 10-7 torr). Following FCP testing, the fracture surfaces were examined using scanning electron microscopy. Transmission electron microscopy was used to determine the size and shape of the -/ precipitates. FCP rates were found to be relatively independent of the temperature, environment and orientation when correlated with the conventional mode I stress intensity factor. Examination of the fracture surfaces showed two distinct types of fracture. One type was characterized by {111( fracture surfaces which were inclined relative to both the loading and crack propagation fractures along {111( plenee. Such features were observed at 25 end 700°C; they were the only features observed for the 25°C tests. The second type had a mecroscopically dull loading appeerenco, was microscopically rough end grew normal to the loading axis. This feature was seen on the specimens tested at 700°C (in both air and vacuum) and had a similar appearance to conventional fatigue fractures. Although in thi~ region the crack plane was macroscopically normal to the loading direction, it deviated microscopically to avoid shearing the ? precipitates. In view of the complex crack growth mechanisms, mixed fracture modes, and lack of any difference in FCP rates, it is hypothesized that the correlation between FCP rates and stress intensity parameter is probably coincidental. The implicotioos for life prediction of higher-temperature turbine components based on conventional fracture mechanics are significant and should he investigated further. effect o f creep, oxidati.on end crystal o r i c , , ~ U o n on high t e m p m a t u r e mu.gue. ~ I ~ O l P ~ i ~ o n .n standard and roft-like g a m m a prime CMSX-
• . Lupinc, v., unorno, ~. and Vimercati, G. Prec. Conf. Soperslloys 1992, Champion, Pennsylvania, USA, 20-24 Sept. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h Dr, Warrendale, PA 15086, USA) 1992 pp 717-726
The fatigue creck'[:)ropagation (FCP) beheviour of <001> axially oriented single edge notch (SEN) tension specimens (R = 0.05) of CMSX-2 has been examined. At 950°C, <100:> oriented cracks propagate faster than <110:> oriented cracks in the (001) plane. The influence of -/ morphology on FCP st 750 and 950~C has been determined, increasing the test temperature from 750 to 950°C lowers the FCP rates especially of the standard heat treated (ST) material (cuboidal -/). FCP rates of the thermomechenically treated (TMT) material, which has a raft-like -/ and which simulates the microstructuro formed after short high-temperature service, are not very sensitive to temperature vadatioos between 750 and 950"C. Higher FCP rates st 950"C for the TMT compared with the ST materiel have been related to fracture morphology. Time-dependent FCP mechanisms were explored at 950°C for cuboidel end raft-like -/materials by performing continuous cycle (triangular weveform) and hold-time tests. Hold-time tests exhibited lower FCP rates. Tests in air had much slower FCP rates than t a m in vacuum st low ~K, especially with hold times. Repeatedly changing the environment from vacuum to air and vice versa,at 950"C with hold time, provides confirmation of the slower propagation rates in air than in vacuum. Oxide-induced closure at the crack tip can explain the drastic environmental effect on FCP rates at low ~K vaiuss, while creep mechanisms can explain the acceleration at high ~K when hold time is added in vacuum.
The influence of ork,,3~6on, t e m p e r a t u r e
and frequenoy
on fatigue
emck growth. Henderson, M. B. and Martin, J. W. Pr~: Conf. Soperalloys 1992, Champion, Pennsylvania, USA, 20-24 sap.t: 1992 ( .TIl.e Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h ur, w a r r e n o a l e , PA 15086, USA) 1992 pp 707-716
The FCG characteristics of SRR99 have been studied in air at 650 and 850~ at 10 and 1 Hz with an R ratio of 0.1, using CT specimens with the following crack planes (hkl) and propagation directions (UVW): (001)[010], (110)[-110], and (111)(I-10]. At 650°C, the (110) and (111 ) crack plane specimens showed a frequency-dependent FCG rate, not apparent in the (001)[010] specimens, due to an increeeed shear stress on the cuboidal cross-slip system giving increased cross-slip at the lower frequency and thereby reducing the reversibility of slip. Homogenization of slip at 850~C prevented this effect. All specimens showed an improved threshold response at 850~ compared with that at 650°C due to enhanced oxide closure of the crack. Within the Paris regime, the (001)1010] specimens demonstrated a lower FCG rate st 850 than at 650~C, due to an increased crack bifurcation at the higher temperature. Conversely, a higher FCG rate with increase in temperature occurs in the (110) and (111) specimens, since the crack path decreases in tortuosity as it changes from propagation along the `//,/' interface to -/'-precipitate cutting. The orientation dependance of FCG rate and fracture path is influenced by the relationship between the crack front and the slip systems available for crack tip shear. At 660~C, those orientations most able to accommodate crack tip shear on primary slip planes that are neer-parallel with the crack front provide the best FCG resiStance, while st 850°C the best FCG response is found for the same orientations that have now developed large-scale ridges as a result of out-of-plane cuboidal slip activity.
L o w cycle fatigue of NIAI deformed near t h e brittie-to-doctlle transition
temperature. Cullers, C. L. and Antolovich, S. D. Prec. Conf. Sueerslloys 1992, Champion, Pennsylvania, USA, 20-24 bept. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h Dr, Warrendsle, PA 15086, USA) 1992 pp 351-359 As pert of s study to investigate the fatigue beheviour of the intarmatallic compound NiAI near its monotonic brittle-to-ductile transition temperature (BD'I-F), prealloyed stoichiomatric NiAl powders were hot extruded and fabricated into tensile end fatig4ue specimens. From the monotonic tests conducted at a nominal strain rate of 10- s- , the BDTI" was found to be approx 650 K. Low-cycle fatigue (LCF) t a m were performed at 600, 675, and 700 K st plastic strain ranges of 0.005-0.01. The percentage of intergranular failure decreased in the fracture morphology of both the monotonic and fatigue tests. For all temperatures and strain ranges in this study, rapid hardening was observed for up to 15 cycles, after which the peak stress increased only slightly for the remainder of the life. As test temperature was increased or strain range decreased, both the initial hardening rate and relative saturation stress decreased. In fatigue specimens, secondary cracks were found in the gauge section near the eventual intrusions/extrusion. Intargrenular surface cracks were seen that could result from planar slip pile-upe at grain boundaries; however, other mechanisms have not been ruled out. No significant improvement in life at a strain range of 0.005 was observed when the test temperature was increased from 600 to 700 K, a change which corresponds to an increase in monotonic tensile ductility from 2 to 18%. Apparently, a cyclic brittle-to-ductile transition did not occur in this temperature range. If thermally activated deformation affects fatigue lives as it does monotonic ductility, the cyclic transition temperature is higher than the monotonic BDTT. More work is necessary to precisely identify the deformation mechanisms thst operate in low-cycle fatigue of NiAI.
Evaluation of mechanical pmpertlea o f a l o w cobalt w r o u g h t superelloy.
Dreshfield, R. L. Prec. Conf. Superalloys 1992, Champion, Pennsylvania, USA, 20-24 Sept. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h Dr, Warrendale, PA 15086, USA) 1992 pp 317-326 The Lewis Research Center procured a 1365kg (30001b) heat of a modified Waspaloy having a reduced cobalt level. The results of a program perfomed at four gas turbine manufacturers which evaluated the mechanical properties of forgings fabricated from the heat are reported. The alloy chemistry selected reduced the nominal Co level from 13.5 to 7.75 wt %. To compensate for the anticipated strength reduction caused by a slight reduction in the amount of % the nominal Al was increased from 1.3 to 1.5% and the Ti was increased from 3.0 to 3.2%. The increases in AI and Ti were intended to increase the amount of `/' in the alloy. Tensile, creep rupture, low-cycle fatigue and cyclic crack growth testa were performed. In addition, the effect of hydrogen on the alloy was determined. It is concluded that, in the event of a Co shortage, s low Co modification of Waspeloy could be substituted for Wsspeloy with little development in those applications which are not creep rupture limited. With some additional development to better control the grain size, it is probable that most of the current Wsspeloy requirements might be mat with a lower Co alloy.
Second generation columnar grain nickel-base superelloy. Cetel, A. D.
and Duhl, D. N. Prec. Conf. Superslloys 1992, Champion, Pennsylvania, LISA, 20-24 Sept. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h
Dr, Warrendale, PA 15086, USA) 1992 pp 287-296 High-temperature strength capabilities similar to those of single-crystal Ni-bsse alloys have been achieved in a second-generation columnar grain alloy designed for advanced military and commercial turbine airfoil applications. This new alloy, designated PWA 1426, offers s 500F (10~C) improvement in metal temperature capability (creep-rupture strength, thermal fatigue and oxidation resistance) over earlier columnar grain alloys (PWA 1422), and equivalent properties to current, production, first-generation single crystal alloys, such as PWA 1480. In applications where PWA 1426 replaces PWA 1480, a major cost saving is realized due to the higher casting yields normally obtained with columnar grain castings relative to single crystals. Alloy properties have been fully characterized and demonstrate that PWA 1426 offers an outstanding combination of high-temperature creep and fatigue strength, as well as excellent oxidation resistance and transverse ductility. Processing studies have shown it to have excellent castability and to be easy to solution heat treat in a production environment. The overall superior combination of properties offered by PWA 1426 has been confirmed through an extensive series of engine tests leading to its incorporation in advanced military and commercial engines.
Prec. Conf. Superalloys 1992, Champion, Pennsylvania, USA, 20-24 Sept. 1992, (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h Dr, Warrendale, PA 15086, USA) 1992 pp 747-755 Alloy 720 is a high-strength cast and wrought turbine disc alloy now in use for up to approx 1200°F (650~C) in Allison's Ta00, T406, GMA 2100 and GMA 3007 engines. In the original composition intended for use as turbine blades, large carbide and beride stringers formed and acted es preferred crack initiators. The stringering was attributed to relstively higher boron and carbon levels. These interstitiels are known to affect creep and ductility of superalloys, but the effects on low-cycle fatigue and fatigue crack propagation have not been studied. Recent emphasis on the totel-life approach in the design of turbine discs necessitates better understanding of the interaction fatigue crack propagation and low-cycle fatigue beheviour at high temperatures. The objective was to improve the damage tolerance of Alloy 720 by systematically modifying 8 and C levels in the master melt, without altering the low-cycle fatigue and strength characteristics of the original composition. Improvement in strain-controlled low-cycle fatigue life was achieved by fragmenting the continuous stringers via composition modification. The fatigue crack propagation rate was reduced by a concurrent reduction of both C and R levels to optimally low levels at which the frequency of brittle second phases was minimal. The changes in composition have been incorporated for production disc forgings. ue.n(m. of high t e m p e r a t u r e elastic-plastic m a l l r o c k g r o w t h evmr m s nickel-base superelloy on t h e life prediction of structural components. Rosenberger, A. H., Ghonem, H. snd Andrieu, E.
Proc. Conf. Superalloys 1992, Champion, Pennsylvania, USA, 20-24
Sept. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h Dr, Warrendale, PA 15086, USA) 1992 pp 737-746
The role of small crack behaviour in life predictions Js addressed with particular reference to cracks growing in the notch plastic zones of geometric stress concentrations. An experimental study of the elastic-plastic fatigue beheviour of small surface cracks in Alloy 718 at 650°C was conducted under global strain control. Ouring cycling, crack lengths were continuously measured using the direct current potential drop technique, while the near field crack mouth opening displacement was measured using a laser interferomatry technique. Crack tip plastic zones were measured by a post-test metallogrephic technique. The anomalous growth heheviour discovered at short crack lengths has been analysed using several driving force parameters in an attempt to consolidate its growth rate with that of long cracks. This analysis has demonstrated that the anomalous growth rate is a transient phenomenon and not an intrinsic feature of the material. The conclusion is that in turbo-machinery, accurate residual life predictions for components of Alloy 718 can he based on the integration of long crack growth rate data for this alloy. Fatigue crack propagation in single crystal CMSX-2 at elevated temperatufa. Antolovich, B. F., Saxena, A. and Antolovich, S. D.
reOpC.Conf. Superalloys 1992, Champion, Pennsylvania, USA, 20-24 t. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h
Dr, Warrendale, PA 15086, USA) 1992 pp 727-736 The fatigue crack propagation beheviour of the Ni-bess superalloy CMSX-2 in single crystal form was investigated. Tests were conducted for two temperatures (25 and 700"C), two orientations ([001][110] end 1001][010]), and in two environments (laboratory air and ultra-high vacuum, 10-7 torr). Following FCP testing, the fracture surfaces were examined using scanning electron microscopy. Transmission electron microscopy was used to determine the size and shape of the -/ precipitates. FCP rates were found to be relatively independent of the temperature, environment and orientation when correlated with the conventional mode I stress intensity factor. Examination of the fracture surfaces showed two distinct types of fracture. One type was characterized by {111( fracture surfaces which were inclined relative to both the loading and crack propagation fractures along {111( plenee. Such features were observed at 25 end 700°C; they were the only features observed for the 25°C tests. The second type had a mecroscopically dull loading appeerenco, was microscopically rough end grew normal to the loading axis. This feature was seen on the specimens tested at 700°C (in both air and vacuum) and had a similar appearance to conventional fatigue fractures. Although in thi~ region the crack plane was macroscopically normal to the loading direction, it deviated microscopically to avoid shearing the ? precipitates. In view of the complex crack growth mechanisms, mixed fracture modes, and lack of any difference in FCP rates, it is hypothesized that the correlation between FCP rates and stress intensity parameter is probably coincidental. The implicotioos for life prediction of higher-temperature turbine components based on conventional fracture mechanics are significant and should he investigated further. effect o f creep, oxidati.on end crystal o r i c , , ~ U o n on high t e m p m a t u r e mu.gue. ~ I ~ O l P ~ i ~ o n .n standard and roft-like g a m m a prime CMSX-
• . Lupinc, v., unorno, ~. and Vimercati, G. Prec. Conf. Soperslloys 1992, Champion, Pennsylvania, USA, 20-24 Sept. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h Dr, Warrendale, PA 15086, USA) 1992 pp 717-726
The fatigue creck'[:)ropagation (FCP) beheviour of <001> axially oriented single edge notch (SEN) tension specimens (R = 0.05) of CMSX-2 has been examined. At 950°C, <100:> oriented cracks propagate faster than <110:> oriented cracks in the (001) plane. The influence of -/ morphology on FCP st 750 and 950~C has been determined, increasing the test temperature from 750 to 950°C lowers the FCP rates especially of the standard heat treated (ST) material (cuboidal -/). FCP rates of the thermomechenically treated (TMT) material, which has a raft-like -/ and which simulates the microstructuro formed after short high-temperature service, are not very sensitive to temperature vadatioos between 750 and 950"C. Higher FCP rates st 950"C for the TMT compared with the ST materiel have been related to fracture morphology. Time-dependent FCP mechanisms were explored at 950°C for cuboidel end raft-like -/materials by performing continuous cycle (triangular weveform) and hold-time tests. Hold-time tests exhibited lower FCP rates. Tests in air had much slower FCP rates than t a m in vacuum st low ~K, especially with hold times. Repeatedly changing the environment from vacuum to air and vice versa,at 950"C with hold time, provides confirmation of the slower propagation rates in air than in vacuum. Oxide-induced closure at the crack tip can explain the drastic environmental effect on FCP rates at low ~K vaiuss, while creep mechanisms can explain the acceleration at high ~K when hold time is added in vacuum.
The influence of ork,,3~6on, t e m p e r a t u r e
and frequenoy
on fatigue
emck growth. Henderson, M. B. and Martin, J. W. Pr~: Conf. Soperalloys 1992, Champion, Pennsylvania, USA, 20-24 sap.t: 1992 ( .TIl.e Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h ur, w a r r e n o a l e , PA 15086, USA) 1992 pp 707-716
The FCG characteristics of SRR99 have been studied in air at 650 and 850~ at 10 and 1 Hz with an R ratio of 0.1, using CT specimens with the following crack planes (hkl) and propagation directions (UVW): (001)[010], (110)[-110], and (111)(I-10]. At 650°C, the (110) and (111 ) crack plane specimens showed a frequency-dependent FCG rate, not apparent in the (001)[010] specimens, due to an increeeed shear stress on the cuboidal cross-slip system giving increased cross-slip at the lower frequency and thereby reducing the reversibility of slip. Homogenization of slip at 850~C prevented this effect. All specimens showed an improved threshold response at 850~ compared with that at 650°C due to enhanced oxide closure of the crack. Within the Paris regime, the (001)1010] specimens demonstrated a lower FCG rate st 850 than at 650~C, due to an increased crack bifurcation at the higher temperature. Conversely, a higher FCG rate with increase in temperature occurs in the (110) and (111) specimens, since the crack path decreases in tortuosity as it changes from propagation along the `//,/' interface to -/'-precipitate cutting. The orientation dependance of FCG rate and fracture path is influenced by the relationship between the crack front and the slip systems available for crack tip shear. At 660~C, those orientations most able to accommodate crack tip shear on primary slip planes that are neer-parallel with the crack front provide the best FCG resiStance, while st 850°C the best FCG response is found for the same orientations that have now developed large-scale ridges as a result of out-of-plane cuboidal slip activity.
L o w cycle fatigue of NIAI deformed near t h e brittie-to-doctlle transition
temperature. Cullers, C. L. and Antolovich, S. D. Prec. Conf. Sueerslloys 1992, Champion, Pennsylvania, USA, 20-24 bept. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h Dr, Warrendsle, PA 15086, USA) 1992 pp 351-359 As pert of s study to investigate the fatigue beheviour of the intarmatallic compound NiAI near its monotonic brittle-to-ductile transition temperature (BD'I-F), prealloyed stoichiomatric NiAl powders were hot extruded and fabricated into tensile end fatig4ue specimens. From the monotonic tests conducted at a nominal strain rate of 10- s- , the BDTI" was found to be approx 650 K. Low-cycle fatigue (LCF) t a m were performed at 600, 675, and 700 K st plastic strain ranges of 0.005-0.01. The percentage of intergranular failure decreased in the fracture morphology of both the monotonic and fatigue tests. For all temperatures and strain ranges in this study, rapid hardening was observed for up to 15 cycles, after which the peak stress increased only slightly for the remainder of the life. As test temperature was increased or strain range decreased, both the initial hardening rate and relative saturation stress decreased. In fatigue specimens, secondary cracks were found in the gauge section near the eventual intrusions/extrusion. Intargrenular surface cracks were seen that could result from planar slip pile-upe at grain boundaries; however, other mechanisms have not been ruled out. No significant improvement in life at a strain range of 0.005 was observed when the test temperature was increased from 600 to 700 K, a change which corresponds to an increase in monotonic tensile ductility from 2 to 18%. Apparently, a cyclic brittle-to-ductile transition did not occur in this temperature range. If thermally activated deformation affects fatigue lives as it does monotonic ductility, the cyclic transition temperature is higher than the monotonic BDTT. More work is necessary to precisely identify the deformation mechanisms thst operate in low-cycle fatigue of NiAI.
Evaluation of mechanical pmpertlea o f a l o w cobalt w r o u g h t superelloy.
Dreshfield, R. L. Prec. Conf. Superalloys 1992, Champion, Pennsylvania, USA, 20-24 Sept. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h Dr, Warrendale, PA 15086, USA) 1992 pp 317-326 The Lewis Research Center procured a 1365kg (30001b) heat of a modified Waspaloy having a reduced cobalt level. The results of a program perfomed at four gas turbine manufacturers which evaluated the mechanical properties of forgings fabricated from the heat are reported. The alloy chemistry selected reduced the nominal Co level from 13.5 to 7.75 wt %. To compensate for the anticipated strength reduction caused by a slight reduction in the amount of % the nominal Al was increased from 1.3 to 1.5% and the Ti was increased from 3.0 to 3.2%. The increases in AI and Ti were intended to increase the amount of `/' in the alloy. Tensile, creep rupture, low-cycle fatigue and cyclic crack growth testa were performed. In addition, the effect of hydrogen on the alloy was determined. It is concluded that, in the event of a Co shortage, s low Co modification of Waspeloy could be substituted for Wsspeloy with little development in those applications which are not creep rupture limited. With some additional development to better control the grain size, it is probable that most of the current Wsspeloy requirements might be mat with a lower Co alloy.
Second generation columnar grain nickel-base superelloy. Cetel, A. D.
and Duhl, D. N. Prec. Conf. Superslloys 1992, Champion, Pennsylvania, LISA, 20-24 Sept. 1992 (The Minerals, Metals & Materials Society, 420 C o m m o n w e a l t h
Dr, Warrendale, PA 15086, USA) 1992 pp 287-296 High-temperature strength capabilities similar to those of single-crystal Ni-bsse alloys have been achieved in a second-generation columnar grain alloy designed for advanced military and commercial turbine airfoil applications. This new alloy, designated PWA 1426, offers s 500F (10~C) improvement in metal temperature capability (creep-rupture strength, thermal fatigue and oxidation resistance) over earlier columnar grain alloys (PWA 1422), and equivalent properties to current, production, first-generation single crystal alloys, such as PWA 1480. In applications where PWA 1426 replaces PWA 1480, a major cost saving is realized due to the higher casting yields normally obtained with columnar grain castings relative to single crystals. Alloy properties have been fully characterized and demonstrate that PWA 1426 offers an outstanding combination of high-temperature creep and fatigue strength, as well as excellent oxidation resistance and transverse ductility. Processing studies have shown it to have excellent castability and to be easy to solution heat treat in a production environment. The overall superior combination of properties offered by PWA 1426 has been confirmed through an extensive series of engine tests leading to its incorporation in advanced military and commercial engines.