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Rolling contact fatigue behaviour of pearlitic rail steels
matrix. Pores, however, existed at prior powder particle boundaries due to dissolution of the adsorbed gases into the matrix in the cold degassed compact. The O entered with powder particles located at alpha/beta phase boundaries, and the hydrogen formed titanium hydride phase inside the alpha phase. Graphs, photomicrographs, spectra. 33 ref.
The characteristic o f rapidly solidified a l u m i n i u m alloys and its appli-
cation. Lien, J. Heat Treatment of Metals (China) (Apr. 1992) (4) 3 4 - 3 6 (in Chinese) The microstructure of the rapidly solidified powder AI-Fe-V-Si alloy displays very fine spherical AI13(Fe,V)3 Si particles dispersed in the AI matrix. This structure provides the alloy with high temperature stability (> 150 °C) and good ductility. The physical, tensile, fatigue, creep, and corrosion properties and the fabricabilities of the alloys with the compositions of AI-8.5Fe-1.7Si-l.3V, AI-6.5Fe-I.3Si-0.6V, and AI-11.7Fe-2.4Si-l.2V are presented and discussed. These AI alloys can be used to replace Ti alloys for aircraft parts exposed in the high temperature environment ranging between 150-400°C. They also cost less than the Ti alloys. Graphs, 10 refs.
improved operational properties o f cupercleen 3.5% N i C r M o V rotor steel.
Mayer, K. H,, Kachler, W. and Konig, H. Clean Steels Technology: Proc. R.I. Jaffee Memorial Symposium, Chicago, Illinois, USA, 2 - 5 Nov. 1992, pp 2 0 5 - 2 1 2 The superclean 3.5% NiCrMoV rotor steel, characterized by low contents of trace elements sulphur, phosphorus, Sn, Sb, arsenic, gas contents (02. N2, H2) and Si, Mn, and AI contents - manufactured on the basis of modern melting technology and based on a careful selection of scrap and a well-matched secondary metallurgy with a ladle furnace - is a very attractive material for the steam turbine manufacturer. By suppression of temper and long-term embrittlement at temperatures > 350 °C, the scope of application of the high-strength and tough 3.5% NiCrMoV rotor steel is increased to s temperature level of approx 500 °C and can be used for the manufacture of steam turbines with a higher thermal efficiency and at lower prime cost. Superclesn melting also offers substantial benefits with regard to creep strength and low-cycle fatigue beheviour since, in contrast to conventional melting, these properties are also distinctly improved. The high low-cycle fatigue strength is of particular interest for plant operating in the peak-load range.
Crack initiation and t o t a l f a t i g u e life o f a carbon steal in v a c u u m and
air. Kujawski, O. and Ellyin, F. ASTM J. Test. Eva/. (Nov. 1992) 20 (6) 391-395 Fully reversed strain-controlled test results of a carbon steel (ASTM A 516 Gr.70) in an ambient atmosphere and in a vacuum of 0.1 mPa are compared. Vacuum data may be reviewed as representing a 'pure" (mechanical) fatigue damage. In the case of an air environment, the rate of fatigue damage accumulation increases owing to the environmental contribution. The test results are described in terms of the crack initiation and total lives. The crack initiation data are fairly well correlated with the plastic strain energy per cycle. The significance of the environment condition on the life prediction procedures is discussed. Graphs, 15 ref.
F a t i g u e - c r e e p interaction steel w i t h h o l d i n g load.
The f a t i g u e properties o f pressure diecast z i n c - e l u m i n l u m based alloys.
Sawalha, K. Diss. Abstr. Int. (Oct. 1992) 53 (4) 281 pp The fatigue behaviour of the cold chamber pressure diecast alloys Mazak3, ZA8, ZA27, M3K, ZABK, ZA27K, K1, K2, and 1(3 was investigated at a temperature of 20 °C. The alloys M3K, ZASK and ZA27K were also examined at temperatures of 50 and 100 °C. The ratio between fatigue strength and tensile strength was established at 20°C at 107 cycles. The fatigue life prediction of the alloys M3K, ZA8K and ZA27K was formulated st 20, 50 and 100°C. The prediction formulae were found to be reasonably accurate. All the experimental alloys were heterogeneous and contained large but varying amounts of pores. These pores were a major contribution and dominated the alloys' fatigue failure. Their effect, however, on tensile failure was negligible. The ZA27K possessed the highest tensile strength but the lowest fatigue strength. The relationship between the fracture topography and the microstructure was also determined by the use of a mixed signal of a secondary electron and a bsckscettered electron on the SEM. The tensile strength of the experimental alloys was directly proportional to the AI content within the alloys. The effect of Cu content was also investigated within the alloys K1, K2, ZA8K end K3, which contained 0, 0.5, 1.0 and 2.0=/0 respectively. It was determined that the fatigue and tensile strengths improved with higher Cu contents. Upon ageing the alloys Mazak3, ZA8 and ZA27 at an ambient temperature for five years, Cu was also found to influence and maintain the metastable Zn-AI (a'm) phase. The Cufree Mazak3 upon ageing lost this metastable phase. The 1.0% Cu ZA8 alloy had lost almost 50% of its metastable phase. Finally, the 2.0°/= Cu ZA27 had merely lost 10% of its metastable phase. The cph Zn contained s limited number of slip systems; therefore, twinning deformation was unavoidable in both fatigue and tensile testing. Cyclic d e f o r m a t i o n , damage, a n d effects o f e n v i r o n m e n t in t h e Ni3AI ordered alloy at elevated t e m p e r a t u r e .
Webb, G. Diss. Abstr. Int. (Oct. 1992) 53 (4) 259 pp Ni3AI alloys are candidate material systems for advanced aerospace applications owing to their unique properties at elevated temperatures. These materials are widely recognized for their beneficial role in strengthening superalloys at elevated temperatures. In monolithic form, these materials suffer from intrinsic grain boundary weakness. Recently the intrinsic brittleness of these alloys has bean solved through control of metallurgical variables. Such advances have stimulated interest in these alloys to the point where fatigue studies are required. The obejctives of this study were to evaluate the effect of composition, temperetu re, and environment on the fatigue properties of Ni3AI polycrystalline alloys. The experimental portion of the study describes these results in which the important metallurgical variables were identified. These include: the role of Cr in alleviating high-tempereture embrittlement; dislocation structures associated with static and cyclic hardening; and crack growth mechanisms at elevated temperature. In carrying out the project, it became clear that the inadequacies of current deformation models posed a major limitation to the understanding and use of Ni3AI. This project provided a unique opportunity to address the important topic of deformation both theoretically and experimentally. This resulted in formulation of a model consistent with all currently observed characteristics for yielding in Ni3AI. The model assumes that deformation Occurs under equilibrium conditions and incorporates this idea within a thermodynamic framework. Experiments were conducted that demonstrate the conditions by which complete thermal reversibility can be obtained in polycrystalline Ni3AI. These results are in accord with the model predictions. TEM experiments on these specimens revealed that when irreversibility is observed, it results from dislocations that do not control yielding. The requirement of complete thermal reversibility indicates that defects previously presumed to control yielding, in fact, play no role in the process.
r u p t u r e m a p o f 1 2 C r 1 M o V heat resistant
Chen, G., Yang, W. and Shu, G. Iron and Steel (China) ( M a y 1992) 27 (5) 4 2 - 4 5 (in Chinese) A fetigue-cresp interaction fracture map for a 12CrlMoV heat-resistant steel with holding load has been constructed by simulation tests under a practical load spectrum, together with its fractogrsphic analysis. Based on the map, a relationship between creep life and holding time has been suggested as a life-prediction criterion to provide a reliable base for safe operation of thermal power plant. Graphs, photomicrographs, 4 ref.
Rolling contact f a t i g u e b e h a v i o u r o f peerlitic rail steals.
Dikshit, V, A. Diss. Abstr. Int. (Oct. 1992) 53 (4) 276 p p Railroad rails can fail by a number of mechanisms including wear and surfaceinitiated rolling contact fatigue (RCF). Higher strength and deformetion-resistant rail steels have been successful in helping to alleviate wear, but have led to concerns about the relationship between material properties and RCF resistance. A simple material model has been developed to predict the RCF life of eutectoid rail steels for weter-lubriceted conditions using an Amsler twin-disc rolling/sliding testing machine. RCF life is found to be a function of the maximum Herlzian contact stress P0, the hardness H, and HPo.This empirical relationship predicts that as P0 increases and/or H decreases, RCF life decreases. The model can be modified by replacing the hardness by the pearlite interlamellar spacing of the steel. The effect of different lubricants can be included by considering the coefficient of friction. Validation studies showed that the model predictions agreed very well with experimental results when the steels used had properties similar to those used in formulating the model. A laboratory analysis of heed-hardened rails, removed from a heavy haul site at various stages of life, has enabled a study to be made of the incidence of RCF cracks and the role of the white etching layer (WEL) found on the rail head. The cracks occurring down the centre of the rail were shown to be associated with the WEL formed very early in the life of the rail. The extent of the WEL and the population of cracks decreased with increasing traffic. Some cracks penetrated beyond the WEL-pearlite interface and grew to a depth that was not always removed during normal maintenance grinding. The crack growth rates found in these rails were approx 8.5 times lower than those found in Amsler test specimens. This work also looked at developing a test procedure to generate subsurfacecontained plastic deformations. An attempt was made to relate an existing wear rate prediction model and the RCF life model to arrive at a relationship to predict the pearlite interlamellar spacing/hardness to minimize the wear rate and maximize the RCF life.
Int J Fatigue November 1993
M e a s u r e m e n t o f plastic zones associated w i t h small f a t i g u e cracks by selected area channeling patterns.
Zhang, Y.-H. and Edwards, L. Mater. Characterization (Oct. 1992) 29 (3) 3 1 3 - 3 2 0 The selected area electron channelling pattern method has been used to measure the plasticity associated with "growing' small fatigue cracks in s 7000-series AI alloy, allowing study of plastic zone development as well as investigation of the mechanisms by which small fatigue cracks and their plastic zones interact with grain boundaries. It was found that both plastic zone size and shape were dependent on both crack length and growth morphology. Naturally initiated Stage I fatigue cracks were predominantly crystallographic in nature and were accompanied by a relatively long, slender plastic zone shape. However, during subsequent growth over one to two grain diameters, this shape evolved, first to a semicircular shape, and finally to the lobed configuration typically found associated with long cracks. The AI-5.80Zn-2.54Mg-1.47Cu alloy discussed is based on the 7075 alloy. Photomicrographs, graphs, 14 ref. Fatigue life o f silicon nitride bails.
Galbato, A. T., Cundill, R. T. and Harris, T.A. Lubr. Eng. (Nov. 1992) 48 (11) 8 8 6 - 8 9 4 Because its specific weight is 40% that of steel, silicon nitride has been considered as a rolling element material in very high-speed ball and roller bearings. Furthermore, similar to steel components, hot pressed silicon nitride rolling components, when properly manufactured, have demonstrated the capacity to fail in a non-catastrophic manner, ie fatigue of the rolling contact surfaces. In this investigation, hot isostatically pressed silicon nitride balls were endurance-tetsted using a NASA five-ball rig and the results were compared against similarly tested VIMVAR MS0 balls. The silicon nitride balls demonstrated fatigue lives many times those obtained for the MS0 balls. Therefore it is concluded that silicon nitride can be effectively employed in applications where steel rolling element life has previously proved to be a limiting factor.
Study on f a u l t reason o f t h e WJSA-1 t y p e engine. Wu, P.Y. J. Mater. Eng. (China) (Aug. 1992) (4) 3 3 - 3 7 (in Chinese) The WJ5A.1 type (No. 850086) engine fault occurred during flight service. Through disassembly and check of the engine, it was found that both the I stage gas turbine blade made of K5 and the support component made of 1Cr18NigTi had been fatiguefractured. The results obtained by macro-micro-frectography and metallography
529
The characteristic o f rapidly solidified a l u m i n i u m alloys and its appli-
cation. Lien, J. Heat Treatment of Metals (China) (Apr. 1992) (4) 3 4 - 3 6 (in Chinese) The microstructure of the rapidly solidified powder AI-Fe-V-Si alloy displays very fine spherical AI13(Fe,V)3 Si particles dispersed in the AI matrix. This structure provides the alloy with high temperature stability (> 150 °C) and good ductility. The physical, tensile, fatigue, creep, and corrosion properties and the fabricabilities of the alloys with the compositions of AI-8.5Fe-1.7Si-l.3V, AI-6.5Fe-I.3Si-0.6V, and AI-11.7Fe-2.4Si-l.2V are presented and discussed. These AI alloys can be used to replace Ti alloys for aircraft parts exposed in the high temperature environment ranging between 150-400°C. They also cost less than the Ti alloys. Graphs, 10 refs.
improved operational properties o f cupercleen 3.5% N i C r M o V rotor steel.
Mayer, K. H,, Kachler, W. and Konig, H. Clean Steels Technology: Proc. R.I. Jaffee Memorial Symposium, Chicago, Illinois, USA, 2 - 5 Nov. 1992, pp 2 0 5 - 2 1 2 The superclean 3.5% NiCrMoV rotor steel, characterized by low contents of trace elements sulphur, phosphorus, Sn, Sb, arsenic, gas contents (02. N2, H2) and Si, Mn, and AI contents - manufactured on the basis of modern melting technology and based on a careful selection of scrap and a well-matched secondary metallurgy with a ladle furnace - is a very attractive material for the steam turbine manufacturer. By suppression of temper and long-term embrittlement at temperatures > 350 °C, the scope of application of the high-strength and tough 3.5% NiCrMoV rotor steel is increased to s temperature level of approx 500 °C and can be used for the manufacture of steam turbines with a higher thermal efficiency and at lower prime cost. Superclesn melting also offers substantial benefits with regard to creep strength and low-cycle fatigue beheviour since, in contrast to conventional melting, these properties are also distinctly improved. The high low-cycle fatigue strength is of particular interest for plant operating in the peak-load range.
Crack initiation and t o t a l f a t i g u e life o f a carbon steal in v a c u u m and
air. Kujawski, O. and Ellyin, F. ASTM J. Test. Eva/. (Nov. 1992) 20 (6) 391-395 Fully reversed strain-controlled test results of a carbon steel (ASTM A 516 Gr.70) in an ambient atmosphere and in a vacuum of 0.1 mPa are compared. Vacuum data may be reviewed as representing a 'pure" (mechanical) fatigue damage. In the case of an air environment, the rate of fatigue damage accumulation increases owing to the environmental contribution. The test results are described in terms of the crack initiation and total lives. The crack initiation data are fairly well correlated with the plastic strain energy per cycle. The significance of the environment condition on the life prediction procedures is discussed. Graphs, 15 ref.
F a t i g u e - c r e e p interaction steel w i t h h o l d i n g load.
The f a t i g u e properties o f pressure diecast z i n c - e l u m i n l u m based alloys.
Sawalha, K. Diss. Abstr. Int. (Oct. 1992) 53 (4) 281 pp The fatigue behaviour of the cold chamber pressure diecast alloys Mazak3, ZA8, ZA27, M3K, ZABK, ZA27K, K1, K2, and 1(3 was investigated at a temperature of 20 °C. The alloys M3K, ZASK and ZA27K were also examined at temperatures of 50 and 100 °C. The ratio between fatigue strength and tensile strength was established at 20°C at 107 cycles. The fatigue life prediction of the alloys M3K, ZA8K and ZA27K was formulated st 20, 50 and 100°C. The prediction formulae were found to be reasonably accurate. All the experimental alloys were heterogeneous and contained large but varying amounts of pores. These pores were a major contribution and dominated the alloys' fatigue failure. Their effect, however, on tensile failure was negligible. The ZA27K possessed the highest tensile strength but the lowest fatigue strength. The relationship between the fracture topography and the microstructure was also determined by the use of a mixed signal of a secondary electron and a bsckscettered electron on the SEM. The tensile strength of the experimental alloys was directly proportional to the AI content within the alloys. The effect of Cu content was also investigated within the alloys K1, K2, ZA8K end K3, which contained 0, 0.5, 1.0 and 2.0=/0 respectively. It was determined that the fatigue and tensile strengths improved with higher Cu contents. Upon ageing the alloys Mazak3, ZA8 and ZA27 at an ambient temperature for five years, Cu was also found to influence and maintain the metastable Zn-AI (a'm) phase. The Cufree Mazak3 upon ageing lost this metastable phase. The 1.0% Cu ZA8 alloy had lost almost 50% of its metastable phase. Finally, the 2.0°/= Cu ZA27 had merely lost 10% of its metastable phase. The cph Zn contained s limited number of slip systems; therefore, twinning deformation was unavoidable in both fatigue and tensile testing. Cyclic d e f o r m a t i o n , damage, a n d effects o f e n v i r o n m e n t in t h e Ni3AI ordered alloy at elevated t e m p e r a t u r e .
Webb, G. Diss. Abstr. Int. (Oct. 1992) 53 (4) 259 pp Ni3AI alloys are candidate material systems for advanced aerospace applications owing to their unique properties at elevated temperatures. These materials are widely recognized for their beneficial role in strengthening superalloys at elevated temperatures. In monolithic form, these materials suffer from intrinsic grain boundary weakness. Recently the intrinsic brittleness of these alloys has bean solved through control of metallurgical variables. Such advances have stimulated interest in these alloys to the point where fatigue studies are required. The obejctives of this study were to evaluate the effect of composition, temperetu re, and environment on the fatigue properties of Ni3AI polycrystalline alloys. The experimental portion of the study describes these results in which the important metallurgical variables were identified. These include: the role of Cr in alleviating high-tempereture embrittlement; dislocation structures associated with static and cyclic hardening; and crack growth mechanisms at elevated temperature. In carrying out the project, it became clear that the inadequacies of current deformation models posed a major limitation to the understanding and use of Ni3AI. This project provided a unique opportunity to address the important topic of deformation both theoretically and experimentally. This resulted in formulation of a model consistent with all currently observed characteristics for yielding in Ni3AI. The model assumes that deformation Occurs under equilibrium conditions and incorporates this idea within a thermodynamic framework. Experiments were conducted that demonstrate the conditions by which complete thermal reversibility can be obtained in polycrystalline Ni3AI. These results are in accord with the model predictions. TEM experiments on these specimens revealed that when irreversibility is observed, it results from dislocations that do not control yielding. The requirement of complete thermal reversibility indicates that defects previously presumed to control yielding, in fact, play no role in the process.
r u p t u r e m a p o f 1 2 C r 1 M o V heat resistant
Chen, G., Yang, W. and Shu, G. Iron and Steel (China) ( M a y 1992) 27 (5) 4 2 - 4 5 (in Chinese) A fetigue-cresp interaction fracture map for a 12CrlMoV heat-resistant steel with holding load has been constructed by simulation tests under a practical load spectrum, together with its fractogrsphic analysis. Based on the map, a relationship between creep life and holding time has been suggested as a life-prediction criterion to provide a reliable base for safe operation of thermal power plant. Graphs, photomicrographs, 4 ref.
Rolling contact f a t i g u e b e h a v i o u r o f peerlitic rail steals.
Dikshit, V, A. Diss. Abstr. Int. (Oct. 1992) 53 (4) 276 p p Railroad rails can fail by a number of mechanisms including wear and surfaceinitiated rolling contact fatigue (RCF). Higher strength and deformetion-resistant rail steels have been successful in helping to alleviate wear, but have led to concerns about the relationship between material properties and RCF resistance. A simple material model has been developed to predict the RCF life of eutectoid rail steels for weter-lubriceted conditions using an Amsler twin-disc rolling/sliding testing machine. RCF life is found to be a function of the maximum Herlzian contact stress P0, the hardness H, and HPo.This empirical relationship predicts that as P0 increases and/or H decreases, RCF life decreases. The model can be modified by replacing the hardness by the pearlite interlamellar spacing of the steel. The effect of different lubricants can be included by considering the coefficient of friction. Validation studies showed that the model predictions agreed very well with experimental results when the steels used had properties similar to those used in formulating the model. A laboratory analysis of heed-hardened rails, removed from a heavy haul site at various stages of life, has enabled a study to be made of the incidence of RCF cracks and the role of the white etching layer (WEL) found on the rail head. The cracks occurring down the centre of the rail were shown to be associated with the WEL formed very early in the life of the rail. The extent of the WEL and the population of cracks decreased with increasing traffic. Some cracks penetrated beyond the WEL-pearlite interface and grew to a depth that was not always removed during normal maintenance grinding. The crack growth rates found in these rails were approx 8.5 times lower than those found in Amsler test specimens. This work also looked at developing a test procedure to generate subsurfacecontained plastic deformations. An attempt was made to relate an existing wear rate prediction model and the RCF life model to arrive at a relationship to predict the pearlite interlamellar spacing/hardness to minimize the wear rate and maximize the RCF life.
Int J Fatigue November 1993
M e a s u r e m e n t o f plastic zones associated w i t h small f a t i g u e cracks by selected area channeling patterns.
Zhang, Y.-H. and Edwards, L. Mater. Characterization (Oct. 1992) 29 (3) 3 1 3 - 3 2 0 The selected area electron channelling pattern method has been used to measure the plasticity associated with "growing' small fatigue cracks in s 7000-series AI alloy, allowing study of plastic zone development as well as investigation of the mechanisms by which small fatigue cracks and their plastic zones interact with grain boundaries. It was found that both plastic zone size and shape were dependent on both crack length and growth morphology. Naturally initiated Stage I fatigue cracks were predominantly crystallographic in nature and were accompanied by a relatively long, slender plastic zone shape. However, during subsequent growth over one to two grain diameters, this shape evolved, first to a semicircular shape, and finally to the lobed configuration typically found associated with long cracks. The AI-5.80Zn-2.54Mg-1.47Cu alloy discussed is based on the 7075 alloy. Photomicrographs, graphs, 14 ref. Fatigue life o f silicon nitride bails.
Galbato, A. T., Cundill, R. T. and Harris, T.A. Lubr. Eng. (Nov. 1992) 48 (11) 8 8 6 - 8 9 4 Because its specific weight is 40% that of steel, silicon nitride has been considered as a rolling element material in very high-speed ball and roller bearings. Furthermore, similar to steel components, hot pressed silicon nitride rolling components, when properly manufactured, have demonstrated the capacity to fail in a non-catastrophic manner, ie fatigue of the rolling contact surfaces. In this investigation, hot isostatically pressed silicon nitride balls were endurance-tetsted using a NASA five-ball rig and the results were compared against similarly tested VIMVAR MS0 balls. The silicon nitride balls demonstrated fatigue lives many times those obtained for the MS0 balls. Therefore it is concluded that silicon nitride can be effectively employed in applications where steel rolling element life has previously proved to be a limiting factor.
Study on f a u l t reason o f t h e WJSA-1 t y p e engine. Wu, P.Y. J. Mater. Eng. (China) (Aug. 1992) (4) 3 3 - 3 7 (in Chinese) The WJ5A.1 type (No. 850086) engine fault occurred during flight service. Through disassembly and check of the engine, it was found that both the I stage gas turbine blade made of K5 and the support component made of 1Cr18NigTi had been fatiguefractured. The results obtained by macro-micro-frectography and metallography
529