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Synthesis of gradient thin films by ion-beam-enhanced deposition
Localized shear d e f o r m a t i o n on an eluminium-Ilthium 8090 alloy during low-cycle fatigue. Xu, Y.B., Wang, L., Wang, Z.G., Zhang, Y., and Hu,
Z.Q, Scr. MetalL Mater. M a y 1991 25, (5), 114,9-1154 Observations on the formation and microstructure of localized shear deformation occurring in an AI-Li-Mg-Cu-Zr alloy in the peak-aged condition (ta) at room temperature during low-cycle fatigue are presented. It is concluded that the deformation mechanism at high applied plastic strain is mainly characterized by localized shear bands in which the 8'-precipitates are intensely sheared by moving dislocations. These bands can cross several grains, leading to coplanar slip. On the other hand. at low applied plastic strain, most dislocations are locally gathered to form sinuous deformation bands. The localized shear deformation bands associated with the sheareble 8'-precipitates reduce the fatigue crack initiation resistance and enhance fatigue crack propagation along these bands. This, rather than the segregation of low melting point impurities, leads to a low value of the macroscopic strain failure for the present AI-Li alloy. Graphs, photomicrographs. 14 refs,
interrelationships among grain boundaries, cavitation and dislocation structure in Cu-15 at.% AI f a t i g u e d at h i g h temperatures. CabanasMoreno, J.G., Gonzalez-Velazquez, J.L, and Weertman, J. R. Scr. Metall. Mater. M a y 1991 25, (5), 1093-1097 During the course of an investigation on the cavitation behaviour during hightemperature fatigue of several low stacking fault energy Cu-AI alloys, some observations were made which suggest that other aspects between grain boundary migration (GBM) and cavitation should be taken into account as well. Non-planar slip has been observed in Cu-15 at.% AI fatigued at high temperatures (around one-half of the melting temperature). When~he fatigue tests are carried out at small total strain amplitudes (<0.001), this dislocation configuration may extend to the grain interiors, At higher strain amplitudes, planar slip predominates inside the grains. However, when GBM occurs, non-planar slip is seen in the region swept out by the migrating boundary. These observations suggest that GBM, dislocation structures near the boundaries, and cavitation are all interrelated. Photomicrographs. 15 refs,
The f o r m a t i o n o f e i t h e r t o n g u e - or ribbon-like e x t r u s i o n s in f a t i g u e d copper polycrystals. Bayerlein, M. and Muhgrabi, H. Acta Metall. Mater. J u l y 1991 39, (7), 1645-1650 The surface morphology of polycrystalline Cu fatigued at temperatures of 107, 298 and 533 K was investigeged by scanning electron microscopy (SEM). Both ribbonand tongue-like extrusions were observed except after fatigue at 533 K, where ribbonlike, complex and needle-like surface structures were apparent. The dependence of the formation of either ribbon- or tongue-like extrusions on the crystallographic orientation of the grains in the direction of the stress axis was investigated by selected-area electron channelling patterns in the SEM. The results suggest strongly that the morphology of extrusions formed at emerging PSBs is controlled by the type and the Schmid factors of the activated slip systems. A model suggested by Polak et el to explain the formation of the tongue-like extrusions was checked for 20 different grains and found not to be valid in general. Graphs, photomicrographs. 28 refs. Synthesis o f g r a d i e n t t h i n f i l m s by ion-beam-enhanced deposition. Liu,
X. Zou, J., Zhou, S., Taniguchi, S., Schroer, A. and Wolf, G.K. Mater. Sci. Eng. A J u l y 1991 A139, ( 1 - 2 ) , 2 2 0 - 2 2 4 Gradient thin films consisting of Si3N4 were prepared on metals (Ni, steel, including 1Cr18Ni9Ti, AI-C fibre, Ni3AI, etc) by ion-beam-enhanced deposition. The coating deposited on one side of the sample has a high resistance (10e ~) while that on the other side has a low resistance (1 n) with s gradual change in the interface region. Composition profiles, hardness, adhesion, fatigue life, corrosion resistance and high-temperature oxidation behaviour were measured and are discussed. Graphs. 7 refs. Corrosion f a t i g u e o f an e l u m i n i u m - l i t h i u m Dies. Abstr. Int. Aug. 1991 52, (2), 295 pp
alloy. Chen, G.-S.
The corrosion fatigue beheviour of an AI-2.5Li-0.12Zr alloy has been studied as a function of heat treatment by performing fatigue experiments on differently aged alloys in dry air, humid nitrogen and 0.5 M NaC1 solutions, The microstructure, tensile properties and electrochemical properties of the alloy were also investigated versus various ageing conditions. The fatigue results are correlated to the material characteristics and are discussed in terms of metallurgical, environmental and mechanical aspects. It was found that ageing treatment decreased the fatigue resistance of the AI-Li-Zr alloy in dry air. However, water reduced the fatigue resistance of the undereged alloys but promoted the fatigue life of the overaged alloys. Hydrogen precharging experiments followed by fatiguing in dry air confirmed that underaged alloys are susceptible to H embrittlement and that overaged alloys are insensitive to the H effect. The results of fatigue tests in 0.5 M NaCI solutions at free corrosion potentials showed that the high-cycle fatigue strength of the alloy was drastically reduced by the environment, while an ageing treatment did not significantly affect the fatigue strength of the alloy in solutions. The experimental results basically indicate that the AI-Li-Zr alloy is susceptible to H-assisted fracture. However, the susceptibility is essentially related to the effectiveness of H transport to the region ahead of the crack tip, which would be profoundly affected by the microstructure and deformation mode of the alloy. It appears that • decrease in slip planarity and an increase in the amount of the 6-phass (AILi), which occur upon ageing, may trap the absorbed H and thus reduce the susceptibility of the alloy to H embrittlement. On the other hand, the evidence suggests that for the AI-Li-Zr alloy tested in NaCI solutions, the fatigue resistance is determined by slip+enhanced dissolution and H embrittlement mechanisms at high stress ranges, whereas the fatigue life is predominetly controlled by pitting-induced crack initiation at low stress ranges. TrF_~alOSive t r e a t m e n t . Gao, H.
ns. Met. Heat Treat. (China) Dec. 1990 11, (4), 7 5 - 7 8 (in Chinese)
The main parameters for the explosive treatment for metals (eg mild steel), for the effect of the explosive treatment on the microstructure and the fatigue behaviour, the dynamic crack growth behaviour during the treatment and the method for restricting crack growth have been studied and discussed. 7 refs.
198
D e v e l o p m e n t o f heat.resistant cast steels f o r e x h a u s t manifolds.
M,, Aklyama, K. Ohtsuka, K. and Itoh, K. Int. J. Mater. Product Technol. 1991 6, (3), 2 4 3 - 2 5 6
Ike,
A new type of heat-resistant cast steel developed for exhaust manifolds is presented. Increased exhaust-gas temperatures accompanying recent trends towards leaner combustion and higher engine outputs have placed severe thermal loads on exhaust manifolds and turbocharger housings. The new type of cast steel displays a better resistance to thermal fatigue than conventional ductile cast irons (DCI) and a better cost performance than Ni-resist (ASTM A439 austenitic ductile cast irons). In the material-design process, the properties required of the material were determined on the basis of statistical analyses. An experiment was then conducted using a test specimen that partially modelled an actual exhaust manifold and a heating simulation was carried out separately from the engine using an exhaust-system simulator. Finally, an endurance test was conducted on an actual exhaust manifold made of the new type of cast steel using a production system. Graphs, photomicrographs. 6 refs. Fatigue m o n i t o r i n g w i t h fuses. La Veaux, R. de, McGlinchey, J. and
Bernstein, R.M. Mater. Eval. Aug. 1991 49, (8), 1042-1045 A method of monitoring the fatigue behaviour in structures is presented that involves the placement of fatigue fuses, which are specially prepared specimens with builtin stress concentrations that fail after a certain strain history. The fuses or coupons are then remotely sensed to determine if any of the legs of the coupons have been broken, then, the fatigue damage to the member the fuse is mounted on can be determined. The fuses are not as complicated as strain gauges and have been thoroughly tested.The units can be used to determine the presence of microcrecks so that early corrective action may be taken. The materials tested were 2024, 6061 and 7075AI and 1018 steel. Graphs, 3 refs. The e x p e r i m e n t a l investigation concerninll t h e new method and its controlling s y s t e m o f s t u d y i n g a n d a u t o m a t : c d e t e r m i n i n g daldN. Wang,
C.-Z., Yu, -J. and Zhu, J. Shanghai Iron and Steel Research Institute Technical Report No 1991-3 1991 21 pp.
A new test method is given for studying da/dN precisely, and a determining system that can be automatically controlled has been established. The system consists of the WZY-l-type AC-potsntial crack monitor developed previously, a microcomputer system and a fatigue test machine. The fatigue crack growth rate (FCGR) da/dN of the metallic materials can be determined automatically by means of the new method and system. Moreover, the highly automated system can obtain good experimental results, which are characterized by high sensitivity, accuracy and reliability. The new, convenient, and effective method and the automatic determining system ere well suited for the experimental investigation of fatigue crack growth. Cr13Ni19Mo2AI and Ti-5AI-4Mo-4Cr-2Sn-2Zr were tested. Graphs. 4 refs.
Influence o f f a t i g u e o n t h e austenitization o f l o w - a l l o y e d quenched and t e m p e r e d steels. Rother, E. and Wolter, F. Harterei-Technische Mitteilungen July-Aug. 1991 46, (4), 2 1 3 - 2 1 5 (in German) The effect of a fatigue loading on the ,x/-/ transformation temperature was analysed post-mortem for an example of a hest-treatsble steel. Results are given for the amount and the direction of modification of the temperature in dependence on the grade of steel, structure and fatigue loading. Graphs. 13 refs.
Joining Corrosion p r e v e n t i o n in w o l d s : a delicate p r o b l e m , van des Goes, J.J.,
and Kon, B.V. Materialen M a y - J u n e 1991 25, (5), 2 7 - 2 9 (in Dutch) The risk of leaks from welds in apparatus due to an undesirable electrochemical attack on the material must be countered at the design and fabrication stages. The main requirement in this connection is correct parent and filler material selection, while the overall weld volume should also be minimized at the design stage. The cracking/fatigue, selective, crevice and erosive*corrosion mechanisms are discussed. Fatigue crack p r o p a g a t i o n in w e a t h e r i n g weldable-steel KT 315 silicon.
Benke, A., Schadlich, S. and Zouhar, G. Steel Res. J u l y 1991 62, (7), 3 2 0 - 3 2 4 Complex loading conditions are typical for structural materials, especially for steels. Fatigue crack propegegion measurements during bend loading were carried out with different load ratios on a newly developed weathering steel KT 315 Si. This steel has an improved resistance to corrosion in comparison with the weathering steel KT 315. Scanning electron microscopy of the fracture surfaces and quantitative microstructure analysis by means of light microscopy were applied to elucidate the relations between microstructure and mechanical properties. An important result of the investigation is that the steel KT 315 Si reveals a lowered mean stress sensitivity of the fatigue threshold value AKth in comparison with that of other ferritic-pearlitic steels of the same strength level. Graphs, photomicrographs. 12 refs. Fatigue analysis o f laser-welded lap joints. Hsu, C. and Albrightt, C.E. Eng. Fract. Mech. 1991 39, (3), 5 7 5 - 5 8 0 The metal fabrication industries have shown an increased interest in laser welding of sheet steel products in recent years. A lap joint is often selected because this joint configuration allows quality welding with less restrictive dimensional tolerances for joints. Recent experiments in the fatigue performance of laser-welded lap joints show that the fatigue performance is dependent on the weld pattern. This investigation establishes a technique for predicting the fatigue response of laserwelded lap joints. A static-stress analysis (Goland and Reissner) is combined with a cyclic-stress-strain analysis (Nuper) to establish a model for calculating the joint stress under cyclic loading. The model accounts for approximately 75% of the reduction in fatigue stress when comparing laser-welded lap joints to unwelded, smooth material. The remaining 25% reduction is attributed to residual stress and/or material property alterations resulting from welding. Graphs. 8 refs.
Int J Fatigue May 1992
Z.Q, Scr. MetalL Mater. M a y 1991 25, (5), 114,9-1154 Observations on the formation and microstructure of localized shear deformation occurring in an AI-Li-Mg-Cu-Zr alloy in the peak-aged condition (ta) at room temperature during low-cycle fatigue are presented. It is concluded that the deformation mechanism at high applied plastic strain is mainly characterized by localized shear bands in which the 8'-precipitates are intensely sheared by moving dislocations. These bands can cross several grains, leading to coplanar slip. On the other hand. at low applied plastic strain, most dislocations are locally gathered to form sinuous deformation bands. The localized shear deformation bands associated with the sheareble 8'-precipitates reduce the fatigue crack initiation resistance and enhance fatigue crack propagation along these bands. This, rather than the segregation of low melting point impurities, leads to a low value of the macroscopic strain failure for the present AI-Li alloy. Graphs, photomicrographs. 14 refs,
interrelationships among grain boundaries, cavitation and dislocation structure in Cu-15 at.% AI f a t i g u e d at h i g h temperatures. CabanasMoreno, J.G., Gonzalez-Velazquez, J.L, and Weertman, J. R. Scr. Metall. Mater. M a y 1991 25, (5), 1093-1097 During the course of an investigation on the cavitation behaviour during hightemperature fatigue of several low stacking fault energy Cu-AI alloys, some observations were made which suggest that other aspects between grain boundary migration (GBM) and cavitation should be taken into account as well. Non-planar slip has been observed in Cu-15 at.% AI fatigued at high temperatures (around one-half of the melting temperature). When~he fatigue tests are carried out at small total strain amplitudes (<0.001), this dislocation configuration may extend to the grain interiors, At higher strain amplitudes, planar slip predominates inside the grains. However, when GBM occurs, non-planar slip is seen in the region swept out by the migrating boundary. These observations suggest that GBM, dislocation structures near the boundaries, and cavitation are all interrelated. Photomicrographs. 15 refs,
The f o r m a t i o n o f e i t h e r t o n g u e - or ribbon-like e x t r u s i o n s in f a t i g u e d copper polycrystals. Bayerlein, M. and Muhgrabi, H. Acta Metall. Mater. J u l y 1991 39, (7), 1645-1650 The surface morphology of polycrystalline Cu fatigued at temperatures of 107, 298 and 533 K was investigeged by scanning electron microscopy (SEM). Both ribbonand tongue-like extrusions were observed except after fatigue at 533 K, where ribbonlike, complex and needle-like surface structures were apparent. The dependence of the formation of either ribbon- or tongue-like extrusions on the crystallographic orientation of the grains in the direction of the stress axis was investigated by selected-area electron channelling patterns in the SEM. The results suggest strongly that the morphology of extrusions formed at emerging PSBs is controlled by the type and the Schmid factors of the activated slip systems. A model suggested by Polak et el to explain the formation of the tongue-like extrusions was checked for 20 different grains and found not to be valid in general. Graphs, photomicrographs. 28 refs. Synthesis o f g r a d i e n t t h i n f i l m s by ion-beam-enhanced deposition. Liu,
X. Zou, J., Zhou, S., Taniguchi, S., Schroer, A. and Wolf, G.K. Mater. Sci. Eng. A J u l y 1991 A139, ( 1 - 2 ) , 2 2 0 - 2 2 4 Gradient thin films consisting of Si3N4 were prepared on metals (Ni, steel, including 1Cr18Ni9Ti, AI-C fibre, Ni3AI, etc) by ion-beam-enhanced deposition. The coating deposited on one side of the sample has a high resistance (10e ~) while that on the other side has a low resistance (1 n) with s gradual change in the interface region. Composition profiles, hardness, adhesion, fatigue life, corrosion resistance and high-temperature oxidation behaviour were measured and are discussed. Graphs. 7 refs. Corrosion f a t i g u e o f an e l u m i n i u m - l i t h i u m Dies. Abstr. Int. Aug. 1991 52, (2), 295 pp
alloy. Chen, G.-S.
The corrosion fatigue beheviour of an AI-2.5Li-0.12Zr alloy has been studied as a function of heat treatment by performing fatigue experiments on differently aged alloys in dry air, humid nitrogen and 0.5 M NaC1 solutions, The microstructure, tensile properties and electrochemical properties of the alloy were also investigated versus various ageing conditions. The fatigue results are correlated to the material characteristics and are discussed in terms of metallurgical, environmental and mechanical aspects. It was found that ageing treatment decreased the fatigue resistance of the AI-Li-Zr alloy in dry air. However, water reduced the fatigue resistance of the undereged alloys but promoted the fatigue life of the overaged alloys. Hydrogen precharging experiments followed by fatiguing in dry air confirmed that underaged alloys are susceptible to H embrittlement and that overaged alloys are insensitive to the H effect. The results of fatigue tests in 0.5 M NaCI solutions at free corrosion potentials showed that the high-cycle fatigue strength of the alloy was drastically reduced by the environment, while an ageing treatment did not significantly affect the fatigue strength of the alloy in solutions. The experimental results basically indicate that the AI-Li-Zr alloy is susceptible to H-assisted fracture. However, the susceptibility is essentially related to the effectiveness of H transport to the region ahead of the crack tip, which would be profoundly affected by the microstructure and deformation mode of the alloy. It appears that • decrease in slip planarity and an increase in the amount of the 6-phass (AILi), which occur upon ageing, may trap the absorbed H and thus reduce the susceptibility of the alloy to H embrittlement. On the other hand, the evidence suggests that for the AI-Li-Zr alloy tested in NaCI solutions, the fatigue resistance is determined by slip+enhanced dissolution and H embrittlement mechanisms at high stress ranges, whereas the fatigue life is predominetly controlled by pitting-induced crack initiation at low stress ranges. TrF_~alOSive t r e a t m e n t . Gao, H.
ns. Met. Heat Treat. (China) Dec. 1990 11, (4), 7 5 - 7 8 (in Chinese)
The main parameters for the explosive treatment for metals (eg mild steel), for the effect of the explosive treatment on the microstructure and the fatigue behaviour, the dynamic crack growth behaviour during the treatment and the method for restricting crack growth have been studied and discussed. 7 refs.
198
D e v e l o p m e n t o f heat.resistant cast steels f o r e x h a u s t manifolds.
M,, Aklyama, K. Ohtsuka, K. and Itoh, K. Int. J. Mater. Product Technol. 1991 6, (3), 2 4 3 - 2 5 6
Ike,
A new type of heat-resistant cast steel developed for exhaust manifolds is presented. Increased exhaust-gas temperatures accompanying recent trends towards leaner combustion and higher engine outputs have placed severe thermal loads on exhaust manifolds and turbocharger housings. The new type of cast steel displays a better resistance to thermal fatigue than conventional ductile cast irons (DCI) and a better cost performance than Ni-resist (ASTM A439 austenitic ductile cast irons). In the material-design process, the properties required of the material were determined on the basis of statistical analyses. An experiment was then conducted using a test specimen that partially modelled an actual exhaust manifold and a heating simulation was carried out separately from the engine using an exhaust-system simulator. Finally, an endurance test was conducted on an actual exhaust manifold made of the new type of cast steel using a production system. Graphs, photomicrographs. 6 refs. Fatigue m o n i t o r i n g w i t h fuses. La Veaux, R. de, McGlinchey, J. and
Bernstein, R.M. Mater. Eval. Aug. 1991 49, (8), 1042-1045 A method of monitoring the fatigue behaviour in structures is presented that involves the placement of fatigue fuses, which are specially prepared specimens with builtin stress concentrations that fail after a certain strain history. The fuses or coupons are then remotely sensed to determine if any of the legs of the coupons have been broken, then, the fatigue damage to the member the fuse is mounted on can be determined. The fuses are not as complicated as strain gauges and have been thoroughly tested.The units can be used to determine the presence of microcrecks so that early corrective action may be taken. The materials tested were 2024, 6061 and 7075AI and 1018 steel. Graphs, 3 refs. The e x p e r i m e n t a l investigation concerninll t h e new method and its controlling s y s t e m o f s t u d y i n g a n d a u t o m a t : c d e t e r m i n i n g daldN. Wang,
C.-Z., Yu, -J. and Zhu, J. Shanghai Iron and Steel Research Institute Technical Report No 1991-3 1991 21 pp.
A new test method is given for studying da/dN precisely, and a determining system that can be automatically controlled has been established. The system consists of the WZY-l-type AC-potsntial crack monitor developed previously, a microcomputer system and a fatigue test machine. The fatigue crack growth rate (FCGR) da/dN of the metallic materials can be determined automatically by means of the new method and system. Moreover, the highly automated system can obtain good experimental results, which are characterized by high sensitivity, accuracy and reliability. The new, convenient, and effective method and the automatic determining system ere well suited for the experimental investigation of fatigue crack growth. Cr13Ni19Mo2AI and Ti-5AI-4Mo-4Cr-2Sn-2Zr were tested. Graphs. 4 refs.
Influence o f f a t i g u e o n t h e austenitization o f l o w - a l l o y e d quenched and t e m p e r e d steels. Rother, E. and Wolter, F. Harterei-Technische Mitteilungen July-Aug. 1991 46, (4), 2 1 3 - 2 1 5 (in German) The effect of a fatigue loading on the ,x/-/ transformation temperature was analysed post-mortem for an example of a hest-treatsble steel. Results are given for the amount and the direction of modification of the temperature in dependence on the grade of steel, structure and fatigue loading. Graphs. 13 refs.
Joining Corrosion p r e v e n t i o n in w o l d s : a delicate p r o b l e m , van des Goes, J.J.,
and Kon, B.V. Materialen M a y - J u n e 1991 25, (5), 2 7 - 2 9 (in Dutch) The risk of leaks from welds in apparatus due to an undesirable electrochemical attack on the material must be countered at the design and fabrication stages. The main requirement in this connection is correct parent and filler material selection, while the overall weld volume should also be minimized at the design stage. The cracking/fatigue, selective, crevice and erosive*corrosion mechanisms are discussed. Fatigue crack p r o p a g a t i o n in w e a t h e r i n g weldable-steel KT 315 silicon.
Benke, A., Schadlich, S. and Zouhar, G. Steel Res. J u l y 1991 62, (7), 3 2 0 - 3 2 4 Complex loading conditions are typical for structural materials, especially for steels. Fatigue crack propegegion measurements during bend loading were carried out with different load ratios on a newly developed weathering steel KT 315 Si. This steel has an improved resistance to corrosion in comparison with the weathering steel KT 315. Scanning electron microscopy of the fracture surfaces and quantitative microstructure analysis by means of light microscopy were applied to elucidate the relations between microstructure and mechanical properties. An important result of the investigation is that the steel KT 315 Si reveals a lowered mean stress sensitivity of the fatigue threshold value AKth in comparison with that of other ferritic-pearlitic steels of the same strength level. Graphs, photomicrographs. 12 refs. Fatigue analysis o f laser-welded lap joints. Hsu, C. and Albrightt, C.E. Eng. Fract. Mech. 1991 39, (3), 5 7 5 - 5 8 0 The metal fabrication industries have shown an increased interest in laser welding of sheet steel products in recent years. A lap joint is often selected because this joint configuration allows quality welding with less restrictive dimensional tolerances for joints. Recent experiments in the fatigue performance of laser-welded lap joints show that the fatigue performance is dependent on the weld pattern. This investigation establishes a technique for predicting the fatigue response of laserwelded lap joints. A static-stress analysis (Goland and Reissner) is combined with a cyclic-stress-strain analysis (Nuper) to establish a model for calculating the joint stress under cyclic loading. The model accounts for approximately 75% of the reduction in fatigue stress when comparing laser-welded lap joints to unwelded, smooth material. The remaining 25% reduction is attributed to residual stress and/or material property alterations resulting from welding. Graphs. 8 refs.
Int J Fatigue May 1992