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Hardness of fatigued copper polycrystals and their relation to their dislocation structure
Low cycle fatigue behsviour of austeniti© F e - 2 8 M n and F e - 2 6 M n - 4 A I alloys. Lee, J.S. and Kim, Y.G. Mater. ScL Eng. A M a y 1990 A125, (1), 49-56 Total strain-controlled (,~,sp(e)t = 3.0%)fatigue properties of the alloys Fe-26Mn and Fe-26Mn-4AI (where the compositions are in approximate wt.%) at room temperature and at 77 K have been investigated. Both alloys display better fatigue resistance at 77 K than at room temperature in the range of 102-104 cycles tested. The increased fatigue resistance of Fe-26Mn alloy is primarily the result of the increase in strength by the increased amount of strain-induced ¢-martensita. In contrast, the better fatigue resistance of Fe-28Mn-4AI alloy at 77 K is mainly attributed to the increase in ductility caused by the formation of strain-induced deformation twinning with decreasing temperature. Graphs, photomicrographs. 14 refs.
Hardness of fatigued copper polycrystals and their relation to their dislocation structure. Obrtlik, K., Brezina, J. and Polak, J. Mater. Sci. Eng. A Apr. 1990 A124, (2), L7-L10 The Vickers hardness was determined for Cu polycrystals cyclically strained at a constant plastic strain amplitude up to fracture. The dependence of the hardness on the plastic strain amplitude exhibits a minimum at a strain of 1 x 10-3, followed by a sharp increase. This is explained in terms of the observed dislocation structure produced during fatigue. Using polishing and sectioning techniques, the same value of hardness has been found on the surface and in the bulk of the material. Graphs, photomicrographs. 10 refs.
Cyclic d e f o r m a t i o n behavior of C u - 1 6 at.% AI single crystals. I. Strain burst behavior. Hong, S.I. and Laird, C. Mater. ScL Eng. A Apr. 1990 A124, (2), 183-201 To investigate strain burst behaviour of planar slip materials, single crystals of Cu-15.3 at.% AI alloys, oriented for easy glide, were cyclically deformed under load and strain control. A huge strain burst (~p = 0.12) observed in a load-controlled fatigue test is related to eesy-glide behaviour after yielding. Strain bursts under strain control proceeded through the crystal in a stepwise manner because the total strain is strictly controlled by • closed-loop system. The experimental observation that each strain burst is accompanied by the sudden appearance of a slip band indicates that they are caused by a sudden activation of dislocation sources. Strain burst behaviour at various strain amplitudes is also discussed in relation to deformation behaviour in load-controlled fatigue tests and monotonic tests. A positive asymmetry (a higher stress in tension) is caused by strain bursts occurring more frequently and more easily during compression behaviour that results from easier cross-slip and a higher mobility of dislocations during compression. Graphs, photomicrographs. 54 refs.
Effect o f mi=rostructure and temperature on high cycle fatigue of powder m e t a l l u r g y ~ l o y . Isomoto, T. and Stoloff, N.S. Mater. Sci. Eng,A Apr. 1990 A124, (2), 171-181 Load-controlled high-cycle fatigue tests were performed on a powder metallurgy superalloy, hot isostaticelly pressed Astroloy, with a fine (0.08p, m) or coarse (0.8-1.2 p,m) -f' phase varied by heat treatment. Tests were carried out in vacuum or in air at 25, 550, 650 and 725 °C. Fracture characteristics were examined by scanning electron microscopy end transmission electron microscopy. The fine-~/' specimens displayed approximately the same fatigue strength as the coarss--y' specimens at all test temperatures, even though they possess greatly different tensile properties. Therefore, the coarse-',/' specimens show higher normalized fatigue resistance than the fine--y' specimens. The fatigue ratio of the coarse--y' specimens increased gradually with increasing temperature to 725 °C, while the fatigue ratio of the fine-'y' specimens increased sharply between 550-725 °C. Both the fine- and the coarse-?' specimens exhibited stage-I crack initiation st the surface and trensgranulsr crack propagation when tested under vacuum. At high stress amplitudes, more extensive stage-I crack initiation occurred in the fine-?' specimens. At low stress amplitudes, the fatigue lives for specimens with both ~' sizes, tested in air, were extended compared with those under vacuum. No contribution of creep damage to the high-cycle fatigue behaviour was found for either microstructure. Graphs, photomicrographs. 12 refs.
Properties of A I - L i alloy 2091-T3 sheet. Taketani, H., McDonald, M.J. and Chionois, W.G. Adv. Mater. Process. Apr. 1990 137, (4), 113-114 The mechanical properties of AI-Li alloy 2091.T3 (Pechiney) are similar to those of the conventional 2024-T3 AI alloy, but with 7% lower density and 10% higher stiffness. The results on tensile, compression and bearing tests of the alloy are presented for longitudinal end long transverse grain orientations. Tension-tension fatigue tests on smooth samples having an oxide film are inferior to those without a brittle film. Fatigue life is improved by removing the film with a deoxidation treatment. The notch sensitivity of the alloy results in a 50% reduction in fatigue resistance. Graphs, photomicrographs.
Int J Fatigue January 1991
Investment-cast =uperalloys challenge w r o u g h t materiels. Lane, J.M. Adv. Mater. Process. Apr. 1990 13"/, (4), 107-108 Investment castings of superalloys by the Microcast-X (MX) method, with a controlled low superheat and a high heat extraction rate, are subsequently hot isostaticeny pressed (HIPed) and heat treated to provide fine-grain microstructure of improved machinability and reduced potential for cracking. The mechanical properties of MX castings of superelloys are claimed to be better than those obtained by conventional investment casting combined with HIP. Applications of MX process include cobelt-bese alloy for hip replacements, and Ni-bese alloys for pressure housings and diffusers in jet engines. The production schedules of MX processes for Ni-bsse superailoy 718 ere outlined, along with the results for tensile properties, stress rupture and both low- and high-cycle fatigue lives. The drawback of the MX process is its limitation to fill in thin sections. Photomicrographs.
Thermal treatment Trends and p r o ~ , of gss-nitdding study. Shen, S. and Tan, C. Mater. Prot. (China) Apr. 1990 23, (4), 4 - 6 (in Chinese) Nitriding can improve greatly the fatigue strength, wear and corrosion resistance of metal materials, and the nitriding temperature is low and the deformation of the nitrided component is small. So it is widely used on components that require small deformation, low dimension tolerance or good wear resistance. However, the common ges-nitriding process takes a lot of time and consumes a great deal of energy; the nitrided white layer is brittle and abrading. To get s 0.30-0.60 mm thick layer with a common ges-nitriding process will take 40-90 h. Much work has been done on shortening the nitriding time and controlling the white layer. The new process developed can shorten the cycle of nitriding and also improve the quality of the nitrided layer without extra equipment or a catalyst. 12 refs.
Effect of ion-nitriding on low cycle impact fatigue strength in SMS0 steel. Maenosono, K. J. Sac. Mater. ScL, Japan Feb. 1990 39, (437), 157-161 (in Japanese) The ion-nitriding treatment has been brought into greater use as a surface hardening technique, for it offers potential advantages such as saving energy, cleanliness and so forth. Though the fundamental mechanical properties of ion-nitrided specimens have been investigated from various points of view, there exist few papers on their fatigue behaviour under repeated impact load. In this study, a series of low-cycle impact fatigue tests were carried out on the ion-nitrided SMS0 steel specimens by using the Matsumura-type impact fatigue testing machine. The results obtained at four impact energy levels of 0.2, 0.3, 0.4 and 0.5 kgf m indicated that the surfacehardened layer of the ion-nitrided specimen behaved in s brittle manner, that is surface cracks initiated at the first impact regardless of the impact energy level. It was concluded that such brittle cracks shortened the fatigue lives of the ion-nitrided specimens, when compared with the results for the annealed SM50 specimens. Furthermore, the above-mentioned fatigue properties are discussed in relation to the fracture mode in monotonic tensile teats. Photomicrographs. 10 refs.
Fatigue fracture behavior of an underaged A I - M g - S i alloy. Jiang, D.M.,
Hang, B.D., Lei, T.C., Downham, D.A. and Lorimer, G.W. Scr. Metall. Mater. Apr. 1990 24, (4), 651-654 Fatigue cracks propagate exclusively in stage I in the underaged AI-Mg-Si alloy 6063 and almost all the fatigue fractures are fecoted. The alloy exhibits heterogeneous deformation, and slip bands ere formed by only one slip system. The increase in stress and ~IK decreases the deformation heterogeneity. However, this increase cannot lead to the activation of two or more slip systems in front of the crack and vary the crack propagation mode. The strong tendency for single slip system activation can be attributed to the high volume fraction and small size of GP zones and the low content of dispersoids. AI-Mg-Si alloy specimens were machined and solution-treated at 530 °C for 30 min, water quenched at room temperature, and aged at 160 °C for 1 h. Tests on the specimens included tensile tests, tension-tension fatigue tests, fatigue tests, resultant fractures by scanning electron microscopy, and the microstructures were examined after aging and after tensile and fatigue tests by transmission electron microscopy. Photomicrographs. 7 refs.
ImprovinQ the properties of titanium alloys by ion implantation. Sioshansl, P. JOM Mar. 1990 42, (3), 30-31 Recent advances in the ion implantation process have shed light on the underlying mechanisms for improved surface properties of Ti alloys (e.g., Ti-6AI-4V). Ion implantation of reactive species such as carbon or nitrogen creates hard-phase carbide or nitride precipitates that impart surface hardness to Ti alloys. Concurrently, the ion implantation process creates disorder in the surface of Ti, destroys the grain boundaries, and is responsible for lower friction of the surface. The ion implantation process duplicates shot peening on a microscopic scale and impacts compressive stress to the surface of the Ti, thereby improving the high-cycle fatigue life of Ti components. Ion implantation also improves the resistance to corrosion and chemical etching of Ti surfaces. Graphs, photomicrographs. 6 refs.
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Hardness of fatigued copper polycrystals and their relation to their dislocation structure. Obrtlik, K., Brezina, J. and Polak, J. Mater. Sci. Eng. A Apr. 1990 A124, (2), L7-L10 The Vickers hardness was determined for Cu polycrystals cyclically strained at a constant plastic strain amplitude up to fracture. The dependence of the hardness on the plastic strain amplitude exhibits a minimum at a strain of 1 x 10-3, followed by a sharp increase. This is explained in terms of the observed dislocation structure produced during fatigue. Using polishing and sectioning techniques, the same value of hardness has been found on the surface and in the bulk of the material. Graphs, photomicrographs. 10 refs.
Cyclic d e f o r m a t i o n behavior of C u - 1 6 at.% AI single crystals. I. Strain burst behavior. Hong, S.I. and Laird, C. Mater. ScL Eng. A Apr. 1990 A124, (2), 183-201 To investigate strain burst behaviour of planar slip materials, single crystals of Cu-15.3 at.% AI alloys, oriented for easy glide, were cyclically deformed under load and strain control. A huge strain burst (~p = 0.12) observed in a load-controlled fatigue test is related to eesy-glide behaviour after yielding. Strain bursts under strain control proceeded through the crystal in a stepwise manner because the total strain is strictly controlled by • closed-loop system. The experimental observation that each strain burst is accompanied by the sudden appearance of a slip band indicates that they are caused by a sudden activation of dislocation sources. Strain burst behaviour at various strain amplitudes is also discussed in relation to deformation behaviour in load-controlled fatigue tests and monotonic tests. A positive asymmetry (a higher stress in tension) is caused by strain bursts occurring more frequently and more easily during compression behaviour that results from easier cross-slip and a higher mobility of dislocations during compression. Graphs, photomicrographs. 54 refs.
Effect o f mi=rostructure and temperature on high cycle fatigue of powder m e t a l l u r g y ~ l o y . Isomoto, T. and Stoloff, N.S. Mater. Sci. Eng,A Apr. 1990 A124, (2), 171-181 Load-controlled high-cycle fatigue tests were performed on a powder metallurgy superalloy, hot isostaticelly pressed Astroloy, with a fine (0.08p, m) or coarse (0.8-1.2 p,m) -f' phase varied by heat treatment. Tests were carried out in vacuum or in air at 25, 550, 650 and 725 °C. Fracture characteristics were examined by scanning electron microscopy end transmission electron microscopy. The fine-~/' specimens displayed approximately the same fatigue strength as the coarss--y' specimens at all test temperatures, even though they possess greatly different tensile properties. Therefore, the coarse-',/' specimens show higher normalized fatigue resistance than the fine--y' specimens. The fatigue ratio of the coarse--y' specimens increased gradually with increasing temperature to 725 °C, while the fatigue ratio of the fine-'y' specimens increased sharply between 550-725 °C. Both the fine- and the coarse-?' specimens exhibited stage-I crack initiation st the surface and trensgranulsr crack propagation when tested under vacuum. At high stress amplitudes, more extensive stage-I crack initiation occurred in the fine-?' specimens. At low stress amplitudes, the fatigue lives for specimens with both ~' sizes, tested in air, were extended compared with those under vacuum. No contribution of creep damage to the high-cycle fatigue behaviour was found for either microstructure. Graphs, photomicrographs. 12 refs.
Properties of A I - L i alloy 2091-T3 sheet. Taketani, H., McDonald, M.J. and Chionois, W.G. Adv. Mater. Process. Apr. 1990 137, (4), 113-114 The mechanical properties of AI-Li alloy 2091.T3 (Pechiney) are similar to those of the conventional 2024-T3 AI alloy, but with 7% lower density and 10% higher stiffness. The results on tensile, compression and bearing tests of the alloy are presented for longitudinal end long transverse grain orientations. Tension-tension fatigue tests on smooth samples having an oxide film are inferior to those without a brittle film. Fatigue life is improved by removing the film with a deoxidation treatment. The notch sensitivity of the alloy results in a 50% reduction in fatigue resistance. Graphs, photomicrographs.
Int J Fatigue January 1991
Investment-cast =uperalloys challenge w r o u g h t materiels. Lane, J.M. Adv. Mater. Process. Apr. 1990 13"/, (4), 107-108 Investment castings of superalloys by the Microcast-X (MX) method, with a controlled low superheat and a high heat extraction rate, are subsequently hot isostaticeny pressed (HIPed) and heat treated to provide fine-grain microstructure of improved machinability and reduced potential for cracking. The mechanical properties of MX castings of superelloys are claimed to be better than those obtained by conventional investment casting combined with HIP. Applications of MX process include cobelt-bese alloy for hip replacements, and Ni-bese alloys for pressure housings and diffusers in jet engines. The production schedules of MX processes for Ni-bsse superailoy 718 ere outlined, along with the results for tensile properties, stress rupture and both low- and high-cycle fatigue lives. The drawback of the MX process is its limitation to fill in thin sections. Photomicrographs.
Thermal treatment Trends and p r o ~ , of gss-nitdding study. Shen, S. and Tan, C. Mater. Prot. (China) Apr. 1990 23, (4), 4 - 6 (in Chinese) Nitriding can improve greatly the fatigue strength, wear and corrosion resistance of metal materials, and the nitriding temperature is low and the deformation of the nitrided component is small. So it is widely used on components that require small deformation, low dimension tolerance or good wear resistance. However, the common ges-nitriding process takes a lot of time and consumes a great deal of energy; the nitrided white layer is brittle and abrading. To get s 0.30-0.60 mm thick layer with a common ges-nitriding process will take 40-90 h. Much work has been done on shortening the nitriding time and controlling the white layer. The new process developed can shorten the cycle of nitriding and also improve the quality of the nitrided layer without extra equipment or a catalyst. 12 refs.
Effect of ion-nitriding on low cycle impact fatigue strength in SMS0 steel. Maenosono, K. J. Sac. Mater. ScL, Japan Feb. 1990 39, (437), 157-161 (in Japanese) The ion-nitriding treatment has been brought into greater use as a surface hardening technique, for it offers potential advantages such as saving energy, cleanliness and so forth. Though the fundamental mechanical properties of ion-nitrided specimens have been investigated from various points of view, there exist few papers on their fatigue behaviour under repeated impact load. In this study, a series of low-cycle impact fatigue tests were carried out on the ion-nitrided SMS0 steel specimens by using the Matsumura-type impact fatigue testing machine. The results obtained at four impact energy levels of 0.2, 0.3, 0.4 and 0.5 kgf m indicated that the surfacehardened layer of the ion-nitrided specimen behaved in s brittle manner, that is surface cracks initiated at the first impact regardless of the impact energy level. It was concluded that such brittle cracks shortened the fatigue lives of the ion-nitrided specimens, when compared with the results for the annealed SM50 specimens. Furthermore, the above-mentioned fatigue properties are discussed in relation to the fracture mode in monotonic tensile teats. Photomicrographs. 10 refs.
Fatigue fracture behavior of an underaged A I - M g - S i alloy. Jiang, D.M.,
Hang, B.D., Lei, T.C., Downham, D.A. and Lorimer, G.W. Scr. Metall. Mater. Apr. 1990 24, (4), 651-654 Fatigue cracks propagate exclusively in stage I in the underaged AI-Mg-Si alloy 6063 and almost all the fatigue fractures are fecoted. The alloy exhibits heterogeneous deformation, and slip bands ere formed by only one slip system. The increase in stress and ~IK decreases the deformation heterogeneity. However, this increase cannot lead to the activation of two or more slip systems in front of the crack and vary the crack propagation mode. The strong tendency for single slip system activation can be attributed to the high volume fraction and small size of GP zones and the low content of dispersoids. AI-Mg-Si alloy specimens were machined and solution-treated at 530 °C for 30 min, water quenched at room temperature, and aged at 160 °C for 1 h. Tests on the specimens included tensile tests, tension-tension fatigue tests, fatigue tests, resultant fractures by scanning electron microscopy, and the microstructures were examined after aging and after tensile and fatigue tests by transmission electron microscopy. Photomicrographs. 7 refs.
ImprovinQ the properties of titanium alloys by ion implantation. Sioshansl, P. JOM Mar. 1990 42, (3), 30-31 Recent advances in the ion implantation process have shed light on the underlying mechanisms for improved surface properties of Ti alloys (e.g., Ti-6AI-4V). Ion implantation of reactive species such as carbon or nitrogen creates hard-phase carbide or nitride precipitates that impart surface hardness to Ti alloys. Concurrently, the ion implantation process creates disorder in the surface of Ti, destroys the grain boundaries, and is responsible for lower friction of the surface. The ion implantation process duplicates shot peening on a microscopic scale and impacts compressive stress to the surface of the Ti, thereby improving the high-cycle fatigue life of Ti components. Ion implantation also improves the resistance to corrosion and chemical etching of Ti surfaces. Graphs, photomicrographs. 6 refs.
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