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Effects of thermomechanical treatments on low cycle fatigue properties of Ti3Al8V6Cr4Mo4Zr alloy
352
Fatigue abstracts
Weidbonding. The mechanism and properties of weldbonded joints. Jones, T.B. Sheet Metal Industries (1995) 72 (9), 27, 30-31
Environmental effects on crack closure during fatigue in an AI-Zn-MgMn alloy. Pyun, S.-I., Orr, S.-J., Chun, Y.-G. and Nam, S.-W. Br. Corrosion J. (1995) 30, 199-202
The relative performances of weldbonded and spot welded joints are discussed along with adhesive bonding for fabrication of steel sheets. The heat build-up in the contact area in the first two to three cycles of current flow is greater with weldbonding without any bonding across the interface between the sheets. An initial joint strength was developed in the period of three to five cycles as a result of solid phase welding across the interface with localized melting on weldbonding. After a solid phase joint was developed, fusion occurred within one cycle for either joining technique. Adhesive bonded structures were prone to failure under impact loading. The fatigue strength of adhesive bonded/weldbonded structures improved significantly due to the adhesives being stronger in shear compared to peel loading conditions. Graphs.
The fatigue crack propagation (FCP) behaviour of peak aged AI-Zn-Mg-Mn alloy has been investigated with reference to that of peak aged AI-Zn-Mg alloy by comparing crack closure in 0.5M Na2SO4 + 0.5M NaCI and 0.5M NazSO4 solutions. Anodic studies were complemented by potentionstatic current transient measurements. For both alloys, the intrinsic FCP rate in the C1containing solution exceeded that in dry air; however, the apparent FCP rates were similar. Crack closure decreased in the order: 0.5M Na2SO4 + 0.5M NaC1 solution, 0.5M NazSO4 solution, dry air. Irrespective of environmental conditions, the addition of manganese to the AI-Zn-Mg alloy reduced the intrinsic FCP rate and crack closure. Specimens in the Cl-containing solution were more slowly repassivated than those in the sulphate solution. In the C1containing solution the AI-Zn-Mg alloy was more slowly repassivated than the AI-Zn-Mg-Mn alloy, in good agreement with the trend of intrinsic FCP. The enhanced intrinsic FCP rate and crack closure in the Cl-contalning solution resulted from an increase in localised corrosion attack on the slip step at the crack tip. Graphs, 12 ref.
Environmental fatigue cracking growth and microscopic damage mechanisms in AA2090, Slavik, D.C. Diss. Abstr. Int. 54, (8) The influences of environment and microstructure on the microscopic damage mechanisms and the intrinsic fatigue crack propagation (FCP) rates are determined for the A1-Li~Cu alloy AA2090. The subgrain size, grain size, and texture are varied with thermo-mechanical processing techniques. Intrinsic da/dN behaviour of the different microstructures is characterized with high mean stress constant Km~x experiments in an ultrahigh vacuum and aqueous 1 wt.% NaC1 solution. Fatigue damage modes are quantitatively identified with fracture facet crystallography measurements, performed using electron back scatter patterns coupled with quantitative tilt fmctography. Vacuum FCP produces tortuous tent-shaped fracture facets and single sloped da/dN-AK power law behaviour independent of the grain size, subgrain size, texture, and AK. Localized slip and deformation band cracking explain near-{Ill} fracture facets, typically along multiple {111 } variants which have a high resolved shear stress within single grains. The fracture mode and FCP rates, compared based on crack tip strain range (AK2/E "~ ys), are insensitive to microstmcture for vacuum FCP. Compared to vacuum FCP, aqueous NaC1 environment accelerates da/dN at all AK, causes new microscopic cracking modes, and promotes multiple da/dN-AK power law regimes for both recrystallized and uureerystallized AA2090. Flat transgranular fracture facets are identified for AA2090 at low A K. 85% of these facets in the uureerystallized plate, and 50% of the facets in the reerystallized coarse grain sheet, cluster within 10° of an average {521} cracking plane. These results are inconsistent with localized dissolution, {100}/{ll0} 'brittle cleavage', or hydrogen enhanced localized plasticity and deformation band cracking. High index cracking may be due to brittle LiA1H4 hydride cracking, though hydrides are not observed for the FCP conditions examined, and published LiAlH4 crystallographic results are not accurate. Work is required to identify hydrides in AA2090, and to establish if the hydride habit or cleavage plane explains observed facet crystallography. Physically based damage mechanisms are not sufficiently developed to predict da/dN-AK for Al-Li-Cu alloys in vacuum or aggressive environments.
Effects of thermomechanical treatments on low cycle fatigue properties of Ti--3AI--SV--6Cr-4Mo-4Zr alloy. Kin~ C.J. J. Mater. Processing Manufact. Sci. (1995) 4, 45-54 As useful engineering data, the fatigue properties of titanium alloys are not well known except for Ti-6AI-4V (c~ + /3). Thus, the low cycle fatigue test was examined on a thermomeehanical treated Ti-3AI-8V-6Cr-4Mo-4Zr (/3C) alloy which worked the grain refinement and controlled the mechanical properties by uniform distribution of alpha precipitates. In every specimen, there was a certain drop point in the %a-Nf curve. Therefore, the classification into two linear equations according to e pal (lower plastic strain amplitude) and %~ (higher plastic strain amplitude) for practical engineering data was attempted. In the relationship between e~ and N~ for each specimen, there was no difference of fatigue property. Due to the high strength there was not always a good effect on the low cycle fatigue property because of its lower ductility. It may be possible to consider that there is a critical transition point of the fatigue crack growth rate which can be influenced by the cyclic loading conditions or the material property. The sensitivity of the transition tendency differs for various reasons. On this point, the Ti alloy, Ti-3A1-SV-6Cr-4Mo-4Zr (/3-C), was a very sensitive material. Graphs, photomicrographs, 17 ref.
Influence of external mechanical Ioadings (creep, fatigue) on oxygen diffusion during nickel o~dation~ Moulin, G., Arevalo, P. and Salleo, A. Oxidation Metals (Feb. 1996) 45, 153-181. The study deals with the influence of various mechanical loadings (fatigue, creep, creep-fatigue) on oxygen diffusion in a particular system, oxidizing nickel. A distinction between the behaviour of the oxide layer and underlying Ni was noted during the first step of oxidation at 550°C, in PO 2 = 1 atm. Meehartical loading causes a decrease of the oxygen mobility through the oxide scale (factor of 103). The oxide thicknesses on Ni undergoing mechanical loadings axe different than for an unloaded sample, due to distinct contributions of the oxygen and Hi fluxes in the growing oxide. In the substrate, the ingress of oxygen becomes easier with a constant tensile load (creep). The intergrannlar oxygen diffusion coefficient, D~, is increased by a factor of 102 with respect to other samples. In creep, oxygen diffusion takes place along grain boundaries of a structure with smaller grains than in unstrained Hi. A short fatigue period during creep-fatigue decreases the sensitivity of Ni to intergranular oxygen diffusion. Photomicrographs, spectra, graphs, 53 ref.
Fatigue strength and fatigue crack propagation in injection molded TiAI. Shibata, H., Tokaji, K., Shiotu, H. and Ohta, Y. J. Jap. Inst. Light Metals (1995) 45, 465--470 The fatigue strength and fatigue crack propagation (FCP) at ambient temperature in injection molded titanium aluminide, TiA1, are described. Axial fatigue tests and FCP experiments have been conducted on injection moulded materials which were sintered at 1350 and 1400°C. The fatigue strength and FCP resistance of the injection moulded materials were considerably lower than those of the cast material, and the material sintered at 1400°C showed higher fatigue strength and FCP resistance than the material sintered at 1350°C. These results may be attributed to many pores contained in the injection moulded materials or in the material sintered at lower temperature, and also due to the difference in microstructure. The SEM examination of fracture surfaces revealed that translamellar cleavage, interlamellar cleavage, and cleavage of equiaxed -y grains were predominant modes of fatigue failure in the injection moulded materials. Graphs, photomicrographs, 21 ref.
Life assessment for integral turbine wheels in consideration of short cracks on example of the nickel base alloy IN 713C [Lelwaasdauervorhersage fur integraigegomene Turbinenrader mater Berucksichtigung kurzer Risse am Beispiel der Nickelbasis-Legle~ang IN 713C] Brandt, U. and Sonsino, C.M. Materialwissen. Werkstoff. (1995) 26, 294-308 Constant and variable amplitude fatigue tests on unnotched specimens under strain controlled axial loading and on notched specimens under load controlled bending were carded out in order to investigate the transferability of unnotcbed specimens data to components. In this case the notched specimen represents the component, the turbine wheel. The operational conditions of a turbine wheel, high temperatures, hold times, different loading rates and the fatigue sequence HOT TURBISTAN, were included in the investigations. Short crack propagation was measured in a scanning electron microscope by identification of load markers on the rupture surface. Additionally CT specimens were tested in order to determine crack propagation of long cracks. Using these test results and corresponding safety factors a better life assessment for turbine wheels is possible, if the concepts of safe life, damage tolerance and total life are applied. Graphs, photomicrographs, 20 refs.
Duration of induction melting of cobalt-chromium alloy and its effect on resistance to deflection fatigue of east denture clasps. Vallitu, P.K. and Miettinen, T. J. Prosthetic Dent. (Mar. 1996) 75, 332-336 This study determined the effect of various durations of induction melting of a Co-Cr alloy on resistance to deflection fatigue. Commercial Co-Cr alloy was melted by high frequency induction for various lengths of time before it was cast into the shape of a denture clasp. The test method used was a constant deflection fatigue test. The fatigue fracture surface of the clasp was examined with a scanning electron microscope, and the surface hardness (Vickers hardness) of the clasps was measured. In clasps with greater fatigue resistance scanning electron microscope photomicrographs revealed a coarse grain structure. The surface hardness of the alloy was least in the group with the lowest fatigue resistance and was higher in groups with greater fatigue resistance. This study suggests that, although some porosities are formed in the middle of the clasps after the alloy is overheated, the fatigue resistance of Co-Cr alloy denture clasps can be increased by lengthening the induction melting period of the alloy. Graphs, photomicrographs, 12 ref
The SRM lifetime prediction rule for the creep fatigue interaction regime supported by a suitable constitutive model. Rubesa, D. and Danzer, R. Zeit. Metallkunde (1995) 86, 8 3 2 4 3 8 The application of conventional lifetime prediction methods requires a certain knowledge about the stress-strain response of a material to the applied load. This should preferably be simulated by an appropriate constitutive model. The empirical mle of strain rate modified linear accumulation of creep damage (the SRM rule) for the lifetime prediction of metallic materials in the creep-fatigue interaction regime has been supported by Chabocbe's viscoplastic constitutive model. An inherent criterion for the validity of a given prediction has been defined. The application of the proposed method and its ability to predict life expectancies in various cyclic loading conditions, different from those fatigue tests required for the calibration of the SRM rule, has been shown using the IN 738 LC superalloy as an example. Graphs, 28 ref.
Fatigue abstracts
Weidbonding. The mechanism and properties of weldbonded joints. Jones, T.B. Sheet Metal Industries (1995) 72 (9), 27, 30-31
Environmental effects on crack closure during fatigue in an AI-Zn-MgMn alloy. Pyun, S.-I., Orr, S.-J., Chun, Y.-G. and Nam, S.-W. Br. Corrosion J. (1995) 30, 199-202
The relative performances of weldbonded and spot welded joints are discussed along with adhesive bonding for fabrication of steel sheets. The heat build-up in the contact area in the first two to three cycles of current flow is greater with weldbonding without any bonding across the interface between the sheets. An initial joint strength was developed in the period of three to five cycles as a result of solid phase welding across the interface with localized melting on weldbonding. After a solid phase joint was developed, fusion occurred within one cycle for either joining technique. Adhesive bonded structures were prone to failure under impact loading. The fatigue strength of adhesive bonded/weldbonded structures improved significantly due to the adhesives being stronger in shear compared to peel loading conditions. Graphs.
The fatigue crack propagation (FCP) behaviour of peak aged AI-Zn-Mg-Mn alloy has been investigated with reference to that of peak aged AI-Zn-Mg alloy by comparing crack closure in 0.5M Na2SO4 + 0.5M NaCI and 0.5M NazSO4 solutions. Anodic studies were complemented by potentionstatic current transient measurements. For both alloys, the intrinsic FCP rate in the C1containing solution exceeded that in dry air; however, the apparent FCP rates were similar. Crack closure decreased in the order: 0.5M Na2SO4 + 0.5M NaC1 solution, 0.5M NazSO4 solution, dry air. Irrespective of environmental conditions, the addition of manganese to the AI-Zn-Mg alloy reduced the intrinsic FCP rate and crack closure. Specimens in the Cl-containing solution were more slowly repassivated than those in the sulphate solution. In the C1containing solution the AI-Zn-Mg alloy was more slowly repassivated than the AI-Zn-Mg-Mn alloy, in good agreement with the trend of intrinsic FCP. The enhanced intrinsic FCP rate and crack closure in the Cl-contalning solution resulted from an increase in localised corrosion attack on the slip step at the crack tip. Graphs, 12 ref.
Environmental fatigue cracking growth and microscopic damage mechanisms in AA2090, Slavik, D.C. Diss. Abstr. Int. 54, (8) The influences of environment and microstructure on the microscopic damage mechanisms and the intrinsic fatigue crack propagation (FCP) rates are determined for the A1-Li~Cu alloy AA2090. The subgrain size, grain size, and texture are varied with thermo-mechanical processing techniques. Intrinsic da/dN behaviour of the different microstructures is characterized with high mean stress constant Km~x experiments in an ultrahigh vacuum and aqueous 1 wt.% NaC1 solution. Fatigue damage modes are quantitatively identified with fracture facet crystallography measurements, performed using electron back scatter patterns coupled with quantitative tilt fmctography. Vacuum FCP produces tortuous tent-shaped fracture facets and single sloped da/dN-AK power law behaviour independent of the grain size, subgrain size, texture, and AK. Localized slip and deformation band cracking explain near-{Ill} fracture facets, typically along multiple {111 } variants which have a high resolved shear stress within single grains. The fracture mode and FCP rates, compared based on crack tip strain range (AK2/E "~ ys), are insensitive to microstmcture for vacuum FCP. Compared to vacuum FCP, aqueous NaC1 environment accelerates da/dN at all AK, causes new microscopic cracking modes, and promotes multiple da/dN-AK power law regimes for both recrystallized and uureerystallized AA2090. Flat transgranular fracture facets are identified for AA2090 at low A K. 85% of these facets in the uureerystallized plate, and 50% of the facets in the reerystallized coarse grain sheet, cluster within 10° of an average {521} cracking plane. These results are inconsistent with localized dissolution, {100}/{ll0} 'brittle cleavage', or hydrogen enhanced localized plasticity and deformation band cracking. High index cracking may be due to brittle LiA1H4 hydride cracking, though hydrides are not observed for the FCP conditions examined, and published LiAlH4 crystallographic results are not accurate. Work is required to identify hydrides in AA2090, and to establish if the hydride habit or cleavage plane explains observed facet crystallography. Physically based damage mechanisms are not sufficiently developed to predict da/dN-AK for Al-Li-Cu alloys in vacuum or aggressive environments.
Effects of thermomechanical treatments on low cycle fatigue properties of Ti--3AI--SV--6Cr-4Mo-4Zr alloy. Kin~ C.J. J. Mater. Processing Manufact. Sci. (1995) 4, 45-54 As useful engineering data, the fatigue properties of titanium alloys are not well known except for Ti-6AI-4V (c~ + /3). Thus, the low cycle fatigue test was examined on a thermomeehanical treated Ti-3AI-8V-6Cr-4Mo-4Zr (/3C) alloy which worked the grain refinement and controlled the mechanical properties by uniform distribution of alpha precipitates. In every specimen, there was a certain drop point in the %a-Nf curve. Therefore, the classification into two linear equations according to e pal (lower plastic strain amplitude) and %~ (higher plastic strain amplitude) for practical engineering data was attempted. In the relationship between e~ and N~ for each specimen, there was no difference of fatigue property. Due to the high strength there was not always a good effect on the low cycle fatigue property because of its lower ductility. It may be possible to consider that there is a critical transition point of the fatigue crack growth rate which can be influenced by the cyclic loading conditions or the material property. The sensitivity of the transition tendency differs for various reasons. On this point, the Ti alloy, Ti-3A1-SV-6Cr-4Mo-4Zr (/3-C), was a very sensitive material. Graphs, photomicrographs, 17 ref.
Influence of external mechanical Ioadings (creep, fatigue) on oxygen diffusion during nickel o~dation~ Moulin, G., Arevalo, P. and Salleo, A. Oxidation Metals (Feb. 1996) 45, 153-181. The study deals with the influence of various mechanical loadings (fatigue, creep, creep-fatigue) on oxygen diffusion in a particular system, oxidizing nickel. A distinction between the behaviour of the oxide layer and underlying Ni was noted during the first step of oxidation at 550°C, in PO 2 = 1 atm. Meehartical loading causes a decrease of the oxygen mobility through the oxide scale (factor of 103). The oxide thicknesses on Ni undergoing mechanical loadings axe different than for an unloaded sample, due to distinct contributions of the oxygen and Hi fluxes in the growing oxide. In the substrate, the ingress of oxygen becomes easier with a constant tensile load (creep). The intergrannlar oxygen diffusion coefficient, D~, is increased by a factor of 102 with respect to other samples. In creep, oxygen diffusion takes place along grain boundaries of a structure with smaller grains than in unstrained Hi. A short fatigue period during creep-fatigue decreases the sensitivity of Ni to intergranular oxygen diffusion. Photomicrographs, spectra, graphs, 53 ref.
Fatigue strength and fatigue crack propagation in injection molded TiAI. Shibata, H., Tokaji, K., Shiotu, H. and Ohta, Y. J. Jap. Inst. Light Metals (1995) 45, 465--470 The fatigue strength and fatigue crack propagation (FCP) at ambient temperature in injection molded titanium aluminide, TiA1, are described. Axial fatigue tests and FCP experiments have been conducted on injection moulded materials which were sintered at 1350 and 1400°C. The fatigue strength and FCP resistance of the injection moulded materials were considerably lower than those of the cast material, and the material sintered at 1400°C showed higher fatigue strength and FCP resistance than the material sintered at 1350°C. These results may be attributed to many pores contained in the injection moulded materials or in the material sintered at lower temperature, and also due to the difference in microstructure. The SEM examination of fracture surfaces revealed that translamellar cleavage, interlamellar cleavage, and cleavage of equiaxed -y grains were predominant modes of fatigue failure in the injection moulded materials. Graphs, photomicrographs, 21 ref.
Life assessment for integral turbine wheels in consideration of short cracks on example of the nickel base alloy IN 713C [Lelwaasdauervorhersage fur integraigegomene Turbinenrader mater Berucksichtigung kurzer Risse am Beispiel der Nickelbasis-Legle~ang IN 713C] Brandt, U. and Sonsino, C.M. Materialwissen. Werkstoff. (1995) 26, 294-308 Constant and variable amplitude fatigue tests on unnotched specimens under strain controlled axial loading and on notched specimens under load controlled bending were carded out in order to investigate the transferability of unnotcbed specimens data to components. In this case the notched specimen represents the component, the turbine wheel. The operational conditions of a turbine wheel, high temperatures, hold times, different loading rates and the fatigue sequence HOT TURBISTAN, were included in the investigations. Short crack propagation was measured in a scanning electron microscope by identification of load markers on the rupture surface. Additionally CT specimens were tested in order to determine crack propagation of long cracks. Using these test results and corresponding safety factors a better life assessment for turbine wheels is possible, if the concepts of safe life, damage tolerance and total life are applied. Graphs, photomicrographs, 20 refs.
Duration of induction melting of cobalt-chromium alloy and its effect on resistance to deflection fatigue of east denture clasps. Vallitu, P.K. and Miettinen, T. J. Prosthetic Dent. (Mar. 1996) 75, 332-336 This study determined the effect of various durations of induction melting of a Co-Cr alloy on resistance to deflection fatigue. Commercial Co-Cr alloy was melted by high frequency induction for various lengths of time before it was cast into the shape of a denture clasp. The test method used was a constant deflection fatigue test. The fatigue fracture surface of the clasp was examined with a scanning electron microscope, and the surface hardness (Vickers hardness) of the clasps was measured. In clasps with greater fatigue resistance scanning electron microscope photomicrographs revealed a coarse grain structure. The surface hardness of the alloy was least in the group with the lowest fatigue resistance and was higher in groups with greater fatigue resistance. This study suggests that, although some porosities are formed in the middle of the clasps after the alloy is overheated, the fatigue resistance of Co-Cr alloy denture clasps can be increased by lengthening the induction melting period of the alloy. Graphs, photomicrographs, 12 ref
The SRM lifetime prediction rule for the creep fatigue interaction regime supported by a suitable constitutive model. Rubesa, D. and Danzer, R. Zeit. Metallkunde (1995) 86, 8 3 2 4 3 8 The application of conventional lifetime prediction methods requires a certain knowledge about the stress-strain response of a material to the applied load. This should preferably be simulated by an appropriate constitutive model. The empirical mle of strain rate modified linear accumulation of creep damage (the SRM rule) for the lifetime prediction of metallic materials in the creep-fatigue interaction regime has been supported by Chabocbe's viscoplastic constitutive model. An inherent criterion for the validity of a given prediction has been defined. The application of the proposed method and its ability to predict life expectancies in various cyclic loading conditions, different from those fatigue tests required for the calibration of the SRM rule, has been shown using the IN 738 LC superalloy as an example. Graphs, 28 ref.