High-temperature low-cycle fatigue (HTLCF) failure mechanisms of aluminide-coated MAR-M002 nickel... more High-temperature low-cycle fatigue (HTLCF) failure mechanisms of aluminide-coated MAR-M002 nickel-base superalloy in air, argon and Ar+5% SO2 atmospheres were investigated at 870 ~ The loading conditions were constant and consisted of creep tension and plastic compression according to the creep plasticity mode of the strain-range partitioning method. The resultant failure mechanisms were investigated using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis. The results obtained indicated that the combination of environmental effect and cyclic loading resulted in an early failure of the coating. This failure acted as the incubation and initiation stages for the HTLCF failure of the coated alloy. However, it was found that under an SO2-containing environment, an accelerated and premature failure was obtained compared to that obtained in argon and air environments. Hence, it is evident that although the aluminide coating provides relatively adeq...
Les aubes de turbine en superalliage base nickel sont soumises lors du fonctionnement a 975˚C a d... more Les aubes de turbine en superalliage base nickel sont soumises lors du fonctionnement a 975˚C a des contraintes de fluage et de compression. L'amorcage et la propagation des fissures sous l'influence de differentes atmospheres gazeuses (gaz passifs, atmospheres oxydantes) ont ete etudies par microscopie electronique a balayage, spectrometrie Auger et diffraction des RX.
Abstract Magnesium alloy foams have the potential to serve as structural material for regular lig... more Abstract Magnesium alloy foams have the potential to serve as structural material for regular light-weight applications as well as for biodegradable scaffold implants. However, their main disadvantage relates to the high reactivity of magnesium and consequently their natural tendency to corrode in regular service conditions and in physiological environments. The present study aims at evaluating the effect of porosity on the corrosion resistance of MRI 201S magnesium alloy foams in 0.9% NaCl solution and in phosphate buffer saline solution as a simulated physiological electrolyte. The magnesium foams were produced by powder metallurgy technology using space-holding particles to control the porosity content. Machined chips were used as raw material for the production of Mg alloy powder by milling process. The microstructure of the foams was examined using optical and scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analysis. The corrosion behavior was evaluated by immersion test and potentiodynamic polarization analysis. The results obtained clearly demonstrate that the porosity has a significant effect on the corrosion resistance of the tested foams. Foams with 14–19% porosity have a corrosion rate of 4–10 mcd and 7–15 mcd in NaCl and phosphate buffer saline solution, respectively, compared to only 0.10 mcd for the same alloy in as cast conditions. This increased corrosion degradation of the Mg foams by more than one order of magnitude compared to the cast alloy may limit their potential application in regular and physiological environments.
Low Cycle Fatigue and Elasto-Plastic Behaviour of Materials—3, 1992
The effects of sulphur containing gaseous environments and air atmosphere on low cycle fatigue (L... more The effects of sulphur containing gaseous environments and air atmosphere on low cycle fatigue (LCF) failure of SAF 2205 and 316 stainless steel were studied at 700°C. The LCF loading was constant and consisted of creep tension and plastic compression following the CP-Mode of the strainrange partitioning method.
Low Cycle Fatigue and Elasto-Plastic Behaviour of Materials, 1987
Unidirectional solidified MAR-M200+Hf nickel base superalloy failed under low-cycle-fatigue loadi... more Unidirectional solidified MAR-M200+Hf nickel base superalloy failed under low-cycle-fatigue loading regime at 975°C. The cycle comprised creep by tension, and plasticity compression loadings. Different environmental gas influence were studied: oxygen (20% in argon), nitrogen (pure) and carbon-dioxide (pure). The crack initiation and propagation under the influence of the different environment was studied by scanning electron microscopy (Incl. chemical microprobe analysis). Auger spectroscopy, and X-ray diffraction. It was found that the chemical reaction between the gas and the alloy at the propagating crack tip controls the LCF failure. Under oxygen, ahead of the crack tip uniphase layer develops, composed of γ′-phase material, internally oxidised (oxide-type ligands develop with active elements atoms within otherwise metallic solid-solution), loosely packed oxide layers develop later. Under CO2 layers of oxycarbides and graphite-like develop. In both cases crack propagates through inter dendritic segregation zone. Under nitrogen propagation is transdendritic with coarse nitrides develop ahead of cracktip.
High temperature, low cycle fatigue (HTLCF) failure mechanisms were studied in unidirectionally s... more High temperature, low cycle fatigue (HTLCF) failure mechanisms were studied in unidirectionally solidified MAR-M200 + Hf nickel-based superalloy in pure N2 and CO2 environments at 975°C. The loading conditions were constant and consisted of creep tension and plastic compression according to the cp mode of the strain-range-partitioning method. The crack initiation and propagation were investigated using scanning electron microscopy, X-ray diffraction and Auger electron spectroscopy. The results obtained indicated that N2 and CO2 atmospheres cannot be treated as passive gaseous environments. On the contrary, these environments have a significant influence on the HTLCF crack growth behaviour. In an N2 environment the fracture was transgranular. This was a result of an intensive chemical interaction between nitrogen and the main alloying elements making up the γ′ phase Ni3(Al, Ti) located inside the dendritic grain regions. In a CO2 atmosphere a partial catalytic decomposition of this environment into its basic components oxygen and carbon was obtained. The fracture was intergranular owing to the preferential chemical interaction of oxygen with elements of the interdendritic microsegregation zones. In both CO2 and N2 environments a uniphase layer was formed ahead of the propagating crack tip. This layer was produced via internal oxidation or nitridation caused by interstitial penetration of oxygen or nitrogen respectively. It was evident that the nature of formation and the properties of the uniphase layer exert a decisive effect on the HTLCF crack growth characteristics, which enables identification of the mechanism of failure under the various tested environments.
Journal of Materials Engineering and Performance, 2000
Creep and stress relaxation resistance of the most common die-cast Mg alloy AZ91D (Mg-9% Al-1% Zn... more Creep and stress relaxation resistance of the most common die-cast Mg alloy AZ91D (Mg-9% Al-1% Zn) are influenced by both casting temperature and injection rate as well as by die temperature and porosity. Relationships between viscoelastic properties of Mg alloy at 150 C and the parameters of die-casting technology are obtained and presented as simple contour plots (isograms). These properties
High-temperature low-cycle fatigue (HTLCF) failure mechanisms of aluminide-coated MAR-M002 nickel... more High-temperature low-cycle fatigue (HTLCF) failure mechanisms of aluminide-coated MAR-M002 nickel-base superalloy in air, argon and Ar+5% SO2 atmospheres were investigated at 870 ~ The loading conditions were constant and consisted of creep tension and plastic compression according to the creep plasticity mode of the strain-range partitioning method. The resultant failure mechanisms were investigated using scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction analysis. The results obtained indicated that the combination of environmental effect and cyclic loading resulted in an early failure of the coating. This failure acted as the incubation and initiation stages for the HTLCF failure of the coated alloy. However, it was found that under an SO2-containing environment, an accelerated and premature failure was obtained compared to that obtained in argon and air environments. Hence, it is evident that although the aluminide coating provides relatively adeq...
Les aubes de turbine en superalliage base nickel sont soumises lors du fonctionnement a 975˚C a d... more Les aubes de turbine en superalliage base nickel sont soumises lors du fonctionnement a 975˚C a des contraintes de fluage et de compression. L'amorcage et la propagation des fissures sous l'influence de differentes atmospheres gazeuses (gaz passifs, atmospheres oxydantes) ont ete etudies par microscopie electronique a balayage, spectrometrie Auger et diffraction des RX.
Abstract Magnesium alloy foams have the potential to serve as structural material for regular lig... more Abstract Magnesium alloy foams have the potential to serve as structural material for regular light-weight applications as well as for biodegradable scaffold implants. However, their main disadvantage relates to the high reactivity of magnesium and consequently their natural tendency to corrode in regular service conditions and in physiological environments. The present study aims at evaluating the effect of porosity on the corrosion resistance of MRI 201S magnesium alloy foams in 0.9% NaCl solution and in phosphate buffer saline solution as a simulated physiological electrolyte. The magnesium foams were produced by powder metallurgy technology using space-holding particles to control the porosity content. Machined chips were used as raw material for the production of Mg alloy powder by milling process. The microstructure of the foams was examined using optical and scanning electron microscopy, X-ray diffraction, and X-ray photoelectron spectroscopy analysis. The corrosion behavior was evaluated by immersion test and potentiodynamic polarization analysis. The results obtained clearly demonstrate that the porosity has a significant effect on the corrosion resistance of the tested foams. Foams with 14–19% porosity have a corrosion rate of 4–10 mcd and 7–15 mcd in NaCl and phosphate buffer saline solution, respectively, compared to only 0.10 mcd for the same alloy in as cast conditions. This increased corrosion degradation of the Mg foams by more than one order of magnitude compared to the cast alloy may limit their potential application in regular and physiological environments.
Low Cycle Fatigue and Elasto-Plastic Behaviour of Materials—3, 1992
The effects of sulphur containing gaseous environments and air atmosphere on low cycle fatigue (L... more The effects of sulphur containing gaseous environments and air atmosphere on low cycle fatigue (LCF) failure of SAF 2205 and 316 stainless steel were studied at 700°C. The LCF loading was constant and consisted of creep tension and plastic compression following the CP-Mode of the strainrange partitioning method.
Low Cycle Fatigue and Elasto-Plastic Behaviour of Materials, 1987
Unidirectional solidified MAR-M200+Hf nickel base superalloy failed under low-cycle-fatigue loadi... more Unidirectional solidified MAR-M200+Hf nickel base superalloy failed under low-cycle-fatigue loading regime at 975°C. The cycle comprised creep by tension, and plasticity compression loadings. Different environmental gas influence were studied: oxygen (20% in argon), nitrogen (pure) and carbon-dioxide (pure). The crack initiation and propagation under the influence of the different environment was studied by scanning electron microscopy (Incl. chemical microprobe analysis). Auger spectroscopy, and X-ray diffraction. It was found that the chemical reaction between the gas and the alloy at the propagating crack tip controls the LCF failure. Under oxygen, ahead of the crack tip uniphase layer develops, composed of γ′-phase material, internally oxidised (oxide-type ligands develop with active elements atoms within otherwise metallic solid-solution), loosely packed oxide layers develop later. Under CO2 layers of oxycarbides and graphite-like develop. In both cases crack propagates through inter dendritic segregation zone. Under nitrogen propagation is transdendritic with coarse nitrides develop ahead of cracktip.
High temperature, low cycle fatigue (HTLCF) failure mechanisms were studied in unidirectionally s... more High temperature, low cycle fatigue (HTLCF) failure mechanisms were studied in unidirectionally solidified MAR-M200 + Hf nickel-based superalloy in pure N2 and CO2 environments at 975°C. The loading conditions were constant and consisted of creep tension and plastic compression according to the cp mode of the strain-range-partitioning method. The crack initiation and propagation were investigated using scanning electron microscopy, X-ray diffraction and Auger electron spectroscopy. The results obtained indicated that N2 and CO2 atmospheres cannot be treated as passive gaseous environments. On the contrary, these environments have a significant influence on the HTLCF crack growth behaviour. In an N2 environment the fracture was transgranular. This was a result of an intensive chemical interaction between nitrogen and the main alloying elements making up the γ′ phase Ni3(Al, Ti) located inside the dendritic grain regions. In a CO2 atmosphere a partial catalytic decomposition of this environment into its basic components oxygen and carbon was obtained. The fracture was intergranular owing to the preferential chemical interaction of oxygen with elements of the interdendritic microsegregation zones. In both CO2 and N2 environments a uniphase layer was formed ahead of the propagating crack tip. This layer was produced via internal oxidation or nitridation caused by interstitial penetration of oxygen or nitrogen respectively. It was evident that the nature of formation and the properties of the uniphase layer exert a decisive effect on the HTLCF crack growth characteristics, which enables identification of the mechanism of failure under the various tested environments.
Journal of Materials Engineering and Performance, 2000
Creep and stress relaxation resistance of the most common die-cast Mg alloy AZ91D (Mg-9% Al-1% Zn... more Creep and stress relaxation resistance of the most common die-cast Mg alloy AZ91D (Mg-9% Al-1% Zn) are influenced by both casting temperature and injection rate as well as by die temperature and porosity. Relationships between viscoelastic properties of Mg alloy at 150 C and the parameters of die-casting technology are obtained and presented as simple contour plots (isograms). These properties
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