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Effects of minor alloying on the microstructures and creep properties of RR2086 superalloys孔永華, Kong, Yonghua. January 2005 (has links)
published_or_final_version / abstract / Mechanical Engineering / Doctoral / Doctor of Philosophy
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Modeling creep behavior in a directionally solidified nickel base superalloyIbanez, Alejandro R. 01 December 2003 (has links)
No description available.
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The influence of sulphidizing attack on the mechanism of failure of coated superalloy under cyclic loading conditions.Govender, Gonasagren. January 1998 (has links)
A systematic study of the effect of sulphidizing atmosphere on the High Temperature Low
Cycle Fatigue (HTLCF) properties of coated and uncoated unidirectionally solidified MARM002
nickel base superalloy was performed at 870°C. The coating systems investigated
were, aluminide coating, three types of platinum modified aluminide coatings, and platinum
coating.
The creep-plasticity mode of the strain range partitioning method was used for creep-fatigue
loading. A constant loading regime (Strain range 6.6 x 10-3
) was used to test the samples
in argon, air and Ar + 5%S02 and a lower strain range of3.8 x 10-3 was used to investigate
the creep-fatigue properties in Ar + 5%S02 only. The results were analysed using scanning
electron microscopy including spot analyses (SEM-EDS), Auger electron spectroscopy
(AES) and X-ray diffraction (XRD) techniques.
The synergistic effect of sulphidizing environment and the creep fatigue loading (Strain
range - 0.66%) resulted in accelerated failure in all the materials systems tested, except for
the TYPE I platinum aluminide coated sample. This coating displayed a "self-healing"
mechanism which enhanced its fatigue life under sulphidizing conditions.
In general, the coatings had an adverse effect on the fatigue properties of the material
systems. This was due to the poor mechanical properties of the coating. The mechanical
properties of the coating was influenced by the coating microstructure and the chemical
composition. The modification of the NiAI zone with platinum in the platinum aluminide
coatings improved the fatigue properties of the coating by altering the crack propagation
mechanism in the NiAl zone. The higher the platinum content in this region the more brittle
it became.
The platinum modified aluminide coating showed an improvement in the corrosion fatigue
properties in the S02 containing environment at the higher strain range when compared with
the uncoated, aluminide coated and platinum coated samples.
However, at the lower strain range all the coating systems performed worse than the
uncoated alloy. This was mainly due to the brittle failure of the coating. The platinum
modified aluminides performed the worst due to the presence of brittle platinum aluminide
phases.
The interdiffusion and interaction of platinum with the substrate alloying elements, resulted
in this coating being ineffective for corrosion protection. The resultant coating layer
produced poor corrosion-fatigue properties.
Although the coating systems did show evidence of resistance to sulphidation and oxidation
there were relatively ineffective under the combination of sulphidizing environment and
fatigue loading due to their poor mechanical properties.
The mechanism of sulphidation was consistent for all the material systems tested with
oxidation proceeding first and sulphidation proceeding at the corrosion scale/substrate
interface. The crack propagation in the coating and substrate was controlled by the
sulphidation attack at the crack tip and failure of the oxide scales formed in the cracks. / Thesis(M.Sc.Eng.)- University of Natal, Durban, 1998.
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Constitutive Modeling and Life Prediction in Ni-Base SuperalloysShenoy, Mahesh M. 01 June 2006 (has links)
Microstructural features at different scales affect the constitutive stress-strain response and the fatigue crack initiation life in Ni-base superalloys. While numerous efforts have been made in the past to experimentally characterize the effects of these features on the stress-strain response and/or the crack initiation life, there is a significant variability in the data with sometimes contradictory conclusions, in addition to the substantial costs involved in experimental testing. Computational techniques can be useful tools to better understand these effects since they are relatively inexpensive and are not restricted by the limitations in processing techniques.
The effect of microstructure on the stress-strain response and the variability in fatigue life were analyzed using two Ni-base superalloys; DS GTD111 which is a directionally solidified Ni-base superalloy, and IN100 which is a polycrystalline Ni-base superalloy. Physically-based constitutive models were formulated and implemented as user material subroutines in ABAQUS using the single crystal plasticity framework which can predict the material stress-strain response with the microstructure-dependence embedded into them. The model parameters were calibrated using experimental cyclic stress-strain histories. A computational exercise was employed to quantify the influence of idealized microstructural variables on the fatigue crack initiation life. Understanding was sought regarding the most significant microstructure features using explicit modeling of the microstructure with the aim to predict the variability in fatigue crack initiation life and to guide material design for fatigue resistant microstructures. Lastly, it is noted that crystal plasticity models are often too computationally intensive if the objective is to model the macroscopic behavior of a textured or randomly oriented 3-D polycrystal in an engineering component. Homogenized constitutive models were formulated and implemented as user material subroutines in ABAQUS, which can capture the macroscale stress-strain response in both DS GTD111 and IN100. Even though the study was conducted on two specific Ni-base superalloys; DS GTD111 and IN100, the objective was to develop generic frameworks which should also be applicable to other alloy systems.
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