Fatigue, hardness and oxidation properties of single crystal, Nickel-base superalloys CMSX-4 and PWA1484 in air and vacuum at 650 degrees centigrade.
- Paper number
IAC-05-C2.3.09
- Author
Ms. Amira Kawar, University of Southampton, United Kingdom
- Year
2005
- Abstract
Aerosols are crucial for understanding the complex changes in climatic patterns. Aerosols enter the atmosphere through natural processes e.g. dust storms, sea salt spray and anthropogenic activities such as burning of fossil fuels and biomass. The geographic distribution of aerosols, their particle size and concentration exerts notable climatic effects. Aerosol transport processes from continents to oceans are poorly understood due to lack of in-situ observations. In the present study we report results of spectral aerosol optical depth (AOD) measurements over the central Bay of Bengal during northeastern monsoon period. During this period the wind flows from northeast to southwest carrying anthropogenic aerosol generated over Indo-Gangetic plains towards the deeper parts of the Bay of Bengal. This season provides an ideal opportunity for studying the dispersal of continental aerosols with marine aerosols.
Spectral AOD measurements were carried out using five-channel (380, 440, 500, 675 and 870 nm) hand-held MICROTOPS Sunphotometer during November10 – December 13, 2007 onboard Oceanographic Research Vessel (ORV), Sagarkanya in the central Bay of Bengal. The daily mean AODs in the 500nm wavelength ranged between 0.16–1.0 with standard deviation 0.015 over open oceans which rose to 0.21 near the coastal regions. Higher AOD values ranging from 0.2 to 0.4 at 500nm were observed near Chennai coast. Relatively lower AOD values ranging between 0.15 - 0.30 were observed about 1100 km away from the coast. The daily mean AODs in 870 nm wavelength band ranged between 0.05–0.47 with low standard deviation 0.012 in open oceans which was 0.16 near coasts.
The mean of daily average of Angstrom exponent, α was found to be 1.23 and mean of daily average turbidity parameter, β was 0.183. Smaller Angstrom exponent (α) together with larger Angstrom turbidity coefficient (β) suggest an abundance of larger aerosol particles near the coast. Air mass back-trajectory analysis was also done to identify potential source regions of aerosols. Back-trajectory analysis shows that during the cruise period, the Bay of Bengal was mainly influenced by air masses from the central and east coast of India and also from winds coming towards Bangladesh.
This paper investigates the fatigue, hardness and oxidation properties of the single crystal, Nickel-base superalloys CMSX-4 and PWA1484. These materials are second generation superalloys containing Rhenium. They are commonly used to manufacture turbine blades for companies such as Rolls Royce Plc and Pratt & Whitney Plc. They are also used to manufacture rocket engine turbopumps in the space industry and have been studied extensively at the NASA Lewis Research Center.
These single crystal superalloys have superior properties such as creep, stress rupture, melt resistance, and thermo-mechanical fatigue capabilities when compared to polycrystalline superalloys. However, it is necessary to investigate the fatigue problems associated with the high stress concentrations experienced in gas turbines and rocket engine turbopump blades.
The project involves cutting, grinding and polishing 18 specimens of CMSX-4 and PWA1484. Half of the specimens are etched using a nitric etch. All the specimens are placed in a furnace at 650 degrees centigrade for a time ranging from 1 to 256 hours. An investigation will be conducted into the effect of heat exposure on the microstructure of both materials and a comparison will be drawn up.
Fatigue testing is conducted by placing notched bars of CMSX-4 in an Instron 8501 servohydraulic machine. A Finite Element model is used to calculate the notch depths necessary to give a stress concentration factor of approximately 2 and to calculate the maximum load which needs to be applied to the specimen so that it is exposed to a strain range of 1.38%. The load is applied using a cycle which is run via a 1-1-1-1 trapezoidal loading waveform at 0.25 Hz and at an R-ratio of 0.1 in air and vacuum conditions.
Another known aspect of single crystal superalloys is their anisotropic behaviour. Therefore, it is necessary to study the effect of orientation on the formation of slip bands in the material. This will be done by conducting Vickers Micro Hardness tests on {001}, {110} and {111} orientated sections in CMSX-4. Moreover, the paper will detail the effect of interdentritic pores on crack initiation and lifetimes. Pores may be located near the surface or deeper within the specimen and detailed analysis of their spatial and size variations on the fracture surface will be carried out. Full results will be available as of May 2005.
- Abstract document
- Manuscript document
IAC-05-C2.3.09.pdf (🔒 authorized access only).
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