• Proceedings of the KSME Conference
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• 2004.04a
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• pp.336-341
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• 2004

This research investigates the feasibility of ultrasonic microscope for nondestructive assessment of thermal degradation in artificially aged commercial Co-base superalloy, FSX414. This alloy has been used for high temperature structure applications such as stationary gas turbine blade and nozzle chamber in fossil plant. Microstructural change was found that the fine carbides became coarser and spheroidized in matrix as aging time increased. The leaky surface acoustic wave velocity gradually decreases by a maximum of 4.7% with increasing aging time up to 4,000hours. However, the longitudinal wave velocity has a little change. Also, it has a good correlation between leaky surface acoustic wave velocity and Vickers hardness. Consequently, LSAW can be used to examine the degree of degradation in thermally aged Co-base superalloy.

• Resources Recycling
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• v.4 no.1
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• pp.52-59
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• 1995

Treating bulk superalloy scrap with molten zinc has been studled to facililate recycling and recovery- of cobalt.Superalloys investigated were the cobalt-base Mar-M-509 and X45 and the nickel-base Rene 80. Charges withZnlscrap ratlos of 1.5-6.5 were heated to 750-9002 far 1-7.5 hours in a nitrogen atmosphere. The moltenzinc dissolved superalloy scrap and zinc was removed by vacuum distillation at 850-Wk for 4-6 hours. Ithas been concluded that the optimum conditions of decomposition for Mar-M-509 and Rene 80 \"ere dissolutiontemperature of about 850k, Znlscrap ratlo of about 5, and dissalution time of about 5.5 hours. The zinc-treatedsuperalloy prouducts were friable and reacted rapidly with acid solutions. Leaching 9mm pieces of unalloyedMar-M-509 or Rene 80 with 5 times the stolchlometric amount oi 6N HCI at 90t ior 3 hours dissolved about1.5-7.270, while leachmg of the minus 20-mesh products dissolved about 89.0-93.0%.ved about 89.0-93.0%.

• Laser Solutions
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• v.2 no.2
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• pp.34-41
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• 1999

A RS840 $CO_2$laser and a powder auto-feeding apparatus have been used to deposit single tracks of Ni-base superalloy on low carbon steel. In this paper, the effects of laser cladding parameters on clad geometry, dilution and microhardness are studied. As a results, the w/h ratio of the clad layer increases with decreasing powder feed rate and increasing laser scan speed. Increase of powder density and decrease of specific energy have little effect on dilution. It was found that the clad layer of the highest hardness has a structure in which fine and leaf like phases are dispersed in ${\gamma}$Ni matrix.

• Korean Journal of Metals and Materials
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• v.47 no.7
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• pp.440-446
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• 2009

Co base superalloys have been widely used for the parts of gas turbine due to their excellent strength, thermal fatigue, oxidation resistance and weldability at high temperature. In this study, directional solidifications were carried out at various solidification rates, including $0.5{\sim}300{\mu}m/s$ in the Co base superalloy FSX-414. The cellular interface were formed at a low solidification rate, $1{\mu}m/s$, and the dendritic interface was found at higher solidification rates, $5{\sim}300{\mu}m/s$. As the spacing of dendrite structure decreased, the size and spacing of eutectics decreased. Dendrite arm spacing decreased with increasing solidification rates and temperature gradient. It was interesting to find the $M_{23}C_{6}$ eutectic microstructure formed between $\gamma$ dendrites. Composition analysis showed that Cr and W were segregated severely between the dendrites, which resulted in the formation of Cr-rich $M_{23}C_{6}$ and W-rich MC carbides.

• Journal of Welding and Joining
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• v.25 no.5
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• pp.45-50
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• 2007

The Ni-base superalloy GTD111 DS is used in the first stage blade of high power land-based gas turbines. Advanced repair technologies of the blade have been introduced to the gas turbine industry over recent years. The effect of the filler metal powder on Transient Liquid Phase bonding phenomenon and tensile mechanical properties was investigated on the GTD111 DS superalloy. At the filler metal powder N series, the base metal powders fully melted at the initial time and a large amount of the base metal near the bonded interlayer was dissolved by liquid inter metal. Liquid filler metal powder was eliminated by isothermal solidification which was controlled by the diffusion of B into the base metal. The solids in the bonded interlayer grew from the base metal near the bonded interlayer inward the insert metal during the isothermal solidification. The bond strength of N series filler metal powder was over 1000 MPa. and ${\gamma}'$ phase size of N series TLP bonded region was similar with base metal by influence of Ti, Al elements. At the insert metal powder M series, the Si element fluidity of the filler metal was good but microstructure irregularity on bonded region because of excessive Si element. Nuclear of solids formed not only from the base metal near the bonded interlayer but also from the remained filler metal powder in the bonded interlayer. When the isothermal solidification was finished, the content of the elements in the boned interlayer was approximately equal to that of the base metal. But boride and silicide formed in the base metal near the bonded interlayer. And these boride decreased with the increasing of holding time. The bond strength of M series filler metal powder was about 400 MPa.

• Journal of the Korean Society for Precision Engineering
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• v.26 no.2
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• pp.16-20
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• 2009

• Korean Journal of Materials Research
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• v.13 no.6
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• pp.381-388
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• 2003

Directional solidification experiments were carried out at 0.5-150 $\mu\textrm{m}$/s in the Co-base superalloy ECY 768. As increasing solidification rate, the dendrite length increased and it reached the maximum at 150 $\mu\textrm{m}$/s, where the tip temperature is close to the liquidus. The liquidus and eutectic temperatures could be estimated by comparing the dendrite lengths and the temperature gradients at the solid/liquid interface and those were estimated as $1424.6^{\circ}C$ and $1343^{\circ}C$ respectively. Between the dendrites just below final freezing temperature, MC carbide and $M_{23}$$C_{6}$ carbide were found. It was confirmed that the script or blocky shape was Ta or W-rich MC carbide, and the lamellar shape was Cr-rich eutectic carbide. The solid/liquid interface morphology clearly showed that the Cr-rich eutectic carbide formed just after the script type MC carbide.

• Proceedings of the KWS Conference
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• 2002.10a
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• pp.798-802
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• 2002

Metallurgical studies on the bonded interlayer of directionally solidified Ni-base superalloy GTD111 joints were carried out during transient liquid phase bonding. The formation mechanism of solid during solidification process was also investigated. Microstructures at the bonded interlayer of joints were characterized with bonding temperature. In the bonding process held at 1403K, liquid insert metal was eliminated by well known mechanism of isothermal solidification process and formation of the solid from the liquid at the bonded interlayer were achieved by epitaxial growth. In addition, grain boundary formed at bonded interlayer is consistent with those of base metal. However, in the bonding process held at 1453K, extensive formation of the liquid phase was found to have taken place along dendrite boundaries and grain boundaries adjacent to bonded interlayer. Liquid phases were also observed at grain boundaries far from the bonding interface. This phenomenon results in liquation of grain boundaries. With prolonged holding, liquid phases decreased gradually and changed to isolated granules, but did not disappeared after holding for 7.2ks at 1473K. This isothermal solidification occurs by diffusion of Ti to be result in liquation. In addition, grain boundaries formed at bonded interlayer were corresponded with those of base metal. In the GTD-ll1 alloy, bonding mechanism differs with bonding temperature.

• Journal of the Korean Society of Safety
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• v.28 no.3
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• pp.18-22
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• 2013

The Co-base super heat resisting alloy ECY768 is employed in gas turbine because of its high temperature strength and oxidation resistance. The prediction of fatigue life for superalloy is important for improving the efficiency. In this paper, low cycle fatigue tests are performed as variables of total strain range and temperature. The relations between strain energy density and number of cycle to failure are examined in order to predict the low cycle fatigue life of ECY768 super alloy. The lives predicted by strain energy methods are found to coincide with experimental data and results obtained from the Coffin-Manson method. The fatigue lives is evaluated using predicted by Coffin-Manson method and strain energy methods is compared with the measured fatigue lives at different temperatures. The microstructure observing was performed for how affect able to low-cycle fatigue life by increasing the temperature.

• Laser Solutions
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• v.3 no.1
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• pp.38-45
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• 2000

A 4㎾ RS840 CO2 laser with a powder auto-feeding apparatus has been used to deposit multiple overlapping tracks of Ni-base superalloy on to low carbon steel. It was found that the surface roughness(turbulence) of an overlapped cladding layer decreased with the increase of the overlapping ratio in an oscillating manner. When the overlapping ratio had values of 0.62, the surface turbulence was lowest. Overlapping ratio offer significant potential for improvement of materials surface properties such as corrosion performance and wear resistance. This paper reports that the overlapping ratio shows best corrosion resistance. The tensile residual stresses generated at the higher overlapping ratio( ＞ 0.45) and the element concentration of Fe increased in the surface layer at the lower overlapping ratio( ＜ 0.45) may lead to worse corrosion resistance.