H.R. Guan

Effects of melt treatment on the cast structure of M963 superalloy

Abstract The cast structure of M963 superalloy is greatly affected by the melt superheating treatment. Melt superheating treatment (below 1923 K) coarsens the grain structure and transforms the blocky MC carbide into Chinese-script one that mostly distributed in dendrite. However, when the melt superheating temperature reaches 2123 K, the grain structure becomes very fine equiaxed, and the morphology of MC carbide changes back to the blocky appearance.

Effect of thermal history on the liquid structure of a cast nickel-base superalloy M963

Using high temperature X-ray diffraction analysis, the liquid structure of a cast nickel-base superalloy M963 after overheating at 1793 K and 1873 K was investigated. It is shown that there exists a Ni3(Al,Ti,Nb)-like cluster and residual MC carbide in the alloy melt superheated at 1793 K. With decreasing temperature, the residual MC carbide particles can further grow in the alloy melt. When the superheating temperature reaches 1873 K, the Ni3(Al,Ti,Nb)-like cluster and residual MC carbide all disappear, and the Ni3(Al,Ti,Nb)-like cluster forms again with decreasing temperature. The microstructure of the solidified alloy had obvious change after overheating at 1793 K and 1873 K. These results indicate that the liquid structure of the M963 superalloy has a close relationship to the thermal history of the alloy melt.

Study of Ni-Cr-Co-W-Mo-B interlayer alloy and its bonding behaviour for a Ni-base single crystal superalloy

A new Ni-Cr-Co-W-Mo-B alloy was selected as an interlayer alloy for transient liquid phase (TLP) bonding of a Ni-base single crystal superalloy. The microstructure and wettability on the substrate of the interlayer alloy were investigated. The microstructure characteristics in the bond during TLP process were evaluated. Single crystal could be achieved during TLP bonding if the crystallographic orientation is maintained in both mating halves

Manufacturing, structure and high temperature corrosion of palladium-modified aluminide coatings on nickel-base superalloy M38

Three palladium-modified aluminide coatings were prepared by conventional pack-cementation aluminizing process on the nickel-based superalloy M38, which was previously electroplated with pure palladium, Pd-20 wt.% Ni alloy, or Pd + Ni composite plating. The structure of all coatings was thoroughly analyzed. A major difference between Pt- and Pd-modified aluminide coatings resided in the fact that the Pd zone was single-phased and the constitutive phase was beta-(Pd-x,Ni1-x)Al. The isothermal oxidation resistance of the Pd-20 wt.% Ni alloy modified coatings was better than that of the other two palladium-containing and conventional aluminide coatings in air at 1000 degreesC. The hot corrosion performance of Pd-Ni-Al coatings was also tested in Na,SO, melt at 900 degreesC. As regards their hot corrosion resistance, they behaved at least as well as commercial Pt-Al coatings under the same testing conditions and remarkably better than conventional aluminide coatings. The behavior of cyclic oxidation of Pd-Ni-Al coating was inspected at 1050 degreesC and its corrosion mechanism was also preliminary discussed

Cyclic oxidation behavior of palladium-modified aluminide coating

(Ni,Pd)AI coating prepared by low-pressure pack cementation on the nickel-base superalloy IN738 predeposited Pd-20 wt.% Ni alloy, and their cyclic oxidation behavior was investigated by TGA, XRD, SEM/EDS and optical microscopy at 1050 degreesC. The C (Ni,Pd)AI coatings show better cyclic oxidation resistance than simple aluminide coatings compared from the cyclic oxidation kinetics and the microstructure degradation of the two types of coatings. Palladium plays a significant role in alumina stabilization and in delaying the degradation of beta-phase

Preparation of a (Ti, Nb, W)C particulate reinforced nickel-base superalloy via super-high temperature treatment of melt

A well-dispersed (Ti,Nb,W)C particulate reinforced nickel-base superalloy was prepared via super-high temperature (above 2123 K) treatment of melt. Scanning electron microscope (SEM) observation and energy dispersive X-ray spectroscopy (EDS) results show that most of the (Ti,Nb,W)C particles have a carbonitride core. Gas analysis shows that nitrogen content in the alloy with super-high temperature treatment of melt is much higher than that in the conventional cast superalloy. The welldispersed (Ti,Nb,W)C particles could be attributed that nitrogen combines with Ti in the alloy melt to produce TiN, which acts as the nucleator to form (Ti,Nb,W)C. This work provided a new way to prepare the TiC particulate strengthened composites

Effect of palladium incorporation on isothermal oxidation behavior of aluminide coatings

A (Ni, Pd)Al coating has been prepared by low-pressure pack cementation on the nickel-base superalloy IN738 with a preplating of Pd–20 wt.% Ni alloy. The coating consists mainly of a single phase of β-Pd(Ni)Al in the outer part and β-Ni(Pd)Al in the inner part. The oxidation behavior of the (Ni,Pd)Al coating at 900–1100°C was studied by TGA, XRD, and SEM/EDS. Results show that the transformation of θ- to α-Al2O3 is more rapid on the (Ni,Pd)Al coating than that on a simple NiAl coating. The addition of Pd to the aluminide coating facilitates the transformation of θ- to α-Al2O3e oxide scale formed and accelerates the diffusion of Ti from the substrate to the coating surface simultaneously.

Cyclic stress response behavior of a carbide-strengthened Co-base alloy under low cycle fatigue at 900 degrees C

chinese acad sci, inst met res, shenyang 110016, peoples r china.;yang, fm (reprint author), chinese acad sci, inst met res, shenyang 110016, peoples r china;fuminyang@sohu.com