Effects of kerosene or distilled water as dielectric on electrical discharge alloying of superalloy Haynes 230 with Al–Mo composite electrode

Abstract

The effects of kerosene and distilled water as dielectrics on the electrical discharge surface alloying of superalloy Haynes 230 are investigated. The 85 at.% Al and 15 at.% Mo composite electrode provided the surface alloying materials. The alloying results obtained using both positive and negative electrode polarities were compared. With negative electrode polarity and alloying in kerosene, many discontinuous piled-layers comprised mostly of Al 3Mo 8 and AlMo 3 phases accumulate on the surface of the N-AlMo-Kero specimen, but alloying in distilled water was unsuccessful because of the difficulty of discharging under such an EDA condition. With positive electrode polarity, the alloyed layers constituted mainly of NiAl phase are formed on the EDA specimens, in either kerosene or distilled water. The alloyed layer of P-AlMo-Kero contains a mixture of NiAl, Al 8Mo 3, Cr 23C 6, and Al 4C 3, while the alloyed layer of P-AlMo-Water contains NiAl, AlCr 2, Al 5Cr, and Al 2O 3 phases. The P-AlMo-Water exhibits the highest hardness, whereas the P-AlMo-Kero has the smallest surface roughness of all the EDA specimens. The superalloy Haynes 230 and the EDA specimens are subjected to isothermal oxidation at 1000 °C in static air. Analyses of oxidation kinetics indicate that the P-AlMo-Water and the P-AlMo-Kero specimens are more resistant to oxidation than the unalloyed superalloy; and the P-AlMo-Kero specimen has the best oxidation resistance among all tested specimens.