Abstract
In the current study, laser-surface alloying (LSA) of Nimonic 80 (a Ni-based superalloy) was conducted using a high-power continuous wave (CW) CO2 laser by simultaneous feeding of predetermined proportion of elemental Si and Al powders with an Ar shroud. After LSA, the microstructure of the alloyed zone was carefully analyzed and found to consist of several intermetallic phases of Ni and Si. The microhardness of the alloyed zone was significantly increased to 500 VHN compared with 250 VHN of the as-received substrate. The high-temperature oxidation resistance of the laser-surface-alloyed specimens (under isothermal conditions) was improved (at temperature ranges between 1223 K and 1423 K [950 °C and 1150 °C]) compared with as-received Nimonic. Even though LSA enhanced resistance to oxidation up to a limited period, continued exposure to extended hours (at a given temperature) led to spallation of scale. It seems that a SiO2-rich adherent scale is responsible for enhanced protection against oxidation in the laser-surface-alloyed specimens. However, the presence of Al2O3 in the oxide film enhances the resistance to spallation by increasing the scale adherence at a higher temperature. The results are supported by a suitable thermodynamic calculation.
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