Oxidation and Hot Corrosion Studies of Laser Hybrid Welded IN617 and P91 Alloys

The present investigation aimed to evaluate the
effect of similar laser hybrid welds on the oxidation and hot corrosion behavior of IN 617 and P91 alloys. The oxidation studies were carried out on the base and welded IN617 and P91 alloys in air in the temperature range 600–800 °C for 100 h. At the same time, hot corrosion tests with or without synthetic coal ash coatings were conducted in a flue gas environment for 1000 h. The oxidation and hot corrosion
kinetics revealed that the change in mass is lower for the
base and welded IN 617 than the P91 alloys at all the expo
sure temperatures. The post-characterization of oxide scales
formed on the surface of the base and welded alloys later to
oxidation and hot corrosion, was done using XRD and SEM
EDS techniques. The oxide phase were identified as NiO and
Cr2O3 on welded IN617 alloys at 600–700 °C and 800 °C,
respectively, whereas as Fe2O3 and Fe2O3–Fe3O4 on welded
P91 alloy at 700 °C and 800 °C, respectively. In the case of
coal ash-coated samples, additional Al2O3 & SiO2 phases
were identified for both base and welded IN 617 and P91
alloys. The non-protective Fe2O3 in the outer scale allowed
oxygen to pass through, thus yielded into much thicker oxide
scales and higher mass gains for P91 alloys, while protective NiO or Cr2O3 oxide scales yielded into low scale thicknesses and mass gains for IN617 alloys.