Isothermal oxidation behavior of electrospark deposited NiCrAlY coatings on a Ni-based single-crystal superalloy

The isothermal oxidation behavior of a NiCrAlY coating prepared by means of electrospark deposition (ESD) technology on second-generation Ni-based single-crystal DD6 was investigated at 1100 °C for 100 h.Surface morphologies, chemical composition, and the phase constitution of the coating were analyzed by scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS) and X-ray diffraction (XRD).The results showed that the as-deposited NiCrAlY coating, with uniform superfine columnar crystals and nanocrystallines, consists of b-NiAl and g-Ni double phases; the oxidation resistance of the DD6 alloy was greatly improved by depositing the NiCrAlY coating, which was covered by two layers of oxides, q-Al2O3 and a-Al2O3, while three layers of oxides, including Ni(Co)O, NiCr2O4, CrTaO4, CoTa2O6 and a-Al2O3, formed on the DD6 superalloy; the interdiffusion zone (IDZ) and secondary reaction zone (SRZ) formed between the NiCrAlY coating and the DD6 superalloy substrate for the interdiffusion; however, no deleterious Kirkendall voids appeared, which may be mainly due to the gradient transition of the elements between the coating and the substrate.Keywords: isothermal oxidation, NiCrAlY coating, electrospark deposition, Ni-based single-crystal superalloy Avtorji so raziskovali izotermi~no oksidacijo NiCrAlY prevleke, pripravljene s tehnologijo elektroiskrilne depozicije (ESD), na drugo generacijo monokristala iz Ni superzlitine DD6 pri ~asu zadr`evanja 100 ur na temperaturi 1100 °C.Povr{insko morfologijo nastale prevleke ter njeno kemi~no in fazno sestavo so analizirali z vrsti~nim elektronskim mikroskopom (SEM), energijskim disperzijskim spektrometrom (EDS) in rentgensko difrakcijo (XRD).Rezultati raziskave ka`ejo, da ima nane{ena NiCrAlY prevleka enovite superdrobne stebri~aste kristale in nanokristalite ter vsebuje b-NiAl in g-Ni dvojne faze.Z nanosom NiCrAlY prevleke se je mo~no izbolj{ala odpornost DD6 zlitine proti oksidaciji.Na DD6 superzlitini nastala prevleka je bila sestavljena iz dveh plasti oksidov, q-Al2O3 in a-Al2O3 medtem ko je tretja plast vsebovala okside Ni(Co)O, NiCr2O4, CrTaO4, CoTa2O6 in a-Al2O3.Interdifuzijska cona (IDZ) in sekundarna reakcijska cona (SRZ) sta nastali med NiCrAlY prevleko in substratom iz DD6 superzlitine, vendar pa niso opazili {kodljivega nastanka por zaradi Kirkendallovega efekta.Ta lahko nastopi zaradi gradientnega prenosa oz.razli~ne hitrosti difuzije elementov s prevleke na substrat in obratno.