Effects Of Heat Treatment And Alloying Elements On The High Temperature Oxidation Behaviors Of MCrAlY (Re) Bond Coat Materials

The paper works at γ/β duplex-phase MCrAlY(Re) alloys, and its main part isthe improvement of the high-temperature anti-oxidation properties of these alloys.The present work studies the microstructural features, the oxidation behaviors andmechanisms of the tested alloys, and subsequently predicted the in-service lifetime ofthose alloys.With the help of back-scattered electron microscopy and energy-dispersiveanalysis, the present work is to study the influences of heat-treatment and alloyingelements on the high-temperature oxidation behaviors of γ/β duplex-phaseMCrAlY(Re) alloys. Heat-treatment homogenizes the distribution of Al-rich phase,which is beneficial to prompt the formation of the α-Al₂O₃protective layer, lower theoxidation rate and improve the anti-oxidation properties of alloys.In order to clarify the influence mechanisms of alloying elements on the testedalloys during the oxidation process, the paper conducted systematic studies on thepartition and precipition of alloying elements, the oxidation kinetics, the compostionand the phase transformation of oxides, and the element-distribution characteristics atthe scale/alloy interface. Compared with the individual addition of Al or Re, thecombined addition of Al and Re could increase the amount of β-phase; strengthen theprecipitation behaviors of α-(Cr,Re) underneath the scale/alloy interface and loweroxidation rate. Additon of3⁵wt.%Pt could form a Pt-rich β-phase. By contrast withthe original alloys, the Pt-modified alloys showed the accelerated phasetransformation, lowered oxidation rate and consumption rate of β-phase. Pt couldsuppress the formation of the internal oxidation and spinels. Alloys with or withoutadding small amount of Dy showed the parellel microstructural features. The effectsof Dy on the tested alloys were sensitive to the temperature and the existence of Re.For MCrAlY alloy, addition of Dy could bring the accelerated phase transformation,the refined oxide grains and the significantly lowered oxidation rate. Under cyclicoxidation at1100℃, Dy addition formed a sole and protective α-Al₂O₃scale, which elminated the cracks and spallations of the oxide scale and internal nitrides. ForRe-containing alloy, Dy had not obvious effects on the refinement of the oxides andinhibited the phase transformation. At800℃, Dy had no influence on theanti-oxidation properties. However, Dy could greatly lower the oxidation rate;suppress the formation of spinels and improve the anti-oxidation resistance at highertemperature.Based on the mechanisms of the consumption of β-phase, a model was proposedto predict the in-service lifetime of the tested alloys. The prediction results revealedthe doubled lifetime of the Dy-modified alloys compared with the original alloys.