High Temperature Oxidation Behaviour Of Al-Si Coatings Made By Different Methods

Two Al-Si coatings on DZ4 superalloy was prepared by different methods.According to GB/T13303-91(Steels Determination Method of OxidationResistance), high temperature oxidation experiments of Al-Si coating on DZ4were carried out at 1100℃in air for 300h. The oxidation kinetic curves of thesuperalloy with different Al-Si coatings were obtained by Origin and the oxidationkinetics equations were obtained by mathematical technique. The Al-Si coatingsafter oxidation experiments were analyzed by SEM, EDS and XRD. The resultindicates both of the two Al-Si coatings on DZ4 superalloy have excellent hightemperature oxidation resistance. The growth ofθ-Al₂O₃ on the surface of thecoatings, which was dominant at the early stage, caused fast mass gain.With timeincreasing,θ-Al₂O₃ has transformed intoα-Al₂O₃ and the oxidation kineticscurves became flat due to the decrease of mass gain. The cracking and spallationof coating tended to be obvious when cooling due to difference of coefficient inthermal expansion between oxide scale, coating and substructure, internal stress inthe coating, and the cavity on the interface of scale/coating. The addition of Siprohibits growth ofβ-NiAl and accelerates the transformation ofβ-NiAl toγ'-Ni₃Al. Theγ'-Ni₃Al has excellent corrosion resistance similar toβ-NiAl. Inaddition, transformation ofβ-NiAl toγ'-Ni₃Al is also conducive to lower theDBTT, by which theα-Al₂O₃ scale has good adhesion and less cracking orspallation was observed. B coating has better high temperature oxidationresistance than A coaing due to more Si-riched M₆C. Si-riched M₆C prohibitsNi/Al interdiffusion and promotes the coating resistance to high temperatureoxidation.