Effect of nano Y2O3-ZrO2 additives on properties of aluminide diffusion coatings on Ni-Based superalloy (type IN625)

In this work, a new type of Y2O3−ZrO2 doped aluminide coating was carried out by the pack cementation process at 900oC for 6 hours with different percentages of (1.0, 1.5, and 1.5) wt% nano Y2O3−ZrO2 added to the pack mixture. A Ni-based superalloy (type IN625 type) was coated with pack powder containing: Al as a source of aluminum; NH4Cl as a source of activator; Y2O3-ZrO2 as a source of reactive element oxide; and Al2O3 as a source of filler metal. The microstructure characterization of the coating was performed by SEM and EDS. It was found that the cross section of the coating obtained was uniform and free from cracking. It consists of three layers: the outer layer, the transition layer, and the inter-diffusion zone. The interface zone features a distinct Cr-rich region and a larger diffusion region extending toward the substrate. Based on the microstructural information of the coatings created at different stages of aluminide, it has been determined that the coating growth in the aforementioned process initially occurs predominantly through inward Al diffusion. It is followed by a transitional stage during which both Ni and Al are diffused outward and inward throughout the growth process. The development of the coating is dominated in the latter stages by the outward dispersion of Ni. Surface XRD analysis shows that the phase structures of coatings are: Al1.1Ni0.9, AlNi, Ni11Zr9, and Ni5Y. The highest value of micro-hardness measurement was 1390 HV at 1.5 wt% nanoY2O3−ZrO2 additive. As a result, the Y2O3−ZrO2 coating has higher micro-hardness and the interfacial bonding force between the coating and the substrate.