Development of Si-bearing 4th generation Ni-base single crystal superalloys

In present study, Si addition (1.0at%) is found to be responsible for a dramatic improvement in high temperature oxidation resistance of 4(th) generation superalloys; this might be attributed to an increase in Al activity induced by Si to promote the formation of protective A1(2)O(3) layer and improved adhesion between the Al2O3 and the substrate due to the presence of Si. However, there are debits associated with Si addition in terms of reduction in both heat-treatment window and microstructure stability. The National Institute for Materials Science has developed two experimental Si-bearing 4(th) generation superalloys that exhibit an excellent balance of resistances against mechanical deformation and environmental attack; their temperature capability of both creep and oxidation properties have reached an average of +40 degrees C over CMSX-4. Hence, the cost-performance of 4(th) generation superalloys can potentially be improved by addition of Si. The present article aims to quantify the properties of these experimental Si-bearing compositions in order to aid the future development of new superalloys with Si additions.