Developing an advanced Si-bearing DS Ni-base superalloy

•An improvement in temperature capability ~20°C against creep has been achieved.•Si slightly partitions to γ phase, and dilutes other elements in present alloy systems.•The larger misfit promotes the formation of fine raft during creep.•The oxidation resistance of the newly designed DS alloy is maintained. In present study, a Si-bearing directionally solidified (DS) Ni-base superalloy (KC-5) has been developed based on the composition of CM247LC with Ti, Mo and Si additions. High temperature creep and oxidation properties of KC-5 have been evaluated. Strain-ageing method coupled with EPMA analysis has been conducted to determine the elemental partitionings between gamma and gamma-prime phases, and high temperature XRD analysis has been performed to determine the lattice misfit between gamma and gamma-prime phases. Experimental results indicate that KC-5 exhibits large lattice misfit toward negative; this has led to early formation of raft and dramatically decrease the creep strain rate. Si partitions toward gamma phase and promotes the formation of continuous Al2O3 on the surface of KC-5 after high temperature oxidation. However, there are debits associated with reduction in heat treatment window and phase instability in this newly designed DS alloy.