Tuning γ/γ′ lattice misfit to discover Pt-Al-Hf superalloys with superior high-temperature compressive strength

For Pt-based superalloys with a γ-γ′ dual-phase microstructure, the lattice misfit between the two phases significantly affects the lattice coherent strain field, thereby dictating their mechanical performance. Here, high-throughput first-principles calculations were used to estimate the lattice misfit at finite temperatures. The calculated lattice misfit for Pt₃Al, Pt₃Sc, Pt₃Ti, Pt₃Zr, and Pt₃Hf at 300 K are −0.985%, 0.525%, −0.316%, 1.405% and 0.903%, respectively. Due to the higher antiphase boundary (APB) energy and shear modulus of both Pt₃Al and Pt₃Hf, the combination of Pt₃Hf with positive lattice misfit and Pt₃Al with negative lattice misfit can optimize the overall lattice misfit in Pt₃(Al_1−xHf_x)₁ through compositional tuning. The calculated lattice misfit for Pt₃(Al_0.625Hf_0.375)₁ is −0.154% at 300 K and approaches zero at elevated temperature. The alloy Pt₈₂Al_11.25Hf_6.75 (at.%) was prepared, and in-situ high-temperature X-ray diffraction measurements reveal lattice misfit of −0.135%, −0.200%, −0.062%, −0.089%, and 0.060% at 298 K, 573 K, 873 K, 1173 K, and 1473 K, respectively, which agree well with the calculated values. High-resolution transmission electron microscopy (HR-TEM) confirms that the γ and γ′ phases form a coherent structure. The near-zero lattice misfit induces a coherent strain field around the γ′ precipitates, effectively impeding dislocation motion. The compressive strengths of Pt₈₂Al_11.25Hf_6.75 at 1173 K and 1473 K were measured as 666.6 MPa and 186.4 MPa, respectively, exceeding those of previously reported Pt-Al-based superalloys.