FATIGUE CRACK PROPAGATION BEHAVIOR OF NEWLY DEVELOPED ALLVAC ® 718PLUS ™ SUPERALLOY Xingbo Liu 1, Shalini Rangarajan 1, Ever Barbero 1, Keh-Minn Chang 1, Wei-Di Cao 2, Richard Kennedy 2, Tadeu Carneiro 3 1 West Virginia University, Morgantown, WV 26505, USA 2 Allvac, An Allegheny Technologies Company, Monroe, NC 28110, USA 3 Reference Metals Company, Bridgeville, PA 15017, USA BACKGROUND Allvac ® 718Plus ™ was developed to Work at a higher temperature than Alloy 718 Possess comparable mechanical properties and thermal stability to Waspaloy at 1300 ° F Have processing characteristics similar to Alloy 718 and much better than Waspaloy Have 20-25% lower cost than Waspaloy Chemical composition of 718Plus ™, Alloy 718 and Waspaloy: Balance Al to Ti ratio with Nb to improve thermal stability and mechanical properties at high temperature Minor elements B and P added to maximize creep resistance Fe, Co and W balanced to improve strength, creep resistance, thermal stability and processing qualities with minimum increase in raw material costs RESEARCH OBJECTIVES Investigate the mechanical properties of Allvac ® 718Plus ™ and compare with Alloy 718 and Waspaloy: Tensile properties at 650 ° C and 704 ° C Stress rupture properties at 704 ° C Fatigue crack propagation at 650 ° C and 704 ° C 3 seconds triangle wave Hold-time fatigue crack propagation Trapezoid wave with 3 seconds seconds loading at maximum stress RESULTS AND DISCUSSION MICROSTRUCTURE OF 718PLUS ™ Main features of the microstructure of 718Plus ™ Strengthening phase γ' uniformly distributed in γ matrix δ phase well distributed on grain boundaries TENSILE AND STRESS RUPTURE PROPERTIES Yielding and tensile strength: 718Plus ™ > Alloy 718 and Waspaloy Stress rupture properties: 718Plus ™ ~ Waspaloy > 718 FATIGUE CRACK GROWTH WITHOUT HOLD TIME At 650 °C: 718Plus ™ > Alloy 718, Waspaloy 718Plus ™ has better FCG resistance at 704 °C than Alloy 718 and Waspaloy at 650 °C Mixture of transgranular and intergranular modes at 650 °C Intergranular mode predominant at 704 °C Clear border present between RT precrack and fatigue at 650 °C Severe oxidation observed during crack growth at 704 °C FATIGUE CRACK GROWTH WITH HOLD- TIME At 650 °C: Waspaloy, 718Plus ™ > Alloy 718 Crack propagation at both 650 °C and 704 °C is predominantly intergranular with a little transgranular cleavage fraction Rough fracture surface covered with lots of oxide products Oxidation of surface more severe at 704 °C than at 650 °CCONCLUSIONS The newly developed 718Plus ™ alloy shows better tensile and stress rupture properties for temperatures up to 704 °C than Alloy 718 Tensile and stress rupture properties of 718Plus ™ alloy are similar to that of Waspaloy for temperatures up to 704 °C For fatigue crack growth without holding time, there is no significant difference between 718Plus ™,Alloy 718 and Waspaloy, but in comparison, 718Plus ™ has the best FCGR resistance and Alloy 718 has the lowest 718Plus ™ shows comparable resistance to hold-time FCG than that of Waspaloy and both alloys show better FCG properties than that of Alloy 718 FUTURE WORK Investigate effect of grain size and alloy chemistry on the hold-time FCG of 718Plus ™ alloy Improve 718Plus ™ alloy’s hold-time FCG properties through thermo-mechanical treatment and microstructural optimization Equilibrium phase diagram of 718Plus ™ alloy Microstucture of 718Plus ™ alloy Fracture surface of 718Plus ™ at 650 °C Fracture surface of 718Plus ™ at 704 °C Fracture surface of 718Plus ™ at 650 °C Fracture surface of 718Plus ™ at 704 °C