Ni基超合金IN738LCの衝突損傷に及ぼす材料劣化の影響

抄録

Nickel-base superalloy IN738LC is widely used for heavy-duty gas turbine buckets. But the buckets in current advanced gas turbines are exposed to extremely high temperature, which induces significant material degradation during service. Therefore an evaluation of the resistance against damage caused by foreign objects is required to establish a material degradation assessment system. In order to investigate the damage caused by impact from a projectile, the long-time aged material at 750°C-900°C up to 24000h of IN738LC are artificially produced and the single-particle fracture test was made on a particle impact test rig. In this study, introducing the fracture model, in which the strain rate controlling process is that dislocations move past γ' precipitates by looping, the critical velocity of impact fracture is explained as a function of projectile size, target thickness, mechanical property such as material elongation and the microstructural parameter of a ratio of the second power of the γ' interparticle distance to the γ' mean diameter. Furthermore, using measured impact loads, the relationship between normalized deformation work induced by impact projectile and impact velocity is discussed.