EFFECT OF POWDER CLEANLINESS ON THE FATIGUE BEHAVIOR OF POWDER METALLURGY NI-DISK ALLOY UDIMET 720

Non-metallic inclusions, which are inherent to the powder metallurgy process, can have a deleterious effect on the fatigue life of turbine disks. An artificial seeding study, where both the size and occurrence rate of the ceramic seeds were well controlled and characterized, was employed as a means of studying the effects of powder dirtiness on fatigue life. Various methods of quantifying cleanliness; quantitative metallography, quantitative fractography, and heavy liquid separation, were evaluated and compared. In addition, extensive metallographic characterization of seeded extrusions and forgings was performed in order to quantify the effect of mechanical processing on inclusion morphology.