Cyclic Crack Propagation Characteristics of the Powder Metallurgical Nickel-Base Alloy Udimet 720 at Elevated Temperatures and Different Dwell Times

摘要

The microstructure and the crack growth behavior of HIPed, and HIPed and forged billets of the powder alloy U720LC were evaluated. Grain size and structure, and defect distribution were investigated using standard metallographic techniques. Crack propagation testing was performed using compact tension and surface crack specimens in order to compare the behavior of long and short cracks at room temperature, 673 K and 873 K. The crack growth rate in both materials increases with increasing temperature, decreasing frequency, and through the introduction of hold time. The crack growth rate also depends on microstructure, being greater for the HIP+forged material. The influence of temperature and microstructure was attributed to changes in crack closure, in surface roughness, and deformation mode.