Effect of Hot Isostatic Pressing on Microstructures and Stress-Rupture Properties of CM 939 Weldable Alloy

Effect of hot isostatic pressing (HIP) treatment on the microstructure and the stress rupture properties of CM 939 Weldable alloy have been investigated. The results shown that the HIP has the function of densification and homogenization, all of the microporosity have been almost removed, the segregation of the alloy have been reduced, the microstructure became better, the stress rupture life of CM 939 Weldable alloy have been obviously improved, Meanwhile, the data dispersion of stress rupture properties have been reduced for the alloy after HIP.

Cohesive Strength and Structural Stability of the Ni-Based Superalloys

The influence of alloying elements on the cohesive strength of metal heat-resistant alloys (HRAs) is analyzed. Special parameters are introduced to characterize the individual contribution of each alloying element. These are the partial molar cohesion energy of the matrix (χ) and the cohesive strength of the grain boundaries (η) and can be calculated by computer modeling based on the density functional theory. The calculating results of the parameters χ and η in nickel HRAs with mono– and polycrystalline structures alloyed with refractory metals are presented. The calculated data are used to select the chemical composition and develop new nickel (Ni) HRAs with superior creep-rupture properties. It is assumed that a similar approach can be used to search for alloying elements that will contribute to increasing the cohesive strength of additive objects. The resistance of coherent γ-γ’ and lamellar (raft) structures in nickel HRAs to the process of diffusion coarsening during operation is analyzed.

Selective Anisotropy of Mechanical Properties in Inconel718 Alloy

Mechanical anisotropy behaviors are investigated in slightly rolled Inconel718 alloy with string-like δ phase and carbides produced during various solid-solution and aging treatments. A weak anisotropy in the strengths and rupture properties at 650 °C is visible, whereas ductility, i.e., reduction in area (RA) and impact toughness (CVN), presents a sound anisotropy behavior. MC carbides promote the operation of slip systems and thus are conducive to weakening the strength anisotropy. The RA anisotropy mainly stems from high-density δ phase particles that provide more crack nucleation sites and stimulate rapid propagation because of the shorter bridge distance between micro-cracks at the rolling direction. In contrast, CVN anisotropy arises from both δ phase and carbides at a lower solid-solution temperature of 940 °C but only depends on carbides at 980 °C where the δ phase fully dissolves. Apart from dislocation motions operated at room temperature, the activated grain boundary processes are responsible for the weak anisotropy of rupture properties at the elevated temperature. This work provides a guideline for technological applications in the hot working processes for Inconel718 alloys.