IN718 has good fabricability, high strength at elevated temperature, and corrosion resistance, and it is widely deployed in many aerospace and other high-performance applications. With the molten pool rapid solidification during laser powder bed fusion (L-PBF), the resulting microstructure is anisotropic and inhibits macro-segregation. The as-built condition usually exhibits lower mechanical properties. Four different heat treatment procedures were designed and tested to study the effect of different heat treatment parameters on the type of precipitates and grain size. The investigated heat treatment procedures showed the formation of equiaxed grain size and a significant amount of γ' and γ" particles at the grain boundary in addition to primary carbide types (MC). Three types of microstructure characteristics and grain size were achieved. Coarse grain size suitable for creep application was achieved by increasing the soaking time at the aging cycle. The formation of serrated grain boundaries suitable for good fatigue and creep properties was achieved by decreasing the stress relief cycle's soaking time and temperature. Fine-grain size, which is preferable for fatigue properties, was achieved by decreasing the soaking time at the solution annealing cycle.

Hydrogen embrittlement (HE) susceptibility was investigated for Alloy 718 and Alloy 945X specimens heat treated to a set of conditions within the specifications of API Standard 6ACRA. Heat treatments were selected to simulate the potential variation in thermal history in thick sections of bar or forged products and produce various amounts of discontinuous grain boundary δ phase in Alloy 718 and M 23 C 6 carbides in Alloy 945X, while maintaining a constant hardness in the range of 35-45 HRC for Alloy 718 and 34-42 HRC for Alloy 945X. Time-temperature-transformation (TTT) diagrams and experimentation were used to select a set of heat treatments containing no δ phase, a small quantity of δ, and a larger quantity of δ in Alloy 718. The presence of δ phase has not been verified for the moderate condition. A similar approach was taken regarding M 23 C 6 carbides in Alloy 945X. Incremental step loading (ISL) tests were conducted under in-situ cathodic charging on circular notch tensile (CNT) specimens in a 0.5 M H2SO4 solution. During the test, the direct current potential drop (DCPD) was measured across the notch to determine the stress intensity associated with unstable crack growth. Results indicate that even very small quantities of δ phase in Alloy 718 are detrimental to HE resistance. Both Alloy 718 and Alloy 945X show decreases in HE resistance with aging, with a greater degradation in Alloy 718.

The solution quenching process is a critical heat treatment process for aluminum alloys to obtain better strength and a homogeneous super solid solution. In this paper, the mechanical properties of Al-5%Cu-0.4%Mn in the as-quenched state are tested. The alloy, designated as ZL205 (Chinese standard), has a chemical composition similar to a 2xxx series aluminum alloy and is used for constructing large thin wall components. The ZL205A alloy shows good performance under loading at room temperature while losing its toughness and exhibiting tensile brittleness, which is unexpected at elevated temperatures (especially at 300 °C). After observing the fracture sections of ZL205A at room temperature and at 300 °C, it may be concluded that one possible reason leading to this phenomenon may be the formation of the T phase at grain boundaries. Such a hypothesis is validated and discussed with the help of SEM observations.

The 13% Cr 0.2%C steel is extensively used in OCTG application. This steel was examined in the double hardened condition at 1040°C/OQ followed by 980°C/OQ as against conventional hardening treatment at 980°C/OQ. It was observed that the double hardening heat treatment resulted in higher carbon dissolution in the matrix without any residual grain boundary necklace carbides while single hardening at 980°C shows remnant grain boundary carbide. Double hardening heat treatment was found to refine the grain size by recrystallization of the defects introduced in first hardening. During double tempering heat treatment, the carbides in the 980°C treatment were coarse and found to nucleate along grain boundary. The double hardened sample on tempering showed an even distribution of carbide throughout without grain boundary carbide. The double hardened sample show improved strength and toughness compared to the single hardened sample at similar tempering conditions. The microstructural analyses at various stages of processing have been correlated to the mechanical properties obtained.

Quench cracks became a challenge in large serial production of martensitic components. The geometry is simple, and concentrations of stresses from the geometry itself were not indicated by numerical simulation. Grain boundary ferrite is presented in the component surface from where the cracks start. An example from another application is interesting to consider; titanium grade 5. Grain boundary alpha on prior beta grain boundaries is not accepted for aerospace applications. The volume for plastic deformation in the phases along the grain boundaries is restricted. The ductile part of the fracture indicates forces from unbalanced quenching and elevated temperature at time of crack start. The general focus for improvement will be overcritical surface temperature, vapor phase break and mix of turbulent/lamellar flow. More effective quenching around the whole component is, in this case, assumed to be better than slower quenching.