With excellent radiation resistance and high temperature strength, the oxide dispersion strengthened (ODS) nickel-based superalloys are deemed as candidate materials for advanced fission and fusion reactor. Since conventional manufacturing processes are difficult to produce components with complex shapes, additive manufacturing becomes an alternative method. In this work, ODS nickel-based superalloy was manufactured by laser metal deposition (LMD) technology using mechanically alloyed powder. The microstructure and high temperature mechanical properties of the as-deposited alloy were analysed. The results indicated that the as-deposited alloys prepared by this method owned anisotropic structure and uniformly distributed high-density oxides, contributing to superior high-temperature performance, in comparison with the samples produced by LMD using pre-alloyed powder and traditional hot extrusion.

Controlling grain size in polycrystalline nickel base superalloy is vital for obtaining required mechanical properties. Typically, a uniform and fine grain size is required throughout forging process to realize the superplastic deformation. Strain amount occupied a dominant position in manipulating the dynamic recrystallization (DRX) process and regulating the grain size of the alloy during hot forging. In this article, the high-throughput double cone specimen was introduced to yield wide-range strain in a single sample. Continuous variations of effective strain ranging from 0.23 to 1.65 across the whole sample were achieved after reaching a height reduction of 70%. Grain size is measured to be decreased from the edge to the center of specimen with increase of effective strain. Small misorientation tended to generate near the grain boundaries, which was manifested as piled-up dislocation in micromechanics. After the dislocation density reached a critical value, DRX progress would be initiated at higher deformation region, leading to the refinement of grain size. During this process, the transformations from low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs) and from subgrains to DRX grains are found to occur. After the accomplishment of DRX progress, the neonatal grains are presented as having similar orientation inside the grain boundary.

Ni-based superalloys are widely used to manufacture the critical hot-end components of aviation jet engines and various industrial gas turbines. The analysis of Ni-based superalloys microstructures is an important research task during the design and development of superalloys. The material microstructure information can only be understood by experts in the long history. Image segmentation and recognition are developing techniques for accelerating the microstructure analysis automatically. Although deep learning techniques have achieved satisfactory performance, they usually suffer from generalization, i.e., performing worse on a new dataset. In this paper, a deep transfer learning method which just needs a small number of labeled images is proposed to perform the microstructure recognition on $\gamma \prime$ phase. To evaluate the effectiveness, we homely prepare two Ni-based superalloys at temperatures 900 ${}^{°}$C and 1000 ${}^{°}$C, and manually annotate two datasets named as W-900 and W-1000. Experimental results demonstrate that the proposed method only needs 3 and 5 labeled images to achieve state-of-the-art segmentation accuracy during the transfer from W-900 to W-1000 and the transfer from W-1000 to W-900, while enjoying the advantage of fast convergence. In addition, a simple and effective software for the Ni-based superalloys microstructure recognition on $\gamma \prime$ phase is developed to improve the efficiency of materials experts, which will greatly facilitate the design of new Ni-base superalloys and even other multicomponent alloys.

It is well known that the solution cooling rate has a great effect on the creep life of superalloys. In this research, three typical cooling rates were applied to generate different distributions of γ’ precipitates for creep tests. Ingots used to make specimens were manufactured by hot extrusion, and the master alloy had the composition of an FGH4096 power metallurgy superalloy. SEM and SESD were used to observe the microstructure’s evolution. The experimental results show that the fastest cooling rate corresponds to the highest creep life as well as the smallest rupture strain, and vice versa. The microscopic observations disclose that with an increasing cooling rate, the size and area fraction of γ’ precipitates decrease, and the rupture mechanism changes from transgranular to intergranular. Moreover, some γ’ precipitates changed to cuboid after the creep test. The results will provide new technological processes to design more creep-resistant, nickel-base superalloys.

In this work, two Ni-based superalloys with 13 wt.% and 35 wt.% Co were prepared via selective laser melting (SLM), and the effects of Co on the microstructure and mechanical properties of the additively manufactured superalloys were investigated. As the Co fraction increased from 13 wt.% to 35 wt.%, the average grain size decreased from 25.69 μm to 17.57 μm, and the size of the nano-phases significantly increased from 80.54 nm to 230 nm. Moreover, the morphology of the γ′ phase changed from that of a cuboid to a sphere, since Co decreased the γ/γ′ lattice mismatch from 0.64% to 0.19%. At room temperature, the yield strength and ultimate tensile strength of the 13Co alloy reached 1379 MPa and 1487.34 MPa, and those of the 35Co alloy were reduced to 1231 MPa and 1350 MPa, while the elongation increased by 52%. The theoretical calculation indicated that the precipitation strengthening derived from the γ′ precipitates made the greatest contribution to the strength.