GH4065A is a newly developed high-performance cast-wrought Ni-base superalloy with ultra-low C and N content used for advanced turbine engine disc. In this study， the alloy’s inclusions of the alloy are characterized and statistically analyzed. To investigate the fatigue fracture mechanism， strain-controlled fatigue tests are conducted at 400 ℃ and 650 ℃ on the fine-grained and coarse-grained samples respectively. The results show that the alloy’s inclusions of the alloy are mainly nitrides. For the fine-grained samples， discrete nitride particles and clustered nitrides both with a critical size larger than the average grain size are responsible for the fatigue crack initiation. When subjected to high-level strains （≥0.9%）， fatigue failure primarily originates from surface nitrides， with rare occurrences of boride and oxide initiation. Surface crack induced by Al₂O₃， rather than boride or MgSiO₃， is found to significantly reduce the fatigue life. Higher fatigue temperature results in reduced life cycles. When under lower levels of strain， however， subsurface/internal nitride-facet initiations dominate and fatigue life is prolonged by the elevated temperature. In the coarse-grained samples， fatigue failures at 400 ℃ are found to be initiated by quasi-cleavage cracking mechanism. Due to the increased grain size， the inclusion-induced crack initiation is suppressed while slip-induced cleavage cracking mechanism becomes predominant.

To investigate the effects of aluminizing coating on the surface integrity and rotational bending high cycle fatigue performance of DD6 alloy， the chemical vapor deposition method is used to aluminize DD6 fatigue samples after standard heat treatment. The cross-sectional microstructure and elemental distribution of DD6 alloy samples with aluminizing coating are analyzed using SEM and EDS， and the high cycle fatigue properties of the uncoated and coated samples are tested at 760 ℃ and 980 ℃， respectively. The results show that the surface area of the sample with aluminizing coating is mainly divided into two layers： inner and outer. The outer layer is mainly composed of the β-NiAl phase， and the inner layer is a diffusion layer， containing many solid solution strengthening elements. The aluminizing coating can slightly reduce the rotational bending high cycle fatigue performance of the alloy at 760 ℃ and 980 ℃ and has a significant impact on the fatigue life in the high-stress amplitude region and a small impact on the low-stress amplitude region. The coupling effect of surface roughness， oxidation damage， and element interdiffusion is the fundamental reason for the difference in fatigue life between uncoated and coated samples.

The hot isostatic pressing process is a usual powder Ti₂AlNb alloy preparation method to deeply study the influence of factors such as the powder-making process on the properties of Ti₂AlNb powder alloy.Ti₂AlNb pre-alloyed powders are prepared by plasma rotating electrode process and electrode induction melting gas atomization， respectively， and their mixed powders are characterized. Ti₂AlNb alloy is prepared using a hot isostatic pressing process.The effects of the powder-preparing process， porosity， and inclusion on the microstructure and mechanical properties of the Ti₂AlNb alloy are investigated. Optimized processes are employed for the forming of various Ti₂AlNb powder metallurgy components. Experimental results show that the powder-making processes affect the durability of the powder alloy， the pore defects caused by slight capsule gas leakage significantly reduce the mechanical properties of the powder Ti₂AlNb alloy， and the inclusions obviously affect the consistency and stability of the room-temperature tensile properties of the powder alloy.