Experimental Study on FGH95 Superalloy Turbine Disk Joint Material by Oblique Laser Shock Processing

The FGH95 superalloy used for turbine disk manufacturing was strengthened by the oblique laser shock processing (OLSP). The laser energy, beam diameter, and number of impacts were selected as the test factors, and the three-factor three-level oblique laser shock processing orthogonal test was carried out. Based on the analysis of variance and range of the surface residual stress, microhardness, roughness, tensile strength, and yield strength of FGH95 superalloy after LSP, the factor level combination of relative best comprehensive performance was obtained. The results showed that, within the 10% confidence level, the order of influencing factors with significant difference is: laser energy > number of impacts > beam diameter. Compared with the unimpacted sample, the microhardness of the material surface was increased by about 25% after OLSP. With the increase of laser energy, the dimple distribution of the sample was more uniform, smaller in size, and shallower in depth. However, the thickness of the affected layer was very low, and there was no significant effect on the tensile properties. In general, and under the test conditions selected in this study, the combination of 8 Joule laser energy, 3 mm beam diameter, and three impacts can be selected to obtain the best comprehensive performance. The results of this paper provide a reference for the OLSP of the FGH95 superalloy turbine disk and other aero engine parts.

Influence of Long-term Aging on Microstructure and Creep Behaviors of FGH95 Nickel-based Superalloy

By means of long-term aging treatment, creep properties measurement and microstructure observation, the influences of long-term aging on the microstructure and creep behaviors of FGH95 Superalloy are investigated. Results show that the fine γ′ particles dispersedly precipitate in the alloy after fully heat treated, and coarser γ′ phase discontinuously distribute along the grain boundaries. After the alloy is long-term aged at 723 K for 500 h, the fine γ′ phase with better cube degree and carbide particles distribute dispersedly in the alloy to enhance the creep resistance of the alloy for possessing a longer creep lifetime at the condition of 923 K and 1034 MPa. The deformed feature of the alloy is that configurations of slipping dislocations and the stacking fault appear in the alloy. As the creep goes on, the cracks initiate and propagate along the boundaries due to dislocations tangling in the grain boundaries for bringing out the stress concentration.

Effects of Cooling Methods on Microstructure and Lattice Parameters of FGH95 Superalloy

By means of different cooling methods, microstructure observation and X-ray diffraction analysis, an investigation has been made into the influences of the cooling methods on the microstructure and lattice parameters of FGH95 superalloy. The results shown that, after the solution treated alloy is cooled at different mediums, fine γ′phase and carbide particles dispersedly distribute in the grain and coarser γ′phase discontinuously precipitates along grain boundaries. After X-ray diffraction analyzed, the γ and γ′phases in “molten salt cooling” alloy possess larger lattice parameters, and a bigger lattice misfit exists in the interface between the γ and γ′phases.

Modeling of Flow Stress of Spray-Forming FGH95 Superalloy under Hot Compression

The hot compressive deformation behavior of the superalloy was investigated at the temperature range from 1050 to 1140 and strain rate range from 0.01 to 10s-1 on Gleeble-1500 thermal simulator. Utilizing hyperbolic sine function and introducing the strain with 4th order polynomial fitting, the constitutive equations of flow stress of spray-forming FGH95 superalloy at high temperature were established. The results show that during the hot compression deformation of the superalloy, the characteristics of dynamic softening were observed, and flow stresses decrease with increasing temperature and decreasing strain rate. The flow stress of the superalloy predicted by the proposed models with 4th order polynomial fit agree with the experimental value well, and the average relative error is 3.64%.