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The effect of two heat treatment processes on microstructures and tensile behaviors of K465 superalloy was investigated and compared. The results show that hot isostatic pressing (HIP) process partly or completely eliminated the micro-porosity to densify K465 alloy, and can effectively reduce the size of γ′ phase and improve the tensile strength and plasticity of K465 alloy. Electron probe micro-analysis (EPMA) studies revealed that the element segregation ratio was smaller in the HIP process alloy than that in the ordinary process alloy. nanoindentation tests revealed that elastic modulus and the hardness in the interdendrite of K465 alloy for HIP process were higher than that for the ordinary process.

To study quantitatively the effect of heat treatment on the microstructure, composition and mechanical property in a new single crystal nickel-based superalloy for industrial gas turbine (IGT) applications, the eutectic fraction, carbide fraction, and the fraction, size, shape and distribution of the γ ́ phase was characterized by quantitative metallographic method, the evolution of chemical composition and hardness between core and inter dendrite was tested through EMPA and nanoindentation. The experimental results indicate that: The eutectic fraction decreases from (0.52±0.08) % to (0.03±0.01) %. The carbides fraction decreases from (0.23±0.04) % to (0.12±0.03) %, and Feret ratio decreases from 3.21±2.54 to 2.14±0.98. The γ ́ fraction increases from (55.66±4.18) % to (73.78±3.24) % in core dendritic region, from (64.82±1.44) % to (70.11±3.10) % in inter dendritic region. The γ ́-size is 406±111(nm) in core dendritic region and 918±384(nm) in inter dendritic region before heat treatment, 359±69(nm) in core dendritic region and 361±57(nm) in inter dendritic region after heat treatment. The γ ́-cuboidal degree is 1.08±0.20 in core dendritic region and 1.14±0.23 in inter dendritic region before heat treatment, 1.08±0.19 in core dendritic region and 1.02±0.14 in inter dendritic region after heat treatment. The solidification segregation coefficient of main segregation elements, such as Re, W, Hf, Ta, Al, and Mo, is closer to 1, with an average decrease of 27% after heat treatment. The hardness and modulus increase in core and inter dendritic, and their inhomogeneity is reduced between cores and inter dendritic. The improvement of properties result from the improvement of size uniformity and cuboidal degree of γ ́, and the reduction of carbides and eutectic through element homogeneity during heat treatment. The solidification segregation coefficient of main segregation elements, such as Re, W, Hf, Ta, Al, and Mo, is closer to 1, with an average decrease of 27% after heat treatment. With the addition of refractory elements, some elements partition to the dendrite core, while other elements tend to accumulate in the interdendritic liquid and then solidify as the interdendritic and eutectic regions during solidification. The hardness and modulus increase in core and inter dendritic, and their inhomogeneity is reduced between cores and inter dendritic. The improvement of properties result from the improvement of size uniformity and cuboidal degree of γ ́, and the reduction of carbides and eutectic through element homogeneity during heat treatment.

ZTC4 alloy prepared by electron beam melting was hot isostatically pressed, the macro-and microstructure were characterized by stereo microscopy and optical microscopy, the tensile properties were tested and the fracture profiles were characterized using scanning electron microscopy. The results show that: The vertical deposition samples exhibit coarsen epitaxial columnar grains and the parallel samples show equiaxed grains, and microstructure are basket-weave α+β phase. The vertical deposition samples exhibit very high ultimate tensile strength and yield strength but poor ductility with elongation and shrinkage, and show generally more planar and faceted fracture morphology. The anisotropy in tensile properties is mainly due to the difference in the orientation of the columnar grains with respect to the tensile test direction, and the characteristics of the minor fracture plane are mainly related to the α colonies.

The morphology of microstructure and PAG was observed by means of LEICA DMIRM metallurgical microscope, the phase was measured by D8 ADVANCE X-ray diffractometer (XRD), and the martensitic transformation point is tested on DIL805A dilatometer after ST. The results show that the PAG size of C250 steel has not a clear growth. The recrystallisation has the priority of nucleation in the PAG boundary. The morphology of martensite presents irregular bans and stringers before recrystallisation, whereas presents blocky thereafter. The intermetallic compounds re-dissolve by ST. With the prolonged of ST time, the Ms point increases before recrystallisation, decreases thereafter; the Mf point does not have a clear change.