Papers by Keyword: γ'

Abstract: Morphology of phase-separated microstructure consisting of cubic disordered A1 and ordered L1₂ phases and tetragonal ordered D0₂₂ phase in Ni-V-X (X=Al, Si) alloys has been investigated by transmission electron microscopy. Ternary Ni-V-Al alloy showed the lamellar structure of D0₂₂ phase with spherical L1₂ particles, while Ni-V-Si ternary alloy indicated the anisotropic microstructure consisting of plate- or diamond-shaped D0₂₂ and plate-shaped L1₂ phases. When a part of element Al is substituted by Si, the morphology of three-phase microstructure (A1/L1₂/D0₂₂) varied depending on the amount of element substitution. When Ni-16.1V-4.0Al-2.8Si (at.%) alloy was aged at 1173K for long time, D0₂₂ plate-like particle aligned along <110> direction and L1₂ particles formed between them in the shape of sphere. In the case of Ni-16.6V-2.8Al-4.0Si (at%) alloy more substituted for Al by Si, cuboidal L1₂ phases were first formed aligning along <100> direction and then plate-shaped D0₂₂ phases precipitated along the <100> direction in the channel of cuboidal L1₂ particles. Such morphological changes with the substitution of the third elements X by Al or Si were able to be explained based on lattice mismatch.

Abstract: This work was studied for the changes of thermal properties on GTD-111 DS (Directional Solidification) gas turbine blade. In this study, gas turbine blades with 24,000~34,000 firing hours was used to get more effective result, gradually applied hot isostatic pressing (HIP) and post-heat treatment for these samples. In the latter steps, we observed changes of γ´ phase affected in material properties, and microhardness test was carried out to evaluate mechanical properties according to changes of γ´ fraction and shape. Experimental result shows, changes of γ´ fraction and shape were affected by HIP and post-heat treatment. And also mechanical properties changes such as micro-hardness related to γ´ phase. In this study, we explained changing transition of microstructure according to γ´ fraction distribution.

Abstract: Inconel 718(Ni-19Cr-18Fe-3Mo-5Nb-1Ti-0.5Al) nickel-base superalloy strengthened mainly by Ni3Nb type γ″ and partially by Ni3Al type γ′ precipitation is today’s most widely used superalloy in the world. China has paid special attention on Inconel 718 research and development. Systematic long-term research project has been conducted in close cooperation among our university, research institutes and factories. The goal of this long-term project is in 2 steps. First step is to improve Alloy 718 to get high quality and the second step is for improving the alloy temperature capability from 650oC to 680-700oC. The basic idea for alloy improvement is still to keep the chemical composition in the range of specification by small adjustment or control of minor elements, such as S, P, N, Si and Mg. The main achievements are segregation control by adjustment of S, P, Si, control of N for cleanliness, micro-alloying of Mg for grain boundary strengthening and control of low S and high P for stress rupture life improvement. Modification of Alloy 718 is based on structure stability study and its improvement in adjustment of main second phase strengthening alloy elements Nb, Ti and Al in total amount and the ratios among them. The goal is to achieve more stable second phase strengthening by control of alloy elements. Experimental results show that the future of modified 718 alloys is very attractive to raise the temperature capability improvement from 650oC to 680-700oC.