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This study investigated the effects of yttrium addition (0wt%–0.5wt%) on the purification, microsegregation and mechanical properties of K417 cast superalloy. The results showed that the addition of Y could significantly reduce the content of oxygen. Purified K417 superalloy with 4∼7ppm O content was obtained after adding a moderate amount of Y. With the increasing Y addition, the segregation degrees of alloying elements (Ti, V and Mo) dropped as a whole, γ′ phase was refined, and the size and volume fraction of γ/γ′ eutectic increased. The decrease in the degree of Ti segregation and the solid solution of Y in carbide periodicity changed the morphology of carbide. When the Y addition increased from 0wt% to 0.1 wt%, the decrease of O content, the refinement of γ′ phase and the formation of rod carbides increased the high temperature tensile strength of the alloy. When the Y addition increased from 0.2wt% to 0.5 wt%, the production of large-size Y-rich phase reduced the mechanical properties of the alloy. The plasticity of the alloy rised and then decreased with increasing Y addition. The appropriate amount of Y addition was about 0.01wt% to 0.05wt%. • The addition of Y hindered the segregation of alloying elements. • High purity K417 alloy with oxygen and nitrogen content of 5ppm was obtained. • Yttrium addition caused the carbide shape to exhibit periodic change in the shape of a block and a rod. • The formation of rod-shaped carbide promoted the improvement of high temperature tensile strength. [ABSTRACT FROM AUTHOR]

The solidification characteristics and high temperature tensile properties of IN713C superalloy were investigated using directional solidification methods at withdrawal rates of 10, 50 and 100 µm/s, respectively. The results show that carbide morphologies change from block and long strip to short rod and granular with increasing withdrawal rate. The increase of withdrawal rate promotes the microsegregation of Mo, Nb and Zr, and contributes to precipitation of the γ/γ' eutectic and boride. With the withdrawal rate increasing from 10 µm/s to 50 µm/s, the high temperature yield strength, ultimate strength and elongation of the IN713C alloy increased by 11.8%, 18.3% and 64% respectively. The increase of the γ/γ' eutectic and boride lead to slight decrease in strength when the withdrawal rate increased from 50 µm/s to 100 µm/s. The fractographic observation of tensile specimen indicates that the integrate carbide particles are an overwhelming majority at a higher withdrawal rate. When the withdrawal rate decreases, the particles become larger and more secondary cracks are generated. The morphology of carbides affects the tensile fracture mechanism of the alloy. With the decrease of carbide size, the crack source of the IN713C alloy changed from brittle carbides to the interface between carbide and matrix. • The continuous microstructures evolution of IN713C alloy during solidification were obtained. • Appropriate withdrawal rate can simultaneously enhance the strength and plasticity of IN713C alloy. • Strip carbides are the source of cracks, and granular carbides strengthen the superalloy. [ABSTRACT FROM AUTHOR]

To further investigate the microstructure characteristic and solidification mechanism, so as to provide knowledge for the microstructure control of a NiTi-Al based high-temperature structural material, the microstructure of Ni-43Ti-4Al-2Nb-2Hf (at.%) alloy ingots prepared by conventional casting (arc-melting) and directional solidification (DS) at various drawing velocities (2 mm.min-1, 18 mm.min-1, 30 mm.min-1 and 60 mm.min-1, respectively) was investigated by means of electron probe microanalyses. Experimental results reveal that the microstructures are composed of NiTi matrix phase, β-Nb phase and Ti2Ni phase for samples obtained by both conventional casting and DS. Conventional casting has an equiaxial structure, while DS has a slender and acicular cellular structure which grows along the [001] orientation preferentially. Small amounts of white β-Nb phase and black Ti2Ni phase co-exist at the grain boundaries or intercellular regions. With an increase in drawing velocity, the NiTi matrix phase is inclined to grow along (100) and (200) crystallographic planes, and the cellular arm spacing reduce gradually, but the directionality of the solidified structure weakens significantly. The homogeneous dispersion of β-Nb phase and the decrease of Ti2Ni phase in DS samples are beneficial to improving the mechanical properties. Solidification mechanism analysis indicates that the dark grey NiTi matrix phase initially precipitates from the liquid phase, and then the divorced eutectic reaction takes place, which produces the light gray matrix phase and β-Nb phase. Finally, the peritectic reaction happens, which generates the black Ti2Ni phase. The complete solidified path of the alloy is L→ NiTi+L → NiTi+ β-Nb+L → NiTi+β-Nb + Ti2Ni. [ABSTRACT FROM AUTHOR]

To clarify the reaction between molten alloy and ceramic shell in the process of investment casting and control the metallurgical quality of alloy, high-temperature wetting experiments of Ni-based superalloy melt on Y 2 O 3 ceramics with different surface microstructures were carried out. The high-temperature wettability and interfacial interactions at 1873 K between Ni-based superalloy melt and Y 2 O 3 ceramics were studied in the present paper. The results showed that the apparent equilibrium contact angle of alloy melt on the substrate firstly decreases from 90.8° to 75.9° and then increases to 87.7°, with the surface roughness of Y 2 O 3 ceramic substrate changed from 0.859 μm to 2.253 μm. The contact conditions between melts and substrates are in accordance with the Wenzel equation, with the surface roughness of ceramic substrate varied between 0.859 μm and 1.311 μm. When that of the substrate continuously increased from 1.311 μm to 2.253 μm, the contact conditions between alloy melts and substrates were in accordance with the Cassie Baxter equation. Based on component analysis, it was found Al aggregated at the interface between Y 2 O 3 ceramics and alloy melts, resulting in the formation of Y 4 Al 2 O 9 and the change of surface tension of the alloy droplet in the process of high temperature wetting. Proper surface microstructure of the ceramic shell can ensure that the melt has enough filling ability and reduce the melt pollution caused by the reaction between melt and ceramic. [ABSTRACT FROM AUTHOR]

This study investigates the influence of vacuum level on the interfacial reactions between K417 melt and Y 2 O 3 crucibles. The results indicate that the interactions between Y 2 O 3 crucibles and the K417 melt include the physical erosion of the crucible inner wall by the melt, and the chemical dissolution of Y 2 O 3 particles in the melt. During the melting process, the vacuum level significantly affects the interface reaction and composition of the alloy. With the vacuum level increasing from 500 Pa to 0.03 Pa, the content of dissolved Y in the alloy increases from 4 ppm to 600 ppm, the thickness of interface reaction layer increases from 0 μm to 213 μm, and the actual sample composition including for uptake of residual gas contamination gradually decreases. Furthermore, the results strongly indicate that, because of the dissolution of Y element in the melt, the segregation of alloying elements (Ti and V) generally decreases, and the morphology of primary carbide transfers from continuous rods and platelets to discrete blocks. The K417 superalloy ingot melted with Y 2 O 3 crucibles at 0.03 Pa has the best composition and the most stable microstructure. • The interactions between Y 2 O 3 crucible and K417 melt include physical erosion and chemical dissolution. • The vacuum level affects the thickness of interface reaction layer and the content of dissolved Y and O in the alloy. • Vacuum level changes the segregation of alloying elements (Ti and V). • The morphology of primary MC carbides transfers from continuous rods and platelets to discrete blocks remarkably. [ABSTRACT FROM AUTHOR]

To obtain appropriate crucible materials for vacuum induction melting of MCrAlY alloys, four different oxide ceramics, including MgO, Y2O3, Al2O3, and ZrO2, with various microstructures were designed and characterized. The high-temperature wettability and interactions between Ni-20Co-20Cr-10Al-1.5Y alloys and oxide ceramics were studied by sessile drop experiments under vacuum. The results showed that all the systems exhibited non-wetting behavior. The contact angles were stable during the melting process of alloys and the equilibrium contact angles were 140° (MgO), 148° (Y2O3), 154° (Al2O3), and 157° (ZrO2), respectively. The interfacial reaction between the ceramic substrates and alloys occurred at high temperature. Though the ceramics had different microstructures, similar continuous Y2O3 reaction layer with thicknesses of about 25 μm at the alloy-ceramic interface in MgO, Al2O3, and ZrO2 systems formed. The average area percentage of oxides in the alloy matrices were 0.59% (MgO), 0.11% (Al2O3), 0.09% (ZrO2), and 0.02% (Y2O3), respectively. The alloys, after reacting with MgO ceramic, had the highest inclusion content, while those with the lowest content were in the Y2O3 system. Y2O3 ceramic was the most beneficial for vacuum induction melting of high-purity Y-containing Ni-based alloys. [ABSTRACT FROM AUTHOR]

A novel crucible-shell "integrated" mold for rapid preparation of supercharged turbines was quantitatively characterized, and the interaction mechanism between refractory and melt was systematically analyzed. The results show that Inconel 713C superalloy is not easy to react with aluminum silicate fiber crucible, and the interaction between them is physical penetration. At the same time, the slag balls in the crucible are easy to peel off into the alloy and form inclusions. The reaction between Inconel 713C superalloy and shell surface material (ZrSiO 4) can be divided into Penetration, Stalling/dissolution, Reaction and Diffusion stages. The interface reaction layer is composed of Nb 2 O 5 , Al 2 O 3 , ZrO 2 , Cr 2 O 3 and TiO 2. The oxide elements produced by the reaction come from the alloy and ceramic shell. Compared with the traditional preparation of turbocharger turbine under discontinuous vacuum, the use of "integrated" mold to prepare turbine under continuous vacuum environment reduces the oxygen, nitrogen and hydrogen content of castings, and the purity of Inconel 713C superalloy is higher and the preparation time is faster, which is conducive to industrial production, which can shed new lights on choosing alternative refractory material for the rapid preparation of high-purity superalloys. • A novel crucible-shell "integrated" mold and its influence on Inconel 713C superalloy's purity were systematically characterized for the first time. • The interaction between alloy and aluminum silicate fiber crucible mainly exists as physical exfoliation of aluminum silicate fibers and slag balls. • The interaction between alloy and ZrSO 4 shell can be divided into penetration, spalling/dissolution, reaction and diffusion stages. • High purity Inconel 713C superalloy was successfully obtained by preparation under continuous vacuum condition. [ABSTRACT FROM AUTHOR]