Abstract
The effect of solidification behavior on the microstructures and mechanical properties of Ni-Cr-Fe superalloy investment casting is given. Metallographic and image analysis have been used to quantitatively examine the microstructures’ evolution. For the parts with the thickness of 3 mm and 24 mm, the volume fraction and maximum equivalent radius of the Laves phase increases from 0.3% to 1.2%, from 11.7 μm to 23.4 μm, respectively. Meanwhile, the volume fraction and maximum equivalent radius of carbides increase from 0.3% to 0.5%, from 8.1 μm to 9.9 μm, respectively. In addition, the volume fraction of microporosity increases from 0.3% to 2.7%. As a result, the ultimate tensile strength is reduced from 1125.5 MPa to 820.9 MPa, the elongation from 13.3% to 7.7%, and the quality index from 1294.2 MPa to 954.0 MPa, respectively. A typical brittle fracture is observed on the tensile fracture. As the cooling rate decreases, the microstructures become coarser.
Highlights
Ni-Cr-Fe superalloy is extensively used in aerospace engines, heavy-duty gas turbines, nuclear power plants, and petrochemical engineering owing to its microstructural stability, good oxidation resistance, and high excellent mechanical properties [1,2]
After the filling and feeding system being cut, the superalloy casting was treated with standard heat treatment via homogenizing treatment at 1095 ◦ C for 2 h, solution at 955 ◦ C for 1 h and aging treatment consisting of 720 ◦ C for 8 h/furnace cooling at 55 ◦ C·h−1 to 620 ◦ C for 8 h before air cooling to room temperature
After the filling and feeding system being cut, the superalloy casting was treated with standard heat treatment via homogenizing treatment at 1095 °C for 2 h, solution at 955 °C for 1 h and aging
Summary
Ni-Cr-Fe superalloy is extensively used in aerospace engines, heavy-duty gas turbines, nuclear power plants, and petrochemical engineering owing to its microstructural stability, good oxidation resistance, and high excellent mechanical properties [1,2]. The section dimension of the casting changes greatly from one part to another owning to the complex structure, which often results in different solidification behavior, multifarious microstructure, and mechanical properties. The effect of solidification behavior on the microstructure and mechanical properties of superalloy casting has been presented in much of the literature concerning the elemental segregation, phase selection and defect formation [4,5,6]. Litao Chang et al [6] investigated the solidification behavior of 720Li superalloy, and pointed out that the formation of γ/γ-eutectic was related with the solute redistribution and enrichment of Al and Ti elements in the residual liquid. A systematic study was carried out to clarify the effect of solidification behavior in different parts on the microstructure evolution and mechanical properties of Ni-Cr-Fe superalloy investment casting
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