Papers by Keyword: Superalloy

Abstract: Functionally gradient materials (FGMs) composed of 3YSZ and IN713LC were developed in three different configurations. A linear-mode FGM had its compositions with a monotonic change in coefficient of thermal expansion (CTE). Negative- and positive-deviated FGMs had their compositions with lower and higher CTEs, respectively, on the ceramic sides. Fracture behaviors of these three types of FGMs were evaluated with aids of residual stress analyses. FGMs with a positive CTE deviation demonstrated the best performance in the experiment. The brittle ceramic side was under high compressive stress, and high tensile stresses were primarily initiated in the metal-rich gradient layers.

Abstract: The optimized condition has been researched, for welding super alloys (Inconel 600, Inconel 625 and Haynes 230), which are used for liquid thruster of an artificial satellite. In the experiment of “bead-on-plate”, these materials are welded using continuous Nd:YAG laser and electron beam. The penetration depth and bead width are measured by optical microscope. The hardness of 1mm depth from welding surface is measured by micro Vickers hardness tester. The tension is tested for measuring the strength of welding part. The tension strength of welding specimen using the Nd:YAG laser is compared with that of the welding specimen using the electron beam.

Abstract: Mechanical and thermal treatments during the manufacturing process inevitably cause the accumulation of residual stresses in parts consisting of materials with complex microstructures. Neutron diffraction is particularly well suited to determine residual stress distributions within the bulk of the component. Due to the nature of a diffraction experiment an inextricable mixture of type I and II residual stresses is measured. The accumulation of type II stresses (microstresses) is strongly related to the microstructure. The impact of changes in the microstructure on neutron diffraction experiments has been investigated on Inconel 718 (IN718) samples.

Abstract: A cast nickel based superalloy M963 was coated by high-velocity oxy-fuel (HVOF) spraying process. The effect of HVOF MCrAlY coating on thermo-mechanical fatigue (TMF) and isothermal fatigue (IF) in M963 was studied to understand fatigue life and failure mechanisms in coated and uncoated M963 alloy. Two types of TMF tests, i.e. in-phase (IP) and out-of-phase (OP), were performed in temperature range of 450~900°C, and IF tests were conducted at 900°C. It was found that the coating had a detrimental effect on fatigue life under OP TMF, while a beneficial effect of the coating existed under IP TMF and IF. Crack initiation time in the coated specimen was shorter than that in the uncoated specimen and the former’s crack density was higher than the latter’s one under OP TMF. The relationship of deformation and fracture response with fatigue life was discussed based on microscopic analysis.

Abstract: Green cutting is ecologically desirable and have been a tendency in the industry field. Water vapor can be introduced in metal cutting as coolant and lubricant due to its pollution-free, generating easily and unneeded disposal. Therefore, water vapor is an environment-friendly coolant and lubricant in machining. This study attempts to understand the effect of water vapor as coolant and lubricant on chip formation. In the comparison experiments to dry and wet cutting, water vapor jet flow from a developed generator is applied into cutting zone directly. When YG8 (K20 in ISO) tools are used to turn titanium alloy TC4 (Ti-6Al-4V), Ni-based super alloy GH3030 and stainless steel 1Cr18Ni9Ti in orthogonal cutting, through quick-stop tests, the photos of polished chip sections microstructure were obtained. And the results suggest that the application of water vapor produces the least BUE, tool-chip contact length but the largest deformation coefficient and shear angle. The water vapor as coolant and lubricant could be a substitution of cutting fluid to carry out green cutting in the machining of difficult-to-cut materials.

Abstract: Transmission electron microscopy was used to study various morphologies of ordered precipitates in Ni3Al-Cr intermetallic alloy. It was found that γ’ precipitates in the interdendritic regions have the microstructure of a nickel base superalloy with its characteristic features. In addition to the primary γ’ precipitates some fine secondary precipitates were found.

Abstract: Hot isostatic pressing (HIP) is the established procedure to process Udimet 700 Powder by Powder Metallurgy (P/M) techniques. In this paper the method of hot explosive pressing (HEP) was applied. Its main feature is the direct method of explosive pressing. To avoid any reaction beforehand, the heating device and the explosive compaction device are separated and brought together very rapidly just a few milliseconds before ignition of the explosive charge. Udimet 700 bulk samples are obtained and investigated by metallographic and mechanical testing.

Abstract: Although the γ"(D022) phase has been known as a strengthen phase for the turbine disk of wrought Ni-base superalloys, the computer simulation of the γ"(D022) precipitation is hardly performed. In this study, it is demonstrated that the phase-field modeling of the complex microstructure developments including γ"(D022) precipitation in Ni-V-X (X=Co,Nb,Fe) alloys. The simulation results obtained are as follows: (1) The complex morphologies of the γ(A1)+γ"(D022) two-phase microstructure, such as the maze-microstructure, the chessboard-microstructure, and the chessboard-like microstructure, in Ni-V-X (X=Co,Nb,Fe) alloys are simulated reasonably by using phase-field method. (2) The morphology of the microstructure is mainly controlled by the elastic strain energy induced from the lattice mismatch. In particular, the tetragonal distortion is a key parameter to control and understand the complex microstructure changes.

Abstract: A recent developed Ni-Cr-Co-Mo-Nb-Ti-Al type nickel-base superalloy, INCONEL 740, has been selected for the application of USC boilers at the temperature above 750°C. This paper focuses on the structure stability improvement of this alloy. Phase computation by Thermo-Calc has been adopted to study main influencing factors on precipitating phases of the alloy and the results show that the ratio of Al/Ti plays an important role. Four new modified alloys in adjustment of Al and Ti contents and in control of Si level were designed and melted for experimental study. The results indicate that the modified alloys exhibit more stable structure stability at 750, 800 and 850°C long time exposure. The newly developed alloy can be adopted for engineering production and application for USC power plants at temperature above 750°C.