Energy Materials 2017: Materials for Gas Turbines: Poster Session
Sponsored by: Chinese Society for Metals
Program Organizers: Jeffrey Fergus, Auburn University; Ji Zhang, China Iron and Steel Research Institute Group

Monday 6:00 PM
February 27, 2017
Room: Hall B1
Location: San Diego Convention Ctr

Session Chair: Jeffrey Fergus, Auburn University

C-11: Effect of Thermal Debinding and Sintering Conditions on Mechanical Properties of Silica-based Ceramic Cores: Jeong-gu Yeo1; JeongSoo Park2; Young-Hwan Kim1; 1Korea Institute of Energy Research; 2Chungnam National University
    Complex shaped ceramic cores are prepared to make internal cooling passages for gas turbine parts. It is investigated in this study the effects of debinding and sintering conditions on silica-based ceramic cores. Green bodies are prepared by ceramic injection molding with fused silica, zircon flour and thermoplastic binders. Green bodies are debinded and sintered with various heating rates, heating times and temperatures. Surface defects are observed after debinding and sintering steps. Flexural strength, microstructural observation and X-ray diffraction patterns are examined with sintered bodies. The crack-free ceramic cores are successfully obtained.

C-12: Microstructures and Deposition Mechanisms of Thermal Barrier Coatings Produced by PS-PVD: Xiaohu Yuan1; 1DongFang Turbine Co., Ltd., DongFang Electric Corporation
    Thermal barrier coatings (TBCs) are used to protect metallic components in land-based and aero-engines, such as vanes and blades from hot gas. TBCs are usually produced by plasma spray (PS) and electron beam physical vapor deposition (EB-PVD). Recently, plasma spray physical vapor deposition (PS-PVD) technology have emerged and exhibited very promising potential in fabricating thermal barrier coatings (TBCs) with well tailored microstructure architecture. In this work, the microstructures and deposition mechanisms of TBCs by PS-PVD were investigated. The microstructure evolution model along both axial and radial directions was built and associated mechanism for the formation of microstructure discussed. A quasi-columnar structure was deposited under a moderate spray condition, with the columnar grain size of less than 20 microns, which revealed satisfying thermal barrier effect comparable to PS TBC and superior thermal shock resistance comparable to EB-PVD TBC.

C-13: Mullitization of Fused Silica on Silica-based Ceramic Cores by Colloidal Alumina Infiltration: Jeong-gu Yeo1; JeongSoo Park2; Young-Hwan Kim1; 1Korea Institute of Energy Research; 2Chungnam National University
    Fused silica has been used to make ceramic cores which formed internal passages for cooling of turbine parts, due to its low thermal expansion coefficient. Surface of fused silica is crystallized to cristobalite at high sintering temperature above 1300 degree Celsius. In the presence of the crystalline phase, it is well knwon that the phase transformation is accompanied by 5% contraction in volume. The volume contraction causes microcracks as well as shrinkage. In this research, the crystallization is controlled by colloidal alumina infiltration technique. The alumina particles are coagulated to silica at pH 4 due to their opposite zeta potential. The coagulation is likely to form (synthesize) mullite, in other words mullitization, instead of crystallization to cristobalite, during sintering at 1300 degree Celsius. Consequently, inhibition of crystallization by mullitization improves the flexural strength and reduces the shrinkage of silica-based ceramic cores.

C-14: Solidification Behavior and Microstructure of Inconel 625 Superalloy under Electromagnetic Field: Tao Wang1; Fei Wang1; Engang Wang1; 1Northeastern University, China
    The solidification behavior and microstructure of Inconel 625 superalloy under electromagnetic field with different electric current and frequency was investigated in laboratory with a undirectional mold. The experimental results show that most of the microstructure of Inconel 625 alloy changed from columnar dendrites to equiaxed grains as applied electromagnetic stirring, and the average equiaxed grain size is greatly refined. The real-time temperature measurement during the solidifying of Inconel 625 superalloy show that the inner temperature distribution in mold is more uniform when the electromagnetic field is applied. The main precipitated phases in Inconel 625 alloy, such as nitride(MN), carbide(MC) and (γ+Laves) eutectic structure, also have changed as applied electromagnetic stirring. The quantity and area proportion of (γ+Laves) and MC is reduced when the electromagnetic field is applied with a suitable current and frequency. The relative mechanism of action is also analyzed.

C-15: Study on the Undercoolability and Single Crystal Castability of Nickel-Based Superalloys: Wang Haiwei1; Ma De-Xin1; Yang Gong-xian1; Gong Xiu-fang1; Zhang Qiong-yuan1; 1Dongfang Turbine Co., Ltd.
    The critical undercooling degree (ΔTN) of nickel-based superalloys has a great relationship with the single crystal castability. This experiment studied the ΔTN of DD483, CMSX-4 and CMSX-6, also analyzed the factors affecting ΔTN, including chemical composition, shell materials and remelting cycle. The results show that when experiment conditions of pouring temperature and shell materials remains the same, three kinds of superalloys have different undercoolability, and the order of the critical nucleation undercooling degree from high to low is CMSX-6, CMSX-4, DD483. Because of the influence of wettability between alloy melt and shell, ΔTN of CMSX-4 in the pure Al2O3 shell is greater than which in EC95 mould (95% pure corundum + 5% quartz). With increasing the number of remelting, shell aging may pollute the alloy melt, leading to a decline in the undercoolability of the alloy.

C-16: Temperature Dependence of the Fracture Behavior of X-750 Alloy and Effect of Heat Treatment: Christopher Marsh1; Djamel Kaoumi2; 1University of South Carolina; 2North Carolina State Univeristy
    X-750 is a nickel-chromium based superalloy applied in a variety of applications such as gas turbines, rocket engines, nuclear reactors. The fracture mechanism of X-750 was investigated at different temperatures both on heat-treated and non-heat-treated samples. Uniaxial tensile tests were conducted from room temperatures up to 900C; fracture surfaces were analyzed by means of SEM observations. The microstructure of both HT and NHT materials were studied utilizing SEM and TEM. Between room temperature and 650C, the fracture surface of HT material evolves from purely intergranular to purely transgranular, while the rupture of the NHT is due to the coalescence of voids induced by decohesion at the MC carbides/matrix interface. Environmentally-induced intergranular cracking and ductility minimum were observed at 750C for both NHT and HT specimen. At higher temperatures such as 900C, the grain boundary mobility during dynamic recrystallization increases and leads to rupture by grain boundary slipping.