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

Monday 2:00 PM
February 27, 2017
Room: 13
Location: San Diego Convention Ctr

Session Chair: Brian Gleeson, University of Pittsburgh; Bruce Pint, Oak Ridge National Laboratory

2:00 PM  
Development of a New High Strength and Hot Corrosion Resistant Directionally Solidified Superalloy DZ409: Juntao Li1; Jiantao Wu1; Ping Yan1; Jianxin Dong2; Lei Wang3; Qiang Zeng1; 1China Iron & Steel Research Institute Group; 2University of Science and Technology Beijing; 3Northeastern University
    A Ta-free directionally solidified superalloy, designated DZ409, was recently developed by Central Iron & Steel Research Institute(CISRI) for heavy IGT(Industry Gas Turbine) blades application. Based on the principles of materials design, several alloy compositions were designed with the control of Ti/Al and W/Mo ratio and partial substitute Ta for Nb. The resultant nominal composition of DZ409 alloy contains 0.1C, 15Cr, 9.5Co, 4.5W, 1.5Mo, 3Al, 4.5Ti, 2Nb, 2Ta and bal.Ni in a weight percentage. The alloy exhibits excellent high temperature mechanical properties, oxidation resistance and hot corrosion resistance properties. Under the condition of 75%Na2SO4+25%NaCl cycled coated at 950℃, the mass loss of DZ409 is similar to DS GTD111. After aging at 950℃for 5000h, no TCP phases were observed, indicating that DZ409 alloy possesses a good microstructure stability.

2:40 PM  Invited
Deposit-Induced Hot Corrosion and Materials Design Strategies to Reduce Its Impact: Brian Gleeson1; 1University of Pittsburgh
    Hot corrosion is an accelerated degradation process that is generally considered to involve deposition of corrosive species (e.g., sulfates) from the surrounding environment to the surface of hot components, followed by destruction of the protective oxide scale. Gas turbine engine components, particularly high-pressure turbine blades and rotors, exposed to harsh environments are apt to encounter two modes of hot corrosion: high temperature hot corrosion (Type I) in the temperature range 850-1000C and low temperature hot corrosion (Type II) in the range 600-800C. This presentation will overview recent research conducted at the University of Pittsburgh to advance understanding of sulfate-based deposit-induced hot corrosion. It will be shown that new insights on alloy/coating composition-structure relations for enhanced corrosion resistance have been established.

3:10 PM  Keynote
Development of High Strength Hot Corrosion Resistant Single Crystal Superalloys Based on Understanding the Effect of Key Elements on Hot Corrosion Behavior: Jianxiu Chang1; Dong Wang1; Langhong Lou1; Jian Zhang1; 1Institute of Metal Research, Chinese Academy of Sciences
    Hot corrosion behavior of several Ni-base single crystal (SX) superalloys with different Cr, Ta and Re contents was investigated using the “deposit recoat” method at 900 oC. It was shown that both Re and Ta can improve the hot corrosion resistance of SX superalloys. The advantage to hot corrosion properties of adding Ta depended on Cr content in the superalloys. Ta was found to exhibit a beneficial effect by promoting the formation of NaTaO3 and TaS2, and therefore inhibiting the formation of liquid Na2MoO4 and Ni-sulfides. Re may alter the activities of elements, and therefore delay the deformation and cracking of the oxide scale, and may enable the self-healing of oxide scale. Based on understanding the hot corrosion mechanism of superalloys, we have developed the first and second generation hot corrosion resistant SX superalloy (DD410 and DD420), which exhibit good high temperature strength, microstructural stability and hot corrosion resistance.

3:30 PM Break

3:50 PM  Invited
Advanced Characterization of the Hot Corrosion Behavior of Gas Turbine Alloys under Burner Rig Test Exposures: Maryam Zahiri Azar1; Kliah Soto Leytan1; Daniel Mumm1; 1The University of California, Irvine
    A low-velocity burner rig test was employed for evaluation of the hot corrosion resistance of selected classes of gas turbine alloys. In this test, standard seawater was sprayed into the combustion chamber for the salt contaminant. Modern characterization techniques were utilized to observe and quantify the hot corrosion attack of the tested materials, and study the degradation mechanisms active for each material system. Of particular interest was correlating the kinetics and mechanisms of hot corrosion attack with the details of the exposure conditions (temperature excursions, sulfur concentration in the fuel, etc.). Furthermore, commercial turbine blades with similar alloys, exposed to real marine gas turbine service environments, were studied and compared to the burner rig tested materials. The burner rig test is validated as appropriate to get comparable materials evolution and degradation behavior results with the real service conditions of gas turbine engines, for assessing alternative materials and coatings.

4:20 PM  Invited
Efforts to Introduce TiAl Alloys for Gas Turbine Applications: Ji Zhang1; Helena Oskarsson2; 1China Iron and Steel Research Institute Group; 2Siemens Industrial Turbomachinery AB
    The development of more efficient gas turbins is where the titanium aluminide alloys come into play as improved fuel efficiency always translates into a need for less weight and higher operating temperatures. This presentation reviews the efforts of China Iron and Steel Research Institute Group and Siemens Industrial Turbomachinery AB to introduce this new material into the low pressure turbine design. The major threats to in-service integrity for TiAl alloys, especially for those made by casting, particular those are posed by the lack of low temperature ductility, acceleration of high temperature creep and high cycle fatigue randomness have been considered and evaluated by laboratory and rig tests. Accordingly, this study demonstrated that developing cast lamellar microstructures with lamellar interfaces parallel to the casting surfaces and meanwhile employing the effects of minor Carbon additions is significant to overcome the TiAl alloys’ unfavorable complications for gas turbine applications.

4:50 PM  
Effect of Alloying Elements (Cr and Al) in Nickel-based Alloys in Molten Sulfate Environments: Kuldeep Kumar1; Hojong Kim1; 1The Pennsylvania State University
    Extreme thermal and chemical environments in gas turbines cause premature failure of turbine materials due to hot corrosion. Contaminants in the fuel during combustion are converted to molten salt deposits composed of low melting alkali halides and sulfates. This study will report the interfacial degradation reactions at the substrate/molten sulfate interface using electrochemical techniques of linear polarization, impedance spectroscopy, and cyclic voltammetry, to elucidate the impact of alloying elements in controlling the degradation reactions at 700 C. This study was guided by the hypothesis that the interfacial degradation behavior is dictated by electrochemical reactions due to the dissociation tendency of molten sulfates (Na2SO4 → 2Na+ + SO42-). The electrochemical corrosion properties will be correlated with exposure tests by characterizing corrosion products using SEM/EDS, XRD, and thermal analysis. Both the electrochemical and exposure tests were conducted in eutectic LiCl-KCl with the addition of 10mol% Na2SO4 under reactive gaseous atmosphere (O2-0.1%SO2).

5:10 PM  Invited
The Materials, Manufacturing and Equipments of the Large Disk Forgings for Industrial Gas Turbines: Shichong Yuan1; 1China National Erzhong Group Co.
    In the 21st century, gas turbines(GT) have become the key equipment which will be prioritized in China with the advantages of large capacity, high efficiency and low emission. As the thermal efficiency of GTs have been improved, the requirement for the high temperature properties and reliability of the turbine disk materials is enhanced. In this paper, it mainly introduces the status and progress of the turbine disk materials for GTs in China. Further, the manufacture technologies of the large superalloy forging are discussed, including the utilization of the world’s largest 800MN hydraulic press and optimal control strategies of the microstructure and mechanical properties.