Relationships between Microstructural Parameters and Time-Dependent Mechanical Properties of a New Nickel-Based Superalloy AD730™
High temperature creep and dwell-fatigue properties of the new nickel-based superalloy AD730™ have been investigated. Three microstructures have been studied in creep (850 °C and 700 °C) and dwell-fatigue (700 °C stress control with trapezoidal signals, and dwell times ranging from 1 s to 3600 s): a coarse grains microstructure, a fine grains one, and single crystalline samples. The aim of this study is to assess the influence of the grain size on creep and creep-fatigue properties. It is demonstrated that fine and coarse grains microstructures perform similarly in creep at 700 °C, showing that the creep properties at this temperature are controlled by the intragranular precipitation. Moreover, both the coarse grains and the fine grains microstructures show changes in creep deformation mechanisms depending on the applied stress in creep at 700 °C. At higher creep temperatures, the coarse grains microstructure performs better and almost no effect is observed by suppressing grain boundaries. During dwell-fatigue tests at 700 °C, a clear effect of the mechanical cycling has been evidenced on the time to failure on both the coarse and the fine grains microstructures. At high applied stresses, a beneficial effect of the cyclic unloading to the lifetime has been observed whereas at lower applied stresses, mechanical cycling is detrimental compared to the pure creep lifetime due to the development of a fatigue damage. Complex creep-fatigue interactions are hence clearly evidenced and they depend on the pure creep behavior reference.
AD730™ ‐ A New Nickel‐Based Superalloy for High Temperature Engine Rotative Parts
The enhancement of efficiency in gas turbine engine s requires the development of new superalloys capable of withs tanding higher temperatures. The development of new industr ial cast and wrought (C&W) disk alloys with required combination of strength, creep and fatigue properties at 700°C is highly desired due to the expensive cost of powder metallurgy. AD7 30, which is the newly nickel base superalloys develope d by Aubert & Duval, was therefore designed to offer a better c ombination between high temperature properties at 700°C and co st compared to other C&W superalloys. This paper descr ibes the alloy design based upon the chemistries of the prev ious experimental alloys Ni30 and Ni33 [1-2]. The contro l f expensive elements contents and the presence of iro n in AD730 alloy confer to this alloy an attractive cost comp ared to other C&W superalloys for disk applications. Gam ma prime solvus was decreased compared to Ni33 in order to i mprove hot workability and (Ti+Nb)/Al ratio was decreased comp ared to Ni30 and Ni33 in order to avoid any risk of Eta-pha se precipitation. It was actually observed that the pr cipitation of the needle-shape Eta-phase predicted by the thermod ynamic databases was not in agreement with experimental re sults obtained on various alloys of the AD730 TM chemical system. Industrial ingots with a diameter equal to 500mm we re produced (Vacuum melting and remelting) and converted to eva luate the mechanical properties and the ability for the conve ntional C&W route. A special attention is made in this paper to the AD730 workability which was highly evaluated with various industrial forging process routes (close-die forging, ring-rol ling...etc). Heat treatment optimization was then performed on this a lloy in regard to tensile and creep properties. The effect of solution heat-treatment temperature and cooling rate after s olution heat treatment were investigated on AD730 . Solution heat treatment temperature has a slight effect on the te nsile strength if the temperature is lower than the gamma prime solvu . Yield strength remains stable and close to 1100MPa at 700 °C. Solution heat-treatment was therefore optimized in regard of grain size in order to increase creep properties. A s most of superalloys strengthened by gamma prime phase, cool ing rate after solution heat-treatment has to be as fast as pos ible to get the highest tensile and creep properties. Oil quenching can be easily performed on AD730 TM without any issues due to the moderate gamma prime content in t he alloy (35-40%) and the fine grain size. Tensile, creep, l ong-term aging performed on a forged disk heat-treated in optimize d conditions, are presented and discussed in this paper. A compar ison with Udimet720 properties and 718Plus TM ones show that AD730 alloy presents a higher combination between cost an d mechanical properties at 700°C than current C&W sup eralloys.
Wood Microbiology: Decay and Its Prevention
Introductory text on the principles of decay and discoloration processes in wood, with emphasis on the major fungal damages which may develop during the growth, storage, and use of wood. The characteristics, detection, effects, and control of microbial attacks are stressed. Provides a synthesis of the current literature on wood microbiology, a rapidly expanding field of study. (Abstractor's note: This is an important resource for conservation researchers studying the decay of wood in art and architecture.) The following is a list of chapter headings: 1) Introduction to wood microbiology; 2) Wood deterioration agents; 3) Characteristics and classification of fungi and bacteria; 4) Factors affecting the growth and survival of fungi in wood (fungal ecology); 5) Fungal metabolism in relation to wood decay; 6) The decay setting: some structural, chemical, and moisture features of wood in relation to decay development; 7) General features, recognition, and anatomical aspects of wood decay; 8) Chemical changes in wood caused by decay fungi; 9) Ultrastructural features of wood decay; 10) Changes caused by decay fungi in the strength and physical properties of wood; 11) Colonization and microbial interactions in wood decay; 12) Decays originating in the stems of living trees; 13) Biodeterioration of stored wood and its control; 14) Wood stains and discolorations; 15) Decay problems associated with some major uses of wood products; 16) Detection of internal decay; 17) Paint mildew and related degradative problems; 18) Natural decay resistance (wood durability); 19) Chemical protection of wood (wood preservation); and 20) Some trends in wood microbiology research and a new emphasis (biotechnology). -- AATA