Measurement of the lattice misfit of the nickel-base superalloy SC16 by high-energy synchrotron radiation
- PDF / 690,193 Bytes
- 5 Pages / 612 x 792 pts (letter) Page_size
- 7 Downloads / 192 Views
CTION
THE single-crystal nickel-base superalloys find their current application in turbine blades for power generation and aircrafts. Compared to directionally solidified superalloys, the single-crystal superalloys have got improved mechanical properties and operate at higher temperatures. While superalloys, which contain refractory elements such as rhenium, belong to a newer generation and exhibit superior performances in mechanical properties and corrosion resistance, alloy SC16 contains only six elements and has a relatively low ␥ ⬘ volume fraction (about 40 pct). It serves, therefore, also as some kind of ideal alloy for scientific investigations; e.g., it allows a relatively easy element analysis in the wide matrix channels. The composition of the alloy used is given in Table I and the typical microstructures both in the as-cast (AC) condition and after standard heat treatment (SHT) are shown in Figure 1. The main property of all Ni-base superalloys is the very high strength (shear resistance and flow stress) at high temperature compared to usual alloys such as steels, accompanied by an increase of the flow stress around 1100 to 1200 K.[1,2] This implies very good creep properties, which allow the in-service use of this class of alloys at very high temperatures (1100 to 1200 K for SC16). It has been reported by Fredholm and Strudel[3] that the creep-deformed microstructure depends on the value and above all the sign of the lattice misfit of the alloy at the creep temperature. This lattice misfit is defined as ␦⫽
a␥ ⬘ ⫺ a␥ 1 (a␥ ⬘ ⫹ a␥) 2
[1]
where a␥ and a␥ ⬘ are the lattice parameters of the ␥ matrix phase and of the ␥ ⬘ phase, respectively, as measured, for instance, by diffraction experiments.[4,5,6] There has been
G. BRUNO, Instrument Scientist, is with the Institute Laue-Langevin, F-38042 Grenoble, Cedex 9, France. Contact e-mail: [email protected] G. SCHUMACHER, Full Researcher, is with the Hahn-Meitner-Institut, D14109 Berlin, Germany. H. CAVALCANTI PINTO, Ph.D. Student, is with the Institute for Materials and Technologies, Technical University of Berlin, D-10587 Berlin, Germany. C. SCHULZE, Development Engineer, is with OSRAM AG, Berlin, Germany. Manuscript submitted January 24, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS A
considerable discussion about the sign of the room-temperature (RT) lattice misfit of this alloy. While Mu¨ller et al.[7,8] have reported a negative lattice misfit at RT, Vo¨lkl et al.,[9] Bru¨ckner et al.,[10] and Schumacher et al.[4] measured a positive value. The difference in the absolute value as well as in the sign of the misfit might have different reasons. First, the misfit ␦ is a differential parameter. Small uncertainties in the measurement of the lattice parameters of the two phases are reflected into large errors in ␦. Second, systematic errors inherent to the investigation methods used may contribute to the different results. Third, the particular kind of specimen used is supposed to severely affect the lattice misfit. Schumacher and co-workers, for example, used grou
Data Loading...
