1997 TMS Annual Meeting: Tuesday Abstracts

STRUCTURE AND PROPERTIES OF INTERNAL INTERFACES: Session IV: Precipitation and Segregation

Session Chairperson: David J. Srolovitz, Dept. of Materials Science & Engineering, University of Michigan, Ann Arbor, MI 48109-2136

1:30 pm INVITED

INFLUENCE OF THE CRYSTALLOGRAPHIC PARAMETERS OF GRAIN BOUNDARIES ON THEIR ENERGETIC, KINETIC AND CHEMICAL PROPERTIES: E. Rabkin, Wolfgang Gust, Max-Planck-Institut für Metallforschung and Institut für Metallkunde, Seestr. 75, D-70174 Stuttgart, Germany

We review the recent experimental data about the dependence of the grain boundary (GB) energy on the misorientation of adjacent grains and on the inclination of the GB plane. The relationship between inclination dependence of the GB energy and the morphology of faccted twin Gbs in Cu and Ag is demonstrated. The kinetics of development of the faccted morphology at the originally flat twin GB in Cu is studied experimentally. The strong influence of small additions of Bi on the chemical compositions of Gbs in Cu is shown. The effect of atomic ordering on the GB energy is considered. The discontinuous ordering reaction in Fe-50 at.% Co alloy in combination with the analysis of the electron backscattered Kikuchi patterns is used to study the atomic mobility in Gbs in the ordered B2 alloy. It is shown that the low energy special Gbs exhibit also the decreased atomic mobility.

2:10 pm

THE EFFECTS OF GRAIN BOUNDARY MISORIENTATION ON M23C6 PRECIPITATION AND SENSITIZATION IN 304 STAINLESS STEEL: Elizabeth Trillo, L.E. Murr, Department of Metallurgical and Materials Engineering, The University of Texas at El Paso, El Paso, TX 79968

The correlation between grain boundary misorientation and energy has been the subject of study even before Stickler and Vinckier (in 1963) demonstrated that sensitization behavior is related to the energy of different types of individual boundaries in the sensitizing temperature range of 500-850°C. This research goes beyond these types of studies by attempting to uncover the role of grain boundary misorientation on M23C6 precipitation behavior in 304 stainless steel. The four materials utilizaed in this study having differing carbon contents (0.01, 0.025, 0.05, 0.07%C) and were heat treated at 670°C for 10 and 50 hours. In addition, the 10 hour samples were deformed (0, 10, and 20% true strain) to observe simultaneous strain effects. Electrochemical Potentiostatic Reactivation (EPR) tests were performed to characterize the sensitization behavior, and the precipitation behavior was observed through the transmission electron microscope (TEM) at 200kV. A "critical nucleation energy" was found to be in the range of 16 mJ/m2 to 265 mJ/m2 which corresponds to the energies of special boundaries, no precipitation was observed on coherent twin boundaries (#16 mJ/m2). This research supported in part by the Patricia Roberts Harris Fellowship.

2:30 pm

GRAIN BOUNDARY SEGREGATION AND PRECIPITATION EFFECTS ON ENVIRONMENT-INDUCED CRACKING: S.M. Bruemmer, Pacific Northwest National Laboratory, P.O. Box 999, Richland, WA

Environment-induced cracking at internal interfaces has long been explained due to local chemistry differences. Widespread use of high resolution analytical techniques (analytical transmission electron microscopy and scanning Auger microscopy) has recently "quantified" this effect by direct correlation's between grain boundary composition and intergranular failure. Examples of this quantification will be presented and critical interfacial compositions identified for various metallic alloys. material susceptibility can often be minimized by controlling segregation and precipitation characteristics at grain boundaries. Compositional anisotropy among internal interfaces, and its effect on cracking, will also be demonstrated and discussed. Work supported by the Office of Basic Energy Sciences, Division of Materials Sciences, U.S. Department of Energy under contract DE-AC06-76 RLO 1830.

2:50 pm

SELECTIVE PRECIPITATION ON GRAIN BOUNDARY: J. Jang, Y.B. Lee*, I.H. Kuk, K.A.E.R.I., P.O. Box 105 Yusong, Taejon, KOREA; *Korea Univ. I Anam-dong, Sungbuk-gu, Seoul, KOREA

Ni-Cr-Fe Alloy (UNS N06690) is being widely used as corrosion resistant tubing material in nuclear power plants and believed beneficial to stress corrosion resistance to have intergranular chromium carbide precipitates (semi-continuously or continuously). Alloys were prepared through VIM and ESR and tubular products were fabricated by pilgering process. Several solution heat treatments were conducted at a relatively rapid heating and cooling rate. Selective precipitation of chromium carbide along grain boundary was observed in this alloy. Even along a single grain boundary carbide precipitates were revealed as very discretely distributed in association with twins. Distribution and orientation relationship of precipitates with grain boundary in association with twins were analyzed through electron microscopy and explained with CSL model.

3:10 pm BREAK

3:30 pm INVITED

ATOMISTIC STUDIES OF SOLUTE-ATOM SEGREGATION AT GRAIN BOUNDARIES IN METALS: SIMULATION AND EXPERIMENTS: David N. Seidman, Northwestern University, Department of Materials Science and Engineering, Evanston, IL 60208-3108

I review our studies of the relationship between the atomic structure of grain boundaries (GB) and solute-segregation in binary metallic alloys. The principal experimental tool utilized to measure segregation is atom-probe microscopy. This is used in conjunction with Monte Carlo techniques (Metropolis algorithm and overlapping distributions MC) to explore the multidimensional GB phase space. Experimentally we determine the five macroscopic degrees of a GB employing transmission electron microscopy and then determine the Gibbsian interfacial excess of solute of the same GB employing atom-probe microscopy. The simulational approach uses lattice statics calculations to determine initially the lowest energy GB structures and then MC simulations to calculate their Gibbsian excesses. The effects of both the macroscopic and microscopic degrees of freedom are studied. It is demonstrated that the Gibbsian excess is a complicated function of both the macroscopic and microscopic degrees of freedom. Also a GB's atomic structure determines the partition between segregation at dislocation's cores and in the elastic stress fields of GB dislocations. It is concluded that none of the geometric criteria discussed in the literature is capable of predicting the propensity for GB segregation. This research is supported by the National Science Foundation, Division of Materials Research.

4:10 pm

INTERFACE ENGINEERING FOR SINTERING CORDIERITE GLASS-CERAMIC COATINGS ON MOLYBDENUM: Thomas A. Kuhr, Guo-Quan Lu, Dept. of MSE, VPI & SU, Blacksburg, VA 24061

An economical technology for laying down thick ceramic coatings on a metal substrate is to tape-cast a ceramic slurry on the metal surface followed by binder burn-out and sintering. We used the technology to produce cordierite coatings on molybdenum for use as electrostatic wafer chucks. A critical issue in the production was adhesion between the two materials after the coatings were sintered at temperatures ranging from 900°C to 1000°C. To solve the problem, thin metallic interlayers were deposited by electroplating on Mo surface before tape-casting. We will discuss the selection and processing of several interlayer materials that significantly enhanced adhesion between the ceramic coating and metal substrate.

4:30 pm

ADVANCE IN STUDY OF NON-EQUILIBRIUM SEGREGATION ON INTERFACE: Xinlai He, Huaiyang Cui, Department of Materials Physics, University of Science and Technology Beijing, 100083, Beijing, China

Equilibrium segregation of solute on interface has been recognized quite a long time. In recent years, there are more interests in non-equilibrium segregation, for example, the boron non-equilibrium segregation on grain boundaries during cooling, annealing and pre-strained treatment has been studied systematically. In 1991, by means of Particle Tracking Autoradiograph (PTA) technique, it was found that boron non-equilibrium segregates on moving boundaries during recrystallization in low carbon steels (X.L.He). In Fe-3%Si alloy with b.c.c. structure, it was observed that no detectable boron segregation on boundaries during continuous cooling and annealing but a stronger boron segregation on moving boundaries during recrystallization (S.H.Zhang, 1992). Recently, in Fe-30%Ni with f.c.c. structure, a significant segregation of boron was shown on recrystallizing boundaries while segregation of boron was hardly observed on primary grain boundaries during recrystallization at high temperature (H.Y.Cui, 1995). These investigations indicate that three characteristics relate with the moving boundary segregation: (1)the segregation accompanied with motion of boundary (2)the degree of the segregation was higher than that at thermodynamical equilibrium (3)the velocity of moving boundary and addition of alloy elements influenced on the segregation process. In order to explain the phenomenon, based on the interaction between dislocations and the moving boundaries during recrystallization, a dislocation relaxation and widening grain boundary mechanism of solute segregation on moving boundaries was proposed.

4:50 pm

MOLECULAR-DYNAMICS SIMULATION OF GRAIN BOUNDARY MIGRATION: B. Schonfelder, S.R. Phillpot, D. Wolf, Materials Science Division, Argonne National Laboratory, Argonne, IL 60439; G. Gottstein, Institute fur Metallkunde und Metallphysik, RWTH Aachen, D-52056 Aachen

Molecular-dynamics simulations are used to induce the migration of a flat (001) twist grain boundary (GB) by anistropically straining a bicrystal of Cu at high temperatures. The observed migration process has the following three characteristic features: (1) the motion of the GB is viscous and continuous; (2) the observed drift velocity is proportional to the applied driving force and thermally activated; (3) the activation energy for migration is significantly lower than either that for GB diffusion or that for self-diffusion in molten Cu. The atomic-level mechanism of grain-boundary migration is discussed. *Work supported by the US Department of energy, BES-Materials Science under Contract No. W-31-109-Eng-38.