Materials Week '97: Monday AM Session

Focusing on physical metallurgy and materials, Materials Week '97, which incorporates the TMS Fall Meeting, features a wide array of technical symposia sponsored by The Minerals, Metals & Materials Society (TMS) and ASM International. The meeting will be held September 14-18 in Indianapolis, Indiana. The following session will be held Monday morning, September 15.

TESTING AND INSPECTION TECHNIQUES FOR STRUCTURAL INTEGRITY EVALUATION AND POWER PLANT LIFE EXTENSION: Session I: Small Specimen Test Techniques

Session Chairs: Prof. James C. Li, Materials Science Program, Department of Mechanical Engineering, University of Rochester, Rochester, NY 14627; Dr. R. Viswanathan, Electric Power Research Institute, 3412 Hillview Ave, Palo Alto, CA 94303

OPENING REMARKS: Fahmy M. Haggag, Advanced Technology Corporation, 661 Emory Valley Road, Suite A, Oak Ridge, TN 37830

8:40 am

USE OF SMALL SPECIMENS FOR EVALUATING STRUCTURAL INTEGRITY OF NUCLEAR REACTOR PRESSURE VESSELS: R.K. Nanstad, D.E. McCabe, M.A. Sokolov, D.J. Alexander, S.K. Iskander, Metals and Ceramic Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6151

The Oak Ridge National Laboratory is engaged in the evaluation of small mechanical test specimens for potential applicability to assessments of structural integrity of nuclear reactor pressure vessels. The Heavy-Section Steel Irradiation Program, funded by the U.S. Nuclear Regulatory Commission, is performing experiments with various types of small specimens for fracture toughness, Charpy impact toughness, crack-arrest toughness, and tensile tests. The use of so-called subside specimens could provide the capability to obtain mechanical property measurements from materials for which the available material is extremely limited. Materials which have been thoroughly characterized in previous studies with relatively large specimens are used for the small specimen evaluations. Both metallurgical and mechanical factors are considered in the evaluation of the test results with a view towards application of the techniques to operating reactor vessels. Research sponsored by the Office of Nuclear Regulatory Research, U.S. Nuclear Regulatory Commission, under Interagency Agreement DOE 1886-8109-8L with the U.S. Department of Energy under Contract DE-AC05-960R22464 with Lockheed Martin Energy Research Corp.

9:00 am

CONFOCAL MICROSCOPY METHOD TO CHARACTERIZE THE MICROHARDNESS INDENTATION TOPOLOGIES AND CONSTITUTIVE BEHAVIOR: T. Santos, G.R. Odette, G.E. Lucas, Department of Mechanical Engineering and Materials, University of California, Santa Barbara, CA 93106

Abstract not available.

9:20 am

APPLICATIONS OF THE STRESS-STRAIN-MICROPROBE TECHNOLOGY TO EVALUATE THE STRUCTURAL INTEGRITY OF METALLIC STRUCTURES: Fahmy M. Haggag, Advanced Technology Corporation, 661 Emory Valley Road, Suite A, Oak Ridge, TN 37830; K. Linga Murty, North Carolina State University, Raleigh, NC 27695-7909

The Stress-Strain Microprobe (SSM) uses an automated ball indentation technique to obtain flow data from a localized region of a test specimen or component. This technique is being used to rapidly determine the yield strength and microstructural condition of a variety of materials including pressure vessel steels, stainless steels and nickel-base alloys. The SSM provides an essentially nondestructive technique for the measurement of local yield strength data. This technique is especially suitable for the study of complex or high variable microstructures such as weldments and weld heat affected zones. In this study yield strength data measured by the SSM are discussed and where possible compared to data obtained by conventional tensile tests. The sensitivity of the SSM to the presence of residual stresses is also discussed.

9:40 am

APPLICATIONS OF THE STRESS-STRAIN MICROPROBE TECHNOLOGY IN FIELD TESTING OF PRESSURE VESSLES PIPING, AND AIRCRAFT ENGINE DISKS-VIDEO PRESENTATION: Fahmy M. Haggag, ADvanced Technology Corporation, 661 Emory Valley Road, Suite A, Oak RIdge, TN 37830

10:00 am BREAK

10:10 am

EVALUATION OF IN-SERVICE MECHANICAL DEGRADING OF COATINGS IN GAS TURBINE BLADES USING A SMALL PUNCH TESTING METHOD: J. Kameda, T.E. Bloomer, Ames Laboratory and CATD, Iowa State University, Ames, IO 50011; Y. Sugita, A. Ito, Electric Power R & D Center, Chubu Electric Power Co., Inc., Nagoya 458, Japan; S. Sakurai, MERL, Hitachi Ltd., Hitachi 317, Japan

The application of the standard mechanical testing method is not suitable for evaluating in-service degradation of gas turbine blade coatings because of the complex shape and localized degradation near surfaces. This paper examines how in-service and thermal environmental attack influence the mechanical properties (22-950'c) of CoNiCrAlY coatings over Rene' 80 substrates in gas turbine blades using a small punch (SP) testing technique in conjunction with scanning Auger microprobe analysis. SP tests have clearly shown strong dependence of environmental condition. In-service operation under combined fuels of kerosene and liquefied natural gas (LNG) led to a two-fold increase in the ductile-brittle transition temperature (DBTT) over coatings observed under mainly LNG due to more extensive oxidation and grain boundary sulfidation. However, the DBTT of coatings did not change during thermal aging at 870°C in air that produced only oxidation. These findings imply that the grain boundary sulfidation would exert a stronger embrittling effect on the CoNiCrAlY coatings than the oxidation. The integrity of blade coatings is discussed based on the SP test result.

10:30 am

LOCAL MECHANICAL PROPERTIES MEASURED BY IMPRESSION TESTS: James C. M. Li, Materials Science Program, Department of Mechanical Engineering, University of Rochester, Rochester, NY 14627

Micro and nano indentations have been used to probe local mechanical properties such as hardness and elastic modulus. However, since most indenters are of conical or pyramidal shape, it is impossible to produce steady state deformation. To solve this problem, cylindrical indenters have been used and it has been shown that a steady impression velocity can be achieved at a constant load and the load and temperature dependences of such velocity are comparable to those of the steady state deformation of tensile or compressive specimens of uniform cross section. Stress relaxation measurements can be performed also using a cylindrical indenter and the stress-strain rate relation obtained is similar to that from steady state measurements. In addition, the impression recovery experiments give indication of the dimensional stability of the material. Work supported by NSF through DMR9623808 monitored by Dr. Bruce MacDonald.

10:50 am

USING INTEGRATED ULTRASONIC TECHNIQUE TO ASSESS RADIATION DAMAGE AND DAMAGE DUE TO SERVICE ENVIRONMENTS: J.A. Wang, Computational Physics and Engineering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37831-6370; Fahmy M. Haggag, Advanced Technology Corporation, 661 Emory Valley Road, Suite A, Oak Ridge, TN 37830

Abstract not available.

11:10 am

AN IMPRESSION TEST METHOD FOR CHARACTERIZATION OF MECHANICAL BEHAVIOR: A REVIEW: M.A. Imam, H.Y. Yu, B.B. Rath, Material Science and Technology Directorate, Naval Research Laboratory, Washington, DC 20375-5320

Mechanical behavior of materials is measured using a simple localized impression testing technique, consisting of a flat-ended cylindrical punch. This method has significant advantages over the conventional approach, such as the need of small specimen volume, constant stress tests at constant load, and temperature and stress dependence of creep rate obtained from a single sample. Over the years, its application has been extended to study elastic modulus, yield strength, ductility, and superplasticity of materials. This approach has also been used to study fatigue, stress relaxation, and mechanical anisotropy of materials. The status of the impression test methodology and its applications are reviewed. The importance of the impression test method as an experimental tool in designing new materials, both bulk as well as thin films, will be discussed.

11:30 am

MICROCRACK METHODOLOGY FOR MORE EFFECTIVE RELIABILITY INSPECTION SCHEDULING OF METALLIC MATERIALS: E.Y. Chen, Physical Metallurgy Laboratory, GE Corporate Research & Development, P. O. Box 8, Schenectady, NY 12301; L. Lawson, 226 Interstate Parkway, Bradford, PA 16701; M. Meshii, Department of Materials Science and Engineering, Northwestern University, Evanston, IL 60208

In many metallic materials, the formation of microcracks is a continuous and often accelerating damage process. In such cases, calculations using conventional reliability theory on the rise of the hazard function (i.e., the probability of failure) show that the idea of equispaced inspections may not be sufficient for avoiding failure prior to the next inspection interval. To better understand the impact of microcracks in structural integrity evaluation, fatigue microcracking will be characterized for a 304 stainless steel from primarily replicas of smooth specimens. Since microcracks form in clusters, they will be analyzed as such in terms of distributions. This has been done by modeling their growth as a semi-Markov process represented by an embedded Markov chain. The simulation takes into account factors such as the stress intensity applied to the crack, the distribution of microstructural obstacles which may retard growth, and the probability that two cracks will coalesce. From these computations, it is seen that the long crack Paris equation does an effective job of predicting microcrack growth when microstructural variables are considered. The derived data in turn allow engineers to schedule inspections based on when detectable cracks would most likely appear, and then space them more closely late in life when the risk of failure increases with the density of cracks is higher.