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from the MSEL Annual Report 1997:  

ADVANCED PROCESSING PROGRAMS:  Metals Data and Characterization

The performance of metals during use and their behavior during processing can be understood and predicted only with the availability of a detailed body of information on their physical properties and microstructure. The value of this information is greatly enhanced if it is developed within the context of models or theories which describe how the measured properties of a metal will vary with changes in composition, microstructure, temperature, geometry, or other parameters. The Metals Data and Characterization Program includes activities which refine the technology for measuring the properties and behavior of metallic materials, and which correlate these properties and behavior to alloy microstructures.

The large majority of metals are used in applications based on their mechanical properties, with other applications based on electronic, magnetic, optical, or other functional properties forming smaller but nonetheless critical markets. Whatever the application, satisfactory long term performance of metallic components demands chemical and microstructural stability, sometimes in the presence of harsh environments. This program identifies those processing, microstructure, and properties characterizations which are critical to U.S. industry for both the processing and the performance of metals, and carries them out within the context of the NIST mission of providing data and standards. A significant part of the program is the use of advanced microscopy techniques to characterize the microstructures which form the basis of the measured properties.

The measurements of microstructural, mechanical, chemical, and optical properties carried out under this program have an impact in a number of different technology sectors:

• Standard test methods are being developed to support the automotive industry in its effort to improve fuel efficiency by shifting to lighter materials, a shift which has highlighted the critical need for improved understanding and control of sheet metal formability. The Metallurgy Division’s effort is being carried out in collaboration with the Manufacturing Engineering Laboratory’s NAMT program and with ATP-supported consortia of U.S. automakers and several universities.

• The accuracy of a high speed laser polarimeter technique for measuring the normal spectral emissivity of metals and alloys at high temperature has been demonstrated by measurements on a standard reference material (molybdenum). The millisecond resolution of the existing system is currently being upgraded to microsecond resolution, which should enable measurements extending to temperatures well above the melting point of refractory metals. These techniques provide industry with benchmark high temperature thermophysical properties measurements.

• Precision measurements of Rockwell Hardness, the primary parameter used to specify the mechanical properties of metals and alloys, are leading to the establishment of traceable national hardness standards. Calibrated test blocks, together with national standards for measurement and calibration procedures, will facilitate the acceptance of a wide range of U.S. products in international markets, as well as minimizing product-acceptance disputes in domestic trade.

• Computational micromagnetic techniques are producing results which are important for understanding magnetization reversal in devices incorporating thin magnetic elements. Micromagnetic head-to-head domain wall structures and energies in thin magnetic strips have been calculated, resulting in a "phase diagram" for transverse and vortex type walls.

International Hardness Intercomparison After developing national hardness standards, NIST researchers are promoting the development of international agreement on hardness scales. An intercomparison study using the new NIST Rockwell C Scale SRM test blocks, conducted by NIST and the National Research Laboratory of Metrology in Japan, showed good agreement at all three levels of hardness for which the NIST standards are produced. An intercomparison of one hardness scale was also conducted with Japan and good agreement was found at four levels of hardness.