Surface Finish Metrology

Technical Contact:	Thomas Brian Renegar
	301-975-4274

The Surface & Nanostructure Metrology Group (683.02) carries out research projects for the measurement and calibration of surface roughness. Surface roughness measurements and specifications impact many industrial products including highways, ship hulls, mechanical components, semiconductors, and optics. Engineering surfaces range in roughness from hundreds of micrometers to small fractions of a nanometer. There is also a wide array of measurement techniques, and a large number of statistical methods for surface texture analysis.

We work with industry and other government agencies on applied surface measurement problems and on the continual improvement of roughness and step height calibrations. We also play an active role on standards committees. For the American Society of Mechanical Engineers (ASME) Standards Committee B46 on the Classification and Designation of Surface Qualities, we lead the Working Group responsible for the revision and maintenance of its national standard ASME B46.1, Surface Texture. For ISO Technical Committee (TC) 213, we lead the Project Team on Optical Methods for areal surface texture measurement, which is currently developing five new international standards in the field.

Recent accomplishments include:

• Development of the web-based Surface Metrology Algorithm Testing System (SMATS),
• Comparisons of the results of different profiling methods on the same surfaces, and
• Participation in an international comparison of roughness and step height measurements from different National Measurement Institutes (NMI’s).

SMATS allows users to test their surface topography analysis software by comparing their calculations for surface parameters such as roughness average (Ra) or rms roughness (Rq) with NIST calculations for the same parameters on the same profiles. Other NMI’s have similar services, but SMATS is unique because its capabilities include 3D surface parameters and estimates of uncertainty.

We have performed comparisons of profiling results obtained with the stylus technique and with three optical profiling methods [1,2]. The results are generally in good agreement but there are a few surprisingly large differences. One of the areas where excellent agreement is obtained is shown below [2].

Comparisons with other laboratories have consistently turned out well. A recent comparison of roughness and step height standards of NMI’s in the Inter-American Metrology System (SIM) showed good agreement of NIST results with Mexico, Brazil, Canada, and Argentina, and was published in Metrologia [3]. During 2009 we are working on similar comparisons under the Asian Pacific Metrology Program and under SIM-EURAMET as well.

Other current projects include the final testing of a new stylus instrument for calibrations of surface roughness and step height. This instrument has a vertical range of twelve millimeters and an rms noise of less than one nanometer. We are also near completion of the re-certification of roughness Standard Reference Materials SRM’s 2073a, 2074, and 2075, currently in stock. We now expect these materials to hold their calibration for 15 years provided measurements are taken on undamaged areas by the user. Longer term projects include the topography measurements of spherical surfaces such as micro-optical components.

References

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[1] Vorburger, Theodore V., Rhee, H G., Renegar, Thomas B., Song, Jun-Feng (John), Zheng, Xiaoyu A. (Alan), “Comparison of Optical and Stylus Methods for Measurement of Rough Surfaces,” International Journal of Advanced Manufacturing Technology 33, pp. 110-118 (2007).

[2] Song, Jun-Feng (John), Vorburger, Theodore V., Renegar, Thomas B., Zheng, Xiaoyu A. (Alan), Rhee, Hyug-Gyo, Libert, John M., Ma, Li, Bogart, K., Ballou, Susan M., Bachrach, B., “Correlation of Topography Measurements of NIST SRM 2460 Standard Bullets by Four Techniques,” Measurement Science & Technology 17, pp. 500-503 (2006).

[3] Doytchinov, K., Kornblit, F., Castellanos, C. C., Oliveira V, J. C., Renegar, Thomas B., Vorburger, Theodore V., “International Comparison of Surface Roughness and Step Height (Depth) Standards, SIM 4.8,” Metrologia 43 (04002) (2006).

Figure 1. Comparison of 2D profiles of a standard bullet master surface (top graph) measured by a stylus instrument and a standard bullet replica measured by three types of profiling optical microscopes [2]. Full scale, left to right, is approximately 1.4 mm. One large vertical division is about 1 µm.