ASTM B748-90(2021) PDF

Overview

ASTM B748-90(2021) - Standard Test Method for Measurement of Thickness of Metallic Coatings by Measurement of Cross Section with a Scanning Electron Microscope (SEM) provides a standardized approach for accurately measuring the thickness of metallic coatings and individual layers in composite coatings. This method is especially effective for thin layers that are difficult to assess using conventional light microscopes. The technique involves preparing a cross-sectional specimen and using a scanning electron microscope to generate precise thickness measurements over small, localized areas.

Key Topics

• Direct Measurement: The method enables direct determination of metallic coating thickness, particularly useful for ultra-thin or multilayer coatings not easily measured by other means.
• Sample Preparation: Accurate results require meticulous specimen preparation-careful cutting, mounting, grinding, and polishing-to ensure that cross sections are perpendicular and boundaries are sharply defined.
• SEM Operation: The method relies on SEMs with adequate resolution (minimum 50 nm). Calibration with a stage micrometer is essential for reliable magnification and measurement.
• Measurement Area: This technique is designed to measure the thickness at specific locations, not to provide average or minimum thickness values across the entire coated surface.
• Measurement Reliability Factors: Several factors can influence accuracy, including surface roughness, cross-section taper, specimen tilt, polishing effects, and sample contrast. Attention to these factors helps prevent errors such as over- or underestimation of thickness.

Applications

The ASTM B748-90(2021) standard test method is widely used in industries where the performance of metallic coatings is critical and tight control over thickness is required. Major applications include:

• Quality Control and Acceptance Testing: The method supports acceptance testing by verifying that coating thickness meets specified requirements for end-use performance.
• Microelectronics and Semiconductors: Accurately measuring the thickness of conductive and protective layers on microelectronic components.
• Aerospace, Automotive, and Manufacturing: Ensuring that functional and decorative metallic coatings-such as nickel, gold, or other alloy layers-meet durability and corrosion resistance standards.
• Research and Development: Providing accurate thickness measurement in material science studies or process development when working with advanced, nano-scale coatings.
• Failure Analysis: Investigating coating failures or performance issues by pinpointing areas with insufficient or excessive coating using SEM-based measurements.

Related Standards

To conduct measurements according to ASTM B748-90(2021), familiarity with related ASTM standards is beneficial:

• ASTM E3: Guide for Preparation of Metallographic Specimens, outlining best practices for specimen cutting, mounting, grinding, and polishing.
• ASTM E766: Practice for Calibrating the Magnification of a Scanning Electron Microscope, crucial for ensuring measurement accuracy and reliability.

Other standards in the field of metallic coatings and SEM techniques may also inform best practices for measurement and process control.

Using ASTM B748-90(2021) helps organizations maintain high-quality metallic coating processes by providing a reproducible, precise, and internationally recognized measurement method. Proper implementation of this standard ensures that only coatings with the correct thickness are accepted, directly impacting product reliability and lifespan in demanding industries.