The standard EHD specimen setup consists of a 3/4“ diameter plain standard ball that is made from carbon chrome steel and has a high grade surface finish to ensure excellent reflectivity. The standard glass disc is coated with approximately 20 nm of chromium and 500 nm of silica. The ball can also be drilled to allow it to be driven during the test at a set slide/roll ratio (SRR). Although the ball has to be reflective, it can be made from different materials. In the past, we have supplied tungsten carbide balls (either plain or drilled) and sapphire discs to enable contact pressures up to 3 GPa. Below is information on some of the existing specimens available:
This is an EHD plain chromium coated disc. This is used for both defining the spectral response curve and creating the master calibration curve for the 3D Mapper (EHD3DMAP).
This is the standard EHD spacer layer disc and is used when the EHD rig is in film thickness measurement mode.
This is an EHD spacer layer disc, blue in colour (150nm of coating) and is used when the EHD rig is producing 3D thickness measurements
Sapphire Disc to be used when the EHD rig is in film thickness measurement mode for contact pressures up to 3GPa
Blue Sapphire Disc to be used when the EHD rig is in 3D film thickness measurement mode for contact pressures up to 3GPa