Use of the Scanning Electron Microscope in Microhardness Testing of High-Hardness Materials

Thin coatings of titanium nitride (TiN), zirconium nitride (ZrN), and hafnium nitride (HfN) are difficult to measure for hardness by any technique other than microhardness measurement. The question of apparent hardness increase with decreasing load has been the subject of much discussion, and many explanations have been offered, such as those of Gane and Cox and of Bulter. Impressions measured at high and low loads on a single hardness standard typically show higher hardness readings with lower loads. Correction factors have been suggested, however, there is still some question concerning the absolute hardness at low loads.

The purpose of this work is to show a technique, using the scanning electron microscope (SEM) and a diffraction grating for a measurement standard, that produces more accurate microhardness readings. Further, data suggest that very thin coatings, on the order of 2 to 5 μm, can be measured for hardness. A hardness standardization and comparison technique was also developed to relate microhardness readings from different hardness scales more accurately. Computer techniques were utilized to fit the hardness data for hardness scale comparisons.