Abstract
The Vickers hardness number (VHN) of pure metals (tin, aluminum, copper and gold) and dental gold alloy was measured using an automatically indenting and reading Vickers hardeness tester (AKASHI・AUTOVICK) under a load of 1, 000 gf with different loading times of 5 to 55 seconds. The samples of pure metals were cold rolled and softened by heating above recrystallization temperatures. The samples of ADAS No.5 gold casing alloys were cold rolled, and then subjected to a softening heat treatment by water quenching (Types I, II, III and IV) or a hardening heat treatment by 450 → 250 ℃/30
min oven cooling (Types III and IV). The results showed that there were no statistically significant differences between the measured values of VHE of a sample with different loading times as for the metals studied except pure tin which had a VHN of 5〜6. The measured values of VHN by AUTOVICK were affected by the brightness of a light source for measurement, and they increased by 1.1 approximately as the voltage of the light source increased by 0.1 V. This was considered to be due to the protuberance caused by plastic flow of metals or slip lines on the surface around the indentation.
