EFFECTS OF ELECTROLYTE CONCENTRATION AND ETCHING TIME ON SURFACE ROUGHNESS OF NI-CR-BE ALLOY

전해질 농도와 식각시간에 따른 비귀금속합금의 표면조도 변화

The purpose of this study was to evaluate the surface roughness of Ni-Cr-Be alloy($Verabond^{(R)}$, Aalba Dent Inc., USA) according to electrolyte concentration and etching time. Total of 150 metal specimens ($12{\times}10{\times}1.5mm$) composed of 5 polisded specimens, 5 sandblasted specimens, 140 etched specimens were prepared. Etched groups were divided into 28 groups by the $HClO_4$ concentrations(10, 30, 50, 70%) and etching times(15, 30, 60, 120, 180, 240, 300 seconds). The mean surface roughness(Ra) and the etching depth were measured with Optical 3-dimensional surface roughness measuring machine(Accura 1500M, Intek Engineering Co., Korea) and observed under SEM. The results obtaind were as follows: 1. Surface roughness(Ra) and etching depth were affected by the order of etching time, electrolyte concentration, and their interaction(P<0.05). 2. Surface roughness(Ra) and etching depth were increased with etching time in 10%, 30% electrolyte concentrations, but they had no significant difference with etching time in 70% (P<0.05). 3. Surface roughness(Ra) and etching depth decreased in the order of 30, 10, 50, 70% electrolyte concentrations from 120 seconds etching time(P<0.05). 4. The remarkable morphologic changes in etched surface were observed along the grain boundaries in 15, 30 seconds of 10%, 30% concentrations and the morphologic changes could be denoted in the grains themselves as well as along the boundaries with the lapse of time. Even though the noticeable morphologic changes also took place in etched surface with 50% concentration, the degree of changes were less than that of changes with 10%, 30%. However, there were little morphologic changes with 70% concentration regardless of etching time. 5. Surface roughness(Ra) of sandblasting group with $50{\mu}m\;Al_2O_3$ had no significant difference with 30%-30 seconds etched group(P<0.05).