Abstract
Plasma immersion ion implantation nitriding (PIII&N) process has several advantages comparing with traditional nitriding method. They are short operation times, less heat deformation of product and low operating temperature, etc, and have potential for modifying the surfaces of dental drills to improve their performances. These dental drills for experiment were divided into three groups including non-nitriding drills and treated by PIII nitridation at 1 hour and 2 hours, respectively. During PIII nitridation, the flow rate of nitrogen (N2) at 100 sccm, temperature at 25℃, voltage of bias at 20 kV and frequency at 500 Hz were conducted. Profile measurement of hardness, Young's modulus and chemical elements and cutting-efficiency test were used to investigate the variation of nitrided time vs. mechanical properties. The experimental results show that both of the hardness and the Young's modulus of nitrided drills are evidently higher than that of untreated drills. The region of increasing in the hardness and the Young's modulus is about 100 nm. The peak value and position and the distribution range of nitrogen concentration and surface hardness of nitrided drills after 2 hours PIII treatment are higher than that after 1 hour treatment. It appears that the profile of hardness varies with nitrogen distribution. The micro-pattern on the surface of drill is an important factor in affecting the cutting efficiency. Drills treated by PIII nitriding in 1 hour can increase the hardness of micro-pattern, and thus increase the cutting efficiency. But the other drills treated by PIII in 2 hrs did not improve their cutting efficiency. This is because the heat and ion bombardment from plasma treatment with longer time soften the pattern on drill surface, which decreases the cutting efficiency.
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