A study on mechanical properties of TiN, ZrN and WC coated film on the titanium alloy surface

Oh, Dong Joon; Kim, Hee Jung; Chung, Chae Heon

Abstract

STATEMENT OF PROBLEMS: In an attempt to reduce screw loosening, dry lubricant coatings such as pure gold or tefron have been applied to the abutment screw. However, under repeated tightening and loosening procedures, low wear resistance and adhesion strength of coating material produced free particles on the surface of abutment screw and increased frictional resistance resulting in screw tightening problems. PURPOSE: The aim of this study was to compare friction coefficient, adhesion strength, vickers hardness and evaluate coating surface of titanium alloy specimens coated with TiN(titanium nitride), ZrN(zirconium nitride) and WC(tungsten carbide). MATERIAL AND METHOD: Titanium alloy(Ti-6Al-4V) discs of 12mm in diameter and 1mm in thickness divided into 4 groups. TiN, ZrN and WC was coated for the specimens of 3 groups respectively, and those of 1 group were not coated. Each group was made up of 4 specimens. In this study, sputtering method was used among the PVD(Physical Vapor Deposition) techniques available for TiN, ZrN and WC coatings. Friction coefficient, adhesion strength, vickers hardness and coating surface of 4 groups were measured.
RESULTS
1. For all three coating conditions, friction coefficient was significantly decreased. Especially, ZrN coated surface showed the lowest value. TiN(0.39+/-0.02), ZrN(0.24+/-0.01), WC(0.31+/-0.03). 2. TiN coating showed the highest adhesion strength, however ZrN coating had the lowest value. TiN(25.3N+/-1.6), ZrN(14.8N+/-0.6), WC(18.4N+/-0.7). 3. Vickers hardness of all three coatings was remarkably increased as compared with that of none coated specimen. TiN coating had the highest Vickers hardness, however WC coating showed the lowest value. TiN(1865.2+/-33.8), ZrN(1814.4+/-18.6), WC(1008.5+/-35.9). 4. The ZrN or WC coated specimen showed a homogeneous and smooth surface, however the rough surface with defects was observed for TiN coating.
CONCLUSIONS
When TiN, ZrN and WC coating applied to the abutment screw, frictional resistance would be reduced, as a result, the greater preload and prevention of the screw loosening could be expected.