A. P. Sanders, Ortho Development Corp., Draper, UT; N. M. Tikekar, C. D. Lee, K. S. R. Chandran, University of Utah, Salt Lake City, UT
An investigation of surface texture issues resulting from a diffusion boriding process for surface hardening of titanium has been undertaken, with the initial objective of producing hardened disks and balls for demonstration and wear testing. The inherent roughness resulting from the boriding process, roughness amplification, and geometric form changes all affect the achievement of desired surface texture. The boriding process yields an inherent roughness < 2 μm Ra. In addition, it appears that pre-existing microscratches may be amplified by the coating growth, resulting in high roughness increases, e.g. from < 0.1 μm Ra to > 1.5 μm Ra, and from < 1.0 μm PV to > 10 μm PV. Further, form changes that occur in titanium during high temperature exposure influence the capability of polishing processes. In order to reduce the impact of these issues, the effects of pre-annealing on ball sphericity and disk flatness have been investigated. Chemical-mechanical polishing is being used to alleviate roughness amplification. These improvements are necessary to achieve nanometer scale roughness while minimizing stock removal during final polishing.
Summary: This abstract discusses issues arising when attempting to achieve a desired surface texture after hardening a titanium surface with titanium boride layers, and the means used to overcome those issues.