Microwave Plasma Assisted CVD of Diamond on Titanium and Ti-6Al-4V

The ultimate goal of this research was to demonstrate a Microwave Plasma assisted Chemical Vapor Deposition (MPCVD) process to coat a Ti-6A1-4V bearing shaft. Preliminary experiments were performed in an ASTeX™ system on flat chemically pure titanium and Ti-6AI-4V coupons. Diamond deposition was also attempted on a Ti-6AI-4V wedge sample which contained a curved surface that simulated the bearing. Although uniform diamond deposition was attained on the flat samples, very poor uniformity was observed on the curved sample. This lack of uniformity was attributed to the difficulty in controlling the plasma-to-substrate distance in a single mode, single frequency reactor and it was believed that by varying the frequency and using a multimode cavity one could solve this problem. Thus, depositions on a titanium rod were performed in a variable frequency MPCVD reactor. It was determined visually that the variable frequency operation provided uniform plasma distribution along the length and circumference of the rod and resulted in a fairly uniform coating. However, scanning electron microscopy revealed that the morphology of the particles was poor and micro-Raman spectroscopy showed weak, broad peaks that were attributable to amorphous carbon. It is believed that by fine-tuning parameters, a uniform diamond film of good quality can be achieved along the entire rod.