Infrared Heat Treatment of Ti-6Al-4V with Electroplated Cu

摘要

The objective of this study is to investigate an innovative infrared technique to enhance adhesion of electroplated Cu on Ti-6Al-4V without dichromate dipping. The ultimate goal is to develop a Cu coating process on Ti-6Al-4V without hazardous hexavalent chromium solution treatments. Copper coatings of around 50 mu m were electroplated on Ti-6Al-4V specimens at a current density of 0.03 A/cm~2 in an acidic copper solution. To improve adhesion of coatings, infrared heat treatments were performed on copper coated samples at different temperatures and durations: 860 deg C for 600 seconds and 875 deg C for 20 to 120 seconds. This was done in the attempt to replace the use of dichromate dipping before electroplating. For samples heat treated at 860 deg C, no bonding existed even after 600 s. It is believed that solid state diffusion prevailed at 860 deg C and 600 s was not sufficient for sufficient diffusion to occur. Adhesion is poor when heat treated at 875 deg C for 20 s. Excellent adhesion was observed when the heat treatment holding time was increased to 40 seconds. For 90 seconds, the surface appearance of coatings partially changed from copper to a grayish color. There was no copper left on the surface after a 120 second heat treatment. From optical microscopic observations on sample cross sections, an interlayer between copper and Ti-6Al-4V was formed when heat treated at 875 deg C for 40 s and longer. The interlayer thickness increased as the holding time increased until depletion of copper. The sheet resistivity of coated specimens was in the order of pure copper for samples heat treated at 875 deg C and less than 90 s. During the 875 deg C heat treatment, solid state diffusion of Cu in Ti-6Al-4V, formation of eutectic solutions, dissolution of copper and Ti-6Al-4V into the liquid phase and formation of intermetallic compounds occurred. The lowest eutectic temperature of 875 deg C played a key role in this innovative process of Cu coating on Ti-6Al-4V.