Metal transfer and microstructure evolution during wire-feed deposition of TiB/Ti composite coating

A new type of Ti flux-cored wire was used to in-situ synthesize two-scale TiB reinforced Ti composite coatings through wire-feed gas tungsten arc cladding, to enhance the surface hardness and wear resistance of Ti6Al4V alloy. Metal transfer modes during wire-feed deposition were investigated by high-speed camera observation in conjunction with arc voltage analysis. The results showed that the metal transfer modes varied from interrupted bridging transfer, slag column transfer, to continuous contact transfer with increasing the wire-electrode distance in 2-6 mm, accompanied by the improvement of process stability. The volume fraction of TiB in coating was governed by metal transfer modes, and can be arranged as: slag column transfer > continuous contact transfer > interrupted bridging transfer. Microstructure analysis revealed that most of TiB2 particles were melted in arc zone while the rest were fully dissolved among the weld pool through in-situ reaction for slag column transfer, while both other two modes caused the inclusion of TiB2 particle aggregations in coatings. Consequently, the coating formed by slag column transfer possessed the maximum hardness (571 HV0.5) and the minimum wear loss (14.10 mg). Worn morphologies analysis revealed that the load-shearing effect of TiB accounted for the superior wear resistance of the coating. This study demonstrates the feasibility of preparing titanium matrix composite coating through wire-based cladding.