Comparison of keyhole and conventional gas tungsten arc welds in commercially pure titanium

Keyhole gas tungsten arc welding (GTAW), a novel process recently developed at CSIRO Manufacturing Science and Technology, Australia, has been used to join commercially pure (CP) titanium. The process enables single pass, out of chamber welding of 12.7 mm thick CP titanium without expensive filler metal addition or joint preparation. The microstructure and mechanical properties of the resultant weld joint have been compared with those of a multipass conventional GTAW joint in CP titanium prepared from plates of the same thickness with a double-V edge preparation and the addition of a matching filler metal. It was shown that the differences in the net heat input and weld thermal cycles associated with the two processes led to similar microstructures, albeit of different degrees of refinement. As a result, the tensile and hardness properties of the two welded joints were similar to each other and comparable to those of the base material. The acicular nature of the fusion zone microstructure in both welds led to a significant increase in their notch toughness over that of the base material. It is concluded that the keyhole GTAW, with its significantly higher productivity combined with the simplicity of proven technology and low capital investment requirements, can be successfully applied in the welding of heavy section CP titanium, without sacrificing the metallurgical quality associated with the GTAW process.