Evaluation of processing parameters on PTA hardfacing surfaces

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Abstract
The process of hardfacing by plasma transferred arc (PTA) has been increasingly accepted in recent years. It has attractive features from the metallurgical point of view, as well as offering low distortion, little dilution, a homogenous structure, and refined coatings. Major innovations and optimized engineering component processing could be achieved if companies had access to a study of different processing parameters. However, owing to the scarcity of literature about the process, comparing it with other welding processes, which contains divergent information in some areas, demands a wider and more systematic study of the effect of the welding variables. This work is intended to contribute to this, and the main objective is to verify the effect of the process variables on the characteristics of a weld bead deposited by the PTA. Using a constant direct current, the influence of the sharpening angle was studied on a tungsten electrode, plasma gas flow, and torch nozzle constriction, using a cobalt-based alloy commercially known as Stellite 6 as the support material. The characteristics of the coating were evaluated in terms of their surface finish, dilution, wettability, and hardness. The results showed that the characteristics of the deposits were determined by the intensity of the current, followed by the nozzle constriction, and that the electrode sharpening angle did not influence the results.

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