Effect of current and atomized grain size distribution on the solidification of Plasma Transferred Arc coatings

Abstract

Plasma Transferred Arc (PTA) is the only thermal spray process that results in a metallurgical bond, being frequently described as a hardfacing process. The superior properties of coatings have been related to the fine microstructures obtained, which are finer than those processed under similar heat input with welding techniques using wire feedstock. This observation suggests that the atomized feedstock plays a role on the solidification of coatings. In this study a model for the role of the powders grains in the solidification of PTA coatings is put forward and discussed. An experiment was setup to discuss the model which involved the deposition of an atomized Co-based alloy with different grain size distributions and deposition currents. X-ray diffraction showed that there were no phase changes due to the processing parameters. Microstructure analysis by Laser Confocal Microscopy, dilution with the substrate steel and Vickers microhardness were used the characterized coatings and enriched the discussion confirming the role of the powdered feedstock on the solidification of coatings.

Development of a device adapted to perform the torch gas tungsten arc welding (GTAW) hardfacing using alloys in powder form

“…The higher the dilution, the more the properties of the coatings are distant from the nominal properties of the alloy. Thus we tried to keep the dilution in the lowest level possible while obtaining a proper metallurgical bonding to the coating, whereas an increase in the dilution causes a decrease in the hardness of the deposit, and this in turn increases the wear volume to deposit diluted as Bond and D'Oliveira (2012). On the other hand it is known that dilution is influenced by the arc current, the deposition rate, speed of the torch, the arc length and frequency of oscillation of the torch second (Balasubrarnanian et al, 2009).…”

Development and Evaluation of the Internal Cladding Process of API 5L X70 Risers with Nickel-based superalloy 625 via PTA Welding

“…Among the welding processes used to carry out the internal cladding of the risers, the Plasma Transferred Arc (PTA) process stands out, being widely used in API 5L X70 cladding applications with Ni-alloys [13] in many industrial areas including chemical processing, nuclear power plants, marine engineering and oil and gas industry, mainly involving corrosion and/or heat resistance [14][15][16][17]. The PTA process is characterized by a high metallurgical quality due to a greater microstructural refining [18][19][20], to the versatility of developing new alloys due to the flexibility of manipulating the chemical composition by mixing powders [21,22] and making composite cladding in which there is a ductile metal matrix and a high hardness material [23][24][25]. Besides these, the PTA process has as operational benefits the smoothness of the deposition of powder without causing oscillation in the melting pool, absence of spatters, independence between heat input and material deposition rate, besides the coaxiality of the powder injection, allowing a high control of the melting pool and the geometry and finish of the cladding [26,27].…”

Wear resistance in hardfacing applied in substrate SAE 1020 using welding process Gas Tungsten Arc Welding (GTAW) alloy Stellite 6 in powder form

“…Such studies have achieved results with excellent quality both in wear resistance as well as corrosion in the maintenance of these properties at higher temperatures. The behavior of these properties is directly related to the process parameters such as welding current, because its intensity and type directly influences the dilution and microstructure of the deposit according to Bond and D'Oliveira (2012) and Madadi et al (2011). The GTAW process has important features, since they have weld beads of high quality, free of debris, rust, and waive any treatment after welding.…”