Abstract Machining procedures of welding deposits are usual and result on cold work hardened surfaces. The cold work effect on cavitation erosion of an austenitic stainless steel surface is assessed. FeCrMnSiB coatings were processed by PTA on AISI 304 plates. Specimens were grouped as the cold work deformed surface (CWHS) and the undeformed polished surface (UPS) specimens. Top surface and transverse section of coatings were analysed for slip lines and hardness changes by light microscopy and Vickers microhardness measurements. Ultrasonic cavitation tests were conducted in accordance to ASTM G32-10. CWHS specimens exhibited slip lines and hardened surfaces while UPS specimens did not show traces of slip lines and had insignificant changes on microhardness. Cold work prior to cavitation indirectly increased the nominal incubation time and reduced the maximum erosion rate. Cold work increases the duration of the acceleration period postponing the onset of the maximum erosion rate and enhancing cavitation resistance.

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.

Surface tailoring with plasma transferred arc (PTA) hardfacing involves the deposition of powder mixtures to produce coatings with an almost unlimited chemical composition. PTA hardfacing is particularly important for processing low weldability alloys, such as those for high-temperature applications, of which NiCrAlC is an example. This study analyzed NiCrAlC coatings processed by PTA using a mixture of elemental powders. Deposition on AISI316L plates was carried out with currents of 100 A and 130 A to induce variations in the chemical composition of the coatings, which were also subjected to isothermal exposure at temperatures of up to 1000 ºC for up to 72 hours in an air furnace. The results show that the aluminide compounds were stable, the coatings that solidified more slowly having the highest hardness after temperature exposure and potentially being suitable for use in high-temperature abrasion environments.

Revestimentos soldados são amplamente usados para proteger componentes mecânicos entretanto a maioria das técnicas de soldagem disponíveis restringe a variedade de ligas de alta resistência que podem ser depositadas. O processo de plasma por arco transferido permite ultrapassar esta limitação ao utilizar material de adição na forma de pó, oferecendo a possibilidade de se customizar a composição dos revestimentos e em consequências as suas propriedades. A elevada resistência mecânica e inercia química das ligas de aluminetos tornam estas ligas atrativas para a proteção de componentes diversos. Entretanto a grande interação com o substrato que ocorre quando do processamento exige que para a otimização das propriedades e soldabilidade seja realizada uma a análise de cada sistema liga e substrato. Neste trabalho foram processados e caracterizados revestimentos utilizando uma liga fundida e triturada de Nb40wt%Al e analisado o efeito do Fe e do C nas características dos revestimentos. O trabalho confirmou que é possível processar revestimentos íntegros de Nb40wt%Al por PTA e que ocorre uma forte interação com o substrato, que vai determinar a microestrutura final e as propriedades do revestimento. Destaca-se que na customização de revestimentos de Nb-Al a diluição tem de ser considerada logo nos estágios iniciais do projeto do revestimento.

Hardfacing is widely applied to components yet the majority of the welding techniques available restrain the variety of hard alloys that can be deposited. Plasma Transferred Arc hardfacing offsets this drawback by using powdered feedstock offering the ability to tailor the chemical composition of the coating and as a consequence its properties. The high strength and chemical inertia of aluminide alloys makes them very suitable to protect components. However, the strong interaction with the substrate during hardfacing requires analysis of each alloy system to optimize its properties and weldability. This work analyzed coatings processed with a cast and ground Nb40wt%Al alloy and the effect of Fe and C on the coatings features. It confirmed that sound Nb aluminide coatings can be processed by plasma Transferred arc hardfacing and will have a strong interaction with the substrate, which determines the final microstructure and properties of coatings. Final remarks point out that during Nb-Al coating tailoring the interaction with the substrate has to be considered at the early stages of design process.