Improving penetrability is a key issue in plasma arc welding (PAW). Increasing plasma energy is one way to improve arc penetrability. Gas focusing plasma arc welding (GF-PAW) platform is self-designed and developed. Role and action mechanism of focusing gas is initially studied. Focusing gas makes no obvious effects on arc pressure distribution and value. Focusing gas changes arc temperature distribution outer orifice, while focusing gas does not affect arc temperature distribution inner orifice. Focusing gas can constrict arc and arc energy increases 210 W with an increase in arc voltage of 1.4 V. GF-PAW can fully penetrate the whole work-piece while PAW can only partially penetrate the work-piece under welding current 150 A. GF-PAW can improve penetrability, and may increase welding speed, and has a potential application in manufacturing.

In this work, an Inconel 625 thin-wall structure was fabricated by the gas tungsten arc welding (GTAW) hot-wire arc additive manufacturing process. The microstructure and mechanical properties of the Inconel 625 samples, extracted from different orientations and locations of the thin-wall structure, were investigated and compared. The results showed that the additively manufactured Inconel 625 component, made by hot-wire GTAW, had good quality. Its microstructure consisted of dendrites, equiaxial crystals, and cellular crystals. The average hardness from the bottom to the top was similar, indicating that the thin wall had good consistency. The plasticity in the deposition direction was better than those in the other three regions, which was related to the dendritic structure in the sedimentary direction.

Super duplex stainless steel UNS S32750 is widely used in marine industries, pulp and paper industries, and the offshore oil and gas industry. Welding manufacturing is one of the main manufacturing processes to make material into products in the above fields. It is of great importance to obtain high-quality welded UNS S32750 joints. The austenite content and ferrite content in UNS S32750 play an important role in determining UNS S32750 properties such as mechanical properties and corrosion resistance. However, the phase proportion between the ferrite phase and austenite phase in the welded joint will be changed during welding. Lots of research has been done on how to weld UNS S32750 and how to obtain welded joints with good quality. In this work, the recent studies on welding UNS S32750 are categorized based on the welding process. The welding process for UNS S32750 will be classified as gas tungsten arc welding, submerged arc welding, plasma arc welding, laser beam welding, electron beam welding, friction stir welding, and laser-MIG hybrid welding, and each will be reviewed in turn. The microstructure and properties of the joints welded using different welding processes will also be discussed. The critical challenge of balancing the two phases of austenite and ferrite in UNS S32750 welded joints will be discussed. This review about the welding process for UNS S32750 will provide people in the welding field with some advice on welding UNS S32750 super duplex stainless steel.

In order to prevent the lead-bismuth eutectic (LBE) corrosion of stainless-steel components used in nuclear reactors, the FeCrAlTiC-xY₂O₃ coatings were prepared on 304 stainless steel (304SS) by laser cladding. After adding Y₂O₃, Y₂TiO₅ and Y₂Ti₂O₇ formed, which have a combined strengthening effect on improving hardness. The 0.2 wt.% Y₂O₃ coating showed the highest hardness as ~489 HV. In the 400 °C wear test, the weight loss of coating samples was less than ~5.2 mg, while the weight loss of 304SS samples was ~35.5 mg. The 0 wt.% Y₂O₃ coating showed the highest wear resistance, indicating that adding Y₂O₃ could result in the decrease of wear resistance. The LBE corrosion behaviors of coatings at 500 °C were investigated. The results showed that a uniform and dense oxide scale with a low growth rate was obtained on the coating surface, and no penetration of LBE into the coating was observed. After 1000 h of corrosion, the oxide scale of coatings grew to merely a ~0.3 μm thickness. The corrosion resistance mechanism of the coating in oxygen-saturated LBE at 500 °C was proposed based on experimental results along with a thermodynamic and kinetic analysis.

Improving the surface performance and service life of 60Si2Mn steel is an important issue in agricultural machinery. A FeCrV15 coating layer may exhibit excellent performance in wear resistance. This research focuses on studying the microstructure and wear resistance of the FeCrV15 coating layer at various scanning speeds through laser cladding. Microstructure, phase distribution, surface hardness, and wear resistance of the coating layers are analyzed using X-ray diffraction (XRD), scanning electron microscopy (SEM), a microhardness tester, and laser confocal microscopy. The results indicate that the FeCrV15 alloy coating consists of γ-Fe, V₈C₇, and Cr₇C₃. The microhardness of the FeCrV15 coatings increases with the increase in the scanning speed. At a scanning speed of 8 mm/s, the highest microhardness reaches 727.5 ± 27 HV, approximately 2.5 times higher than the substrate. The friction and wear test of the coating is conducted using a 4 mm diameter Si₃N₄ ball grinding pair. The coatings prepared at different scanning speeds exhibit lower average coefficients of friction and wear rates compared to the substrate. Both the average coefficient of friction and wear rate decrease with increasing scanning speed. At a scanning speed of 8 mm/s, the lowest average coefficient of friction and the lowest wear rate were observed. The main wear mechanisms of the coating are oxidative wear and adhesive wear, with a small amount of abrasive wear.