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Thick steel plates are frequently used in shipbuilding, pipelines and other related heavy industries, and are usually joined by arc welding. Deep penetration laser-arc hybrid welding could increase productivity but has not been thoroughly investigated, and is therefore usually limited to applications with medium thickness (5-15 mm) sections. A major concern is process stability, especially when using modern welding consumables such as metal-cored wire and advanced welding equipment. High speed imaging allows direct observation of the process so that process behavior and phenomena can be studied. In this paper, 45 mm thick high strength steel was welded (butt joint double-sided) using the fiber laser-MAG hybrid process utilizing a metal-cored wire without pre-heating. Process stability was monitored under a wide range of welding parameters. It was found that the technique can be used successfully to weld thick sections with appropriate quality when the parameters are optimized. When comparing conventional pulsed and the more advanced cold metal transfer pulse (CMT+P) arc modes, it was found that both can provide high quality welds. CMT+P arc mode can provide more stable droplet transfer over a limited range of travel speeds. At higher travel speeds, an unstable metal transfer mechanism was observed. Comparing leading arc and trailing arc arrangements, the leading arc configuration can provide higher quality welds and more stable processing at longer inter-distances between the heat sources. [ABSTRACT FROM AUTHOR]

Highlights: [•] Nanomechanical testing has been performed based on compression of very small pillars (up to 1μm). [•] Pillars are located at grain boundaries decorated by massive martensite–austenite. [•] Pillars are also located inside grains in martensite/bainite. [•] Very high yield strength (>1500MPa) was found in blocky martensite–austenite phases. [•] The scatter is large, possibly due to different orientations or sampling effects. [Copyright &y& Elsevier]

The present investigation was undertaken to study brazing of the commercially available binary NiTi alloy, using Ag–Ti and Ag–Cu–Ti filler metals in a microwave furnace with Ar–H2 atmosphere. Both filler alloys are successful in joining the shape memory alloy NiTi to itself and to other metals such as nickel-based superalloy and stainless steel. However, interface cracks, pores and oxides were observed due to insufficient protection during the heating and cooling stages. [Copyright &y& Elsevier]

Abstract: Selection of chamber gas composition for a viable and time-consuming underwater repair operation is influenced by the final mechanical properties that each shielding environment can offer. Tensile and fracture toughness tests were performed on five bead-on-plate test samples that were welded under different chamber gas environments at 10bar. The chemical composition, microstructure and mechanical properties of the weld metal were investigated. It was found that the pure He chamber gas offers the best visual and mechanical properties required by standards despite its high costs. CO2 chamber gas was discovered to introduce abundant micro and nanopores in the matrix that can potentially degrade the mechanical properties. He–CO2 mixture however, was assessed to be detrimental due to both dominating bainite transformation and distributed pores in the weld metal. The properties of the weld metal using Ar and Ar–He mixtures were found to be slightly poorer than the properties in pure He case, yet better than the rest of the samples. [Copyright &y& Elsevier]

Abstract: In this paper, mathematical approaches were developed for predicting the hyperbaric GMAW process arc behavior and stability. The variation of stochastic parameters is related to the electrical stability that can be resolved into a number of varying parameters. The results show that most of the arc instability can be traced to the frequency domain of the voltage or current waveform. Uncorrelated current and voltage wave frequencies at higher pressures are found to have a great influence on process stability. [Copyright &y& Elsevier]