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American Society for Testing and Materials

Recent advances in friction-stir welding : Process, weldment structure and properties

The metallurgy of zinc-coated steel

Welding Metallurgy of

Wire-feed additive manufacturing (AM) is a promising alternative to traditional subtractive manufacturing for fabricating large expensive metal components with complex geometry. The current research focus on wire-feed AM is trying to produce complex-shaped functional metal components with good geometry accuracy, surface finish and material property to meet the demanding requirements from aerospace, automotive and rapid tooling industry. Wire-feed AM processes generally involve high residual stresses and distortions due to the excessive heat input and high deposition rate. The influences of process conditions, such as energy input, wire-feed rate, welding speed, deposition pattern and deposition sequences, etc., on thermal history and resultant residual stresses of AM-processed components needs to be further understood. In addition, poor accuracy and surface finish of the process limit the applications of wire-feed AM technology. In this paper, after an introduction of various wire-feed AM technologies and its characteristics, an in depth review of various process aspects of wire-feed AM, including quality and accuracy of wire-feed AM processed components, will be presented. The overall objective is to identify the current challenges for wire-feed AM as well as point out the future research direction.

Wire-feed additive manufacturing of metal components: technologies, developments and future interests

A Mossbauer study was made of all the single intermediate phases in the zinc-iron system. These phases were prepared by a heat-treatment method, and the Mossbauer transmission spectrum of each phase was recorded. The spectra were fitted on the basis of the crystal structure of each phase. The computer-fitted results were reported in terms of isomer shift, quadrupole splitting, and line width. These single-phase spectra were used as standards for the analysis of an electrodeposited zinc-iron alloy coating (11 wt pet Fe). The main phase detected in the coating was the δ phase, which was confirmed by X-ray diffraction analysis. The advantages of the Mossbauer spectroscopy technique in comparison with the X-ray diffraction method are discussed.

A mössbauer study of zinc-iron intermediate phases and electrodeposited coatings

Iron aluminide weld overlay coatings are currently being considered for enhanced sulfidation resistance in coal-fired low NO{sub x} boilers. The use of these materials is currently limited due to hydrogen cracking susceptibility, which generally increases with an increase in aluminum concentration of the deposit. The overall objective of this program is to attain an optimum aluminum content with good weldability and improved sulfidation resistance with respect to conventional materials presently in use. Research has been initiated using Gas Tungsten Arc Welding (GTAW) in order to achieve this end. Under different sets of GTAW parameters (wire feed speed, current), both single and multiple pass overlays were produced. Characterization of all weldments was conducted using light optical microscopy, scanning electron microscopy, and electron probe microanalysis. Resultant deposits exhibited a wide range of aluminum contents (5--43 wt%). It was found that the GTAW overlays with aluminum contents above {approximately}10 wt% resulted in cracked coatings. Preliminary corrosion experiments of 5 to 10 wt% Al cast alloys in relatively simple H{sub 2}/H{sub 2}S gas mixtures exhibited corrosion rates lower than 304 stainless steel.

Iron aluminide weld overlay coatings for boiler tube protection in coal-fired low NOx boilers

A metallurgical mechanism for corrosion-fatigue (circumferential) crack initiation and propagation in CrMo boiler tube steels

Theη toG phase transformation in electrodeposited iron-zinc alloy coatings is a rapid diffusional phase transformation occurring in the nanometer-scale microstructure of the coatings. Iron-supersaturated zinc, orη phase, undergoes a decomposition process to an iron-deficient Γ-like, orG, phase at temperatures near 150 it°C. The phase transformation is preceded by a polygonization process, driven by strain energy and/or supersaturation in the material. TheG phase nucleates on boundaries within theη phase and grows into 30- to 80-nm equiaxed grains. The activation energy for the transformation varies with iron content, which may indicate that solute effects influence boundary diffusion of zinc.

Arnold R. Marder

Papers

A mössbauer study of zinc-iron intermediate phases and electrodeposited coatings

Iron aluminide weld overlay coatings for boiler tube protection in coal-fired low NOx boilers

A metallurgical mechanism for corrosion-fatigue (circumferential) crack initiation and propagation in CrMo boiler tube steels

η to G phase transformation in electrodeposited iron-zinc alloy coatings

Identification of nano-precipitates in a ferritic alloy steel using secondary electron STEM imaging