another stage of production. There are also inspection and metrology challenges, and depending on the application, AM is not always faster and less costly than traditional manufacturing. Still in its formative stages, there are possibilities for thermal spray in AM. In the medical field, thermal spraying might be the final stage of a custom 3D-printed body implant. Additive manufactured plastic parts that require conductivity and wear properties can rely on thermal spraying to provide them. There is development being done on spray forming rocket nozzles, and most interesting, research is being conducted on direct writing of thermocouples, strain gauges, integrated wiring, and sensors using thermal spray. C2 Thermal Spray Committee Update David Lee, proxy committee chair, gave the audience an update on the American Welding Society’s C2 Committee on Thermal Spray. This committee establishes standards on thermal spray design, manufacture, inspection, and test methods, as well as develops guides. It also works on standardizing thermal spray symbols and definitions. Presently, AWS has seven publications that offer guides and specifications for thermal spraying, with three new guides in the works on powders, masking, and equipment selection. The committee is composed of 20 members and 10 advisors representing producers, end users, educators, and consultants. Also in the planning stages by AWS Learning is an online learning module that will present the fundamentals of thermal spraying, which will include its science, equipment, materials, variables, and safety. Damage-Tolerant Thermal Spray Coatings Greg Smith (Fig. 2), an ITSA scholarship recipient, spoke of the research being conducted at Stony Brook University on damage-tolerant thermal spray coatings. Understanding how to stop a crack from happening or progressing requires an extensive study of failure modes and experiments in arresting cracks. With thermal spraying, the real challenge is trying to measure an inherently unstable process. Torch, operating parameters, kinetic energy, surface preparation, cooling, and plume character are just some of the factors that enter into reproducibility. One approach for the design of tolerant coatings being researched at the university was to take a lesson from nature, specifically the mollusk shell. Many shells are composed of two layers: a nacreous layer that is damage tolerant, and above it, a hard, thick layer that blunts stresses from outside forces. Using a rod flame spray process, a layer was deposited followed by a polymer infiltration. Then a dense ceramic layer was deposited with the high-velocity oxygen fuel (HVOF) process. Subsequent bending tests showed the outer layer provided good strength. On its fracture, the load was redistributed to the more flexible under layer. Experiments are continuing with this concept. The History of Thermal Spray James Weber, Sulzer Chemtech Tower Field Service, gave an interesting historical perspective on thermal spraying. He claimed thermal spraying got its start from a method patented by Oerlikon in 1882 of spraying lead powders against a fixed surface. The process was developed to make lead plates for batteries. As this process was refined, more patents followed, and lead was the material for early coatings. Thermal spraying really got its boost from the work of Ulrich Schoop, who is considered the “Father” of thermal spraying. In 1909, he patented the first commercially viable thermal spray plant for delivering metal coatings. In 1912, he developed the first practical flame spray wire gun (or pistol, as it was called then), and in 1914, he patented a twin wire arc spray gun. He continued his research into materials and methods of thermal spraying, including plasma spraying, and by the 1930s thermal spraying was considered an accepted process for applying coatings, especially in corrosion prevention. Thermal Spray: Rules of Thumb Daryl Crawmer, Fisher Barton Technology Center, made an interesting presentation on rules of thumb for thermal spraying. He started with his first law, “The only absolute in thermal spray is that there are no absolutes.” Then went on to his second law, “There are no small carrier gas leaks,” and “All carrier gas JULY 2016 / WELDING JOURNAL 47 Fig. 2 — Greg Smith talked about research being conducted at the State University of New York at Stony Brook on nature-inspired, damage-tolerant thermal spray coatings.
Welding Journal | July 2016
To see the actual publication please follow the link above