Materials Performance

DEC 2014

Materials Performance is the world's most widely circulated magazine dedicated to corrosion prevention and control. MP provides information about the latest corrosion control technologies and practical applications for every industry and environment.

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6 DECEMBER 2014 MATERIALS PERFORMANCE NACE INTERNATIONAL: VOL. 53, NO. 12 —Kathy Riggs Larsen UP FRONT New Perspective on Corrosion of Steel in Seawater In a study on microbiologically in- f luenced corrosion (MIC) and the long-term corrosion of mild steel in natural and ultraviolet (U V)- treated coastal seawater, re- searchers at The University of Newcastle (Callaghan, New South Wales, Australia) show that pit- ting plays a key role in MIC of steel in seawater. They suspected pit- ting corrosion was involved that mass loss measurement wasn't registering. They compared corrosion in local natu- ral seawater with the corrosion measured after filtering and sterilizing seawater from the same source using U V radiation. There was little change to the seawater, except that nearly all of the living organisms were effaced. The researchers' work throws new light on what MIC does to steel in seawater. Mass loss is only part of the picture. For applications such as pipelines, pitting is much more significant. Their findings will help predict how MIC may affect existing major infrastructure, includ- ing water injection pipelines, holds in bulk carrier ships, and ballast tanks in older ships. Read the CORROSION paper at dx.doi.org/10.5006/1122 to learn more. Metallic Alloy Is Tough and Ductile at Cryogenic Temperatures A new concept in metallic alloy design, "high-entropy alloys," has yielded a multiple-element material that has tested as one of the toughest on record, with toughness, strength, and ductility that improve at cryogenic temperatures. This multi-element alloy was synthesized and tested through a collaboration of researchers at the U.S. Department of Energ y's (DOE) Lawrence Berkeley and Oak Ridge National Laboratories (Berke- ley, California and Oak Ridge, Tennessee). According to the researchers, high- entropy alloys do not derive their proper- ties from a single dominant constituent or a second phase. Conf igurational entropy increases with the number of alloying elements—counteracting the tendency for compound formation and stabilizing the alloys into a single phase like a pure metal. By combining high- purity elemental starting materials, high-quality samples of CrMnFeCoNi in ~10-mm thick sheets were produced. This alloy crystalizes as a single-phase, face- centered cubic solid with exceptional damage tolerance, tensile strength >1 GPa, and fracture toughness values that are off the charts. For more informa- tion, visit newscenter.lbl.gov. Welding Microstructure Affects Corrosion Resistance of Magnesium Alloy Joints Photo credit: NASA. A team of researchers from the University of Toronto (Toronto, Ontario, Canada) and the Engineering Research Institute of China Nuclear Industry Fifth Construc- tion, Ltd. (Shanghai, China) are exploring the corrosion behavior of magnesium alloy welds. Using the scanning reference electrode technique (SR ET), the team was able to scan a sample weld surface in close proximity (10 µm) to record the instantaneous open cell potential at the surface, which was plotted as a color map to visualize local changes in open cell potential. They observed corrosion behavior relating to the microstructure of the weld and determined that welding conditions are important to ensure corro- sion resistance as well as mechanical per- formance of the joint. The team proposed a model that correlates microstructural changes in the welded region to macro- scopic corrosion observed upon the joint's exposure to corrosive media. To learn more, read the CORROSION paper at dx.doi.org/10.5006/1145. Dispersing Carbon Nanotubes to Improve Coatings Researchers with the UPV/EHU-Univer- sity of the Basque Country (Leioa, Basque Country, Spain) analyzed dispersion of carbon nanotubes throughout epoxy res- ins. Carbon nanotubes improve the prop- erties of resin coatings; however, to enhance these properties, the carbon nanotubes (which tend to form clusters and group together) must be properly dis- tributed throughout the material, and various strategies are used to spread the carbon nanotubes across the polymer matrix. The researchers found the disper- sion of the nanotubes improved consider- ably with copolymers—blocks of different polymers joined by chemical bonds—and the properties of the epoxy resin-based coatings were maintained and even improved in some cases. The researchers chemically transformed one copolymer block (butadiene) to make it compatible with the epoxy resin matrix, then divided another block (styrene). Since it has a covalent bond with the butadiene, the division was on a nanometric scale and nanostructures were produced, enabling the carbon nanotubes to disperse across the epoxy matrix without forming clus- ters. The coating properties could be improved by varying the quantities of copolymers and nanotubes. For more information, visit ehu.es.

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