High-tech options give conventional metals a run for their money

Scientists, engineers and manufacturers are busy modifying existing materials and developing new ones that expand the choices for material of construction. They’re eliminating nano-scale flaws that promote alloy corrosion; impregnating alloys to enhance bearing properties; developing copolymer structures that enhance material performance; and leveraging amorphous metals and engineering thermoplastics for new applications.

Alloy refinements: Oxide scale that forms on the outer surface of steel alloys at high temperatures defends the metal from extreme corrosion, but some carbon can still get through. Scientists at the U.S. DOE’s Argonne National Laboratory have detected a nano-scale flaw that allows carbon to dissolve and diffuse through the oxide scale and cause brittleness and corrosion.

Metal nanoparticles embedded within the oxide scale allow the carbon to penetrate the oxide. Argonne focused on eliminating the networks of iron and nickel nanoparticles and developed laboratory-size batches of alloys that are more corrosion-resistant and exhibit as much as 10 times longer life than commercial alloys with similar chromium contents. The development could reduce costs for the chemical, petrochemical and refining industries when it is commercialized. The findings have the potential to influence metal dusting, carburization, alloy development and surface coatings for high-temperature fuel cell applications.

Sulfonated copolymers: A sulfonated copolymer structure can provide a lower-cost, high-performance material alternative for breathable protective clothing, sensors, actuators, filtration, energy-recovery and antifouling applications.

The selectively midblock sulfonated copolymer technology in Kraton Polymer’s MD9150 and MD9200 products exhibit high water vapor transport, ion exchange, chemical resistance and selective gas permeability. The structure also reduces processing temperatures, which saves energy compared to current technology. Kraton’s products are mechanically suited for wet and dry environments, and will be offered in membrane and solution forms for use in shapes, coatings and laminates.

Babbitt-impregnated materials: Engineered materials that combine carbon’s hardness and wear resistance with graphite’s self-lubricating properties and babbitt’s resistance to galling can provide the properties necessary for high-temperature bearings. Oil-free, self-lubricating bearings made from babbitt-impregnated carbon-graphite can handle dry and submerged environments at up to 350°F.

Metallized Carbon Corp.’s high-temperature bearings made with Metcar grades M-161 and M-162 materials exhibit stability, high strength and low friction. They’re non-galling, won’t score the mating shaft, and provide continuous lubrication for their service life. The materials are applicable to bearings, thrust washers, bearing assemblies and mechanical components used in elevated-temperature applications where conventional lubricating methods are impractical.

Amorphous metals: Stamps and master molds for nano-devices require nano-scale features that conventional materials are unable to provide. A material that is more durable than silicon and stronger than steel shows promise for the manufacture of nano-devices. Yale engineers developed a process that uses amorphous metals (bulk metallic glasses (BMGs)) to mold and imprint fine details — from 13 nanometers to several millimeters — and successfully separate the material intact from the mold.

BMGs are slow-flowing liquids with no structure beyond the atomic level. They can be molded like plastics and are more wear-resistant than metals at normal working temperatures. The grain size of a metal’s internal structure limits the level of detail imprinted, but BMG molds aren’t limited in their detail. Template molds made from this material are long-lasting, reliable and cost-effective. Nano-molds, nano-wires, gears and membranes are among the parts that have been fabricated by molding metallic glass.

Engineered thermoplastics: Engineered thermoplastics provide a safe, cost-effective alternative to metal for fluid-handling systems. Copper, stainless steel and brass water valves are expensive. Copper theft is a rapidly growing crime and the lead used in manufacturing brass alloys is a health hazard. From a design perspective, thermoplastic components can be integrated into a single part, whereas metal involves the mechanical assembly of multiple parts.

SABIC Innovative Plastics offers engineered thermoplastic materials, including Noryl and Ultem amorphous resins and LNP Lubricomp compounds. Noryl and Ultem creep less than semi-crystalline thermoplastic resins and preserve their dimensions and valve sealing abilities longer. Noryl GFN1430V resin reduces fatigue and damage caused by pressure fluctuation because thinner wall sections are possible. The amorphous Noryl polyphenylene oxide (PPO) resin provides better hot-water resistance than semi-crystalline resins and otherwise similar performance.

SABIC’s Fluid Engineering Center of Excellence in The Netherlands offers customers access to testing equipment and scientific resources to assist in developing and evaluating new fluid-handling solutions.

E-mail Contributing Editor Sheila Kennedy, managing director of Additive Communications, at [email protected].