Mission

The Corrosion Science and Technology Group in the Materials Science and Technology Division at the Oak Ridge National Laboratory develops solutions to environment degradation problems through application of fundamental mechanistic understanding, advanced, characterization techniques, laboratory simulation of extreme environments, extensive materials database, industrial collaborations, field studies, and expertise of our technicians and scientists.

Selected Current Research

• Surface Modification: ORNL is developing unique surface modification approaches based on high-temperature gas reactions (oxidation, nitridation, carburization, etc) to form functional near-surface layer and composite structures. The initial focus is for proton exchange membrane (PEM) fuel cell bipolar plates, where low interfacial contact resistance and high corrosion resistance are needed. However, the approach can potentially be leveraged for a wide range of electrochemical applications needing tailored electrical properties and corrosion resistance.

• AFA Stainless Steels: Alumina-forming austenitic (AFA) stainless steels developed by ORNL are a new class of high-temperature alloy family with an increased upper-temperature corrosion limit that is ≥ 50–200°C higher than that of conventional stainless steels. AFA steels deliver this uniquely superior corrosion resistance with high-temperature strengths approaching that of far more expensive nickel-base alloys, and without sacrificing the typical lower cost, formability, and weldability of conventional stainless steels. These unique attributes make them of interest for a wide range of energy production, chemical, and process industry applications.

• Compatibility with Liquid Metals: The Corrosion Science and Technology Group at ORNL operates an active program to assess the compatibility of a variety of materials with liquid metals. Currently, programs are underway using
  - sodium (alternate material compatibility for fast reactors)
  - lithium and lead-lithium (examine coatings for first wall to limit MHD forces for fusion concepts)
  - mercury (mass transfer, cavitation, and embrittlement studies for the Spallation Neutron Source target)
  as working fluids. High temperature experiments with alkali metals (and a variety of salts, too) frequently include both static capsules and thermal convection loops. Two large vacuum chambers (internal dimensions about 125 cm high and 75 cm diameter; include bake-out capability and turbo-pumps capable of generating 10^-6 torr or better at temperatures up to 900°C; external surfaces water-cooled) facilitate thermal convection loop testing of air-sensitive containment materials.

• Corrosion Testing in Fuel Blends: The Corrosion Science and Technology Group at ORNL is currently engaged in compatibility testing associated with ethanol additions to the transportation fuel supply for two programs:
  - Testing of metals (as well as elastomers and plastics with support from other Groups) exposed to intermediate fuel blends is underway to examine susceptibility of the existing storage and dispensing infrastructure to damage resulting from increase in ethanol in transportation fuel. Testing to date has incorporated reference fuel C (synthetic gasoline) and well as CE10a, CE17a, CE20a, and CE25a. These ethanol fuel blends, designated CE##a, contain ##% ethanol in reference fuel C along with standardized amounts of common contaminants to make the fluid more aggressive in a compatibility sense.
  - Work has just been initiated to examine high temperature corrosion associated with E85 type fuels with engine components. Work will include surface analysis of components removed from engine testing and development of laboratory protocols to safely perform electrochemical tests in autoclaves.

• Biomass Studies: Studies of materials issues in biomass systems have concentrated on thermochemical processes, and these require significantly elevated temperatures. The processes range from torrefaction to pyrolysis to gasification where the temperatures are progressively higher and the desired products range from a solid in the case of torrefaction, a liquid for pyrolysis and a gas for gasification. Material degradation issues include molten salt corrosion of metals and refractories, carburization of heat exchanger tubes, wear/corrosion of augers and corrosion and cracking in acidic organic solutions.

• Oxide Dispersion Strengthened FeCrAl alloys: Oxide Dispersion Strengthened FeCrAl alloys exhibit exceptional high temperature creep and corrosion resistance due to the presence of Yttrium rich nano-oxide particles and the formation of a protective alumina scale. Although the lack of a sufficiently profitable market has led major commercial suppliers to stop Fe-based ODS alloy production, the increasing interest in high performance high temperature alloys for fossil energy applications has led Dour Metal Sro. to re-establish the capabilities to produce ODS alloy ODM751. This alloy features an overlapping circumferential grain structure in the tube form, which provides enhanced hoop creep strength. First batches of the new ODS alloys have been characterized by TEM, and the exact replicate of the ODM751 alloy is expected to be produced in the coming months in quantities large enough for extensive characterization in terms of oxidation behavior, creep resistance and weldability. In order to reduce the cost of the new commercial alloy and enhance its performance, the multiple processing steps, powder atomization, mechanical alloying, extrusion, recristallization heat treatment, cold and/or hot working, will be assessed. High temperature creep and oxidation testing on previous ODM751, MA956 and PM2000 FeCrAl ODS alloys are currently on going to improve the lifetime models that have been developed.