Externally-applied coatings such as chromium, cadmium, and even paints can be difficult to apply and, if damaged in service, can lead to catastrophic failure on highlystressed aircraft components such as landing gear. Most coating techniques were developed before stringent environmental regulations became effective and, therefore, are not environmentally friendly. As a result, significant effort is now underway to develop new coating technologies.
The objective of this program was to design, prototype, and characterize a new corrosion resistant steel that could significantly reduce the Department of Defense’s use of cadmium during the rework, maintenance, and manufacturing of structural steel components for aerospace applications.
There were four primary technical tasks within the program. The specific activities within each task resulted from the application of a materials-by-design approach, which integrates processing, structure, property, and performance relations within a multi-level systems structure. Initially, a flow block diagram was generated, and models for the design process were calibrated. An alloy composition and the processing variables were then determined. Next, 300 pounds of the prototype material were acquired and characterized. The prototype showed properties very close to the design objectives, thereby demonstrating the possibility of delivering an entirely new corrosion resistant steel that possesses similar mechanical properties to 300M steel and is compatible with current and emerging aerospace coating processes.
The first prototype alloy, a martensitic steel, met the primary objectives for ductility and corrosion resistance but was approximately 2 HRC (Rockwell C-Scale Hardness) low in hardness and 15 percent low in strength. Most of this strength deficit was due to an improper heat treatment during the forging of the prototype at the mill, necessitating a subsequent high temperature homogenization treatment leading to undesirable grain growth. Model estimates indicate that with correct forging practices, the alloy design would have been within 5 percent of the desired strength goals. The measured MS (martensite start) temperature of the alloy was 25 degrees below predictions, indicating retained austenite may have been responsible for the remaining 5 percent strength deficit. The second iteration prototypes are currently under evaluation. This FY00 funded SEED project transitioned to a core FY01 New Start project (see WP-1224).
The use of mechanistic computational design technology enables the rapid development of entirely new materials and processes at costs that are orders of magnitude below what is incurred through the historical application of “trial and error” discovery methodology.