Copper beryllium (CuBe) is considered the standard material extensively used for highly loaded low wear bushing applications on military aircraft and many other military platforms. This material has an exceptional suite of performance characteristics; strength, stiffness, density, wear resistance, galling resistance, and corrosion resistance that meet the demanding requirements for high stress in articulating mechanical joints. CuBe is however a hazardous material, and there is concern about its continued utilization because of the severe health effects associated with its use.
The objective of this project was to design and develop an environmentally safe alternative alloy that exhibits equivalent or better performance than incumbent AMS 4533 Copper-Beryllium Alloy; 98Cu – 1.9Be; Solution Heat Treated, and Precipitation Heat Treated material. The preference was to design and produce a material alternative that does not vary with component size, and in doing so, this project relied on solid solution alloying and/or precipitation-hardening so that the alloy strength maintains uniform performance properties in the larger-diameter materials.
A step-wise building block approach was executed, which began with a thorough investigation into the materials that supported the performance requirements being pursued. Criteria were set to meet the following requirements: (1) tensile strength greater than 165,000 psi; (2) yield strength at 0.2% offset greater than 140,000 psi; (3) hardness of 36 to 45 Rockwell C (HRC); and (4) meet or exceed the performance of Cu-Be alloys in terms of friction coefficient in dry sliding conditions against low-alloy steels, wear resistance, resistance to galling and spalling, axial fatigue, and rolling contact fatigue.
Utilization of QuesTek’s Systems by Design Chart, which focuses on Processing, Structure, Properties and Performance, led to the identification of the preferred alternative alloy types in the initial base materials down-selection. Two material types—high-strength precipitation strengthened copper alloy and high strength precipitation-strengthened cobalt alloy—were identified as the most promising alloy design concepts for further development.
The next step in the systems engineering process sketched out the microstructures within each concept material to identify the components that had the potential to achieve the desired properties while maintaining thermal processing capabilities that supported kinetic and thermal phase transformation. A thorough material component analysis was performed to ascertain which components provided the desired benefits and supported a microstructure with nano-scale precipitation strengthening to achieve higher strength levels to meet the performance goals.
Developed materials were produced utilizing typical melt processing methods, and characterization testing was performed to evaluate alternative material performance compared to the AMS 4533 standard material. Tests included: ASTM E8 Tensile strength, ASTM E9 Compression strength, ASTM E606 Strain Life, ASTM G98 Galling, ASTM G99 Pin-on-Disk, and ASTM G133 Reciprocating Ball-on-Flat.
Six alternative alloys were designed, developed, produced, and tested in this project. Both the Cuprium (a copper tin alloy that was spray metal formed at Penn State University) and the NGCo-3A alloys had favorable properties, with the NGCo-3A having the superior performance properties from the alloys evaluated and being the material of choice for down-selection. While the tensile strength of the NGCo-3A was highest among all the alloys, yield strength was lower than the baseline material. The fatigue life, friction, and galling behavior of the NGCo-3A are superior to the baseline material.
As an addition to the design and development of an alternative alloy material, this project with the help of Dr. Christiane Beyer at the California State University at Long Beach and her team prepared finite element modeling simulations to explore and evaluate the stress and wear effects of loaded bushing with and without performance enhancements. A finite element model was developed utilizing the standard and alternative bushing alloy materials property information. Full-scale bushing and test setup geometry measurements were entered into the ABAQUS modeling software to support the simulation. The theory was based on mimicking the full-scale bushing tests so a comparison could be performed to support simulation proof of concept. Several case studies were run to help build a simulation data base that would emulate the wear behavior of a material so predictive wear analysis could be performed for developmental purposes.
Full-scale environmental bushing testing was the final task in comparing the material performance of the standard CuBe to the down-selected NGCo-3A alternative alloy. The supplier performing these tests had a special testing rig to apply the high load conditions to the bushing samples. Two test methods were performed to evaluate the baseline and alternative alloy materials. One was a threshold test that evaluated the comparison of a high load low frequency oscillation where the pin was rotated back and forth 25-degrees in each direction through 0-degrees. The other was an endurance test that evaluated the comparison effects of a high static load while rotating at a low speed. Comparison of the visual effects and charted data results identified that the NGCo-3A alternative alloy had equivalent to and slightly better performance than that of the standard CuBe.
One enhanced bushing design identified in the modeling effort, which incorporated a radius as an alternative to the standard chamfer on the bushing ID, was tested along with the standard bushings although no substantial improvement in bushing performance was identified.
The cobalt-based alternative material supports a safe material replacement so the elimination of manufacturing controls for monitoring and hazardous material migration can be eliminated and provide a safer workplace. Future development work would include improving the yield strength of NGCo-3A by refining the grain size, optimizing heat treat, and developing production and commercialization plans.