• Published July 7th, 2024

Comparative Analysis of High-Strength vs Conventionally Processed Tungsten

Ross Dillion, Lisa Powell and Jeremy E. Schaffer

Tungsten, known for its exceptional hardness and high melting point, is a critical material in various high-stress applications, such as aerospace, robotic cables, and industrial manufacturing [1,2]. The properties of tungsten are significantly influenced by its processing techniques, which determine its strength, ductility, and overall performance. In this work, a process for high strength is demonstrated to give 12 to 25 µm (~0.0005 to 0.001 in) wire properties exceeding 6 GPa tensile strength with work energy to fracture (modulus of toughness) greater than 100 mJ/mm3. These properties could give a significant step up in the structural fatigue performance of microcables for robotic manipulation and other applications.

Fort Wayne Metals has developed an advanced processing technique for tungsten that markedly enhances its strength. This high strength processed tungsten undergoes a series of mechanical treatments which can increase the overall ultimate tensile strength by over 30%, and give:

1. Enhanced Tensile Strength: This tungsten exhibits superior tensile strength, making it more resilient under mechanical stress.
2. Improved Ductility: The advanced processing allows for greater ductility at a smaller diameter, reducing the risk of brittle fracture.
3. Uniform Grain Structure: The refined grain structure results in consistent performance across kilometers of material length.

Traditional methods of tungsten processing involve warm working or hot to warm drawing techniques [3]. While these methods are effective, they often leave the material with certain limitations, including:

1. Lower Tensile Strength: Conventionally processed tungsten does not achieve the same level of tensile strength.
2. Brittleness: The traditional processes can result in a more brittle material, increasing the likelihood of fractures under stress [4].
3. Inconsistent Microstructure: Conventional processing can lead to a heterogeneous grain structure, resulting in variable material performance [5].

Figure 1 shows high strength processed tungsten compared to conventionally warm drawn 25 µm (0.001 in) wire. Strength is improved from about 4 to about 5.5 GPa and the work energy to fracture is increased from 40 to 125 mJ/mm3. Figure 2 shows the same source material after further process refinement and a diameter reduced to 12 µm with a strength of nearly 1 million psi or 6.8 GPa.

Figure 1: Stress-strain curve comparing conventionally processed tungsten (as received) with Fort Wayne Metals high strength processed material at 25 µm (0.0010 in) diameter.

Figure 2: Stress-strain curve of Fort Wayne Metals processed tungsten material at 12 µm (~ 0.0005 in) diameter achieving a UTS of nearly 6.8 GPa or 1 million psi.

The advanced processing techniques employed by Fort Wayne Metals lead to a tungsten product that is not only stronger and more ductile but could also be more reliable in critical applications. The high strength processed tungsten from Fort Wayne Metals represents a substantial advancement in properties with greater than 30% strength gains and more than 2-fold toughness increase over conventional tungsten processing, offering enhanced mechanical properties and greater reliability, crucial for demanding applications such as robotic manipulation. Further work is underway toward characterization of structural fatigue durability and total applied performance.

References

1. Summers, Michael P. "Rope selection for rope drive transmissions used in robotic manipulation." (2010).
2. Schaffer, Jeremy E., et al. "Superlative Strength Wire and Cable For Force Transmission." (2020).
3. Briant, Clyde L. "Tungsten: properties, processing, and applications." Advanced materials & processes 154.5 (1998): 29.
4. P. Schade, Wire Drawing Failures and Tungsten Fracture Phenomena. International Journal of Refractory Metals and Hard Materials. Volume 24, Issue 4, 2006, Pages 332-337.
5. Ripoll M.R., et al., Reduction of Tensile Residual Stresses During the Drawing Process of Tungsten Wires. Mater. Sci. Eng. A. 2010;527:3064–3072. doi: 10.1016/j.msea.2010.01.079.

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