【Member Papers】Southern University of Science and Technology --- Investigation of the machinability of (001) single-crystal β-Ga₂O₃ via tribological methodology

      Researchers from the Southern University of Science and Technology have published a dissertation titled "Investigation of the machinability of (001) single-crystal β-Ga₂O₃ via tribological methodology" in Nanotechnology and Precision Engineering.

Acknowlegement

      The authors acknowledge financial support from the Shenzhen Key Laboratory of Intelligent Robotics Flexible and Manufacturing Systems (Grant No. ZDSYS20220527171403009) and the Shenzhen Science and Technology Innovation Commission (Grant No. 20231115111658002). Special thanks to SUSTech Core Research Facilities and the SUSTech Energy Research Institute for Carbon Neutrality for their valuable technical support.

Abstract

      Gallium oxide (Ga₂O₃) is a promising material for next-generation power devices due to its ultrawide bandgap and extremely high critical electric field strength; however, the strong anisotropy and cleavage tendency of Ga₂O₃ pose significant challenges for high-precision surface processing. In this work, a systematic study was conducted through tribological analysis of monocrystalline (001) β-Ga₂O₃. Initially, reciprocal sliding tests were conducted on β-Ga₂O₃ along different crystallographic directions, [100] and [010]. The results revealed that the [100] direction was more wear resistant, while the [010] direction was more prone to failure. Indentation experiments on (001) β-Ga₂O₃ showed extensive slip and cleavage cracking along different crystallographic orientations, indicating that mechanical wear might dominate the wear mode of this material. Subsequently, sliding tests under various environmental conditions revealed that the wear rate was correlated with humidity. Additionally, β-Ga₂O₃ exhibited time-dependent frictional behavior, with its coefficient of friction stabilizing around 0.1, 0.5, and 0.9 at different stages during the wear test. These findings indicate that the frictional behavior of Ga₂O₃ is closely linked to the state of its surface. This study provides critical insights into the tribological behavior of Ga₂O₃ and offers guidance for ultraprecision machining of this material.

Conclusion

      In this study, the machinability and underlying mechanism of (001) single-crystal β-Ga₂O₃ was systematically investigated via tribological methodology. The following conclusions were drawn.

      1.Wear tests conducted along two crystallographic directions, [010] and [100], revealed that β-Ga₂O₃ exhibits severe anisotropic wear behavior. The [100] orientation was identified as the wear-resistant direction, while the [010] orientation exhibited significantly higher wear susceptibility.

      2.Indentation experiments indicated that the deformation and fracture mechanisms of β-Ga₂O₃ were mainly caused by the high-density slip zone along the [010] and [100] directions, which demonstrated that the generated wear debris contributed to the abovementioned material failure.

      3.Sliding tests in the [100] direction under varying environmental conditions showed that the wear rate was increased from 1.5 × 10⁻⁷ mm³/N m in dry air to 4.2 × 10⁻⁷ mm³/N m in humid air (70% RH). This increase in wear rate was attributed to the application of shear stress at the interface between water and β-Ga₂O₃, which promoted the formation of hydroxides that were easily removed as wear debris.

      4.The COF of β-Ga₂O₃ exhibited sliding-cycle-dependent behavior in the stripe test, with values stabilizing at ∼0.1, 0.5, and 0.9 at different wear stages. The wear process progressed through three stages: it began with mild abrasive wear and a low COF, then transitioned to more intense material failure due to a “chain reaction” of wear debris accumulation and crack propagation, resulting in a significant increase in COF.

      These insights enhance the understanding of the wear mechanisms of β-Ga₂O₃ and provide valuable guidance for optimizing processing parameters such as applied load, rotation speed, and abrasive slurry, thus improving the surface finishing quality of (001) single-crystal β-Ga₂O₃.