Abstract：
Monocrystalline barium fluoride (BaF2), known for its exceptional optical properties in the infrared spectrum, exhibits anisotropy that influences surface quality and material removal efficiency during ultraprecision machining. This research explores the impact of anisotropy on the deformation and removal mechanisms of monocrystalline BaF2 by integrating nanoscratch tests with molecular dynamics (MD) simulations. Nanoscratch tests conducted on variously oriented monocrystalline BaF2 surfaces using a ramp loading mode facilitated the identification of surface cracks and a systematic description of material removal behaviors. This study elucidates the effect of crystal orientation on the ductile-brittle transition (DBT) of monocrystalline BaF2, further developing a critical depth prediction model for DBT on the (111) crystal plane to reveal the underlying anisotropy mechanisms. Moreover, nanofriction and wear behaviors in monocrystalline BaF2 are found to be predominantly influenced by scratch direction, crystal surface, and applied load, with the (110) and (100) planes showing pronounced frictional and wear anisotropy. A coefficient of friction model, accounting for the material\'s elastic recovery, establishes the intrinsic relationship between anisotropic friction and wear behaviors, the size effect, and scratch direction. Lastly, MD modeling of nanoscratched monocrystalline BaF2 reveals the diversity of dislocations and strain distributions along the (111) [-110] and [-1-12] crystal directions, offering atomic scale insights into the origins of BaF2 anisotropy. Thus, this study provides a theoretical foundation for the efficient processing of fluorine-based infrared optic materials exhibiting anisotropy.
摘要：
单晶氟化钡（BaF2），以其在红外光谱中的特殊光学特性而闻名，在超精密加工过程中表现出影响表面质量和材料去除效率的各向异性。本研究通过将纳米划痕测试与分子动力学（MD）模拟相结合，探索了各向异性对单晶BaF2的变形和去除机制的影响。使用斜坡加载模式在各种取向的单晶BaF2表面上进行的纳米划痕测试有助于识别表面裂纹和系统地描述材料去除行为。这项研究阐明了晶体取向对单晶BaF2的韧性-脆性转变（DBT）的影响，进一步开发了DBT在（111）晶面上的临界深度预测模型，以揭示潜在的各向异性机制。此外，单晶BaF2的纳米摩擦和磨损行为主要受划痕方向的影响，晶体表面,和施加的载荷，（110）和（100）平面显示出明显的摩擦和磨损各向异性。摩擦系数模型，考虑材料的弹性恢复，建立各向异性摩擦与磨损行为之间的内在关系，尺寸效应，和划痕方向。最后,纳米光栅单晶BaF2的MD模型揭示了沿（111）[-110]和[-1-12]晶体方向的位错和应变分布的多样性，为BaF2各向异性的起源提供原子尺度的见解。因此，本研究为具有各向异性的氟基红外光学材料的高效加工提供了理论基础。
