GOALI: Frictional Ignition of Metals in High-Pressure Oxygen Environments

目前正在开发的富氧化剂分级燃烧（ORSC）和全流分级燃烧（FFSC）火箭发动机在燃料效率和推力方面比传统的燃气发生器发动机循环有显著的改进。ORSC和FFSC动力循环使用预燃室来产生富含氧化剂的燃烧气体流，该燃烧气体流驱动涡轮机，然后与主燃烧室中的剩余燃料一起燃烧。然而，在富含氧化剂的条件下操作火箭发动机的预燃室提出了重大的材料工程挑战;大多数材料在高压富氧环境下容易点火和燃烧。火箭发动机最关心的点火机理之一是由于高速旋转部件在高压富氧环境中的摩擦而引起的摩擦点火。最近两次值得注意的发射失败，Sea Launch的NSS-8和Orbital的Orb-3，被认为是由金属的摩擦点火引起的。这项工作的重点是确定的物理机制，驱动摩擦点火的工程合金在高压氧气。高速滑动磨损的实验表明，摩擦点火的结果从严重的氧化磨损的发病，对应于在摩擦界面处的润滑氧化物tribolayer的故障。这种磨损转变的根本原因知之甚少，可能因具体材料系统而异。该提案将解决这一理解上的差距，首次揭示测试条件和合金化学对几种重要航空航天工程合金上形成的氧化物摩擦层的性能、结构和稳定性的影响。这些见解将连接微观尺度的结构演化过程与宏观尺度的材料现象，如摩擦点火，摩擦学，机械化学和物理冶金领域的重要科学意义。材料科学家可以利用这种理解来设计新的合金，以抵抗灾难性的摩擦点火，火箭发动机设计师可以利用这种理解来实施设计和制造修改，以降低由于金属发动机部件意外点火而导致发动机故障的风险。这些发展将使强大的可重复使用运载火箭成为关键新兴空间技术的基础，例如用于高速天基互联网的卫星巨型星座，可靠的行星际船员和商业运输，以及用于低频射电天文学的大型空间射频望远镜。所有这些都有望改变商业和我们对宇宙的理解。技术总结预测氧化物摩擦层破裂的条件在高速滑动磨损过程中仍然是一个重大的挑战，因为控制摩擦层的生长、性能和热机械稳定性的基本机制知之甚少。这部分是因为氧化物摩擦层似乎通过迭代瞬态氧化过程生长，这使得与常规静态氧化期间形成的氧化物鳞片的直接比较复杂化。结合磨损实验、接触力学理论和冶金热化学，本研究将检验严重氧化磨损的发生与摩擦点火之间的假设关系，并揭示高速滑动过程中氧化物击穿的机制。该项目将开始进行高速磨损试验，以表征几种重要模型材料在高压氧环境下的摩擦、磨损和点火行为。接下来，磨损表面和机械性能的回收样品将其特征在于非原位深入了解驱动氧化物击穿的微观机制。最后，实验结果将结合摩擦加热，氧化物生长和接触力学的物理模型，以确定氧化物击穿和摩擦点火之间的关系。这项工作的结果将揭示关键任务航空航天合金中摩擦层击穿和摩擦点火之间的重要关系，以及在严重氧化磨损开始时驱动氧化物摩擦层生长和降解的物理机制。该奖项反映了NSF的法定使命，并被认为值得通过使用基金会的智力价值和更广泛的影响审查标准进行评估来支持。

Non-Technical Summary The oxidizer-rich staged combustion (ORSC) and full-flow staged combustion (FFSC) rocket engines currently under development offer dramatic improvements in fuel efficiency and thrust over the traditional gas generator engine cycle. ORSC and FFSC power cycles use a preburner to produce an oxidizer-rich stream of combustion gases that drives the turbine, then burns with the remaining fuel in the main combustion chamber. However, operating the preburner of a rocket engine under oxidizer-rich conditions presents significant materials engineering challenges; most materials are susceptible to ignition and combustion under a high-pressure oxygen-rich environment. One of the ignition mechanisms of greatest concern to rocket engines is frictional ignition due to rubbing of high-speed rotating components in high-pressure oxygen-rich environment. Two notable recent launch failures, Sea Launch’s NSS-8 and Orbital’s Orb-3, are believed to have arisen from frictional ignition of metals. This work focuses on determining the physical mechanisms that drive frictional ignition of engineering alloys in high-pressure oxygen. Experiments on high-speed sliding wear suggest that frictional ignition results from the onset of severe oxidational wear, corresponding to a breakdown of a lubricating oxide tribolayer at the rubbing interface. The underlying causes of this wear transition are poorly understood and likely vary according to the specific material system. This proposal will address this gap in understanding, revealing, for the first time, the effects of test conditions and alloy chemistry on the properties, structure, and stability of oxide tribolayers that form on several important aerospace engineering alloys. These insights will connect micro-scale structural evolution processes with macro-scale materials phenomena, such as frictional ignition, with important scientific implications for the fields of tribology, mechanochemistry, and physical metallurgy. This understanding could be used by materials scientists to design new alloys resistant to catastrophic frictional ignition, and by rocket engine designers to implement design and manufacturing modifications that reduce the risk of engine failure due to unintended ignition of metal engine components. These developments will enable robust reusable launch vehicles that will serve as the foundation for key emerging space technologies, such as satellite mega-constellations for high-speed space-based internet, reliable interplanetary crew and commerce transport, and large in-space RF telescopes for low-frequency radio astronomy, all of which promise to transform commerce and our understanding of the universe.Technical SummaryPredicting the conditions under which oxide tribolayers break down during high-speed sliding wear remains a significant challenge because the underlying mechanisms that control the growth, properties, and thermomechanical stability of tribolayers are poorly understood. This is partly because oxide tribolayers appear to grow via an iterative transient oxidation process, which complicates direct comparison with oxide scales formed during conventional static oxidation. Using a combination of wear experiments, contact mechanics theory, and metallurgical thermochemistry, this proposed research will test the hypothesized relationship between the onset of severe oxidational wear and frictional ignition, as well as reveal the mechanisms of oxide breakdown during high-speed sliding. The project will begin with high-speed wear testing experiments to characterize the friction, wear, and ignition behaviors of several important model materials under high-pressure oxygen environments. Next, the wear surface and mechanical properties of recovered samples will be characterized ex situ to gain insight into the micro-scale mechanisms that drive oxide breakdown. Finally, the experimental results will be combined with physics-based models of frictional heating, oxide growth, and contact mechanics in order to determine the relationship between oxide breakdown and frictional ignition. The results of this work will reveal an important relationship between tribolayer breakdown and frictional ignition in mission-critical aerospace alloys, as well as the physical mechanisms that drive oxide tribolayer growth and degradation at the onset of severe oxidational wear.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.