Cutting and Shaping of Hard Ceramics with a CO2-Laser

氮化硅和硅等极硬陶瓷 近年来，碳化物引起了相当大的兴趣 作为许多高温工程的潜在材料， 应用. 在其密集的高强度形式，这些 材料被提议用作结构材料 在发电燃气轮机，以提高其效率 使气体入口温度达到约1400 ℃。 这些 材料也被考虑用于汽车燃气 涡轮机、小型热反应堆、滚柱轴承，以及 先进的燃烧室 硅化合物陶瓷的一个重要缺点是其 极高的硬度，使它们的加工和成型成为 极其困难、繁琐和昂贵的程序。 初步工作已经表明， 与传统的激光器相比， 传统的金刚石研磨。 为了证明可行性 激光成型的难加工材料，一个多 已经进行了学科研究， 管理高- 功率CO2激光束和硅化合物陶瓷。 的 一项研究计划着眼于热传递、材料 激光成形的性质和制造方面 过程 正在建立传热模型， 预测单道、多道和 重叠槽，材料去除率，表面 粗糙度等。与模型相关的材料特性 正在测量，包括表面反射率（如 温度、角度和光束偏振的函数），表面 温度和喷射材料特性（颗粒尺寸 数密度）。 陶瓷的材料特性 在激光治疗之前和之后正在进行研究，例如 作为微观结构， 表面、弯曲强度和抗热震性。 激光 加工是在可变操作下进行的 条件和测量正在进行，以确定 质量、一致性、再现性和可预测性， 过程 加工结果从单一和重叠 凹槽被用于验证热传递模型。

Extremely hard ceramics such as silicon nitride and silicon carbide have generated considerable interest in recent years as potential materials for many high-temperature engineering applications. In their dense high-strength forms, these materials are being proposed for use as structural materials in power-generating gas turbines to increase their efficiency by allowing gas inlet temperatures to about 1400oC. These materials are also being considered for automotive gas turbines, small thermal reactors, roller bearings, and advanced combustion chambers. An important drawback to silicon compound ceramics is their extreme hardness, which makes their processing and shaping an extremely difficult, tedious and expensive procedure. Preliminary work has already shown that vastly higher removal rates are possible with a CO2 laser as compared to the conventional diamond grinding. To demonstrate the feasibility of laser shaping of hard-to-machine materials, a multi- disciplinary research effort has been undertaken to study the basic mechanisms governing the interaction between a high- powered CO2-laser beam and silicon compound ceramics. The research program is looking at the heat transfer, material property and manufacturing aspects of the laser-shaping process. A heat transfer model is being established to predict shape and depth of single, multiple-pass and overlapping grooves, material removal rates, surface roughness, etc. Material properties relevant for the model are being measured, including surface reflectivity (as function of temperature, angle and beam polarization), surface temperatures and ejected material properties (particle size and number density). Material characteristics of the ceramics before and after laser treatment are being investigated, such as microstructure, chemical composition of elements on the surface, flexure strength an thermal shock resistance. Laser machining is being carried out with variable operating conditions, and measurements are being made to determine quality, uniformity, reproducibility and predictability of the process. Machining results from single and overlapping grooves are being used to validate the heat transfer model.