STTR Phase I: Nano-Layered Composites as High-Temperature Hard Coatings

这个第一阶段的小企业技术转移（STTR）项目旨在研究纳米层状涂层的高温性能。选择一种特定的材料系统，优化关键性能，包括硬度、热膨胀与硬质合金刀具的匹配、抗钢工件溶解的稳定性和抗氧化性。纳米层中较强的位错约束使涂层具有较好的高温硬度保持性。对涂层的抗氧化性进行评价。纳米层状涂层的稳定性将通过退火实验和随后的x射线衍射表征来研究。由于希望以更高的速度切削，以及在加工过程中使用冷却剂对环境的担忧日益增加，人们对在一定温度范围内（RT至1100℃）表现良好的刀具涂层非常感兴趣。然而，传统的涂层材料表现不佳，主要是因为它们的硬度随着温度的升高而迅速下降。该提议者最近开发了一类新的涂层，结合了许多纳米级BCC金属和岩盐结构氮化物（如Mo/NbN）的交替层。结果表明，纳米层能显著提高材料的硬度。硬度在高温下保持在30gpa，为探索新的高温稳定涂层提供了机会。纳米层涂层切削工具有潜力使干切削成为传统湿切削方法的实用替代品。此外，它们可以通过允许更高的切削速度来提高自加工经济性。

This Phase I SmallBusiness Technology Transfer (STTR) project aims to investigate high-temperature properties of nano-layered coatings. A specific material system is chosen that optimizes key properties including hardness, thermal expansion match with cemented-carbide tools, stability against dissolution into steel workpieces, and oxidation resistance. The strong dislocation confinement in nano-layers will lead to better high-temperature hardness retention than in monolithic coatings. The oxidation resistance of the coatings will be evaluated. The stability of the nano-layered coatings will be investigated through annealing experiments with subsequent characterization by x-ray diffraction. There is a high level of interest in cutting-tool coatings that perform well over a range of temperatures (RT to 1100 C) because of the desire to cut at higher rates and increasing environmental concerns over the use of coolants during machining. However, traditional coating materials do not perform well, primarily because their hardnesses decrease rapidly as temperature rises. The proposer has recently developed a new class of coatings, combining many alternating nanometer-scale layers of BCC metals and rocksalt-structure nitrides, e.g. Mo/NbN. Results show that nano-layering provides substantial hardness enhancements. Hardnesses 30 GPa are maintained at high temperatures providing an opportunity to explore new high-temperature stable coatings. Nano-layer-coated cutting tools have the potential to make dry cutting a practical alternative to traditional wet cutting methods. In addition, they can improve we-machining economics by allowing higher cutting speeds.