NSF Award
9903698
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. <br/> 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.
