Original Date: 03/08/1999
Revision Date: 01/18/2007
Information : Hard-Metallic-Ceramic Multilayer Coatings
The Applied Research Laboratory at the Pennsylvania State University (ARL Penn State) developed a process for producing a hard-metallic-ceramic multilayer coating for cutting tools. This process, based on ion beam-assisted electron beam-physical vapor disposition (EB-PVD), indicates a tool life extension of 600% to 800% compared to uncoated tools. Earlier research by the ARL Penn State produced a tool life extension of 400% by utilizing single layer TiN coatings which were applied using the EB-PVD system.
Wear resistance in cutting tools depends on four factors:
Material crystal structure covalent and ionic bonds Grain size nano and submicron sizes
Interface structure coherent, semi-coherent, and incoherent structures
Composition TiN/TiB2; TiC/TiB2; TiC/Cr3C2; and TiC/Al2O3
This multilayer coating process controls and tailors these factors in an optimum manner by which the engineered, multilayer material stops cracks at the material interface. This approach also eliminates a major failure mode for hard coatings.
Developed by the ARL Penn State, the EB-PVD system has a unique configuration. The system contains six 45- kilowatt electron beam guns. Typically, two guns are used to heat the target component, while the other four are used to selectively evaporate the three ingots of coating material. The part is manipulated in the resulting vapor stream. The speed of rotation and translation are also determining parameters in the process.
By producing hard-metallic-ceramic multilayer coatings for tools, the ARL Penn State demonstrated substantial tool life extension. Significant cost savings have resulted from an increase in tool utilization and a decrease in downtime for tool changeouts. The multilayer coating also resists wear through a unique mechanism by which the material interface serves as a crack stop.
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