Optimization and Characterization of Si3N4 Layer for Wear Resistant Ti-Al-N/Si3N4 Nano- Composite Coatings

Abstract

Machining Custom 465 steel at high speeds usually at 20-30% lower than ordinary stainless steel leads to excessive tool wear and thereby affecting the tool life. In such case tool life can be increased by coating a nano-composite layer of Ti-Al-N/Si3N4 which exhibits high strength, hardness, toughness, resistance to oxidation and thermal shock. Particularly, Si3N4serves as an interfacial phase in nano-composite layer is thermodynamically stable phase at high temperatures up to 1850˚C along with high oxidation resistance which might reduce the heat flow between tool-workpiece interfaces leading to high thermal stability of cutting tool. Physical vapor deposition techniques can be used to develop Ti-Al-N/Si3N4 nano-composite coating which involves typically 81 trial depositions in order to obtain optimized process parameters for Si3N4. Here we attempt to reduce the number of trails by design and optimization of process parameters which was efficiently achieved at faster rate by applying the Taguchi design. In present work, we used Taguchi orthogonal (L9) array to conduct the 9 experiments and obtained optimum process parameters for Si3N4 coating. Based on the design we deposited Si3N4nanocoating using RF magnetron sputtering process with 4 factor and 3 level process parameters namely, Ar:N2 gas mixture, RF Power, deposition time, and deposition pressure on high speed steel (HSS), tungsten carbide (WC) and Si (100) substrates. Atomic Force Microscopy (AFM) studies were carried for surface roughness, topography, and phase contrast imaging. Glancing incidence X-ray diffraction (GIXRD) studies were performed for the identification and quantification of crystalline and amorphous phase. Field Emission Scanning Electron Microscopy (FE-SEM) studies were performed for the film thickness and grain size of Si3N4layers.