The effect of RF-DC plasma N2-H2 in the selective hardening process for micro-patterned AISI420

TL;DR

This study demonstrates a precise, selective plasma nitriding process on micro-patterned AISI420 steel using RF-DC plasma N2-H2, enabling controlled hardening and 3D micro-texture creation for miniature dies.

Contribution

It introduces a novel selective nitriding technique using RF-DC plasma with nano-carbon masks for micro-patterned steel surfaces.

Findings

Selective nitriding achieved with high nitrogen content in unprinted areas.

Hardness difference of up to 850 Hv between nitrided and non-nitrided regions.

Phase transformation includes martensitic lattice expansion and formation of ε-Fe3N.

Abstract

The high density of RF-DC plasma N2-H2 was used to make precise micro-texturing onto AISI420 has complex textured geometry. The original 2D micro-patterns were drawn onto substrate surface by maskless patterning using by of nano-carbon ink. These micro-patterned specimens were further plasma-nitrided at 673 K for 5.4 ks by 70 Pa using the hollow cathode device. The emissive light spectroscopy shows species in plasma were nitrogen atoms together with NH radicals and nitrogen molecular ions. Unprinted surface areas had selectively nitrided, have high nitrogen solute contents up to 12 mass%. Masked area just corresponded to carbon-mapping from printed nano-carbon inks, while unprinted surface to nitrogen mapping. The hardness profile had stepwise change across the borders between these printed and unprinted areas; e.g., the hardness on unprinted surface was 1200 Hv while it remained to be 350 Hv on printed surface. This selective nitriding and hardening enabled to construct the 3D textured miniature dies and products by chemical etching of printed area. These two peaks were related to extended martensitic lattice by high nitrogen extraordinary solid solution. The phase transformation from martensitic lattice {\alpha}prime-Fe through expanded phase into {\epsilon}-Fe3N lattice.