# Tribological Properties of Plasma-Based Low-Energy Nitrogen Ion Implanted 17-4PH Martensitic Stainless Steel

## TL;DR

This study shows that plasma-based nitrogen ion implantation improves the wear resistance of stainless steel, with optimal performance at 450 °C due to a nanostructured layer.

## Contribution

The study identifies the optimal nitriding temperature (450 °C) that balances nanostructure and CrN precipitation to maximize wear resistance in 17-4PH stainless steel.

## Key findings

- Nitrided layer thickness, nitrogen concentration, and hardness increase with temperature up to 450 °C.
- The 450 °C treatment produces nanocrystalline γ′N and minor CrN, enhancing wear resistance and toughness.
- Wear mechanisms transition from adhesive to oxidative and fatigue after nitriding.

## Abstract

What are the main findings?
Nitrided layer thickness, surface nitrogen concentration, and hardness increase with temperature.Highest wear resistance is achieved at 450 °C with nanocrystalline γ′N and minor CrN.The nanostructure combined with limited CrN precipitation enhances both hardness and toughness, improving resistance to plastic deformation.The wear mechanism undergoes a transition from adhesive to oxidative and fatigue after nitriding process.

Nitrided layer thickness, surface nitrogen concentration, and hardness increase with temperature.

Highest wear resistance is achieved at 450 °C with nanocrystalline γ′N and minor CrN.

The nanostructure combined with limited CrN precipitation enhances both hardness and toughness, improving resistance to plastic deformation.

The wear mechanism undergoes a transition from adhesive to oxidative and fatigue after nitriding process.

What are the implication of the main findings?
Nitriding significantly extends the service life of stainless steel under dry sliding conditions.

Nitriding significantly extends the service life of stainless steel under dry sliding conditions.

This study investigates the tribological properties of 17-4PH martensitic stainless steel modified by plasma-based low-energy nitrogen ion implantation to enhance its surface hardness and wear resistance. The steel was nitrided at temperatures of 350 °C, 450 °C, and 550 °C for 4 h, and the resultant layers were characterized with respect to microstructure, hardness, and composition. Tribological tests were performed using a ball-on-disk tribometer under dry sliding conditions against an Si3N4 ceramic ball, with normal loads of 2–8 N and sliding speeds of 0.15–0.60 m/s. The results demonstrate that the nitrided layer thickness increased from 11 μm to 27 μm and the surface nitrogen concentration rose from 29.7 at.% to 33.1 at.% with increasing temperature, accompanied by an increase in nanocrystallite size from 2 nm to 15 nm and enhanced hardness from 13.51 GPa to 15.66 GPa. All nitrided layers exhibited significantly improved wear resistance relative to the unmodified steel. The layer nitrided at 450 °C demonstrated optimal performance due to a refined nanostructure and minor CrN that enhance plastic deformation resistance and facilitate oxide film formation. While, the 350 °C treated layer exhibits diminished thickness and reduced hardness, and the 550 °C treatment induces excessive CrN precipitation and micro-cracking, consequently compromising both toughness and wear resistance.