Laser-Sustained Plasma (LSP) Nitriding of Titanium: A Review

Abstract

Titanium and its alloys possess several attractive properties that include a high strength-to-weight ratio, biocompatibility, and good corrosion resistance. However, due to their poor wear resistance, titanium components need to undergo surface hardening treatments before being used in applications involving high contact stresses. Laser nitriding is a thermochemical method of enhancing the surface hardness and wear resistance of titanium. This technique entails scanning the titanium substrate under a laser beam near its focal plane in the presence of nitrogen gas flow. At processing conditions characterized by low scan speeds, high laser powers, and small off-focal distances, a nitrogen plasma can be struck near the surface of the titanium substrate. When the substrate is removed, this plasma can be sustained indefinitely and away from any potentially interacting surfaces, by the laser power and a cascade ionization process. This paper presents a critical review of the literature pertaining to the laser nitriding of titanium in the presence of a laser-sustained plasma, with the ultimate objective of forming wide-area, deep, crack-free, wear-resistant nitrided cases on commercially pure titanium substrates.

XPS study of a laser‐nitrided iron surface using a focused pulsed Nd:YAG laser under various conditions

“…As a result, synthesis of the nitride was not complete in the entire melted region, thereby forming a nitride layer with comparatively low thickness. Additional laser irradiation facilitates nitrogen convection, leading to an increase in layer thickness 13 . In contrast, beyond 5 shots, nitrogen convection was achieved in the entire melted region, and thereby, synthesis of the nitride therein was complete.…”

A single parameter approach to enhance the microstructural and mechanical properties of beta Ti-Nb alloy via open-air fiber laser nitriding

“…The advantages include small heat input, fast and clean processing, capability to treat the localised and selected area (without altering the substrate properties) as well as to create a thick (up to a few hundred µm) and metallurgically bonded nitride layer to the substrate. The scientific background of laser nitriding and its development to date have been reported elsewhere [12]. One of the motivations for the continuous development of laser nitriding is driven by hardening the Ti implant surfaces to minimise the wear problems.…”

“…In other words, this is to minimise the crack formation by controlling the size and population of TiN dendrites in the re-melted pools using an energy control method. It is based on the assumption that the formation of oversized and densely populated TiN dendrites, as a consequence of oversupply of laser energy and prolonged laser-material-gas interaction time, can lead to excessive build-up of residual stress in the re-melted pools and eventually cause cracking [12].…”

Investigation into corrosion and wear behaviors of laser-clad coatings on Ti6Al4V

“…Up to now, many surface modification methods have been explored and applied to improve surface properties of titanium alloys [1], including electroplating [2], physical vapor deposition [3], chemical vapor deposition [4], micro-arc oxidation [5], and so on [6][7][8][9]. However, the protective coatings prepared by above methods are usually thin (micrometer scale in thickness) and loose in microstructure, and have a weak bonding with the substrate, whose applications are greatly limited in the harsh corrosion wear environment.…”