Papers by Keyword: Laser Gas Nitriding (LGN)

Abstract: The influence of gas nitriding of commercial pure titanium and Ti-6Al-4V (Ti64) alloy by using a Q-sw laser on the wear loss during rolling contact fatigue is investigated. Despite very good biocompatibility, high strength to weight ratio and corrosion resistance, the tribological properties of titanium alloys are inferior to those of other metal alloys, such as steel. Fretting and wear related aspects become important issues when titanium alloys are used in rolling contact applications. Titanium bearings are employed in applications requiring high strength, light weight, and minimum maintenance (for example, aerospace and defense industries). In this work, a Q-sw laser was used to coat pure commercial titanium and Ti-6Al-4V bearings with TiN in a closed chamber in nitrogen atmosphere. The samples were tested under water by using a thrust-type rolling contact fatigue machine. The microstructure, morphology and crystallographic texture of the layers were observed by laser confocal microscope, scanning electron microscope and electron backscatter diffraction (EBSD). By optimizing the laser processing parameters, such as laser scanning speed, power and beam diameter, thin TiN coats of 1 to 3 mm were produced. The wear loss of the coated samples was at least ten times lower than that of the uncoated bearings.

Abstract: Titanium alloys have successfully been used as surgical implants. Laser gas nitriding (LGN) is an effective method to improve the wear and corrosion resistance of titanium alloys. A nitride strengthened uniform layer, free of cracks, was obtained on the Ti6Al4V alloy by irradiating with a continuous wave Nd-YAG laser in a N₂ environment. The microstructure, electrochemical corrosion and tribological behavior of the alloy before and after LGN were studied by SEM, XRD, potentiostat, microhardness tester and tribometer. The results show that the performance and composition of the surface of the Ti6Al4V alloy were significantly improved by LGN, with better corrosion resistance in simulated body fluid and better wear resistance.

Abstract: A nitrided layer was formed on the NiTi shape memory alloy (SMA) after being irradiated by a continuous wave Nd-YAG laser in a N₂ environment. With optimum process parameters, a compact laser modified gradient layer reinforced with fine TiN particles was achieved. Electrochemical measurements of the laser gas nitrided layer on the NiTi SMA showed that the corrosion potential and the breakdown potential were increased while the corrosion current was decreased as compared with the untreated the NiTi SMA. The polarization resistance of the laser gas nitrided layer on the NiTi SMA was increased significantly while the capacitance was decreased. Based on the EIS spectra, a simple model and an equivalent circuit were proposed to describe the electrode-electrolyte interfaces.

Abstract: The influence of gas nitriding of commercial pure titanium and Ti-6Al-4V (Ti64) alloy by using a Q-sw laser on the wear loss during rolling contact fatigue is investigated. Despite very good biocompatibility, high strength to weight ratio and corrosion resistance, the tribological properties of titanium alloys are inferior to those of other metal alloys, such as steel. Fretting and wear related aspects become important issues when titanium alloys are used in rolling contact applications. Titanium bearings are employed in applications requiring high strength, light weight, and minimum maintenance (for example, aerospace and defense industries). In this work, a Q-sw laser was used to coat pure commercial titanium and Ti-6Al-4V bearings with TiN in a closed chamber in nitrogen atmosphere. The samples were tested under water by using a thrust-type rolling contact fatigue machine. The microstructure, morphology and crystallographic texture of the layers were observed by laser confocal microscope, scanning electron microscope and electron backscatter diffraction (EBSD). By optimizing the laser processing parameters, such as laser scanning speed, power and beam diameter, thin TiN coats of 1 to 3 m were produced. The wear loss of the coated samples was at least ten times lower than that of the uncoated bearings.

Abstract: Laser gas nitriding of Ti-6Al-4V alloy was carried out using a Nd:YAG pulsed laser under pure nitrogen environment at a flow rate of 30 l/min. The microstructure and corrosion behavior of the nitrided samples were examined using scanning electron microscopy, XRD, XPS, and anodic polarization tests in 2M HCl solution. For comparison, untreated samples were tested under the same conditions. After laser treatment, samples showed a relative flat surface with no problems of cracks or delamination of the alloyed tracks. Laser nitriding produced dendritic structures. The microstructure of the laser melted zone consisted of a thin continuous layer followed by a nearly perpendicular growth of dendrites. Below this a mixture of small dendrites and large needles with random orientation was produced. X-ray spectrum and XPS analyses from the surface of the laser nitrided specimen at different depth, confirmed that the thin top layer and large dendrites close to the surface corresponded to TiN. It can be also seen that the strong TiN peaks on the top surface gradually decrease with depth which suggests that the structure beneath the top surface is likely TiN0.3 and ά-Ti mixtures. In general, the corrosion potential of laser gas nitrided specimens was relatively nobler than the untreated sample. Furthermore, the proper laser nitrided specimen exhibited less corrosion current density, passivated more readily and also maintained a lower current density over the duration of the experiment. This was correlated with the formation of very thin, continuous TiNxOy film in an oxidation state that was confirmed by XPS analyses of the passive layers.

Abstract: Fluor-hydroxyapatite (FHA) films were deposited on titanium and laser gas nitrided titanium substrates using sol-gel technique respectively. Typical apatite structures were obtained for all coatings after dipping and subsequent heat treatment from 600°C to 800°C. The obtained films were uniform and dense, with a thickness of 5 μm. The 3-D TiN dendritic structure fabricated on the surface of Ti plate using laser gas nitriding technique in advance should be help anchor the HA/FHA coating and improved the interfacial adherence significantly compared with the naked titanium surface.