Laser Gas Nitriding Research Articles

Two-dimensional code marking and coloration mechanism on titanium alloy surfaces via laser gas nitriding

In this study, a nanosecond laser marking machine was employed to nitride the surface of a Ti-6Al-4V alloy in a nitrogen-rich environment. Consequently, a crack-free and uniform nitriding layer was successfully achieved. Furthermore, a 2D code with enhanced contrast was imprinted on the sample, and subsequently, a durability test was conducted to assess its performance. The impacts of laser power (ranging from 9 to 11 W), scanning speed (17 to 23 mm/s), and line spacing (20 to 40 µm) on the surface morphology, thickness, and color alteration of the nitride layer were systematically investigated through experimental analysis. Utilizing a spectrophotometer, scanning electron microscope, optical microscope, energy dispersive spectroscopy instrument, and other advanced equipment, we further delved into the underlying mechanism of surface color change during laser gas nitriding of a Ti-6Al-4V alloy. Results indicate that an increase in laser power and a decrease in line spacing and scanning speed lead to the generation of higher energy densities on the material surface, intensifying ablation and causing the formation of more molten material. Consequently, this results in the development of more complex surface structures, thicker nitride layers, and lower reflectance. The surface microstructure of the nitride layer exhibits similarities and variations, and the thickness of the nitride layer differs, leading to distinct light absorption and reflection properties on its surface. Consequently, the nitride-layer surfaces prepared under varying laser parameters exhibit diverse contrasts.

Improving the surface characteristics of metallic glass thin ribbons by laser gas nitriding

The single-roll cooling method excels in producing metallic glass ribbons (MGRs), offering rapid cooling rates and exceptional thickness consistency. Nevertheless, a large number of defects including micro-pits and micro-gaps usually appear on the surface of MGRs after the roll forming process, significantly impacting their service life and performance. Laser gas nitriding is a cutting-edge surface modification technology that has been extensively used to improve the comprehensive performance of various metal components. Herein, an attempt was made to simultaneously improve the surface quality and mechanical properties of Zr41.2Ti13.8Cu12.5Ni10Be22.5 MGRs by nanosecond pulsed laser irradiation in a flowing nitrogen atmosphere. The effects of laser irradiation parameters on the surface characteristics of the laser gas nitrided regions were systematically investigated. The experimental results showed that the surface quality of MGRs after laser gas nitriding was enhanced, accompanied by a simultaneous improvement in hardness and scratch resistance. This study underscores laser gas nitriding as a potent strategy to augment the comprehensive surface characteristics of MGRs. This enhancement is poised to significantly extend their service life and reinforce their reliability when utilized as structural and functional materials in sectors such as machinery, national defense, and aerospace.

Experimental investigation on microstructure, mechanical and optical properties of RB-SiC ablated by nanosecond pulsed laser in nitrogen atmosphere

Reaction-bonded silicon carbide (RB-SiC) has gained significant attention owing to its exceptional physical and chemical properties. Improving the photovoltaic efficiency and mechanical properties of RB-SiC is conducive to further enhancing its applicability. Laser gas nitriding is an effective strategy to simultaneously reduce the surface reflectivity and enhance the surface hardness of materials. Accordingly, the evolution of microstructure, mechanical and optical properties of RB-SiC composite ablated by nanosecond pulsed laser in nitrogen atmosphere was comprehensively investigated. After laser gas nitriding, the surface hardness of RB-SiC composite was increased by 10.6–44.6 %. The chemical composition analysis indicated that Si-based nitride was formed on the laser-ablated surface, which was mainly responsible for the hardness enhancement. Additionally, the reflectivity of the laser-ablated surface was reduced by up to 95.2 % compared to the original RB-SiC composite. This study provides a straightforward and effective method to simultaneously improve the mechanical and optical properties of RB-SiC composites.

Effect of Laser Hardening and Gas Nitriding on Wear Resistance of Steel P20: A Comparative Study

Effect of Laser Hardening and Gas Nitriding on Wear Resistance of Steel P20: A Comparative Study

The microstructure and cavitation erosion resistance of Ti6Al4V alloy treated by laser gas nitriding with scanning galvanometer

In this study, the nitrided layer was prepared on Ti6Al4V alloy by laser gas nitriding using the scanning galvanometer (G-LGN). Its typical features were investigated in comparison to that using the diode laser with robot (D-LGN) under the same energy density and treated area. In order to reveal the connections between the cavitation resistance (CE) and characteristics of the nitrided layer, the samples were characterized by OM, SEM, XRD, XPS, laser scanning microscopy, and microhardness tester. Due to using the scanner, the G-LGN method is given a smaller laser spot size (micrometer scale), higher scanning speed, and remelting brought by successive overlapping during processing. Those cause it different from the D-LGN method in the microstructure and CE resistance of the nitrided layer. The results show that the G-LGN sample has a more uniform surface with a lower average surface roughness (Sa = 3.043 μm) compared with the D-LGN sample. Moreover, the TiN dendrites with smaller sizes and an amount of TiN0.3 phase are formed in its nitrided layer. It is interesting that the TiN0.3 phases in the G-LGN sample result in a lower surface hardness (about 700–800 HV) with respect to the D-LGN sample, but a more uniform hardness distribution through the depth direction can be detected. According to the results of the CE test, the G-LGN sample exhibits the lowest cumulative mass loss and mean erosion rate during the whole erosion time in comparison to the substrate and D-LGN sample, suggesting the best CE resistance. Therefore, the G-LGN method will provide competitive advantages over the D-LGN method for the CE protection of the titanium components owing to the improvement in the quality and performance of the nitrided layer as well as the superiority of the scanning galvanometer.

The Microstructure and Cavitation Erosion Resistance of Ti6al4v Alloy Treated by Laser Gas Nitriding with Scanning Galvanometer

The Microstructure and Cavitation Erosion Resistance of Ti6al4v Alloy Treated by Laser Gas Nitriding with Scanning Galvanometer

Hybrid Laser Deposition of Composite WC-Ni Layers with Forced Local Cryogenic Cooling

The purpose of this study was to demonstrate the effect of forced and localized cooling by nitrogen vapours stream under cryogenic conditions during laser deposition of WC-Ni powder on the geometry, microstructure of clad layers and dry sliding wear resistance of the coatings. For this purpose, comparative tests were performed by conventional laser cladding at free cooling conditions in ambient air and by the developed novel process of laser deposition with additional localized cooling of the solidifying deposit by nitrogen vapours stream. Due to presence of gaseous nitrogen in the region of the melt pool and solidifying deposit, the process was considered as combining laser cladding and laser gas nitriding (performed simultaneously), thus the hybrid process. The influence of the heat input and cooling conditions on the geometrical features, dilution rate, share of carbides relative to the matrix, and the fraction share of carbides, as well as hardness profiles on cross sections of single stringer beads was analysed and presented. The XRD, EDS analysis and the sieve test of the experimental powder were used to characterize the composite WC-Ni type powder. The OM, SEM, EDS and XRD test methods were used to study the microstructure, chemical and phase composition of clad layers. Additionally, ball-on-disc tests were performed to determine the wear resistance of representative coatings under dry sliding conditions. The results indicate that the novel demonstrated technique of localized forced cooling of the solidifying deposit has advantageous effect, because it provides approximately 20% lower penetration depth and dilution, decreases tendency for tungsten carbides decomposition, provides more uniform distribution and higher share of massive eutectic W2C-WC carbides across the coating. While the conventionally laser cladded layers show tendency for decomposition of carbide particles and resolidifying dendritic complex carbides mainly M2C, M3C and M7C3 containing iron, nickel, and tungsten, and with Ni/Ni3B matrix. The quantitative relationship between heat input, cooling conditions and the carbides grain size distribution as well as carbides share in relation to the matrix was determined.

Investigation of nitrogen ionization state and its effect on the nitride layer during fiber laser gas nitriding of Ti-6Al-4V alloy

A nitride layer can be formed on the surface of a titanium alloy during laser gas nitriding, to improve the surface hardness and wear resistance of the titanium alloy. Importantly, the nitride layer is influenced by the nitrogen ionization state (nitrogen molecules or nitrogen atoms and ions). No research reports exist on the nitrogen ionization state or the effect on the nitride layer during fiber laser nitriding of titanium alloys. Radiation images that were taken with a high-speed camera and emission spectra that were collected with a fiber spectrometer were used to study the nitrogen ionization state. To study the effect of nitrogen ionization state on the nitride layer, the surface nitrogen and oxygen content were measured with an electro-probe microanalyzer, and the surface morphology of the nitride layer was studied by optical and scanning electron microscopy. The experimental results showed that the laser power density was too low to induce nitrogen ionization during fiber laser gas nitriding of the Ti-6Al-4V alloy. The nitrogen molecules had a lower energy than the nitrogen plasma (nitrogen atoms and ions) and a slower reaction rate with the titanium alloy, which resulted in a low nitrogen content and a few defects in the nitride layer. The relationship between the oxidation and nitriding was competitive; that is, nitrogen and oxygen competed to react with the titanium alloy. As such, a low nitrogen content led to a high oxygen content, and the nitride surface was golden-yellow in color with black markings. • Nitrogen did not ionize during fiber laser gas nitriding of Ti-6Al-4V alloy. • Molecular nitrogen is transferred into the molten pool. • Molecular nitrogen reduces the nitrogen content and minimizes nitride-layer defects. • A low nitrogen content led to a high oxygen content in the nitride layer.

Microstructure and microhardness of a novel TiZrAlV alloy by laser gas nitriding at different laser powers

The Ti–20Zr–6.5Al–4V (T20Z, wt%) alloy surface was treated by the process of laser surface nitriding. The evolution of microstructures and microhardness has been investigated by changing the laser power parameter from 120 to 240 W. All laser-treated T20Z samples show two regions with distinctly different microstructural features, as compared with the untreated substrate: dense TiN dendrites and (α + β) − Ti (remelting zone, RMZ), nanoscale α laths doped with part of β phase (heat-affected zone, HAZ). The formation of TiN dendrites can be analyzed by a series of complex reactions during the process of melting and solidification. The increase in laser power results in the increase in content of TiN dendrite which is mainly due to the increase in energy input. In HAZ, the self-quenching effect leads to the formation of nanoscale α laths and the residue of β phase. Microhardness profile of different regions was measured from the surface to the interior, and the highest microhardness was obtained (~ HV 916.8) in the RMZ, as the laser power was set to 240 W. In the present study, we explained various microstructural characteristics induced by laser surface nitriding treatment.

Hybrid Laser Deposition of Fe-Based Metallic Powder under Cryogenic Conditions

The purpose of this study was to demonstrate the novel technique of laser deposition of Fe-based powder under cryogenic conditions provided by a liquid nitrogen bath. Comparative clad layers were produced by conventional laser cladding at free cooling conditions in ambient air and by the developed process combining laser cladding and laser gas nitriding (hybrid) under cryogenic conditions. The influence of process parameters and cooling conditions on the geometry, microstructure, and hardness profiles of the clad layers was determined. The optical microscopy (OM), scanning electron microscopy (SEM), energy-dispersive spectrometer (EDS), and XRD test methods were used to determine the microstructure and phase composition. The results indicate that the proposed technique of forced cooling the substrate in a nitrogen bath during the laser deposition of Fe-based powder is advantageous because it provides favorable geometry of the clad, low dilution, a narrow heat-affected zone, a high hardness and uniform profile on the cross-sections, homogeneity, and refinement of the microstructure. The influence of the forced cooling on microstructure refinement was quantitatively determined by measuring the secondary dendrite arm spacing (SDAS). Additionally, highly dispersed nanometric-sized (200–360 nm) precipitations of complex carbides were identified in interdendritic regions.

High power diode laser nitriding of titanium in nitrogen gas filled simple acrylic box container: Microstructure, phase formation, hardness, dendrite and martensite solidification analyses

This work presents a detailed microstructure-property correlation of high power diode laser nitrided titanium based on its dendrite and martensite microstructures, structural phase and microhardness. For the laser nitrided titanium, cooling rate was estimated for the first time using empirical power law relationship by considering the martensite width and dendrite arm spacings and the results were validated by analytical thermal model. A processing window was formulated for laser gas nitriding of titanium by relating the experimental parameters such as laser processing parameters, nitrogen gas pressure and titanium nitride phases. The novelty of this work is demonstration of laser nitriding of titanium in laminar flow nitrogen gas environment using a simple acrylic container setup that avoids design and fabrication of a complex gas nozzle delivery system. In this setup, a thin transparent acrylic sheet was used as optical window instead of expensive quartz glass, to transmit high power diode laser beam at 980 nm wavelength to irradiate the substrate work piece in a closed container. This simple laser nitriding technique has created characteristic golden colored TiN surface with high surface hardness. Dendrite and martensite microstructures of the laser nitrided titanium were analyzed by optical and FESEM microscopy. EDAX analysis revealed the presence of nitrogen in laser nitrided titanium and X-ray diffraction confirmed the TiN phases. The microhardness of laser nitrided titanium is six times higher than its substrate.

A Comparison of Gas Nitriding and Laser Nitriding on Industrial Pure Iron and Ti-Induced Iron

Overview of Gas nitriding on the surface of industrial pure iron and laser gas nitriding, research under different nitriding process, the phase, organization and mechanical properties of the nitride layer that is the difference. Plasma sprayed titanium on industrial pure iron surface, the laser nitriding experiments were carried out on the titanium surface. The formation of iron and nitrogen compounds is induced by the combination of titanium nitride. The difference between gas nitriding and laser nitriding is analyzed. The results show that: (1) after gas nitriding, the nitrides formed on the surface of pure iron are mainly ε-Fe2-3N and γ′-Fe4N, the surface hardness is 158 HV, and the increase is 32%. (2) in the 500 W laser power, laser nitriding formed on the surface of Titanium metal layer of pure iron, but not the formation of iron and nitrogen compound, the surface hardness of 168 HV, increased by 46%. (3) under the condition of 500 W laser power, the industrial pure iron was nitrided by laser, without the formation of iron and nitrogen compounds, but the surface hardness of the sample was increased by 20%.

Mehanizmi povečanja trdote površinskih slojev kompozitov zlitine Ti6Al4V med lasersko-plinskim nitriranjem

Mehanizmi povečanja trdote površinskih slojev kompozitov zlitine Ti6Al4V med lasersko-plinskim nitriranjem

Comparison of Titanium Metal Matrix Composite Surface Layers Produced During Laser Gas Nitriding of Ti6Al4V Alloy by Different Types of Lasers

Abstract The article presents the results of a comparative study of the nitriding process of titanium alloy substrate using two lasers with different characteristics of laser beams. One of the applied lasers was a high power diode laser emitting at a dominant wavelength of 808 nm, with a rectangular laser beam spot, and multimode energy distribution across the spot. The second laser was a solid state Yb:YAG disk laser emitting at a wavelength of 1.03 μm, with a circular beam spot, characterized by near Gaussian energy distribution across the spot. In a case of both lasers single stringer beads with a similar width and at similar energy input were produced. As a result of melting of the substrate with a laser beam in a pure gaseous nitrogen atmosphere composite surface layers with in situ precipitated titanium nitrides embedded in the metallic matrix of titanium alloy were produced, in both cases. However, the surface topography and structure is different for the surface layers produce by different lasers at the same processing parameters and width of laser beams.

Tribological Characteristic of Titanium Alloy Surface Layers Produced by Diode Laser Gas Nitriding

AbstractIn order to improve the tribological properties of titanium alloy Ti6Al4V composite surface layers Ti/TiN were produced during laser surface gas nitriding by means of a novel high power direct diode laser with unique characteristics of the laser beam and a rectangular beam spot. Microstructure, surface topography and microhardness distribution across the surface layers were analyzed. Ball-on-disk tests were performed to evaluate and compare the wear and friction characteristics of surface layers nitrided at different process parameters, base metal of titanium alloy Ti6Al4V and also the commercially pure titanium. Results showed that under dry sliding condition the commercially pure titanium samples have the highest coefficient of friction about 0.45, compared to 0.36 of titanium alloy Ti6Al4V and 0.1-0.13 in a case of the laser gas nitrided surface layers. The volume loss of Ti6Al4V samples under such conditions is twice lower than in a case of pure titanium. On the other hand the composite surface layer characterized by the highest wear resistance showed almost 21 times lower volume loss during the ball-on-disk test, compared to Ti6Al4V samples.

Formation of TiN Grid on NiTi by Laser Gas Nitriding for Improving Wear Resistance in Hanks' Solution

Laser gas nitriding (LGN) is a common surface modification method to enhance the wear resistance of titanium (Ti) alloys, which are known to have poor tribological properties. In the present study, a titanium nitride (TiN) grid network was fabricated on the surface of nickel titanium (NiTi) by LGN. The laser processing parameters were selected to achieve nitriding without surface melting and hence to maintain a smooth surface finish. The characteristics of the grid-nitrided samples were investigated by scanning-electron microscopy, X-ray diffractometry, optical microscopy, 2-D profilometry, contact angle measurements and nanoindentation. The wear resistance of the nitrided samples was evaluated using reciprocating wear test against ultra-high-molecular-weight polyethylene (UHMWPE) in Hanks' solution. The results indicate that the wear rates of the grid-nitrided samples and the UHMWPE counter-body in the wear pair are both significantly reduced. The decrease in wear rates can be attributed to the combination of a hard TiN grid and a soft NiTi substrate. In Hanks' solution, the higher hydrophilicity of the nitrided samples also contributes to the better performance in wear test against hydrophobic UHMWPE.

Kinetics of Titanium Alloy Nitriding by Diode Laser

Based on the wide range study of laser gas nitriding (LGN) of commercially pure titanium and the titanium alloy Ti6Al4V by means of high power direct diode laser (HPDDL), the kinetics of nitrogen absorption by the melt pool and related titanium nitrides growth was analyzed. Also a schematic model of nitrogen absorption by the melt pool was proposed. According to the hypothetical model three cases of nitrogen absorption by the melt pool were be distinguished and discussed. It was found that in a case of HPDDL nitriding of the Ti6Al4V alloy the presence of a thin homogenous layer of TiNx on the top surface of melt pool affects the nitrogen absorption kinetics. The process of nitrogen desorption at the cooling stage of melt pool is inhibited by the layer of TiNx as well as by the phase transformation and titanium nitrides formation.

Mechanism of Titanium Matrix Composite Ti/TiN Formation during Diode Laser Gas Nitriding of Ti6Al4V

Three mechanisms of titanium matrix composite Ti/TiN formation during diode laser nitriding of Ti6Al4V alloy in liquid stage were identified and discussed. When the titanium alloy surface is melted by a laser beam the first mechanism of nucleation and growth of d-TiN was identified in the temperature range of melt pool from 1650 up to 2320 °C, when the nitrogen concentration in the Tia solution reaches at least to the concentration limit in a range 20,5 to 22 at. %. Next different mechanism of nucleation of d-TiN was identified in the temperature range of melt pool from 2320 up to 2950 °C. In turn, the third mechanism of d-TiN formation was identified above the melting point of titanium nitrides, i.e. 2950 °C.

Titanium Matrix Composite Ti/TiN Produced by Diode Laser Gas Nitriding

A high power direct diode laser, emitting in the range of near infrared radiation at wavelength 808–940 nm, was applied to produce a titanium matrix composite on a surface layer of titanium alloy Ti6Al4V by laser surface gas nitriding. The nitrided surface layers were produced as single stringer beads at different heat inputs, different scanning speeds, and different powers of laser beam. The influence of laser nitriding parameters on the quality, shape, and morphology of the surface layers was investigated. It was found that the nitrided surface layers consist of titanium nitride precipitations mainly in the form of dendrites embedded in the titanium alloy matrix. The titanium nitrides are produced as a result of the reaction between molten Ti and gaseous nitrogen. Solidification and subsequent growth of the TiN dendrites takes place to a large extent at the interface of the molten Ti and the nitrogen gas atmosphere. The direction of TiN dendrites growth is perpendicular to the surface of molten Ti. The roughness of the surface layers depends strongly on the heat input of laser nitriding and can be precisely controlled. In spite of high microhardness up to 2400 HV0.2, the surface layers are crack free.

Comparation between Laser Surface Nitriding and Nitrogen Plasma Immersion Ion Implantation (N-PIII) on Creep Behavior of Ti-6Al-4V Alloy

Titanium alloys are widely used in machine building, aircraft manufacturing, medicine, motors, chemistry, and biomedicine due to their high strength-to-weight ratio, elasticity, corrosion resistance, and biocompatibility. In particular, Ti-6Al-4V containing (α + β) structure plays a very important role in aerospace industry in the manufacturing of components such as disks and blades for aircrafts turbines and structural forgings. However, one of the major factors limiting the life of titanium alloys in service is their degradation due to gaseous environments, in particular, to environments containing oxygen at elevated temperatures during long-term use. The sensitivity of titanium alloys to high-temperature exposure is a well-known phenomenon. When titanium alloys are heated to temperatures above approximately 800oC, oxygen, hydrogen and nitrogen can penetrate into them. The penetration of these elements increases hardness and brittleness while decreasing the toughness of the alloy. Laser surface nitriding is a technique used to modify the near-surface microstructure and/or composition by melting the surface using a high-power laser beam with reactive gas as a shrouding environment, forming a nitride layer on the surface of Ti–6Al–4V to improve the alloy’s tribological and mechanical properties. The results of laser gas nitriding of Ti–6Al–4V showed a significant increase of microhardness and enhanced erosion resistance significantly compared with untreated Ti–6Al–4V, since the nitride layer acts as a diffusion barrier for inward oxygen diffusion into the alloy, reducing the contribution of oxygen dissolution in the substrate to the total mass gain. Other important technique that was developed for the beneficial modification of surface sensitive properties is Nitrogen Plasma Immersion Ion Implantation N-PIII. A sample is immersed in plasma and subjected to negative high-voltage pulses. In the electrical field, the ions are accelerated to high energies and incorporated into the sample. Enhancing of the hardness and wear process of the materials due to the N-enriched layer caused by diffusion of N in the sample at PIII process can be expected. Both techniques provide an improvement in the creep resistance. The objective of this work was evaluating the creep resistance of the Ti-6Al-4V alloy with superficial treatments of laser nitriding and Nitrogen Plasma Immersion Ion Implantation N-PIII in creep test of Ti-6Al-4V alloy. It was used Ti-6Al-4V alloy as cylindrical bars under forged and annealing of 190 oC by 6 hours condition and cooled by air. The Ti-6Al-4V alloy after the superficial treatment of laser nitriding and N-PIII was submitted to creep tests at 600 oC in the stress of 250 MPa and 319 MPa, under constant load mode. The creep parameters are determined and a comparative analysis is established with the results gotten from the alloy with both treatments. The laser nitrided has showed an improved creep behavior compared with the same alloy with N-PIII coating, with a reduction in the creep rate and increasing the creep lifetime.