Laser Boriding Research Articles

Influence of Laser Beam Power on the Temperature Distribution and Dimensions of the Molten-Pool Formed during Laser Boriding of Nimonic 80A-Alloy

Laser boriding is a surface treatment that involves the simultaneous re-melting and mixing of the alloying material, containing amorphous boron blended with diluted polyvinyl alcohol, with the substrate material (Nimonic 80A-alloy). As a result of high cooling rates, the boride layer is formed from a solidifying molten pool. The thickness of the produced layer depends on the laser treatment parameters, e.g., power of the laser beam, scanning rate, and laser beam radius. These parameters influence the temperature distribution on the cross-section of laser tracks and, thus, directly determine the size of the molten pool, from which the boride layer is formed after crystallization. In the present study, laser borided layers were produced on Nimonic 80A alloy using a CO2 molecular laser. Differences in the laser beam power used resulted in the formation of layers of different thicknesses, which resulted directly from the differences in the temperature distribution in the treated material. The amount of boron in the molten pool directly influenced the obtained hardness of the laser borided layer. It was found that the lower laser beam power had an advantageous effect on the hardness due to the higher percentage of nickel borides and chromium borides in the layer. The reasons for this situation are discussed in detail.

High power diode laser alloying of TiB2 and amorphous-boron with titanium: Phase, microstructure and hardness analyses

Laser alloying creates a new alloy or ceramic composite coating with improved surface properties of materials. This work has developed a hard coating by high power diode laser alloying of preplaced TiB2 and amorphous boron (a-B) layer with Cp-Ti and Ti6Al4V substrates under argon and nitrogen gas shielding, which respectively termed as laser boriding and boronitride techniques. The composite coating was investigated by X-ray diffraction, Energy Dispersive X-ray, Elemental mapping, Optical microscopy and FESEM and Vickers hardness analyses. A simple analytical equation was employed to estimate surface temperature to correlate phase formation behavior. The XRD revealed the formation of TiB2 and TiB phases in the borided surface and TiB2, TiB, Ti4N3B2 phases in the laser boro-nitrided surface. The EDAX and elemental mapping confirmed the boron and nitrogen in the laser boro-nitrided cross section. The optical and scanning electron microscopy revealed that coating predominantly consists of TiB ceramic precipitates. A high hardness in the range 1217–3351 HV0.2 was obtained in the laser borided and boro-nitrided coating cross sections, due to the formation of TiB2 and Ti-B-N phases.

Influence of Microstructure and Chemical Composition on Microhardness and Wear Properties of Laser Borided Monel 400.

In this study, wear properties of Monel 400 after laser alloying with boron are described. Surfaces were prepared by covering them with boron paste layers of two different thicknesses (100 µm and 200 μm) and re-melting using diode laser. Laser beam power density was equal to 178.3 kW/cm2. Two laser beam scanning velocities were chosen for the process: 5 m/min and 50 m/min. Surfaces alloyed with boron were investigated in terms of wear resistance, and the surface of untreated Monel 400 was examined for comparison. Wear tests were performed using counterspecimen made from steel 100Cr6 and water as a lubricant. Both quantitative and qualitative analysis of surfaces after wear test are described in this paper. Additionally, microstructures and properties of obtained laser alloyed surfaces are presented. It was found that the wear resistance increased from four to tens of times, depending on parameters of the laser boriding process. The wear mechanism was mainly adhesive for surfaces alloyed with initial boron layer 100 µm thick and evolves to abrasive with increasing boron content and laser beam scanning velocity. Iron particles detached from counterspecimens were detected on each borided surface after the wear test, and it was found that the harder the surface the less built-ups are present. Moreover, adhered iron particles oxidized during the wear test.

The effect of temperature distribution and cooling rate on microstructure and microhardness of laser re-melted and laser-borided carbon steels with various carbon concentrations

Laser heat treatment was arranged as a laser remelting and laser boriding. Materials with different carbon concentration were used. Three zones characterized the microstructure after laser treatment: re-melted zone (MZ), heat-affected zone (HAZ) and substrate material. The differences in carbon content and physical properties of used materials influenced the obtained microstructure, temperature distribution and hardness. In case of laser re-melted specimens, the limited martensite transformation proceeded only in C20, C45 and C90 steels. As a result of laser boriding the microstructure of MZ contained additionally iron borides. The specimens with higher dilution ratio value were characterized by higher hardness of re-melted zone. The aim of this study was to indicate the possibility of predicting the microstructure and depths of MZ and HAZ with the usage of Ashby and Esterling model. The influence of carbon concentration in steel on the thickness, dilution ratio and hardness of laser-borided layers was determined.

Experimental studies of laser borided low alloy steel and optimization of parameters using response surface methodology

Laser boriding technique was used to form boride layers on EN25 steel. The main aim of this current study is to form the hard laser borided layer on the low alloy steel surface and analyze the effect of process parameters on borided layer hardness, depth, and width. The properties and microstructure (micro-hardness, boride layer width, and depth) are analyzed after laser boriding process with different laser process parameters (power and speed). The micro-hardness of the boride layer was measured using the Vickers micro-hardness tester. The boride depth and width was measured and captured using a machine vision inspection system. The existence of borides formed in the laser treated layer was confirmed via X-ray diffraction technique. The corrosion rates of the laser borided and as received samples are observed in 3% NaCl solution using Potentiodynamic polarization test. The response surface methodology was used to analyze the effects of power, travel speed on the hardness and the boron layer width and depth. The two-factor three-level full factorial design available in response surface methodology was used to develop the regression model for laser boriding process. A multiobjective optimization technique was used to optimize the laser process parameters to maximize the boron layer width and to minimize the boride layer depth. The validation trail assures that the expected value has good conformant with the actual experimental value.

Microstructure and selected properties of Monel 400 alloy after laser heat treatment and laser boriding using diode laser

This study concentrates on describing effects of laser heat treatment of Monel 400 and laser alloying its surface with boron. Surfaces without and with initial boron layers of two different thicknesses (100 and 200 μm) were processed using diode laser. Laser beam power density was constant and equal to 178.3 kW/cm2. To determine the influence of laser beam scanning velocity on final properties of treated surfaces, laser beam scanning velocity was set on four different values: 5, 25, 50, and 75 m/min. Microstructures of pure Monel 400 and Monel 400 alloyed with 100 μm boron content are composed of dendrites. Areas laser alloyed with 200 μm boron layer contain mainly nickel borides. Boron addition in Monel 400 surface results in microhardness increase in which the level depends on boron content and the laser beam scanning velocity. Increasing the thickness of initial boron layer and speeding up the laser beam lead to obtain higher microhardness. On the other hand, areas laser alloyed with 200 μm boron layer using laser beam scanning velocity equal to 75 m/min contain deep cracks which propagate from the surface through the produced layer. Furthermore, it was found that the depths of laser heat-treated areas depend significantly on the boron content. As the result of differences in thermal properties between Monel 400 and boron, depth of re-melted zones in some conditions does not lower with increasing laser beam scanning velocity.

Experimental Investigations on the Effects of Multicomponent Laser Boriding on steels

In this investigation, the effects of the multicomponent (Ni+Cr+B4C) laser boriding on the microstructure, microhardness, ductility and toughness of AISI 1020 steel are studied. Thick, hard, non-acicular and uniform boride layer are obtained as a result of laser boriding. The impact test results indicate that the laser borided specimens treated at higher energy densities of the laser beam have better ductility and toughness as compared with the specimens treated with lower energy densities of the laser beam as well as the continuous and the interrupted borided specimens.

Characterization of laser-borided Nimonic 80A-alloy

Nimonic 80A-alloy belongs to Nickel-based superalloys. Many of them are used in variety branches of industry due to high strength and resistance in aggressive conditions. Moreover, its mechanical properties are kept in high temperature. However, these materials should be coated by appropriate wear protection, under conditions of considerable mechanical wear. Unfortunately, the production of thick borided layer in diffusion boriding required high temperature and long duration of this processes. Therefore, in this study instead conventional diffusion process laser boriding was applied in order to produce boride layer on Nimonic 80A-alloy substrate. Laser alloying is the high-tech process which allows to modify the chemical composition of the surface. Laser boriding was arranged as a single tracks, therefore it was possible to evaluate the influence of laser treatment parameters on thickness and hardness of produced layers. The laser beam power P, laser scanning speed vl and laser beam diameter dl were the variable parameters used during laser alloying.

Laser boriding of 100CrMnSi6-4 steel using BaF2 self-lubricating addition

Laser boriding of 100CrMnSi6-4 steel using BaF2 self-lubricating addition

Effect of borotitanizing on microstructure and wear behavior of Inconel 625

Inconel 625, a nickel-based superalloy, is used in a wide range of applications including the marine and petroleum industries under where it is subjected to harsh conditions such as high temperatures and highly corrosive environments. However, its wear resistance is limited and can be often considered unsatisfactory in some applications. If this alloy were to be used under abrasive wear conditions, its surface would have to be protected by a wear resistant coating. In this study, a two-step thermo-chemical borotitanizing treatment (including an initial boriding step followed by titanium diffusion) is proposed. Microstructural characterization (optical microscopy, scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction) and mechanical properties (including micro-hardness and micro-abrasion wear) of the coated samples were conducted. Microstructural studies revealed a compact, homogenous, silicide-free coating, consisting of four distinct regions: a TiB2 layer, a multi-phase boride layer, a diffusion zone and the substrate. Hardness values were significantly higher than those obtained by standard boriding treatments. Due to the nano-sized boriding agents used, the coatings formed on the surface were thicker than coatings obtained by methods such as nitriding, paste boriding and pack-boriding, and comparable to that of laser boriding. The wear resistance was improved by up to ten times in comparison with untreated Inconel 625. Grooving was the effective wear mechanism in untreated Inconel 625. However the increase in surface hardness achieved by the borotitanizing treatment changed the wear mechanism in the coated samples from grooving to rolling.

Laser alloying of bearing steel with boron and self-lubricating addition

Abstract 100CrMnSi6-4 bearing steel has been widely used for many applications, e.g. rolling bearings which work in difficult operating conditions. Therefore, this steel has to be characterized by special properties such as high wear resistance and high hardness. In this study laser-boriding was applied to improve these properties. Laser alloying was conducted as the two step process with two different types of alloying material: amorphous boron only and amorphous boron with addition of calcium fluoride CaF2. At first, the surface was coated with paste including alloying material. Second step of the process consisted in laser re-melting. The surface of sample, coated with the paste, was irradiated by the laser beam. In this study, TRUMPF TLF 2600 Turbo CO2 laser was used. The microstructure, microhardness and wear resistance of both laser-borided layer and laser-borided layer with the addition of calcium fluoride were investigated. The layer, alloyed with boron and CaF2, was characterized by higher wear resistance than the layer after laser boriding only.

Laser borided composite layer produced on austenitic 316L steel

Abstract Abstract Austenitic 316L steel is well-known for its good resistance to corrosion and oxidation. Therefore, this material is often used wherever corrosive media or high temperatures are to be expected. The main drawback of this material is very low hardness and low resistance to mechanical wear. In this study, the laser boriding was used in order to improve the wear behavior of this material. As a consequence, a composite surface layer was produced. The microstructure of laser-borided steel was characterized by only two zones: re-melted zone and base material. In the re-melted zone, a composite microstructure, consisting of hard ceramic phases (borides) and a soft austenitic matrix, was observed. A significant increase in hardness and wear resistance of such a layer was obtained.

Wear resistance improvement of austenitic 316L steel by laser alloying with boron

Abstract Austenitic 316L steel was known for its good resistance to corrosion and oxidation. Therefore, this material was often used wherever corrosive media or high temperatures were to be expected. However, under conditions of appreciable mechanical wear, this steel had to be characterized by suitable wear protection. In this study, laser boriding was used in order to improve the wear behavior of this material. The composite boride layer consisted of hard ceramic phases (borides and boro-carbides) and a soft austenitic matrix. The significant increase in wear resistance of laser-borided layer was observed in comparison with the untreated 316L steel. The predominant abrasive wear was accompanied by adhesive and oxidative wear evidenced by shallow grooves, adhesion craters and the presence of oxides.

Fracture Microindentation on boride layers on AISI 1020 steel

In this paper, an attempt has been made to enhance the fracture toughness (Kc) of boride layer using multi-component (Ni, Cr and B) laser bonding. The fracture toughness of continuously pack borided, interrupted pack borided and multi-component (Ni, Cr and B) laser borided steel specimens was measured using Vickers microindentation fracture toughness test as per ASTM E384 standard. The fracture toughness of continuously pack borided layer was - 3.3 MPa.m1/2. The fracture toughness of interrupted boride layer was in the range of - 4.9 MPa.m1/2. The fracture toughness of multi-component (Ni, Cr and B) laser borided layer was in the range of 13.8 - 18.3 MPa.m1/2. A significant improvement in fracture toughness of laser treated specimens was observed from the experimental results. This may be due to better distribution of boron, nickel, chromium and other alloying elements due to laser treatment and relatively more uniform boride layer as compared with continuously pack borided layer and interrupted pack borided layer.

Wear resistance improvement of 100CrMnSi6-4 bearing steel by laser boriding using CaF2 self-lubricating addition

Laser-alloyed layer with boron and CaF2 self-lubricating addition was produced on 100CrMnSi6-4 bearing steel. The produced layer was free of cracks or gas pores and uniform in respect of the thickness because of the high overlapping (86%). The microstructure consisted of re-melted zone and heat-affected zone. The re-melted zone included dendritic or globular iron borides with limited percentage of eutectic mixture in which CaF2 particles were located. Martensite and retained austenite occurred in heat-affected zone. Tribofilm, consisting of CaF2, was observed on the worn surface and was the reason for improved wear resistance compared to the laser-alloyed layer with boron only. In areas, in which tribofilm was thin or almost invisible, an intensive abrasive or oxidative wear proceeded.

Laser boriding of 100CrMnSi6-4 steel using CaF2 self-lubricating addition

Laser boriding of 100CrMnSi6-4 steel using CaF2 self-lubricating addition

Gradient boride layers formed by diffusion carburizing and laser boriding

Laser boriding, instead of diffusion boriding, was proposed to formation of gradient borocarburized layers. The microstructure and properties of these layers were compared to those-obtained after typical diffusion borocarburizing. First method of treatment consists in diffusion carburizing and laser boriding only. In microstructure three zones are present: laser borided zone, hardened carburized zone and carburized layer without heat treatment. However, the violent decrease in the microhardness was observed below the laser borided zone. Additionally, these layers were characterized by a changeable value of mass wear intensity factor thus by a changeable abrasive wear resistance. Although at the beginning of friction the very low values of mass wear intensity factor Imw were obtained, these values increased during the next stages of friction. It can be caused by the fluctuations in the microhardness of the hardened carburized zone (HAZ). The use of through hardening after carburizing and laser boriding eliminated these fluctuations. Two zones characterized the microstructure of this layer: laser borided zone and hardened carburized zone. Mass wear intensity factor obtained a constant value for this layer and was comparable to that-obtained in case of diffusion borocarburizing and through hardening. Therefore, the diffusion boriding could be replaced by the laser boriding, when the high abrasive wear resistance is required. However, the possibilities of application of laser boriding instead of diffusion process were limited. In case of elements, which needed high fatigue strength, the substitution of diffusion boriding by laser boriding was not advisable. The surface cracks formed during laser re-melting were the reason for relatively quickly first fatigue crack. The preheating of the laser treated surface before laser beam action would prevent the surface cracks and cause the improved fatigue strength. Although the cohesion of laser borided carburized layer was sufficient, the diffusion borocarburized layer showed a better cohesion.

A study of nanoindentation for mechanical characterization of chromium and nickel borides’ mixtures formed by laser boriding

Laser boriding is the process which improves the wear resistance of Inconel 600-alloy. During this treatment, the surface of base material is coated by paste, including amorphous boron. Then the surface is re-melted by a laser beam. As a consequence of the high overlapping of laser tracks (86%), the uniform laser-alloyed layer is produced, in respect of the thickness. It is easy to identify the mixture of chromium borides (CrB+Cr2B) as well as the mixture of nickel borides (Ni3B+Ni2B) in the microstructure of the re-melted zone by X-ray microanalysis using EDS. In this study, the mechanical properties of both chromium and nickel borides’ mixtures are examined using the nanoindenter with a Berkovich diamond tip. Young's moduli and hardness are measured and compared with the literature data. The load–displacement curves and the indentation images are shown for the selected measurements. The higher average values of Young's modulus (355.11GPa) and hardness (28.25GPa) characterize the chromium borides’ mixture. In case of the nickel borides’ mixture, the average Young's modulus is equal to 287.91GPa, and the hardness of 13.51GPa is measured.

Microstructure and properties of laser-borided Inconel 600-alloy

Nickel-based superalloys are used extensively for a variety of industrial applications involving high temperatures and aggressive environments. However, under conditions of appreciable mechanical wear (adhesive or abrasive), these materials have to be distinguished by suitable wear protection. The diffusion boronizing is the thermo-chemical treatment, which improves the tribological properties of nickel and its alloys. Nevertheless, the long duration of this process is necessary in order to obtain the layers of the thickness up to about 100μm. Instead of the diffusion process, in this study the laser boriding is used for producing boride layer on Inconel 600-alloy. During the laser alloying, the external cylindrical surface of base material is coated by paste, including amorphous boron. Then the surface is re-melted by a laser beam. The high overlapping of multiple laser tracks (86%) causes the formation of uniform laser-alloyed layer in respect of the thickness. Laser re-melted zone, heat-affected zone and the substrate characterize the microstructure. In the re-melted zone, the three areas are observed: compact borides zone consisting of nickel, chromium and iron borides (close to the surface), zone of increased percentage of Ni–Cr–Fe-matrix (appearing in the greater distance from the surface) and zone of dominant Ni–Cr–Fe-matrix percentage (at the end of the layer). The hardness obtained is comparable to that-obtained in case of diffusion boriding. Simultaneously, the laser-borided layers are significantly thicker (about 346 or 467μm depending on the laser power used). The significant increase in their abrasive wear resistance is observed. The wear intensity factors, as well as the relative mass loss of the laser-borided samples, are ten times smaller in comparison with untreated Inconel 600-alloy.

Growth mechanism of the tubular TiB crystals in situ formed in the coatings laser-borided on Ti–6Al–4V alloy

Coatings containing borides were fabricated on titanium alloy by laser boriding treatment. SEM images indicate that some rod-like TiB crystals with a hollow core (filled with α-Ti before etched) are formed in the coatings. The formation of rod-like hollow TiB is attributed to the following aspects: first, because the chemical composition in some areas in the laser melt pool is hypoeutectic and in some other areas is hypereutectic due to the boron atoms dissolved in the melt distributing unevenly during rapid solidification, β-Ti firstly crystallizes as primary phases in the hypoeutectic areas of the melt pool and acts as a heterogeneous nucleus for TiB to crystallize on it, and second, because the bond between B–B is stronger than that between Ti–B and between Ti–Ti. TiB grows along the B–B zig-zag chain as well as normal to the direction of the B–B zig-zag chain to form a tubular structure with a β-Ti core in it.