Property enhancement of diffusion borided layers by laser treatment
TL;DR: In this paper, a low activity boronizing mixture was used for pack boriding of a medium carbon steel to obtain a single phase Fe2B layer, which is desirable in the boride coating for its superior performance and can be achieved in several ways.
Abstract: Tribological properties such as abrasion and erosion resistance of boride coatings on steels have been proven to be outstanding when compared with conventional hardening techniques, e.g., carburizing and nitriding. Pack boriding is a relatively simple and economical technique among all the methods available for boriding. A single phase Fe2B layer is desirable in the boride coating for its superior performance and this can be achieved in several ways. However, the boride coating is often associated with inherent porosity, especially near the surface and this is undesirable from the standpoint of structural integrity of the coating particularly for applications involving highly loaded parts. Laser-based postprocessing is an effective technique for eliminating these undesirable microstructural features without deteriorating the mechanical properties of the coating. In the present investigation, a low activity boronizing mixture was used for pack boriding of a medium carbon steel to obtain a single phase Fe2B...
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TL;DR: In this paper, the accuracy of the produced 3D structures in the range of 0.1mm is the highest possible in the group of welding techniques, while the heat input into the workpiece is less compared to TIG or PTA welding, although a metallurgical bonding to the substrate is guaranteed.
Abstract: Surface coating, repair, and rapid design changes of high-value components and tools are demanding challenges of modern manufacturing technology. In this field, advanced laser-based techniques are of outstanding importance for the related applications in mould and tool, aircraft and aerospace, as well as automotive industry. Many laser cladding solutions have been transferred into industrial series production within the last years. The motivations for the raising interest are given by the typical features of the technology: on the base of closed CAD/CAM chains, a quick and comprehensive treatment even of complex shaped and highly stressed components is possible. The heat input into the workpiece is less compared to TIG or PTA welding, although a metallurgical bonding to the substrate is guaranteed. Furthermore, the precise material deposition even at small partial areas is an advantageous characteristic. The coating materials include metal alloys (Co, Ni, Cu basis, Titanium, and steel), hard metals (e.g., WC/Co, TiC, and VC with metallic binders), and oxide ceramics (Al2O3/TiO2). Typical base materials are steel, cast iron, and lightweight metal alloys based on Aluminum, Titanium, and Magnesium. The accuracy of the produced 3D structures in the range of 0.1 mm is the highest possible in the group of welding techniques. On the other hand, the available system technology (lasers, powder feeders and nozzles, CAD/CAM systems) permits a very easy and successful integration of the laser technology into manufacturing systems. Examples of application are the surface protection of lightweight automotive motor components, repair and quick modifications of metal forming tools as well as the complete restoration of damaged blades and disks of aero engines and gas turbines.
132 citations
TL;DR: A powder mixture of aluminium, titania, and hexa-boron nitride (h-BN) was laser-triggered to undergo SHS (self-propagating high temperature synthesis) and was subsequently alloyed onto a mild steel substrate surface.
Abstract: A powder mixture of aluminium (Al), titania (TiO2) and hexa-boron nitride (h-BN) was laser-triggered to undergo SHS (self-propagating high temperature synthesis) and was subsequently laser alloyed onto a mild steel substrate surface. A nano-structured coating was formed with high microhardness (∼3000 HV0.05 at the cross-section and ∼2600 HV0.2 on the top surface). X-ray diffraction (XRD) identified the presence of aluminium oxide (Al2O3), titanium di-boride (TiB2), titanium nitride (TiN), iron (Fe) and its borides (FeB, Fe2B) in the coating. Scanning electron microscopy (SEM) and high resolution transmission electron microscopic (HRTEM) analysis of the coating revealed nano-fibrous titanium-rich reinforcements in a matrix of nano-crystalline alumina. The thickness of titanium di-boride nano-fibres was an order of magnitude higher than the size of nano-alumina crystallites.
27 citations
Cites methods from "Property enhancement of diffusion b..."
...A number of methodologies have been attempted, like laser surface modification, laser cladding, laser particle injection, pulsed laser deposition and laser surface alloying of pre-placed powders [6–20]....
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TL;DR: Hard nano-structured metal matrix composite (MMC) boride coatings have been synthesized by laser melting of pre-placed powder mixture paste of B4C+−sol-gel derived nano-particulate TiO2 on AISI 1050 (EN43) medium carbon steel and AisI 316L stainless steel substrates as mentioned in this paper.
Abstract: Hard nano-structured metal matrix composite (MMC) boride coatings have been synthesized by laser melting of pre-placed powder mixture paste of B4C + sol–gel derived nano-particulate TiO2 on AISI 1050 (EN43) medium carbon steel and AISI 316L stainless steel substrates. Different coating/processing gas conditions were employed to understand the influence of graphite and nitrogen gas interactions with the coating material at high temperatures. Laser synthesized coatings were characterized by SEM, EDX, FEGSEM, XRD and HRTEM. Results show that it is possible to synthesize nano-structured MMC coatings (with TiB2 and TiB particulates in the ranges of 5–10 nm, 20 nm and 200–500 nm) by employing the combined laser and sol–gel route. Nano-particulate and sub-micron level TiB and TiB2 are found dispersed throughout the metal matrix. Other borides and carbides are present in micro-level patches dispersed in a eutectic matrix. Hardness of the composite coatings is in the range 800–2000 HV0.1. The minimum coefficient of sliding friction obtained in a pin-on-disc set-up was 0.35 (against cemented tungsten carbide) while wear rates (against diamond) were substantially improved (up to 5 fold reduction) over that of the substrates.
27 citations
15 Feb 2007-Materials Science and Engineering A-structural Materials Properties Microstructure and Processing
TL;DR: In this paper, the synthesis of nano-structured boride metal matrix composite (MMC) coatings obtained by laser melting of a pre-placed mixture of B4C+Ti-6Al-4V powders and sol-gel derived nano-particulate Ti(OH)4.
Abstract: This paper reports the synthesis of nano-structured boride metal matrix composite (MMC) coatings obtained by laser melting of a pre-placed mixture of B4C + Ti–6Al–4V powders and sol–gel derived nano-particulate Ti(OH)4. The resulting nano-composite coatings have been characterised in terms of microhardness, microstructure and constituent phase composition. The coatings show evidence of micro-level FeB phases and nano-particulate TiB phases in a (Fe + Fe2B) matrix. One form of the nano-particulate TiB phase is formed in situ as rosettes as a result of dendritic bending while the other form is of irregular shape. The wear resistance of the hardest coating has been tested at 30 mm/s sliding speed and normal loads of 10, 20, 30 and 40 N under dry conditions. The wear resistance of the coating material shows a 17-fold increase compared to that of the EN43 steel substrate material and comparable or better than most reported work. Reduction of Ti–6Al–4V content in the pre-placed powder mixture does not substantially affect the hardness and wear resistance of the coating.
25 citations
TL;DR: In this article, diamond coatings were applied to high speed steel substrates by hot filament chemical vapor deposition on borided or WC-Co-coated high speed steels.
Abstract: Diamond coatings were deposited by hot filament chemical vapor deposition on high speed steel substrates. Iron boride diffusion barrier and WC–Co layers were used as interlayers. At high deposition pressure, the quality of the diamond deposits is poor due to the extensive formation of graphitic deposits. At low pressure, diamond films of better quality were obtained, but their adhesion to the substrate was insufficient. A two-step deposition process at low pressure was developed. In a first deposition step performed at high methane percentage, a high nucleation density was achieved. In a second deposition step, the methane percentage was reduced to achieve continuous, dense, and adherent diamond layers on borided or WC–Co coated high speed steel substrates. Adhesion of these diamond layers on the surface modified high speed steel substrates was tested based on reciprocating sliding tests.
14 citations
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TL;DR: In this paper, a thermal analysis for laser heating and melting materials is derived for a Gaussian source moving at a constant velocity, where the resulting temperature distribution, cooling rate distribution, and depth of melting are related to the laser spot size, velocity, and power level.
Abstract: A thermal analysis for laser heating and melting materials is derived for a Gaussian source moving at a constant velocity. The resulting temperature distribution, cooling rate distribution, and depth of melting are related to the laser spot size, velocity, and power level. As the power is increased to heat the liquid above the boiling point, a transition to deep penetration welding is described. Calculations are presented for 304‐stainless steel which are in agreement with experiment.
520 citations
TL;DR: In this article, the optimum pack thickness required to form boride coating of adequate thickness and property in the case of a low carbon steel boronized at 940°C for 2 h.
Abstract: Boronizing, which involves diffusion of boron atoms into steel substrate to form iron borides, is a well-known diffusion coating process and numerous studies have demonstrated the outstanding tribological properties of boronized steel vis-a-vis carburized or nitrided steels However, the high cost of the boronizing process has severely limited its applications One way to bring down the cost of the boronizing process is to reduce the thickness of the boronizing mixture to be packed around the component (called pack thickness) to the minimum required level without compromising on the properties of the boride coating The present study attempts to estimate the optimum pack thickness required to form boride coating of adequate thickness and property in the case of a low carbon steel boronized at 940°C for 2 h Low carbon steel samples have been boronized with varying pack thickness in the range 2-25 mm and the resulting boride coatings have been examined for thickness, microstructure, microhardness profile and abrasion resistance An analysis of the results obtained indicated that a pack thickness of 10 mm is sufficient to obtain boride coatings of adequate thickness and optimum properties
170 citations
TL;DR: In this article, the high speed sliding wear and friction behavior of a boronized medium carbon steel has been characterized using a friction dynamometer using a hardened tool steel disc The sliding tests were carried out at velocities up to 8 m s −1 and normal loads up to 2 MPa.
Abstract: Steels provided with boronized diffusion coatings are known to exhibit excellent wear resistance at low sliding speeds However, the sliding wear behaviour of boronized coatings at high sliding speed is not known In the present study, the high speed sliding wear and friction behaviour of a boronized medium carbon steel has been characterized using a friction dynamometer The boronized samples were tested against a hardened tool steel disc The sliding tests were carried out at velocities up to 8 m s −1 and normal loads up to 2 MPa These tests indicated that the wear rate of the steel can be reduced by about an order of magnitude as a result of boronizing The coefficient of friction of the boronized steel was higher than that of the unboronized steels especially at higher sliding speeds
100 citations
TL;DR: The only commercial coating processes practised have been the thermochemical diffusion techniques termed boronizing or boriding, whereby borone is diffused into, and combines with, the substrate material forming a single or double phase metal boride layer at, and adjacent to, the surface.
Abstract: Boron, boron carbide, boron nitride, and transition metal borides have many attractive properties, including high melting point and hardness, good wear and corrosion resistance, excellent electrical conductivity, and resistance to attack by molten metals. There therefore appears to be significant scope for enhancing surface properties of metals and ceramics by applying coatings constituted from these materials. Currently, the only commercial coating processes practised have been the thermochemical diffusion techniques termed boronizing or boriding, whereby boron is diffused into, and combines with, the substrate material forming a single or double phase metal boride layer at, and adjacent to, the surface. This review not only describes the various media used for such treatments and their limitations, but attention is also given to the lesser known processes, not yet commercially practised, which provide for the deposition of a wide variety of boron based materials. Such processes, like PVD and CVD...
97 citations