Boriding

About: Boriding is a research topic. Over the lifetime, 1082 publications have been published within this topic receiving 13725 citations.

Sliding and abrasive wear behaviour of boride coatings

Abstract: Polyphase boride coatings constituted by an inner layer of Fe 2 B and an outer layer of FeB were thermochemically grown on iron and medium carbon steel by a pack cementation process. The tribological behaviour of borided samples was investigated under both sliding and abrasion testing conditions. Considerably different values of wear rate were found in different regions of the coatings. The differences were explained on the basis of the crystallographic order of iron borides. The resistance to both types of wear was initially poor due to the presence on the coatings of a thin, friable layer constituted by disordered crystals. Then the resistance increased to a maximum value in regions constituted by compact, highly ordered crystals of Fe 2 B. The resistance to dry sliding of borided samples was better than that displayed by samples submitted to alternative surface treatments (e.g. gas nitriding) and lower that that measured for a WC–Co hard metal coating.

Surface Hardening of Steels: Understanding the Basics

Abstract: Surface Hardening of Steels: Understanding the Basics is a practical selection guide to help engineers and technicians choose the most efficient surface hardening techniques that offer consistent and repeatable results. Emphasis is placed on characteristics such as processing temperature, case/coating thickness, bond strength, and hardness level obtained. The advantages and limitations of the various thermochemical, thermal, and coating/surface modification technologies are compared. Economic concerns and health and safety considerations are also addressed. Recent developments in the understanding of the relationships between microstructure and fatigue and wear performance are reviewed, as are more recently introduced surface hardening processes such as vacuum-related technologies, laser processing, CVD/PVD, and ion implantation. Methods for evaluating hardness patterns and depths of hardness for quality control and failure analysis are described. The book also reviews methods for measuring and controlling case depth, residual stresses, and distortion. Metallurgical comparisons are made between those processes that offer rapid heating and rapid cooling (self quenching) characteristics for example, induction hardening and conventional furnace hardening. While all of the surface engineering methods discussed enhance wear resistance, some such as electroless nickel plating, carbide salt-bath deposition, and chrome platingualso offer resistance to corrosion and oxidation. Wear and corrosion data are provided to demonstrate the benefits of each process. Contents: Process Selection Guide Gas Carburizing Vacuum and Plasma Carburizing Pack and Liquid Carburizing Carbonitriding Nitriding Nitrocarburizing Boriding (Boronizing) Thermal Diffusion (TD) Process Surface Hardening by Applied Energy Surface Hardening by Coating or Surface Modification Appendices: The Iron-Carbon Phase Diagram, Hardness Conversion Tables, Austenitizing Temperatures for Steels Index.

FeB/Fe2B phase transformation during SPS pack-boriding: Boride layer growth kinetics

Abstract: The iron boride layer growth kinetics in mild steel through the spark plasma sintering (SPS) pack-boriding technique is investigated at 850 °C with different boriding durations (maximum 240 min). Results show that both FeB and Fe 2 B layers form and grow on the mild steel surface with the FeB layer on the top of Fe 2 B sublayer in the samples with boriding duration less than 90 min. However, at longer boriding duration, the top FeB layer eventually ceases growing, starts to diminish, and, finally disappears completely by transforming into the Fe 2 B phase. Numerical simulation is implemented to explain this phenomenon. Subsequently, the diffusion coefficient of boron in FeB and Fe 2 B phase is obtained through fitting the experimental results into the model. The simulation results are found to be in good agreement with the experimental results, and the estimated diffusion coefficients of boron in FeB and Fe 2 B phases as 2.33 × 10 −9 and 4.67 × 10 −9 cm 2 /s, respectively. Both the simulation and experimental results reveal that the Fe 2 B mono-phase layer can be obtained through the transformation of FeB to Fe 2 B phase due to the depletion of boron concentration in the boriding medium, and is indifferent to the formation of FeB phase at the very onset of the boriding process. This provides a new approach to overcome the side effect of FeB formation in borided components.

Thermal fatigue cracking of surface engineered hot work tool steels

Abstract: Thermal fatigue cracking is an important life-limiting failure mechanism in die casting tools. It is observed as a network of fine cracks on the surfaces exposed to thermal cycling. The crack network degrades the surface quality of the tool and, consequently, the surface of the casting. Surface engineered materials are today successfully applied to improve the erosion and corrosion resistance. However, their resistance against thermal fatigue is not fully explored. In this work, a selection of hot work tool steel grades was surface modified and experimentally evaluated in a dedicated thermal fatigue simulation test. The surface modifications included boriding, nitriding, Toyota diffusion (CrC), and physical vapour deposition (PVD) of coatings (CrC, CrN and TiAlN), both as single-layers and deposited after nitriding (duplex treatment). Untreated specimens of each tool steel grade were used as references. The test is based on cyclic induction heating and internal cooling of hollow cylindrical test rods. The surface strain is continuously recorded through a non-contact laser speckle technique. Generally, all surface treatments decreased the resistance against surface cracking as compared to the reference materials. The reason is that the engineering processes influence negatively on the mechanical properties of the tool materials. Of the processes evaluated, duplex treatment was the least destructive. It gave a lower crack density than the reference steel, but the diffusion layer is more susceptible to crack propagation. In addition, the single-layered CrN coating showed almost comparable thermal fatigue cracking resistance as the reference material. Finally, the resistance against thermal crack propagation of surface engineered tool steels is primarily determined by the mechanical properties of the substrate material.

Influence of the pack thickness of the boronizing mixture on the boriding of steel

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