Laser Processing of Diffusion Boronized Layer Produced on Monel® Alloy 400—Microstructure, Microhardness, Corrosion and Wear Resistance Tests

The paper presents the results of studies of microstructure, mechanical and physicochemical properties of surface layers produced by laser modification of the diffusion boron layer on Monel® Alloy 400. The diffusion boron layers were produced at 950 °C for 6 h. The gas-contact method was used in an open retort furnace. The process was carried out in a powder mixture containing B4C carbide as a boron source. The next stage was the modification of the boron layer with a diode laser beam of a nominal power of 3 kW. A constant power of 1400 W of the laser beam was used. The scanning speed was variable (successively 5 m/min, 25 m/min, 50 m/min). In order to determine the best parameters, single tracks were created, after which multiple tracks were prepared using previously selected parameters. It was found that both the diffusion borided layer and the laser modified layer had better properties than the substrate material. Both these processes contributed to an increase in corrosion resistance, hardness and wear resistance. It was also found that laser modification caused a slight deterioration of the properties in comparison with the diffusion borided layer. However, the laser modification process resulted in the production of a much thicker layer.

The importance of phase composition for corrosion resistance and thermal oxidation behavior of gas-borided layer produced on nickel alloy

Gas boriding was used to produce the borided layer containing a mixture of chromium and nickel borides on the Inconel®600-alloy. The borided sample was characterized by a higher corrosion potential (−0.953 V) than the non-borided sample (−1.005 V). The corrosion current density was significantly lower for the borided sample. The oxidation at 1000 °C for 24 h caused the formation of different oxides on the surface of the borided sample. Simultaneously, the presence of nickel and chromium borides was confirmed by XRD analysis after the oxidation test. It was concluded, that the gas boriding could be an effective barrier against corrosion and oxidation of Inconel®600-alloy.

Improvement of wear behaviour of titanium by boriding

Purpose The purpose of this paper is to achieve a hard and protective borided layer on commercially pure Ti (grade-2) by applying boriding, and to investigate the changes in its microstructure, hardness, friction and wear behaviors. Design/methodology/approach Pack boriding technique was used to form a hard boron diffusion layer on titanium substrate. A powder mixture of amorphous boron and anhydrous borax was used as a solid-state boriding media, and then the boriding was carried out under inert atmosphere. Findings A thick dual boride layer consisting of a monolithic titanium diboride (TiB2) on the top and titanium monoboride (TiB) whiskers beneath that layer formed at relatively low diffusion temperature under pressured inert argon atmosphere in a boriding media containing boron source and activator. With boriding at specified conditions, very hard (4100 Hv0.01) and thick monolithic TiB2 layer formed on the top-most layer which is required for improved tribological applications. Hardness decreased gradually through the TiB whisker layer and finally reached to the hardness of base material. Originality/value This paper investigates the effects of components of boriding mixture and conditions of thermal treatment on the formation of borided layer and its properties. In previous studies, boriding mixtures containing a boron source, an activator and a filler material was generally used at high temperatures around or above 1,050°C to achieve a thick monolithic layer on the top of the surface of titanium. In the present study, no filler material was used to accelerate the boron diffusion because filler materials may inhibit the diffusion of boron atom through the surface of substrate of titanium. Also, diffusion treatment was carried out under pressurized argon atmosphere at relatively low diffusion temperature to achieve boride layer with the improved hardness and durability.

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

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.