Abstract: Pulsed-DC plasma boriding in an Ar–BCl3 atmosphere was performed for pure titanium and the titanium alloy TiAl6V4 in the temperature range of 700–900°C. The plasma boriding leads to the formation of TiB2 and TiB at the surface for pure titanium as well as for TiAl6V4, depending on the process parameters. These phases were identified using X-ray diffraction (XRD). The amount of boron, oxygen and the alloying elements at the surface and the depth profiles were examined by glow-discharge optical emission spectroscopy (GDOS). The hardness profile was measured on metallographic sections after boriding. The high hardness of the layer is similar to the hardness known for titanium boride layers formed by plasma-assisted chemical vapor deposition (PACVD). Scratch tests indicate that the adhesion strength is relatively high, thus indicating a high potential for industrial applications under tribological conditions.

Abstract: Fluidized bed technology has been successfully used in the formation of different types of coatings e.g. aluminizing [1–3], chromizing [1–3], nitriding [4], carburizing [4], carbonitriding [4]. Limited information however exists on boride coatings obtained using fluidized bed technology, though the method is simple, efficient and environmentally friendly. Boride coatings on steel have been reported to have an excellent combination of properties [5, 6, 10], and titanium borides are well known for their high hardness and excellent corrosion and wear resistance. However, no reference could be cited in the literature concerning Tiboride coatings, on Ti alloys obtained in a fluidized bed reactor. Ti and its alloys, especially with Al, are attracting considerable attention because of their potential use as low-density and high temperature structural materials [14–16]. Their inadequate oxidation resistance at elevated temperatures (>800 ◦C) however limits their practical applications. Addition of alloying elements such as Nb, Si, C, B do improve the oxidation resistance of these alloys, but the amounts of these additives should be controlled at low levels [11]. Use of surface modification techniques such as ion implantation of Al ions in to Ti-Al alloys, produce a high oxidation resistant TiAl3 coating, whose final overall oxidation resistance is nevertheless mitigated by the inherently developed cracks and voids in the coating [12, 13]. On the other hand, thermochemical diffusion processing such as boronizing in fluidized beds is a promising method for improving the oxidation resistance of Ti and its alloys, as it is a flexible and low cost method, yielding boride layers of excellent quality and uniformity. The main advantage of the process of fluidization, is the high rate of mass and heat transfer, which results in a uniform temperature throughout the volume of the reactor and a flash mix of all compounds contained in it, thus yielding high quality coatings [7–9]. Additional advantages arise from, the process capability for quick parameter adjustment, the relatively low capital and operation costs and its being environmentally friendly. Some of the main parameters affecting the quality of the fluidization process and that of the produced coatings, obviously are the properties of solids and fluids used, bed geometry, gas flow rate, type of gas distributor and overall reactor design. This paper presents some of the results produced by a study of boride coatings applied onto Ti-Al-V alloys by the fluidized bed process. The fluidized bed reactor system used for the above and shown schematically in Fig. 1, consisted of the following five main components:

Abstract: The effect of diffusion boriding temperature and time, hot-worked powder billet porosity, and the carbon content within them, on borided layer thickness is studied A difference is established in impregnation at the temperature for eutectic formation in the system Fe ― B within the surface layer of a billet from boriding in the absence of a liquid phase The processes are conditionally called liquid-phase and solid-phase boriding The difference involves a higher impregnation rate and the possibility of porous billet infiltration with melt during liquid-phase boriding Optimum production parameters are determined for boriding

Abstract: The wear resistance of borided powder materials is studied. The maximum wear resistance with dry friction is obtained with carbon-free iron powder borided before hot forging. For abrasive wear operating conditions it is preferable to use borided carbon steel after heat treatment. It is established that coating billets with nickel before boriding provides an increase in wear resistance. Nickel promotes the formation of borides FeB and NiB with high microhardness. The mechanical properties of borided materials are studied.

Abstract: A novel approach to gas boronising has been carried out to systematically test organoboranes as precursors for low pressure gas boronising. The precursors of the group of borane–amine adducts were synthesised and subsequently applied to gas boronising of steel 42CrMo4 (AISI 4140). Characterisation of the boride layers was performed using glow discharge opticalemission spectroscopy, X-ray photoelectron spectroscopy, SEM, and metallography. Ultramicrohardness was also determined and the wear behaviour was simulated. With the precursors borane–triethylamine adduct and borane–diethylamine adduct gas boronising was possible. Single phased iron boride layers of type Fe2 B with a thickness of several micrometres were generated. The carbon, nitrogen, and oxygen contamination of the boride layers was low. The boride layers are not completely compact which results in a lower hardness compared with commercial powder pack boronised samples. The wear behaviour is similar to powder pack boronised steels and is ...

Abstract: Pack boriding of powder metallurgy steels in a powder mixture consisting of ferroboron, carbon ferramanganese and alumina without halides was investigated. Fe-C and low alloy Fe-Ni-Mo-(Cu)-C steel tensile bars were sintered at 1120°C for th in cracked ammonia and then pack barided at 1050°C for 2h. This boriding treatment resulted in the formation of hard surface layers and also in an increase in tensile strength, which was further-enhanced by subsequent heat treatment. In parallel, increases in hardness and density were noted with the formation of a new microstructure in the sample core-an enhanced postsintering effect. It is concluded that the boriding powder mix used was effective for the pack boriding of powder metallurgy steels.

Abstract: Hot pressing is considered for borided and unborided powder blanks. In the hot additional pressing of unborided steel compacts, protection from decarburization is required. The hot pressing of borided blanks should be conducted at 1200°C in the presence of liquid eutectic phase. This produces good quality in the borided layer. Cracks do not arise at the ends of the blanks. The cracks that arise on the side surfaces at the start of deformation are filled by liquid phase in the final stage. The best conditions have been established for heating the blanks made by solid-phase and liquid-phase boriding.