Current Trends in Boriding

In this chapter, the origins of boriding process were mentioned, and the term ‘boriding’ was explained. The various important techniques of producing the boride layers and coatings were indicated together with some of their advantages. The next parts of this book were announced.

The simplified classification of the techniques of boriding was presented in this chapter. The two main groups of the methods were indicated: chemical techniques and physical techniques regarding the technological aspects of boriding process. Such a classification was based on how to produce the active atoms or ions of boron, which might be adsorbed on the surface of metal alloys and could diffuse into the substrate. The most intensively developed techniques were put in the boxes drawn in a broken line, indicating the current trends in boriding.

All the materials, subjected to boronizing using different techniques, were indicated in this chapter. They were classified into two main groups: iron alloys and non-ferrous materials. The preliminary analysis of the produced microstructure was presented. The most popular materials with boride layers were marked with the boxes drawn in a broken line. Boride coatings could be produced on any metal alloy under certain conditions.

All the specified thermochemical techniques of boriding in solid, liquid and gaseous media were characterized and compared in this chapter based on the available literature data. The technological aspects of boriding processes were analyzed, taking into consideration the advantages and disadvantages of each method. The effects of the boriding techniques on the microstructure of borided materials have been indicated. The mechanism of formation of active boron atoms was described. Some issues of the thermodynamics of gas boriding were analyzed. The chemical techniques of boriding were divided into the three groups: boriding in solid media, boriding in liquid media and boriding in gaseous media (see Fig. 2.​1). Due to the need of using the elevated temperature during these processes, they were usually recognized as thermochemical techniques. In the present work, the most intensively developed techniques, put in the boxes drawn in a broken line in Fig. 2.​1, were described in more detail, taking into account the current trends in boriding. Therefore, the most attention in this chapter was devoted to the powder-pack processes, electrochemical boronizing in borax as well as to the gas boronizing with the use of boron halides or boranes.

All the specified physical techniques of boriding, i.e. carried out under glow discharge conditions, boron ion implantation and high-energy techniques were characterized and compared in this chapter based on the available literature data. The technological aspects of boriding processes were analyzed, taking into consideration the advantages and disadvantages of each method. The effects of the boriding methods on the microstructure of borided materials were shown. The mechanism of formation of active boron atoms or ions and the phenomena during re-melting of alloying material together with the substrate were described. The three main groups of physical techniques of boriding were specified: boriding under glow discharge conditions, boriding by ion implantation and the high-energy methods of boriding. The most intensively developed physical techniques were put in the boxes drawn in a broken line in Fig. 2.​1. They were described in more detail, taking into account the current trends in boronizing. Hence, the most attention was devoted to the boriding under glow discharge conditions, especially plasma gas (or paste) boriding, and surface alloying with boron, especially, laser (or plasma) surface alloying.

All the types of microstructure of surface layers with boron were classified. The boriding techniques, resulting in the formation of these types of microstructure, were specified. The developmental prospects of the boriding process were formulated by indicating the most attractive techniques, taking into account their most important features and possibility of their use for boriding of a wide range of materials.