Engineering the Surface with Boron Based Materials

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, appear to hold great potential for the future. The wear, corrosion, and oxidation properties of boron based coatings are described and specific applications are cited.

Corrosion performance and tribological properties of carbonitrided 304 stainless steel

“…The oxide layer of samples treated at high nitrogen content or high carbon content contains low or high amount of fine precipitations from carbon on the surface, respectively. This oxide layer acts as a lubricating layer, which prevents metalto-metal contact, decreases the friction coefficient, reduces adhesive wear and therefore generally reduces the wear [17].…”

“…More investigations are succeeded to maintain and sometimes to improve the corrosion resistance of stainless steels after nitriding [15][16]. It is well known that the formation of nitrogen supersaturated solid solution phase without CrN precipitations should maintain the good corrosion resistance of stainless steel [5,17].…”

Propiedades mecánicas de cermets basados en diboruro de titanio

“…Los resultados presentados corresponden a la media de 5 ensayos realizados con un indentador Tukon a una carga de 10 kg (HV10). Las grietas generadas en las esquinas de las huellas de indentación se usaron para calcular el factor crítico de intensidad de tensiones superficial, K S IC , mediante el modelo semi-empírico propuesto por Shetty et al (11): [1] donde, P es la carga aplicada, P c es la carga umbral para el inicio del agrietamiento, H es la dureza Vickers, b es una constante que depende de la geometría del indentador y que en el caso de la pirámide Vickers vale 0.089 y, finalmente, "a" es el tamaño de la grieta considerada como tipo Palmqvist (12). No se observó agrietamiento para contenidos de fase ligante iguales o superiores al 30% en volumen incluso para cargas de 25 kg.…”

“…La energía requerida para la transformación se obtiene del campo de tensiones en el entorno de la punta de la grieta, lo que reduce el factor de concentración de tensiones. (1). Micrografía SEM obtenida mediante electrones secundarios correspondiente a la superficie de fractura de una probeta Barker.…”

“…El refuerzo mediante el uso de matrices metálicas ha sido una idea comúnmente utilizada no sólo para aumentar la tenacidad del diboruro de titanio (TiB 2 ) sino también su sinterabilidad (1)(2)(3)(4)(5). Metales como el hierro, el cobalto o el níquel fueron los primeros utilizados para la sinterización en fase líquida del TiB 2 .…”