No abstract

Boride layers are typically used to combat the wear and corrosion of metals. For this reason, to improve our knowledge of the boriding process, this research studied the effect of the size of the treated material on the kinetics of the growth of the boride layers obtained during a solid diffusion process. The purpose was to elucidate how the layers’ growth kinetics could be affected by the size of the samples since, as the amount of matter increases, the amount of energy necessary to make the process occur also increases. Furthermore, the level of activation energy seems to change as a function of the sample size, although it is considered an intrinsic parameter of each material. Six cylindrical samples with different diameters were exposed to the boriding process for three different exposure times (1.5, 3, and 5 h). The treatment temperatures used were 900, 950, and 1000 °C for each size and duration of treatment. The results show that the layer thickness increased not only as a function of the treatment conditions but also as a function of the sample diameter. The influence of the sample size on the growth kinetics of the boride layers is clear, because the growth rate increased even though the treatment conditions (time and temperature) remained constant

The effect of the boron potential on the thickness and the mechanical properties of borided layers was evaluated. The boron potential was established by means of the available atoms of boron contained in a control volume inside a cylinder. The cylinders were manufactured from AISI 316L steel, and the boriding treatment was performed using the powder pack technique at a temperature of 1273 K over an exposure time of 6 h. Four different internal diameters of the cylinders were evaluated (3.17, 4.76, 6.35, and 7.93 mm). The mechanical properties were evaluated using the Berkovich instrumented indentation technique. The results showed a clear influence of the boron potential on the mechanical properties of the layers. The hardness of the layers was stablished in the range of 16.22 to 21.16 GPa. Young’s modulus values were stablished in the range of 255.96 to 341.37 GPa. Also the fracture toughness and brittleness of the layers reflected the influence of the boron potential supplied during the boriding process. Finally, the influence of the boron potential on the constant of parabolic growth (K) was also established as a function of the inner diameter of the cylinders.

This study evaluates the tribological behavior of borided AISI 316L steel. The treatment time was set to 2, 4, and 6 h at temperatures of 850, 900, and 950°C for each time duration. The morphology and microstructure of the boride layers were analyzed by scanning electron microscopy (SEM) and X ray diffraction (XRD), respectively. The mechanical properties were evaluated by an instrumented nanoindentation test. The tribological behaviors of the layers were evaluated using a sand/rubber apparatus following the ASTM G-65 standard. The friction coefficient of the boride layers was estimated by means of the tribological pin-on-disk test. The results show that the experimental parameters had a clear influence on the thickness of the boride layers and on their mechanical properties. The volume loss was established in the range of 0.0741 « 0.011 µg to 1.6148 « 0.150 µg. Wear mechanisms such as adhesion and micro-fatigue were mainly observed in the samples exposed for 6 h at 950°C. Finally, the friction coefficient was reduced from 0.7 for the as-received material down to 0.29 for the borided samples. The wear mechanisms were discussed as a function of the scanning electron microscopy observations. It is possible to conclude that single-phase layers of Fe 2 B are more apt to face wear than the FeB/Fe 2 B biphasic layers.

No abstract