Importance of trimethyl borate temperature used during gas boriding for microstructure, nanomechanical properties and residual stresses distribution on the cross-section of the produced layer

The aim of this work was to indicate the possibility of applying organic compounds as a boron source for gas bonding. In the present work the trimethyl borate was used as an organic boron source for gas bonding process. The process was carried out at 950 degrees C for 2 h in gaseous atmosphere composed of N-2-H-2-B(CH3O)(3). The temperature of trimethyl borate influenced on its concentration in gas atmosphere. As a result, depending on B (CH3O)(3) temperature of 20 degrees C or 50 degrees C, it was possible to arranging the two types of process: bonding and borocarburizing, respectively. In the case of gas bonding the single-phase Fe2B layer was produced. The high temperature of B(CH3O)(3) caused release of free atoms of carbon, therefore there existed favorable conditions for carburizing. The produced borocarburized layer consisted of two zones: an outer Fe2B bonded layer and an inner carburized zone. The thickness of boride layer was higher after bonding process than simultaneous borocarburizing process, 10.8 mu m and 7.8 mu m, respectively. Whereas, the depth of zone of carbon diffusion was equal ca. 400 mu m. For nanomechanical properties, as well as, the residual stress distribution the nanoindentation tester Anton Paar NHT3 equipped with the Berkovich diamond tip under a maximum load of 10 mN was used. In both layers, the highest hardness H-IT (7.8-17.9 GPa) and highest Young's modulus (222-368 GPa) were measured in Fe2B layer. However, the presence of thick zone of carbon diffusion was the reason for gradually decrease in hardness in the cross section of borocarburized layer. Moreover, the presence of carburized zone advantageous influenced on residual stresses distribution across the layer. The gradually changes of residual stresses from compressive to tensile were observed in the case of simultaneous gas borocarburized layer. Such a situation was more advantage than those obtained for gas bonded layer.

Automated summary

This study suggests the possibility of using organic compounds as a boron source for gas bonding. It was found that controlling the temperature of the organic boron source at different temperatures can influence bonding and borocarburizing processes. Gas bonding produced a single-phase Fe2B layer, while borocarburized layer consisted of Fe2B bonded layer and inner carburized zone.