Gas Technique of Simultaneous Borocarburizing of Armco Iron Using Trimethyl Borate

• Main Authors: Natalia Makuch, Piotr Dziarski, Michał Kulka
• Format: Article
• Language: English
• Published: MDPI AG 2020-06-01
• Series: Coatings
• Subjects: gas boriding; gas borocarburizing; trimethyl borate; microstructure; hardness; wear resistance
• Online Access: https://www.mdpi.com/2079-6412/10/6/564

The gas boriding process is an appropriate technique used for increasing the hardness and wear resistance of iron and steels. However, the boron halides (e.g., BCl₃, BF₃) are rarely used as a boron source during gas boriding in industry due to the toxic character of these reagents. The possibility of the use of organic compounds as a boron source in plasma assisted processes was the instigation to determine the possibility of applying these agents for gas boriding. In the present work trimethyl borate was used as an organic boron source. The use of a N₂–H₂–B(CH₃O)₃ atmosphere ensured the appropriate conditions for the simultaneous gas borocarburizing of Armco iron. The process was carried out at 1223 K (950 °C) for 2 h. The produced layer consisted of two zones: an outer zone containing a diffusion of boron atoms and an inner zone containing a diffusion of carbon atoms, under the outer zone. Due to the reduction of trimethyl borate with hydrogen, free atoms of carbon were released for the gas atmosphere. Therefore, there existed favorable conditions for carburizing. Unfortunately, the formation of a carburized layer was the reason for the difficult diffusion of boron atoms. As a consequence, the boron diffusion front was hindered, and the outer boride layer was relatively thin (ca. 7.8 µm). The boride layer contained only Fe₂B phase, which was characterized by high hardness in the range from 1103 HV_0.01 to 1546 HV_0.01. The presence of iron borides in the outer layer was also the reason for increased wear resistance in comparison with untreated Armco iron.