Multi-component boron coatings on low carbon steel AISI 1018

8
• Microhardness of about 18-20 GPa
• Young's modulus of 285-295 GPa
• Thermal expansion coefficient of 7.65x10 -6 7°C in the range 200-600 °C, and
9.2x10 -6 /°C in the range 100-800 °C
The characteristics of the FeB phase include [3]:
• Composition with 16.23 wt. % <strong>boron</strong>
• Orthorhombic crystal structure (a=4.053A, b=5.495Å, c=2.946Å)
• Density of 6.75 g/cm3
• Microhardness of about 19-21 GPa
• Young's modulus of 590 GPa
• Thermal expansion coefficient of 23x10 -6 /°C in the range 200-600 °C
2.2.2 Boronizing of Nonferrous Materials
Refractory metals, titanium, nickel, cobalt and their alloys can be <strong>boron</strong>ized by using
special techniques such as gas and plasma <strong>boron</strong>izing, instead of conventional <strong>boron</strong>izing
techniques. Since salt bath and conventional powder <strong>boron</strong>izing techniques are
inapplicable for titanium and refractory metals because of the oxidation on the substrate
and the corrosion from the activator that can cause the porosity in the boride layer [4].
Therefore, the heat treatment for refractory and titanium metals is operated under high
vacuum and high purity argon atmosphere, or with gas (H2-BCI3) <strong>boron</strong>izing technique.
For the refractory metal and titanium, the process is prepared at the temperature
above 1000 °C for approximately 10-15 hours [4]. The boride layer is formed with the
thickness of about 50 µm, and has various high microhardness values as depicted in
Table 2.1. However, the boride layers of tantalum, tungsten, niobium, molybdenum, and