Growth kinetics and wear resistance of vanadium carbide on AISI D2 steel produced by TRD process

Abstract

Vanadium carbide coating was obtained on the surface of AISI D2 steel by thermal reactive diffusion process using molten borax as based salt and vanadium pentoxide as vanadium donor. The process was performed at 900 °C, 940 °C, 980 °C and 1020 °C for 3 h, 4 h, 5 h and 6 h. The Optical Microscopy was used to observe the morphology of cross section of coating layer. Energy Dispersive Spectroscopy was used to analyse the element content of the matrix and the coating layer by spot scanning and line scanning. X-ray Diffraction was used to obtained the phase composition of the coating layer. Microhardness Tester was used to measure the Vickers hardness of the coating layer and matrix. Friction and wear tester were used to explore wear resistance of the coated and uncoated specimens. The results show that the thickness of vanadium carbide coating ranges from 7.54 μm to 19.1 μm under different treatment time and temperatures. The V8C7 and VC x are the main phases contained in the vanadium coating layer. A thickness of about 3 μm transition layer is between the matrix and coating layer and the transition layer has a block effect on the diffusion of iron. The growth rate constants of vanadium carbide coating layer at 900 °C, 940 °C, 980 °C and 1020 °C were obtained as (5.20 ± 0.116) ×10–11 cm2 s−1, (8.91 ± 0.253) ×10–11 cm2 s−1, (1.26 ± 0.020) ×10–10 cm2 s−1, and (1.70 ± 0.036) ×10–10 cm2 s−1 respectively. The activation energy for vanadium carbide layer is 123.3 ± 10.1 kJ mol−1 and the diffusion constant is (2.58 ± 1.96) ×10–5 cm2 s−1. The maximum hardness of vanadium carbide coating layer on the surface of AISI D2 steel can reach 2594HV. The wear rate of untreated and treated specimens was evaluated as 15.58 × 10–13 m3/(N·m), 5.63 × 10–13 m3/(N·m) respectively and the wear resistance of treated specimens by TRD process was about 3 times than untreated specimens.

Investigation of Al-V coatings produced by the thermo-reactive diffusion method

“…The thickness of the hardened coating during pure vanadizing was 5-19 μm on steel [8,12] and 25-35 μm on cast iron [33,34]. At a low concentration of aluminium Al in the reaction powder medium (up to 1.5-2%), the thickness of the hardened layer increased to 35-55 μm.…”

“…The regressive relationship between the coating thickness h and the concentration of aluminium Al and inert filler in the reaction powder medium was obtained on the basis of experimental data (Figure 3). The thickness of the hardened coating during pure vanadizing was 5–19 µm on steel [8,12] and 25–35 µm on cast iron [33,34]. At a low concentration of aluminium Al in the reaction powder medium (up to 1.5–2%), the thickness of the hardened layer increased to 35–55 µm.…”

“…To increase the thickness of the hardening coating and extend the service life of sliding pairs, various additives are used: molybdenum Mo and titanium Ti [13,14], niobium Nb [8,15,16] and chromium Cr [17][18][19][20], copper Cu [21], various composite and ceramic materials [22][23][24][25][26]. Laser, gas or thermal spraying [12,27,28] is often used for surface hardening. However, these methods are expensive and require special equipment.…”

“…It is possible only in the initial period of saturation until the vanadium content reaches the stoichiometric composition for carbide formation. The thickness of vanadium coatings is no more than 20 microns [8,12].…”

Production of Niobium Carbide Layers on High‐Strength Bainitic Steels by Thermochemical Treatment of Thermoreactive Diffusion Followed by Austempering

“…The formation of the layers occurs when carbon or nitrogen diffuses from the substrate to the surface of the material and reacts with CFE or NFE, resulting in a dense carbide or nitride layer with a strong metallurgical bond to the substrate. [14][15][16][17][18] The compounds formed within the layer are thermodynamically more stable than those existing in the base material and the thickness of the layer depends directly on the temperature of the bath, immersion time, type of alloy being treated, and the CFE or NFE used. [19,20] The advantages of the TRD process in coating production when compared with other techniques used on an industrial scale, such as physical vapor deposition (PVD) and chemical vapor deposition (CVD), include an atmospheric pressure process and the use of inexpensive equipment.…”