Microstructure, microhardness and wear resistance of VCp/Fe surface composites fabricated in situ
Graphical abstract
Introduction
Iron-based composite materials reinforced with hard ceramic particles have been actively investigated because of their high strength, high elastic modulus, and improved resistance to wear, creep and fatigue; hence, these properties make them promising structural materials for industrial applications [1]. However, the service life of the composite materials generally relies on their surface properties. So, it is desirable that only the surface layer of the composite material is reinforced by carbide phases, providing high strength and high modulus, while the bulk of the composite material retains its original composition and structure, giving high toughness and high ductility [2].
In recent years, several surface modification techniques, such as laser cladding [3], [4], high-energy electron beam irradiation [5], [6], plasma jet cladding [7], [8], plasma transferred arc (PTA) [9], [10] and in situ synthesis, have been applied to fabricate surface coating materials. Among them, in situ synthesis technique has been considered to be one of the most promising methods for the production of metal matrix composites because of the fine size and thermodynamic stability of the ceramic particulates synthesized in the matrix as well as a strong interfacial bonding between the matrix and the reinforcement phase, providing higher mechanical properties. The most common carbide ceramic materials employed as reinforcement phases for various iron and steel matrices are TiC, WC, VC, etc. In particular, vanadium carbide (VC) is a refractory compound possessing many favorable properties, such as high hardness, certain plasticity and good wettability to metal bonding. This advantageous combination can create a protective coating layer on the surface of the composite material with enhanced resistance against thermal, corrosion and mechanical wear [11]. Up to now, various methods have been successfully applied in producing the VC/Fe surface composites by in situ technique [12], [13]. However, it should be pointed out that a critical control of processing parameters is necessary for the existing processing techniques in order to obtain the ideal microstructure in surface coating layer. Furthermore, the thickness of the surface coating layer produced by those processing techniques is limited to micrometer scale, which cannot significantly prolong the service life of the parts used.
Therefore, the aim of the present work was to fabricate VCp/Fe surface composites by a technique combining infiltration casting with subsequent heat treatment. The demonstrated method is low cost, and the size of surface composites can be easily controlled. In this study, the effects of different heat treatment times at 1164 °C on the phase evolution, microstructure, microhardness and wear resistance of the VCp/Fe surface composites are systematically investigated.
Section snippets
Preparation
For the in situ fabrication of the VCp/Fe surface composites, gray cast iron and vanadium plate (99.99%) were used as carbon and vanadium sources, respectively. The chemical composition (wt.%) of gray cast iron is Fe–2.57C–1.04Mn–1.03Si–0.046P–0.018S. The experimental procedure for processing of the surface composites is described as follows: firstly, a vanadium plate was cut into the size of 10 mm × 10 mm × 1 mm by a numerically-controlled wire-cut EDM machine (Suzhou Nutac Electro Mechanic Co. Ltd.,
Results and discussion
Fig. 2 shows the DSC curve of the specimen, indicating three endothermic peaks at 788 °C, 808 °C, and 1164 °C and an exothermic peak at 1347 °C. The first endothermic peak at 788 °C is attributed to an allotropic change α-Fe → γ-Fe [14], [15], and the second endothermic peak at 808 °C is assigned to β-V2C → α-V2C + β-V2C [15]. The third endothermic peak at 1164 °C is due to the ternary eutectic transformation L → γ-Fe + graphite (G) + V8C7 [15]. The exothermic peak at 1347 °C is related to the formation of
Conclusions
The VCp/Fe surface composites were in situ fabricated by a method combining infiltration casting and a subsequent heat treatment. The effects of different heat treatment times (1, 2 and 3 h) at 1164 °C on the phase evolution, microstructural features, and properties of the composites were investigated. The XRD results showed that the surface composites are mainly consisted of graphite, α-Fe and vanadium carbide phases after heat treatment at 1164 °C for 3 h. The SEM observation revealed that the
Acknowledgement
This work was supported by the National High Technology Research and Development Program of China (863 program, no.2013AA031803).
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