The in situ synthesised TiB 2 /Fe composite coatings were deposited by plasma transferred arc powder surfacing process. The distribution of TiB 2 in the TiB 2 /Fe composite coatings was investigated in this paper. It is found that there is more TiB 2 distributed on the top than at the bottom of the coatings in general. In addition, it is also found that heat input plays an important role in the distribution of TiB 2 in the coatings. A small quantity of TiB 2 whiskers are obtained in the coating with high energy density. While sufficient TiB 2 is produced with appropriate energy density, TiB 2 lumps will be obtained with small total energy input, and the concentration gradient of TiB 2 will appear with a large total energy input. Finally, the metallurgical model of in situ synthesised TiB 2 /Fe composite coatings by plasma transferred arc process is extracted.
ZrB 2 /Fe cladding layer was in situ synthesised by plasma transferred arc powder cladding on mild steel substrate using Zr and B 4 C as the precursor powders. The phase composition and microstructure were investigated by X-ray diffraction analysis, optical microscope, scanning electron microscopy and energy dispersive spectrum. Microhardness of the layer was examined at room temperature. The results show that the phases of the cladding layer are ZrB 2 and iron. ZrB 2 particles have three morphologies: acicular, short rod and block. Reaction process could be divided into four stages according to the state of reactants. ZrB 2 particles gradient distribute in substrate from surface to bottom of the layer. Skeleton-like structure and cluster structure of ZrB 2 are formed in the surface part, and particulate reinforced structure is formed in the middle and bottom part of the layer. The microhardness was greatly improved due to the presence of ZrB 2 particles in comparison with the substrate.
ZrB2/Fe composite coating was in situ synthesised by gas tungsten arc welding cladding process on AISI 1020 steel. Zr, B4C and Fe–B alloy powders were used as precursor powders. The phase composition and microstructure were investigated by X-ray diffraction analysis, optical microscopy, scanning electron microscopy and energy dispersive spectroscopy. Microhardness of ZrB2/Fe composite coating at room temperature was examined. Main phases obtained from Zr and B4C precursor are ZrB2 and α-Fe, and those obtained from Zr and Fe–B precursor are ZrB2 and FeB. In the upper part of these composite coatings, ZrB2 phase mainly grows along temperature gradient direction. The middle part of these composite coatings has the highest ZrB2 content and highest microhardness. Gradient dispersions of ZrB2 reinforcements appeared in the composite coating from the middle to the bottom, leading to gradient dispersions of microhardness. With decreasing dilution rate, ZrB2 content and microhardeness increase.
In order to improve the corrosion resistance of the TiB 2 /Fe composite coatings, high carbon ferrochromium powder was added to the precursor powders. This study evaluates the effect of high carbon ferrochrome added to the composite coating processed by shielded metal arc welding process. The phase composition and microstructure were investigated by X-ray diffraction analysis, scanning electron microscopy (SEM) and energy dispersive spectrum. Vickers hardness was measured from the top surface of the coatings using a Vickers hardness tester. Corrosion property was carried out by a potentiodynamic corrosion test. Thermodynamic analysis was used to make clear of the formation process. It is found that with the amounts of high carbon ferrochromium in the electrodes increasing, the TiB 2 reinforcements in the coatings are replaced progressively by TiC particles and iron boride phase and practically disappear at last. Both the hardness and corrosion resistance of the coatings modified with high carbon ferrochrome have been improved.
In this study, the influence of Y 2 O 3 particles on the weld properties of low carbon steel was investigated by metallographic and mechanical tests. It was found that the microstructure of the fuse zone in the weld beam undergoes a significant change after adding Y 2 O 3 particles. The amount of allotriomorphic ferrite increases, while that of the acicular ferrite decreases. Moreover, the size of the allotriomorphic ferrite decreases with the adding of the Y 2 O 3 particles. On the other hand, the absorbed energy in the Charpy impact test increases, whereas the tensile strength almost keeps unchanged with adding of the Y 2 O 3 particles. Furthermore, the hardness of the weld metal is nearly lowered to the level of that of the base metal due to the adding of the Y 2 O 3 particles.
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