Yong Tian Wang

A Hard and Thick Fe-Based Amorphous Composite Coating

A thick Fe-based amorphous and nanocrystalline composite coating was prepared by in-situ tungsten inert gas (TIG) cladding method. The results show that the cladding coating mainly consists of amorphous phase and nanocrystalline grains. The microstructure study shows that the Fe-based composite coatings have unique microstructure including nano-sized grains surrounded by nano-scale amorphous shell layer (encapsulated structure) and the homogeneously distributed dendrites/cellular crystals. The unique microstructure gives rise to the superior micro-hardness and wear resistance of the coating. The Fe-based coatings have great potential as promising wear-resistance structural materials used in electric power and cement industry.

Microstructure and Properties of Fe-Based Amorphous Composite Coating Prepared by Pulse Laser

The Fe-based amorphous composite coatings were prepared by pulse laser cladding method. The amorphous powder with the size ranging from 100 to 200 meshes was cladded on the low carbon steel plate,and the nominal composition of the powder was (wt.%) Cr:14.95, Mo:25.7, B:1.24, C:3.45, Y:3.40, Fe:51.29. The microstructure, phase composition and hardness were characterized by XRD, SEM, DSC and semi-automatic Vickers hardness tester in this study, respectively. The results show that the coating which is composed of amorphous and nanocrystal phases has the dense structure and metallurgical bonding with the substrate. The hardness of coatings was about 5 times higher than that of the substrate. With the increase of cladding layer, the average hardness of coating showed an increasing trend, and the intrinsic mechanism was discussed.

Hardness Regulation of Fe-Based Amorphous Composite Coatings by Laser Remelting

A Fe-based amorphous composite coating was deposited on a carbon steel substrate by arc spraying, and remelted with different laser energies by the Nd: YAG laser cladding system, in order to improve the mechanical properties of the coatings. The microstructure and microhardness of the composite coatings were investigated. The variation of harndness was measured as a function of the modified layer depth, which indicates that the laser remelting improves the bonding strength and hardness. Increasing the laser power, the quality of coating gets better, but the amorphous volume fraction decreases. It is obtained that the optimal laser electric current for the coating of 280 μm thickness is about 300 A, in which the remelted coating with medium energy densities has the highest average Vickers hardness of 741. Through the volume fraction change of the nanocrytals, the hardness of the composite coating is regulated by the laser power input, which amplified the application fields of the amorphous coatings.

A Fe-Based Amorphous Composite Coating on Al Plate by Electrothermal Explosion Spraying

A Fe-based amorphous composite coating with different thickness on the Al thin plate is prepared by the electrothermal explosion spraying. Compared with other thermal spraying techniques, the electrothermal explosion spraying method can obtain a very high spraying velocity up to 4000m/s. The coating consists of the amorphous matrix and nanocrystal phases (α-Fe)，no laminar phenomenon is observed. The diffusion occurs between the substrate and the coating, showing a diffusion-metallurgical bond. The average hardness of coatings is 8 times larger than that of the Al substrate. The unique hierarchical microstructure at multiple length scales leads to the superior micro-hardness and wear resistance of the coating. The Fe-based composite coatings on Al thin plate have great potential as the promising lightweight wear-resistance structural materials used in the aero technical industry.

An Experimental Study on the Properties of Fe-Based Amorphous Composite Coatings Prepared by Different Processes

Fe-based amorphous composite coatings were deposited on the surface of ASTM-1020 steel plate by different technologies: arc spraying, laser remelting, TIG remelting (with and without water cooling). The microstructure, phase structure and micro-hardness were characterized by using a combination of SEM, XRD and Vickers hardness tester. It shows that the coating prepared by arc spraying presents typical lamellar structure and poor adherence to the substrate. After the remelting treatment, the coating quality is significantly improved by decreasing structure defects such as cracks and pores; the interface shows the metallurgical bonding. The dendritic crystals could be obtained within all the remelted coatings with different appearances. The microstructures of TIG remelted coatings show much more regular and have obvious orientation, which cannot be seen in laser remelted coating. However, the average grain size of the laser remelted coating is much smaller than that of TIG remelted coatings. The micro-hardness values of all of the deposited coatings are much higher than that of the substrate, and the coating prepared by laser remelting shows the highest hardness.

Wear Resistance of a Large Thick Fe Based Amorphous Composite Coating Deposited by Laser Cladding

A large thick Fe based amorphous composite coating was deposited on the carbon steel substrate by laser cladding method. The phase composition and microstructure are characterized using X-ray diffraction and scanning electron microscope, respectively. The results demonstrate that the large thick laser cladding coating has a typical layered structure mainly consisting of amorphous and nanocrystal phases. The wear resistance and microhardness property are tested by the Vickers hardness tester and MLS-225 type wet sand rubber wheel abrasion tester. The results show that the large thick laser cladding coating has excellent wear resistance and hardness.

A Thick Al-Based Composite Coating Cladded by the Amorphous Powder

A 1mm thick Al-based composite coating was fabricated on the TC4 Ti-based substrate by using the amorphous powder and the pulse laser cladding technology. The microstructure, phase composition, hardness and friction of the coating were characterized by SEM, DSC, XRD and frictional wear tester, respectively. The results showed that the coating was composed of the micron-sized crystal phases and small amounts of amorphous matrix; the coating has the dense structure and metallurgically bonds with the substrate. The microhardness of the coating was up to 500-600 HV0.2, which was about two times of that of the TC4 Ti-based substrate. The friction coefficient of the coating was lower than that of the TC4 alloy, which improved the friction and wear properties of the TC4 substrate obviously.

Effect of Mo Content on the Corrosion Resistance of Fe-Based Amorphous Composite Coating

A Fe-based amorphous composite coating doped by molybdenum was fabricated by the pulse laser cladding technology. The substrate was a low carbon steel plate. The nominal composition of the powder in the range from 100 to 200 meshes was (wt.%) Cr:14.95, Mo:25.7, B:1.24, C:3.45, Y:3.40, Fe:51.29, which was selected for the laser cladding process. The microstructure, phase composition, hardness and corrosion resistance of the coatings were characterized by means of SEM, EDS, XRD , DSC and potentiodynamic polarization test. The results show that the coating which was composed of amorphous and nanocrystal phases had the dense structure and metallurgical bonding with the substrate, meanwhile with low porosity and cracks. The addition of molybdenum played an important role in improving the corrosion resistance of the coatings. With the increasing content of molybdenum, the hardness had no significant change, while the corrosion resistance of the coatings significantly increased. From the results of polarization curves, the corrosion current density of the coating added 0 wt.% Mo is higher than that of the coatings added 2 wt.% Mo and 10 wt.% Mo. The molybdenum has a superior effect on the corrosion resistance in Fe-based amorphous composite coating.

Influence of Laser Remelting on the Corrosion Resistance of Fe-Based Amorphous Composite Coatings

The microstructure and corrosion resistance of Fe-based amorphous coatings prepared by laser remelting after arc spraying were studied. The laser remelting process was carried out under different energy inputs, and the processing parameters varied with the different currents, pulse widths and scanning speeds. The corrosion behavior of the coatings in 1 mol/L NaCl solution was studied through potentiodynamic and potentiostatic polarization test. The morphology and microstructure of the coatings were characterized by using X-ray diffraction (XRD), scanning electron microscopy (SEM), and electrochemical analyzer. A Vickers hardness tester was also used to measure the microhardness of the coatings. The analysis of the microstructure shows that the amorphous coatings are composed of amorphous matrix and nanocrystalline phases. The diffusion of elements indicates a metallurgical bonding between the coating and substrate. The electrochemical corrosion results obtained from the Tafel polarization curves verify that the amorphous composite coatings prepared by different methods show no significant differences in their corrosion resistance, while the microhardness of laser remelting coatings increase obviously with the increase of laser currents. The corrosion resistance of laser remelting coatings is improved extensively due to the amorphous matrix and embedded nanocrystals, which popularizes the applications of amorphous coatings to a large extent.

Laser Remelting Effect on the Joint Property of Diffusion Bonding of TiAl Intermetallics and TC4 Alloy

The influence of laser remelting on the mechanical property and fracture behavior of the superplastic diffusion bonding between TiAl intermetallics and TC4 alloy was investigated. The joint bonded by the pre-remelted samples displayed well diffusion, but the mechanical properties of the joint should be further enhanced. The mechanical properties of the joint pre-remelted under the diffusion bonding conditions of 915/80MPa/1h are lower than that of the joint without remelting. After the heat treatment on pre-remelted joint sample at 860, the mechanical properties have been enhanced greatly.