Zong De Liu

Molten Salt Synthesis of CaCu3Ti4O12

CCTO powders were prepared by using molten salt method in the NaCl-KCl system. The effects of temperature and holding time on phase compositions, particle morphology and size have been investigated by X-ray diffraction, scanning electron microscope and laser particle size analyzer. Using CaCO3, CuO and TiO2 as starting materials, CCTO compound could be synthesized at any temperature from 800oC to 1000oC in the NaCl-KCl system. The average particle size increased obviously with the increasing of temperature above 850 oC. Holding time had great effect on grain size and morphology.

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.

Experimental Study on the Fatigue Properties and Reliability for the Steel of Elastic Oil Sump

The elastic oil sump is commonly used as support parts in large-scale thrust bearing. It often operates under fluctuating load conditions during service. So, fatigue analysis of the material of the elastic oil sump is of great significance. In order to obtain the fatigue design data of the material of the elastic oil sump, the systematic tests on uniaxial tension-compression fatigue at room temperature are made. The fatigue limits and the fatigue life curves of the steel of the elastic oil sump are determined at different cyclic stress ratio. The P-S-N equations are calculated by the probabilistic methods. The test results provide a theoretical basis for the safety of life assessment of the elastic oil sump.

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.

Microstructure of In Situ Tic-Mo-Ni And Tic-WC-Mo-Ni Cermets Synthesized by Reactive Hot-Pressing Sintering

TiC-Mo-Ni and TiC-WC-Mo-Ni cermet blocks have been obtained in situ by reactive hot pressing sintering. The phase structure and microstructure of the two cermets were compared to investigate the effect of the addition of WC. The results show that the chemical reactions between Ti, Mo and C in TiC-Mo-Ni system are relatively complete. However, there is a small amount of unreacted C powder in TiC-WC-Mo-Ni system, which is associated with the reaction between Ti and WC. The in-situ carbide grains are very fine with the size range of 0.5-2µm. The boundary morphology between the carbide grains and the binder phase changes from an angular shape to an almost rounded shape with the addition of WC.

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.

Effect of Molybdenum on the Microstructure and Mechanical Properties of TiC/Ni Cermet Cladding Layers

TiC/Ni cermet cladding layer on the surface of 16Mn steel was fabricated with plasma cladding process. Different additions of Mo were 0%, 5%, 10% and 15% in mass percent. The cladding layer was composed of ceramic particles and Ni alloy binder. And the gradient distribution of ceramic particles was observed. And Mo was found in TiC ceramic particles in solid solution. The mechanical properties of the cladding layers with different Mo additions were all better than the cladding layer without Mo. However, the cladding layer with 10% Mo had more defective microstructure and worse mechanical properties.

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.

An Experimental Study on Synthesizing TiC-10Ni Composite Coating Using Electro-Thermal Explosion Ultra-High Speed Spraying

In this work, TiC-10Ni coating was synthesized on copper substrate by electro-thermal explosion directional spraying (EEUSS) method at the discharge voltage of 26kV. Electrical characteristics of the explosion were obtained. The foil was overheated in less 26 microseconds. The total electric energy supplied to the foil was 12.7 times the theoretical amount needed to melt the foil. Phase structure and microstructure of the coating were studied by means of X-ray diffraction (XRD) and scanning electron microscope (SEM). The XRD from the coating surface consists of TiC and the solid solution of Ni, as well as the residual C. The TiC-10Ni coating, which exhibits no pores or cracks, consists of an irregular spheroidal TiC phase embedded in a nearly continuous binder. TiC particles are uniformly distributed and the size of the TiC particle of the coating is less than 1.0 μm because of the solute trapping effect.