Papers by Author: Jing Hua Jiang

Abstract: Zinc protective coatings on high carbon SWRH82B-1 steel were sherardized to markedly improve corrosion resistance of the high-strength steel bridge cable wires (SBCW). Sherardizing parameters have been optimized by optical microscopy (OM) /scanning electron microscopy (SEM), X-ray diffraction (XRD) and potentiodynamic polarization tests. The sherardizing coatings are composed of the loose outer layer (§-FeZn13 phase) and the dense inner layer (δ- FeZn7 phase) with higher hardness. Addition of Y2O3 activator slightly increases the corrosion resistance of sherardized steel wire in comparison with CeO2. A thicker coating corresponds to a higher sherardizing temperature or a longer heating duration, but an extra thick coating is unfavorable for thru-microcrack existed in the inner layer. Good quality of sherardized wires ( higher corrosion resistance and longer duration than conditional hot-dip-galvanized one) can be produced with the zinc-rich powder containing 7.5wt.% CeO2 activator and 25wt. % SiO2 filler under 400°Cfor 6h.

Abstract: Co-Ni coated ZrO2 composite powder was prepared by an optimized ultrasonic electroless plating process to obtain good microwave absorption properties in GHz region. Aggradation mechanism of electroless Co-Ni alloy was analyzed and the principal influencing factors on the depositing rate were investigated by weighting-in-powder. The metallized powder was characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDS) and vector network analyzer. Results showed that ultrafine ZrO2 powder pretreated with sensitization and activation were homogeneously deposited with Co-Ni coating at 358K and pH value of 9, immerged in the optimal plating bath using NaH2PO2 as reductant. The Co-Ni coating deposited in the alkaline plating bath had the depositing rate of above 6µm/h and the average weight ratio of 5.5 for Co/Ni. The new metallized powder was endowed high microwave absorbing properties; the maximum reflection loss reaches to -23dB at the frequency of 9.40 GHz.

Abstract: Squeeze-cast 20vol%SiCw/2024 composite was processed by rotary-die equal-channel angular pressing (RD-ECAP) and tensile-tested at elevated temperatures. RD-ECAP does not require billet removal and reinsertion between ECAP passes and can produce large cumulative deformation of type A in the billet at a controlled extrusion temperature. Tensile specimens were machined from the RD-ECAP processed billets along the longitudinal direction. 16 RD-ECAP passes at 623 K produced an average matrix grain size of about 0.8 μm in the composite. The ECAP processed 20vol%SiCw/2024 composite exhibited 330% elongation to failure when tested at 783 K and the high strain rate of 1.17×10-1 s-1. The values of strain rate sensitivity exponent of the SiCw/2024 composite determined over the strain rates between 10-2 and 1.0 s-1, was 0.39, 0.47 and 0.53 at 763, 773 and 783 K, respectively. The grain sizes of the aluminum alloy matrix in the composite after superplastic deformation increased from 0.8 μm to be about 1.5 μm. There was no cavity found within the uniformly deformed area. The apparent activation energy for the superplastic deformation of the 20vol%SiCw/2024 composite was determined to be 284 kJ·mol-1.

Abstract: An electrolytic sulfurization at room temperature has been introduced in the present work, which process parameters are optimized to the quenched Cr12 substrate. Morphology and microstructure of the sulfide layers are investigated deeply, and their formation mechanism is discussed in detailed. According to optimum parameter of sulfurizing process ( assistant current density of 1.8A/dm2, the saturated rare-earth-halide solution containing 300g Na2S2O3, 60g KHSO3 and 1000ml H2O, 298K/20~40min), the ferrous sulfide coating was easily obtained on the quenched Cr12 substrate with a uniform thickness of above 10μm, no matter about the treated parts with the complex geometrical shapes. The tribological experiment results of a block-on-ring tribometer indicate that the sulfide coatings on hard substrate have a very low friction coefficient and could obviously reduce the wear extent of its counterpart. Compared with the traditional low-temperature process, this sulfurizing technology has such virtues as simple process, heatless, low cost, little deformation, without pollution question, etc., which could be employed for industrial solid lubricant due to the good friction-reducing characteristic of lamellar-structure FeS phase.

Abstract: With the aim to obtain the high cavitation-erosion-resistance coating for the surface safeguard of fluid machinery, two kinds of hard coatings (WC-Cr-Co and Cr3C2-NiCr) were prepared on 1Cr18Ni9Ti substrate by high velocity oxy-fuel spraying (HVOF), which microstructure and performance were investigated respectively by optical microscope, X-ray diffraction, Vickers hardness, scanning electron microscope (SEM), and vibratory cavitation apparatus. The results indicated that these two coatings had the higher hardness and the finer structure than ZG06Cr13Ni5Mo, which is used actual in water conservancy. The results of cavitation erosion continued for 39 hours presented that the mass loss of WC-Cr-Co and Cr3C2 -NiCr coatings increased ceaselessly with time, and the cavitation erosion speeds varied with time. Compared with ZG06Cr13Ni5Mo, their cavitation erosion resistance performances were better due to their higher hardness and finer structure, and WC-Cr-Co coating was much better than Cr3C2-NiCr coating. Obviously, the higher hardness and finer structure could strengthen the cavitation erosion resistance of coating materials.