Yuchun Zheng

Bio: Yuchun Zheng is an academic researcher from Hefei University of Technology. The author has contributed to research in topics: Tungsten carbide. The author has an hindex of 1, co-authored 1 publications receiving 44 citations.

Preparation of nickel-coated tungsten carbide powders by room temperature ultrasonic-assisted electroless plating

Abstract: In this paper nickel (Ni)-coated tungsten carbide (WC) composite powders have been synthesized by ultrasonic-assisted electroless plating with a simplified pretreatment at room temperature as the conventional sensitization and activation steps have not been employed. The growth mechanism of Ni layers and surface morphologies and composition of initial WC powders, pretreated WC powders and Ni-coated WC powders were analyzed by field emission scanning electron microscopy, and energy dispersion spectrometry. The results shows that uniform Ni-coated WC composite powders were successfully synthesized without conventional sensitization and activation steps by ultrasonic-assisted electroless plating at room temperature. The growth mechanism of Ni layers appears as follows: the surfaces of pretreated WC powders appear step-like defects which act as activated sites. Nucleation and the growth of nickel grains take place on the activated sites of pretreated WC powder, and the process repeats continuously on the lath particles with reticulate structure on the as-coated surfaces of previously deposited Ni-cells, finally Ni cells grow up and merge into a layer.

Microstructural and mechanical characterizations of a novel HVOF-sprayed WC-Co coating deposited from electroless Ni–P coated WC-12Co powders

Abstract: In this research, a novel WC-Co coating was deposited from electroless Ni–P coated WC-12Co powders using high velocity oxygen fuel (HVOF) process. Toward this purpose, an electroless Ni–P plating process was used to develop a uniform Ni–P layer on the surface of WC-12Co powders. The obtained Ni–P coated powders were then used as HVOF feedstock material. Microstructural characteristics of the Ni–P coated WC-12Co powders and the resultant coating, which is denoted as Ni–P modified coating, were investigated using X-ray diffractometry (XRD) and high resolution field emission scanning electron microscopy (HR FE SEM). The micro-hardness, elastic modulus and fracture toughness measurements were executed to evaluate the mechanical properties of the Ni–P modified coating. For comparison, the same experiments were performed on two conventional HVOF sprayed WC-12Co and WC-17Co coatings. The Ni–P modified WC-12Co coating showed a dense structure with extremely low porosity of ∼0.3% which was much lower than that of WC-12Co and WC-17Co coatings. Besides, it was observed that the Ni–P modified coating has undergone negligible decarburization of 2.6% as compared to conventional WC-12Co and WC-17Co coatings with that of 16.3 and 17.6%. The Ni–P modified coating showed the maximum hardness of ∼11.45 GPa, while lower hardness values of 10.98 and 10.59 GPa were measured for the WC-12Co and WC-17Co coatings. The fracture toughness of Ni–P modified WC-12Co coating was found to be 9.86 MPa m 1/2 , indicating 71.2 and 61.1% increase in comparison with WC-12Co and WC-17Co coatings, respectively.

Preparation of nickel-coated graphite by electroless plating under mechanical or ultrasonic agitation

Abstract: In this paper, nickel-coated graphite powders were prepared by electroless plating. After a novel and facile pretreatment of graphite, electroless plating was carried out in an alkaline bath having nickel chloride (NiCl 2 ) as a source of nickel and sodium borohydride (NaBH 4 ) as a reducing agent. During the electroless nickel plating, mechanical or ultrasonic agitation was adopted to improve the properties of coating. The coated graphite powders were characterized by field emission scanning electron microscopy (FE-SEM), energy dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). The results show that two different morphologies of Ni–B coatings were achieved on the surface of graphite. Both coatings on graphite are continuous and uniform. For mechanical agitation process, the coating exhibits a sesame-seed slice-like structure which is composed of large spherical grains. The ultrasonic agitation process results in a faster deposition rate and a well-knit membrane-like structure coating free of voids. This is attributed to the easier nucleation and fine particle distribution of nickel nuclei under the ultrasonic agitation.

Electroless copper plating on PC engineering plastic with a novel palladium-free surface activation process

Abstract: This paper proposes a new available palladium-free surface activation process on polycarbonate (PC) engineering plastic before electroless plating Surface morphologies of the original plastic, activated plastic, surface and cross-sections after electroless plating were analyzed by field emission scanning electron microscopy (FE-SEM), energy dispersion spectrometry (EDS) and X-ray diffraction (XRD) The growth mechanism of copper layers was discussed Results show that numerous folds, uneven steps, and other defects appear on the microscopic surface of activated plastic After direct electroless plating, the plating layer on the plastic surface exhibits a closely bound granular distribution Compared with the conventional pretreatment process, the plating layer possesses a similar morphology The growth mechanisms are analyzed as follows: the reactant (Cu 2 + ) in the electroless plating solution disperses and is adsorbed by the plastic surface in the process of Cu plating The Cu particles that settled form the nucleus and grow The growth process involves repeated gathering of nano-level Cu grains to form physically agglomerated Cu granules The Cu grains finally merge to allow closely bound and evenly distributed copper plating