Electroless copper-phosphorus coatings with the addition of silicon carbide (SiC) particles

Cu-P-silicon carbide （SiC） composite coatings were deposited by means of electroless plating.The effects of pH values,temperature,and different concentrations of sodium hypophosphite （NaH2PO2·H2O）,nickel sulfate （NiSO4·6H2O）,sodium citrate （C6H5Na3O7·2H2O） and SiC on the deposition rate and coating compositions were evaluated,and the bath formulation for Cu-P-SiC composite coatings was optimised.The coating compositions were determined using energy-dispersive X-ray analysis （EDX）.The corresponding optimal operating parameters for depositing Cu-P-SiC are as follows：pH 9;temperature,90oC;NaH2PO2·H2O concentration,125 g/L;NiSO4·6H2O concentration,3.125 g/L;SiC concentration,5 g/L;and C6H5Na3O7·2H2O concentration,50 g/L.The surface morphology of the coatings analysed by scanning electron microscopy （SEM） shows that Cu particles are uniformly distributed.The hardness and wear resistance of Cu-P composite coatings are improved with the addition of SiC particles and increase with the increase of SiC content.

Effect of Ostwald ripening of carbide particles on mechanical properties of SCM435 steel during subcritical annealing

The Ostwald ripening of carbide particles occurs during the process of subcritical annealing in SCM435 steel, and the degree of ripening influences the microstructure and mechanical properties of the steel. The effects of Ostwald ripening were studied by simulating different soaking time at 680 ~C using SCM435 steel. The spheroidized specimens were analysed by conducting microstructure and mechanical tests. After increasing the soaking time from 2 to 6 h at 680 ~C during subcritical annealing, the number of carbide particles and the spheroidization ratio increased gradually, and the formability was improved. When the soaking time ranged from 6 to 8 h, the spheroidization ratio was similar; however, the number of carbide particles decreased, and the formability gradually worsened. Therefore, by comprehensively comparing the microstructures and mechanical properties, the optimum soaking time was determined to be 6 h at 680 ~C during subcritical annealing to obtain preferable cold heading. In addition, the carbide particles gradually coarsened when the soaking time was extended from 2 to 8 h. A formula was presented to quantitatively characterize the progress of Ostwald ripening of the carbide particles during the subcritical annealing of SCM435 steel, and the relative error was less than 8.02%.

Study on in-situ WC particles/tungsten wire reinforced iron matrix composites under electromagnetic field

By applying electromagnetic field to a system consisting of tungsten wires and grey cast iron melt,the grey cast iron matrix composite reinforced by either in-situ WC particles or the combination ofin-situ WC particles and the residual tungsten wire was obtained.By means of differential thermal analysis(DTA),the pouring temperature ofiron melt was determined at 1,573 K.The microstructures of the composites were analyzed by using of X-ray diffraction(XRD),scanning electron microscopy(SEM) equipped with an energy dispersive spectrum(EDS) and pin-on-disc abrasive wear test.The obtained results indicated that,with the enhancing frequency of electromagnetic field,the amount ofin-situ WC particles gradually increases,leading to continuous decrease of the residual tungsten wires.When the electromagnetic field frequency was up to 4 kHz,tungsten wires reacted completely with carbon atoms in grey cast iron melt,forming WC particals.The electromagnetic field appeared to accelerate the elemental diffusion in the melt,to help relatively quick formation of a series of small FeW-C ternary zones and to improve the kinetic condition ofin-situ WC fabrication.As compared with the composite prepared without the electromagnetic field,the composite fabricated at 4 kHz presented good wear resistance.

INVESTIGATION OF MULTIPHASE-REINFORCED Si_3N_4 COMPOSITE MATERIAL

By means of whisker reinforce and paricle dispersion, the routes of property improvement on Si3N4 ceramic material have been studied. The medhaniacl properties of Siw/Si3N4 and Siw/Si3N4TiC material was compared, which proved that multiphase reinforce had overlap effect. Microstructure of the rnaterial was investigated by means of SEM and the mechanisms of SiC. and TiCP reinforces had been disussed.

Effect of Ni Addition on Microstructure of Matrix in Casting Tungsten Carbide Particle Reinforced Composite

Microstructure of the matrix directly influences the performance and the application of metal matrix composites. By using vacuum casting-infiltration method to manufacture casting tungsten carbide particle reinforced composite, the addition of Ni can alter the microstructure of the matrix of composite. High carbon chromium steel was chosen as the substrate. The casting process was achieved at 1580 ℃ with vacuum degree of 0.072-0.078 MPa. Padding of the molten steel in each part of the preform was different, and the solidification of each part of the composite was different, too. Microstructure of the matrix was various in different parts of the composite. The Ni addition had enlarged the austenite zone in matrix, which would improve the corrosion resistance of the composite. The phase identification of the composite was performed by X-ray diffraction technique. The result showed that Fe3W3C was the primary precipitated carbide and its composition had a direct link with the decomposition of the casting tungsten carbide particles. The hardness of the matrix mainly depended on the reinforced carbide, i.e. Fe3W3C.