Microstructure and corrosion resistance of Ti-Ni/steel composite materials

Ti-Ni composite sub-micron powders with different compositions were prepared by vacuum melting and atomization technology.These powders,after being mixed with a solution of phenolic resin and alcohol,were applied on the mold cavity wall,by which a casting-infiltration layer was introduced on the surface of ZG45 steel via reactions between the powders and molten steel under the heat released by solidification.The effects of the powders’composition and pouring temperature on the corrosion resistance of the casting-infiltration layer were studied.An optimal casting-infiltration layer with a thickness of~7 mm was obtained by infiltrating the Ti-Ni composite powders containing 35wt.%Ti to ZG45 steel pouring at 1,650℃.The casting-infiltration layer has a good metallurgic bonding with the matrix,and is mainly composed of Fe_(2)Ti phase and continuousγ-(Fe,Ni)solid solution.In the corrosive H_(2)SO_(4) solution,the corrosion potential of the casting-infiltration layer is lower than the matrix,tending to form a passivation film,which lowers the dissolution rate especially when the potential rises to 0.50 V.After dipping in the 10wt.%NaCl solution for 480 h,a lot of corrosion holes appear in the ZG45 steel matrix,while there are no obvious traces of corrosion on the casting-infiltration layer.

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.