Influence of Er_2O_3 content on microstructure and mechanical properties of ZTA-TiO_2 composites

The influence of Er_2 O_3 addition on the phase evolution and mechanical properties of sintered(1600 ℃,4 h) ZTA(yttria stabilized zirconia toughened alumina)-TiO_2 composites was investigated. The SEM and XRD results reveal the formation of a new erbium zirconium oxide,Zr_3 Er_4 O_(12),with a granulate morphology when Er_2 O_3 content is higher than 1 wt%. The grain sizes of both Al_2 O_3 and yttria-stabilized zirconia phases decrease with an increase in the Er_2 O_3 content. The relative density, Vickers hardness and fracture toughness of the composites are found to be strongly dependent on their grain sizes, relative densities and the formation of the Zr_3 Er_4 O_(12) secondary phases. The composite with 5 wt% Er_2 O_3 shows the highest relative density(99.93%), Vickers hardness(1752 HV) and fracture toughness(7.92 MPa·m^(1/2)).

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.