Search

WCP/steel surface composites were endowed with gradient structure and prepared by powder metallurgy. The mechanical properties, thermal fatigue properties and microstructure of the composites with different W content in the transition layers were analyzed by scanning electron microscopy, metallographic microscope, compression and thermal shock tests, and the influence of W addition on the composites performances was examined. The results show that the composition and structure between the composite layer and the substrate layer are varied by adding tungsten powder in the transition layer, the conflicts in stress, strain, and thermal expansion between the composite layer and the substrate layer are decreased. With the mass fraction of tungsten powder increasing, the W can diffuse both into the substrate layer and the composite layer, which leads to a new phase appearing in the transition layer. The bond between the substrate layer and the composite layer is reinforced. When the W content in the transition layer reaches 30% in mass fraction, the compressive strength reaches 553MPa, and thermal fatigue resistance of WCP/steel surface composite is improved.

Al-22Si-2Fe-xMn alloys were prepared by conventional casting and a segment-based inclined cooling plates. It is shown that inclined cooling preparation technology can improve the morphology and size of primary Si, but has limited effect on the needle-shaped Fe-rich phase. The effect of Mn addition on the crystal structure of Fe-rich phase under the condition of inclined cooling was analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD) and transmission electron microscopy (TEM). The hardness and wear resistance of hypereutectic Al-Si alloys with different Mn/Fe mass ratios were also researched by friction and wear test. Results indicate that long needle-shaped Fe-rich phase of tetragonal structure decreases gradually and disappears basically in alloys as the Mn/Fe mass ratio increases by inclined cooling casting hypereutectic Al-Si alloys. When the Mn/Fe mass ratio is 0.7, Fe-rich phase is mainly hexagonal structure block-shaped or fishbone-shaped α-Al15(Fe, Mn)3Si2 phase. By the time, the wear resistance is enhanced compared with no Mn element addition. The wear mechanism gives priority to abrasive wear manner.

By adding TiO2 powder into the preform, Al2O3 particles reinforced 1065 steel matrix composites were prepared by squeeze casting. The influence of TiO2 on the microstructure and mechanical properties of the composites was investigated. The results indicate that TiO2 and Al2TiO5 were produced at the interface between matrix and Al2O3 particles. Hardness and three point bending strength reach 39.0HRC and 743.94MPa respectively, which was 10.0% and 26.4% higher than those of the composites without TiO2 powder. Fracture morphologies show that there is no crack at the interface and Al2O3 particles are transcrystalline rupture. The interface bonding is improved by TiO2 powder for the Al2O3 particles reinforced composites, and the mechanical properties of the composites increase.