材料期刊网

对由铁素体和渗碳体组成的低、中、高碳钢进行振动空蚀实验, 发现它们空蚀破坏的共同特点是铁素体的严重变形和破损. 但由于铁素体的含量及分布形态不同, 材料空蚀破坏的表现形式大不相同: 铁素体含量高的低碳钢以大面积均匀塑性变形为主; 铁素体含量与珠光体含量大致相等并呈网状分布的中碳(亚共析)钢是由于铁素体隆起脱落而破坏; 以珠光体为主的高碳钢是由于铁素体从渗碳体的夹缝中向外挤出、两相分离而破坏. 微射流冲击形成的应力波使低强度相屈服是造成上述破坏的原因.

Cavitation erosion of materials is mainly caused by the impact of strong pressure pulses and high speed micro--jets, which is formed at the end of bubble collapse. Its mechanisms have been intensively studied based on cavitation tests of heterogeneous materials. Generally speaking, the metallic phase, which is softer and has lower yield limit than the other in a material, is damaged first. However, a metallic phase may perform distinctively in different materials. Satisfactory explanation of this phenomenon is far from being achieved and further studies are necessary. 
        The present work is devoted to the mechanical effect of the impact of the cavitation erosion on duplex steels. Vibration cavitation tests were conducted to mild, medium and high carbon steels which are composed of ferrite and cementite. Mass losses of materials during tests were recorded. Investigations were made on the variation of the microstructure and morphology of specimen surfaces by scanning electronic microscope (SEM) and surface profilometer (SP), as well as the peak strength of binding energy of elements by X--ray photo electron spectroscopy (XPS). It was found that the cavitation damage of all the materials tested is characterized by the serious deformation and fracture of the ferrite phase in them. But the appearance of cavitation surfaces differs from each other because the volume (or mass) fraction and distribution of ferrite are different. Mild carbon steel with dominating integral phase of ferrite deforms uniformly. Medium (hypoeutectoid) steel contains approximately the same fraction of reticulated ferrite as that of pearlite (composed of alternating lamellae of ferrite and cementite). Its deformation mainly occurring in ferrite phase makes the reticulated ferrite bulged up and spalled off the surface gradually. High carbon steel mainly composed of pearlite is damaged because the lamellar ferrite is expelled out and splitting occurrs at the phase boundaries between ferrite and cementite. Analysis with the application of stress wave theory shows that the particular patters of damage of these materials are contributed to the yield of lower strength phase caused by compression stress waves produced by the impact of micro--jets.