No abstract

Dental diamond bur is now a regular rotary tool, with its head made of diamond particles embedded into nickel coating, and its shank made of stainless steel. There are strong demands from the dentist on prolongation of usage life and avoiding of breakage. To solve this problem, on the one hand, since diamond is hard to be wetted under the condition of normal temperature and pressure due to the high interfacial energy between diamond and general metals and alloys. Diamond particles coated with titanium layer was used for the preparation of composite electroplating with the intention of improving the interfacial adhesion between diamond and metal matrix; on the other hand, superelastic biomedical NiTi alloy was used as the substrate to improve the flexibility and prevent the breakage. In this study, the optimal preparation parameters of Ni/surface-modified diamond electroplating were determined by orthogonal test, and the bonding conditions between the diamond particles and the NiTi alloy substrate were studied by scanning electron microscope. Further performance comparison of Ni/modified and Ni/un-modified diamond composite electroplating was conducted on a pin-on-disc wear machine under the dry sliding condition, and the material removal volume was used as the evaluating criterion of wear resistance. The results showed that the binding strength between diamond particles and NiTi alloy substrate could be enhanced, as well as the wear resistance, which may give direction on the future design of dental bur.

The present work is an effort to provide experimental results focusing on segregation behavior of phosphorus at grain boundary and the intergranular fracture behavio under low tensile stresses. AES (Auger electron spectroscopy) experiments and dynamic analyses on the non-equilibrium grain-boundary segregation (NGS) of phosphorus and the SEM photos of intergranular fracture in Auger specimens in 12Cr1MoV steel were carried out in this paper. The variation of phosphorus segregation level in grain boundary under different low tensile stresses and at different temperature were obtained. Results show that NGS of phosphorus occurred in the experimental steel while subjected to low tensile stresses. Maximum values of phosphorus segregation level were obtained at the critical times. SEM photos of intergranular fracture in Auger specimens of the test steel show that the intergranular fracture rate increased with increasing concentration of phosphorus. The intergranular fracture behavior is accordant with the segregation behavior of phosphorus at grain boundary.

The microbiological influenced corrosion (MIC) behavior of the low alloy steel with granular-Zn-epoxy and flaky-Zn-epoxy coating in the sulfate-reducing bacteria (SRB) solution was investigated with electrochemical impedance spectroscopy (EIS), X-rays diffraction (XRD), scanning electron microscope (SEM) etc. Results show that the protection effect of the flaky-Zn coating specimen is much better than the granular-Zn coating one. The dissolution of zinc is more severe in granular-Zn coating than in flaky-Zn coating when the specimen immersed in the SRB solution. The shielding property of flaky zinc is much higher than granular zinc in the coating. The flaky-Zn coating is much more compact than the granular-Zn coating and therefore the property of anti-infiltration is much better. We may conclude that the flaky-Zn coating exhibited more favorable corrosion resistance property than the granular one.

Well casing damage is a commonly existing problem in oilfield exploitation in the world. Daqing oilfield is a multiple-zone, heterogeneity sandstone oilfield, where the major influence factors which lead to casing damage are geologic factor, engineering factor, high pressure water injection and chemical factors. Among them, the high pressure water injection is the most important one. Water injection exploitation in Daqing oilfield showed that casing-damage increased with the increasing water injection pressure. However, the mechanism is not totally understood and the control method is not well developed yet. In the present work, the mechanism analysis of casing damage induced by high pressure water injection in Daqing oilfield is proposed. It is found that after high pressure water injection, the sandstone layer will expand and result in the vertical elongation of the casing. The additive tensile stress of the casing induced by vertical strains will cause casing-damage. Besides, the horizontal deformation of clay-stone increases with increasing water content of the formation layers and soaking time. The cohesion of clay-stone and inner friction angle decreased with increasing water quantity. In that case, some high obliquity formation layers which may induce high hypsography pressure difference will cause localized slip along weak formation layer interface in the area of waterishlogged clay-stone. Casing damage and well failure caused by the relative movement of the formation layer interface may therefore occur. The micro-fracture of formation induced by high pressure water injection also educed formation rupture and casing damage.