Superlubricity behaviors of Nitinol 60 alloy under oil lubrication

The tribological tests were performed using Nitinol 60 alloy pin sliding over GCr15 steel disc in the tribometer system. Four kinds of oils were experimentally investigated as lubrication oils for lubricating Nitinol 60 alloy in the boundary lubrication regime. The experimental results were compared with a reference dry friction. It was found that Nitinol 60 alloy can be lubricated significantly and has shown remarkable lubrication performance. A superlubricity behavior of Nitinol 60 alloy was observed under castor oil lubrication. An ultra-low coefficient of friction of Nitinol 60 alloy about 0.008 between Nitinol 60 alloy and GCr15 steel was obtained under castor oil lubrication condition after a running-in period. Accordingly, the present study is focused on the lubrication behaviors of castor oil as potential lubrication oil for Nitinol 60 alloy. In the presence of castor oil, coefficient of friction is kept at 0.008 at steady state, corresponding to so-called superlubricity regime （when sliding is then approaching pure rolling）. The mechanism of superlubricity is attributed to the triboformed OH-terminated surfaces from friction-induced dissociation of castor oil and the boundary lubrication films formed on the contact surface due to high polarity and long chain of castor oil allowing strong interactions with the lubricated surfaces.

Lubrication properties of Nitinol 60 alloy used as high-speed rolling bearing and numerical simulation of flow pattern of oil-air lubrication

The friction and wear tests were performed using Nitinol 60 alloy pin sliding over GCr15 steel disk in a pin-on-disk tribometer system under PAO oil lubrication conditions. It was found that Nitinol 60 alloy can be lubricated well and has shown remarkable tribological performance. Average coefficient of friction （COF） of Nitinol 60 is 0.6 under dry friction; however, average COF decreases to 0.1 under PAO oil lubrication. SEM image of the worn surface shows that Nitinol 60 exhibits excellent wear resistance and the wear mechanism is mainly adhesive wear. Flow pattern of oil-air flow in oil pipe was simulated by FLUENT software with VOF model for acquiring working performance of oil-air lubrication. The optimum velocity of oil and air at the inlet was achieved, which provides the great proposal for the design of experiment of oil-air lubrication of Nitinol 60 alloy. The simulation results showed that the optimum annular flow of flow pattern was obtained when air velocity is 10 m/s and oil velocity is 0.05 m/s. The formation mechanism of annular flow was also discussed in the present study.

Comparison of nickle release and cytocompatibility between porous and dense NiTi alloy

The porous NiTi(pNiTi)samples were produced by sintering evaporation using Ti−50.8Ni(at.%)gasatomized powders.The samples were analyzed by metallographic microscope and X-ray dispersive spectroscopy(XRD).A comparison of nickel(Ni)release and cytocompatibility between pNiTi and dense NiTi(dNiTi)was made.The results showed that the pNiTi has good mechanical properties.Ni releases from pNiTi in vitro and in vivo are more serious than those form dNiTi.The proliferation and differentiation of cells cultured with the pNiTi extracting liquid are significantly worse,and the rate of early apoptosis is higher.In conclusion,pNiTi is mechanically similar to bone,but pNiTi releases more Ni and interferes with cell proliferation and differentiation.A significantly cautious approach should be adopted when using it as a medical implant.

New Nano-Film Single-Rivet Patent Ductus Arteriosus Occluders:A Prospective,Randomized and Double-blind Study

Nitinol alloy occluders are widely used in the transcatheter intervention treatment of congenital heart diseases like patent ductus arteriosus（PDA）.However,nitinol alloy contains high levels of nickel,which can lead to toxic effects in the immune and hematopoietic systems if released in sufficient quantities.A new type of single-rivet occluder coated with nano-film has been developed to limit the release of nickel.In total,23 patients were recruited and randomly assigned to the experimental group（n=12） with the new nano-film single-rivet occluders or the control group（n=11） with the traditional occluders.One case in the control group was lost to follow-up.The remaining 22 cases were followed up at 24 h,7 days,1 month,3 months,and 6 months after the procedure.There were no statistically significant differences in routine blood test,alanine aminotransferase,creatinine,and troponin between the experimental and control groups.Serum nickel concentration in both two groups increased at 24 h after the procedure,peaked at 1 month,and returned to preoperative levels at 6 months.Serum nickel levels in the experimental group were significantly lower than in the control group at 24 h,7 days,1 month,and 3 months after the procedure.These data suggested that the nano-film coating effectively prevented nickel release from the new occluders,and therefore has a preferable safety profile.