ABSTRACT
The nickel-based alloy Inconel 600, strengthened by solution treatment, finds extensive application as a heat exchange pipe material in steam generators within nuclear power plants, owing to its exceptional resistance to high-temperature corrosion. However, fretting corrosion occurs at the contact points between the pipe and support frame due to gas-liquid flow, leading to wear damage. This study investigates the fretting wear behavior and damage mechanism of the nickel-based alloy Inconel 600 and 304 stainless steel friction pairs under point contact conditions in a water environment. Characterization was performed using laser confocal scanning microscopy and scanning electron microscopy equipped with energy-dispersive spectroscopy. Results indicate that the friction coefficient remains consistent across different chloride ion concentrations, while the wear volume increases with increasing chloride concentrations. Notably, friction coefficient oscillations are observed in the gross slip regime (GSR). Moreover, the stability of the oxide layer formed in water is compromised, diminishing its protective effect against wear. In the partial slip regime (PSR), friction coefficient oscillations are absent. An oxide layer forms within the wear scar, with significantly fewer cracks compared to those within the oxide layer in the GSR. It is worth noting that in GSR, the friction coefficient oscillates.
ABSTRACT
The effect of displacement amplitude on fretting wear behavior and damage mechanisms of alloy 690 in air and nitrogen atmospheres was investigated in detail. The results showed that in air, the friction coefficient gradually increased with the increase in displacement amplitude which conformed to the universal law. In nitrogen, however, it had the highest point at the displacement amplitude of 60 µm due to very strong adhesion. Whether in air or nitrogen, the wear volume gradually increased with the increase in displacement amplitude. The wear volume in air was larger than that in nitrogen except at 30 µm. At 30 µm, the wear volume in air was slightly smaller. With an increase in displacement amplitude, a transformation of fretting running status between partial slip, mixed stick-slip, and final gross slip occurred along with the change of Ft-D curves from linear, to elliptic, to, finally, parallelogrammical. Correspondingly, the fretting regime changed from a partial slip regime to a mixed regime to a gross slip regime. With the increase in displacement amplitude, the transition from partial slip to gross slip in nitrogen was delayed as compared with in air due to the strong adhesion actuated by low oxygen content in a reducing environment. Whether in air or nitrogen, the competitive relation between fretting-induced fatigue and fretting-induced wear was prominent. The cracking velocity was more rapid than the wear. Fretting-induced fatigue dominated at 30 µm in air but at 30-60 µm in nitrogen. Fretting-induced wear won the competition at 45-90 µm in air but at 75-90 µm in nitrogen.
ABSTRACT
OBJECTIVE: To study the reference ranges of platelet and related parameters within 24 hours after birth in preterm infants with different gestational ages. METHODS: According to the inclusion and exclusion criteria, a retrospective analysis was performed for the chart review data of 1â070 preterm infants with a gestational age of 23-36+6 weeks who were admitted to the neonatal intensive care unit from January to December in 2018. The reference ranges of platelet parameters were calculated for the preterm infants within 24 hours after birth. RESULTS: There were no significant differences in platelet count (PLT) and plateletcrit (PCT) among the preterm infants with different gestational ages (P>0.05). The late preterm infants (34-36+6 weeks; n=667) had significantly lower mean platelet volume (MPV) and platelet distribution width (PDW) than the extremely preterm infants (23-27+6 weeks; n=36) and the early preterm infants (28-33+6 weeks; n=367) (P<0.05). There were no significant differences in these platelet parameters between the preterm infants with different sexes (P>0.05). The reference ranges of platelet parameters in preterm infants were calculated based on gestational age. The reference ranges of PLT and PCT were (92-376)×109/L and 0.1%-0.394% respectively, for the preterm infants with a gestational age of 23-36+6 weeks. The reference ranges of MPV and PDW were 9.208-12.172 fl and 8.390%-16.407% respectively, for the preterm infants with a gestational age of 23-36+6 weeks; the reference ranges of MPV and PDW were 9.19-11.95 fl and 9.046%-15.116% respectively, for the preterm infants with a gestational age of 34-36+6 weeks. CONCLUSIONS: The MPV and PDW of preterm infants with different gestational age are different within 24 hours after birth, and it is more helpful for clinical practice to formulate the reference range of MPV and PDW according to gestational age.
