Preparation and Performance of Salt Tolerance and Thermal Stability Cellulose Nanofibril Hydrogels and Their Application in Drilling Engineering

The poor salt tolerance,thermal stability,and environmental performance of petrochemicals can severely limit their applications in drilling engineering.In this study,cellulose nanofibril(CNF)hydrogels with improved salt tolerance and thermal stability were prepared,and their filtration performance was evaluated.The hydrogels were prepared through the simultaneous grafting of 2-acrylamido-2-methylpropane sulfonic acid(AMPS)and butyl acrylate(BA)onto the CNF surface through ceric ammoniumnitrate-induced radical polymerization.The modified and original CNF samples were characterized using Fourier Transform infrared spectroscopy(FT-IR)and rheological measurements.The FT-IR analysis results showed that both AMPS and BA were grafted onto the CNF backbone,affirming the successful preparation of the grafted CNFs.The rheological analysis results showed that the modified CNF hydrogels exhibited significantly improved salt tolerance,thermal stability,and“salt-thickening”effect.Moreover,the results of the fluid loss test showed that the modified CNF hydrogels exhibited a much better fluid loss control than the original CNF hydrogels.In addition,after adding 2%modified CNF hydrogels as a filtrate reducer in the drilling fluids prepared with a 6%combined salt solution,the filtrate loss was significantly reduced even after aging for 72 h at 160℃.

Characteristics of Faigue Crack Initiation in Ti-5Al-4Sn-2Zr-1Mo-0.7Nd-0.25Si Alloy

The characteristics of fatigue crack initiation in Ti-5AI-4Sn-2Zr1Mo-O.7Nd-O.25Si alloy wereStudied. Two modes Of fatigue crack initiation were found. The Nd-rich phase particles displaybetter resistance to fatigue crack initiation than the matrix at lower stress.

Microstructural Evolution and Cracking of Pb-free Ball Grid Array Assemblies under Thermal Cycling

Two kinds of CBGA （ceramic ball grid array） assemblies were made by reflow soldering process using two different Pb-free solders. Microstructural evolution and cracks induced by thermal cycling in CBGA assemblies were examined by scanning electron microscopy （SEM） and finite element method （FEM）. Before thermal cycling, intermetallic compounds （IMCs） Cu6Sn5 and Ag3Sn were observed at the solder interface between Cu and Ag metallizations, respectively. After thermal cycling, another IMC Cu3Sn was observed near the Cu pad in both two assemblies and the layers of Cu6Sn5 and Ag3Sn became thicker. As a result of thermal cycling, cyclic stress and strain were accumulated in the solder joint leading to fatigue cracking. Both experiments and FEM revealed that cracks preferred to initiate at the corner of each solder joint. Multi-modes of the crack propagation were found in the two assemblies. Based on Coffin-Manson equation, the thermal fatigue life was calculated and the predicted life showed good agreement with the experimental results.

Influence of Ageing Heat Treatment on the High Cycle Fatigue of an 8090 Al-Li Alloy

Fatigue lives for the smooth and notched specimens of 8090 Al-Li alloy jn the different ageing conditions have been studied. For the smooth samples of 8090 alloy the artificial ageing results in an increase in fatigue life in comparison with natural ageing. On the contrary, the notched specimens of 8090 alloy in the naturally aged condition show higher fatigue life than in the peak-aged. The exposure to either the peak-aged or naturally aged leads to superior fatigue properties of Al-Li alloy to the traditional high strength aluminum alloys of 7075 and 2024, especially in the latter aged condition. In all ageing conditions, i,e. naturally, under-, peak- and over-aged, the peak-aged 8090 alloy displays the highest fatigue life and the over-aged material has a minimum value at the same stress amplitude. The difference in fatigue life is mainly attributable to the size and distribution of strengthening precipitates as well as the wide of precipitate free zones (PFZ's) along grain boundaries.

Friction Stir Welding of Zr_(55)Al_(10)Ni_5Cu_(30) Bulk Metallic Glass to Crystalline Aluminum

The Zr55Al10Ni5Cu30 bulk metallic glass plate were successfully welded to crystalline aluminum plates by using a friction stir welding （FSW） method. The welded zone was examined. No defects, cracks or pores were observed and no other crystalline phases except for aluminum were found in the welded joint. The strength of the joint is higher than that of aluminum. The glassy phase in the stir zone keeps the amorphous state, showing a successful welding. The storage modulus softens over the glass transition. And the weldability was discussed according to this phenomena.

Nucleation of dislocations and twins in fcc nanocrystals: Dynamics of structural transformations

This paper reports on a molecular dynamics study of structural rearrangements in a copper nanocrystal during nucleation of plastic deformation under uniaxial tension. The study shows that the resulting nucleation of partial dislocations on the free surface and their glide occurs through local fcc→bcc→hcp transformations via consistent atomic displacements. We propose an atomic model for the generation of dislocations and twins based on local reversible fcc→bcc→fcc transformations, with the reverse one proceeding through an alternative system. The model gives an insight into possible causes and mechanisms of the generation of partial dislocations and mechanical twins in two and more adjacent planes of plastically deformed nanocrystals. The obtained data allow a better understanding of how plasticity is generated in nanostructured materials.

Failure Behavior of Thermal Barrier Coatings on Cylindrical Superalloy Tube Under Thermomechanical Fatigue

Failure behavior of thermal barrier coatings on cylindrical superalloy tube was investigated under thermome- chanical fatigue （TMF）. Two types of TMF tests, i.e. in phase （IP） and out of phase （OP）, were performed in the temperature range of 450-850℃. All tests were carried out under mechanical strain control at a given period of 300 s. The bond coat NiCrAIY was produced by high velocity oxygen fuel （HVOF）, and the top coat 7%Y203-ZrO2 was deposited by air plasma spraying （APS）. The testing results showed that the OP TMF life was longer than the IP TMF one under the same mechanical strain amplitude. Observations of the fractured specimens revealed that the interface damage and cracking behavior in the two phasing conditions were different. In OP loading, the top coat was cracked and detached from the bond coat while no spallation was found in the IP loading.