Microstructure features and mechanical/electrochemical behavior of directionally solidified Al−6wt.%Cu−5wt.%Ni alloy

The effects of the addition of 5.0 wt.%Ni to an Al−6wt.%Cu alloy on the solidification cooling rate(T),growth rate(V_(L)),length scale of the representative phase of the microstructure,morphology/distribution of intermetallic compounds(IMCs)and on the resulting properties were investigated.Corrosion and tensile properties were determined on samples solidified under a wide range of T along the length of a directionally solidified Al−6wt.%Cu−5.0wt.%Ni alloy casting.Experimental growth laws were derived relating the evolution of primary(λ_(1))and secondary(λ_(2))dendritic spacings with T and V_(L).The elongation to fracture(δ)and the ultimate tensile strength(σ_(U))were correlated with the inverse of the square root of λ_(1) along the length of the casting by Hall−Petch type experimental equations.The reinforcing effect provided by the addition of Ni in the alloy composition is shown to surpass that provided by the refinement of the dendritic microstructure.The highest corrosion resistance is associated with a microstructure formed by thin IMCs evenly distributed in the interdendritic regions,typical of samples that are solidified under higher T.

Effect of Zn, Cu and Ni addition on microstructure and mechanical properties of ascast Mg-Dy alloys

This paper presents some research information on the effects of Zn, Cu and Ni on the microstructure and mechanical properties of as-cast Mg-2Dy(at.%) alloys. The Mg-2Dy alloy is composed of α-Mg and Mg24Dy5 phases. With the addition of 0.5at.%Zn, 0.5at.%Cu and 0.5at.%Ni, respectively, besides α-Mg, the long period stacking order(LPSO) phases containing Zn, Cu, and Ni precipitated in the α-Mg interdentritic boundary. The addition of Ni effectively refined the dendrite arm spacing. The as-cast Mg-2Dy-0.5Ni alloy exhibited the best tensile strengths and elongation. The better mechanical properties were mainly attributed to small secondry dendrite arm spacing(SDAS) and high volume fraction of LPSO phases.

Effects of Ni addition on liquid phase separation and giant magnetoresistance of Cu-Co alloys

The effects of Ni addition on the liquid phase separation and giant magnetoresi stance (GMR) of Cu Co alloys were discussed. The results reveal that Ni additio n can partially restrain the liquid phase separation of Cu Co alloys, resultin g in a decrease of volume fraction for the Co rich particles separated from the liquid phase and in refined microstructures. The composition analyses indicate t hat Ni is dissolved in both the Co rich and the Cu rich phases, but Ni content in the Co rich phase is much higher than that in the Cu matrix. At the same ti me, Ni addition enhance the solubility between Cu and Co, especially Cu in Co s olid solution. Ni alloying into Cu Co alloys can fully prevent the liquid phase separation during melt spinning, which is very beneficial to improve GMR of Cu Co alloys.

Corrosion Resistance of Deformed Cu-Ni Alloy in Seawater

After solutionized, 70Cu 30Ni alloy was deformed in different degrees and then exposed both in NaCl solution and in seawater. The results show that with the increase of deformation, the E c and R p -1 of 70Cu 30Ni alloy decrease more quickly and fluctuate less when the exposure time increases, and the corrosion product films contain more nickel and less chloride because the distribution of dislocations tends to be homogeneous.

Influence of microstructure and surface condition on antifouling property of 90Cu-10Ni alloy in seawater

Through the experiment of natural seawater exposure corrosion, the antifouling properties of the plate specimens of 90Cu 10Ni alloy were studied, which were processed by different deformations, annealing treatments and surface treatments. The results indicate that after exposure corrosion for half a year, the antifouling properties of the specimens are quite different. The specimens processed by suitable deformations, annealing treatment at 650?℃ and pretreatment of surface film possess both good corrosion resistance and antifouling properties. However, the specimens processed by different deformations and annealing treatment at 450?℃ possess lower corrosion resistance, although they are also treated by the pretreatment of surface film; their antifouling properties change with different deformations. The relationships among the corrosion morphology and microstructure with the antifouling property of 90Cu 10Ni alloy are observed under the scanning electron microscopy (SEM).

Cavitation Erosion Behavior of as-Welded Cu12Mn8Al3Fe2Ni Alloy

Cavitation erosion behavior of as-welded Cu12Mn8Al3Fe2Ni alloy in 3.5% NaCl aqueous solution was studied bymagnetostrictive vibratory device for cavitation erosion. The results show that the cavitation erosion resistance ofthe as-welded Cu12Mn8Al3Fe2Ni alloy is much more superior to that of the as-cast one. The cumulative mass lossand the mass loss rate of the as-welded Cu12Mn8Al3Fe2Ni alloy are almost 1/4 that of the as-cast one. SEM analysisof eroded specimens reveals that the as-cast Cu12Mn8Al3Fe2Ni alloy is attacked more severely than the as-weldedone. Microcracks causing cavitation damage initiate at the phase boundaries.

Thermodynamic simulation of metal behaviors in Cu_(2+)−Ni_(2+)−NH_(3)−NH_(4)+−C_(2)O_(4)^(2-)−H_(2)O system

To investigate the behaviors of Cu^(2+)and Ni^(2+)with the change of conditions in Cu_(2+)−Ni_(2+)−NH_(3)−NH_(4)+−C_(2)O_(4)^(2-)−H_(2)O reaction system,mathematical models of thermodynamics based on the principle of mass conservation were established.The simulation results indicate that the precipitation of metal ions from the aqueous phase is a complicated dynamic equilibrium process,during which the coordination reactions of Cu^(2+)and Ni^(2+)with NH3 forming[Cu(NH3)n]^(2+)(n=3−5)and[Ni(NH3)m]^(2+)(m=3−6)are predominant under high pH conditions,respectively.The pH ranges for the simultaneous precipitation of Cu^(2+)and Ni^(2+)are 2.0−6.5 and 2.0−5.5 when[NH3]T equals 0.6 and 4.2 mol/L,respectively,with the prefixed[C_(2)O_(4)^(2-)]T of 0.6 mol/L.Due to the fractional precipitation of Cu^(2+)and Ni^(2+),Cu−Ni composite is obtained after the thermal decomposition of Cu−Ni oxalate complex salts prepared in a pure water system when pH>7.0.By applying the mixed solvent(water/ethanol)as the precipitation medium,the Cu−Ni alloy rods can be finally fabricated with high purity and crystallinity.

Homogeneous Plastic Flow of Fully Amorphous and Partially Crystallized Zr_(41.2)Ti_(13.8)Cu_(12.5)Ni_(10)Be_(22.5) Bulk Metallic Glass

The homogeneous plastic flow of fully amorphous and partially crystallized Zr(41.2)Ti(13.8)Cu(12.5)Ni(10)Be(22.5) bulk metallic glass (Vitl) has been investigated by compression tests at high temperatures in supercooled liquid region. Experimental results show that at sufficiently low strain rates, the supercooled liquid of the fully amorphous alloy reveals Newtonian flow with a linear relationship between the flow stress and strain rate. As the strain rate is increased, a transition from linear Newtonian to nonlinear flow is detected, which can be explained by the transition state theory. Over the entire strain rate interval investigated, however, only nonlinear flow is present in the partially crystallized alloy, and the flow stress for each strain rate is much higher. It is found that the strain rate-stress relationship for the partially crystaltized alloy at the given temperature of 646 K also obeys the sinh law derived from the transition state theory, similar to that of the initial homogeneous amorphous alloy. Thus, it is proposed that the flow behavior of the nanocrystalline/amorphous composite at 646 K is mainly controlled by the viscous flow of the remaining supercooled liquid.

Correlation Between Microstructure and Corrosion Behavior of Two 90Cu10Ni Alloy Tubes

Two kinds of 90Cu10 Ni tubes with different service lives（more than 3 years and only 1 year,respectively）under identical working conditions were studied by an immersion test in a 3.5 wt% NaCl solution and the electron backscattered diffraction（EBSD） technique.The morphology after immersion showed severer corrosion attack at the grain boundaries of the tube with shorter service life compared with the tube with longer service life.The grain boundary characterization distributions（GBCDs） of the two tubes obtained by EBSD revealed more Σ3 boundaries and twins,and larger random boundary meshes in the tube with longer service life.A short immersion test in a modified Livingston＇s solution was conducted to evaluate the tendency to corrosion attack of different types of the grain boundaries.SEM and AFM were used to characterize the corrosion morphologies of the boundaries.A strong correlation between varying depths of corrosion grooves and types of the grain boundaries was obtained.The influence of deviation angle of low Σ boundaries on corrosion resistance of the grain boundaries was also discussed.It is concluded that a special ‘‘grain boundary engineering＇＇（GBE） treatment has been performed on the tube with longer service life.It is proposed that the optimized GBCD is responsible for the better service performance of the tube.

Stabilization of Cu/Ni Alloy Nanoparticles with Graphdiyne Enabling Efficient CO_(2) Reduction

Electrocatalysis has become an attractive strategy for the artificial reduction of CO_(2) to high-value chemicals.However,the design and development of highly selective and stable non-noble metal electrocatalysts that convert CO_(2) to CO are still a challenge.As a new type of two-dimensional carbon material,graphdiyne(GDY),is rarely used to explore the application in carbon dioxide reduction reaction(CO_(2)RR).Therefore,we tried to use GDY as a substrate to stabilize the copper-nickel alloy nanoparticles(NPs)to synthesize Cu/Ni@GDY.Cu/Ni@GDY requires an overpotential(−0.61 V)to 10 mA/cm^(2) for the formation of CO,and it shows better activity than Au and Ag,achieving a higher Faraday efficiency of about 95.2%and high stability of about 26 h at an overpotential(−0.70 V).The electronic interaction between GDY substrate and Cu/Ni alloy NPs and the large specific surface area of GDY is responsible for the high performance.

Microstructures, mechanical properties, and grease-lubricated sliding wear behavior of Cu–15Ni–8Sn–0.8Nb alloy with high strength and toughness

Alloys used as bearings in aircraft landing gear are required to reduce friction and wear as well as improve the load‐carrying capability due to the increased aircraft weights.Cu–15Ni–8Sn–0.8Nb alloy is well known for possessing good mechanical and wear properties that satisfy such requirements.In this study,the microstructure,mechanical properties,and grease‐lubricated sliding wear behavior of Cu–15Ni–8Sn–0.8Nb alloy with 0.8 wt%Nb are investigated.The nanoscale NbNi3 and NbNi2Sn compounds can strengthen the alloy through the Orowan strengthening mechanism.A Stribeck‐like curve is plotted to illustrate the relationship among friction coefficient,normal load,and sliding velocity and to analyze the grease‐lubricated mechanism.The wear rate increases with normal load and decreases with sliding velocity,except at 2.58 m/s.A wear mechanism map has been developed to exhibit the dominant wear mechanisms under various friction conditions.When the normal load is 700 N and the sliding velocity is 2.58 m/s,a chemical reaction between the lubricating grease and friction pairs occurs,resulting in the failure of lubricating grease and an increase in wear.

DENDRITE ARM SPACING OF DIRECTIONAL SOLIDIFICATION STRUCTURE OF HIGHLY UNDERCOOLED MELTS

Directional solidification was performed in Cu 30Ni alloy melt undercooled in the range 105-155 K, and the structure was investigated. The results indicated that the dendrite arm spacings are first dependent on undercooling prior to nucleation. As undercooling increases, the thickness of thermal diffusion field and solute diffusion field decreases due to the ascent of dendrite growth velocity, and the dendrite remelting occurring in solidification abates. So primary and secondary arm spacing all decrease. At the undercoolings higher than 150 K, however, secondary arms degenerate because of the further closing of the primary branches, and enlarge their spacing. The dendrite arm spacings are also related to the position in specimens. At the two ends of specimens, especially the initial end of solidification, the favorable heat dissipation condition leads to smaller spacings. Primary as well as secondary arm spacings always reach their maximum at the central part of the specimens where the local solidification time is the longest.