The effect of particle size of alumina dispersions on the oxidation resistance of Ni-Cr alloys

The oxidation behavior of Ni-Cr alloys with various chromium concentrations and particle sizes of a dispersion of 10 vol.% Al₂O₃ was observed in 1 atm of oxygen at 1000°C. This study was intended to determine the critical chromium concentration to form a protective Cr₂O₃ oxide layer for different Al₂O₃ particle sizes. The oxidation rate of Ni-Cr alloys containing 10 vol.% Al₂O₃ followed a parabolic rate law and a Cr₂O₃ protective layer continuously formed when the oxidation rate decreased rapidly. Times to form a continuous and protective Cr₂O₃ layer during the initial oxidation shortened as the size of the dispersion decreased. The critical chromium concentration to form a protective Cr₂O₃ layer in the oxide scale was 69 wt.% and was related strongly to the particle size of the Al₂O₃ dispersion.     

The oxidation of Ni-70 wt.%Cr in oxygen between 1073 and 1473°K

Oxidation of the relatively simple, two-phase alloy Ni-70 wt.%Cr in oxygen between 1073 and 1473°K results in the formation of a Cr₂O₃ scale containing less than O.5 wt.% Ni in solid solution. The oxidation kinetics are irreproducible for an initial period, which is brief at 1073 and 1273°K but much more pronounced at 1473°K, both in duration and degree. This behavior is associated with the failure of the protective Cr₂O₃ scale. However, after longer periods a compact layer of Cr₂O₃ becomes established under isothermal conditions and results in a change to more reproducible kinetics, especially at 1073 and 1273°K. Oxidation causes chromium depletion and the formation of a single-phase zone which separates the scale and the two-phase bulk alloy. The depth of Cr₂O₃ internal oxide coincides with this zone. The oxidation behavior is compared with that of more Ni-rich, single-phase Ni-Cr alloys, with particular reference to the effects of the constitution of the underlying alloy and the integrity of the protective oxide.     

Effect of thermal treatment on adhesion strength of Cu/Ni-Cr/polyimide flexible copper clad laminate fabricated by roll-to-roll process

In this study, the effect of a Ni-Cr seed layer on the adhesion strength of flexible copper clad laminate (FCCL) was evaluated after thermal treatment. The changes in the chemical composition, morphology and adhesion property were characterized by scanning electron microscopy (SEM), energy dispersive X-ray spectroscopy (EDS), electron probe micro analyzer (EPMA), X-ray photoelectron spectroscopy (XPS), atomic force microscopy (AFM) and 90° peel test. The peel strength of the FCCLs was significantly affected by the thermal treatment and the FCCL with a higher peel strength had a higher thermal stability than that with a lower peel strength. The roughness of the fracture surface for the FCCLs decreased with increasing thermal treatment temperature and holding time. The thermal treatment of the FCCL increased the ratio of the C-N bonds and reduced that of the C-O and carbonyl (CO) bonds in the polyimide.     

飞机起落架作动筒内壁n-Al_2O_3/Ni-Cr复合电刷镀修复

分析了飞机起落架作动筒内壁磨损失效的原因,采用n-Al2O3/Ni-Cr复合刷镀技术,对磨损部位进行了修复,以提高镀层与基体、镀层与工作层间的结合力.结果表明:修复层的硬度及耐磨性与原件相当,该工艺方法简单、可靠.     

Carbide Effects on Creep Crack Growth of Ni-Cr Austenitic Steels

By controlling the carbon content ofFe-15Cr-25Ni alloys,three types ofmicrostructures were obtained:single phaseaustenite (γ),γ+intergranular carbides,γ+intergranular carbides + intragranular carbides.Creep crack growth behaviour of the three alloyshas been compared at 973 K and 1123 K.Intergranular carbides show higher creep crackgrowth resistance than intragranular carbides.Cav-ities nucleate at the triple junctions of grain bound-aries for single phase alloy,but at intergranularcarbides for two-phase alloys.The precipitation ofintergranular carbide not only changes thenucleation mechanism of cavities,but also inhibitsthe growth and coalescence of cavities.The precipi-tation of intragranular carbide obstructs thenucleation and growth of cavities furthermore.     

Ni-Cr alloy electrodepositing technology on Fe substrate and coating performance

The Ni-Cr alloy electrodepositing technology on iron substrate in the chlorid-sulfate solution and the impacts of main processing parameters on coating composition were studied. The optimal Ni-Cr alloy electrodepositing conditions are that the cathode current density is 16 A/dm^2, the plating solution temperature is 30 ℃ and the pH value is 2.5. The bright, compact coating gained under the optimal conditions has good cohesion and 24.1% Cr content. The results show that the coating is composed of crystalline, the average grain size is 82 nm and the higher the Cr content of coating, the larger the rigidity, and the higher the corrosion resistance. The rigidity of coating reaches 78.6（HR30T） and the passivation area broadens to 1.4 V when the Cr content of coating is 24.1%.