Yuan Chen

The mechanical properties of nanocrystalline pure Ni films are degraded due to grain coarsening with exposure for a long time in ambient. In order to further improve the mechanical properties of Ni-based thin films, as-sputtered Mo-W co-doped Ni/Ni₃Al multilayered structures were constructed. When the individual layer thickness (h) is lower than 40 nm, both the average grain sizes and the crystallinity degrees are degraded, showing a tendency for the formation of the amorphous phase. With h = 40 nm, nano-twins were observed as (111) twining interfaces for the multilayers due to the reduction of the stacking fault energy by the co-doping of Mo-W, whereas the nucleation and growth of the nano-twins were limited, without observations for the Mo-W co-doped Ni/Ni₃Al multilayer with h = 10 nm. The hardness of the multilayers was enhanced, and the elastic modulus was reduced at a lower h, owing to the grain refinements and layer interface barriers for strengthening, and the existence of the amorphous phase with the inferior modulus, respectively. The resistance against the fracture was enhanced due to toughening by the lamellar structure for the Mo-W doped Ni/Ni₃Al multilayer at h ≤ 40 nm. Comprehensively, the Mo-W-doped Ni/Ni₃Al multilayer with 10 nm displays a superior mechanical performance.

GH4169 superalloy and Si₃N₄ ceramics were vacuum-brazed with AgCuTi+Cu foam composite filler. The effect of brazing temperature on the microstructure and mechanical properties of the GH4169/Si₃N₄ joint was studied. The results show that the interface microstructure of the GH4169/Si₃N₄ joint is the GH4169 superalloy/TiCu+Ti₂Ni+TiCu₂+Ag(s, s)+TiCu₄+Cu(s, s)+TiN+Ti₅Si₃/Si₃N₄ ceramics. With the increase in brazing temperature, the element diffusion between the base metal and the brazing filler intensifies, and the interfacial reaction layer thickens, which is conducive to the improvement of shear strength. At 850 °C, the maximum shear strength of the joint is 196.85 MPa. After further increases in the brazing temperature, Cu foam dissolves completely, and the Ti-Cu intermetallic compounds increase, which is harmful to the shear strength due to the increases in the brittle phase. However, when the brazing temperature reaches 910 °C, the shear strength of the brazing joint slightly increases under the combined effect of the Ti-Cu intermetallic compounds and the thickness of the reaction layer.

The microstructure, phase composition and mechanical properties of ternary Al-5.4Ni-2Sn (mass fraction) alloy solidified under different high pressures were researched. The results show that the phase composition of the alloy solidified at different pressures is Al, Al₃Ni and β-Sn. The thermodynamic phase diagram of the ternary alloy Al-5.4Ni-2Sn was calculated under the equilibrium condition. The results demonstrate that the solidification process is as follows: L→Al₃Ni→(α-Al + Al₃Ni)_eutectic→(α-Al + Al₃Ni + β-Sn)_eutectic. The hardness values of α-Al phase at ambient pressure, 2 GPa and 4 GPa are 1.5 GPa, 1.62 GPa and 1.99 GPa, respectively. This is an increase of 8% and 32.7%, respectively. The hardness of β-Sn phase decreases by about 31.2% at 4 GPa. When the deformation is 30%, the compressive strength at ambient pressure, 2 GPa and 4 GPa is 538.1 MPa, 1403.2 MPa and 1547.9 MPa, respectively. The compressive strength under high pressure increased by 160.85% and 187.7%, respectively.