稀有金属材料与工程最新文献

Al-La, Al-Ti and Al-La-Ti alloys were prepared to study the effects of Ti and La on the electrical conductivity and strength of alloys. The electrical conductivity, strength and microstructure evolution of alloys before and after homogenization treatment at 500 °C for 8 h were investigated. The results show that when the content of La does not exceed 0.3 wt%, the electrical conductivity of Al-La can keep a high level as 60.35% IACS due to the precipitation of the compounds containing La, Si and Fe. The strength of Al-Ti alloy is rapidly enhanced with the increase of Ti due to the increasing content of Ti atoms in the α-Al solution. When La and Ti are added simultaneously, the strength of alloys is higher than that of Al-La alloys, and the electrical conductivity is decreased compared with that of Al-La alloys but is higher than that of the Al-Ti alloy, which is mainly attributed to the formation of the new secondary phase Ti₂Al₂₀La. Homogenization treatment has little effect on the microstructure of alloys but reduces the number of casting defects, thereby increasing the electrical conductivity of all samples.

TiN/Cu nanocomposite films were deposited on high-speed steel (HSS) substrates by axial magnetic field-enhanced arc ion plating (AMFE-AIP). The effects of substrate bias voltage on chemical composition, microstructure, mechanical and tribological properties of the films were investigated by X-ray photoelectrons spectroscopy (XPS), X-ray diffraction (XRD), nanoindentation and wear measurements, respectively. The results show that the Cu content increases first and then decreases with the increase of the pulse bias voltage, being a low value in the range of 1.3 at%∼2.1 at%. XRD results show that only the TiN phase appears in all the films, and no Cu phase is observed. The preferred orientation of the films changes significantly with the increasing pulse bias voltage. A maximum value of hardness of 36 GPa is obtained under a pulse bias voltage of −200 V, corresponding to the film containing 1.6 at% Cu. Compared to the pure TiN film, the Cu addition in TiN films significantly improves the wear resistance.

Au-TiO₂ nanofilms were prepared on indium-tin oxide glass by magnetron sputtering. The growth of well-aligned Au/TiO₂ nanofilms arrays by magnetron sputtering was presented for the first time. The Au/TiO₂ nanofilms were grown on the surface of indium tin oxide (ITO) substrates. The photocatalytic activity of the prepared Au-TiO₂ nanofilms in an aqueous solution of methylene blue (MB) was evaluated under the irradiation of visible-light. The experimental results show that the use of Au in TiO₂ nanofilms improves photocatalytic activity of the MB organic compound significantly in the aqueous solution under the irradiation of visible light, and the photodegradation rate constants of the prepared Au/TiO₂ nanofilms for the photodegradation of MB are larger than that of pure TiO₂ nanofilms.

A new improved test system was developed based on the non-contact inductance method, which can be used to characterize the piezomagnetic properties of Fe-based amorphous alloy ribbons properly. The studies show that when the test frequency is 1 kHz, the voltage is 0.3 V and the compressive stress σ ≤ 0.1 MPa, the amorphous magnetic material of Fe_73.5Cu₁Nb₃Si_13.5B₉ has excellent piezomagnetic properties, and its ribbons of different specifications exhibit perfect stability and repeatability after repeated experiments. The ribbons are extremely sensitive to tiny stress, and they show a rapidly rising trend of the inductance once the initial pressure is applied on the ribbons. Moreover, the further amplifying experiment indicates that the sensitivity range is 0∼1.5 kPa. In addition, the size of Fe_73.5Cu₁Nb₃Si_13.5B₉ ribbons influence significantly the piezomagnetic property, and the initial inductance and its corresponding S_I-Max value of the ribbons increase substantially along with the sample size increasing; with the same width, the piezomagnetic property is superior to others while the thickness is 33∼36 µm, and S_I-Max is 19.8%. With the same thickness, the ribbons with a width of 20 mm show an excellent piezomagnetic property and the S_I-Max has reached 22.02%.

In order to better understand the effect of the temperature and load on recrystallization behavior of DD5 single-crystal hollow blade tenon, samples with different loads were heat treated at different solution temperatures in a furnace. Optical microscope and scanning electron microscope were used to study the microstructure of recrystallization and size distribution of γ′ phase after solution treatment. Results show that there are no new grains found after solution treatment at 1230 °C/4 h, air cooling. However, the depth of load affected area increases with the bearing load and the size and depth of recrystallized cellular structure with newly-formed γ′ phase particles increase with the load below the solution temperature. Besides, the recrystallized nuclei begin from the dendrite when the solution treatment is 1315 °C/4 h, air cooling. The dendrite arms are passivated and the boundary between dendrite arm and interdendritic space disappear and γ/γ′ phase eutectic structure exists between dendrites in the recrystallization area. Moreover, the recrystallization area and the primary dendritic size gradually increase with the increase in load above the solution temperature.

The effects of different heat treatment parameters on the microstructure and mechanical property of as-extruded Mg-4.8Zn-1.2Y-0.4Zr magnesium alloy were described based on the experimental results and analyses. The results indicate that the microstructure of the alloy changes obviously during heat treatment process. After T4 solution treatment, although the alloy grains grow obviously, the plasticity of the alloy is enhanced greatly. This is mainly due to the massive fish-bone W-phase decomposed into fine granular W phase, which reduces the pinning effect of the grain boundary. After T5 heat treatment, besides W-phase, there is a small amount of Mg-Zn phase precipitated in the alloy, which can improve the performance of the alloy. After T6 heat treatment, the W-phase has been almost completely decomposed into Mg-Zn and Mg-Y phase. The dispersively distributed phases greatly improve the strength and plasticity, which increases the ultimate tensile strength and elongation from 311 MPa and 16.89% in as-extruded alloy to 374 MPa and 21.97%, respectively. At last the most suitable scheme for heat treatment of Mg-4.8Zn-1.2Y-0.4Zr magnesium alloy is (500 °C/2 h+200 °C/48 h).

The effect of minimum temperature on the mechanical properties and reversed austenite content of 9%Ni steel subjected to cryogenic treatment was experimentally investigated. Cryogenic treatment with different temperatures and soaking time were conducted by combining with the newly developed quenching, lamellarizing and tempering (QLT) heat treatment of 9% Ni steel. The results show that the cryogenic treatment at −80 and −110 °C has no obvious influence on the reversed austenite content and mechanical properties of 9%Ni steel. However, the room temperature impact toughness is improved by cryogenic treatment at −140 °C for 24 h, which is attributed to the modification in the reversed austenite morphology from bulks into strips. The volume fraction of the reversed austenite decreases slightly due to the isothermal martensitic transformation at −140 °C. Cryogenic treatment at −196 °C for 24 h increases the volume fraction of reversed austenite and refines the secondary martensite lath, thereby improving both the room temperature impact toughness and cryogenic ductility. The observed results are mainly due to the precipitation of ultra-fine carbides and the increase of internal stress during cryogenic treatment, which provides more nucleation sites for the reversed austenite in the process of tempering.

Nickel based alloy has good corrosion resistance in chloride medium, but its wear resistance is insufficient. In this paper, WC-CoCr coatings were deposited on Inconel617 alloy surface by HVOF (high velocity oxygen fuel). Electron beam remelting process was explored to modify the morphology and the phase composition of the coated layer. The results show that some structural defects of the as-sprayed coating are improved after electron beam treatment. Tribological tests concerning the sliding wear behavior of the tested materials reveal a significant decrease in the wear rate for the alloyed surface in comparison with the base material. After high energy electron beam treatment, the micro-hardness (HV_0.3) of the surface is 11000 MPa which is about 2 times as much as that of the matrix (5500 MPa) due to the formation of new phase (especially the Co₆W₆C phase) with high hardness. Besides the amount of porosity of the coatings is reduced and the grain is refined. EDS spectrum analysis indicates that new elements occur in the proliferation of cladding layer and the substrate achieves a good metallurgical bonding with the coating. Moreover, the corrosion resistance of the cladding layer in salt water is higher than that of the matrix.

Effects of Sr and Ca combined additions (Sr+Ca=0.05wt/%) on the microstructure of A390 aluminum alloy were evaluated by investigating the variation of quantity, size and shape of primary silicon, eutectic silicon, primary α phase and intermetallic phase. The results show that the variation of microstructures results from the synergistic effect of Sr-Ca additions. The loss rate of Sr is reduced with a small amount of Ca; meanwhile, the coarsening effect of primary silicon phase arising from Sr addition is also suppressed. The Sr in A390 aluminum alloy mainly modifies eutectic silicon phase and refines θ phase. Furthermore, Ca principally modifies primary silicon phase and primary α phase. The optimal microstructure is obtained when combined addition of 0.05%Sr-Ca is applied and the atomic ratio of Sr and Ca is 5:1, in which primary silicon phase and eutectic silicon phase as well as primary α phase are all modified significantly compared with those of only 0.05% Sr addition.

Interface fracture often occurs in systems of soft substrate and hard coatings during the service process, which is related to the weak interface strength and the unstable expansion of cracks along the interface induced by the residual thermal stress. The residual thermal stress mainly comes from the mismatch of thermal physical properties between matrix and hard coatings. In this study, a gradient carburized layer was prepared on TC4 substrate before the deposition of TiN(Ti) coatings using double glow plasma carburization. And then the mono- and multilayer TiN(Ti) coatings were synthesized on the carburized layer, forming composite hard coatings. The effect of substrate carburizing on properties of coatings was studied. The results show that the composite coatings' hardness can be increased nearly 2 times and the bonding strength is enhanced to over 80 N, compared with that of mono-and multilayer TiN(Ti) coatings. Also the interface brittle fracture tendency is restrained obviously by the hardened substrate, and the coordinative deformation ability of the coating at extra load is optimized. The composite coating composed of pre-carburized layer and TiN hard coating shows a higher strength and toughness.