Microstructure and some properties of powder-pack borided Ti–5Mo–5V–8Cr–3Al alloy with special attention to the microstructure at the interface TiB/substrate

The borided layer was prepared on the surface of the Ti–5Mo–5V–8Cr–3Al alloy by powder-pack boriding at 1000°C-10h. SEM, EPMA and TEM were used to investigate the effects of alloying elements (Al, V, Mo and Cr) on the growth of TiB whiskers in the borided Ti–5Mo–5V–8Cr–3Al alloy. Wear properties of borided Ti–5Mo–5V–8Cr–3Al alloy were investigated using dry reciprocating friction tests. SEM results show that the thickness of boride layer in Ti–5Mo–5V–8Cr–3Al alloy is thinner than that in the Cp-Ti. This is attributed to the enrichment of alloying elements especially V in TiB/substrate by TEM, which hinders the diffusion of B atoms, thus resulting in the short and thick TiB whiskers in Ti–5Mo–5V–8Cr–3Al alloy. Borided Ti–5Mo–5V–8Cr–3Al alloy has the better wear resistance than as-received alloy.     

Effect of scandium and zirconium alloying on microstructure and gaseous hydrogen storage properties of YFe3

RM₃ compounds (R = rare earth metals, M = transition metals) have rarely been studied for gaseous hydrogen storage applications because of unfavorable thermodynamics. In this work, the hydrogen storage properties of a single-phase YFe₃ alloy were improved by non-stoichiometric composition and alloying with Sc and Zr. Only the Y_1.1–ySc_yFe₃ (y = 0.22, 0.33) alloys consist of a single rhombohedral phase. The Sc substitution for Y leads to the reduction in the unit cell volume of the YFe₃ phase, and thus significantly increases the dehydriding equilibrium pressure and decreases the dehydrogenation temperature. The alloy Y_0.77Sc_0.33Fe₃ delivers a decomposition enthalpy change of 33.54 kJ/mol and a lowest dehydrogenation temperature of 135 °C, in comparison with 38.99 kJ/mol and 165 °C for the alloy Y_1.1Fe₃. The Zr substitution causes a similar thermodynamic destabilization effect, but the composition and microstructure of Y–Zr–Fe alloys need to be further optimized.     

High-pressure hydrogen storage performances of ZrFe2 based alloys with Mn,Ti, and V addition

The microstructure of ZrFe₂-based alloys were modified by alloying with the Mn, Ti, and V, aiming to obtain proper hydriding/dehydriding plateau features for the high-pressure application. The multi-component ZrFe₂-based alloys show a wide tunable range in the plateau pressure via the interaction of Ti, Mn, and V. Further, the V addition plays the best role to improve the hysteresis in absorption-desorption isotherms, while the proper addition amount Ti helps to realize a low plateau slope as well as a high plateau pressure. Among the investigated alloys, Zr_1.05Fe_1.6Mn_0.4 shows a relatively high dehydriding pressure of 20.58 atm at 298 K, while Zr_1.05Fe_1.7Mn_0.2V_0.1 with C15 structure shows the lowest hysteresis. Overall, too much of Ti and Mn would promote the transformation of the C15 to C14 structure with large hysteresis and low plateau pressure.     

Corrosion of New Zirconium Claddings in 500 °C/10.3 MPa Steam: Effects of Alloying and Metallography

With the aim of improving corrosion resistance of rod cladding for in-service and accident conditions, six new zirconium alloys (named N1-N6) have been designed. The contents of Sn and Nb were optimized for better behavior at high-temperature pressurized water, and Fe, Cr, V, Cu or Mo elements were added to the alloys to adjust the corrosion behavior. The current work focused on the rapid corrosion behavior in 500 °C/10.3 MPa steam for up to 1960 h, aiming to test the corrosion resistance at high temperature. The structure of matrix and properties of second-phase particles (SPPs) were characterized to find the main differences among these alloys. All the six alloys exhibited better corrosion resistance than N36, and N1 was shown to have the best performance. A careful analysis of the corrosion kinetics curves revealed that Cr was beneficial for severe condition. Elements Fe, Cr, V, Cu or Mo aggregated into SPPs with different concentrations and structures. This was demonstrated to be the main reason for different corrosion resistance. Due to good processing control, all alloys had a uniform structure and a uniform distribution of SPPs. As for N4, N6 and N36, the existing of large-size SPPs (450 nm) might be a contributing factor of the relatively poor corrosion resistance.     

Impact of ZrO2 alloying on thermo-mechanical properties of Gd3NbO7

The ZrO₂ alloying effect is widely used to optimize the thermo-mechanical properties of potential thermal barrier coatings. In this study, dense x mol% ZrO₂-Gd₃NbO₇ with C222₁ space group were manufactured via a solid-state reaction. The crystalline structure was determined through X-ray diffraction and Raman spectroscopy, when the surface morphology was observed by scanning electron microscopy. ZrO₂-Gd₃NbO₇ had identical orthorhombic crystal structures, and there was no second phase. The crystalline structure of ZrO₂-Gd₃NbO₇ shrunk with the increasing ZrO₂ content as indicated by XRD and Raman results. The heat capacity and thermal diffusivity of ZrO₂-Gd₃NbO₇ were 0.31–0.43 J g⁻¹ K⁻¹ (25–900 °C) and 0.25–0.70 mm²/s (25–900 °C), respectively. It was found that ZrO₂-Gd₃NbO₇ had much lower thermal conductivity (1.21–1.82 W m⁻¹ K⁻¹, 25–900 °C) than YSZ (2.50–3.00 W m⁻¹ K⁻¹) and La₂Zr₂O₇ (1.50–2.00 W m⁻¹ K⁻¹). The thermal expansion coefficients (TECs) were higher than 10.60 × 10⁻⁶ K⁻¹ (1200 °C), which were better than that of YSZ (10.00 × 10⁻⁶ K⁻¹) and La₂Zr₂O₇ (9.00 × 10⁻⁶ K⁻¹). The mechanical properties of Gd₃NbO₇ change little with the increasing ZrO₂ content, Vickers hardness was about 10 GPa, and Young's modulus was about 190 GPa, which was lower than YSZ (240 GPa). Compared with previous work about alloying effects, much lower thermal conductivity was obtained. Due to the high melting point, high hardness, low Young's modulus, ultralow thermal conductivity and high TECs, it is believed that ZrO₂-Gd₃NbO₇ is promising TBCs candidate.     

Metallurgical characterization of Ti-bearing 9Cr low activation martensitic steel

Two heats of low activation martensitic (LAM) steels with Ti and Ta (denominated as 9Cr-Ti and 9Cr-Ta),respectively,developed as candidate structure materials for nuclear reactor were characterized.This paper was focused on the effect of titanium on the microstructures and mechanical properties of 9Cr LAM steel in as-received condition (normalized at 950 ℃ for 30 min with water quenching plus tempered at 780 ℃ for 90 min with air cooling).Chemical analysis and microstructure observation were conducted on 9Cr-Ti and 9Cr-Ta with optical microscopy,X-ray diffraction analysis,scanning electron microscopy and transmission electron microscopy.Impact properties and tensile strengths were measured with Charpy impact experiments and tensile tests.The results indicated that 9Cr-Ti and 9Cr-Ta were fully martensitic steels in as-received condition.MX type and M23C6 type precipitates were observed distributing along boundaries of prior austenite grains and martensite laths in 9Cr-Ti.The addition of titanium accelerated the precipitation of TiC and TiN,and produced much finer grains in 9Cr-Ti than 9Cr-Ta at the same normalization temperature.Mechanical properties tests showed the ductile brittle transition temperatures of 9CrTi and 9Cr-Ta were about-90 ℃ and-85 ℃,respectively.The ultimate tensile strengths at room temperature and 600 ℃ were 680 MPa and 365 MPa for 9Cr-Ti,and 660 MPa and 335 MPa for 9Cr-Ta,respectively.The favorite impact toughness and tensile properties of 9Cr-Ti could be attributed to the fine grains in as-received condition.     

机械合金化及在含氮不锈钢制备中的应用

机械合金化法是新兴的材料制备方法,简要介绍了机械合金化的基本原理,报道了机械合金化法制备高氮不锈钢的研究进展,并对发展趋势及研究方向进行了探讨。     

Facile Synthesis of Yolk-Shell Bi@C Nanospheres with Superior Li-ion Storage Performances

Recently,exploring appropriate anode materials for current commercial lithium-ion batteries(LIBs) with suitable operating potential and long cycle life has attracted extensive attention.Herein,a novel anode of Bi nanoparticles fully encapsulated in carbon nanosphere framework with uniform yolk-shell nanostructure was prepared via a facile hydrothermal method.Due to the special structure design,this anode of yolk-shell Bi@C can effectively moderate the volume exchange,avoid the aggregation of active Bi nanoparticle and provide superior kinetic during discharge/charge process.Cycling in the voltage of 0.01-2.0 V,yolk-shell Bi@C anode exhibits outstanding Li+storage performance(a reversible capacity over 200 mAh g~(-1)after 400 cycles at 1.25 A g~(-1)) and excellent rate capability(a capacity of 404,347,304,275,240,199 and 163 mAh g~(-1) at0.05,0.1,0.25,0.5,1.0,1.8 and 3.2 A g~(-1),respectively).This work indicates that rational design of nanostructured anode materials is highly applicable for the next-generation LIBs.     

镁锂合金表面镍磷合金化处理的研究

超轻型镁锂合金是航天、航空的优质轻型材料,但其性质极其活泼、耐腐蚀性能很差,是制约其推广应用的关键问题,且难于进行表面防腐处理.介绍用ML-20701型镁锂合金表面镍磷合金化粉水溶液,在70～75℃条件下,对表面活化的镁锂合金进行浸泡,在镁锂合金表面沉积耐腐蚀合金膜层,从而提高其防腐性能.这也可作为电镀、电泳的预处理工艺,为镁锂合金采用电镀、电泳涂装进行表面防护装饰,提供了有效解决途径.     

Synergistic alloying effect on microstructural evolution and mechanical properties of Cu precipitation-strengthened ferritic alloys

We report the influence of alloying elements (Ni, Al and Mn) on the microstructural evolution of Cu-rich nanoprecipitates and the mechanical properties of Fe–Cu-based ferritic alloys. It was found that individual additions of Ni and Al do not give rise to an obvious strengthening effect, compared with the binary Fe–Cu parent alloy, although Ni segregates at the precipitate/matrix interface and Al partitions into Cu-rich precipitates. In contrast, the co-addition of Ni and Al results in the formation of core–shell nanoprecipitates with a Cu-rich core and a B2 Ni–Al shell, leading to a dramatic improvement in strength. The coarsening rate of the core–shell precipitates is about two orders of magnitude lower than that of monolithic Cu-rich precipitates in the binary and ternary Fe–Cu alloys. Reinforcement of the B2 Ni–Al shells by Mn partitioning further improves the strength of the precipitation-strengthened alloys by forming ultrastable and high number density core–shell nanoprecipitates.