Process−microstructure−properties relationship in Al−CNTs−Al2O3 nanocomposites manufactured by hybrid powder metallurgy and microwave sintering process

Al−2CNTs−xAl₂O₃ nanocomposites were manufactured by a hybrid powder metallurgy and microwave sintering process. The correlation between process-induced microstructural features and the material properties including physical and mechanical properties as well as ultrasonic parameters was measured. It was found that physical properties including densification and physical dimensional changes were closely associated with the morphology and particle size of nanocomposite powders. The maximum density was obtained by extensive particle refinement at milling time longer than 8 h and Al₂O₃ content of 10 wt.%. Mechanical properties were controlled by Al₂O₃ content, dispersion of nano reinforcements and grain size. The optimum hardness and strength properties were achieved through incorporation of 10 wt.% Al₂O₃ and homogenous dispersion of CNTs and Al₂O₃ nanoparticles (NPs) at 12 h of milling which resulted in the formation of high density of dislocations and extensive grain size refinement. Also both longitudinal and shear velocities and attenuation increase linearly by increasing Al₂O₃ content and milling time. The variation of ultrasonic velocity and attenuation was attributed to the degree of dispersion of CNTs and Al₂O₃ and also less inter-particle spacing in the matrix. The larger Al₂O₃ content and more homogenous dispersion of CNTs and Al₂O₃ NPs at longer milling time exerted higher velocity and attenuation of ultrasonic wave.     

喷涂缠绕保温管用全水发泡聚氨酯组合聚醚的研制

用聚醚多元醇A、聚醚二醇B、聚酯多元醇PS-2915、三乙醇胺、水和其他助剂制备了喷涂管道用全水发泡聚氨酯硬泡组合聚醚,并对其反应性能、黏度进行评价,对使用该组合聚醚和多异氰酸酯PM-200制得的聚氨酯泡沫材料的性能进行研究。结果表明,在合适的原料用量时,制得的组合聚醚黏度较低,与多异氰酸酯PM-200的反应速度满足喷涂管道生产工艺要求。当喷涂制得的聚氨酯泡沫单层厚度7 mm左右,泡沫体具有较高的粘接强度、较好的韧性和较低的导热系数,密度61 kg/m^3的泡沫压缩强度达到526 kPa。制得的喷涂管道产品满足GB/T 34611—2017要求。     

Facile one-pot synthesis of binder-free nano/micro structured dendritic cobalt activated nickel sulfide: a highly efficient electrocatalyst for oxygen evolution reaction

Reasonable design and preparation of non-noble metal electrocatalysts with predominant catalytic activity and long-term stability for oxygen evolution reaction (OER) are essential for electrocatalytic water splitting. Ni foam (NF) is highlighted for its 3D porous structure, impressive conductivity and large specific surface area. Herein, nano/micro structured dendritic cobalt activated nickel sulfide grown on 3D porous NF (Co–Ni₃S₂/NF) has been successfully synthesized by one-step hydrothermal method. Due to the ingenious incorporation of Co, Co–Ni₃S₂/NF electrode shows auspicious electrocatalytic performance for OER compared with Ni₃S₂/NF electrode. As a result, Co–Ni₃S₂/NF needs overpotential of only 274 and 459 mV at current density of 10 and 50 mA cm⁻², respectively, while Ni₃S₂/NF requires overpotential of 344 and 511 mV. At potential of 2.0 V (vs. RHE), Co–Ni₃S₂/NF displays current density of 191 mA cm⁻², while Ni₃S₂/NF just attains current density of only 135 mA cm⁻². Moreover, Co–Ni₃S₂/NF demonstrates excellent stability for uninterrupted OER in alkaline electrolyte. The strategy of designing and preparing cobalt activated nickel sulfide grown on NF renders a magnificent prospect for the development of metal-sulfide-based oxygen evolution catalysts with excellent electrocatalytic performances.     

辅助电流对Cu/Al大功率超声波焊接的影响

为获得更高质量的Cu/Al异质金属接头，开展了Cu/Al电流辅助大功率超声波焊接工艺试验，研究了辅助电流对Cu/Al超声波焊接的界面温度、材料塑性流动、界面中间相分布及接头力学性能的影响。结果表明，复合焊件成型良好，其接头抗拉剪力为3030 N，接头的断裂模式为韧性-脆性复合断裂。在同样的焊接时间0.2 s内，随着电流的增大，Cu/Al界面温度增加，金属塑性流动以及界面扩散也随之增强，这说明辅助电流能明显促进界面冶金；相比长时间0.4 s的超声波焊接，辅助电流能在保证界面温度、材料塑性变形的前提下，能明显减薄了界面IMC层的厚度，这是电流增强Cu/Al接头的主要物理机制。研究结果为优化Cu/Al复合焊接头强度提供了参考。     

Mechanism of heterogeneous distribution of Cr-containing dispersoids in DC casting 7475 aluminum alloy

The actual effective partition coefficients of Mg and Cr in a cross-section of a dendrite arm in a direct-chill (DC)-casting ingot of 7475 aluminum alloy are obtained. Meanwhile, by analyzing the microstructure, the mechanism of the heterogeneous distribution of E (Al₁₈Mg₃Cr₂) dispersoids in this DC ingot is revealed. The results show that the actual effective partition coefficients of Mg and Cr are 0.650 and 1.392, respectively, and they describe the heterogeneous distributions of Mg and Cr along the direction of radius of the cross-section of the dendrite arm of the alloy. After homogenization treatment at 470 °C for 24 h, Mg diffuses uniformly, but Cr hardly diffuses. Both the concentrations of Mg and Cr and the sites of heterogeneous nucleation in the alloy are the determinants of the formation of E dispersoids simultaneously. The heat treatment at 250 °C for 72 h provides a large number of the sites of heterogeneous nucleation of the formation of fine E dispersoids that will be formed in the center of the cross-section during the subsequent heat treatment at higher temperature.     

Microscopic mechanism of perfluorocarbon gas formation in aluminum electrolysis process

In view of the unclear cause of perfluorocarbons (PFCs) emission in the anode effect stage of aluminum electrolysis, the microscopic formation mechanism of PFCs was studied by density functional theory calculation and X-ray photoelectron spectroscopy (XPS). It is found that the discharge of fluorine containing anions ([F]^?) on carbon anode first causes the substitution of C—H by C—F and further results in the saturation of aromatic C—C bonds, leading to the appearance of —CF₃ or —C₂F₅ group through six-carbon-ring opening. Elimination of —CF₃ and —C₂F₅ with F atom could be a likely mechanism of CF₄ and C₂F₆ formation. XPS results confirm that different types of —CF_x group can be formed on anode surface during electrolysis, and the possibility that [F]^? discharges continuously at the C edge and finally forms different C—F bonds in quantum mechanical calculation was verified.     

E2EM's prediction of LaB6 as nucleation substrate for primary Mn-rich phase in Al-Si-Cu-Mn heat-resistant alloy and its refining effect

Edge-to-edge matching (E2EM) model was used to predict the potency of LaB₆ as the heterogeneous nucleation substrate for primary Al₁₃Mn₄Si₈ phase formed during the solidification of Al-Si-Cu-Mn heat-resistant alloy. There are five pairs of orientation relationships (ORs) between LaB₆ and Al₁₃Mn₄Si₈ phases which meet the criteria of E2EM model. One pair of plane ORs ((110)_LaB6//(110)_Al13Mn4Si8) are demonstrated by TEM observation. This strongly indicates that the LaB₆ phase can act as the heterogeneous nucleation substrate for the primary Al₁₃Mn₄Si₈ phase. 1.0 wt.% of Al-2La-1B master alloy was also added into Al-12Si-4Cu-2Mn alloy to evaluate the refining effect by microstructure observation and tensile test. Experimental results show that addition of Al-2La-1B master alloy can significantly refine the primary Al₁₃Mn₄Si₈ phase, supporting the prediction accuracy of E2EM model. However, such refinement of primary Al₁₃Mn₄Si₈ phase does not lead to an improvement in strength. This is due to the larger difference in elastic modulus between the finally formed Al₁₃Mn₄Si₈ phase and aluminum matrix than that of Al₁₅Mn₃Si₂ phase.     

2219铝合金搅拌摩擦焊和钨极保护焊焊接件残余应力的中子衍射研究

利用中子衍射法对2219铝合金搅拌摩擦焊（FSW）和钨极保护焊（TIG）焊接件开展了三维残余应力测量，并对残余应力分布规律进行了分析。结果表明：焊接件的纵向残余应力数值较大；FSW焊接件残余应力整体较TIG焊接件的小；FSW和TIG焊接件的残余拉应力最大值分别为101 MPa和174 MPa，FSW焊接件残余拉应力最大值较TIG焊接件的小；FSW残余拉应力最大值处于轴肩边缘，且前进侧峰值大于后退侧峰值；TIG焊接件残余拉应力最大值处于焊缝边缘。通过中子衍射实验获得的焊接件残余应力分布，将可用于焊接工艺的优化与焊接件的寿命预测。     

仿生聚多巴胺对HMX、TATB和铝粉的界面性能改性

为了研究表面改性方法及表面包覆均匀性、浸润性等性状对含能材料的机械感度、界面力学性能以及工艺性能的影响,仿生贻贝黏附蛋白的作用原理,以多巴胺为前驱体,采用一步法使其在含能材料表面聚合形成一层致密牢固的包覆薄膜聚多巴胺(PDA),制备了改性单质炸药(HMX@PDA、TATB@PDA)和改性铝粉(Al@PDA)。通过扫描电子显微镜、X射线光电子能谱和接触角测试仪对改性含能材料的表面形貌、药柱断裂处微观形貌、元素含量以及表面浸润性能进行了表征,采用国军标(GJB-772A-1997)、巴西实验等标准测试方法对改性含能材料的机械感度、拉伸应力-应变曲线等进行了测试,并将实测性能与未改性含能材料进行了对比分析。结果表明,与HMX晶体比较,HMX@PDA晶体的摩擦感度下降30%,特性落高数值增加一倍;与TATB基药柱比较,TATB@PDA基药柱的拉伸强度提高约15%;与Al粉比较,Al@PDA在HTPB液相中24h后可有效减缓沉降。聚多巴胺对晶体完整致密的包覆性能以及含有丰富活性基团的特性,对含能材料的包覆降感、界面力学性能提升和工艺稳定性提升等方面具有显著的界面改性作用。