粉末冶金法制备SiC_p/2024Al泡沫复合材料的表征(英文)

为了丰富泡沫材料制备工艺、推动其快速发展与广泛应用,以CaCO3为发泡剂采用粉末冶金法制备SiCp/2024Al泡沫复合材料。采用SEM和Magiscan-2A图像分析仪研究了CaCO3发泡剂和SiC颗粒的含量对发泡行为的影响,并且通过Gleeble 1500热模拟机分析了SiC颗粒的含量对压缩性能的影响。结果表明:随着发泡剂的增多,孔隙率和孔径先增加后减小。随着增强体含量的增加,孔隙率和孔径都减小。压缩曲线揭示加入增强体可以改善压缩屈服强度和吸能能力。SiCp/2024Al泡沫复合材料显示为脆性泡沫材料。     

Compressive behavior of SiCp/AlSi9Mg composite foams

Closed-cell AlSi₉Mg foams and SiC_p/AlSi₉Mg composite foams with different SiC_p volume fractions were prepared successfully by means of direct foaming of melt using CaCO₃ blowing agent in this paper. The compressive behaviors of these foams were studied. In comparison with the compressive stress–strain curve of AlSi₉Mg foams that of SiC_p/AlSi₉Mg composite foams is not smooth and exhibits some serrations. At the same relative density of composite foams, the yield stress and collapse stress of the composite foams increase with increasing SiC_p volume fraction. The relationship of yield stress, relative density and SiC_p volume fraction of SiC_p/AlSi₉Mg composite foams with a given particle size was obtained.     

SiO2包覆CaCO3在无保护气氛下制备闭孔泡沫镁（英文）

在熔体发泡法工艺中,发泡剂的分解速度和浸润性直接影响泡沫金属的孔结构和孔隙率。为减缓泡沫镁发泡剂CaCO3的发泡速度并提高与镁熔体的浸润性,采用非均匀形核法,以硅酸钠为原料,盐酸为酸化剂,在CaCO3表面包覆SiO2钝化膜。采用TGA-DTA、XRD、SEM等方法对包覆后CaCO3的热稳定性和包覆层的微观结构进行分析。结果表明:包覆后的CaCO3分解温度提高;包覆层中的SiO2为无定形态;在CaCO3颗粒表面形成网络状结构。对比实验表明:包覆后的CaCO3发泡速度平稳。同时,采用合金化阻燃工艺在无气体保护条件下制备出较大尺寸的泡沫镁试样,并且试样孔径细小,孔结构均匀,孔隙率在60%-70%。     

泡沫镁宏微观结构表征及压缩性能研究

针对熔体发泡法制备泡沫镁存在的困难,使用包覆发泡剂及改进工艺成功制得泡孔均匀的泡沫镁试样。利用OM、SEM、EDS及XRD等分析手段对试样进行宏微观结构表征,结果表明：泡沫镁试样宏观孔以典型的闭孔结构为主,但也存在一些连通孔及少量大孔,它们多是宏观裂纹的产生及扩展位置。泡孔内壁存在一些褶皱缺陷,且弥散分布着许多反应产生的MgO和CaO颗粒,压缩变形过程中,这些部位易产生应力集中,促进微裂纹的形成与扩展。孔壁上主要分布着碳化硅颗粒及生成的Mg2Ca相。测试分析了孔隙率和孔径对泡沫镁压缩力学性能和能量吸收性能的影响,并深入研究其压缩破坏机理,研究发现：随着孔隙率的降低,泡沫镁弹性变形增大,屈服强度升高;随着孔径的增大,泡沫镁屈服强度及平台应力明显减小,表现出显著的孔径效应。随着孔隙率的升高或孔径的增大,泡沫镁的能量吸收性能显著降低。泡沫镁的破坏为解理脆性断裂,这与孔壁组织及镁基体性质有很大的关系。     

胞状AlCu5Mn合金泡沫的压缩性能和能量吸收特性

用熔体发泡法制备孔隙率为51.5%～90.5%、孔结构均匀的胞状铝合金(AlCu5Mn),研究其孔结构、压缩性能、能量吸收能力、能量吸收效率和吸能性能.结果表明:胞状铝合金孔结构由高孔隙率(88.8%)时的大孔径、多边形孔向低孔隙率(62.5%)时的小孔径、球形孔孔结构过渡,其压缩应力(σ)-应变(ε)曲线具有线性变形阶段、屈服平台阶段和致密化阶段三个部分,由线性变形阶段进入屈服平台阶段所对应的ε_s值介于2%～9%之间;屈服强度σ_s~*随着孔隙率的增大而下降,在孔隙率相同的条件下,胞状铝合金的力学性能优于胞状铝和多孔铝合金,其比刚度高于钢;当应变为定值时,胞状铝合金单位体积和单位质量的压缩吸能能力(C和C_m)都随着孔隙率的升高而降低,但是孔隙率在73.5%～82.1%范围内时,其C_m与ε的关系几乎不随孔隙率的改变而改变;对于孔隙率为51.5%～90.5%的胞状铝合金,它们的吸能效率的峰值都大于80%.胞状铝合金的C-σ和C_m-σ关系可以表征其吸能性能,从而可以根据实际工况选择作为减振吸能材料的胞状铝合金的最佳孔结构.     

Production and mechanical properties of nano SiC particle reinforced Ti–6Al–4V matrix composite

Different mass fractions (0, 5%, 10%, and 15%) of the synthesized nano SiC particles reinforced Ti–6Al–4V (Ti64) alloy metal matrix composites (MMCs) were successfully fabricated by the powder metallurgy method. The effects of addition of SiC particle on the mechanical properties of the composites such as hardness and compressive strength were investigated. The optimum density (93.33%) was obtained at the compaction pressure of 6.035 MPa. Scanning electron microscopic (SEM) observations of the microstructures revealed that the wettability and the bonding force were improved in Ti64 alloy/5% nano SiC_p composites. The effect of nano SiC_p content in Ti64 alloy/SiC_p matrix composite on phase formation was investigated by X-ray diffraction. The correlation between mechanical parameter and phase formation was analyzed. The new phase of brittle interfaced reaction formed in the 10% and 15% SiC_p composite specimens and resulted in no beneficial effect on the strength and hardness. The compressive strength and hardness of Ti64 alloy/5% nano SiC_p MMCs showed higher values. Hence, 5% SiC_p can be considered to be the optimal replacement content for the composite.     

SiCp/Al复合材料与Fe36Ni合金超声波钎焊

利用超声波钎焊方法使用ZnAlSi钎料实现了Fe36Ni合金与45%SiC_p/2024Al和55%SiC_p/A356两种复合材料的连接,并得到由SiC颗粒增强的复合焊缝.通过扫描电镜、能谱等方法对焊缝的微观结构以及断口形貌进行了观察,对接头的压剪强度进行了测试,分析了Fe36Ni与两种复合材料钎焊接头微观组织和接头强度的差异.结果表明,在Fe36Ni与两种复合材料的钎缝中,钎料与两侧母材界面均形成良好的冶金结合,SiC颗粒均匀分布于焊缝中.Fe36Ni与45%SiC_p/2024Al的接头抗剪强度为110~145 MPa,Fe36Ni与55%SiC_p/A356的接头抗剪强度为75~85 MPa.Fe36Ni与45%SiC_p/2024Al的接头断裂位置为钎缝中,而Fe36Ni与55%SiC_p/A356的接头断裂位置位于Fe36Ni与钎料的界面上.     

Microstructure and Mechanical Properties of Al356/SiCp Cast Composites Fabricated by a Novel Technique

In this study, SiC_p containing composite powders were used as the reinforcement carrier media for manufacturing cast Al356/5 vol.% SiC_p composites. Untreated SiC_p, milled particulate Al-SiC_p composite powder, and milled particulate Al-SiC_p-Mg composite powder were injected into Al356 melt. The resultant composite slurries were then cast from either a fully liquid state (stir casting) or semisolid state (compocasting). The results revealed that by injection of composite powders, the uniformity of the SiC_p in the Al356 matrix was greatly improved, the particle-free zones in the matrix were disappeared, the SiC particles became smaller, the porosity was decreased, and the matrix microstructure became finer. Compocasting changed the matrix dendritic microstructure to a finer non-dendritic one and also slightly improved the distribution of the SiC_p. Simultaneous utilization of Al-SiC_p-Mg composite powder and compocasting method increased the macro- and micro-hardness, impact energy, bending strength, and bending strain of Al356/SiC_p composite by 35, 63, 20, 20, and 40%, respectively, as compared with those of the composite fabricated by injection of untreated SiC_p and stir casting process.     

The Usability of Boric Acid as an Alternative Foaming Agent on the Fabrication of Al/Al<Subscript>2</Subscript>O<Subscript>3</Subscript> Composite Foams

Pure Al and alumina (2, 5, 10 wt.% Al₂O₃)-added Al composite foams were fabricated through powder metallurgy technique, where boric acid (H₃BO₃) is employed as a new alternative foaming agent. It is aimed to determine the effects of boric acid on the foaming behavior and cellular structure and also purposed to develop the mechanical properties of Al foams by addition of Al₂O₃. Al and Al composite foams with porosity fraction in the range of 46-53% were achieved by sintering at 620 °C for 2 h. Cell morphology was characterized using a combination of stereomicroscope equipped with image analyzer and scanning electron microscopy. Microhardness values were measured via using Vickers indentation technique. Quasi-static compression tests were performed at strain rate of 10^?3 s^?1. Compressive strength and energy absorption of the composite foams enhanced not only by the increasing weight fraction of alumina, but also by the usage of boric acid which leads to formation of boron oxide (B₂O₃) acting as a binder in obtaining dense cell walls. The results revealed that the boric acid has outstanding potential as foaming agent in the fabrication of Al and Al composite foams by providing improved mechanical properties.     

Using ARB process as a solution for dilemma of Si and SiCp distribution in cast Al-Si/SiCp composites

A major challenge in achieving the best potential of SiC_p-reinforced aluminum composites is to homogeneously disperse SiC particles within the aluminum alloys. The presence of coarse Si fibers with non-uniform distribution in cast Al-Si alloys, which may lead to poor mechanical properties, is another important problem that limits the application of these alloys. In order to eliminate these problems, accumulative roll bonding (ARB) process was used in this study as a very effective method for improving the microstructure and mechanical properties of the Al356/SiC_p composite. It was found that when the number of ARB cycles was increased, the uniformity of the Si and SiC_p in the aluminum matrix improved, the Si particles became finer and more spheroidal, the free zones of Si and SiC particles disappeared, the porosity of composite decreased, the bonding quality between SiC_p and matrix improved, and therefore mechanical properties of the composites were improved. The microstructure of the manufactured Al356/SiC_p composite after six ARB cycles indicated a completely modified structure so that its tensile strength and elongation values reached 318 MPa and 5.9%, which were 3.1 and 3.7 times greater than those of the as-cast composite, respectively.     

Fabrication of Al-Mg-Re foams and their corrosion resistance properties

Al-2 wt.% Mg-Re foams with relatively small pore size (∼1 mm) were fabricated by the melt foaming method with the addition of titanium hydride as a blowing agent. The corrosion resistance properties of the Al-Mg-Re foams have been studied and the results compared with those of Al foam and Al-5 wt.% Cu foam. The results show that in order to get Al-Mg-Re alloy foams with good pore structures, Ca and Mg should be added to the pure Al melt before adding the blowing agent; the corrosion resistance properties of Al-Mg-Re foams are better than those of Al foam and Al-Cu foams.     

高强度碳化硅泡沫陶瓷的制备及其抗压强度研究

选用Al2O3、Y2O3作为烧结助剂,通过有机模板复制法及多次浸渍涂覆工艺制备出高强度碳化硅泡沫陶瓷材料。系统地研究了原料组成、烧结温度等工艺参数对制得的碳化硅泡沫陶瓷物相组成、宏观结构、微观结构的影响,同时对陶瓷的气孔率、力学性能等进行了测试。结果表明:通过选取不同PPI值的有机泡沫模板,泡沫陶瓷宏观孔径可控;随着涂覆次数的增加,陶瓷体孔径减小、孔棱直径增加;随着烧结温度的提高,孔棱致密度增加,抗压强度显著提高;在1700℃下获得了20PPI值,气孔率为77%,抗压强度达2.48MPa的碳化硅泡沫陶瓷。     

Deposition of thick TiAlN coatings on 2024 Al/SiCp substrate by Arc ion plating

Aluminum-matrix composites with particulate SiC ceramic reinforcements (Al/SiC_p) have received much attention for space and aircraft propulsion applications. It is imperative to deposit thick hard coatings on these composites for protection. TiAlN coatings with a Ti interlayer were deposited by arc ion plating (AIP) on 2024 Al/SiC_p substrates at various nitrogen flow rates. It was found that when the nitrogen flow rate is increased from 100 sccm to 250 sccm, the deposition rate decreases, the coating hardness increases and the adhesion strength decreases. Based on the above results and the principle of gradient materials, the thick gradient TiAlN coatings with a Ti interlayer were successfully deposited on a 2024 Al/SiC_p substrate to a thickness of 60 μm by continuously increasing the nitrogen flow rate during deposition. Such an achievement can be attributed to the gradient distribution of elements, hardness, and stresses across the coating thickness.     

Microstructures and mechanical properties of Al 2519 matrix composites reinforced with Ti-coated SiC particles

Ti-coated SiC_p particles were developed by vacuum evaporation with Ti to improve the interfacial bonding of SiC_p/Al composites. Ti-coated SiC particles and uncoated SiC particles reinforced Al 2519 matrix composites were prepared by hot pressing, hot extrusion and heat treatment. The influence of Ti coating on microstructure and mechanical properties of the composites was analyzed by scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The results show that the densely deposited Ti coating reacts with SiC particles to form TiC and Ti₅Si₃ phases at the interface. Ti-coated SiC particle reinforced composite exhibits uniformity and compactness compared to the composite reinforced with uncoated SiC particles. The microstructure, relative density and mechanical properties of the composite are significantly improved. When the volume fraction is 15%, the hardness, fracture strain and tensile strength of the SiC_p reinforced Al 2519 composite after Ti plating are optimized, which are HB 138.5, 4.02% and 455 MPa, respectively.     

Effects of foaming parameters on microstructure and compressive properties of aluminum foams produced by powder metallurgy method

Semi open-cell aluminum foams having channels between individual cells were produced using low cost CaCO₃ foaming agent and applying the powder compact melting process. To this end, the aluminum and CaCO₃ powder mixtures were cold compacted into dense cylindrical precursors for foaming at specific temperatures under air atmosphere. The effects of several parameters including precursor compaction pressure, foaming agent content as well as temperature and time of the foaming process on the cell microstructure, linear expansion, relative density and compressive properties were investigated. A uniform distribution of cells with sizes less than 100 μm, which form semi open-cell structures with relative densities in the range of 55.4%–84.4%, was obtained. The elevation of compaction pressure between 127–318 MPa and blowing agent up to 15% (mass fraction) led to an increase in the linear expansion, compressive strength and densification strain. By varying the foaming temperature from 800 to 1000 °C, all of the investigated parameters increased except compressive strength and relative density. The results indicated the optimal foaming temperature and time as 900 °C and 10–25 min, respectively.     

Role of Temperature and SiC<Subscript>P</Subscript> Parameters in Stability and Quality of Al-Si-Mg/SiC Foams

Composites of Al-Si-Mg (A356) alloy with silicon carbide particles were synthesized in-house and foamed by melt processing using titanium hydride as foaming agent. The effects of the SiC_P size and content, and foaming temperature on the stability and quality of the foam were explored. It was observed that the foam stability depended on the foaming temperature alone but not on the particle size or volume percent within the studied ranges. Specifically, foam stability was poor at 670°C. Among the stable foams obtained at 640°C, cell soundness (absence of/low defects, and collapse) was seen to vary depending on the particle size and content; For example, for finer size, lower particle contents were sufficient to obtain sound cell structure. It is possible to determine a foaming process window based on material and process parameters for good expansion, foam stability, and cell structure.     

Fabrication and Wear Behavior of Nanostructured Plasma-Sprayed 6061Al-SiCp Composite Coating

6061Al powder with 15 wt.% SiC particulate (SiC_p) reinforcement was mechanically alloyed (MA) in a high-energy attrition mill. The MA powder was then plasma sprayed onto weathering steel (Cor-Ten A242) substrate using an atmospheric plasma spray process. Results of particle size analysis and scanning electron microscopy show that the addition of SiC particles as the reinforcement influences on the matrix grain size and morphology. XRD studies revealed embedment of SiC_p in the MA-processed composite powder, and nanocrystals in the MA powder and the coating. Microstructural studies showed a uniform distribution of reinforced SiC particles in the coating. The porosity level in the coating was as low as 2% while the coating hardness was increased to 232VHN. The adhesion strength of the coatings was high and this was attributed to higher degree of diffusion at the interface. The wear rate in the coatings was evaluated using a pin-on-disk type tribometer and found to decrease by 50% compared to the 6061Al matrix coating. The wear mechanism in the coating was delamination and oxidative type.     

Wetting of molten Sn-3.5Ag-0.5Cu on Ni-P(-SiC) coatings deposited on high volume faction SiC/Al composite

The wetting of molten Sn-3.5Ag-0.5Cu alloy on the Ni-P(-SiC) coated SiC_p/Al substrates was investigated by electroless Ni plating process, and the microstructures of the coating and the interfacial behavior of wetting systems were analyzed. The SiC particles are evenly distributed in the coating and enveloped with Ni. No reaction layer is observed at the coating/SiC_p/Al composite interfaces. The contact angle increases from ～19° with the Ni-P coating to 29°, 43° and 113° with the corresponding Ni-P-3SiC, Ni-P-6SiC and Ni-P-9SiC coatings, respectively. An interaction layer containing Cu, Ni, Sn and P forms at the Sn-Ag-Cu/Ni-P-(0,3,6)SiC coated SiC_p/Al interfaces, and the Cu-Ni-Sn and Ni-Sn-P phases are detected in the interaction layer. Moreover, the molten Sn-Ag-Cu can penetrate into the Ni-P(-SiC) coatings through the Ni-P/SiC interface and dissolve them to contact the SiC_p/Al substrate.     

Effect of thermal-cooling cycle treatment on thermal expansion behavior of particulate reinforced aluminum matrix composites

Two micron SiC particles with angular and spherical shape and the sub-micron Al2O3 particles with spherical shape were introduced to reinforce 6061 aluminium by squeeze casting technology.Microstructures and effect of thermal-cooling cycle treatment(TCCT) on the thermal expansion behaviors of three composites were investigated.The results show that the composites are free of porosity and SiC/Al2O3 particles are distributed uniformly.Inflections at about 300 °C are observed in coefficient of thermal expansion(CTE) versus temperature curves of two SiCp/Al composites,and this characteristic is not affected by TCCT.The TCCT has significant effect on thermal expansion behavior of SiCp/Al composites and CTE of them after 3 cycles is lower than that of 1 or 5 cycles.However,no inflection is observed in Al2O3p/Al composite,while TCCT has effect on CTE of Al2O3p/Al composite.These results should be due to different relaxation behavior of internal stress in three composites.     

Development of Iron-based Closed-Cell Foams by Powder Forging and Rolling

In the present investigation, an attempt has been made to develop in situ sandwich Fe-based foams using powder forging and rolling. Several metal carbonates are first studied by thermo gravimetric analysis to find out their suitability to be used as foaming agent for iron-based foams. Barium carbonate is found to be the most promising foaming agent among other suitable options studied such as SrCO₃, CaCO₃, MgCO₃, etc. The effects of process parameters such as precursor composition, sintering temperature, foaming temperature and time, and content of foaming agent have been studied. The microstructural characteristics of the sintered precursor have been studied by means of optical and scanning electron microscopy. It was found that a good pore structure can be obtained using 2-3% C in Fe and 3% BaCO₃ as foaming agent and by foaming at around 1350 °C for 3-6 min.