Wear behavior of AI-Si alloy matrix composites reinforced by γ-Al2O3 decomposed from AACH

The Al-Si alloy matrix composite reinforced by γ-Al2O3 particles was produced by adding NH4AlO（OH）HCO3（AACH） into molten Al-Si alloy at 850℃. During stirring γ-Al2O3 particles are formed by the decomposing reaction of AACH. It is found that the γ-Al2O3 particles distribute more uniformly in the matrix by adding AACH than by adding γ-Al2O3 directly. The wear tests show that the volume loss of the unreinforced Al-Si alloy matrix is about 3 times larger than that of the γ-Al2O3 reinforced composites and that of the composites fabricated by adding γ-Al2O3 is larger than that by adding AACH.     

Microstructures and properties of 1.0%Al2O3/Cu composite treated by rolling

The 1.0%Al2O3/Cu （mass fraction） composite was prepared by hot pressing （HP）, then treated by rolling to get a full density. The microstructures and the micro area element distribution of the composite were analyzed by SEM. The density, electric conductivity and tensile strength were also investigated. The experimental results show that the alumina particles are more dispersed and become smaller through a single-pass rolling. The pore existing in the composite is eliminated or closed under the rolling force. The relative density increases from 98.4% to 99.2%. The electric conductivity increases from 88.9%IACS to 91.2%IACS. The tensile strength is increased by 47% from 300 MPa to 440 MPa.     

Microstrucmre and mechanical properties of Al2O3/TiAl composite

Al2O3/TiAl composites were fabricated by PAXD （pressure-assisted exothermic dispersion） method. The effects of Nb205 content on the microstructure and mechanical properties of the composites were investigated. The results show that the ultimate phases of the composite consist of TiAl, Ti3Al, Al2O3 and a small amount of NbA13. SEM reveals that a submicron γ＋（α2/γ） dual phases structure can be presented after sintered at 1 200 ℃, Furthermore, with the increase of Nb205 content, the ratio of TiAl to Ti3Al phase decreases correspondingly, the grains of the corflposites are remarkably refined, and the produced Al2O3 particles are uniformly dispersed. When 6% Nb205 is added, the composite has the best comprehensive properties. It exhibits a Vickers hardness of 4.77 GPa and a bending strength of 642 MPa. Grain-refinement and dispersion-strengthening are the main strengthening mechanisms.     

Internal oxidation thermodynamics and microstructures of Ag-Y alloy

The thermodynamic data of pure Ag and Y were calculated. The phase constitution, composition of micro-region and microstructures of Ag-Y alloy after internal oxidation were investigated by X-ray diffractometry(XRD), energy dispersion spectrometry(EDS) and scanning electron microscopy(SEM). The results show that the internal oxidation behavior of Ag-Y alloy is feasible from the view of thermodynamics. The upper limit of oxygen partial pressure of Ag-Y alloy oxidation is a function of temperature. Two phases (Ag and Y2O3) appear in Ag-Y alloy after the internal oxidation. The surface of Ag-Y alloy is convex because of the volume expansion of oxide in the alloy and the composition of the convex part is Ag. In Ag-Y2O3 sintered bulk Y2O3 particles are distributed inhomogeneously and conglomerated seriously, but they are dispersed uniformly in the Ag matrix after severe plastic deformation.     

Effect of Y203 on microstructure and oxidation of γ-Ni＋γ′-Ni3Al coatings transformed from electrodeposited Ni-Al films at 1 000℃

The electrodeposited Y2O3-dispersed γ-Ni＋γ-Ni3Al coatings on Ni substrates were developed by the conversion of electrodeposited Ni-Al-Y2O3 films with dispersed AI microparticles in Ni matrix into Ni3Al by vacuum annealing at 800 ℃ for 3 h. For comparison, Y2O3-free γ-Ni＋γ＇-Ni3Al coatings with a similar AI content were also prepared by vacuum annealing the electrodeposited microparticle-dispersed composite coatings of Ni-AI under the same condition. SEM and TEM characterizations show that the electrodeposited Y2O3-dispersed γ＋γ＇ coatings exhibit finer grains, a more homogeneous distribution of γ＇, and a narrowed γ＇ phase spacing compared with the electrodeposited Y2O3-free γ-γ＇ coatings. The oxidation at 1 000 ~C shows that the addition of Y2O3 significantly improves the oxidation resistance of the electrodeposited γ＋γ＇coatings. The effect of Y2O3 particles on the microstructure and oxidation behavior of the electrodeposited γ＋y＇ coatings was discussed in detail.     

Effect of Y2O3 on microstructure and oxidation of γ-Ni+γ'-Ni3Al coatings transformed from electrodeposited Ni-Al films at 1 000 ℃

The electrodeposited Y2O3-dispersed γ-Ni γ'-Ni3Al coatings on Ni substrates were developed by the conversion of electrodeposited Ni-Al-Y2O3 films with dispersed Al microparticles in Ni matrix into Ni3Al by vacuum annealing at 800 ℃ for 3 h. For comparison, Y2O3-free (γ-Ni γ'-Ni3Al coatings with a similar Al content were also prepared by vacuum annealing the electrodeposited microparticle-dispersed composite coatings of Ni-Al under the same condition. SEM and TEM characterizations show that the electrodeposited Y2O3-dispersed γ γ' coatings exhibit finer grains, a more homogeneous distribution of γ', and a narrowed γ' phase spacing compared with the electrodeposited Y2O3-free γ γ' coatings. The oxidation at 1 000 ℃ shows that the addition of Y2O3 significantly improves the oxidation resistance of the electrodeposited γ γ'coatings. The effect of Y2O3 particles on the microstructure and oxidation behavior of the electrodeposited γ γ' coatings was discussed in detail.     

Effects of hot rolling on microstructure and properties of a 20 vol. % SiCp／Al composite

A 20 vol.% SiCp/Al composite was fabricated by squeeze casting, of which a new process for fabricating the preform was used by blending Al powder and SiC particulates with average diameters of 10 and 3.5μtm, respectively. The microstructure of the as-cast and the hot-rolled composite was investigated by using TEM, EDS, and SEM, and their tensile properties were measured at room temperature. The results show that the ultimate tensile strength and ultimate elongation of the hot-rolled composite are 80% and 140% higher than those of the as-cast one. The TEM observation result indicates that there are high density of dislocations and dislocation tangles in the hot-rolled composite. Al2O3 layers in the composite resuiting from the surface oxidation of the aluminum powders were damaged to spherical particles during hot rolling. All the results indicate that hot-rolling can improve the mechanical properties of the composite and, therefore, engineering components of the 20 vol.% SiCp/Al composite can be produced by squeeze casting followed by hot-rolling.     

Formation mechanism of intragranular structure in nano-composites

The effect of sintering process and ZrO2 contents on formation of intragranular ZrO2 in Al2O3 matrix was investigated with α-Al2O3 micro-powders and ZrO2 nano-powders as original materials. It is found that the secondphase particles coalesce with the growth of matrix grains during sintering. The process conditions that benefit the growth of matrix grains benefit the formation of intragrains. The formation procedure of intragrains could be described as follows. At first, the particles are driven to agglomerate during densification of the matrix. Some particles move along with the migration of the matrix grain boundaries and tend to further gather， then become intergrains. Those gripped between the matrix grain boundaries become intragrains during the growth of matrix grains.     

Microstructure and mechanical properties of rolled Mg-12Gd-3Y-0.4Zr alloy sheets

The extruded Mg-12Gd-3Y-0.4Zr alloy sheets were rolled from 30 mm to 2.3 mm at 723 K by electric heated rollers,and then different heat treatments were performed to improve their properties.The microstructures and tensile properties of the alloy sheets were investigated,including as-rolled,annealed and T5 treated.The experimental results show that the grains are effectively refined by the rolling process,and the strength of the rolled alloy is greatly enhanced.The annealed alloy exhibits lower strength a...     

Comparison in characterization of composite and sol-gel coating on AZ31 magnesium alloy

An Al2O3 protective coating on magnesium alloy AZ31 was prepared by a repeated direct sol-gel process annealing at 300℃and a composite coating was also deposited using Al2O3 particles dispersed sol followed by phosphating treatment and annealing at 300℃.The morphologies,structures and critical adhesive loads as well as corrosion properties of the coatings were comparatively investigated by scanning electron microscopy(SEM),X-ray diffractometry(XRD),nanoscratch test and electrochemical measurement.The results show that the composite coating has a more uniform,crack-free layer and improved adhesion to the substrate as compared with that of the repeated direct sol-gel coating owing to its lower heat strain.The main phases in both coatings consist ofγ-Al2O3 andδ-Al2O3 derived from annealed alumina sol,and the composite coating has an anticorrosion performance which is superior to that of the repeated direct sol-gel coating.     

高塑高强纳米Al_2O_3-Cu复合材料的组织与性能

利用内氧化法制备出Al2O3弥散强化铜复合材料,通过场发射扫描电子显微镜(FE-SEM)结合X射线衍射等手段,对材料组织结构和性能进行了研究。结果表明:γ-Al2O3弥散相粒子在基体内均匀分布,尺寸约6nm,间距30～50nm;挤压态棒材(φ25mm)经99.8%变形量冷拉拔后,呈现均匀、连续的纤维组织,纤维长宽比大于20,抗拉强度达680MPa;挤压态棒材的电导率87%IACS,软化温度850℃。     

混合稀土对Cu-Al合金薄板内氧化组织和性能的影响

采用内氧化工艺,以工业N2中余氧为氧源,在950℃使Cu-Al-RE合金薄板内氧化成功制备了Al2O3/Cu复合材料,并对其显微硬度、电导率进行测试,用透射电子显微镜(TEM)对内氧化生成相和微观亚结构进行了分析.结果表明,与未添加混合稀土相比,Cu-Al-0.05(Ce+Y)合金950℃×2h内氧化层深度增加了22.8%,表现出明显的稀土催渗作用;TEM分析表明,在铜基体上弥散分布着大量细小均匀的γ-Al2O3颗粒;适晕添加混合稀土改善了合金的导电性,提高了合金的显微硬度,添加0.05%(Ce+Y)的Cu-Al-RE内氧化后综合性能最优.     

机械合金化结合内氧化法制备Al2O3/Cu复合材料

Al2O3/Cu复合材料具有高的强度和高的导电性及优良的抗电弧性能,广泛应用于电子封装材料、电极和电触头材料。采用机械合金化制备亚稳态的Cu-Al-Cu2O合金粉末,经压制成型后,采用新型内氧化工艺进行烧结处理,得到高强度高导电的Cu/Al2O3复合材料。结果表明:机械球磨96h,Al原子已完全固溶于Cu的晶格中。经1183K内氧化处理4h试样组织均匀致密,Al2O3颗粒弥散分布在铜基体上,其硬度高,电导率高。     

Effects of composite scale on high temperature oxidation resistance of Fe-Cr-Ni heat resistant alloy

Fe-Cr-Ni heat resistant alloys with aluminum and silicon addition, alone and in combination, were melted using an intermediate frequency induction furnace with a non-oxidation method. By the oxidation weight gain method, the oxidation resistances of the test alloys were determined at 1,200 ℃ for 500 hours. According to the oxidation weight gains, the oxidation kinetic curves were plotted and the functions were regressed by the least squares method. The results show that the oxidation kinetic curves follow the power function of y = axb (a0,0相似文献   

水热法合成三维纳米氧化铝粉体的研究

以Al(NO3)3为原料,尿素为OH-缓释沉淀剂,采用水热-均匀沉淀法得到了自组装生成的三维"十"字型拟薄水铝石(γ-AlOOH)前驱物。采用XRD、TG-DSC、SEM等方法对产物进行表征,结果表明,该"十"字型微观结构的翼长及长度约50nm,在该三维结构形成过程中,尿素作为OH-缓释剂起决定性作用。前驱物在550℃焙烧2h后得到的γ-Al2O3保持了该三维"十"字微观结构,其表面积为230 m2/g、平均粒径为6nm,对温度、时间、尿素投料比例等影响因素进行了探讨。     

Reaction thermodynamics and kinetics on in-situ Al2O3/Cu composites

１　ＩＮＴＲＯＤＵＣＴＩＯＮＰｕｒｅｃｏｐｐｅｒａｎｄｉｔｓａｌｌｏｙｓｈａｖｅｇｏｏｄｅｌｅｃｔｒｉｃａｌａｎｄｈｅａｔｃｏｎｄｕｃｔｉｖｉｔｙａｎｄｐｏｏｒｍｅｃｈａｎｉｃａｌｐｒｏｐｅｒｔｉｅｓｓｏｔｈａｔｔｈｅｙｃａｎｎｏｔｏｆｔｅｎｍｅｅｔｔｈｅｎｅｅｄｓｏｆｍｏｄｅｒｎｉｎｄｕｓｔｒｙ．Ｉｎｔｈｅｃｏｎｄｉｔｉｏｎｏｆｋｅｅｐｉｎｇｈｉｇｈｃｏｎｄｕｃｔｉｖｉｔｙ,ｈｏｗｔｏｉｍｐｒｏｖｅｔｈｅｍｅｃｈａｎｉｃａｌｐｒｏｐｅｒｔｉｅｓ,ｅｓｐｅｃｉａｌｌｙｈｏｔｓｔｒｅｎｇｔｈａｎ…     

纳米γ-Al2O3的溶胶-凝胶法制备及表征

异丙醇铝为先驱体,异丙醇为溶剂,乙酰乙酸乙酯为螯合剂,聚乙二醇(PEG1000)为分散剂,硝酸为胶溶剂,采用溶胶-凝胶法制备了纳米γ-Al2O3.并采用DTA/TG,XRD,TEM等测试技术对纳米γ-Al2O3粉体进行表征.结果表明,通过溶剂、螯合剂、分散剂和胶溶剂的协同效应,在750℃煅烧条件下,γ-Al2O3粒子形貌为针状结构,长度为20～30 nm;在900℃煅烧条件下,γ-Al2O3粒子形貌为颗粒状,平均晶粒尺寸为10 nm左右;纳米γ-Al2O3粒子尺寸均一、分散性良好.     

纳米Al2O3-40％TlO2复相陶瓷颗粒增强镍基合金复合涂层的摩擦学性能

运用等离子喷涂技术在7005铝合金表面制备Al2O3-40%TiO2纳米结构颗粒增强镍基合金复合涂层,分析其微观结构,研究其在不同载荷和速度条件下的摩擦磨损性能。结果表明：复合涂层主要由γ-Ni、α-Al2O3、γ-Al2O3和金红石型-TiO2等相组成,其摩擦因数和磨损失重较镍基合金涂层显著降低。在轻载3 N 时,复合涂层磨损表面的接触应力较低,主要发生微观切削磨损;当载荷上升至6~12 N时,接触应力高于磨损表面的弹性极限应力,复合涂层的磨损机理变为多次塑变磨损、微观脆性断裂磨损和磨粒磨损。随着速度的增大,磨损表面的接触温度逐渐升高,复合涂层以多次塑变磨损、疲劳磨损和粘着磨损为主。     

Cu-Al合金内氧化产物及其体积分数的测定

利用萃取方法研究了Cu-Al合金的内氧化产物及其晶 体结构,测定了Al2O3的体积分数.分析表明该方法简单、有效,既可用于内氧化的动 力学研究,又可利用其进行定性定量分析,本实验条件下Cu-Al2O3复合材料的增强体以 晶内纳米γ-Al2O3为主,含有一定量的界面θ-Al2O3和α-Al2O3.