搅拌铸造SiCp/2024复合材料热挤压-轧制变形组织及性能

利用搅拌铸造-热挤压-轧制工艺制备SiCp/2024复合材料薄板。通过金相观察(OM)、扫描电镜(SEM)及力学测试等手段研究了该复合材料在铸态、热挤压态及轧制态下的显微组织及力学性能,分析了材料在塑性变形过程中显微组织及力学性能的演变。结果表明,该复合材料铸坯主要由80～100μm的等轴晶组成,粗大的晶界第二相呈非连续状分布,SiC颗粒较均匀地分布于合金基体中;热挤压变形后,晶粒沿挤压方向被拉长,SiC颗粒及破碎的第二相呈流线分布特征;轧制变形后,基体合金组织进一步细化,晶粒尺寸为30～40μm,SiC颗粒破碎明显,颗粒分布趋于均匀,轧制变形对挤压过程中形成的SiC颗粒层带状不均匀组织有显著的改善作用。数学概率统计指出,塑性变形有利于提高颗粒分布的均匀性。力学测试表明,塑性变形后,复合材料的抗拉强度、屈服强度和延伸率显著提高。SiCp/2024铝基复合材料主要的断裂方式为:合金基体的延性断裂、SiC颗粒断裂及SiC/Al界面脱粘。     

多重结构Ti-B4C/Al2024复合材料的组织和力学性能

为了研究多重结构对铝基复合材料力学性能的影响,将气雾化态Al2024合金粉末与球磨不同时间的Ti-10%(质量分数,下同)B_4C复合粉末混合,采用热压烧结和热挤压的方法制备多重结构Ti-B_4C/Al2024复合材料。通过X射线衍射(XRD)、扫描电镜(SEM)、透射电镜(TEM)和拉伸试验机对不同材料的显微组织与力学性能进行观察和测试,并对多重结构复合材料的强韧化行为进行讨论。结果表明:Ti-B_4C/Al2024复合材料多重结构包括基体Al2024、核壳结构Ti/Al₁₈Ti_2Mg_3组织和B_4C颗粒。向Al2024中加入5%预先球磨6h后的Ti-B_4C粉末时,其屈服强度从107MPa提高到122MPa,并且表现出与热挤压Al2024合金几乎相同的伸长率。当球磨时间延长至12h时,试样5TB-12h的伸长率可达到16.4%。然而,复合材料的伸长率随着Ti-B_4C添加量的增加而降低。     

双屏蔽(B4C-W)/6061Al层状复合板设计与性能

基于B₄C和W良好的屏蔽中子和γ射线性能,采用6061铝合金作为基体,设计了一种新型双屏蔽(B₄C-W)/6061Al层状复合材料,通过放电等离子烧结后加热轧制成板材,对制备的复合材料微观组织和力学性能进行了研究。结果表明,屏蔽组元B₄C和W颗粒均匀地分布在6061Al基体中,层界面、B₄C/Al、W/Al异质界面之间结合良好,无空隙和裂纹。在颗粒与基体界面处形成扩散层,扩散层的厚度约为6 μm (W/Al)和4 μm (W/Al)。轧制态的(B₄C-W)/6061Al层状复合板的屈服强度(109 MPa)和极限抗拉强度(245 MPa)明显优于烧结态的复合材料,但断裂韧性降低。强度提高的原因主要是轧制后颗粒的二次分布、均匀性及界面结合强度提高,基体合金的晶粒尺寸减小,位错密度增加。层状复合板的断裂方式为基体合金的韧性断裂和颗粒的脆性断裂。      

Enhancement of mechanical properties of aluminium/epoxy composites with silane functionalization of aluminium powder

In this study, the effect of surface modification of aluminum powders on the tensile, fracture, and tribological behaviors of aluminum/epoxy composites was investigated. Aluminum powders were surface-modified with 3-aminopropyltriethoxysilane. Aluminium/epoxy composites were fabricated by cast molding method using 10 wt.% untreated and silane-treated aluminium powders. Tensile, mode I fracture, and tribological tests were performed on both composites. The results showed that the tensile modulus and strength of silane-treated aluminum/epoxy composites were ～9% and ～12% greater, respectively than those of untreated aluminum/epoxy composites. The results also showed that the fracture toughness and wear resistance of silane-treated aluminum/epoxy composites were ～32% and ～56% greater than that of untreated aluminum/epoxy composites. Scanning electron microscope (SEM) examination showed the improvement of tensile and fracture properties of silane-treated aluminum/epoxy composites was attributed to the improved dispersion and bonding of aluminum particles in the epoxy, due to the silanization of aluminium powders.     

Formation of Al3Ti/Mg composite by powder metallurgy of Mg–Al–Ti system

Abstract

An in situ titanium trialuminide (Al₃Ti)-particle-reinforced magnesium matrix composite has been successfully fabricated by the powder metallurgy of a Mg–Al–Ti system. The reaction processes and formation mechanism for synthesizing the composite were studied by differential scanning calorimetry (DSC), x-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy-dispersive x-ray spectroscopy (EDS). Al₃Ti particles are found to be synthesized in situ in the Mg alloy matrix. During the reaction sintering of the Mg–Al–Ti system, Al₃Ti particles are formed through the reaction of liquid Al with as-dissolved Ti around the Ti particles. The formed intermetallic particles accumulate at the original sites of the Ti particles. As sintering time increases, the accumulated intermetallic particles disperse and reach a relatively homogeneous distribution in the matrix. It is found that the reaction process of the Mg–Al–Ti system is almost the same as that of the Al–Ti system. Mg also acts as a catalytic agent and a diluent in the reactions and shifts the reactions of Al and Ti to lower temperatures. An additional amount of Al is required for eliminating residual Ti and solid-solution strengthening of the Mg matrix.     

Effect of Al(OH)<Subscript>3</Subscript> Particle Fraction on Mechanical Properties of Particle-Reinforced Composites Using Unsaturated Polyester as Matrix

The effect of particle fraction on mechanical properties of particle-reinforced composites was studied using tensile and hardness testing. Unsaturated polyester (UP) was used as polymer matrix, and aluminum hydroxide as the reinforcing particles. The fracture morphology of tensile samples was observed by scanning electron microscopy (SEM). The results showed that the tensile strength and absorbed energy increased to a maximum at 10% particle content and then decreased. With increasing content of aluminum hydroxide, the elastic modulus increased, and the fracture elongation decreased. The SEM showed that the failure of the Al(OH)₃/UP composites was one of macroscopically brittle fracture. In addition, the study showed that appropriate amount of filler can enhance the surface hardness of Al(OH)₃/UP composite.     

粉末热压成形工艺对WCp/2024Al复合材料力学性能的影响

采用真空热压方法制备了WC颗粒增强2024铝基复合材料(WCp/2024Al),并利用XRD,SEM,拉伸性能测试等检测手段研究了复合材料的热压温度和WC颗粒尺寸对WCp/2024Al复合材料力学性能的影响.结果表明,热压温度是控制复合材料发生界面反应的关键因素之一,并且界面反应所生成的反应产物导致复合材料的强度和塑性...     

Y2O3表面改性Al2O3P增强6061Al复合材料组织与性能

采用液相包裹法对Al₂O₃微粉进行稀土Y₂O₃表面改性,用挤压铸造法制备表面经稀土Y₂O₃改性的Al₂O_3P/6061Al复合材料,并对复合材料的显微组织及拉伸性能进行分析和研究。结果表明:表面经稀土Y₂O₃改性的Al₂O₃微粉能均匀的分布于基体中,界面润湿性得以改善,复合材料组织更加均匀。TEM观察表明:改性粉体在制备复合材料前后表面存在颗粒状包裹层。对其表面进行EDAX分析,结果显示含有Y,Al和O元素。粉体XRD图谱中有Y₂O₃衍射峰的存在。拉伸性能测试表明:改性粉体对Al合金增强效果明显增加,抗拉强度提高29.8％,屈服强度提高38.4％,延伸率提高10.3％。对拉伸断口进行SEM分析,改性后复合材料断口韧窝更加均匀、丰满,材料表现出良好的塑性。     

Studies on the fracture and flexural strength of Al/Sip composite

Pure aluminum matrix composite reinforced with a high volume fraction of silicon particles (Al/Si_p) was fabricated by gas-pressured infiltration. The results of four point flexural strength tests show that Al/Si_p has low flexural strength. The analysis of the fractograph reveals the fracture mechanism of Al/Si_p. The fracture of Al/Si_p is primarily dominated by the fracture of brittle silicon particles and the subsequent link up of damage through the matrix. The pre-existent microcracks in silicon particles that were made during the process of compacting will also lower the flexural strength of Al/Si_p composite. The hybrid particle reinforced pure aluminum matrix composite (Al/Si_p+SiC_p) was fabricated in the same way. Results show the flexural strength can be improved by 11.3% compared with Al/Si_p when 6 vol.% silicon particles are replaced by silicon carbide particles with the same volume fraction and size. The reason is that SiC_p with higher fracture stress and higher elastic modulus can prevent the rapid expansion of cracks through the composite and lower the stress in silicon particles.     

Fabrication of AA6061/Al2O3p composites from elemental and alloy powders

The tensile properties and microstructures of AA6061/Al₂O_3p composites fabricated by the pressureless infiltration method under a nitrogen atmosphere were examined. Since the spontaneous infiltration of molten metal into elemental powders bed as well as alloy powders bed occurred at 700°C for 1 hour under a nitrogen atmosphere, it was possible to fabricate 6061 Al matrix composite reinforced with Al₂O_3p irrespective of the type of metal powders. Both MgAl₂O₄ and MgO were formed at interfaces between Al₂O₃ and the matrix. In addition, MgAl₂O₄ was formed at within the matrix by in situ reaction during composite fabrication. Fine AlN was formed by in situ reaction in both composites. A significant strengthening in the composites occurred due to the formation ofin situ AlN particle and addition of Al₂O₃ particles, as compared to the commercial alloy, while tensile properties in the both elemental and alloy powders composites showed similar trend.     

In situ TiC particles reinforced Ti6Al4V matrix composite with a network reinforcement architecture

TiC particles reinforced Ti6Al4V (TiCp/Ti6Al4V) composite with a network TiCp distribution has been successfully fabricated by reaction hot pressing of coarse Ti6Al4V particles and fine carbon powders. TiC particles are in situ synthesized around the boundaries of the Ti6Al4V particles, and subsequently formed into a TiCp network structure. Contrary to the typical Widmanstätten microstructure for the monolithic Ti6Al4V alloy, an equiaxed (α + β) microstructure for the Ti6Al4V matrix of the composite is formed. This is due to the isotropic tensile stress generated by the network TiCp structure and the mismatch of coefficients of thermal expansion (CTE) during the phase transformation. The prepared composite exhibits superior compressive strength before and after heat-treatment due to the reinforcement network architecture and the relatively large matrix region with an equiaxed microstructure.     

A study of damage under tensile loading in a new Al-Si-Fe alloy processed by the Osprey route

The mode of damage in tension of a new Al-Si-Fe alloy made by spray deposition was studied. This alloy has a composite type structure composed of silicon and intermetallic particles in an aluminium matrix. In situ tensile tests in the SEM, with gold microgrids deposited on the surface of the specimen as an indicator of local plastic strains, provide us with a better understanding of the damage process from crack initiation to fracture. In the T4 temper, the first cracks appear in silicon particles; they initiate shearings and/or decohesions in the matrix, which develop along grain boundaries. Just before the brittle failure of the sample, the generalized microcracking involves both silicon-particle cracking and grain-boundary decohesions.     

Study on graphite fiber and Ti particle reinforced Al composite

Graphite fiber and Ti particle-reinforced aluminum matrix composite were produced by squeeze casting technology. A small amount of needle aluminum carbide at graphite fiber and Al interface was observed, and TiAl₃ intermetallic compound at Ti particle and Al interface was detected. Tensile strength and bending strength of the composite have been measured. The fracture surface of the composite after tensile and bending tests was observed; graphite fiber-reinforced Al was brittle fracture, whereas Ti particle-reinforced Al was ductile fracture. The corresponding fracture mechanism was discussed.     

Evolution of manufacturing parameters in Al/Ni3Al composite powder formation using blending and mechanical milling processes

Aluminu–matrix composites produced by Ni₃Al intermetallic particles are increasingly used in aerospace and structural applications because of their outstanding properties. In manufacturing of metal–matrix composites using powder metallurgy blending and milling are important factors. They control the final distribution of reinforcement particles and porosity in green compacts which in turn, strongly affect the mechanical properties of the produced PM materials. This paper studies different conditions for producing composite powders with uniform dispersion of Ni₃Al particles in aluminum powders and improved physical and mechanical properties. The results indicated that an intermediate milling time for fabrication of composite powder, better than prolonged and shortened ones, causes better microstructure and properties. It was shown that addition of 5 vol.% Ni₃Al particles, produced by 15 h mechanical alloying to aluminum powders, and then 12 h blending operation provides an appropriate condition for producing Al–Ni₃Al composite powder.     

Capability of mechanical alloying and SPS technique to develop nanostructured high Cr,Al alloyed ODS steels

Abstract

Oxide dispersion strengthened (ODS) Fe alloys were produced by mechanical alloying (MA) with the aim of developing a nanostructured powder. The milled powders were consolidated by spark plasma sintering (SPS). Two prealloyed high chromium stainless steels (Fe–14Cr–5Al–3W) and (Fe–20Cr–5Al+3W) with additions of Y₂O₃ and Ti powders are densified to evaluate the influence of the powder composition on mechanical properties. The microstructure was characterised by scanning electron microscope (SEM) and electron backscattering diffraction (EBSD) was used to analyse grain orientation, grain boundary geometries and distribution grain size. Transmission electron microscopy (TEM) and scanning transmission electron microscopy (STEM) equipped with energy dispersive X-ray spectrometer (EDX) were used to observe the nanostructure of ODS alloys and especially to observe and analyse the nanoprecipitates. Vickers microhardness and tensile tests (in situ and ex situ) have been performed on the ODS alloys developed in this work.     

Microstructure and Tensile Properties of Yttria Coated-Alumina Particulates Reinforced Aluminum Matrix Composites

The liquid-phase coating method was used to deposit Y2O3 ceramic on the surface of α-Al2O3. The coated-Al2O3p/6061AI composites were produced using squeeze casting technology. The microstructure and tensile properties of the composites were analysed and studied. The results showed that the coated AI2O3 particles are able to disperse homogeneously in the aluminum liquid. The microstructure of the composites is more even in comparison with that of as-received powders. The tensile testing indicated that mechanical properties of the coated-AI2O3p/6061AI composites are better than those of uncoated particles. In the composite with 30% volume fraction, the tensile strength, yield strength as well as elongation is increased by 29.8%, 38.4% and 10.3%, respectively. The SEM analysis of fracture indicated that the dimples of the coated-Al2O3p/6061Al composites are more even.     

Fabrication of Al2O3–20 vol.% Al nanocomposite powders using high energy milling and their sinterability

In this study, alumina-based matrix nanocomposite powders reinforced with Al particles were fabricated and investigated. The sinterability of the prepared nanocomposite powder at different firing temperature was also conducted. Their mechanical properties in terms of hardness and toughness were tested. Alumina and aluminum powder mixtures were milled in a planetary ball mill for various times up to 30 h in order to produce Al₂O₃–20% Al nanocomposite. The phase composition, morphological and microstructural changes during mechanical milling of the nanocomposite particles were characterized by X-ray diffraction (XRD), transmission electron microscope (TEM), scanning electron microscope (SEM) techniques, respectively. The crystallite size and internal strain were evaluated by XRD patterns using Scherrer methods.A uniform distribution of the Al reinforcement in the Al₂O₃ matrix was successfully obtained after milling the powders. The results revealed that there was no any sign of phase changes during the milling. The crystal size decreased with the prolongation of milling times, while the internal strain increased. A simple model is presented to illustrate the mechanical alloying of a ductile–brittle component system. A competition between the cold welding mechanism and the fracturing mechanism were found during powder milling and finally the above two mechanisms reached an equilibrium. The maximum relative density was obtained at 1500 °C. The harness of the sintered composite was decreased while the fracture toughness was improved after addition Al into alumina.     

挤压后SiC_P／Al─1．45wt％Cu金属基复合材料的微断裂机理

从粉末法ＳｉＣ_Ｐ／Ａｌ－１．４５ｗｔ％Ｃｕ复合材料原位单轴拉伸变形过程的扫描电镜动态观察入手，研究在拉伸载荷下复合材料的变形和微断裂机理。发现裂纹在强化相与基体的界面上形成，并引起界面分离。随应力增加，在许多更小ＳｉＣ粒子与基体的界面上裂纹张开位移明显增加。最终断裂由多重裂纹扩展和局部化裂纹聚结引起。ＳｉＣ粒子加入将增强对基体塑性的约束。这将抑止裂纹在基体中的扩展，特别是最终断裂前局部化裂纹的聚结。建议进一步的工作应同断裂前材料组织中微损失积累分析相联系。     

Microstructure and mechanical properties of hot extruded 6016 aluminum alloy/graphite composites

The incorporation of graphite particles into AA6016 aluminum alloy matrix to fabricate metal/ceramic composites is still a great challenge and various parameters should be considered. In this study, dense AA6016 aluminum alloy/(0-20 wt%) graphite composites have successfully been fabricated by powder metallurgy process. At first, the mixed aluminum and graphite powders were cold compacted at 200 MPa and then sintered at 500 ℃ for 1 h followed by hot extrusion at 450 ℃. The influence of ceramic phases(free graphite and in-situ formed carbides) on microstructure, physical and mechanical properties of the produced composites were finally investigated. The results show that the fabricated composites have a relative density of over 98%. SEM observations indicate that the graphite has a good dispersion in the alloy matrix even at high graphite content. Hardness of all the produced composites was higher than that of aluminum alloy matrix. No cracks were observed at strain less than 23% for all hot extruded materials.Compressive strength, reduction in height, ultimate tensile stress, fracture stress, yield stress, and fracture strain of all Al/graphite composites were determined by high precision second order equations. Both compressive and ultimate tensile strengths have been correlated to microstructure constituents with focusing on the in-situ formed ceramic phases, silicon carbide(SiC) and aluminum carbide(Al_4 C_3). The ductile fracture mode of the produced composites became less dominant with increasing free graphite content and in-situ formed carbides. Wear resistance of Al/graphite composites was increased with increasing graphite content. Aluminum/20 wt% graphite composite exhibited superior wear resistance over that of AA6016 aluminum alloy.     

Mechanism of in situ formation of AlN in Al melt using nitrogen gas

In situ processing of AlN particle reinforced aluminum composites was investigated using a gas bubbling method with nitrogen gas as the gaseous precursor and pure aluminum as the starting matrix in the temperature range of 1173–1573 K. The products were characterized using XRD, SEM, and EDS techniques. Experimental results showed that it is feasible to synthesize AlN particle reinforced Al composites in situ using purified nitrogen gas. Significant AlN was synthesized by bubbling deoxidized N₂ through Al melt. The AlN particles synthesized in situ were small in size (<10 m) and were enriched in the top part of the product formed in the crucible. Directly bubbling commercial purity nitrogen gas did not lead to formation of significant AlN due to the deleterious effect of the trace oxygen impurities in the bubbling gas. The deleterious effect of trace oxygen impurities on the mechanism of formation of AlN in the Al-N system was critically analyzed from both thermodynamic and kinetic points of view. Chemisorption of O₂ molecules at the gas bubble-Al melt interface is more favorable and much faster than that of N₂, thereby inhibiting chemisorption of N₂ molecules. Significant AlN can be formed only at the content of oxygen below a critical value in the N₂ bubbling gas.