Optimizing the milling characteristics of Al-SiC particulate composites

The present investigation focuses on the face milling characteristics of LM25Al-SiC particulate composites produced through stir casting. Experiments were conducted according to an L27 orthogonal array and mathematical models were developed for such machining characteristics as flank wear, specific energy and surface roughness whose adequacy was checked. The insignificant effects present in the models were eliminated using a t-test. Goal programming was employed to optimize the cutting conditions by considering such primary objectives as maximizing the metal removal rate and minimizing tool wear, specific energy and surface roughness.     

HA/Ti composite for biomedical application by mechanical milling

In order to overcome the poor mechanical properties of HA and the low bioactivity of Ti,HA/Ti composites with various compositions were prepared by mechanical milling.The effects of milling condition and the composition on the microstructure,the density and the hardness of the composites were studied.The results show that during the ball milling process.Ti particles are refined and the homogeneity of the HA/Ti mixtures is improved;HA will partially decompose due to the existence of Ti and high sintering temperature.The microstructure of HA/Ti composites is highly dependent on the milling condition and the composition.In the microstructure.Ti phase connects to be a continuous network,and HA/Ti mixtures disperse in the network.The longer the milling time,the finer the network will be.The density of HA/T composites decreases with the content of HA increasing and the milling time prolonging,because HA deteriorates the sinterability of Ti.The hardness of HA/Ti composites increases firstly with the content of HA increasing,and then drops when the content of HA exceeds 30%.Addition of HA will strengthen the HA/T composite but will decrease the density of the composite,which accounts for the effect of HA on the hardness of the composites.     

高能球磨对3%C-Cu粉末压制特性的影响

针对石墨／铜基复合材料存在烧结膨胀的特点，提出用粉末压制、真空热压烧结和热挤压相结合的致密化工艺。为给后续的烧结提供相对密度较高、质量好的冷压坯，采用刚性模常温单向压制方法研究高能球磨3％C—Cu（质量分数）粉末的压制压力与相对密度的关系，用黄培云压制理论考察球磨粉末的压制特性。用扫描电镜和场发射扫描电镜分别研究高能球磨粉末的微观组织和微区成分。结果表明，压制压力相同时，粉末压坯相对密度随高能球磨时间的延长而逐渐减小。高能球磨时间相同时，粉末压坯相对密度随压制压力的增加而增大。随着高能球磨时间的延长，粉末体越来越难压制。压制压力和保压时间分别为700MPa和30s时，所得粉末压坯的质量较好。     

Distribution of SiC particles in semisolid electromagnetic-mechanical stir-casting Al-SiC composite

The distribution of SiC particles in Al-SiC composite can greatly influence the mechanical performances of Al-SiC composite. To realize the homogeneous distribution of SiC particles in stir-casting Al-SiC composite, semisolid stir casting of Al-4.25 vol.%SiC composite was conducted using a special electromagneticmechanical stirring equipment made by our team, in which there are three uniformly-distributed blades with a horizontal tilt angle of 25 ° to mechanically raise the SiC particles by creating an upward movement of slurry under electromagnetic stirring. The microstructure of the as-cast Al-SiC composites was observed by Scanning Electron Mcroscopy(SEM). The volume fraction of SiC particles was measured by image analysis using the Quantimet 520 Image Processing and Analysis System. The tensile strength of the Al-4.25 vol.%SiC composites was measured by tensile testing. Results show that the Al-4.25 vol.%SiC composites with the homogeneous distrbutin of SiC particles can be obtained by the electromagnetic-mechanical stirring casting with the speed of 300 and 600 r·min-1 at 620 °C. The differences between the volume fraction of Si C particles at the top of ingot and that at the bottom are both ~0.04 vol.% with the stirring speed of 300 and 600 r·min-1, which are so small that the distribution of SiC particles can be seen as the homogeneous. The tensile strength of the Al matrix is enhanced by 51.2% due to the uniformly distributed SiC particles. The porosity of the composite mainly results from the solidification shrinkage of slurry and it is less than 0.04 vol.%.     

Effects of SiC volume fraction and aluminum particulate size on interfacial reactions in SiC nanoparticulate reinforced aluminum matrix composites

The SiC nanoparticulate reinforced Al-3.0 wt.% Mg composites were fabricated by combining pressureless infiltration with ball-milling and cold-pressing technology at 700 °C for 2 h. The effects of SiC nanoparticulate volume fractions (6%, 10% and 14%) and Al particulate sizes (38 μm and 74 μm) on interfacial reactions were investigated by SEM, TEM and X-ray diffraction. The results show that the MgO at the interface between SiC nanoparticulate and molten Al can provide a barrier for the diffusion of Si, C and Al. Using Al particulate (74 μm) as raw material, the Al₄C₃ phase was not found in the composites containing 6 vol.% and 10 vol.% SiC, but presented in the composites containing 14 vol.% SiC. When SiC content up to 14 vol.%, the products of MgO around SiC nanoparticulate are not enough to provide effective protection from the reaction between SiC and molten Al, therefore the diffusion of Si, C and Al can take place to produce Al₄C₃ and Si phases. Using 38 μm Al particulate as raw material, the fine Al particulate possesses the high reaction activity and can easily be embedded into the gap among the big Mg particulate segregated at the interface, resulting in the appearance of exposure surface of SiCp to the Al and the forming of diffusion channels for the atomics C, Si and Al. So, the formations of Al₄C₃ and Si phases were occurred.     

Laser shock processing of Al-SiC composite coatings

Laser shock processing (LSP) is a technique of surface treatment (similar to shot peening) in which laser-induced mechanical shocks develop compressive stresses in the material. The stresses are of sufficient intensity to modify microstructure and properties of the coatings. In the present study, laser shocks of power density of 5 to 8 GW/cm² power density, generated by means of a neodymium-glass laser, were used to treat Al + SiC composite coatings deposited by means of a HVOF spraying technique. The laser processed samples were metallographically prepared, and their microstructure was investigated by optical microscope and SEM. The latter was also used to investigate the surface morphology of the laser treated specimens. Finally, the microhardness and oscillating wear resistance of the coatings were tested and compared to data obtained for as-sprayed samples.     

Influence of high-energy ball milling on Al-30Si powder and ceramic particulate

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Nanocomposite formation and size reduction of Terfenol-D particles during mechanical milling

Mechanical milling of Terfenol-D (Tb_0.3Dy_0.7Fe_1.97) was conducted under both dry and wet conditions. Nanoparticles of Terfenol-D were produced by mechanical milling, where Terfenol-D polycrystalline bulk samples were ball milled under argon atmosphere. Size reduction was found to be the main result of the dry mechanical milling. The magnetization and coercivity of the milled sample correlated with the particle size. Different results were obtained when using wet grinding. Nanocomposite of (Dy,Tb)₂O₃–Fe was found to form via the decomposition of (Tb_0.3Dy_0.7Fe_1.97) and the formation of rare earth oxides.     

机械合金化Ti-Al复合粉末的结构及显微形貌(英文)

研究了不同球磨时间内Ti-Al复合粉末显微结构及成分的演变。随着球磨时间的延长,原始粉末的形貌发生了一系列变化,从球磨2h的扁平状变为球磨6h的细小的等轴状。球磨8h后粉末的晶粒尺寸达到纳米级,平均约为17nm。对钛铝复合粉末的演化机理进行了分析。在球磨过程中,铝逐渐融入钛晶格形成钛的固溶体。球磨不同时间的粉末中钛铝反应的起始温度的差热分析表明,机械合金化细化了复合粉末,显著降低了钛、铝反应的起始温度。     

高能球磨制备Ti-50%Al复合粉末的表征(英文)

采用高能球磨法制备了Ti-50%Al(摩尔分数)复合粉末,利用SEM、TEM、HREM、HAADF-STEM分析手段对复合粉末颗粒的表面形貌、结构及组成进行了表征。在球磨过程中钛、铝之间逐渐发生反应并形成无序的Ti/Al相;球磨9h后铝逐渐融入钛中,产生纳米晶钛铝固溶体,同时引起大量高密度位错。合金化后粉末的元素组成接近原始成分,但分布极不均匀。     

Fabrication of SiC particulate reinforced AZ91D composite by vacuum-assisted pressure infiltration technology

The AZ91D Mg matrix composites reinforced by SiC particulate with the sizes of 11 μm, 21 μm and 47 μm were successfully fabricated respectively by vacuum-assisted pressure infiltration technology. Microstructures and particulate distributions were analyzed with scanning electron microscope (SEM), X-ray diffraction (XRD) and transmission electron microscope (TEM). The coefficient of thermal expansion (CTE) measurements was performed from 75 °C to 400 °C at a heating rate of 5 °C/min. The results show that the uniform distribution of SiC particulate in metal matrix and density over 98% in theoretical density of composites were fabricated. Only MgO phase was detected at the interface and no brittle phases of Al₄C₃ and Mg₂Si were discovered. The desirable coefficients of thermal expansion of composites were achieved. The intensity of dislocation generation nearby SiC particulate increases significantly with the increasing of SiC particulate size. Therefore, this technology is a potential method to fabricate Mg matrix composites reinforced by SiC particulates with the desirable microstructures and CTE.     

螺纹铣削的数控加工工艺研究

传统的螺纹加工方法不能满足高效率、高质量的生产要求。该文从螺纹铣刀的类型、螺纹铣削的刀具轨迹和切削参数以及螺纹铣削的编程等方面,分析了螺纹加工的工艺性。通过合理规划生产中一个实例的加工工艺,并在加工中心上加工出该产品且满足了产品的技术要求。由于一次装夹成形,工作效率大大提高。     

机械球磨Ti_(50)Al_(50)复合粉的压制特性

研究了机械球磨Ti50 Al50 复合粉的组织与压制特性。结果表明 ,球磨导致粉末硬度增加 ,压制特性变差 ,这是由于球磨使层片结构细化 ,Ti和Al组元晶体缺陷增加和晶粒细化造成的 ;但球磨 3h形成纳米晶复合粉后 ,尤其是在球磨 7.5h开始发生非晶转变后 ,进一步球磨 ,粉末压制特性变化并不明显     

CNTs含量对CNTs/Al5083复合材料力学性能的影响

利用高能球磨和冷压烧结工艺制备出碳纳米管（CNTs）增强Al5083复合材料,并对球磨过程中CNTs的演变及成型后复合材料的力学性能和形貌进行研究。结果表明,在球磨过程中,通过机械力的作用下带动钢球将CNTs切断,长径比变小,并均匀地分散在Al基体中;在CNTs含量为2wt%下,复合材料抗拉强度和屈服强度分别达到294和239 MPa,硬度达到95 HV5,复合材料的力学性能最好。通过观察复合材料的断口,随着碳纳米管含量的增加,复合材料的断口形貌从韧性断裂向脆性断裂转变。     

Fabrication of Ti-Cu-Ni-Al amorphous alloys by mechanical alloying and mechanical milling

Ti-based amorphous alloy powders were synthesized by the mechanical alloying (MA) of pure elements and the mechanical milling (MM) of intermetallic compounds. The amorphous alloy powders were examined by X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM). Scanning electron micrographs revealed that the vein morphology of these alloy powders shows deformation during the milling. The energy-dispersive X-ray spectral maps confirm that each constituent is uniformly dispersed, including Fe and Cr. The XRD and DSC results showed that the milling time required for amorphization for the MA of pure elements was longer than that of the MM for intermetallic compounds. The activation energy and crystallization temperature of the MA powder are different from those of the MM powder.     

Effect of ball milling process on the microstructure of titanium-nanohydroxyapatite composite powder

Titaninm-nanohydroxyapatite （Ti-nHA） composite powders, composed of titanium with 10 vol.% and 20 vol.% of nano-hydroxyapatite, were milled in a planetary ball mill using alcohol media to avoid excessive heat. XRD and SEM were performed for characterization of the microstructure, and the homogeneity of Ti/HA nanocomposite powder was evaluated by EPMA with prolonged ball milling time. The results show that under the condition of wet milling, the grain size of Ti-nHA composite powders is decreased with the increase in ball milling time and the amount of the addition of nHA. While for milling of 30 h, the nanocomposite powder with free structure, which consists of the nano-hydroxyapatite （nHA） particles and titanium （Ti） phase, is obtained. Three stages of milling can be observed from the dement mapping of Ti, Ca, and P by EPMA; meanwhile, it is found that the nHA would be more homogenously distributed after milling for 30 h.     

Processing and mechanical properties of SiC particulate reinforced AZ91 composites fabricated by stir casting

The influence of stirring parameters （stirring temperature, stirring speed and stirring time） on the particle distribution of 10%（volume fraction） SiC particulate reinforced AZ91 composites （SiCp/AZ91） was studied. It is found that it is necessary for 10μm SiC particulate reinforced AZ91 composites to stir the molten composites in semi-solid condition with vortex formation, or else the cluster of the reinforcements would not be eliminated. Compared with the monolithic alloy, the SiCp/AZ91 composite has higher strength, especially for yield strength, but the elongation is reduced. For the as-cast composite, the particles often segregate within the grain boundary regions. Extrusion can effectively reduce the segregation of SiC particles and improve the mechanical properties of the composite. The extrusion-induced reduction in particle size varies with extrusion temperatures and extrusion ratios. The effect of extrusion-induced reduction in particle size on the mechanical properties of the composites is not always beneficial.     

碳化物/钢基复合材料原料球磨效果及其电子理论分析

对碳化钛、碳化钨/钢基复合材料原料粉体进行了球磨试验和相应粒度变化等的SEM等分析.结果表明:作为硬质相的WC、TiC球磨细化效果最佳;作为基体材料的体心立方金属球磨效果较好(且Mo＞Cr＞Fe),面心立方镍的球磨效果较差,石墨仅初期球磨效果好.运用固体与分子经验电子理论,结合原料单质的键性质和晶体结构特征分析了实验结果,并依据计算得到的价电子结构参数(nA值与η值及键络均衡性)剖析了以上复合材料原料单质球磨行为的差异.     

Amorphization of Al---Cu---Fe quasicrystalline alloys by mechanical milling

The amorphous phase is formed from as-solidified Al---Cu---Fe alloy powder, which is mainly composed of the quasicrystalline phase, by mechanical milling. The structure and morphology of the milled powders were monitored by X-ray diffraction, scanning electron microscopy, and transition electron microscopy respectively. Experimental results indicate that quasicrystalline alloys are more easily amorphized than the corresponding crystalline alloys. No intermediate metastable phase appeared during the whole process. The crystallization behavior of the amorphous powders has been examined by thermal annealing and differential thermal analysis.