闭孔泡沫Mg2Si/Al复合材料的制备及压缩性能研究

采用熔体发泡法,以原位自生Mg2Si/Al复合材料为基体,CaCO3作发泡剂,通过控制温度和搅拌参数,成功制备出不同密度的闭孔泡沫铝。通过静态压缩性能试验发现:泡沫Mg2Si/Al复合材料的压缩过程具备泡沫金属压缩变形的三阶段(弹性变形、应力平台区、致密化阶段)特征;压缩屈服强度和平台应力均随密度增加而增大;屈服点附近应力值下降,应力平台区出现锯齿波形,暴露出孔壁的脆性破裂特征。经过人工时效热处理,泡沫Mg2Si/Al复合材料的屈服强度显著增大。通过观察孔壁的微观组织发现,Al基体被孔壁中粗大的Al+Mg2Si伪共晶组织所割裂。     

Al/Al2O3复合材料伪半固态触变模锻成形

在粉末成形的基础上,结合金属半固态加工技术提出了金属/陶瓷复合材料伪半固态触变模锻成形工艺,并成功制备出 Al/Al₂O₃复合材料杯形件。微观组织观察及力学性能分析表明制件微观组织致密、力学性能优异。当铝体积分数增加到37%时,不同成形压力下复合材料制件抗弯强度可达430~690 MPa,断裂韧性达8.5~16.8 MPa·m1/2,与原位反应及高温氧化工艺相比抗弯强度及断裂韧性大幅度提高。同时分析了成形温度、成形压力等工艺参数对制件性能的影响。研究结果证明采用该工艺成形金属/陶瓷复合材料是可行的。     

B4C增强Al基复合材料的研究进展

综述了当前B4C增强Al基复合材料的研究现状,通过对比不同制备工艺所得复合材料的拉伸强度、硬度、耐磨性能和延伸率等力学性能,总结了粉末冶金法、高能球磨法、无压渗透法、搅拌铸造法以及其他制备技术的优缺点,提出复合材料制备过程中存在的问题及解决方法;此外还介绍了B4C的强化机制;并对B4C增强Al基复合材料未来发展方向和研究重点进行了展望。     

离心铸造Mg2Si 和Si 自生增强锌基复合材料的组织与性能

采用热模金属型工艺, 离心铸造Zn-27Al-9.8Mg-5.2Si 和Zn-27Al-6.3Mg-3.7Si 合金, 获得了内层聚集大量块状初生Mg₂Si 、少量初生Si, 中层不含初生Mg₂Si 和初生Si, 外层含有初生Mg- Si 和初生Si 的自生锌基复合材料。离心铸造Zn-27Al-3.2Mg-1.8Si 合金, 获得了不含初生Mg₂Si 和初生Si 的单层材料。考察了复合材料的组织形貌, 检测了复合材料的硬度和耐磨性, 分析了复合材料的断裂模式。结果表明: 复合材料的内层因聚集大量的初生Mg₂Si 和初生Si 具有较高的硬度和较优的耐磨性。复合材料的断裂方式为脆性断裂, 含共晶Mg₂Si 和共晶Si 的中层在断裂中比含块状初生Mg₂Si 和初生Si 的内层经历了更多的塑性变形。      

Al2O3/Al复合材料氧化生长的动力学研究

通过热重分析实验,研究了Al-Mg-Si合金熔体在高温空气气氛中直接氧化的孕育期与工艺温度及母合金中Mg、Si含量的关系,摸清了铝合金本体氧化的表观活化能与母合金Mg、Si含量的关系,证实了Al-Mg-Si合金直接氧化过程符合Arrhenius公式.     

原位内生Al/M g2Si/S i 复合材料铸态组织研究

利用普通重力铸造方法, 制备了原位内生A l/Mg₂Si/S i 复合材料。研究了体系中加入过量Si 后的显微组织, 并利用Al-Mg₂Si-Si 三元相图进行分析。结果表明, 过量Si 使复合材料中的大长径比的Al+ Mg₂Si 二元共晶向小长径比的Al+ Mg₂Si+ Si 三元共晶转化, 并使α-Al 以球状晶粒析出, 从而改善了显微组织, 显著提高了复合材料的室温拉伸性能。      

(Mg2B2O5w+ND)/ZK60镁基复合材料的摩擦磨损性能研究

在湿球磨条件下以600 r/min高能球磨混粉,并将球磨后的粉末经过热压烧结-热挤压成型制备(Mg2B2O5w+ND)/ZK60镁基复合材料。研究了(Mg2B2O5w+ND)/ZK60镁基复合材料在不同载荷和转速下的干摩擦磨损性能。结果表明:干摩擦条件下,材料的摩擦系数随着滑动距离的增加会经历跑和阶段和稳定阶段;材料的质量磨损率随着转速的增大而降低,随着载荷的增大而增大,且基体镁合金的质量磨损率始终低于复合材料。随着摩擦载荷和转速的增加,材料的摩擦系数减小,然后逐渐趋于平稳。混杂增强的镁基复合材料相比基体合金具有更低的摩擦系数。     

纳米Al2O3颗粒增强新型铜基自润滑复合材料

以Cu-Ni-Y₂O₃-MoS₂-Graphite混合粉为基体,加入质量分数分别为0%、1%、2%、3%、4%的纳米Al₂O₃增强相,采用粉末冶金方法制备纳米Al₂O₃增强新型铜基自润滑复合材料。结果表明：随着铜合金粉末中纳米Al₂O₃颗粒含量的增加 , 所制备自润滑复合材料样品的密度下降,但硬度和压溃强度先上升后下降,在Al₂O₃含量为2%时硬度从HV 23.7增加到HV 35.1,压溃强度从189 MPa提高到276 MPa。由石墨和MoS₂组成的混合固体自润滑材料的摩擦系数小且稳定,约0.12。Al₂O₃质量分数为2%的样品磨损量最小,是未加Al₂O₃试样磨损量的1/7～1/8。铜基体经过镍、纳米Al₂O₃等弥散颗粒强化和固体润滑相石墨和MoS₂的加入,所制备的材料已具有一定的自润滑性能。     

Al2O3-SiO2纤维增强ZL108合金复合材料的强度特性

用低成本的Al₂O₃-SiO₂系纤维作为增强相,通过加压铸造法制作ZL108合金复合材料,并对该复合材料和ZL108合金进行不同温度下的时效处理和压缩试验。通过DSC、EPMA和TEM分析认为:经488K、0.5h时效处理(T6处理)的V_f 20%的复合材料在573K以下的压缩屈服强度低于ZL108合金,是由于基体中的Mg与Al₂O₃-SiO₂纤维在加压铸造过程中起化学反应而生成MgAl₂O₄,损耗了基体中的大量Mg,导致基体铝合金时效硬化效果很差,所以压缩屈服强度低下。623K、720h保温后的V_f 20%的复合材料的压缩屈服强度比ZL108合金要高得多,是由于在这种温度环境下对ZL108合金来说是过时效,所以纤维的增强怍用显得明显。在高温(673K)下V_f 20%的复合材料的屈服强度比ZL108台金高一倍左右。不论在什么温度场合下V_f5%的复合材料的屈服强度比V_f 20%的复合材料都低。     

Al2O3颗粒增强纯铝基复合材料的研究

本文探讨了用粉末冶金法,采用常规的冶金加工设备和工艺,制造Al₂O₃颗粒增强纯铝基复合材料的可行性。研究了不同Al₂O₃体积含量复合材料的显微组织及力学性能。初步试验了二次热挤压变形对颗粒分布和对基体强化的影响。结果表明,Al₂O₃颗粒与纯铝粉混合,加压烧结制备的复合材料,组织致密,颗粒分布均匀,随Al₂O₃含量增加,复合材料强度、硬度及弹性模量大大提高,Al₂O₃含量小于10%时,塑性不降低。二次热挤压有助于提高颗粒分布的均匀性;并使基体显著强化。     

钠钙玻璃上Mg2Si薄膜的制备及其电学性质

采用磁控溅射技术和退火工艺在钠钙玻璃衬底上制备了Mg_2Si半导体薄膜,研究了Mg膜厚度对Mg_2Si薄膜结构及其电学性质的影响。在钠钙玻璃上分别溅射两组相同厚度(175nm)的P-Si和N-Si膜,然后在其上溅射不同厚度Mg膜(240nm、256nm、272nm、288nm、304nm),低真空退火4h制备一系列Mg_2Si半导体薄膜。通过X射线衍射仪(XRD)、扫描电子显微镜(SEM)、霍尔效应测试仪对Mg_2Si薄膜的晶体结构、表面形貌、电学性质进行表征与分析。结果表明:采用磁控溅射技术在钠钙玻璃衬底上成功制备出以Mg_2Si(220)为主的Mg_2Si薄膜。随着沉积Mg膜厚度的增加,Mg_2Si衍射峰逐渐增强,薄膜表面更连续,电阻率逐渐减小,霍尔迁移率逐渐降低,载流子浓度逐渐增加。此外,Si膜导电类型和Mg膜厚度共同影响Mg_2Si薄膜的导电类型。溅射N-Si膜时,Mg_2Si薄膜的导电类型随着Mg膜厚度的增加由P型转化为N型;溅射P-Si膜时,Mg_2Si薄膜的导电类型为P型。可以控制制备的Mg_2Si半导体薄膜的导电类型,这对Mg_2Si薄膜的器件开发有着重要的指导意义。     

The effect of Li on the tensile properties of cast Al–Mg2Si metal matrix composite

The effects of both Li modification and cooling rate on the microstructure and tensile properties of an in situ prepared Al–15%Mg₂Si composite were investigated. It was found that the addition of 0.3%Li reduces the average size of Mg₂Si primary particles from 30 to 6 μm. The effect of cooling rate was investigated by the use of a mold with different section test bars. The results showed an increase in both UTS and elongation values with reduction in section thicknesses corresponding to increasing cooling rates. Adding Li also raised the tensile strength and elongation values and reduced the number of decohered particles observed in fracture surfaces thereby increasing the alloy's ductility. Data scatter and unexpected low tensile values of 3 mm sections were attributed to casting defects observed in fracture surfaces. Large clusters of Mg₂Si particles and eutectic cell boundaries were found to be potential crack propagation paths in this alloy.     

Melt growth and characterization of Mg2Si bulk crystals

We have grown Mg₂Si bulk crystals by the vertical Bridgman method using a high-purity Mg (6N-up) source. The grown crystals were single-phase Mg₂Si and had well-developed grains (1-5 mm³). Laue observations and SEM-EDX observations confirmed that crystalline quality in the grains was single crystal with stoichiometric composition. Electron concentration of the single crystalline specimens grown from 6N-up-Mg was 4.0 × 10¹⁵ cm^− 3 at room temperature (RT). This value is more than one order of magnitude lower than that of specimens grown from 4N-Mg [(5-7) × 10¹⁶ cm^− 3]. The Hall mobility of 14,500 cm²/Vs was observed at 45 K in the crystals grown from 6N-up-Mg. We also found that Al impurity plays an important role in the crystals grown from a low-purity Mg source. From the optical absorption measurement, we estimated that the indirect energy gap was about 0.66 eV at 300 K and about 0.74 eV at 4 K.     

Bulk crystal growth of Mg2Si by the vertical Bridgman method

Mg₂Si were grown by the vertical Bridgman (VB) method in crucibles made of chemical vapor deposition (CVD) pyrolytic graphite (PG) in order to minimize the reaction and sticking of molten Mg-Si during growth. Congruent crystallization was derived from a stoichiometric melt of Mg₂Si, and incongruent crystallization was derived from nonstoichiometric melts having Mg/Si ratios of 85:15, 70:30 and 60:40. Grown samples were characterized by X-ray diffraction and electron-probe microanalysis, and their power factors were calculated from the Seebeck coefficients and electrical conductivities measured from room temperature to 773 K. The grown crystals were single-crystal-like and had high Seebeck coefficients at the temperatures from 500 to 773 K. A sample derived from a stoichiometric melt had a Seebeck coefficient of −470 μV/K and the highest power factor, 7.8×10⁻⁶ W/cm K² at 373 K, was calculated for the sample derived from a melt with an Mg/Si ratio of 70:30.     

Thermoelectric properties and power generation characteristics of sintered undoped n-type Mg2Si

Fabrication of sintered undoped n-type Mg₂Si, initiated from pre-synthesized all-molten polycrystalline Mg₂Si powder, was carried out using a Plasma Activated Sintering technique. The thermoelectric properties were evaluated from room temperature up to 861 K. The maximum dimensionless figure of merit was estimated to be 0.60 at 861 K. For output power measurements, the length and cross-sectional area of Mg₂Si elements equipped with Ni electrodes were varied from 6 to 15 mm and 2 × 2 to 4 × 4 mm², respectively. For the 3 × 3 × 7.5 mm³ element, the maximum output power density was 1.43 Wcm^-2 with the temperatures of the cool and hot sides being 373 K and 873 K (ΔT = 500 K), while the highest output power was 203 mW for the sample of 4 × 4 × 7.5 mm³ at ΔT = 500 K. The results of aging tests for 11,000 h with the hot side at 873 K and the cool side at 373 K under atmospheric conditions showed that the fabricated device elements possess sufficient durability at high power-generation operating temperatures.     

Epitaxial growth of Fe3Si/CaF2/Fe3Si magnetic tunnel junction structures on CaF2/Si(111) by molecular beam epitaxy

The Fe₃Si(24 nm)/CaF₂(2 nm)/Fe₃Si(12 nm) magnetic tunnel junction (MTJ) structures were grown epitaxially on CaF₂/Si(111) by molecular beam epitaxy (MBE). The 12-nm-thick Fe₃Si underlayer was grown epitaxially on CaF_2/Si(111) at approximately 400 °C; however, the surface of the Fe₃Si film was very rough, and thus a lot of pinholes are considered to exist in the 2-nm-thick CaF₂ barrier layer. The average roughness (Ra) of the CaF₂ barrier layer was 7.8 nm. This problem was overcome by low-temperature deposition of Fe and Si at 80 °C on CaF₂/Si(111), followed by annealing at 250 °C for 30 min to form the Fe₃Si layer. The Ra roughness was significantly reduced down to approximately 0.26 nm. A hysteresis loop with coercive field H_c of approximately 25 Oe was obtained in the magnetic field dependence of Kerr rotation at room temperature (RT).     

高能超声对Mg2 Si / AZ91D 复合材料的影响

为改善原位颗粒增强镁基复合材料的性能,采用原位合成技术制备了Mg2Si/AZ91D复合材料,通过在熔体中施加高能超声,研究了超声时间和超声功率对复合材料组织性能的影响.结果表明:随着超声时间的延长或超声功率的增大,复合材料中粗大的汉字状Mg2Si相变得细小、分布均匀,同时细小分布均匀的球化状β-Mg17Al12相增多;超声时间为6 min、超声功率为1.2 kW时,组织中呈短棒状的Mg2Si颗粒和球化状β-Mg17Al12相分布均匀,且复合材料的抗拉强度和伸长率达到最大,分别为220.5 MPa和2.6%,较未施加超声的复合材料试样提高了22.3%和38.9%;再延长处理时间或增大输出功率,组织有粗化的趋势,复合材料的抗拉性能及伸长率也呈现先升后降趋势.