铸造冷却速度对Mg-4.4Zn-0.3Zr-0.4Y挤压态合金组织性能的影响

本文通过两种不同冷却速度制备成分相同、铸造组织特征不同的Mg-4.4Zn-0.3Zr-0.4Y铸态合金,研究不同铸造组织特征对挤压变形态合金组织和力学性能的影响。研究结果表明：与空冷铸造合金相比较,通过水冷冷却增大了熔体冷却速度,使铸态组织得到细化,抑制了W-相（Mg3Y2Zn3相）的形核,并促进了I-相（Mg3YZn6相）的生成,获得了更大体积分数的准晶相(I-相)。经过挤压变形后,水冷铸造合金中的再结晶晶粒细小均匀,经过挤压变形破碎的细小I-相颗粒弥散分布在基体上,{0002}基面织构得到弱化,而{101 ?2}织构强度增强,从而使挤压态Mg-4.4Zn-0.3Zr-0.4Y合金的强度和塑性都得到了大幅的提高。水冷铸造Mg-4.4Zn-0.3Zr-0.4Y合金经过挤压变形后,屈服强度和抗拉强度分别达到297.0MPa和327.3MPa,与空冷铸造挤压态合金相比分别提高了46.4MPa和21.4MPa。水冷铸造Mg-4.4Zn-0.3Zr-0.4Y挤压态合金的延伸率达到14.8%,与空冷铸造挤压态合金相比增大了4.7%。     

Ce添加对Zn-0.6Cu-0.3Ti合金组织与耐蚀性能的影响

将稀土Ce添加到Zn-0.6Cu-0.3Ti合金中，设计熔炼Zn-0.6Cu-0.3Ti-(0.3～0.6)Ce系列合金，采用X射线衍射仪(XRD)、扫描电镜(SEM)、电化学腐蚀测试等研究了Ce添加对Zn-0.6Cu-0.3Ti合金组织与耐蚀性能的影响。结果表明，添加稀土Ce后，Zn-0.6Cu-0.3Ti合金中析出CeZn5微米颗粒，其分布于Zn基体内部或者相界面处，促进Zn基体以枝晶方式生长，并细化Zn枝晶和二次枝晶。Ce的添加在整体上提高了Zn-Cu-Ti合金的自腐蚀电位，降低合金的自腐蚀电流密度，添加0.3%Ce后，Zn-0.6Cu-0.3Ti合金的自腐蚀电流从2.76×10-3 A/cm2快速降低到5.85×10-4 A/cm2，腐蚀时间越长，Ce含量对Zn-Cu-Ti-Ce合金腐蚀性能的影响越弱。含Ce合金阻抗谱只有一个容抗弧，在腐蚀初期，Ce含量对容抗弧半径影响较小，随着腐蚀时间的延长，Ce的影响越来越明显，总体呈增大趋势。     

热挤压Mg-6Zn-xCu-0.6Zr(x=0,0.5,1.0,1.5)合金的显微组织及力学性能

对Mg-6Zn-x Cu-0.6Zr(x=0,0.5,1.0,1.5)合金进行了熔炼并浇注在金属模中,然后进行了挤压成形试验。结果表明:铸态合金随着Cu含量的增加晶粒逐渐细化,第二相含量增多,其组织由α-Mg、MgZn_2及Mg Zn Cu相组成。合金经挤压后力学性能明显提高,其中挤压ZK60合金的动态再结晶较弱,晶粒细化程度较小。铸态合金组织中的第二相在挤压过程中被打碎,并沿着挤压方向分布。挤压态合金晶粒细化程度明显,其平均晶粒尺寸可达到10~13μm。Mg Zn Cu相呈短棒状分布在晶界,而Mg Zn2相呈细小的颗粒状分布在基体上。挤压态合金力学性能改善的原因可归结为细晶强化、第二相弥散强化及固溶强化综合作用的结果。其中挤压态Mg-6Zn-1.0Cu-0.6Zr力学性能最优,其抗拉强度、屈服强度及伸长率分别达到320.22 MPa,240 MPa和11.48%。     

轧制-深冷处理对生物可降解Zn-3Cu合金显微组织、力学和耐腐蚀性能的影响EI北大核心CSCD

本文采用冷轧和深冷处理等手段对生物可降解Zn-3Cu合金进行处理,研究了轧制-深冷处理对合金试样的显微组织、力学性能和耐腐蚀性的影响。结果表明:Zn-3Cu合金轧制过程中发生动态再结晶过程。随变形量的增大,晶粒显著细化,CuZn_(4)相沿轧制方向进一步被拉长。经深冷处理后,Zn-3Cu合金的基体相晶粒尺寸更小,CuZn_(4)相变形程度更低,抗拉强度、屈服强度和硬度均明显得到加强,其中60%-DCT达到最大抗拉强度(287.9±3.7) MPa和最大屈服强度(263.1±4.9) MPa。随着轧制变形量增加,轧制-深冷处理的Zn-3Cu合金耐腐蚀性能不断减弱,但相同变形量轧态Zn-3Cu合金,经过深冷处理后的耐腐蚀性能显著提升。40%变形量轧制-深冷处理的Zn-3Cu合金具有最优异的耐腐蚀性能。     

轧制变形量对Zn-3Cu合金显微组织、力学和耐腐蚀性能的影响

本文以Zn-3Cu合金为研究对象。研究了轧制变形量对Zn-3Cu合金的显微组织、力学性能和耐腐蚀性能的影响。研究结果表明,随着轧制变形量的增加,Zn-3Cu合金基体晶粒细化程度不断加深,合金中的CuZn5相沿着轧制方向不断被拉长并出现部分断裂。Zn-3Cu合金的强度先增后减,塑性不断增强,60%变形量的Zn-3Cu合金具有最高的屈服强度,达到了263.1 ± 4.9 MPa。 随着变形量增加,轧态Zn-3Cu合金的耐腐蚀性能逐渐减弱,铸态Zn-3Cu合金表现优异的耐腐蚀性能。     

两种变形Zn-Cu-Ti锌合金的组织与性能

采用熔铸、挤压的方法制备了Zn-1.0Cu-0.2Ti(简称ZCT)和Zn-1.0Cu-0.2Ti-0.05Mg(简称ZCTMg)两种变形锌合金,分析了两种合金的相组成,观察了合金的微观组织,测试了合金的拉伸性能和蠕变性能,研究了合金的微观组织和性能之间的关系.结果表明,ZCT和ZCTMg两种合金均主要由η相、ε相和TiZn15相组成;ZCTMg合金的铸态组织较ZCT有一定细化,挤压态合金的抗拉强度由ZCT的212.35 MPa提高到ZCTMg的248.90 MPa; ZCTMg合金的抗蠕变性能较ZCT合金有明显提高,合金稳态蠕变速率由ZCT的2.17×10-5 s-1降低到ZCTMg的3.68×10-7 s-1,晶界上的微纳米级TiZn15相粒子和较大的晶粒是提高合金蠕变性能的主要原因.     

Sr对Mg-10Zn-4Al-0.3Mn合金显微组织和力学性能的影响

以Mg-10Zn-4Al-0.3Mn为基体合金,分别加入不同含量的Sr元素,制备了3种合金。试验观察可知,Mg-10Zn-4Al-0.3Mn基体合金的铸态组织由α-Mg基体与沿晶界分布的准晶相Q组成。加入Sr后,亚稳态准晶相Q转变为平衡相τ相Mg32(Al,Zn)49与共晶相ε相(Mg51Zn20)。随着Sr添加量的增加,合金的抗拉强度、屈服强度以及断后伸长率均呈先上升后下降的趋势,有效提高了合金的拉伸性能。当Sr含量为0.3%时,三者均达到最佳值,抗拉强度、屈服强度以及断后伸长率分别达到195 MPa、147 MPa和7.4%,同时平均晶粒尺寸也减小到最小值37μm。     

热挤压Zn-2Cu-0.5Zr合金的力学性能与降解行为

针对可降解锌基植入物面临的关键问题,制备了一种兼顾综合力学性能和降解行为的新型热挤压Zn-2Cu-0.5Zr (质量分数,%)合金。该合金的微观组织由Zn基体相、CuZn5相和Zn22Zr相构成。得益于均匀分布的第二相颗粒和基体相晶粒的进一步细化,热挤压Zn-2Cu-0.5Zr合金的综合力学性能显著优于Zn和Zn-2Cu合金,屈服强度、极限抗拉强度和断后延伸率分别提升至192 MPa、213 MPa和61%。此外,基体相晶粒的细化使得热挤压Zn-2Cu-0.5Zr合金表面生成的腐蚀产物层更加均匀致密,因而显著改善了基体的不均匀降解模式。     

Mg-3.52Sn-3.32Al合金轧制板材的组织和力学性能

采用同步轧制工艺对Mg-3.52Sn-3.32Al合金挤压板材在603 K进行了小变形轧制实验,用XRD、OM、SEM和TEM分析了挤压板材和轧制板材的相组成和微观组织,并测试了室温拉伸性能。结果表明:热轧后,合金板材的相组成未发生变化,仍由α-Mg基体、颗粒Mg2Sn相和块状Mg17Al12相组成。但第二相大量析出,且发生明显的动态再结晶,晶粒尺寸为5～10μm。在细晶强化、加工硬化和第二相强化的共同作用下,轧制板材的综合拉伸力学性能显著提高,抗拉强度和屈服强度分别由挤压板材的270、193 MPa提高至332、297 MPa,提高幅度分别为23%和54%。此时,伸长率为5.0%。     

铸造冷却方式对Mg-4.4Zn-0.3Zr-0.4Y挤压态合金组织及性能的影响

采用2种不同铸造冷却方式制备成分相同、组织特征不同的Mg-4.4Zn-0.3Zr-0.4Y镁合金,研究不同铸造组织特征对挤压变形态合金组织和力学性能的影响。结果表明:与空冷铸造合金相比,水冷增大了熔体冷却速度,使合金铸态组织得到细化,抑制了W-相(Mg_3Y_2Zn_3相)的形核,并促进了I-相(Mg_3YZn_6相)的生成,获得了更大体积分数的准晶相(I-相)。经过挤压变形后,水冷铸造合金中的再结晶晶粒细小均匀,I-相颗粒经过挤压破碎后弥散分布在基体上,{0002}基面织构得到弱化,而■织构强度增强,从而使Mg-4.4Zn-0.3Zr-0.4Y挤压态合金的强度和塑性都得到了大幅提高。水冷铸造合金经过挤压变形后,屈服强度和抗拉强度分别达到297.0和327.3 MPa,与空冷铸造挤压态合金相比分别提高了46.4和21.4 MPa。水冷铸造挤压态合金的延伸率达到14.8%,与空冷铸造挤压态合金相比增大了4.7%。     

Mo-Si-B系材料的性能及制备

综述了Mo-Si-B系材料的研究进展。主要就材料在各种环境中的氧化性能、单相和多相材料的力学性能、材料的电学性能和热学性能等方面的研究进展进行了介绍。通过无压烧结方法,在1600℃合成了7种不同原料配比的Mo-Si-B系材料。用X射线衍射仪分析了材料的物相组成,确定了最佳的B与Si的原子比为0．865。但是无压烧结法得到的材料致密度不够,还需要对合成工艺作进一步的研究。     

(0.96Bi_(0.5)Na_(0.5)TiO_3~-0.04BaTiO_3)-(0.98K_(0.5)Na_(0.5)NbO_3~-0.02LiTaO_3)无铅压电陶瓷的结构分析与性能研究

研究了(1-x)(0.96Bi_0.5Na_0.5TiO_3-0.04BaTiO_3)-x(0.98K_0.5Na_0.5NbO_3-0.02LiTaO_3)(BNTBT-KNNLT)体系在0≤x≤0.07这一组分区域的结构和性能.X射线衍射谱发现,这一系列组分在室温下形成纯钙钛矿型固溶体,没有其他杂相产生.(111)峰的峰位和峰形随组分的变化有规律的变化.随着KNNLT组分的加入,压电及介电等性能有比较明显的改变.压电性能随KNNLT的加入出现最大值.当x=0.02时,压电常数d_(33)=125 pC/N.介电常数在室温下随组分的增加而增加.电滞回线的结果显示,尽管在BNTBT中掺杂了KNNLT,这一系列的压电陶瓷仍然具有较大的矫顽场.当x=0.02时,室温下介电常数和剩余极化强度分别为:ε_r=1455,P_r=32.3 μC/cm~2.实验结果表明适量的KNNLT掺杂进BNTBT中可以改善BNTBT的压电和介电性能.     

Preparation and properties of C/C−ZrB2−SiC composites by high-solid-loading slurry impregnation and polymer infiltration and pyrolysis (PIP)

Ultrahigh-temperature ceramics were added to C/C composites to meet their application requirement in a high-temperature oxidizing environment. C/C−ZrB₂−SiC composites were fabricated by high-solid-loading slurry impregnation with polymer infiltration and pyrolysis. The dispersion and rheological behavior of ZrB₂ slurry and the microstructural, mechanical, and ablation properties of the C/C−ZrB₂−SiC composites were investigated. Results indicated that a well-dispersed and low-viscosity ZrB₂ slurry was obtained using 0.40 wt.% polyethyleneimine as a dispersant at pH 5. Ceramics were uniformly distributed in the short-cut fiber layer and needle-punched area. The flexural strength of the C/C−ZrB₂−SiC composites was 309.30 MPa. The composites exhibited satisfactory ablation resistance under the oxyacetylene flame of 2500 °C, and the mass and linear ablation rates were 0.40 mg/s and 0.91 μm/s, respectively. A continuous and compact ZrO₂ layer, which could effectively reduce the diffusion rate of oxygen and protect the composites from being ablated, was formed.     

Superconductivity and ferromagnetism in Pd doped Y9Co7

The ferromagnetic superconductor Y₉Co₇ was chemically doped to yield the solid solution Y₉Co_7-xPd_x for 0 < x < 0.4. The lattice parameter a does not depend on x, whereas c increases with increasing Pd content up to x = 0.2, the palladium solubility limit. The transition from ferromagnetism (T_C = 4.25 K) to superconductivity (T_sc = 2.4 K) was observed only for the parent Y₉Co₇ compound. For the lowest tested Pd doping level (x = 0.05), ferromagnetism is enhanced strongly (T_C = 9.35 K) and superconductivity is not seen above 1.8 K. The Curie temperature rapidly increases from 4.25 K to about 10 K for a Pd concentration of x = 0.1 and remains almost unchanged for Y₉Co_6.8Pd_0.2.     

Synthesis and thermoelectric properties of the quaternary type-I Si clathrates K8-δGaxAlySi46-x-y

The effects of substituting Ga atoms with Al on the thermoelectric properties of the ternary Si clathrate K₈Ga₈Si₃₈ were assessed over the temperature range of 10–700 K. For this purpose, the series of quaternary Si clathrates K_8-δGa_xAl_ySi_46-x-y (x + y ≈ 8; 0 ≤ y < 8) was synthesized by heating mixtures of K, Ga, Al and Si at temperatures between 1223 and 1353 K. The lattice constant of K_8-δGa_xSi_46-x was found to increase with the Al content, y, and Al substitution also significantly changed the transport properties of the clathrate, even though Al and Ga are isovalent. Electrical resistivity measurements showed that the conduction mechanism changed from variable range hopping conduction to metallic conduction with increasing y. The Seebeck coefficient, S, was negative for all of the samples, indicating that the dominant carriers were electrons, while the absolute value of S decreased with y. All specimens had approximately the same value of thermal conductivity, κ, on the order of 1.4 W/Km at 300 K, except for K_7.7Al_7.5Si_38.8. K_7.5Ga_4.8Al_3.0Si_38.7 exhibited the largest power factor, and therefore the highest thermoelectric dimensionless figure of merit, ZT, with a value of 0.066 at 550 K. This value is approximately six times that of the ternary Si clathrate K_7.4Ga_7.7Si_38.9.     

FeCuNbSiB非晶纳米晶带材软磁性能和压磁性能研究

本文主要研究了Fe73.5Cu1Nb3Si13.5B9纳米晶带材在不同的热处理工艺和压应力条件下的软磁性能变化情况.结果表明:带材在550℃×1h热处理工艺时将晶化成纳米晶材料,此时带材软磁性能最好;纳米晶带材的|μ|,受压应力影响大,尤其是在小于0.2MPa压应力作用下,软磁性能变化非常敏感,|μ|随压力增加而迅速下降;带材Q值在小于0.2MPa压应力作用下变化非常敏感,Q值随压力增加而迅速下降.当压应力大于0.2MPa时,Q值随压应力变化不明显,压应力不影响带材Q值随频率的变化规律.     

Fe-Co软磁合金磁性能及机械性能的研究

Fe-Co合金是重要的软磁材料,应用广泛.本文综述了化学成分、合金元素、有序度、晶粒尺寸、磁场、杂质和应力对其磁性能和机械性能的影响.并分析了Fe-Co合金的应用前景和发展趋势.     

Sn改性Ti-Zr-Cu-Ni钎料的微观组织和力学性能

采用自制Ti-Zr-Cu-Ni-Sn钎料钎焊TA2钛合金,研究了不同Sn元素含量改性Ti-Zr-Cu-Ni钎料的熔化特性、微观组织及物相、润湿及熔蚀性、接头拉伸强度。研究表明,Sn含量增加,Ti-Zr-Cu-Ni-Sn钎料固、液相线温度基本升高,但温度差值基本变窄,可更好地抑制钎焊界面脆性化合物形成。Ti-Zr-Cu-Ni-5Sn钎料组织由Ti、Zr基体和晶体相构成,Sn倾向与Ti、Zr结合形成Ti₂Sn₃、Ti₆Sn₅、Zr₅Sn₃等低熔点共晶相。Sn≤1.5%时,随Sn含量增加,钎料对TA2钛合金的润湿性逐渐变差;继续增加Sn,钎料润湿性改善,添加5%Sn的钎料对基体润湿最佳。添加5%Sn并降低Cu、Ni总量的改性钎料对TA2钛合金熔蚀减弱。相同钎焊工艺下,添加5%Sn接头的强度和塑性均有提升。钎焊温度升高,Ti-Zr-Cu-Ni钎料产生更多强化物相,致接头强度大幅提升,而Ti-Zr-Cu-Ni-5Sn钎料产生的含Sn物相强化作用对接头强度提升有限;相...     

Strengthening of transparent spinel/Si3N4 nanocomposites

In response to a need for improving the mechanical properties of optically transparent ceramics, the nanocomposites approach is used to strengthen transparent magnesium-aluminate spinel with Si₃N₄ nanodispersoids. The as-processed nanocomposites are found to be >70% transparent in the critical infrared wavelength range of 3-4.5 μm. Mie scattering combined with absorption by the Si₃N₄ nanodispersoids explains quantitatively the IR transmission behavior of these nanocomposites. The nanocomposites are also found to be transparent in the visible region. Upon heat treatment (1000 °C for 4 h in air), the optical properties of the nanocomposites remain unchanged. However, the heat treatment results in a 29% increase in the average strength, accompanied by almost doubling of the Weibull modulus, and an 85% increase in the indentation toughness. The improvements in mechanical properties after the heat treatment in these nanocomposites are explained qualitatively, based on generally accepted arguments involving surface-oxidation-induced surface compression and flaw-healing. While further work is needed to fully understand and exploit these effects, this first report on transparent nanocomposites could have broad implications for the creation of mechanically robust, transparent ceramics of the future.     

Elastic and optical properties of zinc-blende CrSb and its effective mass

The elastic, optical, and effective mass properties of CrSb in zinc-blende（ZB） phase were investigated.The calculations were carried out using the full-potential linearized augmented plane wave plus local orbital according to the density functional theory. The results of elastic calculations by generalized gradient approximation and local density approximation approximations indicate that ZB CrSb is a ductile material and its Debye temperature is rather low. Band structure and density of state calculations introduce the ZB CrSb as a half-metal with spin polarization of100 %. In metal state, 16 th and 17 th bands cut off the Fermi level. Calculations study the effective mass, Fermi velocity,and Fermi surface at 16 th and 17 th bands. In continue,optical quantities such as dielectric function, energy loss function, and optical conductivity were investigated.