纳晶Cu-Ag双峰材料热传导行为特性研究

采用热压烧结法制备了具有双峰结构的纳晶Cu-Ag复合材料和纳晶Cu金属材料,采用激光法测定了试样在不同温度(200~400 K)下的热导率。测量结果显示,2种纳晶金属材料热导率随晶粒尺寸的增加而增加,并且随温度的降低而减小。在300 K下平均晶粒尺寸为150 nm的纳晶Cu-Ag双峰材料试样的热导率为163.45 W/m·K,分别占粗晶Cu和粗晶Ag的40.7%和38.1%。本研究引入并改进了卡皮查热阻理论模型对试样热导率进行了数值计算,计算结果与实验数据基本一致,纳晶Cu-Ag双峰材料热导率明显低于单晶Cu/Ag块体,纳晶金属材料热导率随着晶粒尺寸的增加而增加,验证了纳晶Cu-Ag双峰材料热导率在一定的晶粒尺寸范围内具有尺寸效应。     

Effects of saccharin on microstructure and property of electro-deposited Ni-Fe alloys

The Ni-Fe alloy coatings were prepared by electro-deposited method, and the effects of the saccharin content in the electrolytes on the microstructure of the coatings were studied by using X-ray diffractometry(XRD), scanning electron microscopy(SEM) and transmission electron microscopy(TEM). The results show that the saccharin content in the bath affects the plating rates and the current efficiency remarkably. As the saccharin content increases, the grain size of the Ni-Fe alloys decreases. The average grain size of the deposits varies from 13 nm to 10.8 nm as the saccharin content increases from 0 g/L to 8 g/L. Accordingly, the microhardness of the as-cold deformed samples increases from Hv 600 to Hv 656.     

Effect of Ambient Temperature on the Electrochemical Properties of La_4MgNi_(17.5)Co_(1.5) Hydrogen Storage Alloy

The effect of different ambient temperatures on the electrochemical properties of La_4MgNi_(17.5)Co_(1.5)hydrogen storage alloy was investigated.The X-ray diffraction pattern shows that the alloy consists of LaNi5-type phase and A_5B_(19)-type(Ce_5Co_(19) + Pr_5Co_(19)) phase.With the increase of the ambient temperature,the maximum discharge capacity of the alloy electrodes increases from 353.33(283 K) to 379.25 mAh/g(308 K),and the cyclic stability(S_(100)) of the electrodes decreases from 80.19(283 K) to 52.04%(308 K) due to the acceleration of pulverization,corrosion and oxidation at higher ambient temperature.Moreover,it is found that the increase of the temperature can accelerate the diffusion rate of hydrogen in the alloy(D) and increase the exchange current density(I_0).which are beneficial for improving the activation performance and the high-rate dischargeability(HRD) of the alloy electrodes.The activation cycles of the electrodes decrease from 4(283 K) to 1(308 K),and the HRD_(900) of the electrodes sharply increases from 66.36(283 K) to 95.64%(308 K).     

Effect of strain rate on microstructural evolution and thermal stability of 1050 commercial pure aluminum

Effects of strain rate on the microstructure evolution and thermal stability of 1050 commercial pure aluminum processed by means of split Hopkinson pressure bar (SHPB) and Instron?3369 mechanical testing machine were investigated. Samples in the deformed state and after various annealing treatments at 423?523 K (150?250 °C) for 1 h were characterized by TEM and hardness test. The result reveals that the samples in the deformed state were mainly composed of elongated subgrains/cells with high density of dislocations. Microstructures of the quasi-static compressed aluminum were quite stable throughout the temperature range studied, and no significant grain growth was observed. However, for the dynamic impacted one, recrystallized grains with an average grain size of 4.7 μm were evolved after annealing at 523 K (250 °C) for 1 h. It is suggested that the annealing behavior of this dynamic deformed aluminum is a continuous process of grain coarsening, rather than the traditional discontinuous recrystallization for the quasi-static compressed aluminum.     

120°模具室温ECAP制备工业纯钛的压缩变形本构关系

在Gleeble-1500热模拟机上对120°模具室温Bc方式ECAP变形8道次制备的平均晶粒尺寸约为200 nm的工业纯钛进行等温变速压缩实验,研究超细晶工业纯钛在变形温度为298~673 K和应变速率为1×10-4~1×100s-1条件下的流变应力行为。结果表明:变形温度和应变速率均对流变应力具有显著影响,峰值应力随变形温度的升高和应变速率的降低而降低;流变应力在变形初期随应变的增加而增大,出现峰值后逐渐趋于平稳,呈现稳态流变特征。采用双曲正弦模型确定了超细晶工业纯钛的变形激活能Q=104.46 kJ/mol和应力指数n=23,建立了相应的变形本构关系。     

Research Progresses on Thermal Stabilization of Metal Nanocrystalline Alloys

纳米晶体材料由于内部存在高的晶界分数,晶粒长大的驱动力较高,导致常温及高温下的热稳定性较差,给这类材料的加工和使用带来了障碍。本文从热力学与动力学两方面介绍了现阶段二元纳米晶合金热稳定性研究领域的主要进展,分别介绍了热力学稳定研究中的Trelewicz/Schuh（TS）模型、Wynblatt/Ku（WK）模型,Koch等人所用的方法,以及动力学稳定基本理论等主要模型,并对各模型进行了对比分析及客观总结。     

Solute segregation at grain boundaries in superplastic SiO2-doped TZP

Grain boundary structure, chemical composition, and bonding state in superplastic SiO₂-doped TZP and undoped TZP were investigated by high resolution electron microscopy (HREM), energy dispersive X-ray spectroscopy (EDS) and electron energy loss spectroscopy (EELS) using a field emission type transmission electron microscope (FE-TEM). No amorphous phase was observed at any grain boundaries in either SiO₂-doped TZP or undoped TZP. Yttrium ions segregated over a width of 4–6 nm at grain boundaries in both materials, and silicon ions segregated over a width of 5–8 nm at grain boundaries in SiO₂-doped TZP. The average dihedral angle between grain boundaries in SiO₂-doped TZP was as high as 80°, which agreed well with the fact that no grain boundary had glass phase. The strain energy is accumulated by the dissolution of silicon ions into the tetragonal zirconia lattice. However, the grain boundary energy of SiO₂-doped TZP is likely to be low enough to compensate the increase of strain energy near grain boundaries. OK-edge EELS spectra taken from grain boundaries in SiO₂-doped TZP were shifted 3–4 eV to the higher energy side in comparison with those from the grain interior. This may suggest that the chemical bonding is strengthened at grain boundaries by the presence of solute silicon. The strengthening may be responsible for the enhanced superplasticity in SiO₂-doped TZP.     

Influence of Al on the microstructure and mechanical properties of Cr–Zr–(Al–)N coatings with low and high Zr content

Low Zr (S1) and high Zr (S2) quaternary Cr–Zr–(Al–)N coatings with increasing Al content were deposited by d.c. reactive magnetron sputtering. The structure, fracture cross-section morphology and mechanical properties of the coatings were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), nanoindentation, scratch testing and Vickers micro-indentation testing. All the coatings present an fcc NaCl-type B1 structure; in the low Zr content coatings, the diffraction peaks shift towards higher angles as the Al content increases. The grain size is approximately constant in a range from 6 to 8 nm, except for high Zr content films where a significant decrease in crystalline order is observed (grain size ~ 2.5 nm). In both series, the microstructure changed from equiaxed to columnar with increasing Al content. The highest hardness and strongest adhesion values were achieved in coatings with lower Zr and Al content. Conversely, the coatings with high Zr and the highest Al content exhibited an abrupt decrease in hardness, adhesion strength and toughness.     

AlCrTaTiZrV高熵合金氮化物扩散阻挡层的制备及其热稳定性

为研究氮气含量的变化对AlCrTaTiZrV高熵合金薄膜性能的影响,检验在最佳氮气含量下厚度为15 nm的(AlCrTaTiZrV)N扩散阻挡层的热稳定性。采用直流磁控溅射设备在N型Si(111)基底上溅射不同氮气含量的高熵合金氮化物;选取最佳氮气含量为制备条件,在硅基底上沉积15 nm厚的AlCrTaTiZrVN₁₀高熵合金氮化物为扩散阻挡层,并在阻挡层顶部沉积50 nm厚度的Cu膜,最终形成Si/AlCrTaTiZrVN₁₀/Cu三层堆叠结构。利用真空退火炉将Si/AlCrTaTiZrVN₁₀/Cu薄膜体系在500 ℃下进行不同时间的退火处理,用以模拟恶劣的工作环境。利用场发射扫描电子显微镜(FESEM)、原子力显微镜(AFM)、X射线衍射仪(XRD)及四探针电阻测试仪(FPP)对试样的表面形貌、粗糙度、物相组成及方块电阻和进行表征。试验结果为:当氮气含量低于10%时,高熵合金氮化物薄膜为非晶结构。当氮气含量为20%时,高熵合金氮化物薄膜呈现FCC结构,并随着氮气含量的增加,薄膜的结晶性得到提高。薄膜表面的粗糙度在氮气含量为10%时最低,R_a仅为0.124 nm。三层堆叠结构500 ℃退火8 h后,Cu表面发生团聚,薄膜的方阻维持在较低的0.070 Ω/□,且并未发现Cu-Si化合物。厚度为15 nm的非晶结构AlCrTaTiZrVN₁₀薄膜在500 ℃退火8 h后,依旧可以抑制Cu的扩散,表现出了优异的热稳定性及扩散阻挡性能。     

The effect of saccharin addition and bath temperature on the grain size of nanocrystalline nickel coatings

Nanocrystalline nickel coating was synthesized by direct current electrodeposition from a Watts bath at the current density of 100 mA/cm² and pH = 4. The effect of saccharin addition (0-10 g/l) and bath temperature (45-65 °C) on the average grain size of the deposits was investigated by XRD technique. The results showed that the average grain size decreased from 426 nm to 25 nm as the saccharin concentration increased from 0 to 3 g/l, while further increase in saccharin concentration had no significant effect. Theoretical model also indicated a non-linear function for dependence of grain size on saccharin concentration, which was in accordance with experimental results. The experimental results showed that the increases in the bath temperature had no considerable effect on the average grain size of the deposits. A theoretical formula was also established for the temperature dependence of the grain size.     

退火处理对La1．5Mg0．5Ni7．0贮氢合金相结构和电化学性能的影响

研究了退火温度对A287型La1.5Mg0.5Ni7.0合金的相结构和电化学性能的影响。结果表明：铸态合金由LaNi，相、LaMgNi4相、（La，Mg）Ni3相以及Gd2Co7型相组成，退火处理后，合金由Gd2Co7型相、Ce2Ni7型相和PuNi3型（La，Mg）Ni3相组成：随着退火温度升高，PuNi3型相的丰度减小，ce2Ni7型相的丰度增加，（La，Mg）Ni3相的a轴参数、c轴参数和晶胞体积均增大；经1073K保温24h退火后，合金电极具有最高的放电容量（391．2mAh／g），退火温度升高，合金的最大放电容量略有降低：合金电极的循环稳定性随着退火温度的升高不断提高，在1173K时合金电极经150次循环后其电极容量保持率C150／Cmax=82％；合金的高倍率放电性能（HRD）随退火温度升高略有增加，在1173K时，合金电极的HRD最好（HRD900=89．0％）；交换电流密度I0、极限电流密度I1及氢扩散系数D随着退火温度的升高而增大。     

高功率脉冲磁控溅射管内壁沉积Cr薄膜结构及性能

由于管腔空间限制,物理气相沉积领域中管内壁沉积薄膜的均匀性和质量有待研究和改善。采用高功率脉冲磁控溅射技术(HiPIMS)在直径40 mm、长度120 mm的20#碳钢管内表面进行Cr薄膜沉积,并探究管内不同位置沉积Cr薄膜的结构和力学性能。采用SEM分析薄膜的截面形貌和厚度变化,采用AFM分析薄膜的表面形貌和表面粗糙度变化,采用XRD分析薄膜的晶相结构和晶粒尺寸,采用球-盘式旋转摩擦磨损试验机对薄膜的耐摩擦磨损性能进行测试。结果表明,随着管内深度的增加,距管口距离为15 mm(位置1)、45 mm(位置2)、75 mm(位置3)和105 mm(位置4)位置的膜层厚度分别为1 690 nm、827 nm、210 nm和0 nm。从位置1到位置3,所沉积的Cr薄膜表面粗糙度由12.6 nm下降到4.8 nm,晶粒尺寸由15 nm增加到38 nm,摩擦因数由0.68上升到0.89。     

The structure and microhardness evolution in submicrocrystalline molybdenum processed by severe plastic deformation followed by annealing

A possibility to form submicrocrystalline structure in molybdenum using severe plastic deformation treatment by torsion under high pressure (HPT) at elevated temperatures has been studied. Quantitative parameters of grain–subgrain structure have been obtained by optical microscopy and transmission electron microscopy methods. Thermal stability of microstructure and mechanical properties have been studied. It is established that HPT results in the formation of a submicrocrystalline structure in Mo and in disappearance of residual porosity. The average grain size of HPT-Mo is 0.2 μm. The formation of submicrocrystalline structure enhances significantly (by 2.4 times) the microhardness of Mo relative to that in the as-received (before HPT treatment) state. It is found that grain growth begins at 1173 K and develops intensively at T⩾1273 K.     

An investigation of thermal stability and microhardness of electrodeposited nanocrystalline nickel-21% iron alloys

The thermal stability of an electrodeposited nickel-21% iron alloy with an average grain size of approximately 14 nm was investigated. Samples were annealed for 90 mins in the temperature range of 373–773 K. The results of this study showed that grain growth started after annealing at and above 400 K. Two regimes of grain growth were identified. It is suggested that the low temperature regime (below 575 K) is accommodated mainly by the grain boundary diffusion, while the high temperature regime is assisted by the lattice diffusion. The microhardness results also confirm the presence of these two regimes. The position of the (111) XRD peaks indicated a sudden decrease in the lattice parameter after annealing at 773 K, which is attributed to the loss of connectivity of the nanosize grains. The variation of hardness with grain size followed the Hall-Petch relationship.     

The effects of heat treatments on hardness and wear resistance in Ni-W alloy coatings

The relationship of processing parameters, microstructure, and mechanical responses of the electrodeposited nickel-tungsten alloys exposed to elevated temperatures in the range 700-1100 °C are investigated. Reverse pulse electrodeposition technique is employed to control the tungsten content and nanocrystalline grain size of the deposits. The application of heat treatment at 700 °C on the alloy with high tungsten content (22 at.%) and small grain size (3 nm) gives hardness enhancement and a small decrease in wear resistance. Prolonging annealing duration and increasing annealing temperature promote more grain growth and reductions of both hardness and wear resistance, despite the formations of secondary phases. For alloys with lower tungsten contents (6% and 13%) and larger grain sizes (13 and 56 nm), higher degrees of grain growth coupled with monotonic decline of hardness are observed. The study indicates that the electrodeposited nickel-tungsten alloys with a high tungsten content potentially serve as strong candidates for high temperature applications.     

Effect of Annealing Temperature and Strain Rate on Mechanical Property of a Selective Laser Melted 316L Stainless Steel

In the present work, 316L stainless steel specimens are fabricated by selective laser melting (SLM) via optimized laser process parameters. The effects of two extrinsic factors, i.e., strain rate and annealing temperature, on the mechanical performance of SLM-processed parts are studied. The two intrinsic factors, namely strain rate sensitivity m and work hardening exponent n, which control the tensile properties of the as-built samples, are quantified. Microstructure characterizations show that cellular structure and crystalline grain exhibit apparently different thermal stability at 873 K. Tensile testing reveals that the yield strength decreases from 584 ± 16 MPa to 323 ± 2 MPa, while the elongation to failure increases from (46 ± 1)% to (65 ± 2)% when annealing temperature varies from 298 K to 1328 K. The n value increases from 0.13 to 0.33 with the increase in annealing temperature. Due to the presence of fine cellular structures and high relative density achieved in as-printed 316L samples, a strong dependence between tensile yield strength and strain rate is observed. In addition, the strain rate sensitivity of the SLM-produced 316L part (m = 0.017) is much larger than that of conventional coarse-grained part (m = 0.006), whereas the n value increases slightly from 0.097 to 0.14 with increasing strain rate.     

Microstructure and properties of AZ31 magnesium alloy with rapid solidification

Rapidly solidified (RS) AZ31 magnesium alloy ribbons were made using melt spinning technique. The results show that its microhardness increases with the wheel speed, and after heat treatment, the microhardness of the ribbons produced at 1 600 r/min also increases. Rapid solidification leads to reduction of grain size. When the wheel speed reaches 1 600 r/min, no Mg17 Al12 phase precipitates, while heat treatment at 200℃ leads to precipitation of Mg17 Al12 phase. Al-Mn intermetallic compounds with size no larger than 10 nm appear in as-spun ribbons. The corrosion potential of the as-cast ingots is lower than that of the as-spun ribbons.     

Effect of F Doping on Fabrication and Superconductivity of SmO1-xFδFeAs Compound

研究了F掺杂对铁基超导体SmO0.7F0.3FeAs的制备和性能的影响。利用二次固相反应在1120℃保温40h制备出超导临界转变温度(Tc)为56.5K的SmO0.7F0.3FeAs超导体样品,其临界电流密度Jc为2.4×105A/cm2(10K,0T)。研究发现,SmO1-xFxFeAs样品的Tc受F含量的强烈影响,晶格参数的变化也是诱导SmO1-xFxFeAs超导体的Tc变化的原因之一。在此基础上详细研究了F元素过掺杂对铁基超导体SmO1-xFδFeAs(δ>x)制备参数和性能的影响。F元素过量时,在不降低SmO1-xFδFeAs超导性能的情况下,F元素过掺杂可以一定程度地降低样品制备时的热处理温度和极大地缩短热处理时间。1100℃时保温20h制备的SmO0.7F0.35FeAs和SmO0.7F0.4FeAs样品的Tc分别为56和55K;其临界电流密度Jc分别为1.9×105和1.7×105A/cm2(10K,0T)。     

节镍型高氮奥氏体不锈钢固溶处理加热过程中的组织演变

对节镍型高氮奥氏体不锈钢进行固溶处理,通过控制加热温度和保温时间,研究高氮奥氏体不锈钢组织的变化规律。结果表明,800℃保温1 h后微观组织中出现混晶,在变形组织的晶界处产生细小的动态再结晶晶粒。在900～1050℃,随温度的升高,再结晶晶粒数量增多,尺寸增大。保温时间的增长会导致晶粒逐渐长大。在1200℃保温,晶粒尺寸从保温0. 5 h时的70μm增长到保温1 h时的117μm,此时晶粒最为均匀。平均晶粒尺寸随时间的变化呈抛物线增长,符合Beck方程:D=105.1t^0.45。并根据试验得到试验钢的最佳热处理方式为1050～1200℃保温1 h。      

冷轧及热处理对Al0.3CoCrFeNi高熵合金组织及性能的影响

利用X射线衍射仪、扫描电镜、透射电镜和拉伸试验等手段,研究了75%压下量的冷轧及1073 K下保温1 h热处理后不同冷却方式(空冷和炉冷)对Al_0.3CoCrFeNi高熵合金微观组织和力学性能的影响。结果表明:铸态以及冷轧态Al_0.3CoCrFeNi合金均为FCC单相结构,经热处理后炉冷及空冷合金均为FCC+BCC双相结构。铸态合金经冷轧以后强度显著提升但塑性大幅度下降。因细晶强化、孪晶以及析出相强化作用,热处理后炉冷合金具有良好的综合力学性能,其抗拉强度为1289 MPa,约为铸态试样的两倍(719 MPa),最大伸长率为28.7%。因析出相增多以及孪晶尺寸增大,与空冷合金相比,炉冷合金在不损失塑性的前提下,抗拉强度增加。