高能球磨制备Al-Pb纳米相复合结构合金中纳米相Pb体积分数对其长大行为影响（英文）

利用X射线衍射仪、扫描电子显微镜和透射电子显微镜研究了高能球磨制备的Al-Pb纳米相复合结构合金中纳米相Pb的体积分数对其长大行为的影响。结果表明,尽管Al-Pb纳米相复合结构中组成相的尺寸均在纳米量级,不同体积分数的纳米相Pb的长大行为均遵循三次方定律。纳米相Pb的粗化速率随其体积分数的增加而增加,增加幅度大于理论在此成分范围内的预测。纳米相Pb的粗化激活能不随合金成分而变化。纳米相Pb的粗化受溶质原子沿溶剂基体的晶界扩散所控制。     

机械合金化制备具有纳米相复合结构的Al-Pb互不溶体系中Pb相的粗化动力学和添加Cu对其粗化的影响

利用X射线衍射仪、扫描电子显微镜和透射电子显微镜研究了机械合金化制备的具有纳米相复合结构的Al-Pb互不溶体系中Pb相的粗化动力学和添加Cu对其粗化的影响。结果表明在573、623、673和723 K退火不同时间后，尽管Al-Pb纳米相复合结构合金中组成相的尺寸均在纳米量级，Pb相的平均颗粒尺寸与退火时间之间仍满足三次方定律。Pb相的粗化激活能为84.80 kJ/mol，此值接近于基体Al的晶界自扩散激活能。这表明Pb相的粗化受晶界扩散控制。添加Cu降低了Pb相的粗化速率，这与Cu在Al和Pb相的界面偏聚，降低了Al/Pb的界面能有关。添加Cu后，Pb相的长大激活能增加。     

机械合金化制备具有纳米相复合结构的Al-Pb互不溶体系中Pb相的粗化动力学和添加Cu对其粗化的影响（英文）

利用X射线衍射仪、扫描电子显微镜和透射电子显微镜研究了机械合金化制备的具有纳米相复合结构的Al-Pb互不溶体系中Pb相的粗化动力学和添加Cu对其粗化的影响。结果表明在573、623、673和723 K退火不同时间后,尽管Al-Pb纳米相复合结构合金中组成相的尺寸均在纳米量级,Pb相的平均颗粒尺寸与退火时间之间仍满足三次方定律。Pb相的粗化激活能为84.8 kJ/mol,此值接近于基体Al的晶界自扩散激活能。这表明Pb相的粗化受晶界扩散控制。添加Cu降低了Pb相的粗化速率,这与Cu在Al和Pb相的界面偏聚,降低了Al/Pb的界面能有关。添加Cu后,Pb相的长大激活能增加。     

基于相场法的Cr浓度对Fe-Cr合金中α′相析出的影响

基于Cahn-Hilliard扩散方程,采用时间和空间函数定义场变量描述成分随时间演变,通过相场模型对Fe-35Cr、Fe-40Cr和Fe-45Cr合金的失稳分解行为进行模拟研究,分析沉淀相体积分数、平均粒径和粒度分布变化。结果表明,随着时效时间增加,Fe-Cr合金中α′相由最初的蠕虫状,逐渐长大并向椭球状或棒状转变。随着Cr含量升高,α′相的平均半径逐渐增大,平衡体积分数逐渐增大,形核、长大及粗化速率加快。模拟结果有助于理解Fe-Cr合金的相分解和高温双相不锈钢的设计。     

机械合金化制备的Al-Pb纳米相复合结构的研究进展

综述了近年来机械合金化制备的Al-Pb纳米相复合结构的研究进展,介绍了Al-Pb纳米相复合结构的形成机理,以及纳米相复合结构的热稳定性、热学和力学性能。     

镍基高温合金沉淀相粗化之后的硬度退化及其各向异性特征

镍基高温合金广泛应用于制造军事和民用工程领域中的关键热端部件,在服役过程中内部沉淀相容易发生粗化,并导致材料力学性能退化。本文结合有限元模拟和机理分析,研究镍基高温合金材料发生沉淀相粗化之后的硬度变化特性,并探讨相关变化与材料微结构演化的关联。结果表明：合金硬度随沉淀相粗化的发生而显著退化,并呈现出各向异性特征,总体来说,当沉淀相体积分数较低或沉淀相粗化程度不高时,其硬度随加载角度增大而先逐渐增加后又逐渐降低;而对于沉淀相体积分数和沉淀相粗化程度均较高的合金,硬度则随加载角度增大而单调升高,合金硬度的相关变化与沉淀相的形状、大小和分布特性密切相关;材料微结构的改变导致内部位错的形核、增殖和运动特性发生变化,进而影响宏观材料的硬度。     

Al-Pb合金的快速定向凝固及其模拟

对Al-Pb合金开展了快速定向凝固实验,并根据实际凝固条件模拟计算了合金的组织演变过程.结果表明,当凝固速度不变时,Pb相粒子尺寸及其分布范围随Pb含量的增加而增大;当合金成分不变时,Pb相粒子尺寸及其分布范围随凝固速度的增加而减小.模拟结果与实验数据吻合较好,展现了快速定向凝固条件下Al-Pb合金的凝固组织形成过程.     

Sn对Al-Pb偏晶合金凝固过程及组织的影响

研究了添加第三组元Sn对定向凝固Al-Pb合金组织的影响.结果表明,添加微量Sn能降低Al-Pb合金液-液相变时两液相间的界面能,促进富Pb相液滴形核和弥散型Al-Pb合金凝固组织的获得;随着Sn添加量的增加,弥散相体积分数增大,液-液相变温度区间和液-液-固三相温度区间之和增大,初生弥散相粒子和偏晶反应弥散相粒子的尺寸均增大;添加Sn促进Al-Pb合金中凝固界面枝晶化,这一方面促进弥散相液滴/粒子沿凝固方向均匀分布,另一方面,促进弥散相液滴/粒子沿定向凝固合金晶界分布.     

机械合金化制备的Al-Pb-Cu合金结构与摩擦性能

用机械合金化方法制备了Al-Pb-Cu合金。X射线衍射（XRD）和扫描电镜（SEM）分析表明，随机械合金化的进行，Al-Pb-Cu合金中相继有Cu9Al4和CuAl2相形成，在随后的烧结过程中，CuAl2相农渐增加，而Cu9Al4相逐渐消失，最终获得了在Al基体上弥散分布为Pb相和CuAl2相的组织，与Al-Pb二元合金相比，Cu的加入在一定程度上抑制了Pb相的长大，摩擦磨损性能测定表明，Al-Pb-Cu合金的摩擦磨损性能比相同方法制备的Al-Pb二元合金有了较大提高，当Cu含量（质量分数）为4．5％时，合金的耐磨性最佳。     

纳米晶SmCo7合金的相失稳及伴随的晶粒长大

采用放电等离子烧结(SPS)技术制备出致密的纳米晶单相SmCo7合金块体。以此纳米晶合金为初始材料,通过系列退火实验系统研究其晶格参数、物相组成和显微组织随晶粒长大的演变特征。结果表明:纳米晶SmCo7相(1:7H)从室温至600℃都能保持很好的相稳定性和热稳定性。通过XRD分析和TEM观察证实,纳米晶SmCo7相的失稳分解和晶粒的突发长大是伴随发生的,即在较高温度(高于600℃)条件下纳米化稳定的SmCo7相会分解为Sm2Co17相(2:17R)和SmCo5相(1:5H),同时晶粒组织会急剧粗化;其中SmCo5相会以圆形析出物的形式均匀分布于晶界处和晶粒内部;随着晶粒的长大,六方结构的纳米晶SmCo7相的晶格参数a和单胞体积均线性减小,而轴比c/a则变化不大。     

Friction and wear characteristics of hot-extruded leaded aluminum bearing alloys

The friction and wear characteristics of hot-extruded Al-Pb alloys with lead contents in the range 0–25 wt.% and as-cast Al-Pb alloys with lead content of 20 wt.% were investigated under dry-sliding conditions using a pin-on-disc test machine. It was found that hot extrusion greatly decreased the porosity that was caused by powerful stirring and considerably improved the mechanical properties of stircast Al-Pb alloys, including wear behavior. The coefficient of friction and wear rate decreased with increasing lead content, and especially the antiseizure property of hot-extruded Al-Pb alloys containing 20 wt.% and 25 wt.% lead were improved remarkably. Optical observation revealed that the reason for this was the formation of a black compact film of lubricant that covered almost the entire worn surface of specimens at a highly applied load level. This film is a mixture of different constituents containing Al, Fe, Si, O, and Pb.     

磁场作用下Al-Pb偏晶合金的凝固过程

在恒定磁场作用下对Al-Pb合金进行定向凝固实验, 考察了合金成分、凝固速度、恒定磁场对凝固组织的影响. 模拟研究了恒定磁场作用下Al-Pb合金定向凝固组织的形成过程, 分析了磁场的影响机理和合金成分、凝固速度、磁场强度对弥散型凝固组织获得的影响. 模拟和实验均表明恒定磁场促进弥散型偏晶合金凝固组织的形成.     

Surface modification of Al-Pb alloy by high current pulsed electron beam

Al-Pb alloy was modified by high current pulsed electron beam and the microstructure, hardness and tribological characteristics were characterized by scanning electron microscopy, electronic microanalysis probe microanalysis, Knoop hardness indentation and pin-on-disc type wear testing machine. The results show that the microstructure and hardness can be greatly improved, and the modification layer consists of a molten zone, an overlapped zone of heat-affected and quasistatic thermal stress-affected zone and a transition zone followed by the substrate. The tribological properties of high current pulsed electron beam irradiated Al-Pb alloy are correspondingly improved largely. Optical observation and scanning electron microscopy analysis reveal that the low wear rate and lowest level in coefficient of friction at high load level for irradiated Al-Pb alloy are due to the formation of a lubricious tribolayer covering the worn surface, which is a mixture of Al2O3, Pb3O4 and silicate. The wear mode varies from oxidative wear at low load to film spalling at high load and, finally, adhesive wear.     

Temporal evolution of the nanostructure of Al(Sc,Zr) alloys: Part II-coarsening of Al3(Sc1−xZrx) precipitates

The coarsening behavior of four Al(Sc,Zr) alloys containing small volume fractions (<0.01) of Al₃(Sc_1−xZr_x) (L1₂) precipitates was investigated employing conventional transmission electron microscopy (CTEM) and high-resolution electron microscopy (HREM). The activation energies for diffusion-limited coarsening were obtained employing the Umantsev–Olson–Kuehmann–Voorhees (UOKV) model for multi-component alloys. The addition of Zr is shown to retard significantly the coarsening rate and stabilize precipitate morphologies. HREM of Al(Sc,Zr) alloys aged at 300 °C reveals Al₃(Sc_1−xZr_x) precipitates with sharp facets parallel to {1 0 0} and {1 1 0} planes. Coarsening of Al-0.07 Sc-0.019 Zr at.%, Al-0.06 Sc-0.005 Zr at.% and Al-0.09 Sc-0.047 Zr at.% alloys is shown to be controlled by volume diffusion of Zr atoms, while coarsening of Al-0.14 Sc-0.012 Zr at.% is controlled by volume diffusion of Sc atoms.     

Ca含量对AZ61-1.2Y镁合金耐蚀性能的影响

利用静态失重法研究了不同Ca含量对AZ61-1.2Y镁合金腐蚀速率的影响。用金相显微镜、扫描电子显微镜观察试样的微观组织、表面腐蚀形貌。结果表明,添加1%的Ca(质量分数,下同)时,合金的晶粒得到了明显的细化,组织和成分更加均匀;当Ca含量大于1%时,合金的析出相增多,并产生粗化、偏聚的现象。在两种浓度的腐蚀介质中（0.5%和3.5%的NaCl水溶液）,合金的腐蚀速率均随着Ca含量的增加呈现先减小后增大的趋势,其中当Ca含量为1%时合金的腐蚀速率均达到最低,耐蚀性能得到明显的改善。     

A model for the yield strength of overaged Al–Zn–Mg–Cu alloys

A model for the yield strength of multi-component alloys is presented and applied to overaged Al–Zn–Mg–Cu alloys (7xxx series). The model is based on an approximation of the strengthening due to precipitate bypassing during precipitate coarsening and takes account of ternary and higher order systems. It takes account of the influence of supersaturation on precipitation rates and of volume fraction on coarsening rates, as well crystallographic texture and recrystallisation. The model has been successfully used to fit and predict the yield strength data of 21 Al–Zn–Mg–Cu alloys, with compositions spread over the whole range of commercial alloying compositions, and which were aged for a range of times and temperatures to produce yield strengths ranging from 400 to 600 MPa. All but one of the microstructural and reaction rate parameters in the model are determined on the basis of microstructural data, with one parameter fitted to yield strength data. The resulting accuracy in predicting unseen proof strength data is 14 MPa. In support of the model, microstructures and phase transformations of 7xxx alloys were studied by a range of techniques, including differential scanning calorimetry (DSC), electron backscatter diffraction (EBSD) in an SEM with a field emission gun (FEG-SEM).     

Coarsening kinetics of γ′ precipitates in cobalt-base alloys

The expeditious development of novel cobalt-base γ–γ′ alloys as possible next generation superalloys critically depends on achieving a comprehensive understanding of the coarsening kinetics of ordered γ′ precipitates. This paper discusses the coarsening of L1₂ ordered Co₃(W, Al) precipitates in a model ternary Co–10Al–10W (at.%) alloy during isothermal annealing at 800 and 900 °C. The experimentally determined temporal evolution of average size of the γ′ precipitates suggests classical matrix diffusion limited Lifshitz–Slyozov–Wagner coarsening at both temperatures. The γ′ coarsening rate constants have been determined using a modified coarsening rate equation for non-dilute solutions. Furthermore, using the Cahn–Hilliard formulation for interfacial energy, the γ/γ′ interfacial energies at the respective annealing temperatures have been correlated to the concentration profile across the interface that has been experimentally determined using atom probe tomography. The calculated interfacial energies are in comparable range with those observed in nickel-base superalloys. Additionally, this analysis has permitted, for the first time, the determination of the gradient energy coefficient for γ/γ′ interfaces in Co-base alloys, a critical input for phase-field and other simulation models for microstructural evolution.