Crystallisation of oxygen-stabilised amorphous phase in a Zr50Cu50 alloy

The crystallisation of the oxygen-stabilised amorphous phase in a Zr₅₀Cu₅₀ alloy has been investigated by means of neutron diffraction and electron microscopy. The crystallisation microstructure consists of ZrO₂, Zr₂Cu and Zr₇Cu₁₀. A two-stage crystallisation mechanism is suggested: (i) primary crystallisation of Zr₂Cu and (ii) formation of nanocrystals ZrO₂ and Zr₇Cu₁₀. In (i), it is proposed, Zr₂Cu crystallises from the oxygen-stabilised amorphous phase, leaving an oxygen- and copper-enriched matrix ; Zr₂Cu rapidly grows and eventually attains a grain size of about 100 nm. In (ii), it is suggested, the residual amorphous matrix crystallises into nanocrystals ZrO₂ and Zr₇Cu₁₀ due to the sluggish growth of ZrO₂ and to the already formed ZrO₂ which acts as a growth barrier to Zr₇Cu₁₀. In this case there is no particular orientation relationship between Zr₂Cu and Zr₇Cu₁₀.     

添加2wt％ Cu对Zr-4合金显微结构和耐腐蚀性能的影响

研究了在Zr-4合金中添加2 wt％ Cu的合金显微组织及其在500℃和10.3 MPa过热蒸汽中的耐腐蚀性能.结果表明,该合金经过热轧、冷轧以及经2h、580℃真空退火处理后,得到以α-Zr为基体的显微组织,合金中主要存在四方结构的Zr2Cu和密排六方结构的Zr(Fe,Cr,Cu)2第二相,Zr2Cu相有长度1～4 μm、厚度约1μm的片状和直径300～500 nm的球形两种形态,并且都会富集一定量的Fe元素.在10.3 MPa、500℃过热水蒸汽中,添加2 wt％Cu的Zr-4合金不发生疖状腐蚀,表明Cu是改善锆合金耐疖状腐蚀性能的有益元素.     

Cu含量及T6处理对电力金具用铝合金组织性能的影响

探究了Cu含量与时效工艺对Al-Cu-Mg-Si系合金显微组织、力学性能以及耐腐蚀性能的影响。研究表明,随Cu含量的增加,铸态铝合金中Al₂Cu相数量增加、尺寸不断增大,形貌由点状转为粗网状,铸态铝合金的强度也随之提升,耐蚀性能下降。在180 ℃×(4~28) h时效区间内,整体上合金硬度先上升后下降,0.5%Cu、1.5%Cu合金在8 h时达到峰值,2.5%Cu合金在12 h时达到峰值。530 ℃固溶+180 ℃×8 h时效后,铝合金中析出Al₂Cu相,随着Cu含量的增加,Al₂Cu相的含量增加,硬度显著上升,2.5%Cu含量的合金抗拉强度达到最大值325.0 MPa,屈服强度达到258.8 MPa,伸长率为4.5%,其强度与传统的电力金具用铸铁相当。     

Effect of Aging on the Microstructure and Mechanical Properties of 1460 Alloy

Effects of the aging temperature on the hardening response,the tensile properties and the precipitate microstructure evolution of 1460 alloy were studied in this work.It was found that Al3(Sc,Zr) and d0(Al3Li) phases were precipitated from the matrix at the very early aging stage,while the precipitation of T1(Al2Cu Li) and h0(Al2Cu) was much slower than that of the d0 phase.When aging at higher temperature(160 and 190 °C),the d0,T1 and h0 phases tended to form simultaneously and grow up very quickly.Conversely,the d0 and h00(Al2Cu) phases were precipitated separately and more dispersive at lower aging temperature(130 °C).Taken together,the alloy aged at 160 °C exhibited improved mechanical properties owing to the uniform dispersion of the fine T1 precipitates.     

In Situ Scattering Studies of Crystallization Kinetics in a Phase-Separated Zr-Cu-Fe-Al Bulk Metallic Glass

Thermal stability and the crystallization kinetics of a phase-separated Zr-Cu-Fe-Al bulk metallic glass were investigated using in situ high-energy synchrotron X-ray and neutron diffraction, as well as small-angle synchrotron X-ray scattering. It was revealed that this glass with excellent glass-forming ability possesses a two-step crystallization behavior. The crystalline products and their evolution sequence are more complicated than a homogeneous Zr-Cu-Al glass with average glass-forming ability. The experimental results indicate that a finely distributed nanometer-sized cubic Zr₂Cu phase forms first and then transforms to a tetragonal Zr₂Cu phase, while the matrix transforms to an orthorhombic Zr₃Fe phase. The strength of the Zr-Cu-Fe-Al composite containing cubic Zr₂Cu phase and glass matrix increases, and the plasticity also improves compared to the as-cast Zr-Cu-Fe-Al bulk metallic glass. Our results suggest that the formation of multiple and complex crystalline products would be the characteristics of the Zr-Cu-Fe-Al glass with better glass-forming ability. Our study may shed light on the synthesis of bulk-sized glass-nanocrystals composites of high strength and good plasticity.     

Low Frequency Electromagnetic Casting of 2195 Aluminum-Lithium Alloy and Its Effects on Microstructure and Mechanical Properties

In this study,the low frequency electromagnetic casting(LFEC) technology was adopted to fabricate 2195 Al-Li alloy.The microstructure and solid solubility of as-cast 2195 alloys,as well as the second phase precipitation and tensile properties after aging,were investiagated and compared with the counterpart direct chill casting 2195 alloy.Our results indicate that LFEC can significantly improve the microstructure and metallurgical quality of as-cast alloy,and increase the number density of θ'(Al_2 Cu) and T_1(Al_2 CuLi) phases during aging treatment due to the enhanced solubilities of alloying elements.The tensile properties of 2195 aged alloy cast by LFEC were hence improved evidently.     

Studies of the transport properties in the layered κ-phase ET2Cu[N(CN)2]Hal (Hal = Cl1−xBrx and I) salts. 3 Superconducting compositions Hal = Cl1−xBrx (0.5 ≤ × ≤ 1)

Temperature dependences of resistance and in plane thermopower were studied for the ET₂Cu[N(CN)₂]Cl_1−xBr_x salts for the compositions showing metallic and superconducting properties at ambient pressure (0.5 ≤ × ≤ 1). Complex relations between a character of these dependences and sample compositions were established.     

Electron microscopy and X-ray diffraction studies of rapidly quenched Zr---Ni and Hf---Ni ribbons with about 90 at.% Ni

The structure of melt-spun ribbons of the alloys Zr₉Ni₉₁, Zr₁₀Ni₉₀ and Hf₁₁Ni₈₉ was investigated by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Ribbons of the Zr₉Ni₉₁ and Zr₁₀Ni₉₀ alloys prepared at a high cooling rate (ribbon thickness d=11 μm) were characterized by an amorphous matrix with a few per cent of quenched-in crystallites. The ribbon of the Hf₁₁Ni₈₉ alloy prepared with the same thickness (i.e. at the same cooling rate) exhibited a nanocrystalline grain structure of the HfNi₅ phase. Thicker ribbons of the Zr₉Ni₉₁ alloy (d=17–22 μm), for which the quench rate was correspondingly lower, were obtained as a b.c.c. Ni(Zr) solid solution phase with a grain size of nearly 1 μm. A high resolution (HR) TEM study of one of the Zr₉Ni₉₁ crystalline ribbons revealed a fine structure of the interior of the crystallites which can be attributed to an ordering on the Zr sublattice over distances of several nanometres within the b.c.c. grains.     

Cu含量对重力铸造Al-Cu-Mg-Sc合金组织及力学性能的影响

在重力铸造条件下制备了不同Cu含量(4%~6%,质量分数,下同)Al-Cu-Mg-Sc合金,采用500 ℃×4 h＋520 ℃×6 h的双级固溶,水冷后进行175 ℃×5 h时效。通过维氏硬度测试、室温拉伸性能测试试验、扫描电镜分析(SEM)等手段,研究了不同Cu含量对试验合金显微组织和力学性能的影响,进而优化Al-Cu-Mg-Sc铝合金成分。结果表明,经热处理后,随Cu含量从4.26%提高至5.58%,Al₂Cu析出相含量持续提高,热处理后合金屈服强度从191 MPa提升至216 MPa,抗拉强度从323 MPa提升至355 MPa,伸长率维持在13%附近。然而,当Cu含量较高时(6.13%),微观组织中Al₂Cu相体积分数较高,固溶后进入基体的Al₂Cu相数目有限,有大量Al₂Cu相残留在晶界处,经过时效处理后,合金的强化效果不能随Cu含量的增加而继续提升。因此整体上,随Cu含量提高,时效态高Cu含量合金的硬度和抗拉强度先增加随后趋于平稳,断后伸长率呈现先增加后降低的规律。Cu含量为5.58%的铸造Al-Cu-Mg-Sc铝合金时效后获得最佳综合性能,其硬度为117 HV,抗拉强度和屈服强度分别为355 MPa、216 MPa,断后伸长率为13.5%。     

Effect of cooling rate on crystallization of metallic Zr–Cu–Ni glass

X-ray diffraction (XRD) and differential scanning calorimetry (DSC) were employed to investigate the effect of cooling rate on crystallization behavior of metallic Zr₇₀Cu₂₀Ni₁₀ glass. It is found that all DSC traces of the metallic Zr₇₀Cu₂₀Ni₁₀ glasses under different cooling rates exhibit two exothermic peaks, indicating that the crystallization of metallic Zr₇₀Cu₂₀Ni₁₀ glass proceeds through a double-stage mode. In our previous studies, we have concluded that the first exothermic reaction mainly corresponds to the precipitation of the Zr₂Cu phase, and the second one is mainly due to the formation of nanoscale Zr₂Ni particles. It is observed that there exists a close relationship between the cooling rate and thermodynamic parameters of metallic Zr₇₀Cu₂₀Ni₁₀ glass, such as the onset crystallization temperature T_x, the first peak temperature T_p1 and the second one T_p2. The above three thermodynamic parameters reach a maximum when the surface velocity is 30 m/s. This effect is just similar to that of the Ni concentration, which has been discussed in our previous works. The activation energy for crystallization and the local Avrami exponent of metallic Zr–Cu–Ni glass under isothermal annealing conditions also exhibit a similar tendency with the cooling rate.     

Types of mechanical relaxation by hydrogen in intermetallic compounds

Hydrogen in polycrystalline intermetallic compounds generally produces extremely broad damping spectra, indicating the presence of short-range as well as long-range relaxation mechanisms. These are discussed on the basis of vibrating-reed results on Zr₆₅Cu_27.5Al_7.5, Zr₆₅Cu_17.5Ni₁₀Al_7.5, and CuZr₂ alloys. A relaxation peak at 270 K observed in all three cases is interpreted as a Zener-type relaxation of hydrogen in the CuZr₂ lattice. The differences found at higher temperatures — a second relaxation peak in the ternary and quaternary alloys but an exponential increase of damping in CuZr₂ — are related to different grain sizes and can be attributed to an ‘intercrystalline Gorsky effect’ due to elastic anisotropy mismatch strains.     

Characterization of the Convoluted 3D Intermetallic Phases in a Recycled Al Alloy by Synchrotron X-ray Tomography and Machine Learning

Fe-rich intermetallic phases in recycled Al alloys often exhibit complex and 3D convoluted structures and morphologies. They are the common detrimental intermetallic phases to the mechanical properties of recycled Al alloys. In this study, we used synchrotron X-ray tomography to study the true 3D morphologies of the Fe-rich phases, Al₂Cu phases and casting defects in an as-cast Al-5Cu-1.5Fe-1Si alloy. Machine learning-based image processing approach was used to recognize and segment the different phases in the 3D tomography image stacks. In the studied condition, the β-Al₉Fe₂Si₂ and ω-Al₇Cu₂Fe are found to be the main Fe-rich intermetallic phases. The β-Al₉Fe₂Si₂ phases exhibit a spatially connected 3D network structure and morphology which in turn control the 3D spatial distribution of the Al₂Cu phases and the shrinkage cavities. The Al₃Fe phases formed at the early stage of solidification affect to a large extent the structure and morphology of the subsequently formed Fe-rich intermetallic phases. The machine learning method has been demonstrated as a powerful tool for processing big datasets in multidimensional imaging-based materials characterization work.     

La-Ce混合稀土对Mg-Al-Mn合金力学性能及耐蚀性能的影响

研究了La-Ce混合稀土对Mg-Al-Mn合金组织形貌、力学性能及耐蚀性的影响。采用T-1200CB坩埚炉冶炼稀土含量(质量分数)分别为4.63%、5.81%、6.18%的Mg-Al-Mn合金。在箱式电阻炉中对研究试样进行430 ℃保温24 h的固溶处理,然后进行200 ℃保温24 h时效处理。对不同热处理状态的试样进行组织观察,对固溶时效后的试样进行拉伸、硬度及盐雾腐蚀试验,从而分析La-Ce混合稀土对Mg-Al-Mn合金显微组织、力学性能及耐蚀性的影响。研究表明,随着合金中的La-Ce混合稀土含量的增加,Mg₁₇Al₁₂相逐渐被Al₄(La, Ce)相代替;硬度、抗拉强度和伸长率都逐渐减小,力学性能下降;合金的腐蚀速率逐渐下降,耐蚀性提高。     

Horizontally Solidified Al–3 wt%Cu–(0.5 wt%Mg) Alloys: Tailoring Thermal Parameters,Microstructure, Microhardness,and Corrosion Behavior

In the present experimental investigation, Al–3 wt%Cu and Al–3 wt%Cu–0.5 wt%Mg alloys castings are produced by a horizontal solidification technique with a view to examining the interrelationship among growth rate(G_R), cooling rate(C_R), secondary dendrite arm spacing(λ_2), Vickers microhardness(HV), and corrosion behavior in a 0.5 M NaCl solution.The intermetallic phases of the as-solidified microstructures, that is, h-Al_2Cu, S–Al_2CuMg, and x-Al_7Cu_2 Fe, are subjected to a comprehensive characterization by using calculations provided by computational thermodynamics software, optical microscopy, and scanning electron microscopy/energy-dispersive spectroscopy. Moreover, electrochemical impedance spectroscopy and potentiodynamic polarization tests have been applied to analyze the corrosion performance of samples of both alloys castings. Hall–Petch-type equations are proposed to represent the HV dependence on λ_2. It is shown that the addition of Mg to the Al–Cu alloy has led to a considerable increase in HV; however, the Al–Cu binary alloy is shown to have lower corrosion current density(i_(corr)) as well as higher polarization resistance as compared to the corresponding results of the Al–Cu–Mg ternary alloy.     

时效处理对挤压成型2195铝锂合金组织和力学性能的影响

研究了热处理对挤压态2195铝锂合金组织和力学性能的影响。结果表明,固溶处理和人工时效处理对挤压合金的力学性能有显著的增强作用,这与析出相的类型、尺寸、数量密度和分布有关。2195铝锂合金在时效过程中的析出顺序为过饱和固溶体(SSSS)→GP区+δ′/β′(Al₃(Li,Zr))→δ′+θ′(Al₂Cu) +T₁ (Al₂CuLi)→θ′+T₁;其中T₁相在析出强化中起主导作用。2195铝锂合金经过525 ℃×60 min固溶后在170 ℃人工时效的峰时效时间是36 h,此时抗拉强度、屈服强度和伸长率分别为579 MPa、537 MPa和5.5%。     

Microstructure and Corrosion Properties of Duplex-Structured Extruded Mg-6Li-4Zn-xMn Alloys

The extruded Mg-6Li-4Zn-xMn (x = 0, 0.4, 0.8, 1.2 wt%) alloys were prepared, and the microstructure of the test alloys was investigated by optical microscopy, scanning electron microscopy and transmission electron microscopy. The corrosion properties were determined by electrochemical measurements and immersion measurements in 3.5% NaCl solution. The results indicate that the extruded Mg-6Li-4Zn-xMn alloys are mainly composed of α-Mg phase, β-Li phase, Mn precipitates and some intermetallic compounds (MgLi₂Zn). With the addition of Mn, stable corrosion products were formed on the surface of the test alloy, which can effectively inhibit further corrosion progress and improve the corrosion resistance. Mg-6Li-4Zn-1.2Mn alloy exhibits the best corrosion resistance, attributed to grain refinement, the improvement of the stability of corrosion product film and uniform distribution of fine second phases.     

冷却速率对FeSiBCuNb合金条带磁学和耐腐蚀性能的影响

采用X射线衍射仪(XRD),振动样品磁强计(VSM),电化学工作站以及扫描电子显微镜(SEM)等试验仪器对辊速为14.65和43.96 m/s旋淬制备的Fe73.5Si13.5B9Cu1Nb3(C1和C2)合金条带进行了测试分析.XRD结果显示,低冷速下制备获得了非晶/纳米晶双相(C1)合金,高冷速制备的合金(C2)为...     

电弧熔丝增材制造ER2319铝堆积金属的组织性能及T6热处理工艺优化

通过正交试验、光学显微镜、SEM、TEM等方法研究了T6热处理工艺对电弧熔丝增材制造ER2319堆积金属的组织与性能的影响,通过多元线性回归得出了T6热处理后堆积金属抗拉强度随工艺参数变化的数学模型,并分析了组织演变机制。结果表明, T6热处理工艺参数对堆积金属力学性能影响的显著度排序为:时效时间>时效温度>固溶时间>固溶温度。基于强度变化模型优化出的T6热处理工艺参数为固溶温度538 ℃、固溶时间42 min、时效温度185 ℃和时效时间23 h,使得堆积金属的抗拉强度较未热处理前提高了48.4%。固溶温度由538 ℃提高至553 ℃或固溶时间由42 min增加至82 min均会导致堆积金属中α-Al晶粒显著粗化且晶界局部过烧严重;固溶时间的增加还会导致第二相θ-Al₂Cu粗化且数量减少,降低堆积金属力学性能;时效温度或时效时间的增加会提高纳米级亚稳相θ′-Al₂Cu、θ″-Al₂Cu的析出驱动力,可显著提高沉淀强化效果。     

预变形对Zr-Sn-Nb合金淬火时效晶粒及析出相的影响

采用SEM附带的背散射电子通道衬度（ECC）像、二次电子（SE）像及能谱（EDS）分析技术,研究了β相水淬后预变形处理对Zr-Sn-Nb合金在时效过程中再结晶和第二相析出的影响规律.结果表明,未引入预变形直接时效时所得组织中再结晶晶粒尺寸粗大且形状不规则,第二相粒子尺寸差异也较大,其中尺寸大的第二相粒子为含Cu的Zr₃Fe,主要沿原β晶界分布;预变形后再时效的组织中再结晶晶粒显著细化且尺寸均匀,第二相粒子尺寸差异减小,大尺寸的Zr₃Fe粒子主要沿α再结晶晶界分布.无论有无预变形或时效时间长短,晶粒内部析出相均为弥散分布的小尺寸Zr（Fe,Cr,Nb）₂粒子.引入预变形会减弱沉淀相沿晶界析出和急剧长大的倾向,使锆合金的微观组织和第二相分布特征改变.     

Zr-Sn-Nb-Fe-Cr与Zr-Nb-Fe锆合金电阻点焊工艺及显微组织

Zr-1.0Sn-0.50Nb-0.50Fe-0.14Cr与Zr-1.30Nb-0.30Fe锆合金是目前正在研制开发核燃料组件用两种新型Zr(-Sn)-Nb-Fe系锆合金. 针对新型燃料组件骨架压力电阻点焊,采用不同的焊接工艺参数对Zr-1.0Sn-0.50Nb-0.50Fe-0.14Cr导向管与Zr-1.30Nb-0.30Fe焊舌片进行研究,并对较优焊接参数下的焊接接头力学性能、显微硬度、金相显微组织及熔核区形貌和析出相进行了分析. 结果表明,增大焊接电流和减小焊接压力,焊点剪切力和熔核尺寸随之增加,断裂方式由界面断裂转变为纽扣断裂;焊接电流对熔核尺寸及剪切力影响最大,焊接压力的增加,焊点剪切力和熔核尺寸均减小,但焊接压力的适当增大提高了形核稳定性. 在电阻点焊不平衡的急速冷却条件与电磁搅拌作用下,熔核区形成非平衡淬火针状板条状组织结构,析出的细小Fe₂(Nb_0.35, Zr_0.65)和Fe₂ (Nb_0.3, Z_r0.7)第二相粒子呈圆形或长条棒状分布于基体α-Zr与β-Zr晶粒内、晶界处及板条组织中,从而提高了熔核区及热影响区的显微硬度,含Nb的细小弥散析出FCC第二相增强了焊缝抗水侧腐蚀性能.