Microstructure and mechanical properties of two-phase Cr–Cr2Nb, Cr–Cr2Zr and Cr–Cr2(Nb,Zr) alloys

The microstructures and mechanical properties of binary and ternary Cr-based alloys containing Nb, Zr, or both Nb and Zr, have been studied in both the as-cast and annealed conditions. The level of alloying in each instance was targeted to lie below, or approximately at, the maximum solubility in chromium. The as-cast microstructures of these alloys consisted of Cr-rich solid solution surrounded by small amounts of interdendritic Cr–Cr₂X eutectic structure. Annealing at 1473 K resulted in solid-state precipitation of the Cr₂X Laves phase in the Cr–Nb and Cr–Nb–Zr alloys, but not in the Cr–Zr alloys. The binary Cr₂Nb phase consisted of an extensively twinned ({111}<112> twins) C15 structure whereas the presence of Zr modifies its appearance substantially; the twinned C15 structure persists. Oxides were occasionally present and their compositions were qualitatively determined. Vickers hardness primarily depended upon the volume fraction of the Cr₂X Laves phase present. Age hardening due to solid-state precipitation of Cr₂X Laves phase within the Cr-rich matrix was observed in the Nb-containing alloys. The room temperature bend strength of the alloys was strongly affected by the presence of grain-boundary Cr₂X phase. It is considered that porosity as well as oxides in the alloys also lowers their bend strength.     

Zr含量对铸造AlSi7Mg0.4合金力学性能的影响

研究了添加Zr元素的重力铸造AlSi7Mg0.4合金的微观组织和力学性能.结果 表明,在含Zr的铸态合金中生成了(Al,Si)3(Zr,Ti)和π-Fe相,Zr的添加使合金的晶粒尺寸减小;经过T6热处理后富Fe相中的Mg和少量粗大的(Al,Si)3(Zr,Ti)相重溶到基体中,减小了金属间化合物的尺寸,生成了与基体有共...     

On orientation relationship of the Ti5Si3 precipitates in a TiAl alloy

The orientation relationship (OR) and interface structure between ζ-Ti₅Si₃ precipitates and γ-TiAl phase in a Ti–Al based alloy composed of γ-TiAl and ₂-Ti₃Al lamellae have been investigated using transmission electron microscopy. Various orientation relationships defined by a pair of parallel directions and planes are discussed with the method of basic vector transformation matrix in the reciprocal space from γ-TiAl to ζ-Ti₅Si₃ precipitate phase and two new kinds of orientation relationships between ζ-Ti₅Si₃ and γ-TiAl phases have been found. Periodical interface fringes at γ-TiAl/ζ-Ti₅Si₃ interface are analyzed according to the Moiré fringes and interface misfit dislocations.     

Lattice matching of D023 and D022 phases in Al-6at.%(Ti,V,Zr) systems

Composite quaternary alloys with 21–22 vol.% of Al₃M (M = Ti,V,Zr) were made by vacuum arc melting. Two inlermetallic phases were found in alloys: one is V rich D0₂₂-Al₃(Ti,V,Zr) and the other is Zr rich D0₂₃-Al₃(Ti,V,Zr). Measured lattice constants of precipitate phases were strongly dependent on the composition of transition elements in precipitates and generally obeyed Vegard's rule. The lattice misfits between Al₃M phases and the matrix did not change much in alloys while the lattice misfit between D0₂₂ and D0₂₃ Al₃M phases was found to decrease with an increase in Ti content implying that the interface between both phases became more smooth, hard to distinguish and separate. A geometrical model was made for the lattice matching between two, D0₂₂ and D0₂₃ Al₃M phases. Titanium has been found to act as a retarding element to separation into D0₂₃ and D0₂₂ phases and the pre-existing phase may have been L₁₂ or D0₂₃ phase.     

The effects of trace Sc and Zr on microstructure and internal friction of Zn–Al eutectoid alloy

The damping properties of Zn–22 wt.% Al alloys without and with Sc (0.55 wt.%) and Zr (0.26 wt.%) were investigated. The internal friction of the determined by the microstructure has been measured in terms of logarithmic decrement (δ) using a low frequency inverted torsion pendulum over the temperature region of 10–230 °C. An internal friction peak was separately observed at about 218 °C in the Zn–Al alloy and at about 195 °C in Zn–Al–Sc–Zr alloy. The shift of the δ peak was found to be directly attributed to the precipitation of Al₃(Sc, Zr) phases from the alloy matrix. We consider that the both internal friction peak in the alloy originates from grain boundary (GB) relaxation, but the grain boundary relaxation can also be affected by Al–Sc–Zr intermetallics at the grain boundaries, which will impede grain boundary sliding. In addition, Al–Sc–Zr intermetallics at the grain boundaries can pin grain boundaries, and inhibit the growth of grains in aging, which increases the damping stability of Zn–22 wt.% Al alloy.     

Effect of aluminium content on the anodic behaviour of copper-aluminium alloys in 3.5 wt% NaCl solution

Anodic behaviour of heterogeneous Cu-Al alloys in 3.5 wt% NaCl solution has been investigated as a function of aluminium content by potentiodynamic polarization, cyclic voltammetry and potentiostatic current transient experiments and compared to pure Cu and homogeneous Cu-Al alloys. The specimens were subjected to various anodic potentials and subsequent analyses by scanning electron microscopy (SEM) supplemented with energy dispersion spectroscopy (EDS). The pure Cu and single -phase Cu-Al alloys showed that a relatively thick protective CuCl film forms at active-passive transition potentials and transforms into CuO or Cu(OH)₂ at the passivation potential, resulting in high limiting current densities. However, the Cu-10 wt% Al alloy is passivated to Al(OH)₃, impeding the transformation of the thick CuCl layer which contains AlCl or Al(OH)₂Cl salt into CuO or Cu(OH)₂. At high applied anodic potential, the Cu₂(OH)₃Cl phase forms on the deteriorated passive film Al(OH)₃.     

Defect structures and phase transitions of FeRh alloys deformed at high speed deformation

Fe–Rh alloys of Rh concentrations ranging from 40 to 50at.% and of B2 phase were deformed by use of a compression machine capable of running tests at high speeds of impact. Induced complicated substructures and phases were examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), and positron annihilation spectroscopy (PAS). A characteristic arrangement of L1₀ domains was observed, along with very small transformed A1 domains and dispersed in the residual B2 matrix. On the basis of the experimental results, we suggest a coupling of a pair of shears along {112}11−1_B2 for the transformation mechanisms from B2 to L1₀ and A1 phases.     

多级均匀化处理对Al-Cu-Li-Sc-Zr合金微观组织与性能的影响EI北大核心CSCD

通过DSC测定Al-Cu-Li-Sc-Zr合金中Al_(3)(Sc,Zr)弥散相的析出温度,为确定Al_(3)(Sc,Zr)弥散相粒子析出的保温温度与保温时间,制定四种三级均匀化制度。随后将四种均匀化样品经过热轧、固溶、时效等处理后进行室温拉伸对比其力学性能,并通过样品的时效硬化曲线计算表观激活能,采用SEM与EDS分析均匀化后样品的第二相形貌与成分,EBSD表征固溶后样品的晶粒取向特征。结果表明:多级均匀化处理过程中第二阶段温度为460℃的均匀化制度相比于410℃的均匀化制度更利于Al_(3)(Sc,Zr)弥散相粒子的析出,在细化晶粒组织、抑制再结晶的同时,也促进后续时效处理过程中含Li强化相的析出,通过晶界强化、织构成分以及析出相的复合作用提升合金力学性能。另外,由于Al_(3)(Sc,Zr)弥散相粒子的析出,热变形退火后合金中大量亚晶微观组织得以保留,合金在室温拉伸过程中变形均匀,伸长率提高。     

Impurity effects on the nucleation and growth of primary Al3(Sc,Zr) phase in Al alloys

Impurity effects on the nucleation and growth of primary Al₃(Sc,Zr) phase have been investigated in high purity Al alloys and commercial purity Al alloys, respectively. In the case of high purity Al alloys, primary Al₃(Sc,Zr) phases were found to be pushed to grain boundaries ahead of the solidification front. Such type of primary Al₃(Sc,Zr) phase did not contribute to the heterogeneous nucleation, and thereby the grain refinement of Al alloys. In the case of commercial purity Al alloys, the presence of Fe, Si, Cu, Mg, Ti, and other impurities significantly enhanced the heterogeneous nucleation of primary Al₃(Sc,Zr) phase. Most primary Al₃(Sc,Zr) phases were found to be located within the α-Al matrix, and kept an identical orientation relationship with the α-Al matrix. Furthermore, the presence of the impurities also changed the growth mode on the primary Al₃(Sc,Zr) phase. In the case of commercial purity Al alloys, a peritectic to eutectic reaction was induced due to the presence of the impurities. A layered growth was observed leading to a narrow particle size distribution. In contrast, in the case of high purity Al alloys, a featureless structure was observed. This investigation demonstrates that impurities and their concentrations are important factors affecting the nucleation and growth of primary Al₃(Sc,Zr) phases, and thereby for the successful grain refinement in Al-based alloys.     

Magnetic properties of melt spunSmFe11Ti-Sm2TM17 pseudobinary alloys

Several alloys in the SmFe₁₁Ti-Sm₂TM₁₇ (TM=Co/Fe/Cu/Zr) pseudobinary system containing O-90 wt.% Sm₂TM₁₇ were prepared by the melt spinning technique. A maximum as-spun coercivity of 4.6 kOe was obtained for the alloy containing 10 wt.% Sm₂TM₁₇ at a substrate velocity of 15 m/s. The coercivity is enhanced to 5.3 kOe after annealing at 800°C for 1 h. XRD (X-ray diffractometry) and TEM (transmission electron microscopy) were used to investigate the microstructure of the alloys. It is suggested that the grain refinement, doping of the 1-12 phase with Sm and other elements, and reduced free iron might be the main causes coercivity enhancement     

Influence of Si content on microstructure of TiAl alloys

A systematic study of four ternary TiAl-based alloys with constant Ti content of 52.2at.% and variable Si content ranging from 0.3 to 2.7at.% (Al in balance) was conducted. The alloys were prepared from elemental powders via a route including powder mixing, precompaction, cold extrusion, and reactive hot-isostatic pressing. All investigated alloys contain the intermetallic compounds γ-TiAl, ₂-Ti₃Al, and ζ-Ti₅(Si,Al)₃. The microstructure can be described as a duplex structure (i.e., lamella γ/₂ regions distributed in a γ matrix) containing ζ precipitates. With increasing Si content, the number of primary ζ precipitates increased and the γ grain size became finer while the lamellar volume fraction decreased slightly.     

Solidification Studies of 3003 Aluminium Alloys with Cu and Zr Additions

The effects of Cu and Zr additions, on the microstructure formation, precipitation and ingot cracking, in commercial 3003 Al alloys have been studied. The investigation was carried out by characterizing the grain structure in DC-cast rolling ingots, and studying the solidification microstructure of Bridgman directionally solidified samples. To better understand the influence of the different Cu and Zr contents on the phase precipitations, differential thermal analysis (DTA) experiments were performed. Results from the ingot microstructure analysis show that in commercial alloys with relatively high contents of Cu and Zr, no significant differences in measured grain sizes compared to conventional 3003 Al alloys could be found. However, only Zr containing alloys exhibited significantly larger grain sizes. Increased grain refiner and/or titanium additions could compensate for the negative effects on nucleation normally following Zr alloying. Different types of precipitates were observed. Based on DTA experiments, increased Cu and Zr contents resulted in the formation of Al2Cu phase, and increased solidification range. It was also found that increased Mn content favors an early precipitation of Al6(Mn,Fe) giving relatively coarse precipitates. It was concluded that the Cu alloying has a detrimental effect on hot tearing.     

Effect of minor alloying with Al on oxidation behaviour of MoSi2 at 1200°C

Effect of Al alloying in small concentrations on oxidation behaviour of molybdenum di-silicide (MoSi₂) at 1200°C has been investigated. MoSi₂–2.8 and 5.5 at.% Al alloys possessed 0.5, and 2.5 at.% Al in solid solution, respectively, and dispersoids of -Al₂O₃. On the other hand, MoSi₂–9 at.% Al alloy possessed 3.1 at.% in solid solution in MoSi₂ and Mo(Si,Al)₂ phase, besides -Al₂O₃ dispersoids. The kinetics of oxidation of all the alloys followed a parabolic rate law. The oxidation rate was higher in the MoSi₂–Al alloys in comparison to MoSi₂, with weight gain values varying by an order of magnitude. The MoSi₂–5.5 and 9 at.% alloys demonstrated closely related oxidation characteristics and proved to be more resistant to oxidation than MoSi₂–2.8 at.% Al alloy. The oxide scale comprised of SiO₂ in MoSi₂, mixture of SiO₂ and -Al₂O₃ in MoSi₂–2.8 at.% Al alloy, and -Al₂O₃ in case of MoSi₂–5.5 and 9 at.% Al alloys. The mechanism of oxidation has been analysed using thermodynamic and kinetic considerations.     

含Al耐热奥氏体不锈钢的团簇式成分设计

表面生成Al2O3保护膜的奥氏体不锈钢具有良好的高温服役性能,为了使Al强烈促进铁素体的生成需要精确匹配奥氏体稳定元素Ni和Al的含量。为此,本文先引入“团簇加连接原子”结构模型,解析该类不锈钢的成分特征,确定其16原子团簇式,进而结合当量计算并基于橡树岭实验室推出的成分,固定C含量(质量分数)为0.1%,设计了固定Ni含量提高Al(代替Cr)含量和固定Al含量提高Ni(代替Fe)含量两个成分系列,分别为Al _x Si_0.05Nb_0.15-Fe_8.7Ni_3.0Mn_0.3-Cr_3.6-x Mo_0.2(x=0.8,1.0和1.1)和Al₁Si_0.05Nb_0.15-Fe_11.7-y Ni _y Mn_0.3-Cr_2.6Mo_0.2(y=3.2,3.4,3.7和4.0),研究了Ni和Al的不同匹配对固溶水淬(1250℃/1.5 h)加时效态(800℃/24 h)奥氏体稳定性的影响。Ni含量为3.0的16原子团簇式,Al含量为0.8时为单相奥氏体;Al含量为1.0和1.1时,奥氏体失稳而铁素体形成。在Al含量为1.0的16原子团簇式中,Ni含量为3.2~4.0时均为单相奥氏体。即在16原子团簇式模型下Al_0.8(2.45%)和Al₁(3.08%)分别需要Ni_3.0(20.00%)和Ni_3.2(21.43%)以避免形成铁素体,最终确定该类不锈钢的理想团簇式为[(Al,Si,Nb)₁-(Fe,Ni,Mn)₁₂](Cr,Mo,W)₃。     

Characterization, Processing, and Alloy Design of NiAl-Based Shape Memory Alloys

The microstructures and phase transformations in binary Ni-al, ternary Ni-Al-Fe, and quaternary Ni-Al-Fe-Mn shape memory alloys (SMAs) were investigated by light and electron microscopy, electron and X-ray diffraction, and differential scanning calorimetry. The effects of alloying additions (B, Fe, and Mn) on martensite stability, shape recovery, and tensile ductility were also studied. NiAl-based SMAs can be made ductile by alloying with B for enhanced grain boundary cohesion and Fe for improved bulk properties. Iron has the undesirable effect that it decreases the martensite → austenite transformation temperatures (A_p). Fortunately, A_p can be increased by decreasing the “equivalent” Al content of the alloy. In this way, a high A_p temperature of 190°C has been obtained without sacrificing ductility. Recoverable strains of 0.7% have been obtained in a Ni-Al-Fe alloy with A_p temperature of 140°C. Manganese additions (2–10%) lower A_p, degrade hot workability, and decrease room temperature ductility. Good-quality, ductile SMA ribbons have been produced by melt spinning. However, additional alloy design is required to suppress the aging-induced embrittlement caused by Ni₅Al₃ formation.     

微量Sc对Al-Zn-Mg合金焊接接头组织和性能的影响

使用光学显微镜、扫描电镜和透射电镜分析了Al-Zn-Mg合金和含微量钪的Al-Zn-Mg合金钨极氩弧焊接头的微观组织,并对其力学性能和耐应力腐蚀性能进行了对比。结果表明：在传统Al-Zn-Mg合金板材熔合线附近的热影响区出现再结晶和晶粒异常长大,而含钪Al-Zn-Mg合金基体中热稳定性优良的纳米Al₃(Sc, Zr, Ti)相在焊接过程中能阻碍晶界迁移,抑制再结晶晶粒的形核和长大,进而细化熔合线附近的组织。同时,含微量钪的Al-Zn-Mg合金焊接接头的强度明显比传统合金的高,其强化效果主要来源于熔合线附近区域的细晶强化和二次Al₃(Sc, Zr, Ti)相的弥散强化。     

Characterization of phase development in non-isothermally annealed mould-cast and heat-treated Al–Mn–Sc–Zr alloys

The effect of Mn addition on microstructure and mechanical properties during isochronal annealing in the temperature range of 20 °C–570 °C of the mould-cast and heat-treated Al–Sc–Zr alloys with a various content of Mn and Zr was studied. The electrical resistometry together with the microhardness (HV0.3) measurements were compared to microstructure development. The microstructure development was examined by scanning electron microscopy, transmission electron microscopy and electron diffraction. Relative resistivity changes and the microhardness of the mould-cast and heat-treated Al–Mn–Sc–Zr alloys exhibit similar dependence on annealing temperature. Precipitation of the Al₃Sc particles is responsible for the peak microhardness in all these alloys. The microhardness decrease is slightly delayed during the isochronal annealing and during the high temperature heat treatment in the mould-cast alloy with the higher Zr-content due to a higher oversaturation of Zr. The decomposition sequence of the oversaturated solid solution of the studied Al–Mn–Sc–Zr alloys is compatible with the recently published decomposition sequence of the Al–Sc–Zr system and also with the formation of Mn,Fe-containing particles. It seems very probable that the addition of Mn does not influence the decomposition of solid solution of the ternary Al–Sc–Zr system.     

Analytical electron microscopy of Sm(Co,Fe,Cu, Zr)9

Electron microscopic studies of as-cast Sm(Co,Fe,Cu,Zr)₉ magnets revealed a hexagonal phase of the type Sm₂(Co,Fe,Cu,Zr)₁₇ with crystal lattice parameters of a=0.84 nm and c=3.2 nm. After a solid solution treatment, only rhombohedral (3R) and hexagonal (2H) grains were found. After an additional annealing treatment at 800°C, grains with a microcellular precipitation structure similar to the one found in Sm(Co,Fe,Cu,Zr)_7.5 magnets occurred. In addition, in the as-cast and after-aged samples, other, partly unidentified Cu- or (Co,Fe)-enriched phases were detected     

Effect of beta flecks on mechanical properties of Ti–10V–2Fe–3Al alloy

The effects of beta flecks on tensile properties and low-cycle fatigue life were investigated at room temperature for Ti–10V–2Fe–3Al alloy. It was found that beta flecks had a significant influence on tensile ductility and low-cycle fatigue life. The greater the volume fraction of beta flecks (P_A) or maximum area of beta flecks (S_max), the lower the tensile ductility and low-cycle fatigue life. Extensive scanning electron microscopy (SEM) and light microscopy (LM) observation showed that under tensile load, cracks preferentially nucleated at β grain boundaries of beta flecks, then grew, connected and propagated along grain boundaries to form characteristics of intergranular fracture and quasi-cleavage fracture. While under an alternating load, beta flecks acted as sites for low-cycle fatigue crack nucleation due to inhomogeneous alternating strains between soft GB and aged beta matrix. The presence of beta flecks accelerates both the crack nucleation and early crack propagation.     

Comparison of hydrogen storage characteristics between as-cast and melt-spun TiCr1.1V0.5Fe0.1Mn0.1 alloys

Hydrogen storage characteristics of as-cast and melt-spun TiCr_1.1V_0.5Fe_0.1Mn_0.1 alloys were investigated by pressure–composition–temperature (PCT) tests, X-ray diffraction (XRD) and scanning electron microscopy (SEM). XRD showed that both the as-cast and the melt-spun alloys were similarly consisted of V based BCC phase and Ti_1.07Cr_1.93 phase. However, PCT tests showed that the melt-spun alloy, with larger hysteresis between hydrogen absorption and desorption, had higher hydrogen storage capacity than the as-cast alloy. More interestingly, the phase compositions of the two fully hydrogenated alloys were entirely different. The as-cast and the melt-spun alloys should have different atomic motion mechanisms during the course of hydrogenation.