添加WC改善Ni3Al的焊接性能

Ni3Al金属间化合物是一种潜在的高温结构材料的耐磨材料，由于含有较多易氧化元素，它的焊接性能一直未得到有效的解决。本文研究了WC／Ni3Al复合材料焊条中的WC含量对焊接性能的影响。当焊条中不含WC时，Al大量被氧化，形成球形氧物夹杂，焊接表面沿夹杂／基体界面出现细微裂纹。当焊条中含质量分数5％WC时，WC溶解，析出W2C，部分Al被氧化，基体转化成Ni3(AlTi)C，形成碳化物包裹氧化物／金属间化合物的复合材料。当焊条中的WC含量升高达到30％时，由于溶解C的保护作用，焊层中的Al不被氧化，可获得无裂纹的焊接面，形成碳化物／金属间化合物复合材料。     

Cu6Sn5和Ni3Sn4结构性能的第一原理计算

基于密度泛函理论的第一原理,计算了锡基无铅焊点界面常见的金属间化合物Cu6Sn5和Ni3Sn4的平衡晶格常数、合金形成焓以及弹性常数,分析了结构稳定的电子机制.结果表明,Cu6Sn5较Ni3Sn4合金形成能负,因此Cu6Sn5在热力学上更稳定,其合金化能力也较强.在力学性能方面,两相均属脆性相,表现出弹性各向异性,而Ni3Sn4的键合作用较强,弹性模量、剪切模量均大于Cu6Sn5,但Cu6Sn5表现出更好的塑性.从电子结构的角度,Cu6Sn5的成键主要来自于Cu原子d,p轨道与Sn原子p杂化,而Ni原子d轨道与Sn原子p轨道的强烈杂化作用是Ni3Sn4成键的主要原因.     

孔结构对Ni3Al金属间化合物多孔材料抗腐蚀性能的影响（英文）

采用元素粉末反应合成的方法并用尿素作为造孔剂制备Ni3Al金属间化合物多孔材料。用电化学和浸泡实验表征Ni3Al金属间化合物多孔材料在6 mol/L KOH溶液中的抗腐蚀行为。系统研究孔结构对材料抗腐蚀性能的影响。研究结果表明:孔隙率较大的Ni3Al金属间化合物多孔材料较孔隙率较小的样品腐蚀更严重,这是由于孔隙率较大的样品具有复杂的联通孔结构以及较大的比表面积。然而,材料的腐蚀速率与比表面积并不成正比,这是因为随着孔隙率的增大,材料的孔径大小、孔径分布以及孔隙形状都随之变化。不同孔隙率大小的Ni3Al金属间化合物多孔材料在碱溶液中均表现出较好的抗腐蚀性能。     

钢/铝异种金属添加粉末的激光焊接

采用光纤激光器对1.4 mm厚DC51D+ZF镀锌钢和1.2 mm厚6016铝合金平板试件进行添加Mn、Zr粉末的激光搭接焊试验,利用金相显微镜、显微硬度仪、扫描电镜、X射线衍射仪、微机控制电子万能试验机等研究焊接接头各区域的金相组织、显微硬度、断口形貌、主要物相与接头的力学性能。结果表明:在钢/铝激光焊中添加Mn、Zr粉末,焊接接头平均抗剪强度与没有添加粉末相比,有所提高,其中添加Zr粉末的提高效果明显;Mn、Zr粉末的添加改变了钢/铝界面的元素分布、物相组成及微观组织形态,添加Mn能提高熔池金属的流动性,利于钢/铝界面结合,而添加Zr,焊缝区晶粒细小,形成新的ZrFe3.3Al1.3韧性相,抑制Fe-Al脆性金属间化合物生成。因此,添加Mn、Zr均改善了钢/铝焊接接头的力学性能。     

等离子熔覆制备Fe3Al金属间化合物的组织结构

为了提高钢铁表面的抗高温腐蚀性能,应用电弧喷涂和等离子弧熔覆方法在碳钢表面制备Fe-Al金属间化合物涂层。通过对熔覆层及其与钢基体界面的组织结构分析,认为该方法可以在钢基表面获得致密、无夹杂的铁铝金属间化合物层,合金层与基体间完全冶金结合;熔覆层主要由Fe3Al,FeAl和α-Fe相构成。在试验条件下所获得的铁铝合金层,其最高显微硬度可达到514HV。     

激光熔化沉积成形新型多组元Ni3Al合金的组织与力学性能

设计了一种新型多组元Ni₃Al合金Ni₄₅Co₂₃Fe₉Al₁₁Ti₁₂,并采用激光熔化沉积(LMD)技术成功制备了合金。使用X射线衍射、扫描电镜、万能试验机等研究了沉积态合金的微观组织和室温力学性能。结果表明：LMD制备的Ni₄₅Co₂₃Fe₉Al₁₁Ti₁₂合金的晶粒为沿沉积方向外延生长的粗大柱状晶,晶粒由无侧向分枝的胞状枝晶组成,枝晶内部和枝晶间区域均由网状FCC基体和块状γ′相组成,且枝晶间区域的γ′相尺寸大于晶内。LMD成型的Ni₄₅Co₂₃Fe₉Al₁₁Ti₁₂合金具有良好的室温性能,其屈服强度达到879 MPa,抗拉强度为1160 MPa,断裂伸长率为9.5%,综合力学性能远优于同类合金,其屈服强度的显著提高可能与高密度γ′相...     

Cr3C2/Ni3Al表面耐磨堆焊材料的焊接性

Cr3 C2/Ni3 Al复合材料是一种极具潜力的高温表面耐磨堆焊材料,焊接性对于该材料的推广应用至关重要.将真空烧结制得的Cr3 C2-NiAl-Ni焊条堆焊于碳钢和耐热钢表面,可形成无焊接裂纹的Cr3 C2/Ni3Al复合材料堆焊层,表明Cr3 C2/Ni3 Al复合材料具有良好的焊接性,适于作为铁基材料表面耐磨堆焊材料推广应用.分析认为,Cr3 C2/Ni3 Al复合材料具有良好焊接性的原因在于:(1)焊接过程中,Cr3 C2发生溶解再析出,熔池中的C优先被氧化,保护了Al的氧化.(2)从铁基材料基材中扩散入到焊层中的Fe元素和Cr3 C2溶解而固溶于焊层中的Cr元素有效地改善了Ni3 Al基体的焊接性.     

高速电弧喷涂Fe-Al/WC复合涂层的组织结构及其滑动磨损性能研究

采用粉芯丝材和高速电弧喷涂技术(HVAS)制备了Fe-Al／WC金属间化合物基复合涂层，并研究了涂层的显微组织和从室温至650℃的滑动磨损性能。结果表明，涂层的成分为Fe-13．87Al-17．27C-3．35W-2．59Ni-1．27Cr-18．140(％)，主要相是Fe3Al、FeAl和α-Fe，还有少量WC、W2C和A12O3；添加WC硬质相后提高了复合涂层的平均硬度，从而提高了复合涂层的耐磨性；高温下磨损面形成了大面积的氧化物保护层，降低了复合涂层的摩擦因数，分析认为剥层磨损是复合涂层的主要磨损机理。涂层中Fe3Al和FeAl金属间化合物相较高的高温强度和硬度，能有效地阻碍裂纹的产生、扩展及扁平颗粒的断裂，从而使复合涂层表现出优异的高温耐磨性。高速电弧喷涂技术配-Fe-Al／WC粉芯丝材是一种新型、优质、高效、低成本的耐高温涂层制备技术，具有很大的应用潜力。     

铝合金/镀锌钢板Nd:YAG激光+MIG电弧复合热源熔-钎焊接头的组织与性能(英文)

基于铝合金和镀锌钢在熔点上的差异,以ER4043(AlSi5)为填充材料,采用大光斑Nd:YAG激光+MIG电弧复合热源焊接工艺实现两者的熔-钎焊接,研究熔钎焊接头组织和性能。铝合金/镀锌钢板熔钎焊接头分为熔焊接头和钎焊缝两部分,熔焊缝组织由α(Al)等轴晶和晶界上短棒状的Al-Si共晶组织组成,焊趾处的富锌区为α-Al-Zn固溶体和Al-Zn共晶组织。钎焊缝为Fe-Al金属间化合物层,厚度为2~4μm,金属间化合物包括FeAl2、Fe2Al5和Fe4Al13,其中FeAl2和Fe2Al5位于近钢侧的紧密层,而Fe4Al13则呈舌状或锯齿状向熔焊缝内生长。接头抗拉强度随着焊接电流和激光功率的增大呈先增大后减小的趋势,最高可达247.3 MPa。拉伸断裂位置一般位于熔焊缝的熔合区,为以韧性断裂为主的混合断裂。接头内硬度的最大值位于钎焊缝处,然后分别沿着两侧钢板和铝合金熔焊缝逐步降低。     

合金元素对Ni3Al（010）面反相畴界能影响的第一性原理研究

采用第一性原理投影缀加波赝势和广义梯度近似方法研究不同铝含量以及主要合金化元素Ti、Mo、Ru、Pd、Ta、W、Re和Pt等对Ni3Al(010)面反相畴界能的影响规律,并结合合金元素与第一近邻原子的相互作用关系对其进行讨论。结果表明:随着铝含量的增加,Ni3Al(010)面的反相畴界能显著升高;在富镍条件下,优先占据Ni3Al镍亚点阵位置的合金元素Ru、Pd和Pt会降低Ni3Al(010)面的反相畴界能,而优先占据Ni3Al铝亚点阵位置的合金元素Ti、Mo、Ta、W和Re则会增大Ni3Al(010)面的反相畴界能;合金元素对Ni3Al反相畴界能的影响既与该合金元素在化合物中亚点阵的优先占位相关,又与该合金元素与化合物中Ni与Al原子的键合强度相关。     

Combustion synthesis of Ni3Al by SHS with boron additions

The preparation of Ni₃Al intermetallic compound from elemental powder compacts with the addition of boron was conducted by self-propagating high-temperature synthesis (SHS) in this study. Effects of the boron content, preheating temperature, and particle size of the reactants on the combustion characteristics, as well as on the composition and morphology of final products were studied. Experimental observation indicates that the addition of boron results in a significant increase in the flame-front propagation velocity, leading to a two-stage combustion process preceded by the fast propagation of the flame front and consecutively followed by prolonged bulk combustion. However, the combustion temperature was slightly decreased by adding boron in the sample. The boron addition also contributed to a decrease in the activation energy associated with the combustion synthesis of Ni₃Al from 97.8 to 86.4 kJ/mol. In contrast to the presence of an intermediate phase (NiAl) and the unreacted Ni in the final burned product of the boron-free samples, complete reaction yielding a single-phase product of Ni₃Al was achieved for the boron-added samples. Moreover, the addition of boron also increased the density of the final products up to above 80% relative to the density of the Ni₃Al compound.     

Notch sensitivity of heavily cold-rolled Ni3Al foils

The notch sensitivity of 95% cold-rolled Ni₃Al foils was examined using double U-notched tensile specimens. The foils were found to be essentially insensitive to the presence of the notch. Plastic deformation occurred locally at the notch root to relieve the stress concentration, resulting in the notch insensitivity.     

A novel ultrafine-grained Ni3Al with increased cyclic oxidation resistance

An ultrafine-grained (UFG) Ni₃Al was fabricated by annealing an electrodeposited Ni–Al composite in vacuum at 600 °C for 2 h. The UFG Ni₃Al, compared to a compositional-similar but coarse-grained (CG) alloy prepared by arc-melting, exhibited a greatly increased cyclic oxidation resistance at 900 °C. Microstructural investigation showed that the CG alloy grew a scale with a high susceptibility to buckling and cracking because of the formation of large voids at the scale/metal interface, but that the UFG alloy grew an adherent scale, because its typical structure prevented the formation of the interface void during oxidation.     

Deformation behavior of Ni3Al single crystals during nanoindentation

The deformation behavior of (1 1 1), (1 1 0) and (0 0 1) oriented Ni₃Al single crystals was investigated by means of nanoindentation. Upon loading with the blunt and sharp indenter tips, the crystal deforms elastically in the initial stage followed by plastic deformation of which the onset is characterized by an obvious displacement burst (or pop-in) in the loading curve. This pop-in corresponds to homogeneous nucleation of dislocation loops under the indenter. When a sharp indenter tip was used, a major pop-in can be identified at a large load (7 mN for (1 1 1) crystal) in the plastic regime on loading. The major pop-in may be correlated with the special dislocation structure of the K–W locks in the Ni₃Al crystals that are formed during loading. The pop-in behavior during plastic deformation of Ni₃Al crystals is found to be closely related to the crystal orientation, pre-existing dislocation density in the sample surface, loading rate, and holding (at a constant sub-critical load) time as well. Pop-ins were also observed at critical loads in unloading processes.     

High temperature thermal expansion characteristics of Ni3Al alloys

The thermal expansion of Ni₃Al alloys with and without ternary additions have been investigated with the aid of a dilatometer. The Ni₃Al alloys were studied over the temperature range 25–1000 °C. The coefficient of thermal expansion of all the aluminides studied in this investigation varies linearly with the temperature. The coefficient of thermal expansion of Ni₃Al is found to show an increase with the decrease in Al content from stoichiometric composition. B and Zr additions decrease the value of Ni₃Al alloys at room temperature while Hf and Ti additions do not alter it significantly.     

Shear-induced chemical disordering in Ni3Al at different temperatures

Molecular dynamics simulations have been used to study shear-induced chemical disordering in Ni₃Al lattices at different temperatures and strain rates. Shearing determines the formation of an amorphous layer, the thickness of which increases linearly with the square root of time. The rate at which the amorphous layer grows is both shearing rate- and temperature-dependent. A linear correlation between the amorphous layer growth rate and the shear modulus is found. This suggests that mechanical properties could play a central role in shear-induced disordering processes.     

Recrystallization and grain growth in Ni3Al with and without boron

The recrystallization and grain growth of boron-free and boron-doped (500 ppm by weight) Ni₃Al polycrystals were investigated in the temperature range 700–1000°C. The levels of deformation were 17% reduction in length in compression for both alloys and 40% rolling reduction applied only to the boron-doped alloy. For alloys with or without boron, the Kolmogorov-Johnson-Mehl-Avrami relationship holds, with the Avrami exponent near unity, and the recrystallization rate is very slow. The activation energies for recrystallization are respectively 480 and 492 kJ/mol for boron-free and boron-doped to 40%. The grain growth kinetics obey a power law with the time exponent ranging from 0·2 to 0·4. The boron effect at 500 ppm was found to be small on both recrystallization and grain growth in Ni₃Al.     

Enthalpies of formation of Ni3Al: Experiment versus theory

Using Al solution calorimetry, enthalpies of formation of Ni₃Al in the L1₂ structure ranging from-41.3 to -42.3 kJ/mol were determined at temperatures from 300 to 1123 K. These enthalpies are substantial for an intermetallic compound and display a slight temperature dependence, which is contained within the experimental error. This temperature dependence is related to the lack of any transformations of the compound, which remains ordered up to the melting temperature. The measured enthalpies were combined with other thermodynamic data to estimate the excess entropy of formation of Ni₃Al. The high degree of ordering in the compound is reflected in the large negative value of the excess entropy,whose absolute value exceeds those for other high melting temperature intermetallic compounds. The full-potential linearized augmented Slater-type orbital method (FLASTO) was used to calculate the enthalpies of formation of paramagnetic and ferromagnetic Ni ₃ Al. These enthalpies of formation indicate the compound to be a weak ferromagnet, and they are in good agreement with the calorimetric data.