Microstructure and strength of B2-ordered (Ni,Co)Al

A transmission electron microscopy (TEM) investigation of the morphologies and crystal structures of precipitates in supersaturated B2-ordered (Ni,Co)Al has revealed that rod-like precipitates of the (Ni,Co)₂Al phase with a hexagonal structure form parallel to the <111> direction of the B2 matrix. By aging at temperatures below 973 K, a long period superlattice structure of hexagonal (Ni,Co)₂Al was formed. The (Ni,Co)Al hardens appreciably by the precipitation of these phases. An energy dispersive spectroscopy (EDS) was used to analyze the compositions of each phase formed in the B2-(Ni,Co)Al. The effects of the dispersion of the (Ni,Co)₂Al phase on the temperature dependence of the strength of the B2-(Ni,Co)Al have been investigated over a temperature range from 298 K to 1173 K.     

Microstructures and morphologies of B2-Ordered NiAl(Co) and FeAl(Co)

Fine dispersion of disordered phases is obtained in a Ni-Al-Co and Fe-Al-Co ternary system. A transmission electron microscopy investigation has been performed in the present work on the precipitation of supersaturated B2-ordered (Ni,Co)Al and α-Fe in B2-ordered FeAl(Co) with different stoichiometries. Precipitation behavior and hardening were investigated by measuring the hardness variation. The hardness of (Ni,Co)Al and B2-FeAl(Co) increased appreciably by the fine precipitation of (Ni,Co)₂Al, α-Fe, and overage softening occurred after prolonged aging. In case of B2-ordered (Ni,Co)Al, the (Ni,Co)₂Al phase had a hexagonal structure and took a rod-like shape with the long axis of the rod parallel to the 〈111〉 directions of the B2 matrix. By aging at temperatures below 873 K, a long period superlattice structure appeared in the hexagonal (Ni,Co)₂Al phase. The orientation relationship between the (Ni,Co)₂Al precipitates and the B2-(Ni,Co)Al matrix was (0001)_p//(111)_B2 and $[\bar 12\bar 10]_p //[\bar 110]_{B2}$ , where the suffix p and B2 denote the (Ni,Co)₂Al precipitate and the B2-(Ni,Co)Al matrix, respectively. (Ni,Co)Al hardened appreciably by the fine precipitation of the (Ni,Co)₂Al phase. On the other hand, in case of B2-FeAl(Co), the disordered α-Fe phase was present as a precipitate in a B2-FeAl(Co) matrix and had a cubic-cubic orientation with the matrix. At the early aging periods, prismatic dislocation loops formed in the B2-FeAl(Co) matrix. B2-FeAl(Co) matrix was typically hardened by the precipitation of α-Fe.     

RETRACTED ARTICLE: A study on the microstructure of precipitation strengthened B2-ordered NiAl

Microstructural control to produce a multiphase structure and there by improve the high temperature strength as well as low temperature ductility of intermetallics has received much attention. A transmission electron microscopy investigation has been performed in the present work on the precipitation of supersaturated B2-ordered (Ni,Co)Al and α-Cr in B2-ordered β-NiAl with different stoichiometry. Precipitation behavior and hardening were investigated by measuring the hardness variation. The hardness of (Ni,Co)Al and β-NiAl increases appreciably by the fine precipitation of (Ni,Co)₂Al and α-Cr, and overage softening occurs after prolonged aging. In the case of B2-ordered (Ni,Co)Al, the (Ni,Co)₂Al phase has a hexagonal structure and takes a rod-like shape with the long axis of the rod parallel to the 〈111〉 directions of the B2 matrix. By aging at temperatures below 873 K, a long period superlattice structure appears in the hexagonal (Ni,Co)₂Al phase. The orientation relationship between the (Ni,Co)₂Al precipitates and the B2-(Ni,Co)Al matrix is found to be (0001)_p//(111)B2 and [[`1]\bar 12[`1]\bar 10]_p//[[`1]\bar 110]_B2, where the suffixes p and B2 denote the (Ni,Co)₂Al precipitate and the B2-(Ni,Co)Al matrix, respectively. (Ni,Co)Al hardens appreciably by fine precipitation of the (Ni,Co)₂Al phase. On the other hand, in the case of B2-NiAl, perfect lattice coherency is retained at the interfaces between the α-Cr particles and the matrix during the initial stage of aging. After prolonged aging, a loss of coherency occurs by the attraction of matrix dislocations to the particle/matrix interface followed by climbing around the particles.     

PRECIPITATION HARDENING IN B2-ORDERED NiAl BY Ni2AlTiCOMPOUND

1. IlltroductionA significant improvement in the high temperature strength has been attained by form-ing a two phase mixture of B2-ordered NiAl and L21-Ni2AlTi (H phase) precipitates[1]. TheHeusler phaJse (Ni2AlTi) has a unit cell composed of eight B2 unit cells, in which Al andTi atoms occuPy ordered sites on one sublattice. Field et al.l2] studied the microstructuresof the allOys along line between the pseudobinary NiAl and Ni2AlTi and obtained an indi-cation of spinodal ordering in…     

Microstructure of Co precipitation strengthened B2-ordered NiAl

A transmission electron microscopy investigation on the phase decomposition of B2-ordered (Ni,Co)Al supersaturated with Ni and Co has revealed the precipitation of (Ni,Co)₂Al which has not been expected from the reported equilibrium phase diagram. The (Ni,Co)₂Al phase has a hexagonal structure and takes a rodlike shape with the long axis of the rod parallel to the 〈111〉 directions of the B2 matrix. By aging at temperatures below 873 K, a long period superlattice structure appears in the hexagonal (Ni,Co)₂Al phase. The orientation relationship between the (Ni,Co)₂Al precipitates and the B2-(Ni,Co)Al matrix is found to be (0001)_p//(111)_B2 and [ $ \bar 1 $ 2 $ \bar 1 $ 0]_p//[ $ \bar 1 $ 10]_B2, where the suffix p and B2 denote the (Ni,Co)₂Al precipitate and the B2-(Ni,Co)Al matrix, respectively. (Ni,Co)Al hardens appreciably by the fine precipitation of the (Ni,Co)₂Al phase.     

MICROSTRUCTURES AND MECHANICAL PROPERTIES OF β-NiA1 CONTAINING α-Fe PRECIPITATES

1. 'IntroductionThe BZ-structural intermetallic, NiAI, has received considerable attention because ofits potential for high temperature applicationsll)21. Its advalltages are the low density of5.95g/cm' (approximately two-thirds the density of nickel-base superalloys), excellent thermal conductivity (four to eight times that of nickeLbase superalloys) and good oxidationresistance at high temperature. However, before the compound can be exploited for thispurpose its low ductility at low tempe…     

HARDENING OF L1_2-ORDERED Co_3Ti BY PRECIPITATION OF FCC-Co PHASE

1.IntroductionLlz-orderedC03Tihasat6ractedm1lchattentionbecauseofitsp0sitivetemperaturedependenceofstrengthI1t2],thehighesttemperatureatwhichthestrellgthattainsitshigh-estval..[2]andhighductilityoverawiderangeoftemperature[3].Thestrellgthlevel,however,isnotashighasthat0fNi3ALbasedall0ys[2].Acc0rdingt0thereI,ortedCo-Tibinaryphasediagram[']?theryi-C.,Tiphaseexistsoveracompositi0nrangeapproximatelyfrom2Ot025m0l%TiasshowninFig.l.Thes0lubility0fTiinCohasbeenwellestab-lishedbecausetheprecipit…     

Precipitation of Icosahedral Quasicrystalline Phase, R-phase and Laves Phase in Ferritic Alloys

Ferritic heat resistant steels involving precipitation of intermetallic phases have drawn a growing interest for the enhancement of creep strength, while the brittleness of the intermetallic phases may lower the toughness of the alloy.Therefore, it is necessary to optimize the dispersion characteristics of the intermetallics phase through microstructural control to minimize the trade-off between the strength and toughness. The effects of α-Fe matrix substructures on the precipitation sequence, morphology, dispersion characteristics, and the stability of the intermetallic phases are investigated in Fe-Cr-W-Co-Si system. The precipitates of the Si-free Fe-10Cr-I.4W-4.5Co (at%) alloy aged at 873K are the R-phase but those of the Si-added Fe-10Cr-1.4W-4.5Co-0.3Si (at%) alloy are the icosahedral quasicrystalline phase. The precipitates in both the Si-free and Si-added alloys aged at 973K are the Laves phase. Matrix of the alloys is controlled by heat treatments as to provide three types of matrix substructures; ferrite, ferrite/martensite mixture and martensite. The hardening behavior of the alloys depends on the matrix substructures and is independent of the kinds of precipitates. In the alloys with ferrite matrix, the peak of hardness during aging at 873K shifts to longer aging time in comparison with that in the alloys with lath martensite matrix which contain numbers of nucleation sites.     

Co对Cu-Cr合金组织和性能的影响

研究了Cu-Cr-Co合金经80%变形量冷轧和450 ℃时效后的组织和性能,并与Cr-Cr合金进行了对比。结果表明, Cu-0.66Cr-0.05Co和Cu-0.62Cr-0.22Co合金的性能在450 ℃时效4 h时达到峰值,此时的抗拉强度、硬度及导电率分别为376 MPa和410 MPa、143.7 HV0.5和138.4 HV0.5、84.1%IACS和66.2%IACS。峰时效态Cu-Cr-Co合金析出相为体心立方结构(bcc),并与基体呈Nishiyama-Wassermann取向关系,Co含量对Cu-Cr-Co合金的晶粒形貌几乎没有影响。与Cu-Cr合金相比,Co的加入使合金时效的时间延长,硬度有所增加,抗软化性能提高,但抗拉强度和导电率均下降。由于Cu和Co在422 ℃以上具有一定的固溶度,在时效过程中部分Co逐渐固溶进基体中,形成固溶体,并没有与预测一样分布在析出相外围,降低了合金综合性能。     

固溶处理及时效对镍钛形状记忆合金组织演化及力学性能的影响

将镍钛形状记忆合金Ni50.9Ti49.1（摩尔分数）在1123 K固溶处理2 h,然后分别在573、723和873 K时效2h。采用透射电镜、高分辨率透射电镜、扫描电镜和压缩实验,系统研究固溶处理和时效对镍钛合金组织演化及力学性能的影响。结果表明：固溶处理有助于消除原始镍钛样品中的Ti2Ni相,但不能消除TiC相。固溶处理导致镍钛合金中原子排列的有序畴界。在所有时效镍钛样品中,Ni4Ti3析出相、R相和B2奥氏体相共存于室温下的镍钛基体上,然而在873 K时效的镍钛样品中,可以观察到马氏体孪晶。在573和723 K时效的镍钛样品中,细小密集的Ni4Ti3相均匀分布在镍钛基体上,而且与B2基体保持共格关系。然而,在873 K时效的镍钛样品中, Ni4Ti3相尺寸非常不均匀,和B2基体保持共格、半共格和非共格关系。在723 K时效的条件下,细小均匀的Ni4Ti3相阻碍位错运动,导致最大的位错滑移临界分切应力,因此镍钛样品表现出最高的屈服强度。     

基于FactSage的Fe-15Mn-8Al-0.25C低密度钢的组织及力学性能

借助FactSage数值模拟软件对Fe-(10~20)Mn-(5~10)Al-(0~0.5)C系低密度钢的凝固及冷却路径、相变及析出相进行了研究,利用FactSage软件中的FSstel数据库对该体系的垂直截面图进行计算,分析了Mn、Al及C元素对凝固及冷却过程中相变及析出相的影响,并得到了Fe-15Mn-8Al-0.25C低密度钢的平衡凝固相变路径图。结果表明,Fe-15Mn-8Al-0.25C低密度钢中热力学计算出的平衡相有液相、铁素体、奥氏体和κ-碳化物, 由1600 ℃冷却至600 ℃完整的平衡相变路径为:液相→液相+铁素体→液相+铁素体+奥氏体→铁素体+奥氏体→铁素体+奥氏体+κ-碳化物。C和Mn含量的增加可扩大Fe-15Mn-8Al-0.25C低密度钢奥氏体相区,Al元素增加缩小奥氏体相区。κ-碳化物的析出温度随着Al与C含量的增加而升高,Al与C元素均可促进κ-碳化物析出。Fe-15Mn-8Al-0.25C低密度钢800 ℃时效3 h后的抗拉强度为602 MPa,屈服强度为520 MPa,断后伸长率为28.6%,时效5 h后的抗拉强度为729 MPa,屈服强度为685 MPa,断后伸长率为22.4%,随着时效时间增加,试验钢的强度增加,断后伸长率降低。Fe-15Mn-8Al-0.25C低密度钢的密度为6.99 g/cm³,相比普通钢材减重效果达10.4%。     

Microstructure and strengthening mechanism of Ni3Al intermetallic compound

Structural studies have been performed on precipitation hardening found in Ni₃Al-base ordered alloys using transmission electron microscopy. The γ′ phase hardens appreciably by the fine precipitation of disordered γ. The strength of γ′ increases over the temperature range of experiment by the precipitation of fine γ particles. The peak temperature where a maximum strength was obtained shifted to higher temperature. Superlattice dislocations dissociate into fourfold Shockley partial dislocations in a uniform supersaturated solid solution of the γ′ phase. Dislocations are attracted into the disordered γ phase and dissociate further in the particles. At any stage of aging, dislocations cut through the particles and the Orowan bypassing process does not occur even in the overaged stage of this alloy system. When the applied stress is removed, the dislocations make cross slip into (010) plane, while those in γ precipitates remain on the (111) primary slip plane. The increase of high temperature strength in γ′ containing γ precipitates is due to the restraint of cross slip of dislocations from (111) to (010) by the dispersion of disordered γ particles. The orientation dependence of strength is decreased by the fine precipitation of a disordered γ phase.     

Precipitation behavior of B2-ordered aluminide

Fine dispersion of disordered phases is obtained in Ni−Al−Cr and Fe−Al−Co temary systems. A transmission electron microscope investigation has been performed on the precipitation of α-Cr in B2-ordered β-NiAl with different stoichiometry and α-Fe in B2-FeAl(Co) compound. Precipitation behavior and hardening were investigated by measuring the hardness variation. The hardness of NiAl and FeAl increases appreciably with the fine precipitation of α-Cr and α-Fe, and over-age softening occurs after prolonged aging. In the case of B2-NiAl(Cr), perfect lattice coherency is maintained at the interfaces between the α-Cr particles and the matrix during the initial stage of aging. After prolonged aging, a loss of coherency occurs by the attraction of matrix dislocations to the particle/matrix interface, followed by climbing around the particles. On the other hand, in the case of B2-FeAl(Co), the disordered α-Fe phase is present as a precipitate in the B2-FeAl(Co) matrix and has a cubic-cubic orientation with the matrix. At the early aging periods, prismatic dislocation loops formed in the B2-FeAl(Co) matrix. B2-FeAl(Co) matrix is typically hardened by the precipitation of α-Fe.     

Dislocation loops and phase decompositions of B2-FeAl(Co) compound in Fe–Al–Co ternary system

Phase decompositions in B2-FeAl(Co) compound were investigated by means of transmission electron microscopy. Precipitation behavior and hardening were investigated by measuring the hardness variation. The disordered α-Fe phase is present as a precipitate in B2-FeAl(Co) matrix and has a cubic-cubic orientation with the matrix. At the early aging periods prismatic dislocation loops formed in B2-FeAl(Co) matrix. The loops have a Burgers vector of a<100> and have a shape of square with their sides lying on the {100} plane of the B2-FeAl(Co) matrix. As the aging time is prolonged, the dislocation loops disappear and α-Fe precipitates form at the locations of dislocation loops. B2-FeAl(Co) matrix is hardened typically by the precipitation of α-Fe.     

高强高导电CuCrZr合金时效过程中析出相的演化规律

对固溶态CuCrZr合金经不同温度时效后的析出相进行显微观察,并对其电导率进行了测试。结果表明:450 ℃时效30 min的析出相为5 nm以下的单质Cr相,并且与基体呈cube-on-cube取向关系。450 ℃峰值时效120 min时析出相为CrCu₂Zr相和Cr相,尺寸为10nm左右,且与基体共格;600 ℃和800 ℃过时效30 min后析出相主要演变为球状的Cr相和棒状的Cu₄Zr相。在600 ℃时效处理后部分棒状析出相已显著长大至50 μm左右,而800 ℃时效处理后几乎看不到细小的析出相,其中棒状Cu₄Zr析出相长大至200 μm以上,球状纯Cr析出相也接近50 μm。CuCrZr合金在450 ℃时效时导电率随时效时间的延长不断增高,在120 min后达到最大值且几乎不再变化。根据析出相转化率与导电率的线性关系,建立了合金在400、450、500和600 ℃下的析出动力学方程。     

Effect of Cu on the evolution of precipitation in an Fe–Cr–Ni–Al–Ti maraging steel

The evolution of precipitates in an Fe–Cr–Ni–Al–Ti stainless maraging steel alloyed with Cu was investigated during aging at 525 °C. Atom probe tomography was used to reveal the development of precipitates and to determine their chemical composition. Two types of precipitates were observed to form during the aging process. Based on their chemical composition these are assumed to be NiAl B2 and Ni₃(Ti,Al) (η-phase). The two phases of precipitates were found to develop independently of each other and the addition of Cu was found to accelerate precipitation. However, the effect of Cu on the nucleation of these phases is different: on the one hand, in the case of NiAl, Cu is incorporated and thus reduces the activation energy by reducing the lattice misfit; on the other hand, Cu acts as a nucleation site for the precipitation of Ni₃(Ti,Al) by forming independent Cu clusters.     

Microstructure of aluminized stainless steel 310 after annealing

The aluminized coating on type 310 stainless steel prepared by high-activity Al pack cementation method has been annealed at 900 °C for 12 h to transform the brittle δ-Fe₂Al₅ phase into the more ductile β-FeAl phase. The microstructure is studied in detail with transmission electron microscopy. The thick outer layer has β-(Fe, Ni)Al as matrix with cube-like Cr₂Al precipitates. The interfacial layer has a thin layer of metastable FCC phase (layer I) and then mixed β-(Fe, Ni)Al grains and α-(Fe, Cr) grains (layers II and III). The Cr₂Al precipitates are present in the β-(Fe, Ni)Al grains in layer II but not in those in layer III, while β-FeAl precipitates are present in the α-(Fe, Cr) grains in both layers. The orientation relationships between various phases, the formation of the layers, and the precipitation of Cr₂Al in β-(Fe, Ni)Al are discussed.     

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。     

Morphology of M23C6 precipitation in L12-ordered Ni3(Al, Cr)

A transmission electron microscope investigation has been performed on the morphology of M₂₃C₆ precipitation in L1₂-ordered Ni₃(Al, Cr) containing 0.1–0.5 mol% of carbon. By aging at temperatures around 1073 K after solution annealing at 1423 K, fine octahedral-shaped precipitates of M₂₃C₆ bounded by {111} facets appear first on the dislocations and then in the matrix. The shapes of the precipitates are not always equilateral but tetragonal or elongated octahedral ones appear during aging. Planar growth faults were observed in some of the octahedral precipitates. After prolonged aging or by aging at higher temperatures, these shapes of precipitates become unstable. The M₂₃C₆ precipitates then adopt a rod-like morphology elongated parallel to the 100 directions and characterized by steps bounded by {111} facets.     

TiAl金属间化合物中（Al,Ag）3Ti,Ti3AlC的析出形态

用透射电镜观察了在不同温度，不同时间时效时Ｌｌ０－ＴｉＡｌ金属间化合物中形成的Ｌｌ２－（Ａｌ，Ａｇ０３Ｔｉ，Ｔｉ３ＡｌＣ析出相的形态以及与基体之间的位向关系，讨论了析出相的形态与ＴｉＡｌ基体间的错配度的关系。