Al对CNTs增强Nb/Nb5Si3复合材料组织和性能的影响

以Nb、Si、CNTs和Al粉末为原料,采用放电等离子烧结法(SPS)原位合成了Nb-20Si-2 mass%CNTs-xAl(x=0、1、2、3、4 mass%)复合材料。利用扫描电镜(SEM)、电子探针微区分析(EPMA)和X射线衍射(XRD)等对复合材料的组织结构进行了分析,研究了Al对CNTs增强Nb/Nb5Si3复合材料的组织和性能的影响。结果表明:Al能部分固溶于Nb5Si3和Nbss相中,多余的Al会与Nb反应生成AlNb3相,较均匀地分布中Nb5Si3相中,并大部分聚集在Nb/Nb5Si3的界面处。Al元素的加入能明显改善Nb/Nb5Si3复合材料的断裂韧性,随着Al含量的增加,复合材料的断裂韧性先升高后降低,其中Al含量为2 mass%时达到最大值,即6.94 MPa·m^1/2,相对于未加时提高了约56.9%。同时Al元素还能有效降低Nb/Nb5Si3复合材料高温氧化速度,提高高温抗氧化性能,而Al元素的加入量越高,其高温抗氧化性能越好。     

定向凝固对Nb-14Si-22Ti-2Hf-2Al-4Cr合金组织和高低温力学性能的影响

采用光悬浮炉在氩气环境下制备了成分为Nb-14Si-22Ti-2Hf-2Al-4Cr的定向凝固试棒,研究了凝固工艺对合金相组成、组织形貌和高低温力学性能的影响,并与电弧熔炼态的合金进行了比较。结果表明,定向凝固试样相组成与电弧熔炼态相比没有发生变化,均由Nb基固溶体(Nb solid solution, NbSS)和Nb/Si化合物Nb5Si3组成,定向凝固合金NbSS呈枝晶状,硅化物呈板条状沿着生长方向分布。与电弧熔炼态相比,定向凝固速度为15和10 mm/h的合金在1250 ℃的抗压缩强度从电弧熔炼态的290 MPa分别提高到约442和493 MPa;15 mm/h的定向凝固后,合金的室温断裂韧性从电弧熔炼态的12 MPa·m1/2增加到15 MPa·m1/2。通过光悬浮定向凝固法制备的该合金具有优良的高低温力学性能     

多相Nb硅化物的断裂韧度和高温力学性能

通过机械合金化和热压烧结制备了4种近理论密度的Nb-xSi-2Fe（x=3,6,10,16）原位复合材料。X射线衍射（XRD）分析表明：制备的复合材料均由铌固溶体（Nbss）相、Nb3S i相、Nb5S i3相和Nb4Fe3Si5相组成。各物相的平均晶粒尺寸为3μm,并且呈等轴状。Nb-Si-Fe复合材料随着S i含量的增加断裂韧度减小,Nb-Si-Fe室温断裂韧度大于11MPam1/2,Nbss相的塑性变形能够减小界面的应力集中延迟裂纹的形核从而改善这些复合材料的断裂韧度。Nb-Si-Fe复合材料在1 300℃时的抗拉强度随S i含量的增加而增加。复合材料在1 300℃时的抗拉强度为112~237 MPa,拉伸延伸率为54%~95%,室温断裂韧度大于11 MPam1/2。     

Ti对Nb-20Si-5Al超高温合金性能的影响

采用放电等离子烧结法(SPS)制备了Nb-20Si-5Al-xTi(x=0,18,20,22,摩尔分数)超高温合金,研究了Ti加入量对Nb-20Si-5Al合金的室温断裂韧度和高温抗氧化性的影响。结果表明,随着Ti加入量的增加,超高温合金的相组成由Nbss、Nb₅Si₃和Al3Nb相转变成为Nbss、(Nb,Ti)5Si3和Ti相。Ti能明显改善Nb-20Si-5Al超高温合金的断裂韧度和高温抗氧化性能,随着Ti加入量的增加均先提高然后降低,在Ti加入量为20%时,合金断裂韧度最大,为7.41 MPa·m^1/2,相比未加Ti时提高了约56.9%,其高温氧化速率最低,为0.72×10^-4g²/(cm⁴·h)。添加Ti元素后,其氧化产物中出现Ti₂Nb₁₀O₂₉、TiNb₂O₇、TiO₂等,可以提高其氧化膜的致密性,从而提高高温抗氧化性能。     

Ti对SPS烧结Nb/Nb5Si3复合材料组织和性能的影响

以Nb、Si和Ti粉末为原料,采用放电等离子烧结(SPS)技术对Nb-20Si、Nb-20Si-5Ti、Nb-20Si-15Ti和Nb-20Si-24Ti材料进行原位合成。利用扫描电镜(SEM)、电子探针微区分析(EPMA)和X射线衍射(XRD)等手段对材料的组织结构进行分析,探讨Ti对复合材料组织和性能的影响规律。结果表明,Ti元素的加入使得复合材料中Nb5Si3相转变成(Nb,Ti)5Si3,随着Ti加入量的增加,组织中出现了单质的Ti相,当Ti含量达到24%时,组织中还会出现Nb3Si相;同时Ti的加入会降低复合材料的硬度,提高其高温抗氧化性能。     

Comparative studies on densification behavior,microstructure, mechanical properties and oxidation resistance of Mo-12Si-10B and Mo3Si-free Mo-26Nb-12Si-10B alloys

Two bulk Mo-Si-B based alloys (Mo-12Si-10B and Mo-26Nb-12Si-10B (at.%), abbreviated as 0Nb and 26Nb alloy respectively) were fabricated by mechanical alloying and then hot pressing. Comparative studies were carried out on the densification behavior, microstructure, room-temperature fracture toughness, elevated temperature compression and oxidation resistance of these two alloys. The results showed that alloy 0Nb was composed of (Mo), Mo₃Si and Mo₅SiB₂, while alloy 26Nb was free of Mo₃Si and had higher (Mo) content and a little γNb₅Si₃. Compared to the alloy 0Nb, alloy 26Nb presented better compactibility, higher room-temperature fracture toughness (8.84 ± 0.17 vs. 6.77 ± 0.20 MPa·m^1/2) and elevated temperature compression strength (851.7 ± 11.7 vs. 644.2 ± 10.2 MPa) but worse oxidation resistance.     

W和W-Mo对等离子烧结Nb/Nb5Si3复合材料显微组织的影响

利用等离子烧结(SPS)技术,对Nb-20Si,Nb-20Si-10W和Nb-20Si-10W-10Mo试样进行了烧结,主要研究了W和W-Mo对Nb/Nb5Si3复合材料显微组织的影响.利用扫描电镜(SEM)观察显微组织,X射线衍射仪(XRD)分析相组成,电子探针微观分析(EPMA)进行成分分析.结果表明:烧结样品相对密度达到99.59%;W可以很好地固溶在Nb/Nb5Si3复合材料中,且显微组织没有变化;W-Mo固溶后显微组织有明显变化,出现了单质Nb相,W和Mo复合固溶的Nb相固溶体,并且有部分Nb固溶在W相中,在Nb5Si3相中没有发现固溶现象.     

Effect of Cr on Microstructure and Fracture Toughness of Nb-20Ti-16Si-xCr Alloys

The present paper reported the phase stability and microstructures evolution of Nb-20Ti-16Si-xCr (x = 0～20at.%) in-situ composites as function of Cr addition. It was suggested that with the addition of Cr less than 7%, the silicide phase in as-cast Nb-20Ti-16Si alloy was Nb3Si. The silicides changed to be α-Nb5Si3 by the addition of Cr above 7%. It was found that annealing of 1300 ℃ for 100 h could result in the decomposition of Nb3Si to NbSS and α-Nb5Si3 in Cr containing Nb-20Ti-16Si based alloys by means ...     

合金化元素Ti对Laves相Cr_2Nb力学性能及耐蚀性的影响

采用真空非自耗电弧熔炼工艺制备了Cr2Nb-XTi(X=5,10,15,at%)合金,利用光学显微镜(OM),X射线衍射(XRD)仪,扫描电镜(SEM)对电弧熔炼态铸锭的组织进行了研究,探讨了合金化元素Ti的含量对Laves相Cr2Nb力学性能及耐蚀性的影响。结果表明:3种成分的电弧熔炼态合金凝固组织主要由C15-Cr2(Nb,Ti)相和六方的β-(Ti,Nb)以及体心立方结构的β-(Nb,Ti)相组成。在5Ti和10Ti合金冷速较小的铸锭上部凝固组织中出现了亚稳相C14-Cr2(Nb,Ti)。通过对合金力学性能研究表明,随合金化元素Ti含量的增加,Laves相Cr2Nb合金的显微硬度逐渐降低,断裂韧性增大,当Ti含量达到15at%时,合金的断裂韧性达到了3.1 MPa·m1/2,比单相Laves相Cr2Nb提高1倍。另外,对腐蚀性能的测试表明,Ti含量增加材料腐蚀性能下降,但15Ti合金仍表现出良好的耐蚀性。     

Processing and mechanical properties of a molybdenum silicide with the composition Mo–12Si–8.5B (at.%)

Alloys with the nominal composition Mo–12Si–8.5B (at.%) were prepared by arc-melting or powder-metallurgical processing. Cast and annealed alloys consisted of approximately 38 vol.% α-Mo in a brittle matrix of 32 vol.% Mo₃Si and 30 vol.% Mo₅SiB₂. Their flexure strengths were approximately 500 MPa at room temperature, and 400–500 MPa at 1200°C in air. The fracture toughness values determined from the three-point fracture of chevron-notched specimens were about 10 MPa m^1/2 at room temperature and 20 MPa m^1/2 at 1200°C in air. The relatively high room temperature toughness is consistent with the deformation of the α-Mo particles observed on fracture surfaces. Three-point flexure tests at 1200°C in air and a tensile test at 1520°C in nitrogen indicated a small amount of high temperature plasticity. Extrusion experiments to modify the microstructure of cast alloys were unsuccessful due to extensive cracking. However, using powder-metallurgical (PM) techniques, microstructures consisting of Mo₃Si and Mo₅SiB₂ particles in a continuous α-Mo matrix were fabricated. The room temperature fracture toughnesss of the PM materials was on the order of 15 MPa m^1/2.     

Effects of Ni,Co, B,and Ge on the microstructures and mechanical properties of Nb-Ti-Si ternary alloys

Nb-Si in situ composites with a nominal composition of Nb-22Ti-12Si-X (at.%, X represents Ni, Co, B, or Ge) are prepared using non-consumable arc melting technology. The effects of the alloying elements on the microstructures and mechanical properties are investigated. The Nb-22Ti-12Si ternary alloy consists of Nbss and Nb₃Si. A new phase of Ti₂Ni or Ti₂Co is introduced into the ternary system after adding Ni or Co. The addition of 6% Ge promotes the formation of Nb₅Si₃ and creates significantly finer microstructures. The values of the high temperature strength and room temperature fracture toughness of Nb-22Ti-12Si-6Ge are 566.33MPa and 12.81 MPa·m^1/2, respectively, which are approximately 88.2% and 18.5% higher than those of Nb-22Ti-12Si (300.98 MPa and 10.81 MPa·m^1/2). The addition of 3% B changed the morphological features and induced the appearance of large fine rosettes, which is favorable for restraining the crack propagation, and it also leads to a 22.3% increase in room temperature fracture toughness compared with the Nb-22Ti-12Si ternary alloy.     

Effects of B and Si on the fracture toughness of the Nb–Si alloys

Nb–Si alloys have been widely considered as the potential candidate materials for turbine applications. Optimal amounts of B and Si addition to Nb–18Ti–14Si (at%, F1) were identified based on Nb–Ti–Si–B phase diagram. Nb–18Ti–14Si–4.5B (F2) had been obtained desirable (Nb) + T2 eutectic and significantly improved fracture toughness from 7.85 (F1) to 11.98 MPa m^1/2. With extra 3Si addition, F3 (Nb–18Ti–17Si–4.5B) consisted of primary T2 and (Nb) + T2 eutectic, it retained comparable fracture toughness of 11.76 MPa m^1/2, even excessive amounts of primary T2 do not compromise fracture toughness.     

钛的电阻钎焊技术研究

研究了Ｔｉ－２４Ａｌ－１１Ｎｂ－２Ｓｉ和Ｔｉ－２４Ａｌ－１１Ｎｂ－５Ｓｉ金属间化合物合金的热轧组织与性能,结果发现：随着变形量的增加,两种合金第二相Ｔｉ５Ｓｉ３变得细小且趋向于均匀分布。变形量越大,合金的室温四点弯曲程度越大,含Ｔｉ５Ｓｉ３较多的Ｔｉ－２４Ａｌ－１１Ｎｂ－５Ｓｉ合金的弯曲强度较高。两种合金的室温弯曲断口形貌均为准解理形式,两相界面结合较强。高温拉伸试验表明：随变形量的增大,Ｔｉ－２４Ａｌ－１１Ｎｂ－２Ｓｉ合金的拉伸强度和塑性都增加。Ｔｉ－２４Ａｌ－１１Ｎｂ－５Ｓｉ合金由于变形量较大和较高的强化相体积含量,拉伸强度明显较Ｔｉ－２４Ａｌ－１１Ｎｂ－２Ｓｉ合金的为高,但塑性却大为降低     

Effect of Gallium on microstructure and mechanical properties of Nb–Si eutectic alloy

In this paper, we report a significant improvement in mechanical properties of near eutectic Nb–Si alloys by addition of Gallium (Ga) and control of microstructural length scale. A comparative study of two alloys Nb-18.79 at.%Si and Nb-20.2 at.%Si–2.7 at.%Ga were carried out. The microstructure refinements were carried out by vacuum suction casting in water cooled thick copper mold. It is shown that addition of Ga suppresses Nb₃Si phase and promotes β-Nb₅Si₃ phase. The microstructural length scale and in particular eutectic spacing reduces significantly to 50–100 nm in suction cast ternary alloys. Compression test shows a strength of 2.8 ± 0.1 GPa and plasticity of 4.3 ± 0.03%. In comparison, the binary Nb-18.79 at.%Si alloy processed under identical conditions exhibit coarser length scale (300–400 nm) and brittle behavior. The fracture toughness of Ga containing suction cast alloy shows a value of 24.11 ± 0.5 MPa√m representing a major improvement for bulk Nb–Si eutectic alloy.     

PROCESSING AND PROPERTIES OF Nb_3Al ALLOYS

ＰＲＯＣＥＳＳＩＮＧＡＮＤＰＲＯＰＥＲＴＩＥＳＯＦＮｂ_３ＡｌＡＬＬＯＹＳＨＡＮＡＤＡＳｈｕｊｉ；ＴＡＢＡＲＵＴａｔｓｕｏａｎｄＧＮＭＡＭＯＯＲＴＨＹＲａｊａｐｐａ（ＩｎｓｔｉｔｕｔｅｆｏｒＭａｔｅｒｉａｌｓＲｅｓｅａｒｃｈ，ＴｏｈｏｋｕＵｎｉｖｅｒ?..     

球磨时间和热压温度对粉末冶金Nb-16Si-22Ti-2Al-2Hf-2Cr合金显微组织和室温力学性能的影响

采用粉末冶金法制备了Nb-16Si-22Ti-2Al-2Hf-2Cr合金,研究了粉末球磨时间（5、10、20 h）及热压烧结温度（1500、1600 ℃）对合金组织和室温力学性能的影响。结果表明：热压烧结后的合金由Nb基固溶体NbSS、Ti基固溶体TiSS和硅化物Nb5Si3三相组成。随着球磨时间的延长,Nb5Si3和TiSS的含量增加,而NbSS的含量减少。室温硬度随球磨时间延长和热压烧结温度的升高而提高,20 h/1600 ℃热压烧结合金硬度值最高,HV硬度达到11500 MPa。1500和1600 ℃热压烧结下合金的断裂韧性随着粉末球磨时间的延长均呈下降的趋势,5 h/1500 ℃热压烧结合金断裂韧性值最高,为10.14 MPa·m1/2。     

定向凝固Nb-Ti-Si基超高温合金的组织与室温条件断裂韧性

采用真空自耗电弧熔炼法制备了Nb-Ti-Si基超高温合金的母合金锭,在2050℃的熔体温度下实现了合金的有坩埚整体定向凝固.测定了电弧熔炼态与定向凝固试样的室温条件断裂韧性,采用SEM,EDS等方法分析了凝固速率V分别为10,20和50 μm/s的整体定向凝固组织、单边切口梁弯曲试样的断口形貌及裂纹扩展路径,并讨论了其断裂机理.结果表明:合金的整体定向凝固组织主要由沿着试棒轴向挺直排列的横截面为多边形的初生(Nb,X)5Si3 (X代表Ti,Hf和Cr元素)棒与耦合生长的层片状Nbss/(Nb,X)5Si3共晶团(Nbss表示铌基固溶体)组成.整体定向凝固显著提高合金的室温条件断裂韧性KQ,且V=50μm/s时的最高,达16.1 MPa·m1/2,较电弧熔炼态试样的KQ提高了50.5％.定向凝固试样中Nbss与(Nb,X)5Si3沿垂直于受力方向的定向排列以及粗糙的Nbss产生的裂纹桥接和偏转,增大了裂纹扩展阻力,从而提高了合金的室温条件断裂韧性.     

Microstructural evolution and mechanical properties of an Nb–16Si in-situ composite with Fe additions prepared by arc-melting

This paper deals with phase constitutions, microstructural evolutions, and mechanical properties of Nb–16Si–xFe in-situ composites (where x = 2, 4, 6 at.%, referred as to 2Fe, 4Fe and 6Fe alloys, hereafter) prepared by arc-melting. It is found that with additions of Fe, Nb₄FeSi silicide arises and microstructures of as-cast samples are consisted of dendritic-like Nb_SS phase, Nb₃Si block, and Nb₄FeSi matrix in the 2Fe and 4Fe alloys, and of the dendritic-like Nb_SS phase and Nb₄FeSi matrix in the 6Fe alloy. When heat-treated at 1350 °C for 100 h, part of the Nb₃Si phase decomposes in the 2Fe and 4Fe alloys, and the 6Fe alloy shows no change in microstructure as compared with the as-cast one. The Nb₄FeSi silicide is found to be brittle, its fracture toughness and elastic modulus are first obtained, having values about 1.22 MPa m^1/2, and 310 GPa, respectively. The fracture toughness of the bulk as-cast and heat-treated Nb–16Si–xFe samples are changed slightly by the Fe additions, which is in a range of 9.03–10.19 MPa m^1/2. It is interesting that at room temperature, strength is improved by the Fe additions, whereas at 1250 °C and 1350 °C the strength decreases. As the Fe content increased from 2 at.% to 6 at.%, for example, the 0.2% yield strength increases from 1410 MPa to 1580 MPa at room temperature, decreases from 479 MPa to 385 MPa at 1250 °C.     

等离子电火花烧结TiAl-Nb复合材料的显微组织与断裂韧性(英文)

将钛铝预合金粉末和铌粉按照摩尔比9:1混合均匀,再采用等离子电火花烧结技术在1250°C、50MPa下烧结5min制备细晶钛铝基复合材料。采用X射线衍射、电子扫描、透射以及电子探针探讨烧结样品中显微组织、相成分的分布及晶粒度。结果表明:合金的显微组织主要由大量的层片γ相、O相、Nbss(Nb固溶相)以及B2相组成;室温烧结样品的断裂韧性高达28.7MPa·m1/2,韧性铌固溶相在裂纹尖端以塑性延伸的方式吸收断裂能,从而提高了合金的断裂韧性;B2相以也会促进裂纹的侨联和分叉。对合金各相的显微硬度也进行了测试。     

Martensitic transformation of Ti-18Nb(at.%) alloy with zirconium

The addition of 3%～9% Zr on the martensitic transformation of Ti-18Nb(at.%) alloy was investigated. The results of microstructure and X-ray diffraction (XRD) analysis show that the phase constitution of as-quenched Ti-18Nb-9Zr(at.%) alloy consists of the retained matrix and martensite, while that of the other three alloys is single martensite. No trace of athermal phase was found in any of the as-quenched alloys. Unlike the effect of Nb addition on the martensitic transformation start temperature Ms of Ti-1...