Al含量对Nb-Ti-C合金组织的影响

利用真空非自耗电弧炉制备了不同Al含量的Nb-21Ti-4C(βNb-Ti)合金,研究了Al元素含量变化对Nb-21Ti-4C合金组织和晶格常数的影响。研究表明:铸态条件下合金由枝晶生长的Nb基固溶体(Nbss),碳化物((Nb,Ti)C),Nb3Al和枝晶间Nbss/MC共晶组织构成;Al元素部分固溶进入Nbss和MC中,随着Al含量增加,以Nb3Al相生长在Nbss内部。Al元素含量增加,使得Nbss枝晶先变大后变小。1100℃,24h热处理后,Nbss内部析出针状或片状碳化物和Nb3Al,导致Nbss晶格常数增大;枝晶间碳化物内部Nbss进一步长大,Nb原子的析出和Al元素固溶含量变化导致碳化物晶格常数改变。     

Si元素含量对激光快速成形制备Nb-Si二元合金显微组织演变的影响

以铌粉和硅粉为原料,采用双通道同轴送粉制备了四种不同Si元素含量的Nb-Si二元合金,通过扫描电镜（SEM）、能谱仪（EDS）及X射线衍射仪（XRD）等分析了合金的显微组织演变及维氏硬度.结果表明,硅含量由7%增加至25%,合金的显微组织由Nb_SS+Nb₃Si转变为初生Nb_SS+（Nb_SS/Nb₃Si）共晶,硅含量为18%时,呈Nb_SS/Nb₃Si全共晶组织,硅含量提高至25%,合金中出现初生β-Nb₅Si₃相,并仍存在Nb_SS/Nb₃Si共晶组织.铌和硅粉末在激光作用下原位反应并快速凝固,显著细化了Nb-Si合金的显微组织.随硅含量增加,硅化物含量逐渐增加,合金显微硬度由746 HV增至1 342 HV.     

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。     

DIRECTIONALLY SOLIDIFIED MICROSTRUCTURE OF AN ULTRA-HIGH TEMPERATURE Nb-Si-Ti-Hf-Cr-Al ALLOY

The directionally solidified samples of an ultra-high temperature Nb-Si- Ti-Hf-Cr-Al alloy have been prepared with the use of an electron beam floating zone melting (EBFZM)furnace, and their microstructural characteristics have been analyzed. All the primary dendrites of Nb solid solution (Nbss), euteetic colonies of Nbss plus (Nb, Ti)3 Si//(Nb, Ti)5 Si3 and chains of (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates align along the growth direction of the samples. With increasing of the withdrawing rate, the microstructure is refined, and the amounts of Nbss (Nb, Ti)3 Si/(Nb, Ti)5 Si3 euteetic colonies and (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates increase. There appear nodes in the (Nb, Ti)3 Si/(Nb, Ti)5 Si3 plates.     

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。     

粉末冶金碳化物强化铌合金组织演变及其力学行为

采用机械球磨与热压烧结相结合的粉末冶金法对不同球磨时间Nb-35Ti-6Al-5Cr-8V-5C合金的粉末变形行为,微观组织结构和力学行为进行研究。结果表明:随着球磨时间的增加,Nb-35Ti-6Al-5Cr-8V-5C复合粉末中的块状金属颗粒首先变形为片状后在碰撞挤压作用下破碎成絮状,TiC粉末均匀的分布于片状金属粉末表面;Nb-35Ti-6Al-5Cr-8V-5C合金由Nbss和(Nb,Ti)C两相构成,各合金碳化物体积分数均为11%左右,Ti元素主要分布于Nbss晶界和碳化物内,Al、Cr、V元素主要分布于Nbss晶粒内,Nbss和(Nb,Ti)C相尺寸均随球磨时间增加而尺寸减小;Nbss晶粒细化及强化相碳化物弥散化导致合金的室温压缩力学性能和塑性变形能力显著提高,压缩变形后合金Nbss与碳化物具有良好的界面结合能力,但是碳化物内部存在明显的近似平行分布的裂纹;数据对比表明,粉末冶金法制备Nb-35Ti-6Al-5Cr-8V-5C合金的力学性能优于电弧熔炼法。     

凝固速率对铌基共晶自生复合材料定向凝固组织的影响

铌基共晶自生复合材料（NBISC）经真空自耗电弧熔炼成母合金锭，采用高温度梯度的电子束区熔装置制备定向凝固的试样，分析其组织特征。结果表明：Nb基固溶体（Nbss）相、（Nb，Ti）3Si相和（Nb，Ti）5Si3相为NBISC材料的主要组成相；在电了束区熔条件下，随着电子枪移动速率的提高，NBISC材料共晶组织变细，组织中片层状的共晶团增多，块状或板条状的（Nb，Ti）3Si／（Nb，Ti）5Si3相尺度减小、数量增多，组织趋于规则、分布更均匀，组织的定向性增强，定向效果显著。     

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.     

碳化物对铌基多相合金力学性能和组织结构的影响

采用纳米压痕和原子力显微镜对Nb-21Ti-4C-x Al(x:0,5,10,15 at%,下同)、Nb-35Ti-4C及Nb-25Ti-8C合金Nbss、(Nb,Ti)C、Nb3Al及相界面的力学性能和变形行为进行了研究。研究表明:Ti、Al元素合金化能有效提高Nbss的硬度,且Al强化效果优于Ti;高硬度的碳化物、Nb3Al与Nbss界面结合良好是理想的增强相。热处理后(Nb,Ti)C内部析出二次Nbss,改善了碳化物的变形行为,提高了韧性;热处理后Nbss内部组织均匀化及位错密度降低导致Nbss硬度下降。Ti、Al、C原子含量变化及热处理对Nbss的弹性模量影响不大。     

Effects of B addition on the microstructure and properties of Nb silicide based ultrahigh temperature alloys

Four Nb silicide based ultrahigh temperature alloys with compositions of Nb–22Ti–16Si–5Cr–4Hf–3Al–xB (x = 0, 2, 5 and 10, respectively) (at%) were prepared by vacuum non-consumable arc melting. The effects of B content on the phase selection, microstructure, oxidation resistance at 1250 °C, room-temperature fracture toughness and microhardness of the alloys were investigated. The results showed that the microstructures of the four alloys were all comprised of primary silicide blocks, Nbss dendrites and eutectic colonies. However, the crystal structures or types of silicides and the amounts of constituent phases obviously varied with increase in B content in the alloys. The oxidation resistance of the alloys was significantly ameliorated by B addition. The room temperature fracture toughness of the alloys was improved with 2 at% B addition but degraded with 5 or 10 at% B addition. The microhardness of Nbss rose slightly with increase in B content in the alloys, while that of silicides was dependent on their crystal structures, types and concentrations of alloying elements.     

Effect of Alloying on the Microstructure and Fracture Toughness of Nb-Mo-Si Alloys

It was found that typical Nbss /Nb5Si3 eutectic lamellar structure formed in the Nb-Mo-Si alloy. The interface between Nbss and Nb5Si3 phases was so strong that the alloy fractured mainly in the cleavage mode. In this paper, the fourth element was added with the aim of modifying interface structure. The microstructural characterization and the fracture toughness of Nb-17Si-10Mo ternary alloy doped with Ga, In, Zn and V, respectively, were investigated. It was revealed that the lamellar structure maintained ...     

Mechanical alloying behavior of Nb–Ti–Si-based alloy made from elemental powders by ball milling process

Nb-Ti-Si-based alloy powders were prepared by mechanical alloying(MA) of elemental particles.The evolutions of morphology,size,phase constituents,crystallite size,lattice strain,composition and internal microstructure,etc.,of the alloy powders were analyzed by X-ray diffraction(XRD),scanning electron microscopy(SEM),energy-dispersive spectroscopy(EDS),laser particle size analyzer and transmission electron microscope(TEM) analyses.The alloy particles are gradually refined and their shapes become globular with the increase in milling time.The diffraction peaks of Nb solid solution(Nbss) phase shift toward lower29 angles during ball milling from 2 to 5 h,and after that Nbss diffraction peaks shift toward higher 29 angles with the increase in milling time from 5 to 70 h,which is mainly attributed to the alteration of the lattice parameter of Nbss powders due to the solution of the alloying element atoms into Nb lattice to form Nbss.During ball milling process,the decrease in crystallite size and increase in lattice strain of Nbss powders lead to continuous broadening of their diffraction peaks.A typical lamellar microstructure is formed inside the powder particles after ball milling for 5 h and becomes more refined and homogenized with the increase in milling time.After 40-h-ball milling,the typical lamellar microstructure disappears and a very homogeneous microstructure is formed instead.This homogeneous microstructure is proved to be composed of only supersaturated Nbss phase.     

Al-V合金预磨状态对Al-Fe-V-Si-Nd机械合金化过程中显微组织演化的影响

采用高能球磨法制备Al89.5Fe6 .4V0 .7Si2 .4Nd合金粉末 ,并用X射线衍射技术研究了球磨过程中的组成。发现经 60h高能球磨 ,合金粉末的微观组织由Al非晶和Al3V相组成 ;Al V合金的预磨状态影响Al89.5Fe6 .4 V0 .7Si2 .4Nd合金机械合金化过程中显微组织演化。     

Microstructure Development of Directionally Solidified Nb-Ti-Si Based Ultrahigh Temperature Alloy

Integrally directional solidification of an Nb-Ti-Si based ultrahigh temperature alloy was performed in an ultrahigh temperature and high thermal gradient furnace with the use of ceramic crucibles. The microstructural evolution with the withdrawing rate increasing during directional solidification was revealed. The integrally directionally solidified microstructure was composed of couple grown lamellar (Nbss+(Nb,X)5Si3) eutectic colonies and a few hexagonally cross-sectioned (Nb,X)5Si3 columns (X represents...     

粉末冶金Nb-35Ti-6Al-5Cr-8V合金组织演变及其力学行为

采用粉末冶金法对不同球磨时间的Nb-35Ti-6Al-5Cr-8V合金机械合金化粉末塑变行为,热压烧结材料的微观组织结构和力学行为进行了研究。研究结果表明：塑性良好的Nb-35Ti-6Al-5Cr-8V粉末随着球磨时间增加首先变形为大尺寸的片状、后经持续的加工硬化破碎成絮状;热压烧结能够制备微观组织可控晶粒细化的Nb-35Ti-6Al-5Cr-8V合金,合金由单一的Nbss相构成,Ti、Al、Cr、V元素固溶引起Nb晶格尺寸减小0.0685 ?;随着球磨时间增加合金晶粒明显细化进而显著提高了合金的维氏硬度和室温压缩强度,其变化符合材料硬度和强度的Hall-Petch规律。粉末冶金制备Nb-35Ti-6Al-5Cr-8V合金的各项力学性能明显优于熔铸法制备合金。     

高温热处理对Nb-Ti-Cr-Si基超高温合金显微组织的影响

为了研究高温均匀化及时效热处理对Nb-Ti-Cr-Si基超高温合金显微组织的影响,对样品进行均匀化处理,于1200-1500°C保温24h,随后于1000°C保温24h进行时效。结果表明,热处理后的组织主要由Nbss、（Nb,X）5Si3和Cr2Nb组成。随着均匀化处理温度的升高,电弧熔炼态的树枝状Nbss转变为等轴状,原先花瓣状的Nbss/（Nb,X）5Si3共晶组织消失,转变为分布于Nbss基体上的小块状（Nb,X）5Si3组织。Cr2Nb的形貌随均匀化处理温度的升高而发生明显变化。当均匀化处理温度达到1300°C以上,原先粗大的Cr2Nb发生溶解,在随后的冷却过程中在Nbss基体上沉淀析出细小、密集的针状Cr2Nb。经高温均匀化和时效复合处理后,Nbss基体上析出更为细小、密集的沉淀相Cr2Nb,使得Nbss、（Nb,X）5Si3和Cr2Nb相中Ti、Hf和Al元素的含量差别缩小。     

Nb-16Si-10Ti-10Mo-5Hf原位复合材料拉伸性能及其变形机制

采用机械合金化和放电等离子烧结方法制备了Nb-16Si-10Ti-10Mo-5Hf原位复合材料。采用不同温度下的拉伸试验评价了其力学性能,结合其不同温度下的断口形貌研究了其变形机制。结果表明,复合材料的微观组织由Nbss(铌固溶体)、金属间化合物Nb_5Si_3和少量的Nb_3Si相组成,晶粒呈等轴状。室温和1200℃抗拉强度分别为413和496 MPa。从室温到1200℃拉伸断裂方式为Nb5Si3相解理脆性断裂,1200℃拉伸延伸率仅为1.2%;然而,在1300℃拉伸试验中,其拉伸延伸率为27%,这归因于Nbss延性的增加和界面/晶界强度的降低;在1400℃和更高的温度,材料具有极大的塑性或超塑性,塑性变形机制由晶内滑移转变为晶界滑移。晶界滑移在三叉晶界处产生的应力集中通过软化的Nbss协调而释放,从而避免了早期断裂。     

Mechanical properties and fracture behavior of an Nb-Silicide in situ composite

An Nb-Silicide in situ composite with a nominal composition of Nb-16Si-10Ti-10Mo-5Hf (at. %) was fabricated by mechanical alloying followed by hot-pressing sintering. The microstructure consisted of an Nb solid solution, Nb₅Si₃ and a small amount of Nb₃Si. This in-situ composite exhibited good balance of strength between ambient temperature and high temperatures; the ultimate tensile strength was 413 and 496 MPa at room temperature and 1200 °C, respectively. The tensile fracture behavior was dominated by cleavage of the Nbss and Nb₅Si₃ at 1200 °C and lower temperatures. However, the fracture behavior was governed by ductile rupture of Nbss at 1300 °C and higher temperature, which was ascribed to both the increased ductility of Nbss and the decreased interface strength. At 1400 °C and higher temperature, the material exhibited extensive plasticity or superplasticity; the dominant deformation mechanism was grain boundary sliding at 1400 °C and higher temperature.     

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。     

High-Temperature Oxidation Behavior of Laser-Surface-Alloyed Ti with Si and Si + Al

This study concerns an attempt to enhance the resistance to high-temperature isothermal and cyclic oxidation of Ti in dry air by laser-surface alloying (LSA) with Si and Si+Al. LSA was carried out by codeposition of alloy powders during lasing under the predetermined, optimum-processing routine that ensured formation of a compact, well-adherent, crack-free and homogeneous alloyed zone. The results of oxidation kinetics in the temperature range 950–1150 K for 1–400 hr indicate that surface alloying with Si imparts excellent oxidation resistance up to 1050 K. However, at a higher temperature of 1150 K, surface alloying with 3Si+Al yields a better resistance to oxidation. A detailed characterization of the microstructure and distribution of the phases within the scale and alloyed zone following oxidation studies has been undertaken to suggest the possible mechanism for enhanced oxidation resistance of Ti imparted by laser-surface alloying.