Ti含量对NiAl-Cr(Mo)共晶合金凝固组织的影响

添加Ti降低了NiAl-Cr(Mo)共晶合金凝固过程中NiAl/Cr(Mo)共晶生长速度,导致NiAl/Cr(Mo)胞状共晶组织的粗化,并因合金偏离共晶成分而促进先共晶NiAl相的形成.在添加Ti的NiAl-Cr(Mo)共晶合金中,Ti主要分布在基体NiAl相中.随着Ti含量的提高,过饱和的NiAl(Ti)基体发生分解,促进了Ni2AlTi相的形成,并且NiAl/Cr(Mo)胞状共晶组织发生退化.Ni-33Al-28Cr-3Mo-5Ti共晶合金的NiAl基体中析出细小的Cr(Mo)相,Cr(Mo)共晶相中析出细小的NiAl相.     

Nb对HP合金组织与蠕变断裂强度的影响

随 Nb 含量的增加,HP 合金蠕变断裂强度的变化表现出极大值特征。在含碳0.4(wt%)的HP 合金中添加0.5(wt%)以下的 Nb,主要起固溶强化作用;当 Nb 量约1.5(wt%)时,可以获得最佳的蠕变断裂强度。其原因是在共晶组织中形成了形态复杂的共晶 NbC,在晶内析出了高度弥散的二次 NbC,以及由于 Nb 的加入提高了组织稳定性;当 Nb 量进一步提高时,由于共晶 NbC 形成了片层状共晶团以及晶内 M_(23)C_6大量减少使蠕变断裂强度下降。     

Cr含量对Nb-Si基超高温合金组织和室温断裂韧性的影响

采用真空非自耗电弧熔炼的方法制备了4种名义成分为Nb-22Ti-16Si-4Hf-3Al-x Cr(x=0,3,5和10,原子分数,%)的合金,并于1450℃保温50 h进行了均匀化处理,研究Cr含量对Nb-Si基超高温合金电弧熔炼态和热处理后组织,及其电弧熔炼态下室温断裂韧性的影响。结果表明:添加Cr没有改变硅化物的晶型(均为γ(Nb,X)5Si3),但其含量随Cr含量的增加而增加,而Nbss/γ(Nb,X)5Si3共晶的含量则逐渐降低;添加Cr还促进了Nbss/(Nb,X)5Si3/Cr2(Nb,X)三相共晶的形成,且该共晶的含量随合金中Cr含量的增加而增加。经1450℃/50 h热处理后,原电弧熔炼态的Nbss枝晶和共晶组织消失,且合金组织明显变得均匀。Cr含量为0,3%和5%的合金组成相为Nbss和γ(Nb,X)5Si3,而在Cr含量为10%的合金中则出现了Nbss,γ(Nb,X)5Si3和Cr2(Nb,X)的三相平衡组织。电弧熔炼态下合金的室温断裂韧性随Cr含量的增加呈现降低的趋势。     

Nb-Ti-Cr-Si基超高温合金有坩埚整体定向凝固组织的演化

分析了Nb-Ti-Cr-Si基超高温合金有坩埚整体定向凝固试样不同区域的组织,结果表明未熔区的组织由初生相Nbss、块状的(Nb,X)5Si3和少量的小块状Cr2Nb组成。在过渡区初生相Nbss依附在未熔区的Nbss优先生长,Nbss/(Nb,X)5Si3共晶组织生长比较混乱,在初生相Nbss枝晶间出现了富Ti的Nbss/Cr2Nb共晶团。稳态区组织中Nbss和(Nb,X)5Si3定向排列,实现了整体定向凝固。固/液界面形态为树枝状,在糊状区出现了Nbss/(Nb,X)5Si3、富Ti的Nbss/(Nb,X)5Si3和Nbss/Cr2Nb三种共晶组织,根据组织分析的结果并总结了其凝固路径,测试了不同区域组织的显微硬度,结果表明稳态区的(Nb,X)5Si3的显微硬度最高。     

铌硅化物基超高温合金表面包埋渗Al改性硅化物涂层的组织结构

分别采用两步包埋渗法和包埋共渗法在铌硅化物基合金表面制备了Al改性硅化物抗氧化涂层.两步包埋渗法是先在合金表面包埋渗Si制备(Nb,X)Si2(X表示Ti,Cr和Hf元素)涂层,然后再将渗Si试样于800～1000℃包埋渗Al.结果表明:当渗Al温度达到860℃时渗入(Nb,X)Si2层中的Al可形成(Nb,Ti)3Si5Al2相;当渗Al温度达到900℃时渗入的Al还可穿过(Nb,X)Si2层在渗Si层与基体之间形成(Nb,Ti)(Al,Si)3层.经1150℃/20h Si-Al包埋共渗后在合金表面形成的涂层具有多层复合结构:外层主要由(Nb,Ti)3Si5Al2和(Nb,Ti)(Al,Si)3组成;中间层上部为(Nb,X)Si2,下部为低硅化物(Nb,X)5Si3;内层由基体相(Nb,Ti)Al3和柱状晶(Cr,Al)2(Nb,Ti)组成.     

高温热处理对Nb-Ti-Si基共晶自生复合材料组织及成分分布的影响

采用真空非自耗电弧熔炼法制备了Nb-Ti-Si基共晶自生复合材料的母合金锭,分别于1300,1400,1500和1600℃保温50小时对其进行了均匀化处理,然后于1100℃保温50小时进行了时效处理.热处理后的组织主要由Nbss和(Nb,X)5Si3(X代表Ti,Cr和Hf元素)组成,但经1600℃/50h和1600℃/50h 1100℃/50h热处理后的组织中出现了HfO2.热处理后,Nbss的晶格常数较电弧熔炼态的有所升高,Ti,Cr和Al仍然倾向于固溶在Nbss中,而Hf则倾向于固溶在硅化物中.随着热处理温度的升高,Cr,Ti和Al在Nbss和大块硅化物(Nb,X)5Si3中的分配比降低,而Hf的则略有升高.     

Mg对共晶Al-2%Fe合金显微组织的影响

为了消除粗大针状富铁相对Al-Fe合金组织和性能的不良影响,在金属型铸造共晶Al-2?合金中添加了质量分数为0.2%一0.8%的合金元素Mg,利用光学显微镜和电子探针研究了Mg对共晶合金组织以及富铁相形态的影响.研究结果表明:共晶Al-2?合金组织为针状Al3Fe相与(α-Al)相所组成的非规则共晶组织;添加Mg后,合金组织转变为由树枝状初生(α-Al)和枝晶间网状分布共晶体所组成的亚共晶组织,富铁相尺寸显著降低;随着Mg添加量的增加,初生(α-Al)枝晶二次枝晶间距增大,一次枝晶出现熔断.     

Nb、Cr和Mo对新型β/γ-TiAl合金组织与相变的影响

为了研究TiAl合金中β相稳定元素对显微组织及相变温度的影响,本文在Ti-43Al合金的基础上,通过单独与复合添加Nb、Cr、Mo 3种合金元素,获得了新型β/γ-TiAl合金,并系统研究了3种元素的作用规律.结果发现:Nb促使合金形成片层结构,Cr、Mo使合金分别形成近γ组织和针状魏氏组织;3种元素对β相的稳定能力为Mo>Nb>Cr;复合添加Nb、Cr、Mo元素对β相的稳定作用比单一添加更为显著;3种不同元素对α+β+γ三相区范围有显著影响,对α2+γ→α转变的共析温度(te)影响较大,而对γ→α的转变温度(tα)影响较小,Ti-43Al-4Nb-2Mo-0.2B合金的α+β+γ三相区最窄约为15℃,而Ti-43Al-6Nb-0.2B合金的α+β+γ三相区最宽约为95℃,Ti-43Al-4Nb-1Cr-1Mo-0.2B合金的α+β+γ三相区为55℃.     

电弧熔炼Nb-Ti-Si-Cr-Hf-Al-B-Y超高温合金母合金锭的组织形成和成分分布特点

采用真空非自耗电弧熔炼然后再真空自耗电弧熔炼的方法制备了Nb-Ti-Si-Cr-Hf-Al-B-Y超高温合金的母合金锭,分析了其在不同位置的组织组成及成分分布特点.发现母合金锭的组织主要由Nbss与(Nb,X)5Si2两相组成.在母合金锭的边缘部位,组织主要由(Nbss (Nb,X)5Si3)共晶团组成,此外还有少量的Nbss枝晶;但在母合金锭的中央部位,组织由初生(Nb,X)5Si3块或板条以及(Nbss (Nb,X)5Si3)共晶团组成.母合金锭中的成分分布特点为Si含量由锭边缘向中央逐渐升高,而由锭下部到上部逐渐降低;Ti含量的变化则为由锭边缘向中央,由锭下部到上部逐渐减少.     

适于真空铸造的新合金

最近Armco公司研制成功两种适应于真空铸造的新合金:CA53和Nitronic 19D。CA53是一种Cr-Si-Nb-Ti合金,标准成分为:0.03％C、5.0％Cr、3.0％Si、0。30％Nb和0.15％Ti。含Cr和Si有助于相平衡,提高耐氧化性能。在1090℃下仍保持稳定的铁素体组织。适合于干燥环境下应用并用来代替较贵的D5S合金。     

A study on the influence of Mo, Al and Si additions on the microstructure of annealed dual phase Cr–Ta alloys

The effects of additions of 5 at.% Mo, Al and Si on the long-term annealed microstructures of a two phase Cr–Cr₂Ta alloy have been studied. Following 200 h at 1300 °C, the lamellar eutectic constituent of all the alloys disintegrated into discrete particles of the Laves phase embedded within a Cr-rich solid solution phase, along with the formation of fine Laves phase precipitates. One of the predominant differences between the three alloying additions was the extent of the C14 to C15 polytypic transformation of the Cr₂Ta-based Laves phase. With Mo and Al additions, the Cr₂Ta Laves phase transformed from C14 to either C15 or intermediate hexagonal polytypes following 200 h annealing at 1300 °C. In contrast, Si additions stabilised the C14 polytype, with no transformation to other polytypes observed after prolonged annealing at 1000, 1100 and 1300 °C.     

Effect of Nb on the Microstructure and Mechanical Properties of Cast NiAl-Cr（Mo） Eutectic Alloy

The microstructure and mechanical behaviors of NiAl-28Cr-5Mo-1Nb eutectic alloy were investigated by using scanning electron microscopy, X-ray diffraction, transmission electron microscopy and compression tests, respectively. The alloy is mainly composed of three phases, which are the gray lamellar Cr（Mo） plate, black NiAI matrix and semicontinuously distributed Cr2Nb-type Laves phase. Through Nb addition, NiAl-Cr（Mo）/Nb alloy exhibits a reasonable balance of high temperature strength and room temperature compression ductility and its mechanical behaviors are superior to the NiAl-28Cr-6Mo eutectic alloy at all temperature. The elevated temperature compression deformation behavior of NiAl-Cr（Mo）/Nb alloy can be properly described by power-law equation.the National High Technology Committee of China （No. 863-715-005-0030） for financial supports.     

Influences of Alloying Elements W, Mo, Cr and Nb on Retained Beta Phase in 47Al Based near γ-TiAl Alloys

The influences of alloying elements W, Mo, Cr, and Nb on retained β phase in 47Al based near γ-TiAI alloys have been studied.The results reveal that the amount of retained β phase is increased by the addition of Cr, Mo, W in rising rank, although the distribution of β phase in Cr-bearing alloys is different from that of Mo- or W-bearing alloys. For Nb-doped alloys, no retained β was found even when 5 at. pct Nb was added. The as-cast microstructural features and the distribution of the β phase in the different alloy families were compared and interpreted in terms of the different segregation behaviour of these elements in Ti.     

Microstructure evolution of directionally solidified Nb–Si alloy

Abstract

By taking the method of liquid–metal cooled directional solidification, alloys with a nominal composition of Nb–14Si–24Ti–10Cr–2Al–2Hf (at-%) were prepared under different conditions. Alloys were initially directional solidified with different withdrawal rates (R?=?1·2, 6, 18 mm min^?1) at 1750°C and subsequently heat treated at 1450°C for 10 h. These processes aimed to investigate the microstructure of directionally solidified (DS) and heat treated (HT) alloys by XRD, SEM, and EDS. The microstructure of DS alloy was composed of (Nb,Ti)_SS, (Nb,Ti)₅Si₃, and Laves phase Cr₂Nb, and the former two components formed (Nb,Ti)_SS+(Nb,Ti)₅Si₃ eutectics. In addition, (Nb,Ti)₅Si₃ laths only presented in DS1·2 alloy. With the increasing withdrawal rates, the microstructure of alloy altered from hypereutectic into pseudo-eutectic, accompanied with the eutectic morphology transformation from petaloid into coupled. Also, the dimension of constituent phases reduced. However, after heat treatment, the constituent phases did not change. The petaloid morphology of eutectics in DS specimens disappeared and coupled eutectic transferred into network. The block or needle-like Cr₂Nb gathered along the boundary between (Nb,Ti)₅Si₃ and (Nb,Ti)_SS, and the overall alloy composition became homogenisation.     

Effects of Si addition on mechanical properties and superelasticity of Ti–7.5Nb–4Mo–2Sn shape memory alloy

Effects of 0–2.1 at.% Si additions on microstructure and mechanical properties of a Ni-free biomedical superelastic β-Ti alloy, Ti–7.5 at.%Nb–4 at.%Mo–2 at.% Sn (Ti–7.5Nb–4Mo–2Sn), were investigated. The alloys after annealing at 973 K mainly contain β and α″. As the concentration of Si is higher than 1 at.%, Ti₅Si₃ particles can be found in the alloys, and the number density of the particles increases with the increasing of silicon’s concentration. The addition of Si promotes the strength of the Ti–7.5Nb–4Mo–2Sn due to the Si solid solution strengthening effect and fine Ti₅Si₃ precipitates. However, as the Si concentration reaches 2.1%, the alloy exhibits a brittle fracture. The 0.5–1.6 at.% Si additions improve the superelasticity of the Ti–7.5Nb–4Mo–2Sn alloy by increasing the critical stress for inducing martensite (σ_SIM).     

TiAl和Mo5Si3金属间化合物基高温结构材料及其合金化研究

对比分析了ＴｉＡｌ和Ｍｏ５Ｓｉ３金属间化合物的性能特点,应用前景和存在问题,并对这两种金属间化合物的合金化研究作了综述和展望。近来研究微量镁和镍在ＴｉＡｌ合金中的作用发现,微合金化可提高变形合金的热加工工艺性能和促进铸造合金组织的细化,是ＴｉＡｌ金属间化合物进一步合金化研究的重要方向。根据模量计算和常用合金元素在Ｍｏ５Ｓｉ３相中溶解度的测定,结果,讨论了以合金化韧化Ｍｏ５Ｓｉ３化合物的潜力。     

Modification of β-Al5FeSi Compound in Recycled Al-Si-Fe Cast Alloy by Using Sr, Mg and Cr Additions

The effects of Sr,Mg,Cr,Sr/Mg and Sr/Cr combined additions on the Fe-containing intermetallic phase in a recycled Al-Si-Fe cast alloy are investigated.The experimental results show that the additions of Cr and Sr/Cr successfully modified the platelet and flake-likeβ-Al-5FeSi phases （β-compound） into the fibrousα-Al-8Fe-2Si （α-compound）.The additions of Sr and Sr/Mg were less effective to modify theβ-compound into theα-compound,while the eutectic Si was fully modified into the fibrous morphology.A small secondary dendrite arm spacing （DAS） was found in the Sr-added,Cr-added and Sr/Cr-added alloys,especially in a steel mold.The Sr,Sr/Cr and Sr/Mg combined additions modify the eutectic Si simultaneously.A sludge phase was found in the addition of Cr-added,Sr/Cr-added and Mg-added alloys,especially in the graphite mold casting.The volume fraction ofβ-compounds was decreased by the addition of various modifying elements. The Cr and Sr/Cr combined additions are very effective to modify theβ-compound for the recycled Al-Si-Fe based alloys.     

Microstructure and mechanical properties of Hf and Ho doped NiAl–Cr(Mo) near eutectic alloy prepared by suction casting

The microstructure and mechanical properties of 0.15 at.% Hf and 0.2 at.% Ho doped Ni–33Al–28Cr–6Mo near eutectic alloys prepared by conventionally casting and suction casting were investigated. The results reveal that the addition of Hf and Ho results in the formation of HfAlNi₂ and HoNi₂Al₃ phases respectively along the NiAl and Cr(Mo) phase interface in intercellular regions. Compared with the conventional-cast alloy, the suction casting optimizes the microstructure of the alloy further, which can be characterized by the refined NiAl/Cr(Mo) eutectic lamellar, high proportion of eutectic cell, and fine and homogeneously distributed HfAlNi₂ and HoNi₂Al₃ phases. In addition, the compression tests show that the suction-cast alloy has better mechanical properties, which can be attributed to the fine microstructure and uniform distribution of the HfAlNi₂ and HoNi₂Al₃ phases.     

放电等离子烧结制备Nb-Si-Ti-Al-Hf-Cr合金的显微组织及力学性能

以预合金化的粉末尺寸D50为3.3μm的NbSS固溶体相细粉末,粉末尺寸D50分别为22.1μm和23.5μm的Nb5Si3和Cr2Nb化合物粉末为原料,采用放电等离子烧结技术制备NbSS/Nb5Si3两相合金和NbSS/Nb5Si3/Cr2Nb三相合金,研究显微组织形貌、室温和高温力学性能及高温氧化性能。结果表明:两相合金的显微组织由NbSS基体和呈均匀岛状分布的Nb5Si3组成,三相合金中NbSS有相互连接成基体的趋势,而Nb5Si3和Cr2Nb相也以块状散布在NbSS中。NbSS/Nb5Si3两相合金和NbSS/Nb5Si3/Cr2Nb三相合金的室温断裂韧性值KQ分别达到15.1MPa·m1/2和11.3MPa·m1/2,室温下合金中NbSS相以韧窝型断裂为主,对Nb-Si基合金的室温断裂韧性有利,而Nb5Si3和Cr2Nb相为脆性断裂。1250℃时NbSS/Nb5Si3/Cr2Nb合金的压缩强度高于NbSS/Nb5Si3合金,但当温度上升到1350℃时两者强度出现反转。Cr2Nb相对合金高温抗氧化性能有利,1250℃下静态氧化100h时NbSS/Nb5Si3合金的氧化增重为233mg/cm2,大于NbSS/Nb5Si3/Cr2Nb合金的175mg/cm2。     

Solid solution strengthening of transient liquid phase bonded nickel based superalloy

This paper aims at probing and quantifying the effect of filler alloy chemistry on solid solution strengthening mechanism of transient liquid phase bonded of a cast Ni–Fe–Nb based superalloy. Bonding was performed using three different nickel based filler alloys including Ni–4·5Si–3·2B, Ni–7Cr–4·5Si–3·2B–3Fe and Ni–15·2Cr–4B. The hardness of isothermal solidification zone was proved to be the controlling factor for the shear strength of the joints. It is concluded that the initial chromium content of the filler alloy and the extent of base metal dissolution, which in turn is controlled by the initial boron content of the filler alloy, play important roles in strengthening of the isothermal solidification zone. Bonding using Ni–15·2Cr–4B resulted in eutectic free joint with the highest shear strength.