哈氏C-2000合金在等温氧化时第二相沉淀析出行为（英文）

研究了哈氏C-2000合金在800℃/100 h空气中等温氧化后合金基体中第二相的沉淀行为。氧化后基体中析出了富Mo相,可确定该富Mo相为具有金刚石结构的Mo3Ni3C型碳化物。富Mo相沿晶界和晶内分别呈现出非连续和连续条状形貌特征。然而,经深腐蚀后,晶内和晶界处形貌均发生了变化,即,沿晶界出现了大量白色絮状物,晶内则出现了具有金刚石结构的腐蚀坑。由于富Ni和富Cr区域具有更负的电极电位,因而使得这些区域在深腐蚀后更易被侵蚀。     

哈氏C-2000合金在800°C和1000°C的氧化行为(英文)

研究哈氏C-2000合金在(800°C,1000 h)和(1000°C,100 h)时的氧化行为。分别利用增重法、SEM、XRD和XPS表征氧化动力学和氧化膜的形貌特征。合金在800°C和1000°C时均基本满足抛物线速率规律。此外,由于退火孪晶提高了合金化元素及氧原子的扩散速率,因此,降低了合金的高温抗氧化性能。在800°C时,氧化膜微观结构主要是由NiO和Cr1.3Fe0.7O6组成。此外,初始退火孪晶结构在氧化后依然可见,且临近氧化膜附近出现了富Mo相。然而,在1000°C时,氧化膜的微观结构由细小的铬氧化物和粗大的镍氧化物颗粒通过相互镶嵌而构成,同时,在临近氧化膜处几乎无富Mo相出现。     

Ni3Al-Mo合金1100℃初期高温氧化行为研究

研究了Ni3Al-Mo合金在1100℃下暴露时间为1h的氧化行为,利用扫描电子显微镜(SEM)、能量衍射谱(EDS)和X射线衍射等手段观察分析了氧化层的表面形貌、微观组织结构成分,并结合氧化动力学曲线分析,探明了Ni3Al-Mo合金1100℃高温氧化初期的氧化机理。研究结果表明,在1100℃氧化初期(1 h内),Ni3Al-Mo合金表面氧化层中存在一个富Mo层,并随着时间延长而增厚,表明合金中Mo元素没有发生氧化挥发。1100℃时Ni3Al-Mo合金试样表面形成NiO+富Mo层+NiAl2O4多层结构氧化层。随着氧化时间的增长,形成NiO层的颗粒逐渐增大,氧化层孔隙增多变得疏松,与基体结合力减弱,试样从炉中取出,在冷却过程中由于NiO氧化层热膨胀系数大,致使氧化层翘曲并剥落。     

β型Ti-Mo-O合金的高温氧化及相析出行为

利用OM、XRD、EPMA、维氏硬度计并结合第一性原理计算调查了Ti-15Mo-xO(x=0.1,0.2,0.3,0.4,0.5,质量分数,%)合金在873 K和1073 K下的氧化行为,以及837 K下的α相析出行为。结果表明,在873 K,氧化产物均由TiO2、Ti3O和Ti6O组成,且O含量对合金的氧化行为无明显影响,均主要由Ti向基体外扩散控制。在1073 K,尽管各合金的氧化产物均为TiO2,但O含量对合金的氧化行为具有明显影响：低O合金中,氧化过程由O与基体金属的氧化反应和O向基体内扩散共同控制;而随O含量增加,其转变为O向基体内扩散,抗氧化性能显著提高。在873 K下时效10 h和100 h后,析出的α相随O含量和时效时间的增加而增多,富Mo贫O的β相晶格常数减小,富O贫Mo的α相c值增大,a值基本不变,c/a值增大。时效前后合金硬度随O含量增加而增大,然而,在相同O含量条件下,随着α相的析出,合金元素Mo和O在两相中重新分配,导致时效后合金的硬度降低。     

Ti3Ni4析出相对富镍TiNi合金阻尼行为的影响

采用动态机械分析仪（DMA）、透射电镜（TEM）和示差扫描量热分析仪（DSC）等手段，系统地研究了时效处理对TiNi合金阻尼行为的影响规律及其微观机制。结果表明，第二相粒子对合金阻尼行为具有不同的影响。细小、弥散的Ti3Ni4相提高了TiNi合金相变过程中马氏体的阻尼值，粗片状的Ti3Ni4相对阻尼行为的影响较小。     

超高Ti耐磨钢第二相粒子的析出行为研究

超高Ti耐磨钢(w(Ti)=0.2%～0.6%)中第二相粒子的类型、形态、尺寸、分布及数量等对其性能具有重要影响,但是在生产过程中很难精准控制。为此,利用金相显微镜、扫描电镜SEM、电子探针EPMA、夹杂物自动分析仪ASPEX等对超高Ti钢中第二相粒子的析出行为进行了研究分析。结果表明：超高Ti钢中第二相粒子主要有两种类型,一种为长条状形态的Ti+Mo+C粒子,另外一种为方形或三角形等规则形状的TiN粒子;连铸坯原始枝晶大小决定了第二相粒子分布的均匀性,原始枝晶尺寸越小,第二相粒子分布就越均匀,如果第二相粒子均匀分布在枝晶间,团簇状现象会减轻,因而需要对连铸工艺严格控制,以防止粗大的枝晶;第二相粒子析出过程中,Ti和N元素首先析出形成TiN相,然后Ti和Mo元素以含Mo的Ti+Mo+C粒子形式析出;Ti+Mo+C粒子析出方式有两种,一种是直接以先析出的TiN粒子为核心外延生长,另一种是单独析出形核长大。     

多相Ni3Al基高温合金微区氧化行为

以多相Ni₃Al基高温合金为对象,通过热处理得到了3种微区结构：枝晶干γ’+γ两相区、枝晶间β相和包裹着枝晶间β相的γ’包覆层,研究了不同微区组织在1000℃的等温氧化行为。3个微区在氧化初期呈现出不同的氧化行为：γ’包覆层处为明显的双层氧化膜结构,呈现胞状凸起,外部是混合层(Ni O、Ni Fe₂O₄和Al₂O₃),内部为单一Al₂O₃层,而枝晶干γ’+γ两相区和枝晶间β相形成单层Al₂O₃膜。随着等温氧化时间的延长,由于晶格扩散占据主导地位,不同微区氧化膜厚度差显著缩小,3个微区的氧化膜组成逐渐趋于一致,形成致密单一的Al₂O₃层。     

双晶体NiTi形状记忆合金在无/有应力作用时效下的Ni_4Ti_3相沉淀行为模拟(英文)

运用相场方法研究双晶体NiTi形状记忆合金分别在无应力和有应力作用下时效过程中Ni4Ti3相的沉淀行为,模拟研究两种不同初始过饱和度(Ni含量分别为51.5%和52.5%,摩尔分数)的NiTi基体并考虑外加应力的影响。模拟结果表明,在无应力作用的体系中,当体系Ni原子初始浓度相对较低(51.5%Ni)时,Ni4Ti3相以非均匀的方式析出,其中晶界上存在大量的Ni4Ti3变体,晶界内大部分区域无变体;当体系Ni原子初始浓度较高(52.5%Ni)时,Ni4Ti3在整个双晶体系中均匀析出。在所研究的两种初始浓度下,一定大小的外加应力将直接导致Ni4Ti3变体在整个模拟体系中均匀析出,而两晶粒中变体的类型分布有所不同。     

高钨镍基高温合金K416B富W相的析出行为

研究了K416B合金中富W相的析出行为与合金浇注温度和凝固速率的关系。结果表明,在相同冷却速率下,合金的浇注温度由1500℃降低到1450℃时,晶粒尺寸明显减小。在不同浇注温度下,合金中均有块状α-W相在残余共晶中析出,α-W相形貌差别不大。合金的残余共晶中存在大尺寸的M6C相,而残余共晶的边缘处有小尺寸的M6C相。高凝固速率时,合金中富W相数量减少、尺寸减小,表明富W相析出受到明显抑制。对于铸造高钨镍基高温合金,选择合适的浇注温度以及保温体系加快凝固初期的冷却速率,可以控制富W相的析出和转变,从而优化合金性能。     

Haynes230合金在1100℃的恒温氧化行为

利用SAXD和SEM(EDAx)研究了Haynes 230合金在1100℃的恒温氧化行为.结果表明:氧化膜主要由Cr2O3和(Ni、Mn、Cr)3O4组成.随着氧化时间的延长,形成了多层氧化膜.外部的(Ni、Mn、Cr)3O4氧化膜可以阻止内部Cr2O3氧化层的挥发.氧化增重近似遵循抛物线规律.由于Cr和Mn的快速向外扩散,靠近氧化膜的基体化学成分发生变化,从而导致合金表层组织恶化,形成沿晶界分布的富Al的内氧化物、孔洞以及无碳化物区域.     

Corrosion behavior of Ni-base alloys for advanced high temperature water-cooled nuclear plants

Due to the projected requirement for highly enhanced efficiency in power generation, the environment in advanced high temperature water-cooled nuclear systems becomes more rigorous compared to conventional fossil and nuclear power plants. The corrosion behavior of candidate alloys Inconel 617, 625, and 718 exposed to supercritical water was studied by a variety of analytical techniques. Grain boundary engineering (GBE) was performed on the alloy 617 to compare its corrosion behavior with the as-received samples. The results indicate that the GBE-treated alloy 617 samples showed the best response and the alloy 718 samples showed the worst corrosion resistance. Pitting observed on the alloy 718 samples was more serious than that on the alloy 625 samples. The effect of the alloying elements and the GBE treatment on the corrosion behavior is discussed.     

析出相对含Ca镁合金腐蚀行为的影响

利用XRD、SEM、TEM和EDS等方法表征了Mg-Al-Zn-xCa(x=0、1.25%、1.74%、2.53%)合金腐蚀前后的组织结构,并采用失重法、电化学法、扫描探针显微镜(SPM)研究了合金腐蚀行为。结果表明：合金主要由α-Mg、β-Mg₁₇Al₁₂、Al₂Ca和(Mg,Al)₂Ca 组成。随着Ca含量的增加,合金组织中枝晶臂减小,主要沿晶界分布的Mg₁₇Al₁₂尺寸、数量逐渐减小, Al₂Ca由骨骼状连接成网状,(Mg,Al)₂Ca增多长大。腐蚀测试结果显示：添加Ca后的合金中α+β共晶减少,导致腐蚀通道变窄且比例减小。Ca元素能够使阳极自腐蚀电位升高,形成的Al₂Ca阴极相抑制了析氢过程。合金中主要析出相Al₂Ca 与α-Mg的电势差小于β-Mg₁₇Al₁₂与α-Mg的电势差。     

GH3230合金M23C6型碳化物的析出行为

研究了固溶态GH3230合金在800~1100 ℃时效不同时间下的碳化物析出行为。结果表明:GH3230合金固溶态组织主要为γ相+初生粒状碳化物M₆C+少量晶界粒状碳化物M₂₃C₆。试验合金在800~1100 ℃短时时效后,晶界和晶内析出的碳化物主要为M₂₃C₆型。其中晶界粒状M₂₃C₆型碳化物有沿着晶内长大的倾向,并逐渐变成胞状碳化物。在同一时效温度下,晶内碳化物析出数量会随着时效时间的增加而增加,此后会逐渐回溶,回溶开始的时间会随着时效温度的提高而逐渐提前。     

The effects of Cr and Al concentrations on the oxidation behavior of oxide dispersion strengthened ferritic alloys

The oxidation of six oxide dispersion strengthened (ODS) ferritic alloys was investigated at 1050 °C in air up to 200 h. Al plays the dominant role in improving the oxidation resistance of the ODS alloys. Cr and Y are of importance in forming the stable Al₂O₃ scale. To produce the dense alumina layer with enhanced adherence to the metal substrate, the concentrations of Al and Cr should be larger than 2 and 14 wt.%, respectively.     

Element diffusion during fabrication of EB-PVD NiAl coating and its 1100 °C isothermal oxidation behavior (II)

A two-layer NiAl coating can be deposited by electron beam physical vapour deposition (EB-PVD) on Ni-based superalloy, and the isothermal oxidation test at 1100 °C in air was conducted to evaluate the oxidation behavior of the coating. The dominant phase changed from β-phase to γ′-phase with the oxidation going on. Oxide ridges can be detected on the surface of the as-processed coating, oxide scales on the coating surface can be divided into two categories including the primary scales and the secondary scales formed only after the spallation of the primary scales. The primary scales form to connect the isolated oxide ridges, while the secondary scale's peak clipping effect may cause the surface morphology more and more even.     

Effects of water vapour on isothermal oxidation of chromia-forming alloys in Ar/O2 and Ar/H2 atmospheres

Fe9Cr, Fe17Cr and Fe25Cr alloys were subjected to isothermal oxidation in Ar/O₂ and Ar/H₂ atmosphere at 700 °C as high temperature corrosion for 48 h. Oxidation weight change measurement showed increasing Cr content reduced the oxidation rate. The oxidized Cr alloys were analysed using SEM, TEM and XRD. The addition of water vapour accelerates the onset of breakaway oxidation kinetics for Fe9Cr. The presence of water vapour promotes internal oxidation of Cr within Fe9Cr. For Fe17Cr and Fe25Cr, the water vapour effect is not significant due to the large Cr reservoir due to continue growth of Cr₂O₃.     

Formation of interfacial voids in cast and micro-grained γ′-Ni3Al during high temperature oxidation

Specimens of cast and micro-grained γ′-Ni₃Al, which were produced with vacuum casting and unbalanced magnetron sputter deposition, respectively, were isothermally oxidised in air at 1473 K for different periods of time. The formation of interfacial voids at the alloy/oxide interface was observed with SEM, which indicated that there were more interfacial voids formed in the cast Ni₃Al than in the micro-grained alloy under the same oxidation conditions. A phenomenological equation describing the fraction of the void projected areas was established, in which the impingement and coalescence between voids during their growth was taken into consideration. It was elucidated that low vacancy density in the micro-grained Ni₃Al due to the high creep, re-crystallisation and the enhanced Al diffusion reduced the void percentage. Also, it was confirmed that aluminium evaporation, perhaps supplemented by surface diffusion, supplied most Al to the oxide scales formed above the interfacial voids.     

Influence of grain size on the oxidation behavior of NbCr2 alloys at 950-1200 °C

The oxidation behavior of mechanically alloyed microcrystalline NbCr₂ intermetallics was investigated at 950-1200 °C in air by SEM in comparison with coarse-grain cast alloys. Results indicate that the mechanically alloyed alloys possess a better oxidation resistance and are less permeable to nitrogen than the cast alloys. At 1200 °C, the mechanically alloyed NbCr₂ alloys show a better resistance to scale spallation than the cast materials. The differences observed above are attributed to the finer grains increasing the relaxation of the oxide scale stress and improving the adhesion of the oxide layer on the matrix.     

The oxidation of nanocrystalline Ni3Al fabricated by mechanical alloying and spark plasma sintering

Nanocrystalline Ni₃Al was fabricated through mechanical alloying of elemental powders and spark plasma sintering. The nanocrystalline Ni₃Al has a nearly full density after being sintered at 1223 K for 10 min under a pressure of 65 MPa. Isothermal and cyclic oxidations of nanocrystalline Ni₃Al were tested at 1173–1373 K with intervals of 100 K. The results indicate that nanocrystalline Ni₃Al exhibits excellent isothermal and cyclical oxidation resistance. The oxide scales consist primarily of dense and continuous -Al₂O₃. The grain refinement is beneficial for improving the oxidation resistance of Ni₃Al by providing more nucleation centers for the Al₂O₃ formation, promoting the selective formation of Al₂O₃ and improving the adhesion of oxide scales to the matrix.     

Identification by photoelectrochemistry of oxide phases grown during the initial stages of thermal oxidation of AISI 441 ferritic stainless steel in air or in water vapour

Room temperature photoelectrochemistry was used to characterise oxide phases grown during the initial stages of oxidation of the ferritic stainless steel AISI441 at 650°C and 850°C in synthetic air or in water vapour. Grazing incidence X-ray diffraction and Raman spectroscopy were additionally used to discuss PEC results. Haematite Fe₂O₃ (∼2.0 eV), chromia Cr₂O₃ (3.0 and 3.5 eV) and their mutual solid solution (∼ 2.5 eV) were detected by their respective bandgap values determined from photocurrent vs. energy curves. The Cr/Fe ratio of the films increased with time/temperature and was higher in air-grown than in H₂O-grown oxides. Observation of photocurrent vs. potential curves indicated that chromia was N-type in all specimens, resulting from thermodynamic equilibrium with the metallic substrate and not with the gas phase.