Effect of the pore size on the creep deformation behavior of Ni-Fe-Cr-Al porous metal

The effect of the pore size on the creep deformation behavior of new Ni-Fe-Cr-Al powder porous metal was investigated. Two different powdered porous metals having different average pore sizes of 580 μm and 800 μm were used. Creep tests were conducted at 1073 K under three different compressive stresses between 0.5 and 1.5 MPa. The Ni-Fe-Cr-Al porous metals mainly consisted of the three phases of γ′-Ni, γ′ and Ni_1.1Al_0.9. The materials exhibit secondary creep behavior following a power law characterized by creep exponents of 3.7 for the 580 μm and 2.5 for the 800 μm porous metals. The stress exponent values that appeared as two creep exponent values could be made to converge to one value, 3.06, using the new concept of the estimated stress (as determined by the area fraction of the porous metal). This study also presents a creep deformation analysis method that can be applied regardless of the pore size or the presence of a porous structure.     

Effect of grain size reduction on high temperature oxidation of binary two-phase alloys

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High temperature oxidation behavior of Ni-Cr-Al based powder porous metal

This study investigated the high temperature oxidation behavior of newly developed Ni-Cr-Al powder porous metal. High temperature isothermal oxidation tests were conducted at 900, 1000 and 1100 °C temperatures for 24 h under an atmosphere of 79% N₂ + 21% O₂ gas. Oxidation weight gain vs. time curves represented typical oxidation behavior of parabolic shape. Weight gain increased with increasing oxidation temperature. Ni-Cr-Al porous metal mainly created oxides such as α-Al₂0₃, Cr₂O₃, NiCr₂O₄. The α-Al₂0₃ oxide could be still maintained up to 1100 °C oxidation temperature as a thick and stable protective layer. It was noted that Ni-Cr-Al porous metal had better high temperature oxidation resistance than those of other Ni-based and Fe-based porous metals. The catastrophic degradation of oxidation resistance especially at very high temperature was not observed up to 1100 °C in this porous metal. The micro-mechanism of high temperature oxidation of Ni-Cr-Al porous metal was also discussed.     

The influence of metal lattice vacancies on the oxidation of high temperature materials

When an oxide scale grows on a metal by the outward diffusion of cations, it is anticipated theoretically that lattice vacancies will be injected into the metal substrate. Experiments are reviewed which provide direct evidence for vacancy injection, including X-ray and electron microscope observations of the growth of vacancy dislocation loops and optical microscopy of voids. The influence of a vacancy supersaturation on the kinetics of oxidation is discussed in detail, but the effects are shown to be small in practical cases. The main consequence of vacancy injection is shown to be the eventual breakdown of the initial scale and subsequent growth of a duplex porous oxide. In some cases, this transition has undesirable consequences such as carburization/decarburization of the underlying metal and “breakaway” oxidation.     

Effect of Cr on high temperature oxidation of TiAl

The oxidation behavior of TiAl-Cr（mole fraction of Cr：0-20%） was investigated at 1 173 K in air. The microstructure and composition of the oxide scale were studied by X-ray diffractometry（XRD）, scanning electron microscopy（SEM） and electro-probe micro-analyses（EPMA）. The results show that with the addition of Cr content from 0 to 8%, the oxidation resistance decreases, especially at 3%, which is mainly attributed to the doping effect of Cr^3＋. TiAI-Cr（mole fraction of Cr： 15%-20%） has good oxidation resistance, and the protective alumina layer is preferentially formed on the surface of TiAI alloy, which is due to an increase of mole ratio of Al to Ti in TiAl-Cr alloys.     

Effects of particle size and forming pressure on pore properties of Fe-Cr-Al porous metal by pressureless sintering

With increased hydrogen consumption in ammonia production, refining and synthesis, fuel cells and vehicle industries, development of the material components related to hydrogen production is becoming an important factor in industry growth. Porous metals for fabrication of hydrogen are commonly known for their relative excellence in terms of large area, lightness, lower heat capacity, high toughness, and permeability. Fe-Cr-Al alloys not only have high corrosion resistance, heat resistance, and chemical stability but also ductility, excellent mechanical properties. In order to control powder size and sintering temperature effects of Fe-Cr-Al porous metal fabrication, Fe-Cr-Al powder was classified into 25-35 μm, 35-45 μm, 45-75 μm using an auto shaking sieve machine and then classified Fe-Cr-Al powders were pressed into disk shapes using a uniaxial press machine and CIP. The pelletized Fe-Cr-Al specimens were sintered at various temperatures in high vacuum. Properties such as pore size, porosity, and air permeability were evaluated using perm-porosimetry. Microstructure and phase changes were observed with SEM and XRD. Porosity and relative density were proportionated to increasing sintering temperature. With sufficient sintering at increasing temperatures, the pore size is expected to be gradually reduced. Porosity decreased with increasing sintering temperature and gradually increased necking of the powder.     

Effect of Fe on the high temperature oxidation of TiAl alloys

An alloy of 51.23Ti−48.73Al−0.4Fe (at.%) was oxidized at 800, 900 and 1000°C in air to determine the effect of Fe on oxidation. The scales formed consisted of an outer TiO₂ layer, an intermediate Al₂O₃ layer, and an inner mixed (TiO₂ Al₂O₃) layer, typical of conventional TiAl alloys. A small amount of dissolved Fe ions was weakly segregated in the outer TiO₂ layer and also in the inner (TiO₂−Al₂O₃) mixed layer. Ti₂AIN and TiN were detected in the scale in some instances. A thin, oxygen-affected Ti₃Al sublayer formed at the oxide-substrate interface. The overall oxidation kinetics and the scale morphology were not affected by Fe-addition.     

Cr元素对钢高温氧化行为的影响

利用热重及同步热分析仪对Cr元素含量0.8%(1#)、3.0%(2#)和5.0%(3#)的3种试验钢进行900~1050℃温度区间,氧化时间30 min的氧化增重试验,建立了试验钢氧化动力学模型,对氧化动力学模型预测值与试验值进行平均误差和相关性分析;采用SEM分析氧化膜形貌,研究了Cr元素含量对钢高温氧化行为的影响。结果表明:在不同氧化温度条件下,Cr元素含量不同的3种试验钢氧化增重曲线均呈上升趋势;1#、2#和3#试验钢氧化过程动力学模型预测值与试验值的平均误差小于7.0%,相关系数R大于0.99;氧化温度低于980℃时,随Cr元素含量增加抗氧化能力增强;氧化温度达到1050℃时,3#试验钢表层氧化膜Cr_2O_3进一步反应生成气态CrO_3,抗氧化能力降低。     

钎焊中高温氧化对硬质合金的影响

研究了YG-11C硬质合金在900、950、1000℃下加热的氧化行为,并测试了在钎焊过程中受氧化的硬质合金刀头性能。结果表明,硬质合金在900℃以上加热10 min发生氧化,硬质相WC和粘结相Co被氧化成WO3和Co WO4;氧化后的硬质合金发生变形及增重,随温度升高,氧化现象更严重,变形增重更明显;高温钎焊后的硬质合金刀头表面氧化后,微观组织变得疏松多孔,硬度及耐磨性明显降低。     

不同孔径分布多孔钛的力学性能

从生物学角度出发设计并制备2种不同孔径分布的多孔钛,并研究其力学性能。采用造孔剂烧结方法制备孔隙率为36%~63%的多孔钛,通过室温压缩测试其力学性能。多孔钛的弹性模量和抗压强度分别在2.662~18 GPa和94.05~468.57 MPa范围内,且都随着孔隙率的增加而降低。抗压强度和孔隙率的关系曲线呈现完全的线性特征,表明抗压强度主要受孔隙率的影响,几乎不受孔径的影响。Gibson-Ashby力学关系分析结果显示：常数项C值的差异说明孔径分布对多孔钛的屈服强度有一定的影响;密度指数n值均大于临界值3,表明这2种不同孔径的多孔钛的变形方式相同,为孔壁的屈曲作用。     

合金元素对Co-Al-W合金高温氧化行为的影响

研究新型Co-Al-W合金在800和900℃空气中氧化动力学及元素Mo、Nb、Ta和Ti对合金高温氧化行为的影响。结果表明:在800℃氧化100 h后,Co-8.8Al-9.8W(摩尔分数,%)和Co-8.8Al-9.8W-2Ta合金的质量增加较小,表明其抗高温氧化能力较强;在900℃氧化时,Co-8.8Al-9.8W-2Mo、Co-8.8Al-9.8W-2Nb、Co-8.8Al-9.8W-2Ta和Co-8.8Al-9.8W-2Ti合金的质量增加小于Co-8.8Al-9.8W合金的,表明加入合金元素可以提高合金的抗高温氧化能力;在不同温度下,Co-Al-W合金氧化膜表面出现团聚、开裂和脱落现象;氧化膜分为3层,外层为Co3O4氧化物,中间层为W、Al和合金元素的复杂氧化物,内层为Co和Al的氧化物。从合金氧化动力学曲线来看,在800℃时合金元素增强Co-Al-W合金抗高温氧化能力由强至弱依次为Ta、Ti、Mo、Nb;在900℃时按Ti、Ta、Mo、Nb顺序依次减弱。     

合金元素对Nb-Ti-Al-C合金氧化行为的影响

利用真空非自耗电弧炉制备不同Al含量的Nb-25Ti-8C合金,研究Nb-Ti-Al-C合金的组织结构及其高温氧化行为。研究表明,Nb-25Ti-8C-(0,5,10)Al合金由Nbss和(Nb,Ti)C两相构成;Nb-25Ti-8C-15Al合金由Nbss、(Nb,Ti)C和Nb3Al三相构成。800~1000℃氧化过程中,合金氧化膜为由Nb2O5,Ti O2,Al2O3,Nb O2及Ti Nb2O7多种氧化物构成的混合氧化膜。Ti、Al活性元素可优先与氧发生选择性氧化,抑制氧化物Nb2O5生成,提高氧化膜致密度和合金抗氧化性,并且氧化温度越高,Al元素改善铌合金抗氧化性能效果越明显。Nb-25Ti-8C合金800℃氧化时表现出良好的抗氧化性能,1000℃氧化时Nb-25Ti-8C-x Al合金的抗氧化性能明显优于C-103。随氧化温度升高,氧化膜中Nb2O5含量增加,导致氧化膜与合金基体的内应力增大,引起外层氧化膜脱落。碳化物中C元素以CO2形式挥发导致氧化层表面形成氧化空洞。     

Platinum-catalyzed high temperature oxidation of metals

Samples of Al, Cr, Ni, and Zr were sputter-coated with porous Pt-films with a particle size of 20-30 nm. Thermal oxidation of these samples was studied by gas phase analysis (GPA) and secondary ion mass spectrometry (SIMS). SIMS analysis on partly Pt-coated samples of Al, Cr, Ni, and Zr at different oxide depths in areas with Pt and in areas away from Pt indicates an enhanced inward oxide growth in the Pt area and mm-ranged distance from Pt-area. Weight gain measurements on Pt-coated Ni samples show a reduced or increased oxidation rate depending on the amount of porous Pt-coating. Pt has two effects on the thermal oxidation of metals and the overall effect of Pt on the oxidation of metals depends on the mechanism of oxide growth in the absence of Pt.     

CeO2对Cr-Al渗层组织和高温氧化性能的影响

采用浆料包渗法,以Cr2O3,粉为渗Cr源,纯Al粉为还原剂,NH4Cl作为活化剂,Al2O3,为惰性添加剂,蛋白质(鸡蛋清)为粘结剂,在Cu表面预先镀Ni随后浆料包渗Cr、Al,制备Cr-Al共渗层.研究了稀土氧化物CeO2对Cr-Al渗层的组织和氧化性能影响.结果表明:渗剂中添加CeO2氧化物后,渗层组织由Cr、Al的固溶体为主转变为Ni3Al金属间化合物和固溶体两相混合;与不加稀土氧化物相比,改性后渗层氧化增重由纯铜的1/6降低到1/11,氧化产物为Cr2O3、Al2O3和少量的NiO,氧化层致密,没有明显的裂纹和空洞出现,改善r铜表面抗高温氧化性能.     

SiC颗粒尺寸对喷射沉积铝硅复合材料高温疲劳性能的影响

采用喷射沉积法制备SiCp/Al-7Si复合材料,研究SiC颗粒尺寸对复合材料低周疲劳性能的影响.结果表明:SiC颗粒尺寸对复合材料疲劳性能的影响显著.在相同体积分数下,小尺寸SiC颗粒复合材料的间距小、承载能力强,表现出较高的疲劳寿命,疲劳裂纹主要在SiC颗粒与基体脱粘处以及小尺寸颗粒团聚处形核并扩展.而在SiC颗粒...     

铁基合金粉末氧化行为

采用质量变化、氧含量测定、XRD、SEM和能谱分析研究铁基合金粉末500℃氧化行为及氧化机理。结果表明,氧化质量增量、氧含量随时间变化明显,前期呈线性关系,后期则呈抛物线关系;前期由于氧化时间较短,铁基合金粉末颗粒与氧反应不明显,后期氧与颗粒表面反应,生成Fe、Cr和Ti的氧化物,并形成致密的氧化膜;铁基粉末形成(Fe,Cr)2O3相,随着氧化时间的延长,形成的(Fe,Cr)2O3相衍射峰强度增强。     

高温运行对镍基异种金属接头力学性能的影响

对12Cr1MoV和0Cr17ni12Mo2两种管材的镍基异种金属接头进行焊后状态和高温运行后状态对比试验。结果表明,高温运行使异种钢接头σ-ε图中曲线移动,反映了高温运行后异种钢接头的屈服强度和塑性有所下降;高温运行使异种钢接头的各项力学性能指标σb,σ0.2,δ5,ψ均略有下降,该结果与接头组织变化及12Cr1MoV钢珠光体组织中碳化物球化倾向等不利因素有关;高温运行对异种钢接头断口部位及宏观断口形貌特征无大的影响;高温运行后异种钢接头拉伸试样仍断在母材处,表明镍基异种钢接头的抗拉强度是比较满意的。     

The high temperature oxidation of aluminium-implanted iron

Aluminium was implanted into iron at different doses between 1 × 10¹⁴ and 1.5 × 10¹⁷ atm cm^?2. Oxidation tests were carried out in oxygen during 100–120 h in the temperature range 720–1020 K. Doses of 5 × 10¹⁶ atm cm^?2 had to be achieved to observe a notable inhibition of the oxidation process. In these conditions, the formation of two ternary oxides was detected but the spinel phase Fe Al₂O₄ seemed to be responsible for the observed blocking effect.     

金属结合剂金刚石多孔砂轮磨削温度的实验研究

制备了不同孔隙率的金属结合剂细粒度和微粉金刚石多孔砂轮并进行了不同材质石材的磨削性能实验.采用热电偶测温法,研究了不同孔隙率、不同磨粒粒度的金属结合剂金刚石多孔砂轮对两种不同工件材料的磨削温度特性.实验结果表明,不同孔隙率、不同磨粒粒度的金属结合剂金刚石砂轮的磨削温度均随着转速及切深的增加而增加;细粒度的金属结合剂金刚石砂轮随着孔隙率的增大,磨削温度降低;而微粉金属结合剂金刚石砂轮则表现出和细粒度金属结合剂金刚石砂轮不同的特性,即孔隙率达到一定值时,随着孑L隙率继续增大,磨削温度反而升高;同一孔隙率金属结合剂金刚石砂轮,细粒度金刚石砂轮的磨削温度要低于微粉金刚石砂轮的磨削温度.