反应合成法制备FeAl金属间化合物多孔材料的曲折因子(英文)

以Fe、Al元素粉末为原料,采用反应合成方法,利用Kirkendall效应造孔制备的FeAl金属间化合物多孔材料是继陶瓷和金属多孔材料之后发展的一种新型多孔材料。曲折因子是表征多孔材料孔隙特征的重要参数。基于Darcy原理和 Hagen-Poiseuille方程研究FeAl多孔材料的曲折因子。结果表明,FeAl多孔材料的曲折因子小于具有相同孔结构的不锈钢多孔材料的曲折因子。在本研究范围内,根据 Hagen-Poiseuille方程计算得知,FeAl多孔材料的曲折因子为2.26,而具有相同孔结构的不锈钢多孔材料的曲折因子为2.92。并由造孔机理探讨了FeAl多孔材料曲折因子较小的原因。     

FeAl金属间化合物多孔材料压缩力学性能研究

针对本课题组采用元素混合粉偏扩散-反应合成-粉末烧结方法制备的Fe-40at%Al金属间化合物多孔材料,采用单轴压缩实验研究其压缩应力-应变曲线特征以及孔隙率对其力学性能的影响规律,并通过扫描电镜实验揭示其微观断裂机理。结果表明：FeA1多孔材料的压缩应力-应变曲线可分为弹性、屈服、强化和破坏四个阶段,其中较大孔隙率的FeAl多孔材料表现出明显的非线性弹性特征;随着孔隙率的增大,其压缩屈服极限变化不大,而弹性模量和抗压强度显著降低;其断口特征宏观上表现为脆性断裂,微观上为微观沿晶断裂。比较FeAl多孔材料的理论值E_*和实测值E可知,非均匀Plateau多孔结构细观力学模型不适合高密度多孔材料,但可以较好地预测中密度多孔材料的弹性模量。     

NiCrdMoNb合金化层对TiAl金属间化合物抗氧化性能的影响

探讨了利用双层辉光等离子渗金属技术（GDPSAT）溅射NiCrMoNb合金化层对TiAl金属间化合物静止空气中高温氧化抗力的影响，结果表明，不处理的TiAl由于TiO2为主的氧化层的剥落抗氧化性能较差，而TiAl-NiCrMoNb合金层由于形成了致密，晶粒细小的富Al2O3层而使TiAl抗氧化性能大大提高，合金层与基体之间存在互扩散，Ni,Cr，Mo,Nb的界面富集导致界面化学性质的很大改变。     

孔隙率对Ti-Al金属间化合物多孔材料拉伸性能的影响

采用元素混合粉偏扩散-反应合成-粉末烧结方法制备了Ti-Al金属间化合物多孔材料,对其进行了拉伸试验研究,分析其拉伸变形特征,揭示出孔隙率对拉伸性能的影响规律以及拉伸断裂微观机理。结果表明:Ti-Al多孔材料的拉伸应力-应变曲线大致可分为弹性、屈服、强化和破坏4个阶段,无颈缩现象;力学性能指标(如弹性模量、屈服极限和强度极限等)均随孔隙率的增大而减小,延伸率远低于5%,呈现出明显的室温脆性;断口特征宏观上表现为脆性断裂,微观上同时存在穿晶断裂与沿晶断裂,其断裂机理与Ti-Al金属间化合物致密体的显微组织密切相关。     

Ni_3Al金属间化合物多孔材料的抗盐酸腐蚀性能

以Ni、Al元素混合粉末为原料,用偏扩散-反应合成-烧结的粉末冶金法制备Ni3Al金属间化合物多孔材料,在室温20℃下pH为2和3时以及90℃下pH=2时研究Ni3Al金属间化合物多孔材料在盐酸溶液中的腐蚀动力学曲线、孔结构稳定性和表面形貌变化以及Tafel曲线,并与Ni金属多孔材料进行比较。结果表明:Ni3Al金属间化合物多孔材料在盐酸中的质量损失率显著地低于Ni多孔材料的,且Ni3Al金属间化合物多孔材料的孔结构在腐蚀介质中长期稳定,并显示出优异的抗盐酸腐蚀能力。     

WC/FeAl金属间化合物基金属陶瓷涂层的冷喷涂制备

采用WC/Fe/Al混合粉末,通过机械合金化制备40v0l％ WC/Fe(Al)固溶体复合粉末,利用冷喷涂沉积涂层并结合热处理原位反应制备了WC/FeAl金属间化合物基金属陶瓷涂层.研究了球磨时间对复合粉末相结构、晶粒尺寸及组织结构的影响,并分析了冷喷涂WC/FeAl金属间化合物基金属陶瓷涂层的组织和显微硬度.结果表明,机械合金化可获得WC陶瓷颗粒呈微/纳米多尺度分布的WC/Fe(Al)金属陶瓷复合粉末,球磨36 h的复合粉末基体相平均晶粒尺寸约为90 nm,冷喷复合涂层组织致密、多尺度WC颗粒在基体中均匀弥散分布,涂层显微硬度约为1060 HV0.3,涂层在650℃热处理后发生Fe(Al)固溶体向FeAl金属间化合物的原位转变,制备出了WC/FeAl金属间化合物基金属陶瓷涂层.     

Fe-Al金属间化合物抗氧化性能研究现状

Fe-Al金属间化合物在高温下表面形成一层致密的Al2O3膜,具有极优良的抗氧化、耐腐蚀性能,在汽车、煤炭和石化工业得到广泛的应用。本文综述了Fe-Al金属间化合物在高温含氧气氛中氧化行为的研究现状,重点阐述了Fe-Al金属间化合物发生选择性氧化的临界铝浓度、氧化动力学、形成保护性氧化膜的温度条件以及影响氧化膜完整性的因素。介绍了Fe-Al金属间化合物作为涂层材料在阻氚渗透材料中的应用。     

热爆法制备FeAl基金属间化合物多孔材料（英文）

以Fe、Al粉末为原料,采用热爆法制备FeAl基金属间化合物多孔材料,研究烧结温度对其相组成、孔结构以及抗氧化性能的影响。结果表明:Fe-Al的热爆反应发生在636°C,1000°C烧结后得到单相FeAl金属间化合物多孔材料;多孔材料的开孔率达65%,其主要由连续的颗粒骨架、骨架之间的大孔隙和骨架内部的小孔隙构成;孔隙主要来自粉末压坯颗粒之间存在的原始大孔隙、烧结过程中熔化的Al颗粒在毛细作用下发生流动形成的原位大孔隙以及析出过程中在Fe-Al产物颗粒之间形成的小孔隙。此外,FeAl多孔材料在650°C空气气氛中表现出较好的抗高温氧化性能。     

Fabrication of porous FeAl-based intermetallics via thermal explosion

Porous FeAl-based intermetallics were fabricated by thermal explosion (TE) from Fe and Al powders. The effects of sintering temperature on phase constitution, pore structure and oxidation resistance of porous Fe-Al intermetallics were systematically investigated. Porous Fe-Al materials with high open porosity (65%) are synthesized via a low-energy consumption method of TE at a temperature of 636 °C and FeAl intermetallic is evolved as dominant phase in sintered materials at 1000 °C. The porous materials are composed of interconnected skeleton, large pores among skeleton and small pores in the interior of skeleton. The interstitial pores in green powder compacts are the important source of large pores of porous Fe-Al intermetallics, and the in-situ pores from the melting and flowing of aluminum powders are also significant to the formation of large pores. Small pores are from the precipitation of Fe-Al intermetallics particles. In addition, the porous specimens exhibit high resistance to oxidation at 650 °C in air.     

Effects of porosity on tensile mechanical properties of porous FeAl intermetallics

Uniaxial tensile tests and scanning electron microscopy (SEM) experiments were carried out on the porous FeAl intermetallics (porosities of 41.1%, 44.2% and 49.3%, pore size of 15–30 μm) prepared by our research group to study the macroscopic mechanical properties and microscopic failure mechanism. The results show that the tensile σ–ɛ curves of the porous FeAl with different porosities can be divided into four stages: elasticity, yielding, strengthening and failure, without necking phenomenon. The elastic modulus, ultimate strength and elongation decrease with the increase of porosity and the elongation is much lower than 5%. A macroscopic brittle fracture appears, and the microscopic fracture mechanism is mainly intergranular fracture, depending on the Al content in the dense FeAl intermetallics. In addition, the stochastic porous model (SPM) with random pore structure size and distribution is established by designing a self-compiling generation program in FORTRAN language. Combined with the secondary development platform of finite element software ANSYS, the effective elastic moduli of the porous FeAl can be determined by elastic analysis of SPM and they are close to the experimental values, which can verify the validity of the established SPM for analyzing the elastic properties of the porous material.     

Effect of chromium on the oxidation resistance of TiAl intermetallics

The effect of 10 at.%Cr on the oxidation resistance of TiAl intermetallic compound at 800–1100°C in air was investigated. The results indicated that 10 at.%Cr equally substituting for Ti and Al in TiAl alloy had duplex effects on the isothermal kinetics of DAL At lower temperatures (800–900°C), Cr increased the oxidation rates as a result of the doping effect of Cr in the scale and at higher temperatures (1000–1100°C), especially at 1100°C, Cr significantly reduced the oxidation rates as a result of the formation of a continuous Al₂O₃ film on the surface. 10 at.%Cr only substituting for Ti in TiAl alloy remarkably reduced the oxidation rates at all temperatures by about two orders of magnitude. Moreover, 10 at%Cr significantly improved the cyclic-oxidation rsistance of TiAl alloy.     

Effect of yttrium additions on the oxidation of nickel

The oxidation of Ni, Ni-0.1 wt.% Y, and Ni-0.3 wt.% Y alloys was carried out in the temperature range 500–900°C at p_{O 2}= 1 atm.Work supported by the Division of Basic Energy Sciences, U.S. Department of Energy.     

Comparisons of high temperature oxidation behavior between reactive-sintered and melted Ti-45at.%Al-1.6at.%Mn intermetallics

In order to investigate high temperature oxidation behavior, isothermal oxidation experiments for Ti-45at.%Al-1.6at.%Mn intermetallics prepared by both reactive sintering and melting were carried out in both oxygen and air environments at temperatures of 900, 1000 and 1100°C. In the oxygen environment, reactive sintered Ti-45at.%Al-1.6at.%Mn was found to have excellent oxidation resistance due to the formation of a continuous A1₂O₃ layer at temperatures up to 1100°C; however, when melted it showed very poor oxidation resistance at and above 1000°C. Weight gains of the melted specimen after 12 hours, especially at the temperature of 1000°C and 1100°C, were nearly 12 times that of the reactive sintered one. In air, the reactive-sintered intermetallics showed a poorer oxidation resistance man did that in the oxygen environment. Especially, the weight gains in air were 6 times larger than the weight gains in oxygen when oxidized at 1100°C for 12 hours.     

The influence of yttrium additions on the oxidation resistance of a directionally solidified Ni-Al-Cr3C2 eutectic alloy

Isothermal oxidation of a directionally solidified Ni-Al-Cr₃C₂ eutectic alloy results in development of an external -Al₃O₃-rich scale. However, this scale breaks down after relatively short times at temperature and a less protective Cr₂O₃-rich scale is formed, together with substantial internal oxide in the alloy. In an attempt to maintain the external -Al₂O₃-rich scale and prevent damaging subscale oxidation, modified yttrium-containing directionally solidified alloys have been developed. The oxidation resistance of these alloys at 1000 and 1100°C in flowing air has been investigated and found to be considerably better than that of the corresponding yttrium-free alloy. At both temperatures an external -Al₂O₃-rich scale is produced and is retained for much longer periods than on the yttrium-free alloys during isothermal and thermal cycling oxidation. Some scale breakdown does occur during thermal cycling at 1100°C, but -Al₂O₃ is able to re-form as the surface oxide. However, although external -Al₂O₃-rich scales are retained for long periods on these alloys, some oxide penetration into the alloy beneath these scales does occur where coarse carbide fibers intersect the alloy surface. This is associated with relatively poor scale integrity at these intersections.     

高孔隙率多孔钛的制备及微弧氧化改性

以商业用纯钛粉为原料,添加造孔剂碳酸氢铵,通过真空烧结的方法制备了多孔钛。再在浓度为10%稀硫酸溶液的电解液中对制备的多孔钛进行微弧氧化处理。将微弧氧化(MAO)改性后的多孔钛浸泡于模拟体液(SBF)中检测其生物活性,并采用SEM和XRD对改性前后多孔钛及矿化后的样品进行了表征。结果显示,制备的多孔钛孔隙率为70%,其孔结构主要包括两类：即尺寸为几百微米的相互贯通的大孔和分布在大孔壁上的尺寸为几微米的小孔。在电压为100 V下氧化2 min能在多孔钛壁上形成厚度为几百纳米的多孔TiO膜层,且该膜层能诱导磷灰石的形成。这表明,微弧氧化处理后的多孔钛具有优异的生物活性。     

The effects of yttrium ion implantation on the oxidation of nickel-chromium alloys. II. Oxidation of yttrium implanted Ni-20Cr

Yttrium ions were implanted into an alloy of nickel containing 20 wt.% chromium. The oxidation weight gains of the implanted alloy, as well as unimplanted Ni-20Cr, were measured in 1 atm. of oxygen at temperatures between 815°C and 1100°C. Though a yttrium fluence of 2×10¹⁵ ions/cm² increased the weight gained at a given time for the implanted alloy compared to the unimplanted alloy, a fluence of 7.5×10¹⁶ ions/cm² considerably retarded the oxidation process. This retardation was caused both by a reduction in the duration of transient oxidation and by a reduction in the rate of parabolic oxidation that follows the transient stage. Examination of oxidized specimens revealed that the higher fluence yttrium implantation caused an earlier formation of Cr₂O₃, thus shortening the time during which NiO forms and contributing to the reduced time and weight gain during transient oxidation. This accelerated formation of Cr₂O₃ is explained by reference to the yttrium-implantation-induced amorphous phase present on the alloys, the formation of small grains of nickel-chromium solid solution within this amorphous phase, and the presence of NiCr₂O₄ at the oxide/gas interface. Potential causes of the reduced rates of parabolic oxidation are also discussed.     

The yttrium effect on the corrosion resistance of CO2-laser processed MCrAlY coatings

To improve the corrosion resistance and to study the effect of yttrium in the behavior of coatings produced by thermal spraying MCrAlY (M=Ni, Co) powders, CO₂ laser processing was conducted. Three methods were used: (1) a combination of gas flame and plasma spraying in air followed by laser glazing in argon, (2) low-pressure plasma spraying (LPPS) and laser glazing in argon, and (3) LPPS and laser-gas (O₂) alloying. Laser glazing in argon of the MCrAlY coatings sprayed in air promoted formation of weakly adherent agglomerates of Al–Y oxides and an alumina-chromia solid solution. Glazing in argon atmosphere of LPPS CoNiCrAlY and NiCrAlY coatings caused the formation of nickel aluminides besides the formation of Y–Al compounds. Gas (O₂)-alloying of these coatings produces continuous and adherent (yttrium-containing) alumina and chromia layers. The effects of yttrium on the characteristics of the oxides formed in the coatings during laser glazing, laser-gas alloying, and high-temperature oxidation is discussed. This work also investigated the oxidation resistance of the laser-processed MCrAlY coatings in air and in the presence of 85 mol/o V₂O₅–Na₂SO₄ fused salt at 900°C.