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A kinetic analysis of multistep electrochemical reactions involving partial diffusion transport of intermediates between the near-electrode layer and the bulk electrolyte is performed within theory of generalized variables (theory of similarity).
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Expressions relating the partial diffusion coefficients, macroscopic flow velocity, and mutual diffusion coefficient are obtained.
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The GB channel formation has been described as a relaxation process accompanying GB interdiffusion of Sn and Cu atoms with unequal partial diffusion coefficients (DSn>amp;gt;DCu).
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Within the framework of the Boussinesq approximation, as a function of the relationship between the partial diffusion factors, we have investigated an isothermal three-component gas mixture with respect to linear stability.
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CO2 evolution is assumed to increase due to enhanced mineralization and partial diffusion from the carbonate horizon at the depth of the seasonal frost.
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| The microstructure and mechanical properties of powder metallurgy(PM) Ti alloy doped with rare earth element Nd were investigated by using optical microscopy, scanning electron microscopy and transmission electron microscopy. The results show that addition of rare earth element can improve the density, tensile strength and elongation of PM Ti alloy. The alloy containing 1.0% Nd(mass fraction) has a relative density of 99%, tensile strength of 1080 MPa and elongation of 6%. The above mechanical properties are... The microstructure and mechanical properties of powder metallurgy(PM) Ti alloy doped with rare earth element Nd were investigated by using optical microscopy, scanning electron microscopy and transmission electron microscopy. The results show that addition of rare earth element can improve the density, tensile strength and elongation of PM Ti alloy. The alloy containing 1.0% Nd(mass fraction) has a relative density of 99%, tensile strength of 1080 MPa and elongation of 6%. The above mechanical properties are almost the same as those of Ti-6Al-4V. The contribution of rare earth element to the density lies in that transient liquid phase occurs during sintering, and the rare earth element can scavenge oxygen from the powder surface, purify the particle interface and activate the sintering process. The increase of density, the decrease of the oxygen content of Ti substrate along with the existence of Nd oxides improve the mechanical properties of PM Ti alloy. However, the sintering temperature for Nd-containing alloy should be controlled properly. An excessively high sintering temperature can lead to agglomeration of Nd-rich liquids and coarsening of grains, hence deteriorates the mechanical properties of PM Ti alloy. | 利用光学显微镜、扫描电镜(SEM)和透射电镜(TEM)等手段研究了在粉末Ti合金中添加稀土元素对烧结坯的显微组织和力学性能的影响。结果表明,添加稀土元素可以有效提高烧结坯的致密度、室温抗拉强度和延伸率,其中含1.0%Nd(质量分数)的材料致密度达99%,抗拉强度1080MPa,延伸率6%,接近锻造Ti 6Al 4V合金的性能水平,而且制备成本明显降低。稀土元素对致密度的贡献主要归因于在烧结过程中产生瞬时液相,同时稀土元素能够夺取粉末颗粒表面的氧,净化原始颗粒界面,提高粉末颗粒的烧结活性。致密度的提高,Ti合金基体氧含量的降低以及第二相Nd氧化物的存在都有助于材料力学性能的提高。然而含Nd合金的烧结温度应控制在一个合适的范围内,过高的烧结温度将导致瞬时富Nd液相的聚集和元素的偏扩散,以及由于扩散条件改善后的晶粒过度长大,反而不利于材料力学性能的提高。 | Ti-46.5%Al(mole fraction) intermetallic compound filter materials with overall porosity of 38.3%(48.2%) were fabricated through elemental powder cold roll forming and reactive synthesis. The TiAl alloy filter material with maximum porosity was fabricated under cold pressure of 35.3×10~443.1×10~4 N(with the roller diameter of 200 mm), heating rate of 0.33 K/s, and thermal retardation time of 50 and 60 min at 873 and 1 473 K, respectively. The results show that the microstructure of TiAl filter material consists... Ti-46.5%Al(mole fraction) intermetallic compound filter materials with overall porosity of 38.3%(48.2%) were fabricated through elemental powder cold roll forming and reactive synthesis. The TiAl alloy filter material with maximum porosity was fabricated under cold pressure of 35.3×10~443.1×10~4 N(with the roller diameter of 200 mm), heating rate of 0.33 K/s, and thermal retardation time of 50 and 60 min at 873 and 1 473 K, respectively. The results show that the microstructure of TiAl filter material consists of TiAl and Ti_3Al phases, and that the content of Ti_3Al phase increases with the sintering temperature. The most probable aperture of the TiAl alloy filter material is 2.56 μm, and its maximum aperture and air permeability are 11.8 μm and 3.219×10~(-5) m·Pa~(-1)·s~(-1), respectively. The prime reasons are considered to be the existence of the porosity in sheet bars and Al self-diffusion in the process of reactive synthesis. | 以Ti、Al元素粉末为原料,通过冷轧成形和两阶段反应合成法,制备出孔隙度为38.3%～48.2%的Ti 46.5%Al(摩尔分数)金属间化合物过滤材料。具有最大孔隙度为48.2%的TiAl合金过滤材料的制备工艺为:冷轧压力35.3×104～43.1×104N(轧辊直径200mm),烧结过程升温速率0.33K/s,分别在873和1473K温度下保温50和60min。研究表明:真空烧结后,TiAl合金由TiAl和Ti3Al两相组成,Ti3Al相含量随烧结温度升高而增加;所制备的TiAl合金过滤材料的最可几孔径可达2.56μm,对应的最大孔径为11.8μm,透气度为3.219×10-5m·Pa-1·s-1;原轧坯中的孔隙及Al元素偏扩散造孔是形成过滤材料孔隙的主要原因。 | Ti-Al alloy sheets were fabricated successfully by element powder cold roll forming and reactive synthesis. The size and relative density of sheet bars were 500 mm×230 mm×1.5 mm, 85.9% respectively. The effects of process parameters on the fabrication of sheet bars and the vacuum sintering behavior of sheets at different temperatures were investigated. The results show that the moderate flowability of element powders, low rolling velocity and stable rolling pressure are needed for the process of Ti, Al element... Ti-Al alloy sheets were fabricated successfully by element powder cold roll forming and reactive synthesis. The size and relative density of sheet bars were 500 mm×230 mm×1.5 mm, 85.9% respectively. The effects of process parameters on the fabrication of sheet bars and the vacuum sintering behavior of sheets at different temperatures were investigated. The results show that the moderate flowability of element powders, low rolling velocity and stable rolling pressure are needed for the process of Ti, Al element powder cold rolling. After the sintering, microstructure of Ti-Al alloy sheet consists of Ti-Al and Ti_3Al phases, and the content of Ti_3Al phase increases with the sintering temperature. The increment of Ti-Al sheets porosity is 21%32%, and the prime reasons are considered to be the existence of the porosity in sheet bars and Al self-diffusion in the process of reactive synthesis. During the low pressure(<10 kPa) vacuum sintering process, the external pressure works effectively in the transient liquid phase stage. The effect of the low external pressure on porosity of sintered sheets increases with the increment of the size of the element powder particles and the sintering temperature. | 以Ti、Al元素粉末为原料,在粉末轧机上无包套冷轧成尺寸为500mm×230mm×1.5mm的板坯,其相对密度达85.9%。研究了不同工艺参数对Ti、Al元素粉末轧制板材的影响。取小样在不同温度下进行真空无压烧结,研究了板坯的真空烧结行为。结果表明:Ti、Al元素粉末冷轧过程要求适中的粉末流动性、低的轧制速度以及一定大小且较稳定的轧制压力。真空烧结后,Ti Al合金由Ti Al和Ti3Al两相组成,Ti3Al相含量随烧结温度升高而增加。烧结坯孔隙度大幅度增加,增加量为21%32%。原板坯中的孔隙及偏扩散是造成烧结坯孔隙的主要原因。低压(<10kPa)真空烧结过程中,外压仅有效作用于短暂的液相阶段,粉末粒度越粗,烧结温度越高,烧结坯孔隙度受这种低压强的影响程度越大。 | | |
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偏扩散
partial diffusion
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