Types Of Second Phase Particles Research Articles

Microchemistry evolution during industrial DC casting and subsequent homogenization of aluminum alloy AlMn0.5Mg0.5 (AA 3105)

The properties of non-heat treatable Al wrought alloys are influenced by the materials microchemistry in terms of the portion of alloying elements either in solid solution or in precipitated form. In the present study we analyze the phase selection during solidification as well as the changes in solute level and particle state during subsequent homogenization of the Al-Mn alloy AA 3105 (ISO AlMn0.5Mg0.5). Characterization of the microchemistry reactions is performed by a combination of optical and scanning electron microscopy with differential scanning calorimetry and measurements of thermoelectric power as well as specific electrical resistivity. The results are underpinned by CALPHAD simulations of the second-phase particles in the as-cast state, while the changes in solute level as well as volume, size and type of second-phase particles during homogenization are tracked with a statistical microchemistry simulation tool named ClaNG. Owing to the high Si content of the present alloy the as-cast state is dominated by α-Al(Fe,Mn)Si phase constituent particles together with a few Al6(Mn,Fe) and Mg2Si phases. Homogenization is characterized by the formation and redissolution of Mg2Si and, at higher temperatures, dispersoids of the α-Al(Fe,Mn)Si phase.

Elastoplastic analysis of AA7075-O aluminum sheet by hybrid micro-scale representative volume element modeling with really-distributed particles and in-situ SEM experimental testing

• Presents a novel computationally-efficient reconstruction of 3D RVE model of second-phase particle-strengthened AA7075-O sheet with real distribution of particles based on FIB-SEM techniques. • Three types of second-phase particles (i.e., irregularly-shaped iron-rich particle Al 3 Fe, elliptically-shaped particle MgZn 2 , and needle-like particle CuAl 2 ) are determined using SEM-based EDS and EBSD techniques. • Presents a systematic study of the overall elastic-plastic response by developing and applying a hybrid experimental analysis and computational modeling framework. • Good agreement is observed in the comparison of RVE results with that of in-situ SEM tensile tests, indicating that the real 3D microstructure-based RVE models can accurately predict the plastic deformation and interfacial failure evolution in AA7075-O sheet. This paper addresses the challenge of reconstructing randomly distributed second-phase particle-strengthened microstructure of AA7075-O aluminum sheet material for computational analysis. The particle characteristics in 3D space were obtained from focused ion beam and scanning electron microscopy (FIB-SEM) and SEM-based Electron Backscatter Diffraction/Energy Dispersive X-ray Spectrometry (EBSD/EDS) techniques. A theoretical framework for analysis of elastic-plastic deformation of such 3D microstructures is developed. Slip-induced shear band formation, void initiation, growth and linkage at large plastic strains during uniaxial tensile loading were investigated based on reconstructed 3D representative volume element (RVE) models with real-distribution of particles and the results compared with experimental observations. In-situ SEM interrupted tension tests along transverse direction (TD) and rolling direction (RD), employing microscopic-digital image correlation (μ-DIC) technique, were carried out to investigate slip bands, micro-voids formation and obtain microstructural strain maps. The resulting local strain maps were analyzed in relation to the experimentally observed plastic flow localization, failure modes and local stress maps from simulations of RVE models. The influences of particle size, shape, orientation, volume fraction as well as matrix-particle interface properties on local plastic deformation, global stress-strain/strain-hardening curves and interfacial failure mechanisms were studied based on 3D RVE models. When possible, the model results were compared with in-situ tensile test data. In general, good agreement was observed, indicating that the real 3D microstructure-based RVE models can accurately predict the plastic deformation and interfacial failure evolution in AA7075-O aluminum sheet.

Evolution of micro-chemistry during solidification and homogenisation of AA 3xxx aluminium–manganese alloys

An important aspect of the characterisation of non-heat-treatable Al alloys is the constitution of the material in terms of its alloying elements in solid solution and, in turn, volume, size, morphology and species of second-phase particles. These constitutional characteristics, conveniently summarised as micro-chemistry, have an impact on physical and mechanical materials properties of Al semi-finished products. In the present study, the evolution of micro-chemistry in the Al–Mn alloys of the AA 3xxx series during solidification and homogenisation is analysed. Especially, we focus on the impact of additional alloy elements, including Si, Mg and Cu, on the phase selection during solidification and the changes in solute level and volume, size and type of second-phase particles during subsequent homogenisation.

Enhanced corrosion resistance of Mg–Sn–Zn–Al alloy by Y microalloying

A significant enhancement in corrosion resistance by Y microalloying was achieved for the Mg–8Sn–1Zn–1Al (wt%) alloy in the extruded condition. Average corrosion rates obtained by immersion tests in 0.6 M NaCl solution at 25 °C were 4.2 and 12.7 mm y−1 for the alloys with and without microalloying with 0.04 wt% Y, respectively. Microstructural investigations indicated that the enhanced corrosion resistance is a result of a transition in a type of second-phase particles toward lowering the difference in electrochemical nobility between the α-Mg and these particles, thereby reducing the susceptibility of the alloy to microgalvanic corrosion.

Microstructure and mechanical properties of Gd-modified AZ80 magnesium alloys

The microstructure and mechanical properties of AZ80 alloy with different Gd contents were investigated. The results reveal that a minor addition of Gd could lead to a change in the type of second phase particles from Al–Mn to Al–Gd–Mn, and the primary rare earth phase is Al8GdMn4 instead of Al2Gd in the AZ80–0.3Gd alloy. New strip-like Al3Gd and block-shaped Al2Gd phases are formed successively with the increase of Gd content. Al2Gd phase becomes the dominating rare earth phase in AZ80–2.0Gd and AZ80–4.0Gd alloys. Tensile test indicates that the mechanical properties are improved obviously with a proper Gd content. However, excessive Gd addition results in the decrease of mechanical properties due to the formation of coarse block-shaped Al2Gd phase. AZ80–0.9Gd alloy exhibits the optimal mechanical properties among all the experimental alloys, in which the ultimate tensile strength (UTS), yield strength (YS) and elongation are 210, 130 MPa and 8.2%, respectively.

Study of microstructure and precipitates of a Zr-2.5Nb-0.5Cu CANDU spacer material

Synchrotron X-ray diffraction, scanning electron microscopy, and transmission electron microscope bright field and high angle annular dark field were employed to investigate the microstructure and precipitates of a Zr-2.5Nb-0.5Cu alloy wire, with potential application as a spacer in the CANDU® reactor design. Results show that three types of microstructure co-exist in the alloy: Widmanstätten structure, α-Zr grains without precipitates and α-Zr grains with precipitates. In the meantime, three types of second phase particles are detected: β-Nb, Zr2Cu and Zr2Fe, which have different distributions within the microstructure. The β-Nb precipitates are observed to be extensively distributed among the α plate boundaries and twin interfaces in the Widmanstätten structure, whereas the Zr2Cu and Zr2Fe precipitates are only found in the α plate boundaries. The orientation relations of the Zr2Cu precipitates with respect to the α-Zr and β-Nb are found to be (013)Zr2Cu//(0001)α(013)Zr2Cu//(0001)α, [03¯1]Zr2Cu//[1¯100]α and (013)Zr2Cu//(011)β−Nb, [03¯1]Zr2Cu//[2¯1¯1]β−Nb respectively.

Effect of Ce addition on the microstructure and tensile properties of extruded Mg–Zn–Zr alloys

The microstructure and tensile properties of extruded Mg–Zn–Zr–Ce alloys with different Ce contents were investigated. Ce addition to ternary Mg–Zn–Zr alloy resulted in significant grain refinement as well as a change in the type of second phase particles from MgZn to Ce(Mg1−xZnx)11, which has a C-centered orthorhombic structure with lattice parameters of a=0.999nm, b=1.146nm, and c=0.976nm. However, fine MgZn2 precipitates were found to exist in the extruded alloys regardless of the level of Ce content. The yield and ultimate strengths of the extruded alloys were significantly increased by Ce addition although the presence of coarse Ce(Mg1−xZnx)11 particles has an adverse effect on ductility.

Zr-1Nb-xGe合金在400℃过热蒸汽中耐腐蚀性能的研究

利用高压釜腐蚀实验研究了Zr-1Nb-xGe(x=0,0.05,0.1,0.2,质量分数,%)合金在400℃,10.3 MPa过热蒸汽中的耐腐蚀性能;利用SEM和TEM分别观察了合金和氧化膜的显微组织。结果表明:添加Ge可以改善Zr-1Nb合金的耐腐蚀性能,当Ge含量为0.05%时效果最佳。在Zr-1Nb-xGe合金中存在4种第二相,分别是β-Nb,Zr(Nb,Fe,Cr)2,Zr(Nb,Fe,Cr,Ge)2和尺寸较大的Zr3Ge。Ge在Zr-1Nb合金α-Zr基体中的最大固溶含量在0.05%~0.1%之间,固溶的Ge可以有效延缓氧化膜中显微组织的演化,从而改善合金的耐腐蚀性能;当Ge含量超过合金的固溶含量时,会形成Zr(Nb,Fe,Cr,Ge)2以及尺寸较大的Zr3Ge第二相,Zr3Ge会使耐腐蚀性能降低。

Microstructure refinement and strengthening mechanisms of a 12Cr ODS steel processed by equal channel angular extrusion

• The first successful severe plastic deformation of 12Cr ODS steels. • Significantly refined and homogeneous microstructure in ODS steels. • Shear stress induced drastic variation of geometry of Y 2 O 3 nanoparticles. • Strengthening arising primarily from grain refinement. Multiscale microstructure refinement of a 12Cr-ODS steel by equal channel angular extrusion (ECAE) was investigated by numerous microscopy techniques. The as-HIPped material showed a bimodal microstructure. Three types of second phase particles, including Y 2 O 3 , (Cr, Fe) 23 C 6 and Cr oxide, were observed. After ECAE, the large matrix grains and Cr rich particles were effectively refined, and yttrium oxide nanoparticles surrounding ultrafine grain boundaries were redistributed. Geometry change of nanoscale yttrium oxide particles was also observed. An increased hardening by ∼35% was related to ECAE induced refinement of microstructures.

Nano-sized SiC particle reinforced NiTi alloy matrix shape memory composite

The near-equiatomic NiTi alloy matrix shape memory composite reinforced by nano-sized SiC particles was successfully fabricated using powder metallurgy/sintering process. A large number of randomly dispersed nano-sized SiC particles and the resultant several types of second-phase particles in the matrix of the NiTi shape memory alloy were able to greatly reinforce the matrix of the alloy while just slightly affecting its phase transformation characteristics. The fabricated NiTi alloy matrix composite possesses lower density, higher storage modulus and almost the same equivalent strength as the dense NiTi shape memory alloy, yet still exhibiting the shape memory effect and a steady linear superelasticity.

EFFECT OF Bi ADDITION ON THE CORROSION RESISTANCE OF Zr-lNb ALLOY IN DEIONIZED WATER AT 360 °C AND 18.6 MPa

The effect of Bi contents on the corrosion resistance of Zr-1Nb-xBi (x=0.05—0.3, mass fraction, %) was investigated in deionized water at 360 and 18.6 MPa by autoclave tests. The results show that the corrosion resistance of Zr-1Nb alloy can be improved by adding Bi, and the more the Bi content is, the better the corrosion resistance is. TEM and EDS analyses on the microstructures of the alloys show that there are two types of second phase particles (SPPs), including ZrNbFe and β- Nb. The Bi contents have little effect on the type, size and amount of SPPs, 0.3%Bi can be completely dissolved in α-Zr matrix and has no influence on the solution content of Nb in α-Zr matrix. From the fracture and inner surface morphology of oxide films observed by SEM, it can be seen that the Bi dissolved in the α-Zr could noticeably slow down the microstructural evolution of oxide film, including the propagation of micro-cracks and the transformation from columnar grains to equiaxed grains in the oxide film.

Growth of anodic oxide films on AC2A alloy in sulphuric acid solution

Growth behaviour of anodic oxide films on AC2A Al cast alloy was investigated in sulphuric acid solution using SEM, optical microscope (OM) and confocal scanning laser microscope (CSLM) and energy dispersive spectroscopy (EDS). The AC2A alloy contains three different types of second-phase particles: Al–Cu, Al–Cu–Fe–Si and Al–Si particles. The growth of anodic oxide films was critically retarded by the presence of non-reactive particles of Al–Si, while little effect was observed by the presence of active particles of Al–Cu and Al–Cu–Fe–Si. The most severe retardation effect on the growth of anodic films on AC2A alloy resulted from agglomerated Al–Si particles.

The influences of multiscale-sized second-phase particles on ductility of aged aluminum alloys

Commercially aged aluminum alloys commonly contain second-phase particles of three class sizes, and all contribute appreciably to the mechanical properties observed at the macroscopic scale. In this article, a multiscale model was constructed to describe the individual and coupling influences of the three types of second-phase particles on tensile ductility. The nonlinear relationships between the parameters of particles, including volume fraction, size, aspect ratio, shape, and ductility, were then quantitatively established and experimentally validated by the measured results from disc-shaped precipitate containing Al-Cu-Mg alloys and needle-shaped precipitate containing Al-Mg-Si alloys, as well as by using other researchers’ previously published results. In addition, we discuss extending this model to predict the fracture toughness of aluminum alloys.

Behavior of Second-Phase Particles in Al5052 Alloy during Anodizing in a Sulfuric Acid Solution: CSLM Observation

The behavior of second-phase particles during anodizing of Al5052 alloy in 16 wt% sulfuric acid solution was investigated by confocal scanning laser microscopy (CSLM). Two different types of second-phase particles were observed in the Al5052 alloy, Al-Mg particles and Al-Mg-Fe particles. The Al-Mg particles showed a groove-type morphology because of selective dissolution of Mg during anodizing, while Al-Mg-Fe particles showed a protrusion-type morphology in the CSLM height image (top view). The CSLM contrast image of cross sections of the anodic oxide film showed the presence of two different types of imperfections in the anodic oxide film, bright- and dark-type imperfections. The bright-type imperfections were determined to contain metallic iron, indicating that the metallic iron had been transferred from the substrate into the oxide film without oxidation during anodizing; this reflects the incident laser beam strongly to give a bright CSLM contrast image. The dark-type imperfections were explained by a scattering of the laser beam with vacant or irregularly structured regions, resulting from the selective dissolution of Mg. © 2004 The Electrochemical Society. All rights reserved.

Computer experiment on superposition of strengthening effects of different particles

Particle-hardening materials, particularly high strength aluminum alloys, usually contain two or more types of second-phase particles. While the strengthening effect of mono-dispersed particles has been studied extensively and hence well formulated, a rational and consolidated evaluation of superposed hardening effects of different particle mixtures is still an open problem both experimentally and theoretically. A computer simulation technique is utilized to examine the details of the problem. The technique developed is based on the circle-rolling approach of Morris et al. The strengthening stress τ p due to the mixture of different particles is determined by examination of a dislocation-slip process through the particles on one slip plane and along one slip direction under the action of an applied shear stress τ. Two kinds of particle mixtures are investigated. One consists of hard or unshearable point-like particles and soft or shearable point-like ones. The other is a mixture of two types of unshearable plate-like particles. The simulation results indicate that the superposition law can be well described by an equation τ α = n α/2 A τ α A+ n α/2 B τ α B where n A and n B are the density fractions of A- and B-particles, τ A and τ B the strengthening stresses due to pure A- and B-particles, and the exponent α varies between 1.0 and 2.0. Application to the spherical precipitates predicts that a bi-modal particle size distribution can give rise to about an 8% increment in strengthening stress with regard to a single size distribution that is normally produced by conventional aging. For a mixture of { θ′ (or θ″)+T 1} in Al–Cu–Li alloys the simulation predicts that the larger T 1-plates may either reduce or increase the strengthening effect depending on the particular circumstances. A structure comparison factor κ AB is introduced to describe the various effects. Calculated values using the simulation method compare favorably with those determined experimentally.

Note on the topography of the oxide films formed on aluminum in high temperature water

A topographical study was made of the oxide film formed during the early stages of corrosion on two Ni- and Fecontaining Al alloys and 2S Al. The results give additional evidence that irregular features on the oxide film surfaces are related to the presence and type of second phase particles, and it is shown that irregularities develop during the early stages of corrosion and film formation. By correlating the topography of the oxide films with the information obtained by examining cross sections, the results show the specific role the second phase particles play in influencing topography. (P.C.H.)

Corrosion of Aluminum Alloys In High Purity Water in the Range 150 C – 340 C

Abstract Examination of the cross-section of the film on aluminum and its alloys, while attached to the metal, reveals that the second phase particles play an important part in the corrosion pattern. The 2S aluminum contains at least two types of second phase particles, one of which corrodes more rapidly while the other corrodes more slowly than the surrounding aluminum. The majority of second phase particles in the 157 alloy corrode more slowly than the surrounding aluminum. 6.4.2, 4.6.5, 3.2.3