Influence of Mo content on microstructure and mechanical properties of β-containing TiAl alloy

The influence of Mo content on the microstructure and mechanical properties of the Ti-45Al-5Nb-xMo-0.3Y (x=0.6, 0.8, 1.0, 1.2) alloys was studied using small ingots produced by non-consumable electrode argon arc melting. The results show that small quantities of β phase are distributed along γ/α₂ lamellar colony boundaries as discontinuous network in the TiAl alloys owing to the segregation of Mo element. The γ phase forms in the interdentritic microsegregation area when the Mo addition exceeds 0.8%. The β and γ phases can be eliminated effectively by subsequent homogenization heat treatment at the temperature above T_α. The evolution of the strength, microhardness and ductility at different Mo contents under as-cast and as-homogenization treated conditions was analyzed, indicating that excessive Mo addition is prone to cause the microsegregation, thus decreasing the strength and microhardness obviously, which can be improved effectively by subsequent homogenization heat treatment.     

Effect of Al addition on microstructure and mechanical properties of Mg−Zn−Sn−Mn alloy

The microstructure and properties of the as-cast, as-homogenized and as-extruded Mg−6Zn−4Sn−1Mn (ZTM641) alloy with various Al contents (0, 0.5, 1, 2, 3 and 4 wt.%) were investigated by OM, XRD, DSC, SEM, TEM and uniaxial tensile tests. The results show that when the Al content is not higher than 0.5%, the alloys are mainly composed of α-Mg, Mg₂Sn, Al₈Mn₅ and Mg₇Zn₃ phases_. When the Al content is higher than 0.5%, the alloys mainly consist of α-Mg, Mg₂Sn, MgZn, Mg₃₂(Al,Zn)₄₉, Al₂Mg₅Zn₂, Al₁₁Mn₄ and Al₈Mn₅ phases. A small amount of Al (≤1%) can increase the proportion of fine dynamic recrystallized (DRXed) grains during hot-extrusion process. The room- temperature tensile test results show that the ZTM641−1Al alloy has the best comprehensive mechanical properties, in which the ultimate tensile strength is 332 MPa, yield strength is 221 MPa and the elongation is 15%. Elevated- temperature tensile test results at 150 and 200 °C show that ZTM641−2Al alloy has the best comprehensive mechanical properties.     

Effect of thermal exposure on microstructure and mechanical properties of Al−Si−Cu−Ni−Mg alloy produced by different casting technologies

The effect of thermal exposure at 350 °C for 200 h on microstructure and mechanical properties was investigated for Al−Si−Cu−Ni−Mg alloy, which was produced by permanent mold casting (PMC) and high pressure die casting (HPDC). The SEM and IPP software were used to characterize the morphology of Si phase in the studied alloys. The results show that the thermal exposure provokes spheroidization and coarsening of eutectic Si particles. The ultimate tensile strength of the HPDC alloy after thermal exposure is higher than that of the PMC alloy at room temperature. However, the TEPMC and TEHPDC alloys have similar tensile strength around 67 MPa at 350 °C. Due to the coarsening of eutectic Si, the TEPMC alloy exhibits better creep resistance than the TEHPDC alloy under studied creep conditions. Therefore, the alloys with small size of eutectic Si are not suitably used at 350 °C.     

Effect of deformed microstructure on mechanical properties of Ti-22Al-25Nb alloy

Effect of the deformed microstructure on mechanical properties of an orthorhombic （Ti2klNb） based alloy of Ti-22Al-25Nb （mole fraction, %） has been investigated. It was found that the deformed microstructures in different portions of a flee forged rod with diameter of 30 mm were quite different and thus resulted in the different mechanical properties after the same subsequent heat-treatment. One deformed microstructure with less primary α2/O particles and a larger and equiaxed B2 grains resulted in poor RT ductility, but the other one with a relatively larger amount of the primary α/O particles and non-equiaxed B2 grains had good combination of the tensile strength and ductility both at RT and 650 ℃. It was also found that two different deformed microstructures were obtained for the hot rolling plates with thickness of 3 mm even processed under an identical nominal rolling and the same post-deforming heat treatment conditions. One only has 3.5% of RT tensile elongation and the other up to 8%.     

Effect of Cu on microstructure and mechanical properties of 2519 aluminum alloy

The effect of Cu on the microstructure and mechanical properties of 2519 aluminum alloy was investigated by means of tensile test, microhardness test, transmission electron microscopy, and scanning electron microscopy. The results show that when the content of Cu is less than 6.0%, the strength of 2519 aluminum alloy increases with the increase of Cu eontent; when the content of Cu is more than 6.0%, the strength of the alloy decreases. The hardening effect of the aged alloy is accelerated at 180℃ and the time to peak age is reduced, but the plasticity of the alloy gradually decreases with the increase of Cu content. However, the hardening effect of the aged alloy decreases with the increase of Cu as the content of Cu is over 6.0%. The optimal content of Cu of 2519 aluminum alloy is 6.0%, at which the alloy has best tensile strength and plasticity.     

Preparation and mechanical properties of Ni-Cr-Al alloy by EB-PVD

Ni-Cr-A1 alloy was deposited by electron beam-physical vapor deposition(EB-PVD) method. The microstructure was investigated on as-deposited and long-term aged alloy. The results indicate that grain on surface of asdeposited alloy is about 185 nm in size, and a laminated structure in cross-section is observed. However, after aging for 16 and 120 h at 760℃, the laminated structure is dissolved, and the individual grain can be seen clearly. Columnar crystals form on the evaporation side, and exquiaxed grains form on the substrate side. The major precipitate is γ‘ phase after prolonged aging at 760℃. Mechanical properties of the Ni-Cr-A1 alloy were also studied. The results show that the fracture of as-deposited alloy has mixed type at room temperature, and intergranular fracture among columnar crystals is observed. Compared to that of as-deposited alloy, fracture of alloy after aging for 16 and 120 h at 760℃ appears to involve ductile fracture with dimples.     

Effects of Fe content on microstructure and properties of Cu–Fe alloy

Cu–Fe alloys with different Fe contents were prepared by vacuum hot pressing. After hot rolling and aging treatment, the effects of Fe content on microstructure, mechanical properties and electrical conductivity of Cu–Fe alloys were studied. The results show that, when w(Fe)<60%, the dynamic recrystallization extent of both Cu phase and Fe phase increases. When w(Fe)≥60%, Cu phase is uniformly distributed into the Fe phase and the deformation of alloy is more uniform. With the increase of the Fe content, the tensile strength of Cu–5wt.%Fe alloy increases from 305 MPa to 736 MPa of Cu–70wt.%Fe alloy, the elongation decreases from 23% to 17% and the electrical conductivity decreases from 31%IACS to 19%IACS. These results provide a guidance for the composition and processing design of Cu–Fe alloys.     

High temperature mechanical properties and microstructure of die forged Al−5.87Zn−2.07Mg−2.42Cu alloy

The high temperature mechanical properties (250 °C) and microstructure of a die-forged Al−5.87Zn− 2.07Mg−2.42Cu alloy after T6 heat treatment were investigated. High temperature tensile tests show that as the temperature increases from room temperature to 250 °C, the ultimate tensile strength of the alloy decreases from 638 to 304 MPa, and the elongation rises from 13.6% to 20.4%. Transmission electron microscopy (TEM) and electron backscattered diffraction (EBSD) were applied for microstructure characterization, which indicates that the increase of tensile temperature can lead to the coarsening of precipitates, drop of dislocation density, and increase of dynamic recovery. After tensile testing at 250 °C, a sub-grain structure composed of a high fraction of small-angle grain boundary is formed.     

Effect of minor Sc and Zr on microstructure and mechanical properties of Al-Zn-Mg-Cu alloy

1 Introduction The microstructure and properties of aluminium alloys are strongly affected by adding small quantities of scandium. Minor Sc may improve the temperature of recrystallization and fracture toughness, decrease the sensitivity of stress corrosi…     

Effect of Mg-Zn-Y quasicrystals on microstructure and mechanical properties ofAZ91 alloy

The influence of the additions of Mg-Zn-Y quasicrystals-containing master alloy on the microstructures and mechanical properties of AZ91 alloy under conventional casting condition was studied using XRD, SEM equipped with energy dispersive spectrometer （EDS）. The results show that the microstructure of Mg-Zn-Y quasicrystals reinforced AZ91 alloy consists of a-Mg supersaturating solid solution, β-Mgl7All2 phase and quasicrystals phase. Quasicrystals particles with excellent elevated temperature stability are dispersively distributed in the α-Mg matrix or at grain boundaries. After the addition of quasicrystals-containing master alloy, the matrix microstructure of AZ91 alloy is obviously grain-refined. The morphology of β-Mg17Al12 phase changes from continuous nets to discrete nets. At room and elevated temperatures mechanical properties of AZ91 alloy are also improved dramatically. The utility of Mg-Zn-Y quasicrystals as a reinforced phase provides new theoretical basis and technical support for the composite strengthening of magnesium alloys.     

Effect of hot extrusion on microstructure and mechanical properties of quasicrystal-reinforced Mg-Zn-Y alloy

The microstructure and mechanical properties of as-cast and as-extruded Mg-Zn-Y alloy （Mg-11 %Zn- 0.9%Y, mass fraction） containing Mg3 YZn6 quasicrystal were studied. The eutectic icosahedral quasicrystal phase （I-phase） is broken and almost distributes along the extrusion direction, and fine I-phase with nano-size is precipitated during the extrusion. The a-Mg matrix grains are refined due to recrystallization occuring during the hot extrusion. Some {1012} twins are observed in the extruded ZW1101 alloy. And {0002}（1010） fiber texture is formed in matrix alloys after hot extrusion. The extruded alloy exhibits high strength in combination with large elongation at room temperature. The strengthening mechanism of the as-extruded alloy was discussed.     

Effects of cerium on the microstructure and mechanical properties of AZ31 alloy

AZ31 alloy with Ce addition was studied. The influence of Ce contents on the microstructure and tensile properties of the alloy was analyzed. Ce addition results in the formation of AlzCe and the annealed microstructure is improved by the addition. There was no recrystallization of the alloy after rolling, however, it did occur after annealing. The alloy can be strengthened by adding Ce and the alloy with 1.05 wt.% Ce possessed the best synthetical properties of all the tested alloys. As rolled, σb and δof this alloy are 321 MPa and 6.9%, and as annealed, they are 259 MPa and 21.8%.     

Effect of Gd content on microstructure and dynamic mechanical properties of solution-treated Mg−xGd−3Y−0.5Zr alloy

The effect of Gd content ranging from 6.5 wt.% to 8.5 wt.% on microstructure evolution and dynamic mechanical behavior of Mg?xGd?3Y?0.5Zr alloys was investigated by optical microscopy, X-ray diffraction, scanning electron microscopy and split Hopkinson pressure bar. The microstructure of as-cast Mg?xGd?3Y?0.5Zr alloys indicates that the addition of Gd can promote grain refinement in the casting. Due to the rapid cooling rate during solidification, a large amount of non-equilibrium eutectic phase Mg₂₄(Gd,Y)₅ appears at the grain boundary of as-cast Mg?xGd?3Y?0.5Zr alloys. After solution treatment at 520 °C for 6 h, the Mg₂₄(Gd,Y)₅ phase dissolves into the matrix, and the rare earth hydrides (REH) phase appears. The stress?strain curves validate that the solution-treated Mg?xGd?3Y?0.5Zr alloys with optimal Gd contents maintain excellent dynamic properties at different strain rates. It was concluded that the variation of Gd content and the agglomeration of residual REH particles and dynamically precipitated fine particles are key factors affecting dynamic mechanical properties of Mg?xGd?3Y?0.5Zr alloys.     

Effect of Y content on microstructure and mechanical properties of 2519 aluminum alloy

The effects of yttrium（Y） content on precipitation hardening, elevated temperature mechanical properties and morphologies of 2519 aluminum alloy were investigated by means of microhardness test, tensile test, optical microscopy（OM）, transmission electron microscopy（TEM） and scanning electron microscopy（SEM）. The results show that the tensile strength increases from 485 MPa to 490 MPa by increasing Y content from 0 to 0.10%（mass fraction） at room temperature, and from 155 MPa to 205 MPa by increasing Y content from 0 to 0.20% at 300 ~C. The high strength of 2519 aluminum alloy is attributed to the high density of fine 0＇ precipitates and intermetallic compound AICuY with high thermal stability. Addition of Y above 0.20% in 2519 aluminum alloy may induce the decrease in the tensile strength both at room temperature （20 ℃） and 300℃.     

Magnetic properties and microstructure of nanocomposite(Nd,Pr)–Fe–B ribbons by doping Nb element

Effects of Nb addition and annealing treatmen on magnetic properties and microstructure of(Nd0.4Pr0.6)9Fe76–xNbxB15(x = 0–4) ribbons were systematically investigated by means of vibrating sample magnetometer(VSM) and X-ray diffraction(XRD). The extra phases with nonmagnetic(Nd,Pr)1.1Fe4B4phase and metastable compound(Nd,Pr)2Fe23B3 crystallized during quenching the Nb-free alloy. Moreover, the nonmagnetic(Nd,Pr)1.1Fe4B4phase does not diminish during the following annealing treatment. The addition of Nb to(Nd,Pr)–Fe–B alloy suppresses metastable(Nd,Pr)2Fe23B3 and nonmagnetic(Nd,Pr)1.1Fe4B4phases. The intrinsic coercivity increases from 397 kA m-1for the Nb-free sample to1,091 kA m-1for the 4 at% Nb-doped sample optimally annealed. The Nb-free sample has the magnetic properties with Js= 1.04 T, Jr= 0.66 T, and(BH)max= 43.5 kJ m-3By comparison, the magnetic properties of the 4 at% Nbdoped sample were 0.97 T, 0.68 T, and 65.7 kJ m-3respectively. The significant improvement of magnetic properties mainly originates from the finer grains of the ribbons by introducing Nb.     

Microstructure and properties of Cu−2Cr−1Nb alloy fabricated by spark plasma sintering

Cu?2Cr?1Nb alloy was fabricated by spark plasma sintering (SPS) using close coupled argon-atomized alloy powder as the raw material. The optimal SPS parameters obtained using the L₉(3⁴) orthogonal test were 950 °C, 50 MPa and 15 min, and the relative density of the as-sintered alloy was 99.8%. The rapid densification of SPS effectively inhibited the growth of the Cr₂Nb phase, and the atomized powder microstructure was maintained in the grains of the alloy matrix. Uniformly distributed multi-scale Cr₂Nb phases with grain sizes of 0.10?0.40 μm and 20?100 nm and fine grains of alloy matrix with an average size of 3.79 μm were obtained. After heat treatment at 500 °C for 2 h, the room temperature tensile strength, electrical conductivity, and thermal conductivity of the sintered Cu?2Cr?1Nb alloy were 332 MPa, 86.7% (IACS), and 323.1 W/(m·K), respectively, and the high temperature tensile strength (700 °C) was 76 MPa.     

Effects of minor Sc on microstructure and mechanical properties of Al-Zn-Mg-Zr alloy welded joint

Two kinds of AI-6.0Zn-2.0Mg-0.12Zr and AI-6.0Zn-2.0Mg-0.2Sc-0.12Zr alloy plates were prepared by ingot-metallurgy. The alloy plates with 3 mm thickness were welded by argon shield welding method, and the mechanical properties and microstructures of the two welded joints filled with AI-Mg-Sc welding wire were studied comparatively. The results show that firstly, minor Sc can raise the mechanical properties of the Al-Zn-Mg-Zr base alloy greatly. The reason for the increment is the fine grain strengthening, precipitation strengthening and the substructure strengthening caused by Al3（Sc, Zr）. Secondly, η phase （MgZn2） and grain size in the heat-affected zone of the alloy without Sc become coarse obviously, the η＇ phase （MgZn2） in the heat-affected zone of the alloy with Sc becomes coarse also, but the grain size has no visible change. Al3（Sc, Zr） particles are rather stable and can inhibit the movement of dislocation/land sub-grain boundaries, overaging softening is not serious. Thirdly, adding minor Sc can raise the strength of welded joint remarkably, the tensile strength of alloy with Sc increases from 395 MPa to 447 MPa and the welding coefficient increases from 0.7 to 0.8 as well. The reason for the high strength of welded joint with Sc addition is the fine grain strengthening, precipitation strengthening and the increasing of resistance to thermal cycling softening caused by Al3（Sc, Zr）.     

Microstructure and high-temperature mechanical properties of near net shaped Ti−45Al−7Nb−0.3W alloy by hot isostatic pressing process

Near net shaped Ti−45Al−7Nb−0.3W alloy (at.%) parts were manufactured by hot isostatic pressing (HIP). The microstructure and high-temperature mechanical properties of the alloy were investigated by X-ray diffractometry (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The results show that at a temperature of 700 °C, the peak yield stress (YS) and ultimate tensile stress (UTS) of alloy are 534 and 575 MPa, respectively, and the alloy shows satisfactory comprehensive mechanical properties at 850 °C. The alloy exhibits superplastic characteristics at 1000 °C with an initial strain rate of 5×10⁻⁵ s⁻¹. When the tensile temperature is below 750 °C, the deformation mechanisms are dislocation movements and mechanical twinning. Increasing the tensile temperature above 800 °C, grain boundary sliding and grain rotation occur more frequently due to the accumulation of dislocations at grain boundary.     

Microstructure and mechanical properties of bulk nanocrystalline Al–Fe alloy processed by mechanical alloying and spark plasma sintering

Nanocrystalline Al–5 at.% Fe alloy powders produced by mechanical alloying were consolidated by spark plasma sintering. The sintered sample showed high strength >1000 MPa with a large plastic strain of 15% at room temperature and 500 MPa at 350 °C. Microstructure characterizations by transmission electron microscopy and atom probe tomography revealed that the sintered samples are composed of α-Al and Al₆Fe nanocrystalline regions with 90 nm in diameter and a minor fraction of Al₁₃Fe₄ phase and coarsened 0.5–1 μm α-Al grains. This bimodally grained feature is attributed to the relatively large plastic strain for the strength level of 1000 MPa at room temperature.     

Effect of Mn content on microstructure and mechanical properties of modified ZA-27 alloy

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