Phase transformation and properties of quasicrystal particles/Al matrix composites

Diffusion controlled phase transformations and tribological properties and hardness of Al 65 Cu 20 Cr 15 quasicrystal particles(QC p)/Al matrix composites have been studied. The mixtures of the quasicrystal particles with volume fractions of 15%, 20%, 25% , 30% and pure Al powder were hot pressed at 600, 650, 700 ℃. During the diffusion controlled phase transformation induced by hot pressing, a simple cubic icosahedric quasicrystal (SIQC) phase transforms into stable Θ phase with the microstructure of monoclinic of Al 13 Cr 2 through a transitional faced cubic icosahedric quasicrystal (FIQC), a decagonal quasicrystal (DQC) and an approximant of decagonal quasicrystal (DA) phases. And G. P. zones and Al Cu precipitates, θ′ Al 2Cu and θ Al 2Cu, are separated out from the Al matrix respectively after hot pressing. The QC p/Al composites have double strengthening effect after hot pressing. One is the strengthening of the particles that reinforce the matrix Al; the other is the dispersion strengthening of the precipitates in the Al matrix. The hardness of the composites increases with increasing volume fraction of quasicrystal particles. The maximum hardness reaches 1 200 MPa, being 4 times that of Al. The frictional coefficient and the wear rate of the QC p/Al are lower than those of Al. In comparison with SiC p/Al matrix composites, QC p/Al composites have higher hardness and lower frictional coefficient.

Microstructural evolution and phase transformation during partial remelting of in-situ Mg_2Si_p/AM60B composite

The microstructural evolution and phase transformations during partial remelting of in-situ Mg2Sip/AM60B composite modified by SiC and Sr were investigated. The results indicate that SiC and Sr are effective for refining primary α-Mg grains and Mg2Si particles. After being partially remelted, a semisolid microstructure with small and spheroidal primary α-Mg particles can be obtained. The microstructural evolution during partial remelting can be divided into four stages： the initial rapid coarsening, structural separation, spheroidization and final coarsening, which are essentially caused by the phase transformations of β→α, α＋β→L and α→L, α→L, and α→L and L→α, respectively. The Mg2Si particles have not obvious effect on the general microstructural evolution steps, but can slower the evolution progress and change the coarsening mechanism. During partial remelting, Mg2Si particles first become blunt and then become spheroidal because of melting of their edges and corners, and finally are coarsened owing to Ostwald ripening.

Microstructure,phase transformation and mechanical properties of NiMnGa particles/Cu composites fabricated by SPS

Microstructure,phase transformation and mechanical properties of NiMnGa particles/Cu composites prepared by spark plasma sintering method were investigated by SEM,EDS,XRD,susceptibility measurements and mechanical tests.The NiMnGa particles were found to react with Cu matrix and the composites exhibited a similar crystal structure to the Cu matrix.The martensitic transformation and Curie transition of the composites were weakened due to the composition change of NiMnGa particles caused by reactions.With increasing NiMnGa particles content,the martensitic transformation and Curie transition of the composites were enhanced to some extent.However,the martensitic transformation temperature and Curie transition temperature were decreased by~50 K as compared to those of the original NiMnGa particles.The compressive strength of the composites increased with the increase of NiMnGa particles content,whereas the compressive strain was decreased gradually.

Preparation of NiTip/Al composites with controllable phase transformation and damping behavior by friction stir processing

The NiTip/1060Al composites were prepared using a pre-aging and friction stir method(FSP)to enhance the low-temperature damping performance of the aluminum alloy and accommodate various service temperatures.The bonding between NiTi particles and the 1060Al matrix is well established after FSP,and no new phases are formed in the composites.The phasetransformation peak temperature of NiTip/1060Al composites gradually shifts to lower temperatures with increased aging temperature of NiTi particles.At room temperature,the 550℃-NiTip/1060Al composite exhibits superior damping performance,with an internal friction value 144%higher than that of the FSP-1060Al alloy.However,at-91℃,the 650℃-NiTip/1060Al composite demonstrates better damping performance,with an internal friction value 158%higher than that of the FSP-1060Al alloy.The NiTip/1060Al composites exhibit the internal friction peak of NiTi phase-transformation in the temperature range from-91℃to 60℃.This characteristic results in significantly better damping performance compared to the FSP-1060Al alloy and other high-damping aluminum matrix composites.

Phase Evolution and Oxidation Resistance of YSZ/(Ni,Al) Composite Coatings in CH_4 Atmosphere

YSZ/（Ni, Al） composite coatings with different Ni：Al mole ratios were deposited on superalloy Inconel 600 by electrophoretic deposition（EPD） technique, followed by sintering in CH_4 atmosphere at 1 100 ℃for 2 h and isothermally oxidation at 1000 ℃ for 50 h. After sintering at 1100 ℃ for 2 h in CH_4 atmosphere, besides ZrC and t-ZrO_2 phases, the phase constitutes of Ni：Al mole ratios with 1：3, 1：2, and 1：1 were（Zr, Al）C, AlNi_3 and Ni phases, respectively. A remarkable difference in the oxidation behaviors of YSZ/（Ni, Al） composite coatings with different Ni：Al mole ratios was observed. For YSZ（Ni：Al=1：3） coated sample, oxidation at 1000 ℃ causes decomposition of the（Zr,Al）C solid solution to metallic Al, and then most of the Al is oxidized to Al_2O_3. For the YSZ（Ni：Al=1：2） coated sample, oxidation at 1000 ℃ mainly causes decomposition of the AlNi_3 phase. For YSZ（Ni：Al=1：1） coated sample, after oxidation at 1000 ℃, most of the Ni is oxidized to Ni O phase, and tolerated 50 h of oxidation and finally cracked and spalled from the specimen. YSZ（Ni：Al=1：3） and YSZ（Ni：Al=1：2） coated samples show superior oxidation resistance than that of YSZ coating. The different oxidation resistance mechanisms of YSZ/（Ni, Al） composite coatings sintered in CH_4 atmosphere were discussed.

Interface of quasicrystal and crystal

A model on the coexisting phase of quasicrystal-crystal is proposed, with which we concretely investigate the inter- face effects for coexisting phases of one-dimensional orthorhombic quasicrystal-isotropic crystal and three-dimensional icosahedral quasierystal-cubic crystal. The phason strain fields which play an important role in some processes are determined. Some factors affecting the strain fields, e.g., the material constants of phonon, phason, phonon-phason coupling of the quasicrystal and the elastic modulus and the size of the crystal are also explored.

Preparation of Al-Cu-Fe-(Sn,Si) quasicrystalline bulks by laser multilayer cladding

（A165Cu20Fe15）100-xSnx （x=0, 12, 20, 30） and A157SitoCulsFe15 powders were cladded on a medium carbon steel （45# steel） substrate by laser multilayer cladding, respectively. The phases and properties of the produced quasicrystalline bulks were investigated. It was found that the main phases in the A165Cu2oFe15 sample were crystalline L-Al13Fe4 and icosahedral quasicrystal together with a small volume fraction of 0-A12Cu phase. The volume fraction of icosahedral phase decreased as the Sn content in the （A165Cu20Fe18）100-xSnx samples increased owing to the formation of β-CuSn phase. The increase of Sn content improved the brittleness of the quasicrystal samples. The morphology of the solidification microstructure in the Al57Si10Cu18Fe15 sample changed from elongated shape to spherical shape due to the addition of Si. The nanohardness of the laser multilayer cladded quasicrystal samples was equal to that of the as-cast sample prepared by vacuum quenching. In terms of hardness, the laser cladded A157Si10Cu18Fe15 quasicrystalline alloy has the highest value among all the investigated samples.

Effects of load mode on mechanical properties of ZrO_2(2Y)/TRIP steel composites

The ZrO 2 (2Y)/TRIP steel composites were prepared by vacuum hot pressing sintering. The room temperature static tensile and dynamic yield strength were tested using the static tensile and Split Hopkinson Pressure Bar methods, respectively. The effects of load mode on the static and dynamic mechanical behaviors were studied. The results show that the static tensile strengths of the composites decrease with the increase of ZrO 2 content, for the weak bonding of ZrO 2/ZrO 2. Under the dynamic load, the matrix TRIP steel produces the martinsitic phase transformation, which improves the dynamic strength and deformation ability of the composites. When the volume fraction of ZrO 2 exceeds 20%, the strain hardening coefficient and the dynamic deformation ability of the composites decrease.

Shear transformation zone dependence of creep behaviors of amorphous phase in a CuZr-based bulk metallic glass composite

The creep behaviors of the amorphous phase in a CuZr-based bulk metallic glass composite(BMGC)are studied by nanoindentation.Samples fabricated via higher cooling rates are found to exhibit more prominent creep,but a smaller shear viscosity.The volume of the shear transformation zones(STZs)in the amorphous phase calculated based on a cooperative shear model increases with the cooling rate.The evolution of excess free volume created during creep deformation is clarified.A looser atomic arrangement leads to a larger STZ volume,thus facilitating creep deformation.This study gives a better understanding of the deformation behaviors of the amorphous phase in BMGCs.

PHASE TRANSFORMATION IN RAPIDLY SOLIDIFIED AI-Cu-Fe ALLOY

By means of rapid solidification, two Al65Cu20Fe15 powders were prepared with water and liquid N2 as the respective cooling agent. Both powders are composed of a qnasicrystalline icosahedral phase and a crystalline hexagonal phase, with the water-cooled alloy having a higher crystalline phase content. In the isothermal an nealing process, the crystalline phase in the water-quenched alloy begins to decrease at 500℃ and then disap pears at 600～700℃. At about 800℃, new crystalline phases form, and at 900℃, the quasicrystalline phase disappears. Conversely, in the liquid N2 quenched alloy, the quasicrystalline phase starts to decrease at about 500℃. and the hexagonal phase decomposes into new crystalline phases. At 700～800℃, the quasicrystalline phase disappears. For the water-cooled sample, the quenching at 100～200C makes the crystalline to quasicrystalline phase transformation start at a lower temperature and the crystallization of the quasicrystal occur at a higher temperature. For the liquid N2 quenched alloy, the quenching at 100～400℃, did not affect its phase transformation at high temperature.

Phase transformation behavior of Al_9(Mn,Ni)_2 eutectic phase during heat treatment at 600°C in Al-4Ni-2Mn alloy

The morphology evolution and phase transformation of Al9(Mn,Ni)2 eutectic phase in an Al-4Ni-2Mn alloy during heat treatment at 600°C were studied by scanning electron microscopy(SEM)and transmission electron microscopy(TEM).Results show that nearly all of the eutectic fibers change into prolate ellipsoid and spherical particles in the process of heat treatment,and Ostwald ripening phenomenon occurs in the eutectic region with the increase of the heat treatment time.Besides,a phase transformation from Al9(Mn,Ni)2 to O-phase is confirmed.The morphologies of the transformed particles indicate that the O-phase preferentially nucleates on the specific crystal plane of the Al9(Mn,Ni)2 eutectic phase and grows in a certain direction.During the phase transformation,the(010)[001]slip system in O-phase is activated,and the resultant slip traces appear on the surface of some O-phase particles.

Fabrication and evaluation of high-performance 3D interpenetrated network structures SiC/Al composites with high-purity plate-like a-SiC framework

To reinforce compatibility with the thermophysical and mechanical properties of SiC/Al composites for electronic packaging to improve the stability and reduce fatigue failure of electronic integrated devices,a novel 3D SiC reinforced framework with interpenetrated plate-like a-SiC grains was synthesized.A small amount of doped a-SiC was seeded to induce the transformation of b-SiC to plate-like a-SiC at 2,300℃,forming a high-purity a-SiC strongly bonded framework.Vacuum/gas pressure infiltration of Al alloy was subsequently used to manufacture the 3D interpenetrated network structure SiC/Al(SiC3D/Al)composite.Characterization results showed that 15%(in mass)seeds provided the composite with the optimal comprehensive performance,including a low coefficient of thermal expansion(CTE)of 5.54×10^(-6)K^(-1),a high thermal conductivity(l)of 239.08 W·m^(-1)·K^(-1),the highest flexural strength of 326.84 MPa,and a low thermal deformation parameter(TDP)of 0.023.High-purity plate-like grains enhanced the purity of the framework promoting a significant improvement in l.As the seed content increased to 20%(in mass),both CTE and l reached optimal values of 5.22×10^(-6)K^(-1)and 243.14 W·m^(-1)·K^(-1),but the mechanical properties declined by 10.30%.The synergistic effect of the well-bonded interface and the high-purity 3D SiC framework balanced excellent mechanical properties and multiple thermal functions.

Modeling bending behavior of shape memory alloy wire-reinforced composites: Semi-analytical model and finite element analysis

In this study,we propose a novel and simple exact semi-analytical model for superelastic Shape Memory Alloy(SMA)wire reinforced composites subjected to bending loads.In order to study the mechanical response of the composite during loading/unloading,a Representative Volume Element(RVE)is extracted to examine the bending response of the composite.Analytical moment–curvature,and shear force-shear strain relations are derived based on a 3-Dimensional(3 D)thermomechanical SMA model and Timoshenko beam theory.The composite Simpson’s rule is adopted to numerically solve the exact analytical moment–curvature and shear force-shear strain relationships.Results including the moment–curvature response,axial stress distribution along the vertical and longitudinal directions,martensite volume fraction,and the tip deflection are reported and validated against 3 D finite element simulations.The influence of temperature,martensite volume fraction distribution,and matrix stiffness on the mechanical performance of the composite is also investigated.In particular,the composite is found to behave superelastically under certain conditions of temperature,SMA volume fraction,and elastic stiffness of the matrix.Such behavior is advantageous in applications requiring large recoverable strains or high energy dissipation density.

Outstanding specific yield strength of a refractory high-entropy composite at an ultrahigh temperature of 2273 K

We reported on the mechanical properties and microstructural evolution of a W_(20)Ta_(30)Mo_(20)C_(30)(at.%)re-fractory high-entropy composite(RHEC).The RHEC exhibited outstanding yield strength at both 2273 and 1873 K.Microstructural investigations revealed that the as-cast RHEC had a triple-phase structure con-sisting of FCC dendrites,HCP matrix,HCP-BCC eutectic structure,and FCC-BCC eutectoid structure,and exhibited high-density defects owing to the complex phase transformations during solidification.After annealing at 2273 K,the precipitation of the BCC phase from the FCC dendrites and the decomposition of the HCP phase into the FCC-BCC eutectoid structure was observed to significantly refine the grain sizes of all triple phases.After compression at 2273 K,the ceramic phases and solid solution precipitated out from each other,which helps to avoid persistent softening after the yielding of RHEC.Further analyses sug-gested that the dominant deformation mechanisms of the BCC phase and HCP phase are dislocation glide and transformation-induced plasticity;whereas those of the FCC phase are twinning-and transformation-induced plasticity.The outstanding yield strength of this RHEC at ultrahigh temperatures may originate from the high-content ceramic phases and the structural metastability of the multi-principal composition.These findings provide a novel strategy to design RHECs by alloying high-content nonmetallic elements,which contributes to further breaking through their performance limits at ultrahigh temperatures.

Oxygen addition for improving the strength and plasticity of TiZr-based amorphous alloy composites

The addition of a small amount of oxygen improves the mechanical properties,especially plasticity,of Ti_(45.7)Zr_(33)Ni_(3)Cu_(5.8)Be_(12.5) amorphous alloy composites(AACs)at room temperature(298 K).Compared to the plasticity of AACs without added O(5%),the plasticity of the composites with 0.73 at.%O(nominal composition)was much higher(11%).Even at O content higher than 0.73 at.%,the AACs exhibited good plasticity.The highest plasticity of∼12.3%was observed with 2.87 at.%O.Two distinct mechanisms are proposed to explain the enhanced plasticity of the AACs.At low O content,although deformation-induced phase transformation was suppressed,a substantial amount of α" martensite was formed.The microstructural features of α" martensite,such as thinner laths and homogeneous distribution,induced the formation of multiple shear bands in the amorphous matrix.At high O content,deformation-induced phase transformation was seriously suppressed.A dispersed nanoωphase was formed during rapid solidification in AACs with O content higher than 1.45 at.%.This resulted in a weakening in the anisotropy ofβdendrites and led to their homogenous deformation.Furthermore,multiple shear bands were formed in the amorphous matrix.Apart from plasticity,the strength of the AACs also increased with an increase in the O content.This phenomenon was explained in terms of three mechanisms,viz.the solid-solution-strengthening effect of O,fine-grain strengthening of β dendrites,and secondary phase strengthening by the nano ω phase.

Recycling of High Ferrous Bauxite Reducing Slag for Synthesis of CaAl_2Si_2O_8-Al_2O_3-CaAl_(12)O_(19) Composite

CaAl2 Si2 O8- Al2 O3- CaAl12 O19） （CAS2- Al2 O3 -CA6 ） composite was synthesized through reaction sintering alumina and bauxite reducing slag. The CAS2-Al2 O3-CA5 composite was mainly composed of α-Al2O3 , CAS2 , and CA6. Gehlenite （Ca2 Al2 SiO7 , C2 AS） phase was effectively transformed to CASe and CA6 through high-temperature reaction sintering under weak oxidizing atmosphere at 1400 ℃for 4 h. SEM （scanning electron microscopy） and EDS （energy dispersive spectroscopy） analysis indicated that black and needle-shaped Al2O3, rhombic or irregular polygonal shaped FeAl2O4 , and glassy phase Ca2 Al2 SiO7 disappeared after the reaction sintering. The light gray and flaky hexagon crystals of CaAl12 O19 （10 μm） and the grainy particles of Al2O3 （2-7 μm） were observed in the CASe-Al2 O3-CA6 composite. The gray crystals of CASe act as the binding phase and are distributed around CA6 and Al2O3. CAS2-Al2O3-CA6 composite exhibits high refractoriness and service temperature, which are 1 650 ℃ and 1 450 ℃, respectively. Reaction sintering of alumina and bauxite reducing slag is a feasible method for the synthesis of CAS2-Al2 O3-CA6 composite.

相变对TiNi合金薄壁管中波速的影响

形状记忆合金在受到强冲击荷载作用时会发生相变,而相变对其结构件的动态力学响应影响显著。本文采用同时考虑静水压力和偏应力影响的相变临界准则,推导了增量型的相变本构模型。基于广义特征理论,得到了复杂应力状态下特征波速的解析表达式。特征波速不仅和材料本身的力学参数(如拉压不对称性和混合相的模量)有关,还和材料所处的应力状态有关。对因相变导致体积膨胀的TiNi合金而言,拉压不对称性系数的增大会提高慢波的波速,而对快波几乎没有影响。在相变椭圆的短轴处(α=90°),慢波的波速最低,并随混合相无量纲模量的增大而显著减低,混合相无量纲模量由2增加至5时,波速降低幅度为36.2%,而快波的波速达到最大值c_(0),和混合相的模量无关;在相变椭圆的长轴处(α=180°),慢波的速度达到最大值,而快波的波速达到最小值c_(2)。

Ti和Nb微合金化对CuZr基相变增韧非晶复合材料组织性能的影响

以典型B2相增韧非晶复合材料形成合金Zr_(48)Cu_(48)Al_(4)为基础,分别研究了Ti、Nb微合金化添加对其凝固组织和性能的影响规律。研究发现,与基础合金相比,微合金化显著改变了B2相的组织形貌(包括大小、数量、形状),其中Ti微合金化降低了B2晶体相的形核能力,提高了非晶和非晶复合材料的形成能力;而Nb微合金化则提高了B2相的稳定性,并大幅提高了非晶相与B2相的硬度以及非晶复合材料的强度和压缩塑性(分别达到了1470 MPa和21.5%)。本研究为非晶复合材料的成分设计与制备提供了实验依据,对开发高性能相变增韧非晶复合材料具有参考价值。

Zirlo合金和M5合金的微观组织和微区成分

利用高分辨透射电子显微镜和能谱仪对Zirlo合金和M5合金进行了微观组织和微区成分分析。结果表明:M5合金中圆球状的第二相弥散分布在晶界上和晶粒内,尺寸约为50 nm;第二相的主要成分为Zr元素和Nb元素,第二相为体心立方结构的β-Nb相;在Zirlo合金中弥散分布着两种尺寸不同的第二相粒子,一种为体心立方结构的β-Nb,尺寸为20~40 nm;另一种为密排六方结构的Fe_(2)Nb_(0.4)Zr_(0.6)相,尺寸约为100 nm。