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1.
AbstractIt was recently found that the addition of special elements leading to the deviation from the three empirical rules for the achievement of high glass-forming ability causes new mixed structures consisting of the amorphous phase containing nanoscale compound or quasicrystal particles in Zr–Al–Ni–Cu–M (M ? Ag, Pd, Au, Pt or Nb) bulk alloys prepared by the copper mold casting and squeeze casting methods. In addition, the mechanical strength and ductility of the nonequilibrium phase bulk alloys are significantly improved by the formation of the nanostructures as compared with the corresponding amorphous single phase alloys. The composition ranges, formation factors, preparation processes, unique microstructures and improved mechanical properties of the nanocrystalline and nanoquasicrystalline Zr-based bulk alloys are reviewed on the basis of our recent results reported over the last two years. The success of synthesizing the novel nonequilibrium, high-strength bulk alloys with good mechanical properties is significant for the future progress of basic science and engineering. © 2000 Published by Elsevier Science Ltd. 相似文献
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旨在优化AZ91镁合金凝固组织,通过OM和XRD设备研究了不同离心压力和冷却速度对AZ91镁合金凝固组织演变的影响,结果表明,随着离心压力的增大,合金晶粒尺寸细化,第二相β(Mg12Al17)析出量减少,不保温试样,β相形态由粗大连续网状向细小断续状转变,保温试样,β相为粒状弥散分布晶内,压力增大,颗粒数量减小,粒径细化.同等凝固压力下,增大冷速,一次β相析出量增多,二次β相析出量减少.XRD分析表明,增大离心压力β相峰值略微减弱,α-Mg的晶格常数减小. 相似文献
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In the present work, the local atomic ordering and the wear performance of ZrCuAlAg bulk metallic glass (BMG) samples with different diameters have been studied using transmission electron microscopy (TEM) plus autocorrelation function analysis, and pin-on-disc dry sliding wear experiments. Differential scanning calorimetry and TEM studies show that smaller diameter BMG sample has higher free volume and less local atomic ordering. The wear experiments demonstrate that with the same chemical composition, the smaller BMG sample exhibits higher coefficient of friction, higher wear rate, and rougher worn surface than those of the larger ones. Compared with larger BMG sample, the faster cooling rate of the smaller sample results in looser atomic configuration with more free volume, which facilitates the formation of the shear bands, and thus leads to larger plasticity and lower wear resistance. The results provide more quantitative understanding on the relationship among the cooling rate, the local atomic ordering, and the wear performance of BMGs. 相似文献
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The mechanical properties of newly developed Cu52.5 − xTi30Zr11.5Ni6Alx (x = 0, 1, 1.5, 2 at.%) bulk amorphous alloys were investigated under compressive condition. They exhibit high fracture strength of 2212 MPa, 2165 MPa, 2209 MPa and 2286 MPa, respectively. Three distinct vein patterns corresponding to the different zones can be observed on the fracture surfaces of the samples. Fracture propagation along two different directions and formation of striated vein patterns may contribute to the higher compressive fracture strength of the tested Cu-based bulk amorphous alloys. 相似文献
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In the present work, Al–Zn–Mg–Cu alloy was aged by non-isothermal cooling aging treatment (CAT). At high initial aging temperature (IAT), the hardness was decreased with the decreased cooling rate. However, when IAT was lower than 180 °C, the hardness was increased with the decreased cooling rate. Conductivity was increased with the decreased cooling rate regardless of IAT. The tensile strength, yield strength and conductivity of Al alloy after (200–100 °C, 80 °C/h) CAT were increased 2.9%, 8.1% and 8.3% than that after T6 treatment, respectively. With an increase of IAT and decrease of cooling rate, the fine GP zone and η′ phase were transformed to be larger η′ and η precipitates. Moreover, continuous η phase at grain boundary was also grown to be individual large precipitates. Cooling aging time was decreased about 90% than that for T6 treatment, indicating cooling aging could improve the mechanical properties, corrosion resistance and production efficiency with less energy consumption. 相似文献
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High-temperature deformation behavior of Ti60 titanium alloy 总被引:2,自引:0,他引:2
Weiju Jia Yigang ZhouJianrong Liu Qingjiang Wang 《Materials Science and Engineering: A》2011,528(12):4068-4074
Isothermal compressions of near-alpha Ti60 alloy were carried out on a Gleeble-3800 simulator in the temperature range of 960-1110 °C and strain rate range of 0.001-10.0 s−1. The high-temperature deformation behavior was characterized based on an analysis of the stress-strain behavior, kinetics and processing map. The flow stress behavior revealed greater flow softening in the two-phase field compared with that of single-phase field. In two-phase field, flow softening was caused by break-up and globularization of lamellar α as well as deformation heating during deformation. While in the single-phase field, flow softening was caused by dynamic recovery and recrystallization. Using hyperbolic-sine relationships for the flow stress data, the apparent activation energy was determined to be 653 kJ/mol and 183 kJ/mol for two-phase field and single-phase field, respectively. The processing map exhibited two instability fields: 960-980 °C at 0.3-10 s−1 and 990-1110 °C at 0.58-10 s−1. These fields should be avoided due to the flow localization during the deformation of Ti60 alloy. 相似文献
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采用热模拟实验对含Sc超高强Al-Zn-Cu-Mg-Zr合金在应变速率为0.001~10s-1、变形温度为380~470℃的条件下进行了热压缩实验.研究了实验合金的流变应力行为和微观组织演变.结果表明:流变应力随变形温度升高而下降;随应变速率增加峰值应力也相应增加.随变形温度升高和应变速率降低,合金动态再结晶的程度加深,亚晶尺寸变大.含Sc超高强Al-Zn-Cu-Mg-Zr合金,形成了Al3Sc弥散相,该相可强烈抑制再结晶.合金主要软化机制为动态回复伴随动态再结晶. 相似文献
9.
Yi Yang Di Xu Sheng Cao Songquan Wu Zhengwang Zhu Hao Wang Lei Li Shewei Xin Lei Qu Aijun Huang 《材料科学技术学报》2021,73(14):52-60
The compression behavior of a Ti-23.1 Nb-2.0Zr-1.0O (at.%) alloy was investigated at strain rates from 0.1 s-1 to 1000 s-1 and temperatures from 100 ℃ to 200 ℃ on a Gleeble 3800 system and Split Hopkinson Pressure Bar (SHPB) compressive tester.Optical microscopy,electron backscatter diffraction (EBSD),X-ray diffraction (XRD) and transmission electron microscopy (TEM) were employed to characterize the microstructure evolution during the deformation.Numerous deformation phenomena,including dislocation slip,twinning of both {332}<113> and {112}<111> modes,stress-induced α" martensite (SIMα") and stress-induced ω (SIω) transformations,were observed.The preferred activation of twinning and SIω transformations was observed in the sample compressed at lower temperatures and/or higher strain rates.The underlying mechanism is that twinning and stress induced phase transformations are attribute to higher stress concentrations at β grain boundaries and additional energy supplied by a higher strain rate,as well as high stacking fault energy because of higher temperature. 相似文献
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A356 alloy was solidified with cooling rate enhanced by phase transition cooling (PTC) of Ga + In + Sn mixed alloy, and then solution treated at 540 °C, 500 °C and 450 °C for different time, followed by quenching and immediately natural aging. Evolution of the corresponding microstructure and hardness with the solution temperature and time were studied. The as-cast sample was hardened due to the refined microstructures, the large solubility of Si- and Mg-clusters in Al matrix and the nano-scale Si precipitates. The modification of eutectic Si was verified to depend on the initially solidified morphology of Si, the solution temperature and time, for example, the Si particles subjected to high cooling rate and high solution temperature become more readily spheroidized. The age hardening, from the hardness tests and differential scanning calorimetry (DSC) results, was ascribed to be associated with the Guinier–Preston (GP) zones. It can be concluded that an optimal combination of solidification with heat treatment may achieve the better mechanical property but with the less product cost. 相似文献
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Effects of crystalline particles on mechanical properties of strip-cast Zr-base bulk amorphous alloy 总被引:1,自引:0,他引:1
Jung G. Lee Dong-Geun Lee Sunghak Lee Kyung-mox Cho Ikmin Park Nack J. Kim 《Materials Science and Engineering: A》2005,390(1-2):427-436
Effects of crystalline phase particles formed in a strip-cast Zr-base bulk amorphous alloy on strength, ductility, and fracture toughness were investigated by directly observing microfracture processes using an in situ loading stage installed inside a scanning electron microscope chamber. The compressive and fracture toughness test results indicated that strength, ductility, and fracture toughness of the strip-cast amorphous alloy were higher than those of the as-cast monolithic amorphous alloy, although the strip-cast alloy contained a considerable amount (4.5 vol.%) of hard, brittle crystalline particles. According to the in situ microfracture observation, crystalline particles were easily cracked under low stress levels, acted as blocking sites of shear band or crack propagation, and provided initiation sites of multiple shear bands. Thus, the improvement of mechanical properties in the strip-cast alloy could be explained by mechanisms of (1) blocking of crack propagation, (2) formation of multiple shear bands, and (3) crack deflection by crystalline particles. 相似文献
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冷却速度对过共晶Al-Si合金的初晶Si微细化的影响 总被引:9,自引:0,他引:9
通过检测过共晶Al- 2 0 %Si- 1%Cu - 0 .5 %Mg - 0 .5 %Mn合金在不同变质处理下的组织变化 ,研究了冷却速度对初晶Si微细化的影响 .结果表明 :在 5 10 0℃ /s的不同冷却速度下 ,未变质合金的初晶Si粗大 ,为 5 0 12 0 μm ,冷却速度对初晶Si尺寸的影响较显著 ;磷变质或双重变质条件下 ,冷却速度的变化对初晶Si细化的影响较小 .双重变质剂具有同时细化共晶Si及初晶Si的作用 ,使初晶Si比磷变质更细小 ,可使初晶Si小于 2 0 μm 相似文献
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The effects of different solidification rates after pouring on the microstructures,microsegregation and mechanical properties of cast superalloy K417 G were investigated.Scheil-model was applied to calculate the temperature range of solidification.The casting mould with different casting runners was designed to obtain three different cooling rates.The microstructures were observed and the microsegregation was investigated.Also,high temperature tensile test was performed at 900?C and stress rupture test was performed at 950?C with the stress of 235 MPa.The results showed that the secondary dendrite arm spacing,microsegregation,the size and volume fraction of γ'phase and the size of γ/γ'eutectic increased with decreasing cooling rate,but the volume fraction of γ/γ' eutectic decreased.In the cooling rate range of 1.42?C s~(-1)–0.84?C s~(-1),the cast micro-porosities and carbides varied little,while the volume fraction and size of phase and γ/γ' eutectic played a decisive role on mechanical properties.The specimen with the slowest cooling rate of 0.84?C s~(-1) showed the best comprehensive mechanical properties. 相似文献
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A bulk glass Zr52.5Ni14.6Al10Cu17.9Ti5 alloy with 6 mm diameter is prepared by pre-melting sponge zirconium together with other pure metal elements and followed by injecting cast. In the samples, the content of oxygen is chemically analyzed in the level of 706 ppm (atomic concentration), which significantly affects the crystallization and the microstructure. When the bulk glass samples are annealed at the temperature far below the crystallization temperature(Tx), the predominant phases of Zr2Ni0.67O0.33 and Zr2Ni compounds crystallize and uniformly distribute on glass matrix. These predominant phases will grow and join together to form net-shape phase when the annealed temperature is in the range of Tx to above Tx. The glass matrix phase separated by the net-shape phase into the size of about 25 μm at 703 K to 15 μm at 823 K almost fully transforms into Zr2Ni and a small amount of Zr2Cu and Zr4Al3. At annealing temperatures far above Tx, Zr2Cu and Zr4Al3 compounds crystallize by phase separation to form nanostructure with nano-scale phases of Zr2Cu and Zr4Al3 compounds distributed on the matrix of Zr2Ni. The micro-compressive tests by Nanoindenter II reveal that the bulk glass phase has a lower elastic modulus and lower microhardness. Increasing the annealing temperature, the modulus and microhardness for the crystallized microstructure increase. With the phase separation taking place, the modulus and microhardness for the nanostructure are improved slightly. But the different deformational mechanism between micro-scale and bulk specimens is unknown. 相似文献
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In this investigation, the effect of periodic melt shearing process and cooling rate on an Al–Fe alloy was studied. Microstructural examinations were conducted by X-ray diffraction, optical and scanning electron microscopy coupled with energy dispersive spectrometry (EDS). Experimental results suggest that shearing above melting point can refine the alloy structure and improve the morphology of intermetallic phases and; the level of refinement is increased by increase of shearing time. Also, increasing cooling rate through reduced sections, decreases grain size and secondary dendrite arm spacing (SDAS) and improves the microstructure of Al–Fe alloy. The results of hardness test showed that increasing cooling rate and time of melt shearing reduce the hardness of Al–Fe alloy. 相似文献
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Cooling rate induced variation in microstructure and magnetic structure was investigated in the as-cast Nd60Fe30Al10 alloy. Because the cooling rate was different from the periphery to the center regions, apparent evolution from a full amorphous to a partial precipitated crystalline structure was observed in one as-cast sample. Corresponding to different microstructures, two magnetic domain structures, i.e. fine strip-like domains in sub-micron scale and sunflower-like domains in micron scale, were observed at the periphery and the center of a cross section, respectively. The variation of magnetic properties was discussed in the view of exchange interaction coupling. 相似文献
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S.A. Souza C.R.M. Afonso P.L. Ferrandini A.A. Coelho R. Caram 《Materials science & engineering. C, Materials for biological applications》2009,29(3):1023-1028
Titanium alloys present a combination of properties that makes them suitable materials for various medical applications, and there is special interest in Ti–Cu alloys for the fabrication of dental prostheses. The addition of Cu to Ti lowers the melting point of the alloy, as well as leading to the development of desirable mechanical properties. In this study a eutectoid alloy was prepared and heat treated, then cooled at various cooling rates. The eutectoid structure (α + Ti2Cu) was observed for all cooling rates used, and evidence of α′ martensite was found for cooling rate higher than 9 °C s–1. Lower cooling rates resulted in higher modulus values. This was attributed to the volume fraction of the α and Ti2Cu phases. Higher cooling rates produced structures with lower modulus values and greater hardness, a result attributed mainly to the development of a martensitic structure. 相似文献