Nb-7Ta合金再结晶退火温度研究

研究了退火温度对棒材组织、硬度及力学性能的影响,确定了变形量对铌钽合金棒再结晶退火温度的影响规律.结果表明,随变形量的增大,材料的再结晶退火温度降低.变形量为90%时,锻造棒材的再结晶退火温度为1000～1050℃;变形率95%时,轧制棒材的再结晶退火温度为950～1000℃.     

退火工艺对AZ31镁合金组织与性能的影响

研究了热处理工艺对AZ31镁合金轧制板材的显微组织和力学性能的影响。试验表明，AZ31镁合金轧制板材在退火过程中发生了静态再结晶现象，200℃时可以观察到再结晶现象，再结晶温度为200～250℃。分析了退火温度和退火时间对合金显微组织、晶粒尺寸、硬度以及力学性能的影响规律。     

微量Er对高强铝合金组织与性能的影响

借助力学性能测试和光学金相（OM）、X射线衍射（XRD）、扫描电镜（SEM）、透射电镜（TEM）与能谱（EDS）的观察和分析，研究了微量Er对高强铝合金Al-6Zn-2Mg的力学性能、微观组织结构、时效硬化特性及再结晶行为的影响。结果表明：Er能非常显著地细化合金的晶粒组织，这是因为初生Al3Er作为非均质形核核心，能提高形核率，从而有效地细化晶粒；Er能够较大幅度地提高合金的拉伸力学性能，细晶强化与析出强化是合金的主要强化机制；Er可加快合金的时效进程，提高时效强化效果；同时，Er可以抑制合金再结晶，提高再结晶温度，这是由于细小的二次Al3Er质点钉扎位错和亚晶界而引起的。     

掺杂稀土元素镧对TZM合金板材再结晶行为的影响

采用粉末冶金和轧制工艺分别制备TZM合金和掺杂稀土元素镧的La-TZM合金板材,通过对其在1000、1100、1200、1300、1400、1500、1600℃退火后样品的金相组织、力学性能进行分析与对比,研究掺杂稀土元素镧对TZM合金再结晶温度的影响。研究表明,TZM合金的开始再结晶温度为1200℃左右,La-TZM合金的开始再结晶温度约为1300℃。La2O3在TZM合金的晶界处形成细小的第二相,阻碍了晶界的迁移,提高了TZM合金板材的再结晶温度。     

CP276铝—锂合金的固液温度研究

探讨了固溶温度对CP276铝-锂合金显微组织和力学性能的影响,研究证明,提高固溶温度可以促进Ci、Li原子向基体溶解,进而提高合金时效的沉淀强化效果,并且发现,该合金经固溶处理后可得到未完全再结晶组织,这种微观组织将对基体产生“组织强化效应”,随着固溶温度升高,合金的再结晶程度也有所增加,从而使组织强化效应受到削弱,力学性能测定结果显示,CP276合金的理想固溶温度为530℃左右。     

Cr对Cu-Ag-Cr合金再结晶行为的影响

采用真空熔炼方法制备了Cu-Ag和Cu-Ag-Cr合金,利用硬度测试、金相显微观察和透射电镜分析等方法,研究了Cr对Cu-Ag-Cr合金再结晶行为的影响.结果表明,微量Cr的加入,使合金中形成细小、弥散分布的析出相对位错和亚晶界具有强烈的钉扎作用,而有效抑制合金的再结晶,使Cu-Ag合金的再结晶软化温度提高150℃以上;同时还能显著细化合金的再结晶晶粒.     

Cu对AgCe合金机械性能及再结晶温度的影响

通过力学性能测试和金相分析,研究了Cu对AgCe合金机械性能和再结晶温度的影响.结果表明:AgCe合金中添加Cu后,使合金的硬度提高48,强度提高178MPa,再结晶温度提高150℃左右,同时在大变形量下延伸率有一定提高.     

微量Cr元素对Cu-Ag合金力学性能的影响

采用真空熔炼方法制备了Cu-Ag和Cu-Ag—Cr合金，通过力学性能测试、金相显微镜和透射电镜分析等方法，研究了微量Cr对CuoAg合金组织和性能的影响。结果表明，添加微量cr元素能够明显提高Cu-Ag合金的再结晶温度和强度，Cu-Ag-Cr合金经450℃退火2h后的抗拉强度仍高达423MPa，能够满足高强高导铜合金高温性能的要求；微量Cr对Cu-Ag合金的强化主要来源于再结晶晶粒细化强化，第二相粒子析出强化和亚结构强化等。     

Be对7475铝合金组织及性能的影响

采用再结晶退火和时效硬化两种热处理方式,研究了Be对7475铝合金组织及性能的影响.结果表明,0.023%的Be能细化7475铝合金晶粒,提高其综合力学性能,并能提高再结晶温度,延长再结晶孕育期,降低再结晶速度,同时还加快了该合金的时效硬化进程.     

热轧历程对MGH754合金板材组织与性能的影响

通过扫描电镜成像系统与光学显微镜分析研究了不同热轧历程对MGH754合金板材组织衍变和性能的影响.研究表明:MGH754合金板材动态再结晶的晶粒大小随着热轧温度的升高而增加；低温后,MGH754合金板材显微硬度很高,说明合金内部仍旧存在高的位错密度.初轧温度为1150℃,终轧温度为1050℃时,合金退火未发生完全的二次再结晶.     

Corrosion resistance of TiO2 films grown on stainless steel by atomic layer deposition

Titanium dioxide (TiO₂) films have been deposited onto stainless steel substrates using atomic layer deposition (ALD) technique. Composition analysis shows that the films shield the substrates entirely. The TiO₂ films are amorphous in structure as characterized by X-ray diffraction. The electrochemical measurements show that the equilibrium corrosion potential positively shifts from − 0.96 eV for bare stainless steel to − 0.63 eV for TiO₂ coated stainless steel, and the corrosion current density decreases from 7.0 × 10^− 7 A/cm² to 6.3 × 10^− 8 A/cm². The corrosion resistance obtained by fitting the impedance spectra also reveals that the TiO₂ films provide good protection for stainless steel against corrosion in sodium chloride solution. The above results indicate that TiO₂ films deposited by ALD are effective in protecting stainless steel from corrosion.     

Improvement in corrosion resistance of CrN coated stainless steel by conformal TiO2 deposition

A conformal titanium dioxide (TiO₂) layer was deposited onto chromium nitride (CrN) coated stainless steel by atomic layer deposition technique, and the electrochemical corrosion test on the CrN single-layer and TiO₂/CrN double-layer coated sample was carried out. The equilibrium corrosion potential of the double-layer coated sample shifted positively compare to that of the single-layer coated one. Moreover, the corrosion current density decreased significantly with the TiO₂ deposition, revealing that better corrosion resistance was obtained after the deposition of the TiO₂ layer. The improvement in corrosion resistance after the TiO₂ deposition was attributed to the blocking of the through-thickness cracks or pinholes in the CrN layer.     

A new type of pilot arc power source used for A．C． plasma arc welding of aluminum alloys

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Influence of pre-treatment on the surface composition of Al-Zn alloys

The influences of pre-treatments on the composition of Al-Zn alloys, containing 0.6-1.9 at.%Zn, are investigated using scanning and transmission electron microscopies, glow discharge optical emission spectroscopy and ion beam analysis. Alkaline etching, anodic alkaline etching and electropolishing result in zinc enrichments, just beneath the oxide/hydroxide films on the alloy surfaces. The enriched alloy, about 4-5 nm thick, contains zinc in solid-solution with aluminium, up to about 18 at.%. The highest and lowest enrichments are produced by alkaline etching and electropolishing respectively. For a given pre-treatment, the enrichment increases with increase in zinc content of the bulk alloy.     

Effect of small amounts of alloyed tin on the electrochemical behaviour of aluminium in sodium chloride solution

Binary model AlSn alloys containing 30–1000 ppm (by weight) Sn were investigated by electrochemical polarization in 5 wt% chloride solution and subsequent characterization of corrosion morphology. In the homogenized and rolled condition, tin concentration only slightly affected electrochemical behaviour up to 500 ppm, and the pitting potentials were all about −0.8 V_SCE. However, alloy containing 1000 ppm Sn was significantly activated by lowering of the passivity-breakdown potential to −1.38 V_SCE. Annealing at 300 °C caused significant segregation of Sn to the metal surface, and all specimens, independent of bulk Sn concentration, became nearly similarly active with breakdown potentials around −1.2 V_SCE. Corrosion on 300 °C-annealed specimens was uniformly distributed by polarization below the bulk pitting potential of −0.76 V_SCE. Moreover, the activation effect was temporary, and corrosion was significantly reduced as the segregated Sn was etched away from the surface. Thick oxide, formed during water quenching on high Sn concentration samples, containing 500 and 1000 ppm Sn, introduced partial passivation during polarization test. Annealing at 600 °C caused increasing activation with increasing Sn concentration, caused by Sn enrichment at the metal surface by dealloying of aluminium during anodic polarization in chloride solution. Corrosion was localized in the form of grain boundary corrosion for alloyed Sn concentration less than and equal to 500 ppm and pitting following the triple grain boundaries for 1000 ppm.     

Effect of tunneling barrier as spacer on exchange coupling of CoFeB/AlOx/Co trilayer structures

Magnetic tunneling junctions (MTJs) have a sandwiched structure, which comprises a top ferromagnetic (FM1) layer, an insulating tunneling layer (spacer), and a bottom ferromagnetic (FM2) layer. Exchange coupling in MTJs has been extensively widely examined because the effect of spacer thickness on the ferromagnetic spin-coupling can be exploited in read-head sensors, spin-valve structures, and magntoresistance random access memories (MRAMs). In this investigation, MTJs were deposited in the sequence, glass/CoFeB(50 Å)/AlO_x(d)/Co(100 Å), where the thickness of the AlO_x layer d = 12, 17, 22, 26 or 30 Å. Saturation magnetization (M_s) results demonstrate that the exchange coupling strength and coercivity (H_c) can be varied considerably by varying the tunneling barrier AlO_x spacer. The X-ray diffraction patterns (XRD) include a main peak from hexagonal close-packed (HCP) Co with a highly (0 0 2) textured structure at 2θ = 44.7°, and AlO_x and CoFeB are amorphous phases. The full width at half maximum (FWHM) of the Co (0 0 2) peak declines as the AlO_x thickness increases, revealing that the Co layer becomes more crystalline. The magnetic results reveal that the magnetic characteristics are related to the Co crystallinity. The exchange coupling strength increases with AlO_x thickness. The coercivity (H_c) also increases, because the Co crystallinity is eliminated.     

Evolution of surface chemistry and morphology of oxide scale formed during initial stage oxidation of modified 9Cr–1Mo steel

Initial stage oxidation characteristics of the modified 9Cr–1Mo steel in ambient air at 650 °C have been investigated, for exposure times ranging from 5 to 500 h. Oxygen flux from the gas phase causes high initial oxidation rate, but the growth kinetics do not follow parabolic law. In “as-received” condition, binary oxides of Fe and Cr were found as native oxides. Upon oxidation, segregation of Mn resulted in the formation of MnCr₂O₄ along with FeCr₂O₄ and binary oxides of Fe, Cr and Mn. Thus, the initial oxide scale constitutes multiple oxides with delineated interface, unlikely to have a layered structure.     

Effect of cooling rate on oxidation resistance and powder ignition temperature of AM50 alloy with addition of yttrium

This paper focused on the effect of cooling rate on oxidation resistance and ignition temperature (T_i) of AM50 alloy. Y addition of 0.0 wt%, 0.15 wt%, 0.28 wt%, 0.45 wt% and 1.00 wt%, respectively was added to the AM50 alloy. The result showed that the oxidation resistance was directly affected by the microstructure. Rapid solidification (RS) had a positive effect on improving the oxidation resistance. It is noticeable that no Al₂Y intermetallic compound was found in the microstructure after RS. Elemental Y dissolved in the solid solution increased with increasing Y addition after RS. It is confirmed that Y addition dissolved in the solid solution and phase distribution were key factors for improving the oxidation resistance.     

Synthesis of nanoporous copper by dealloying of Al-Cu-Mg amorphous alloys in acidic solution: The effect of nickel

Dealloying of Al-Cu-Mg based amorphous alloys in 1 M HCl solution and the effect of a minor amount of Ni in the precursor alloy were explored. A crystalline, Cu-rich, nanoporous structure with a pore diameter of 10–30 nm was formed as a result of the selective dissolution of Al and Mg and the reorganization of the remaining Cu. The entire specimen was fully dealloyed after prolonged exposure to a HCl solution. The nanoporous structure is finer (e.g. 10 nm) in the alloy containing Ni, likely because Ni suppresses the surface diffusion of Cu. The decrease in surface diffusion, in turn, suppresses the coarsening of the ligaments in the dealloyed layer enabling tunable porosity development. Electrochemical reactivity after the synthesis of nanoporous Cu was enhanced by a factor of 150 with Ni and 50 without Ni compared to a planar Cu electrode of the same overall dimensions.     

Atomistic simulations of the characteristics of TiSiN nanocomposites of various compositions

We performed classical molecular dynamics simulations of thermodynamically preferred structures of Ti_(50-x)Si_xN₅₀ (x ≤ 0.3) nanocomposites of various compositions containing up to a quarter of million of atoms. We focus on the formation and growth of TiN nanocrystals, and investigate how the Si content affects their number, size distribution, Si content in them, and thickness of the amorphous phase between them. We observe 3 important cases, namely frequent formation of large crystals below 3% of Si, formation of fine nanocrystalline structures (with quantitatively correct experimental crystal size) around 7% of Si, and amorphization at and above 15% of Si. The results represent the first attempt to predict the structure of TiSiN or similar nanocomposite systems using classical molecular dynamics simulations, and they are compared with experimental measurements of material hardness and electrical resistivity.