激光熔覆Ni-Al2O3复合涂层的微观结构与耐腐蚀性能研究

目的 解决Cr-Ni系不锈钢在重腐蚀工业环境中本体耐腐蚀性能不足的问题。方法 采用激光熔覆技术制备Ni-Al2O3复合涂层,利用X射线衍射、扫描电镜、能谱仪(EDS)和显微硬度计、电化学工作站等技术研究所制备涂层的微观结构、相组成和元素分布,分析Al2O3含量对复合涂层形貌、显微硬度和耐腐蚀性能的影响规律。结果 复合涂层组织均匀、无明显缺陷,与基体之间存在明显的冶金结合区,沿着该复合涂层深度方向的微观结构依次呈现为胞状晶、定向生长的柱状晶及细小的等轴晶,物相则由均匀分布于复合涂层顶部的Al2O3颗粒和金属间化合物(Fe-Ni、Fe-Ni-Cr固溶体)构成。随着Al2O3含量的增大,复合涂层的显微硬度呈先增大后减小的趋势,腐蚀电位呈先增大后减小的趋势,而失重腐蚀速率和腐蚀电流密度呈先减小后增大的趋势,涂层的耐腐蚀性能呈先增强后减弱的趋势。在Ni-x%Al2O3(x为0、0.15、0.25、0.35,质量分数)复合涂层中,Ni-25%Al2O3复合涂层具有较高的显微硬度和良好的耐腐蚀性能,该涂层的显微硬度达到1 026.3HV,腐蚀失重速率为0.15 mg/(cm².h),腐蚀电压和腐蚀电流密度分别为–326.6 mV和38.6 µA/cm²。当继续增加Al2O3的含量时,气孔和裂纹等缺陷开始增多,复合涂层的显微硬度和耐腐蚀性能均呈现下降趋势。研究表明,Ni-x%Al2O3(x≤25)复合涂层的显微硬度和耐腐蚀性能的变化由细晶强化、固溶强化和颗粒强化协同作用所致。结论 激光熔覆Ni-25%Al2O3复合涂层具有较高的硬度和良好的耐腐蚀性,可以有效防护Cr-Ni系不锈钢,提高重腐蚀工业环境下机械零件的耐蚀性和使役寿命。     

Mo含量对FeCoCrNiMox高熵合金等离子喷焊层组织与性能的影响

目的 研究不同Mo元素添加量对FeCoCrNiMox(x=0、0.5、1、1.5)高熵合金等离子喷焊层组织和性能的影响,以期望获得一种高硬度、耐腐蚀的喷焊层,用于改善传统工模具表面防护与使用寿命的问题。方法 采用等离子喷焊技术在Q235A低碳钢表面制备了不同Mo含量的高熵合金喷焊层,通过X射线衍射仪(XRD)、光学显微镜(OM)、扫描电子显微镜(SEM)、能量色散X射线光谱仪(EDS)表征其微观组织与相结构,借助显微硬度计和电化学工作站对喷焊层的硬度和耐腐蚀性能进行测试。结果 随着Mo含量x从0逐渐增加到1.5,喷焊层的晶界胞状枝晶组织(枝晶内为白色富Mo相,枝晶间为灰色富Fe、Ni相)逐渐增加,合金微观组织变得细小;喷焊层的硬度由204.4HV0.2增加至706.8HV0.2;喷焊层在3.5%NaCl溶液中呈现出明显的钝化行为,腐蚀电位由?0.753 V增大到?0.412 V,腐蚀电流密度由1.23×10^?4 A/cm²减小到3.80×10^?6 A/cm²,点蚀电位由?0.642 V增大到?0.371 V,具有优异的耐腐蚀性能。结论 所设计的FeCoCrNiMox合金及相应的等离子喷焊工艺,满足对喷焊层高耐磨以及耐腐蚀性的要求,有望应用于传统工模具的表面防护与修复。     

激光熔覆CoCrNiMnTix高熵合金涂层组织及耐磨性能研究

目的 针对高铁制动盘等高速强力磨损的关键件,设计激光熔覆CoCrNiMnTix高熵合金涂层,提高表面的硬度和耐磨性。方法 采用激光熔覆技术在Q235钢表面制备CoCrNiMnTix高熵合金涂层,利用XRD和SEM对涂层微观组织进行表征,通过显微硬度计和纳米压痕仪测试涂层硬度,运用摩擦磨损试验机和三维形貌仪研究涂层的摩擦磨损性能。结果 在激光熔覆CoCrNiMnTix涂层中,随着Ti含量的增加,涂层物相由单一的FCC相转变为FCC+Laves相。由于固溶强化以及Laves相含量增多,涂层的显微硬度不断提高,CoCrMnNiTi硬度达到523HV0.1,最高纳米硬度达到6.91 GPa。CoCrNiMnTix系涂层的弹性模量大小相近。随着Ti含量的增加,涂层的耐磨性呈现升高趋势,当Ti的摩尔分数增加至0.75时,涂层具有最好的耐磨性,但进一步增加Ti含量时,由于脆硬性的Laves相逐渐增多,磨损形式由低Ti含量时的粘着磨损逐渐转变为高Ti含量时的磨粒磨损,使涂层耐磨性能下降。结论 激光熔覆CoCrMnNiTix涂层可以显著提高基体的耐磨性,Ti的摩尔分数为0.75时,在FCC基体中形成了少量Laves相,既提高硬度,又实现强韧配合,涂层表现出最佳的耐磨损性能。     

Mo元素对激光熔覆AlCoCrFeNiMox高熵合金涂层组织性能的影响(英文)

采用激光熔覆的方法制备AlCoCrFeNiMox高熵合金涂层。研究Mo元素含量对涂层微观结构、硬度及耐腐蚀性的影响。结果表明,随着Mo含量的增加,微观组织从富(Al, Ni)的体心立方（bcc）相和富(Mo-Cr-Fe)的σ相,转变为富(Fe, Ni)的bcc相、富(Mo-Cr-Fe)的σ相、富(Al-Fe-Mo)的σ相与少量AlN相。此外,涂层的显微硬度（HV1）从6154.4 MPa增加到10652.6 MPa。随着Mo含量的添加,涂层在3.5%（质量分数）氯化钠溶液中的自腐蚀电位升高,当Mo含量为x=1.0时,涂层的耐腐蚀性能最好。     

NdCeFeB快淬带相互作用与磁性能

采用感应熔炼制备名义成分为(Nd_1-xCe_x)_2.4Fe₁₄B (x=0, 0.2, 0.4, 0.6, 0.8, 0.8, 1.0)的快淬带,研究了Ce取代量对快淬带的相组成、磁性能和微观结构的影响。XRD结果表明,所有快淬带均呈现四方结构(Nd, Ce)₂Fe₁₄B相,当Ce取代量超过x=0.6时,快淬带中出现CeFe₂相并且CeFe₂含量随着Ce取代量的增加而增加。快淬带的剩磁、剩磁比（M_r/M_s）和晶格常数随着Ce含量的增加而减小,当Ce取代量为x=0.2时,快淬带的磁性能为矫顽力1.31×10⁶ A/m,最大磁能积103 kJ/m³。通过小回线和δM曲线研究了快淬带的矫顽力机理和晶粒间交换耦合,在每个样品中都观察到正的δM值,证实了交换耦合相互作用的存在。Ce含量为x=0.2时δM最大值达到0.76,说明快淬带晶粒间交换耦合效应最强,这一结果与剩磁比的变化一致。SEM观察发现,Ce取代量的增加恶化快淬带的柱状晶结构。     

碳含量对激光熔覆CoCrFeMnNiCx高熵合金涂层摩擦磨损和耐蚀性能的影响

采用激光熔覆技术在 45 钢基体上制备了不同碳含量(等摩尔比)的 CoCrFeMnNiC_x( x = 0,0. 03,0. 06,0. 09, 0. 12,0. 15)高熵合金涂层。 通过 X 射线衍射(XRD)、扫描电镜( SEM)、HVS-1000A 型显微硬度计、RST5000 型电化学工作站、UMT-2 型摩擦磨损试验机等表征和测试手段研究了不同碳含量对激光熔覆 CoCrFeMnNiC_x 高熵合金涂层物相结构、显微硬度、摩擦磨损及耐腐蚀性能的影响。 结果表明,当碳含量 x 由 0 逐渐增加至 0. 09 时,高熵合金相结构由 FCC 固溶体转变为 FCC 固溶体和 M23C6 相共存,合金微观组织变得细小;熔覆层硬度由 183. 20 HV_{0. 2} 增加至 223. 48 HV_{0. 2} ; 涂层的摩擦因数降低,耐磨性能变强;腐蚀电位由-469 mV 增大至-348 mV,腐蚀电流密度由 14. 95 μA·cm^-2 减小为 2. 29 μA·cm^-2 ,耐腐蚀性增强。 当碳含量 x 由 0. 09 逐渐增加至 0. 15 时,合金相结构再次转变为 FCC 固溶体,且合金微观组织恢复粗大状态;熔覆层硬度与耐腐蚀性降低,但耐磨性能却先减弱后增强。 合金在碳含量为 0. 09 时,硬度最高且耐腐蚀性能最强;在碳含量为 0. 15 时,耐磨性最强。     

双主相混合稀土基RE-Fe-B磁体的磁性能和抗腐蚀性改进

为了实现稀土资源的平衡应用且降低RE-Fe-B稀土永磁材料的价格,针对混合稀土基永磁材料进行研究,分别采用单、双主相工艺制备了名义成分[(Pr,Nd)_1-xMM_x]_30.3(Fe,Co)_balM_0.73B_0.98 （x=0.3,0.5和0.7,质量分数）的磁体,对比研究其磁性能和抗腐蚀性。研究发现：双主相工艺制备的磁体相比单主相工艺制备的同成分磁体展现了优越的磁性能和抗腐蚀性。当x=0.5,双主相磁体的磁性能为B_r=1.308 T,H_cj=799.98 kA/m和(BH)_max=325.6436 kJ/m³,远高于同成分的单主相磁体的性能（B_r=1.297 T,H_cj=746.8868 kA/m 和(BH)_max=317.8428 kJ/m³）。这种改进源于富稀土相分布的改进以及主相晶粒间和晶粒内部耦合作用的增强。当双主相磁体暴露在湿热环境下时,磁体中不仅存在富稀土相腐蚀,也存在主相晶粒的腐蚀成粉现象,这主要是由于富稀土相与水蒸气和氧气反应时产生氢气,导致主相晶粒被氢化,由于主相晶粒间和晶粒内部的镧铈分布差异,产生大的应力,导致其表现出区别于单主相磁体的腐蚀行为。     

固溶处理Mg-0.5Zr-1.8Zn-xGd生物可降解镁合金的微观组织、力学性能和腐蚀性能

研究了Mg-0.5Zr-1.8Zn-xGd (x=0,0.5,1.0,1.5,2.0,2.5,质量分数,%) 镁合金经过470 ℃和10 h固溶处理后的组织、力学性能和耐腐蚀性能。结果表明,Gd含量在0%~2.5%范围内,随着Gd含量增加,合金晶粒尺寸逐渐减小。当Gd含量低于1.5%时,合金元素几乎完全固溶于合金基体中,第二相主要由纳米尺度的(Mg,Zn)₃Gd析出颗粒组成。当Gd含量在1.5%~2.5%范围时,合金中出现未固溶的微米尺度的(Mg,Zn)₃Gd相,并且该相数量和尺寸随着Gd含量增加而增加。由于组织均匀分布和纳米尺寸的第二相颗粒存在,Mg-0.5Zr-1.8Zn-1.5Gd合金具有优异的力学性能和耐腐蚀性能。在120 h浸泡实验中,Mg-0.5Zr-1.8Zn-1.5Gd合金平均腐蚀速率首先降低,然后增加,接着缓慢降低,最后,随着浸泡时间延长,腐蚀速率最终变得稳定。     

挤压态Mg–1.8Zn–0.5Zr–xGd(0≤x≤2.5%)生物镁合金微观组织演化及降解机理

目的 提高Mg–0.5Zr–1.8Zn–xGd(x=0、0.5%、1.0%、1.5%、2.0%、2.5%)生物镁合金在模拟体液中的耐腐蚀性能。方法 先对Mg–0.5Zr–1.8Zn–xGd合金进行固溶处理,然后利用反向挤压技术对其进行组织细化处理,采用OM、SEM、EDS、EBSD和TEM分析了挤压后Mg–0.5Zr–1.8Zn–xGd合金的晶粒形貌、织构特征、相组成和表面腐蚀形貌。利用电化学工作站和静态腐蚀测试了挤压后合金的耐腐蚀性能。利用XPS对Mg–0.5Zr–1.8Zn–xGd合金腐蚀前、后的表面元素及其化学状态进行表征。结果 挤压温度和挤压比分别为360 ℃和7.7时,合金都发生了较为完全的动态再结晶。随Gd含量的增加,晶粒尺寸逐渐减小,耐腐蚀性能先增强后减弱。当Gd质量分数为1.5%时,合金具有较好的耐腐蚀性能,其静态腐蚀速率约为0.447 mm/a;Gd质量分数为1.5%时,合金中析出了少量的纳米级圆棒状(Mg,Zn)3Gd相颗粒和纳米级椭圆球状Mg2Zn11相颗粒,且随着Gd含量的增加,合金中第二相颗粒的数量及体积分数逐渐增大。Mg–0.5Zr–1.8Zn–1.5Gd合金在SBF中浸泡120 h内,随浸泡时间的增加,腐蚀过程分3个阶段,首先合金表面Mg(OH)2腐蚀产物的生成及增厚导致腐蚀速率在腐蚀初期快速降低,随后致密的Mg(OH)2、(Ca,Mg)3(PO4)2和Ca10(PO4)6(OH)2腐蚀产物的生成及增厚导致腐蚀速率缓慢降低,最后腐蚀产物的生成与溶解达到动态平衡导致腐蚀速率逐渐趋于稳定。结论 挤压变形能够显著细化Mg–0.5Zr–1.8Zn–xGd合金的晶粒,均匀化和弥散化析出相分布,有效改善镁合金在模拟体液中的耐腐蚀性能。     

冷喷涂辅助原位合成FeCoxCrAlCu高熵合金涂层组织性能研究

利用冷喷涂辅助原位合成高熵合金涂层的方法,在45_^#钢基体表面成功制备出不同Co含量的FeCo_xCrAlCu(x=0,0.5,1,1.5,2)高熵合金涂层。通过XRD、SEM、EDS、TEM、显微硬度计、磨料磨损试验机、电化学工作站等设备,检测分析了Co含量的变化对合金涂层相结构、显微组织,硬度、耐磨性及耐腐蚀性的影响。结果表明：合金涂层是由简单的FCC+BCC双相混合结构组成,Co含量的改变对涂层相组织的数量影响不大;随着Co含量的增加,合金涂层中显微组织的枝晶数目增加,并且得到明显粗化,通过面扫得显微组织中枝晶内富集Fe,Cr,Co元素,枝晶间富集Cu元素,Al均匀的分布在整个涂层中;随着Co含量的增加,硬度先增加后减小,在Co=1时合金涂层硬度达到最大为555.6HV;合金涂层中最小的摩擦系数为0.361;在3.5wt.%NaCl腐蚀介质中,合金涂层相比与45_^#钢基体具有较正的自腐蚀电位(E_corr=-0.325V),说明涂层耐腐蚀性比基体好。     

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

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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.     

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.     

Optimization of transparent conducting oxide ZnO compound thickness in terms of four alloys thermo-physical performance aggregates

ZnO is one of the well-known metal oxide semiconductors, which has been found, in the last four decades, to be very useful as transparent conductors and UV detectors in optoelectronic devices. This binary compound that showed quantum confinement effects in accessible size ranges was elaborated using several techniques. In the present work, the sprayed pyrolysis technique was carried out to prepare undoped ZnO crystals with different controlled thicknesses.Particularly, and parallel to recently performed measurements, a recently proposed range of optimal layer thickness d is validated, through original conjoint morphological-structural-physical investigations.     

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.     

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.     

The effects of sealing on cracking tendency of anodic films on 2024 aluminum alloy after heating up to 300 °C

The influence of sealing methods on cracking tendency of anodic films on 2024 alloys after heating was studied. The anodic films were sealed by the methods of ambient water, boiling water, nickel fluoride and potassium dichromate, respectively. The results showed that the sealing mechanisms had important effects on initiation of cracks in anodic films during sealing process. The condensation of sealing products resulted in cracking of anodic films during sealing in boiling water, nickel fluoride solution and ambient water. On heating, the thermal stress was released mainly by widening and deepening of the originally initiated cracks during sealing. The cracks may penetrate through the anodic films and have detrimental effect on corrosion resistance of the films. The dichromate sealed anodic film showed an obviously decreased cracking tendency, which was attributed to the lower hydration extent and the opening pores during sealing process. Even after heating, there was no crack observed in the film. The result suggests that an “opening sealing” mode is beneficial to decrease the cracking tendency of anodic films during sealing and heating processes.     

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.