氧化镧对履带堆焊层合金微观组织与耐磨性的影响

目的研制一种新型含氧化镧(La_2O_3)堆焊装甲车履带用药芯焊丝,通过细化堆焊层合金的微观组织,提高堆焊层合金的耐磨性。方法采用堆焊的方法制作堆焊层合金,采用金相显微镜观察了其表面显微组织,并测定了其表面洛氏硬度和耐磨性。结果堆焊层合金微观组织由粒状贝氏体、马氏体和残余奥氏体组成。未加氧化镧的堆焊层合金初生奥氏体晶粒粗大,其平均尺寸在42μm,耐磨性为6000 min/g;当药芯焊丝中加入质量分数为2.5%的氧化镧之后,堆焊层合金的奥氏体晶粒尺寸最小,其平均尺寸为36μm,耐磨性为12 300 min/g。铝酸镧(LaAlO_3)的(001)面与奥氏体(100)面之间的二维错配度为3.81%。结论铝酸镧作为γ-Fe的异质形核核心最有效,说明堆焊层合金中铝酸镧可以使初生奥氏体的晶粒尺寸得到细化,从而改善了履带堆焊层合金的耐磨性。     

合金元素Nb对细化连铸辊堆焊层金属组织的影响

研制了三种不同合金元素Nb加入量的药芯焊丝。采用金相显微镜和扫描电镜对其显微组织和断口形貌进行了观察,采用X射线衍射仪对其相结构进行了分析,采用图形分析软件对其奥氏体晶粒度进行了统计。结果表明,堆焊层金属的显微组织含有板条马氏体和少量铁素体;堆焊层金属的断口类型以韧脆性断口为主;合金元素Nb加入量为0.15%时,其显微组织最细小且分布最均匀,断口韧窝更加均匀、细小;加入合金元素Nb使奥氏体晶粒尺寸明显减小,由22.7μm减小到20.3μm;合金元素Nb细化奥氏体晶粒尺寸是细化堆焊层金属显微组织的主要原因。     

Al3Ti4B中间合金对Mg-7Al-0.4Zn-0.2Mn合金显微组织和性能的影响

研究了Al3Ti4B中间合金对Mg-7Al-0.4Zn-0.2Mn合金的显微组织、力学性能及耐腐蚀性能的影响.结果表明:当Al3Ti4B加入量小于0.3%(质量分数)时,合金的平均晶粒尺寸显著减小;当Al3Ti4B加入量为0.3%时,合金组织显著细化,平均晶粒尺寸由未变质合金的135μm细化到30 μm,合金拉伸力学性能和耐腐蚀性能最好;当加入量超过0.3%时,晶粒粗化;具有密排六方结构的高熔点化合物Tm2(靠=2 980℃)和AlB(%=980℃)均可作为一Mg的异质核心,大量异质结晶核心的存在是导致α Mg晶粒细化的主要原因.     

MgCO_3对AZ81镁合金晶粒的细化行为及影响机制

添加不同量的MgCO_3对AZ81镁合金进行晶粒细化实验,结果表明:MgCO_3对AZ81镁合金细化效果明显,当加入量w(MgCO_3)=1. 2%时,合金晶粒最小;随后继续增加MgCO_3加入量,晶粒又开始变粗大。经X射线衍射发现MgCO_3加入后,合金中出现新的Al4C3相;经计算,Al4C3与α-Mg晶格常数相近,晶粒错配度小,Al4C3成为α-Mg基底的异质形核质点从而细化晶粒。     

Y2O3对粒状贝氏体堆焊金属相变和力学性能的影响

目的 研究稀土氧化物Y2O3对粒状贝氏体堆焊金属相转变以及力学性能的影响.方法 采用金相显微镜和场发射扫描电镜对堆焊金属的微观组织进行观察,采用金相显微镜观察并统计出奥氏体晶粒度,采用XRD对堆焊金属表面物相进行测定,采用显微硬度计和电子万能试验机测量不同Y2 O3质量分数堆焊金属的硬度和拉伸性能,采用透射电子显微镜对堆焊金属微观结构进行表征.结果 Y2O3能够有效细化堆焊金属的初生奥氏体晶粒,尺寸由51.2μm减小到40.1μm,大块先共析铁素体尺寸明显减小,组织分布均匀,且M/A岛弥散分布.堆焊金属中残余奥氏体相数量随着Y2O3质量分数的增加而逐渐降低,马氏体相体积分数增加.Y2O3的加入明显提升堆焊金属的力学性能,显微硬度由(272±13)HV提升至(312±8)HV;抗拉强度由(764±10)MPa提升至(885±12)MPa,且延伸率增加了4%.结论 Y2 O3的加入能够细化堆焊金属的初生奥氏体晶粒,促进形成均匀细化的粒状贝氏体组织,M/A岛的数量逐渐增加,且M/A岛中马氏体相数量增加,粒状贝氏体堆焊金属的力学性能显著提高.     

稀土元素Y对铁基耐磨堆焊层组织和性能的影响

通过改变稀土元素Y在高铬铸铁耐磨合金体系中的添加量，研究Y元素对堆焊层组织和性能的影响，从而使堆焊层组织发生良性转变，达到提高堆焊合金耐磨性的目的。采用药芯焊丝混合气体保护法明弧堆焊的方法在母材Q235钢表面制作堆焊合金，采用XRD、SEM对堆焊层进行微观组织观察及物相表征；通过洛氏硬度计、湿砂橡胶轮式磨损测试机进行宏观硬度测试、磨损性能测试，并观察磨损形貌，对堆焊层耐磨性进行评价。结果发现，堆焊层主要由奥氏体(γ-Fe)、铁素体(α-Fe)、M₇(C,B)₃、M₂B相组成，添加适量的稀土元素Y后，可以使硬质相分布更加均匀，晶粒更加细小。随着Y元素添加量的提高，堆焊层的硬度、磨损量呈现先减小后增加的趋势。Y元素添加量为1.6%时，堆焊层硬度为67.5 HRC，较未添加时提高17.2 HRC；此时磨损量最小为0.864 g，磨损机制为磨粒磨损。     

激光重熔功率对不锈钢改性层性能影响研究

为研究激光功率对316L不锈钢改性层微观组织结构和耐腐蚀性能的影响，采用纳秒脉冲激光对不锈钢表面进行重熔试验。建立激光重熔不锈钢瞬态非线性温度场模型，研究过程中的温度分布及变化规律，并通过试验探究激光功率对改性层微观形貌、元素分布及耐腐蚀性等影响规律。结果表明：不锈钢表面经过激光重熔生成了一层铬和铁氧化物，基体相由α-Fe向γ-Fe转变；当激光功率为5 W时，重熔生成的改性层微观形貌最佳、耐腐蚀性能最强。在激光作用下，不锈钢的微观组织结构致密化，晶核变大、晶粒细化，不锈钢表面的Cr、Mn等元素固溶于奥氏体中，产生微观组织较为致密且耐腐蚀元素含量较多的改性层。     

稀土La对ZCuPb20Sn5合金组织与性能的影响

研究了不同稀土La加入量对ZCuPb20Sn5合金组织和性能的影响。结果表明,与未加入稀土La相比,ZCuPb20Sn5合金组织中的铅颗粒增多且分布密集,α基体数量增多;合金的力学性能得到不同程度的改善,稀土La加入量从0%增加到0.04%,ZCuPb20Sn5合金抗拉强度从163.49 MPa增加到255.27 MPa,伸长率从4.7%增加到15.75%,硬度从77 HBS增加到84 HBS,但La含量超过0.04%时力学性能呈现降低趋势,最佳稀土La加入量为0.04%。     

稀土镧对Al-0.6Mg-0.7Si-0.2Mn汽车板材机械及腐蚀性能的影响

采用SEM、OM、拉伸试验（常温/高温）、弯曲试验和晶间腐蚀试验等测试方法,对添加不同含量稀土元素镧的Al-Mg-Si-Mn合金组织、机械性能及耐腐蚀性能等进行研究,分析稀土元素镧对合金机械和腐蚀性能的影响。结果表明,随La元素的添加,合金的铸态组织逐渐细化,第二相形貌得到了改善,同时减薄了该合金型材粗晶区厚度,提高了Al-Mg-Si-Mn合金的机械性能和耐腐蚀性能。当La添加量为0.2 wt.%时,晶粒细化效果最好,型材粗晶区最薄;La含量大于0.2 wt.%时,过量的La形成的初生相与合金晶粒细化剂中的Ti相互作用,减少了异质形核核心的数量,导致晶粒粗化现象,恶化合金的机械性能和耐腐蚀性能。     

TiC对Ni35A堆焊层组织及摩擦磨损性能的影响

利用等离子弧对Ni35A及加入10%TiC的Ni35A预压块体进行堆焊试验,借助金相显微镜、X射线衍射仪、维氏硬度计及摩擦磨损试验机研究堆焊层组织及磨损性能。结果表明,堆焊层主要由(Fe,Ni)固溶体组成,加入TiC粉末后,堆焊层含硬质相Ni_3Ti及TiC,合金晶粒明显细化;焊层硬度增加,表层硬度提高了73%;磨痕深度、磨痕宽度、磨损量较Ni35A堆焊层的分别降低了38.9%、25.0%、57.6%。     

Electrochemical and quantum chemical assessment of two organic compounds from pyridine derivatives as corrosion inhibitors for mild steel in HCl solution under stagnant condition and hydrodynamic flow

In this study, the inhibitive performance of two pyridine derivatives as corrosion inhibitors for mild steel was examined under stagnant condition and hydrodynamic flow in HCl solution at 25 °C. Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques were employed. To explore the inhibitors adsorption mechanism, Langmuir isotherm and quantum chemical studies were used. The results of electrochemical measurements show that the inhibitor concentration has a positive effect on its efficiency while for hydrodynamic condition, it is vice versa. Corrosion attack morphologies were observed at stagnant and hydrodynamic conditions to verify qualitatively the results obtained by electrochemical methods.     

Yield surface of polycrystalline thin films as revealed by non-equibiaxial loadings at small deformation

A biaxial device developed at DiffAbs beamline of the SOLEIL synchrotron facility has been employed to determine the applied strains in film–substrate composites using both X-ray diffraction and digital image correlation measurements. Such an experimental combination is used for the first time to determine the yield surface of a polycrystalline thin film deposited on a polyimide substrate. In situ biaxial tensile tests under different biaxial planar load ratios were performed on W/Cu nanocomposite thin films deposited on flexible substrates. The effect of loading path on the yield stress of W/Cu nanocomposites is presented by considering a large range of proportional loadings. By comparing experimental results with theoretical models, this study reveals the brittle behaviour of W/Cu nanocomposite thin films at small deformations.     

Fe:NiOx阳极催化膜电极过程动力学研究

利用射频反应磁控溅射制备Fe:NiOx阳极催化膜,对其在电解液中的电极过程进行分析,明确整个电极过程的控制步骤--电化学步骤.根据实验结果及塔菲尔方程求出电化学步骤的重要动力学参数(塔菲尔斜率b,交换电流密度i0),并通过XPS和SEM分析影响过电势的因素.     

Conducting polymers as free radical scavengers

The potential antioxidant activity of conducting polymers in biomedical applications has been evaluated by determining radical scavenging ability using the stable ,-diphenyl-β-picrylhydrazyl (DPPH) free radical and correlating this with the reducing strength of the polymer. Commercial soluble polyaniline grafted to lignin, poly(anilinesulfonic acid), and polypyrrole, were found to be very efficient scavengers of DPPH radicals, reacting with 2-4 DPPH radicals per aniline or pyrrole monomer unit. Shifts in IR bands in the case of a polyaniline powder pointed to polymer oxidation and methoxy-substitution as likely mechanisms. All of the conducting polymers had low formal potentials (ca. 150 mV (Ag/AgCl) at pH 7), similar to those of catechin-type polyphenol antioxidants. On the other hand, the formal potentials of pyrrole and aniline were quite high (ca. 700 mV), and the reaction of aniline with DPPH radicals was limited, while o-methoxyaniline with a lower formal potential (ca. 500 mV) neutralised DPPH radicals in a 1:1 ratio.     

Raman spectroscopy analysis of polypyrrole films as protective coatings on iron

In situ Raman spectroscopy was used to study the redox modifications of electropolymerized polypyrrole (Ppy) films used as protective coatings on iron. A preliminary study of the redox behavior of Ppy on platinum was carried out for highlighting the most sensitive bands to potential variations: the 1560–1620 cm⁻¹ as well as the 930 and 980 cm⁻¹ peaks show a strong dependence on the applied potential. In situ Raman spectra of Ppy on iron were recorded at different times after immersion in a 3% NaCl solution. They formally display the same peaks as those found for platinum, allowing to characterize the redox state of the Ppy film at the solution/film interface. Additional ex situ Raman spectra allowed to identify the corrosion products at the Ppy/metal interface. These results complement kinetics analysis early developed to understand the protection mechanism and its loss.     

Semiconducting polyfluorenes as materials for solid-state polymer lasers across the visible spectrum

We report a detailed study of the gain properties of three polyfluorenes: poly(9,9-dioctylfluorene-co-9,9-di(4-methoxyphenyl)fluorene (F8DP), poly(9,9-dioctylfluorene-co-benzothiadiazole) (F8BT), and a Dow proprietary copolymer, Dow Red F. The emission spectra of these conjugated polymers span the full visible spectrum from 400 to 800 nm. We observe amplified spontaneous emission (ASE) with peak wavelengths at 452, 576 and 685 nm for F8DP, F8BT and Red F, respectively. Low stimulated emission thresholds in the region of 0.1–0.45 μJ per pulse are demonstrated for planar asymmetric waveguides. Variable stripe length gain measurements at the peak ASE wavelengths show large net gains up to 66 cm⁻¹. Very low loss coefficients, in the range of 3.2–14.8 cm⁻¹, were also found.     

Nanobeads of zinc oxide with rhodamine B dye as a sensitizer for dye sensitized solar cell application

Cost effective, ruthenium metal free rhodamine B dye has been chemically adsorbed on ZnO films consisting of nanobeads to serve as a photo anode in dye sensitized solar cells. These ZnO films were chemically synthesized at room temperature (27 °C) on to fluorine doped tin oxide (FTO) coated glass substrates followed by annealing at 200 °C. These films consisting of inter connected nanobeads (20-40 nm) which are due to the agglomeration of very small size particles (3-5 nm) leading to high surface area. The film shows wurtzite structure having high crystallinity with optical direct band gap of 3.3 eV. Optical absorbance measurements for rhodamine B dye covered ZnO film revealed the good coverage in the visible region (460-590 nm) of the solar spectrum. With poly-iodide liquid as an electrolyte, device exhibits photon to electric energy conversion efficiency (η) of 1.26% under AM 1.5G illumination at 100 mW/cm².     

Cr doping effect in B-site of La0.75Sr0.25MnO3 on its phase stability and performance as an SOFC anode

La0.75Sr0.25CryMn1-yO3(LSCM) (y=0.0-0.6) composite oxides were synthesized by a complexing process of combining ethylene diamine tetraacetic acid (EDTA) and citrate. X-ray diffraction (XRD), temperamre-programmed reduction, electrical conductivity, I-V polarization, and impedance spectroscopy were conducted to investigate the Cr doping effect of La0.75Sr0.25MnO3 on its phase stability and electrochemical performance as a solid-oxide fuel cell (SOFC) anode. The chemical and structural stabilities of the oxides increased steadily with increasing Cr doping concentration, while the electrical conductivity decreased on the contrary. At y ≥ 0.4, the basic perovskite structure under the an-ode operating condition was sustained. A cell with 0.5-mm-thick scandia-stabilized zirconia electrolyte and La0.75Sr0.25CryMn1-yO3 anode de-livered a power density of～15 mW.cm-2 at 850℃.     

Synthesis and characterization of single phase LixBC (x=0.5 and 1.0), using Li hydride as a starting material

The hole-doped Li_xBC (x<1) has been theoretically predicted to exhibit superconductivity. In this report, preliminary information about the atomistic structure, thermal stability and magnetic property was presented on the single phase Li_xBC (x=0.5 and 1.0), using Li hydride as a starting material. The hydrogen concentration in Li_xBC (x=0.5) is about 0.7 mass% (Li_0.5BC-H_0.18), and the hydrogen desorption occurs around 700 K. The absence of superconductivity might originate from the modified atomistic structure, detected by Raman spectroscopy. We propose that the hydrogen concentrations can be varied for realizing superconductivity in Li_xBC (x<1).     

SiO2–Al2O3–glass composite coating on Ti–6Al–4V alloy: Oxidation and interfacial reaction behavior

A SiO₂–Al₂O₃–glass composite coating was prepared on Ti–6Al–4V alloy by air spraying and subsequent firing. The oxidation behavior of the specimens at 800 °C and 900 °C for 100 h was studied. The thermal shock resistance of the coating was tested by heating up to 900 °C and then quenching in water. The composite coating acted as an oxygen migration barrier and exhibited good resistance against high temperature oxidation, thermal shock, and oxygen permeation on the Ti–6Al–4V alloy. Coating/alloy interfacial reaction occurred, forming a Ti₅Si₃/Ti₃Al bilayer structure. A thin Al₂O₃ rich layer formed beneath the composite coating during oxidation at 900 °C.