铸造镁合金AZ91D金相腐蚀方法研究

对砂型和金属型铸造AZ91D试样进行了铸态下与固溶处理后金相腐蚀研究,对压铸AZ91D试样进行铸态金相腐蚀和EBSD试验研究。结果表明,铸态砂型和金属型试样树枝晶形状显示六重对称性特征,一次枝晶间夹角为60°,固溶处理后晶粒尺寸变大。压铸试样冷却速度快,枝晶不能充分生长,难以显示六重对称性特征,EBSD试验能够准确测量压铸试样的晶粒尺寸和晶粒取向。

Sm_2Co_(17)型永磁材料金相样品的腐蚀条件研究

用三种金相腐蚀剂和不同的腐蚀时间对Sm2Co17型永磁材料进行腐蚀,通过扫描电子显微镜(SEM)结合X射线能谱仪(EDS)对Sm2Co17型永磁材料的金相腐蚀条件进行了研究。结果表明,0.5ml硝酸、2ml乙酸、100ml蒸馏水的配比,腐蚀60s能清晰显示晶界、晶粒表面以及晶粒中的富Zr和富Sm析出相。与最常用金属材料腐蚀剂和金相腐蚀手册提供的配方腐蚀剂相比,本实验确定的腐蚀条件得到的金相SEM照片更为清晰。

适用图像仪测定M—A相的腐蚀方法

比较研究了三种腐蚀方法对图像仪测定低碳低合金高强钢焊接相晶区M—A相的适用性。分析了误差来源,讨论了误差修正方法。

不同腐蚀工艺对单晶Ge位错密度与微观形貌的影响

为提高单晶Ge位错腐蚀工艺的准确度,采用金相腐蚀观察法计算了单晶Ge的位错密度,分析了腐蚀时间、抛光条件、腐蚀温度对位错微观形貌的影响。结果表明:腐蚀时间过长或过短,位错腐蚀坑形貌无法正常观测,腐蚀时间10 min时,位错腐蚀坑形貌观测效果最佳;机械抛光会产生划痕和污渍,化学抛光可以得到更光洁的材料表面,腐蚀后更易观测位错腐蚀坑形貌;相同腐蚀时间和抛光条件下,温度越高腐蚀速率越快,通过增加腐蚀温度可以有效提高腐蚀效率。

大块锆基非晶合金Zr_(53.5)Cu_(26.5)Ni_5Al_(12)Ag_3的盐雾腐蚀行为

采用铜模吸铸法制备直径为5 mm的Zr53.5Cu26.5Ni5Al12Ag3,用电化学极化曲线方法考察该大块锆基非晶合金及相应的晶态合金在55℃中性盐雾气氛下腐蚀120 h的腐蚀行为,并用金相显微镜、SEM和EDS对腐蚀前后试样的表面形貌和成分进行观察与分析.极化曲线测试结果表明,在55℃中性盐雾气氛下,大块锆基非晶合金比相同成分的晶态合金具有更好的耐盐雾腐蚀性能,腐蚀120 h后,Icorr=9.922×10-7A/cm2,比同条件下的晶态合金小3个数量级.SEM分析表明非晶合金表面没有发生明显的腐蚀,表面保持光洁.EDS分析表明非晶合金腐蚀产物为Al的氧化物,相应的晶态合金表面腐蚀产物为Al和Ni的氧化物.

无铼镍基单晶高温合金的显微组织表征

采用螺旋选晶法制备一种新型无铼镍基单晶高温合金,研究金相腐蚀剂对合金显微组织的影响,以及合金元素的偏析和合金的显微组织。运用金相显微镜(OM)、扫描电镜(SEM)、能谱仪(EDS)、电子探针(EPMA)、X射线衍射(XRD)、电化学萃取、电化学工作站以及图像处理软件Image pro plus(IPP)等技术方法,对镍基单晶高温合金进行表征和研究。结果表明:镍基单晶高温合金铸态组织由γ基体相、γ'强化相以及γ/γ'共晶相组成;不同的金相腐蚀剂会形成不同的显微形貌,这是由γ基体相和γ'强化相在相应腐蚀溶液中的自腐蚀电位决定的,对于γ'相体积分数的评估,应当选用腐蚀掉γ'相的图片用于计算;铸态镍基单晶高温合金偏析严重,Cr、Co、W元素偏析于枝晶干,Al、Ta元素偏析于枝晶间。

材料表面位错密度的测量方法研究

不同加工处理方法在材料表面产生的晶体缺陷直接决定已加工表面的微观组织结构特征,并影响其使用性能,其中位错的演变尤为显著。对材料加工表面位错参数进行准确的测量与分析,是全面把握材料加工表面微观结构和宏观性能的关键。论文重点阐述了几种主流的位错测量方法及其应用现状,对比了不同测量和分析方法的局限性和应用范围,展望了加工表面材料位错密度测量分析技术的发展趋势。

ASTM A216 WCA铸钢低倍组织及微观组织实验研究

针对ASTM A216 WCA铸钢材料,采用金相腐蚀和低倍侵蚀法获得了不同冷却速率下材料的金相图及低倍腐蚀图,并且进行了分析。结果表明,随冷却速率的增大,先共析铁素体的晶粒尺寸减小,体积分数增大,针状铁素体增多;重力作用对实际铸钢件在凝固过程中柱状晶向等轴晶的转变(CET)有重要影响。

Microstructures,corrosion and mechanical properties of as-cast Mg-Zn-Y-(Gd)alloys

Long period stacking ordered（LPSO） structure phases were prepared by conventional solidification method in Mg（94）Zn3YxGd（3-x）（x=3,2,1.5,1,mole fraction） alloys,the microstructures,corrosion and compressive mechanical properties of which were investigated,separately.The results reveal that the microstructures of the as-cast Mg（94）Zn3YxGd（3-x） alloys,with n（Zn）/n（Y＋Gd）=1：1,consist of α（Mg） phase,Mg3Zn3RE2（W） phase,Mg（12）ZnRE（14H-LPSO） phase and a few bright cube-shaped Mg-Y-Gd phases.The formation and the distribution of LPSO-phase in the alloys can be influenced by the content of Gd.The volume fraction of 14H-LPSO phase increases first and then decreases with the increase of the Gd content.For the electrochemical impedance spectroscopy（EIS） measurement,a R（Q（R（QR））） model was used to fit the test results in 3.5%（mass fraction） NaCl solution at room temperature.The corrosion current densities of all samples are about 10-（-5） A/cm-2.When x（Gd）≤1%,Mg-Zn-Y-（Gd）alloy shows good corrosion resistance,which is better than that of the commercial AZ91 D magnesium alloy.The corrosion rate increases when the Gd content is higher than 1.5%.At room temperature,the compressive properties of Mg-Zn-Y-（Gd） alloys increase remarkably with the increase of the volume fraction of LPSO phase.In addition,the pinning effect of W-phase and dispersive cube-shaped Mg-Y-Gd phase is beneficial to improving the mechanical properties of as-cast Mg（94）Zn3YxGd（3-x） alloy in deformation process.

Effect of Zr addition on microstructure and properties of Al-Mn-Si-Zn-based alloy

Effects of Zr addition on the microstructure, mechanical and electrochemical properties of Al-Mn-Si-Zn alloy were investigated. Transmission electron microscopy （TEM） observations reveal that, in as-annealled state, the precipitates in the Zr-containing alloy are finer and more dispersive than those in the Zr-free alloy. Whereas, in simulated brazing state, a weaker precipitation is found in the Zr-containing alloy. Tensile testing results indicate that, with Zr additon, comprehensive mechanical properties of the as-annealed alloys could be significantly improved but weakened for the simulated brazing alloy. Electrochemical testing results reveal that, with Zr addition, the corrosion resistance of the as-annealed alloy decreases. However, after the simulated brazing treatment, such a negative effect of Zr element on the corrosion behavior of the alloy could be negligible.

Effects of magnesium chloride-based multicomponent salts on atmospheric corrosion of aluminum alloy 2024

Atmospheric corrosion of aluminum alloy 2024 （AA2024） with salt lake water was simulated through a laboratory- accelerated test of cyclic wet-dry and electrochemical techniques. Effects of the soluble magnesium salt contained in the salt water were investigated by scanning electron microscope （SEM）, transmission electron microscope （TEM）, energy dispersive spectrometer （EDS）, electron probe micro analyzer （EPMA）, X-ray diffraction （XRD）, infrared transmission spectroscope （IR）, and atmospheric corrosion monitor （ACM）. The results showed that, with the deposition, atmospheric corrosion of AA2024 could occur when the relative humidity （RH） was lower than 30%. A main crystalline component of corrosion products, layered double hydroxides （LDH）, [Mg1-xAlx（OH）2]^x＋ Clx-·mH2O （LDH-C1）, was determined, which meant that magnesium ion played an important role in the corrosion process. It not only facilitated the corrosion as a result of deliquescence, but also was involved in the corrosion process as a reactant.

In vitro corrosion and biocompatibility of phosphating modified WE43 magnesium alloy

Phospahting coated WE43 magnesium alloy was prepared by an immersion method. The microstructure, corrosion resistance and biocompatibility of the coated alloy were investigated. Scanning electron microscopy （SEM） and X-ray diffraction （XRD） were used to examine the microstructure and the composition of the coated alloy. The corrosion resistance was studied by means of potentiodynamic polarization method and the biocompatibility of the surface modified WE43 alloy was evaluated by （3-（4,5）-Dimethylthiazol-2, yl）-2,5-diphenyltetrazolium bromide （MTT） and hemolysis test. The results show that the phosphating coating can enhance the corrosion resistance of WE43 alloy and can be a good candidate to increase the biocompatibility of WE43 alloy.

Effects of Ag contents in Sn-xAg lead-free solders on microstructure,corrosion behavior and interfacial reaction with Cu substrate

The effects of Ag on the microstructure and corrosion behavior of pre-soldering Sn-xAg lead-free solders,and on the formation of intermetallic layer of the solders with Cu substrate were investigated.The Ag contents(x)were 0,3.0,3.5,4.0,and5.0 wt.%.The Ag content played a role in the morphology of Ag3 Sn phase in the solders.The microstructure analysis showed that theβ-Sn phase was surrounded by eutectic networks in the 3.0 Ag and 3.5 Ag solders and large plate-like Ag3 Sn formed in the 4.0 Ag and5.0 Ag solders.Nonetheless,the Ag content slightly impacted the corrosion behavior of the as-cast solders as characterized using potentiodynamic polarization test.After soldering,only a single layer of a Cu6 Sn5 intermetallic compound formed at the Sn-xAg/Cu interface.By comparison,the Cu6 Sn5 intermetallic layer of the Ag-doped solders was thinner than that of the 0Ag solder.The fine Ag3 Sn particles in the eutectic networks precipitating in the 3.0 Ag and 3.5 Ag solders effectively hindered the growth of Cu6 Sn5 grains compared to large plate-like Ag3 Sn in the 4.0 and 5.0Ag solders.

Corrosion behavior of novel Cu-Ni-Al-Si alloy with super-high strength in 3.5% NaCl solution

A novel Cu?6.5Ni?1Al?1Si?0.15Mg?0.15Ce alloy with super-high strength was designed and its corrosion behavior in3.5%NaCl solution at25°C was investigated by the means of SEM observation,TEM observation and XPS analysis.The alloy after solution treatment,80%cold rolling and aging at450°C for1h had the best comprehensive properties with hardness of HV314,electrical conductivity of19.4%IACS,tensile strength of1017MPa,and average annual corrosion rate of0.028mm/a.The oxides and chloride products formed at first,followed by the formation of dyroxides products.The alloy showed super-high strength,good electrical conductivity and corrosion resistant because Ni2Si hindered the precipitation of large NiAl at the grain boundary and the denickelefication of the alloy.

Fabrication and Emission Properties of a n-ZnO/p-GaN Heterojunction Light-Emitting Diode

We report the fabrication and characterization of light-emitting diodes based on n-ZnO/p-GaN heterojunctions. The n-type ZnO epilayer is deposited by metalorganic chemical vapor deposition （MOCVD） on a MOCVD grown Mg-doped p-GaN layer to form a p-n heterojunction. During the etching process, the relation between the etching depth and the etching time is linear in a HF and NH4 CI solution of a certain ratio. The etching rates of the SiO2 and ZnO are well controlled,which are essential for device fabrication. The current-voltage relationship of this heterojunction shows a diode-like rectifying behavior. In contrast to previous reports,electroluminescence （EL） emissions are observed by the naked eye at room temperature from the n-ZnO/p-GaN heterojunction under forward-and reverse-bias. The origins of these EL emissions are discussed in comparison with the pho- toluminescence spectra.

Microstructure and corrosion behaviors of as-rolled Mg-Zn-Er alloy sheets

The corrosion behaviors and mechanism of the as-rolled Mg-x Zn-0.5Er(x=0.5, 2.0, 3.0 and 4.0, in wt.%)alloys were investigated. The potential difference between the second phase and matrix was determined by the type and size of the second phases. The dominated nano-scale W-phase on matrix in the Mg-0.5Zn-0.5Er alloy induced a sharp local pitting corrosion. However, as the volume fraction of the coarse W-phase or I-phase increased, the corrosion reaction was inclined to happen around the coarse W-phase or I-phase preferentially, leading to an obvious uniform corrosion and great acceleration of corrosion rate. The long-term immersion(14 d) results indicated that the corrosion resistance decreasing sequence was Mg-0.5Zn-0.5Er > Mg-2.0Zn-0.5Er > Mg-3.0Zn-0.5Er > Mg-4.0Zn-0.5Er.

Effect of metallic phase species on the corrosion resistance of 17M/(10NiO-NiFe_2O_4) cermet inert anode of aluminum electrolysis

NiFe2O4-based cermet inert anodes with metallic phase compositions of Cu, Ni and 85Cu15Ni were prepared by cold pressing-sintering. Their corrosion resistance was also investigated in Na3 AIF6-Al2O3 melts. The resuits show that the metallic phase species in cermets have no effect on the concentration of impurities in bath during electrolysis, the total steady-state concentration of impurities is almost the same, i.e. between 4.12 × 10^-4- 4.80 × 10^-4. There exists metal preferential corrosion for the cermet inert anode with metal Ni as metallic phase. For NiFe2 O4-based cermets, the cermet with metal Cu as metallic phase exhibits better corrosion resistance than the others.

Effect of fluoride treatment on corrosion behavior of Mg-Ca binary alloy for implant application

The influence of hydrofluoric acid（HF） treatment on the corrosion behavior of the Mg-0.5Ca alloys was investigated by immersion specimen in sodium hydroxide and HF solutions with various concentrations and durations at room temperature.Microstructural evolutions of the specimens were characterized by atomic force microscopy,X-ray diffraction,field-emission scanning electron microscopy.The corrosion resistance was examined through potentiodynamic polarization and immersion test in Kokubo solution.The results revealed that the fluoride treated Mg-0.5Ca alloys produced by immersion in 40% HF provided more uniform,dense and thicker coating layer（12.6 μm） compared with the 35% HF treated specimen.The electrochemical test showed that the corrosion resistance of fluoride treated specimen was 35 times higher compared with the untreated Mg-0.5Ca alloy specimen in Kokubo solution.In vitro degradation rate of the fluoride treated specimens was much lower than untreated Mg-0.5Ca alloy in Kokubo solution.After immersion test the surface of 40% HF treated sample showed a few corrosion dots,while untreated specimens were fully covered by corrosion products and delamination.Fluoride treated Mg-0.5Ca alloy with 40% HF is a promising candidate as biodegradable implants due to its low degradation kinetics and good biocompatibility.

Effect of crystal orientations and precipitates on corrosion behavior of Al-Cu-Li single crystals

The effect of the crystal orientations and precipitates on the corrosion behavior of Al-Cu-Li single crystals was studied by scanning electron microscopy, transmission electron microscopy, optical microscopy, immersion testing in exfoliation corrosion solution, and electrochemical testing. The results show that the corrosion rates of different orientations of the aged Al-Cu-Li alloy increase in the order of (001) 1 phase deteriorated the corrosion resistance of the Al-Cu-Li alloy, and the degree of deterioration differed in different crystal plane orientations. The severe localized corrosion of the aged alloy propagates along the crystallography and extends along the {111}Alplane in the form of corrosion bands.

Transformation mechanism of secondary phase and its effect on intergranular corrosion in laser wire filling welding Ni-based alloy/304 stainless steel

To clarify the transformation mechanism of secondary phase and the mechanism of intergranular corrosion in laser welding Ni-based alloy (Hastelloy C-276)/304 stainless steel with filler wire,the secondary phase was analyzed by electron probe micro-analysis (EPMA) and transmission electron microscopy (TEM).The evaluation of intergranular corrosion resistance of the welded joints was conducted by double-loop electrochemical potentiokinetic reactivation(DL-EPR) method,and at the same time the chemical compositions of the corrosion surface were analyzed by energy-dispersive spectrometry (EDS).The results show that p phase has complete coherence relationship withμphase,and the coherent relationship is described as[001]p//■and[430]p//[0001]μ.Theμphase is rapidly transformed from p phase,which is the inhomogeneous phase transformation.The transformation of secondary phase will increase the susceptibility to intergranular corrosion.Therefore,the transformation of secondary phase should be avoided in the welding process.