Effect of yttrium addition on the oxide scale of AM50 magnesium alloy

This paper focused on the effect of yttrium (Y) addition on oxidation resistance of AM50 alloy. The oxide scale on the surface was studied. Elemental Y in solid solution played an important role in improvement of oxidation resistance and formation of oxide scale. Yttrium (0.28 wt%) addition in AM50 alloy could greatly enhance the oxidation resistance. Furthermore, with increasing Y addition, the scale/substrate adherence was increased. However, when Y addition exceeded 0.28 wt%, it was decreased.     

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.     

Effect of Ce on solidification and mechanical properties of A360 alloy

The effect of Ce addition on the AA A360 (Al-10%Si-0.5%Mg) alloy was investigated using equilibrium thermodynamic calculation, thermal analysis, differential scanning calorimetry (DSC) and scanning electron microscopy (SEM). The purpose is to study the variations that occur during solidification and precipitation with different Ce additions, as well as their effect on the mechanical properties. The results show that the Ce addition decreases the eutectic (α_Al + Mg₂Si) temperature. The solidus temperature also decreases with the increasing Ce addition. The precipitation enthalpy determined using DSC decreases with the Ce addition, while precipitation takes place more rapidly and intensively, indicating increased reaction kinetics. The mechanical properties like hardness and tensile strength also increase with the Ce addition. The phase that contributed to the hardness of the investigated alloy was composed of Al, Ce, Mg and Si.     

Interactive effect of cerium and aluminum on the ignition point and the oxidation resistance of magnesium alloy

This paper focused on the interactive effect of cerium (Ce) addition and aluminum (Al) content in magnesium alloy on ignition point and oxidation resistance. Ce content played an important role in improving the oxidation resistance of Mg alloy. Ignition point ascended with increasing Ce content. 0.25 wt% Ce content in Mg alloys could greatly improve tightness of the oxide film of Mg alloys. However, when Ce content in the alloy exceeded its solid solubility, ignition point descended. Furthermore, Al content in the alloy also influenced the ignition point. The higher the Al content was, the lower the ignition point.     

温度梯度和冷却速率对ZL205A合金凝固组织及性能的影响

由于在不同温度梯度下ZL205A合金冷却速率对凝固组织的影响不同,采用不同壁厚的阶梯状结构的合金,在不同凝固条件下制备厚度不同的合金试样,探究了冷却速率及温度梯度对合金凝固组织及T5处理后合金抗拉伸强度及延伸率的影响,同时探索了合金的相变规律与组织和性能的关联效应。实验结果表明：由壁厚差引起的温度梯度对合金的微观组织及形貌会产生一定的影响,降低温度梯度的合金力学性能显著提升,T5处理后合金的抗拉伸强度达到506 MPa。     

Effect of yttrium on the cyclic oxidation behaviour of HP40 heat-resistant steel at 1373 K

The effect of rare earth elements on cyclic oxidation behaviour of HP40 at 1373 K has been investigated. The results demonstrate that 0.06 wt.% addition of Y effectively improves the cyclic oxidation resistance of such Si-containing alloy. By observing the cross-section of the scale, it is found that Y facilitates the formation of Si-rich internal oxide, which improves the spalling resistance of the scale. As a result, compared with the sample without Y addition, on which the spinel layer is discontinuous, a continuous duplex scale of chromia overlaid by manganese-rich spinel is kept at the outmost of the Y-modified alloy.     

Ce对Ni—Cr—Cu合金抗氧化性的影响

作者研究了添加0.1％和0.8％Ce的Ni—Cr—Cu合金在空气中1200℃100小时等温氧化和500小时循环氧化。Ni—Cr—Cu合金中添加微量Ce后,显著降低了氧化速率,增加了氧化膜的剥落抗力。氧化速率降低是添加Ce后各种效应综合作用的结果。它们是:(1)由于Cr的扩散加快,富Cr保护膜更迅速形成;(2)聚集在膜/合金界面附近的含Ce氧化物与空位复合,减少了膜/合金界面的空洞;(3)固溶于氧化膜中的含Ce氧化物阻碍了Cr~(3+)沿氧化物晶界的短程扩散。 提高耐剥落抗力主要原因是:(1)添加Ce使氧化膜晶粒变细,从而改善了塑性变形和适应热应力的能力;(2)0.8Ce合金中稀土氧化物“钉扎”(Keying)作用改善了膜与合金粘附性,并改变了热应力的分布状态。     

Beneficial Effects of Ce Implantation into Preformed Cr2O3 Scales on the Subsequent Oxidation of Ni–20Cr Alloy

The influence of Ce implantation into preformed Cr₂O₃ scales with a dose of 1 × 10¹⁷ ions/cm² on the subsequent oxidation behavior of Ni–20Cr alloy at 1050°C in air has been investigated. The pre-oxidation was carried out at 1050°C in air for 0.5 and 1 hr respectively Cr₂O₃ and NiCr₂O₄ formed on Ni–20Cr alloy. The oxidation rate was decreased remarkably due to Ce implantation regardless of whether it was implanted into the alloy or into the pre-formed oxide scales, and the beneficial effect decreased with increasing pre-oxidation time, the alloy implanted directly with Ce had the lowest oxidation rate constant. During cyclic oxidation (350 cycles) Ce implantation played a similar benefical effect on the oxide-spallation resistance for blank and pretreated alloys. The result indicates that Ce incorporated into the oxide scale affected the diffusion of the reaction species and also the spallation resistance of the oxide scales. The change of the oxidation process is attributed to the segregation of Ce at the oxide grain boundaries     

Effect of pre-oxidation on the hot corrosion of CoNiCrAlYRe alloy

The effect of pre-oxidation on the resistance to hot corrosion was examined by corroding the CoNiCrAlYRe alloy at 900 °C in molten Na₂SO₄. Preoxidized specimens featured strong adhesion of oxide scale with uniform multi-layered structure. The time of pre-oxidation was crucial for controlling Al content sufficient for subsequent hot corrosion. However, direct corrosion yielded a defective and non-protective oxide scale, which allowed detrimental penetration of sulfur into substrate. Sulfur migrating along phase boundary was trapped by yttrium to diminish slightly sulphidation. Thus, two advantages of proper pre-oxidation treatment were presented, as keeping repairing for Al₂O₃ scale and inhibiting sulfur penetration.     

超声波开始导入时的熔体温度对Al-Cu合金铸锭组织的影响

研究超声波开始导入时的熔体温度(即熔体过热度)对铝铜合金铸锭组织的影响,分析超声波处理条件下,熔体过热度对铝铜合金铸锭细化率的影响因素.结果表明,随着开始导入时熔体过热度的增加,铸锭的细化效果大幅度地降低.     

Comparison of the oxidation of high-sulfur Ni-25Cr-5Al alloys in as-cast and as-sputtered states

To understand the effect of sulfur on the oxidation of nanocrystalline (NC) alloys, a high-sulfur alloy having a chemical composition similar to a coarse-grained (CG) cast alloy of Ni-25Cr-5Al-1S (wt.%) was fabricated using magnetron sputtering. The oxidation of the two alloys in isothermal and cyclic conditions in air at 1000 °C shows that the alumina scale formed on the cast alloy was susceptible to spallation, whereas the alumina scale on the sputtered alloy was intrinsically adhesive. The result indicates that the nanocrystallization of alloys helps to eliminate the detrimental “sulfur effect” on oxidation, through minimizing the segregation of sulfur to the scale/alloy interface.     

Mg-Y-Ce阻燃镁合金表面膜的阻燃机理

通过同时加入Y和Ce获得了阻燃效果优异的Mg-Y-Ce阻燃镁合金,实现了镁合金在大气条件下的无保护熔炼,Mg-Y-Ce合金由工业纯Mg(99.9%,质量分数)、Mg-25%Y(质量分数)中间合金和纯Ce(99.5%,质量分数)在电阻炉中于保护性气氛(CO2+0.5%SF6)下熔配而成。AES(PHI550 ESCA/SAM)和XRD(X’Pert Pro MPD)表面分析结果表明:当Mg-3Y-4.5Ce阻燃镁合金在高温下暴露于大气中时,其表面膜为双层膜,外层主要由Y2O3组成,而内层Y和Ce含量极低,以Mg和MgO为主。基于高温氧化热力学分析,建立了Mg-Y合金在高温下的选择性氧化模型,获得了Mg-Y合金能够发生选择性氧化的Y浓度阈值(约为7%,质量分数)。分析了Ce在Mg-Y合金选择性氧化中的第三元素效应,Ce起到了吸气剂的作用,可以抑制氧向合金内部扩散,从而抑制Y元素的内氧化。     

新型铝青铜及其喷涂层中Ce元素的作用(英文)

采用一次共装熔炼、砂型铸造Al含量超过Cu-Al二元合金共析点的新型铝青铜合金Cu-14Al-4.5Fe,在45#中碳钢表面制备铝青铜等离子喷涂层。通过扫面电镜、X射线衍射分析、电子探针、透射电镜和显微硬度计分析Ce元素对新型铝青铜合金及喷涂层表面组织形貌和维氏硬度的影响。结果表明:添加0.6%Ce到铸态合金及喷涂层可以使细化的κ相均匀分布于基体,并提高材料硬度。等离子喷涂层快速凝固,保留铝青铜涂层中Fe元素的过饱和固溶体,避免生成(α+γ2)共析相。含Ce喷涂层中的堆垛层错是提高材料力学性能的因素。     

Ce对Fe-Cr合金高温氧化行为的影响

Fe-15Cr 和 Fe-30Cr 合金在1000至1200℃空气中氧化时,表面富铁氧化伤的发展导致保护性Cr_2O_3层衰退,氧化速率增大。添加 Ce 可延迟衰退过程的发生,从而大幅度减低氧化速率。随氧化温度和合金成份变化,Cr_2O_3层衰退的开始时间和发展特征随之改变,Ce 对氧化行为的影响因而呈现出规律性的变化。研究发现,合金中 Cr 的内氧化使 Cr_2O_3层形成小舌包卷合金并使其氧化成富铁氧化物。这是Cr_2O_3层衰退的原因之一。含 Ce 合金中 Ce 的优先内氧化则降低自氧化层进入合金的氧浓度,抑制Cr 的内氧化。氧浓度降低还能促进 Si 的内氧化物在氧化层/合金界面集聚。     

Effect of alloy grain size and silicon content on the oxidation of austenitic Fe-Cr-Ni-Mn-Si alloys in pure O2

Austenitic Fe-18Cr-20Ni-1.5Mn alloys containing 0, 0.6, and 1.5 wt.% Si were produced both by conventional and rapid solidification processing. The isothermal and cyclic oxidation resistance of the alloys were studied at 900°C in pure O₂ to elucidate the role of alloy microstructure and Si content on oxidation properties. The conventionally-processed, large-grained alloy that contained no silicon formed Fe-rich nodules during oxidation. The nodule formation was effectively eliminated by either reducing the alloy grain size by rapid solidification or by adding Si to the alloy. The lowest weight gains were achieved when a continuous silica layer formed between the alloy and the external chromia scale. The formation of the continuous silica layer required a ombination of fine alloy grain size and high Si content. The presence of S in the alloy was found to be detrimental to oxide scale adherence when the silica layer was continuous.     

Ce对铸造Al—Cu合金凝固过程影响的研究

为了探索改善高强度铸造Al-Cu合金抗热裂性能的途径,采用液淬的方法,通过测量热平衡曲线、溶质浓度分布及金相显微分析等手段,研究了0．2％,Ce对Al-4．5Cu和高强度铸造Al-Cu－Mn-Ti合金的凝固过程的影响;研究结果表明,Ce的加入,改变了试验合金的凝固特性影响了合金的枝晶生长行为,其综合作用使合金组织明显细化和均匀化,且二次晶臂发达,对提高高强度铸造Al-Cu合金抗热裂性能具有积极作用。     

离子注入Ce+的Ni20Cr合金在1050℃空气中氧化动力学特征

采用热重分析方法研究了Ni20Cr及经预氧化处理后的合金表面离子注入Ce+后在1050℃空气中的恒温氧化动力学及循环氧化行为.结果表明,离子注入对经预氧化处理后合金氧化行为的影响与合金表面直接注入的效应类似,可降低合金氧化速率和改善氧化膜粘附性.认为抗氧化性能的提高与Ce+改变氧化机制及降低氧化膜/合金界面处因阳离子向外扩散产生的空位数量有关.     

Microwave-assisted synthesis of lanthanum conversion coating on Mg–Li alloy and its corrosion resistance

Lanthanum-based conversion coating on Mg–Li alloy has been prepared by a microwave-assisted method. X-ray diffractions (XRD) indicate that the intermetallic compounds of lanthanum are formed on Mg–Li alloy surface. Scanning electron microscopy (SEM) images show that the coating has different morphologies and special structures. The corrosion resistance was assessed by means of potentiodynamic polarization curves and electrochemical impedance spectra (EIS). The results indicate that this coating significantly reduces the corrosion rate of Mg–Li alloy in NaCl solution. A comparing experiment indicates that the coating prepared by microwave-assisted process has superior corrosion resistance to the coating obtained at room temperature.     

The solidification path related columnar-to-equiaxed transition in Ti–Al alloys

Columnar-to-Equiaxed Transition (CET) of binary Ti–Al alloys and multi-component Ti–48Al–2Cr–2Nb alloys is studied using Bridgman solidification technique. The effect of aluminum concentration and growth rate on CET is determined. It is found in Ti–46Al and Ti–50Al alloy ingots equiaxed grains develop ahead of the moving solid–liquid interface with a growth rate of 500 μm/s; microstructures in Ti–49Al alloy stay columnar dendrites with the same growth rate. CET in Ti–Al alloys are not only influenced by growth rate, but also by the solidification path that is related to alloying composition. CET in Ti–Al alloys is predicted using the dendritic growth model based on the criterion of growth at marginal stability. According to the calculated results and directionally solidified microstructures, values of the nucleation undercooling for α and β phases are given. The growth rates to avoid CET in Ti–48Al–2Cr–2Nb alloy are suggested.     

Effect of Zr on the Oxidation Properties of Fe3Al Intermetallic Compound

This review is concerned with the effect of the addition of zirconium as a third element on the heat-resisting properties of Fe3Al intermetallic compounds and explains their high-temperature oxidation mechanism. The Fe3Al and Fe3Al-0.05Zr specimens were isothermally oxidized in the temperature range of 1173～1473 K in synthetic air for 100 h. The formation of the alumina layer approximately obeyed the parabolic rate law, with the exception of short initial stage. The parabolic rate constant values for the Zr-doped Fe3Al decreased at all tested temperatures. Fe3Al revealed massive spallation, whereas Fe3Al-Zr produced a fiat, adherent oxide layer. The microstructure investigations of the alumina scales grown thermally on the Fe3Al-Zr alloy by means of SEM-EDS showed that they were 1.5～2 μm thick and consisted of a small inner columnar layer and an equiaxed outer grain layer. Additionally, very fine (50～150 um) oxide particles rich in Zr were found across the alumina scales. The addition of Zr significantly affected the oxidation behavior of Fe3Al by improving the adherence of the α-Al2O3 scale. TEM-SAD investigations of the alumina scales on samples prepared using the FIB (Focused Ion Beam) method confirmed the presence of small tetragonal zirconia grains near the scale/gas and alloy/scale interfaces, most of which were formed along alumina grain boundaries(gbs). Zr gb-segregation was found using HRTEM. The role of preferential formation of zirconium oxide along the alumina scale grain boundaries and the effect of Zr gb-segregation on oxidation and scale growth mechanisms were analyzed by means of two-stage oxidation experiments using 16O2/18O2. The SIMS oxygen isotope profiles for the Fe3Al-Zr alloy oxidized at 1373 K, after two-stage oxidation experiments, revealed that oxygen anion diffusion is predominant compared to that of aluminum cation diffusion.