Hard coatings on aluminium alloy surfaces produced using microplasma oxidation

Abstract

The present paper reports on the production of oxide coatings on an aluminium alloy by microplasma oxidation and on their properties. The surface characteristics of the coatings were determined by surface and structural analytical techniques, i.e. SEM and X-ray diffraction. Thermo-analysis of the coatings was evaluated by means of differential scanning calorimetry and thermogravimetric analyses. It was ascertained that the coatings with a mixture of crystallised γ-Al₂O₃ and α-Al₂O₃ have significant microhardness, good electric resistance and good thermostability.     

氧化处理时间对Ti6Al4V微弧氧化陶瓷膜的影响

采用交流微弧氧化法于：Na：SiO3-KOH-(NaPO3)6溶液中在％6A14V表面形成了氧化物陶瓷膜．利用扫描电镜、电子探针及X射线衍射研究了陶瓷膜的组织形貌、元素的分布和相组成．研究表明：在恒定的微弧氧化电参数(U =500V,U-=100V和f=600Hz)下,随氧化时间延长,电流密度逐渐降低,膜层厚度不断增加;相对致密均匀的膜分为3层：过渡层、致密层与疏松层．膜层主要由TiO2(锐钛矿和金红石)相组成,延长处理时间,锐钛矿相及金红石相的相对含量发生变化,金红石相TiO2逐渐增多,而锐钛矿相TiO2减小．膜层相的形成过程可分为两个阶段。     

氧气流量对LY12铝合金微弧氧化膜致密性的影响

通过调整工艺参数与氧气流量在LY12铝合金表面获得均匀、致密的微弧氧化膜层。利用SEM、XRD及电化学工作站等研究膜层的厚度、微观形貌、相组成以及耐腐蚀性能,讨论通氧微弧氧化作用机制,并分析氧气流量对膜层致密性的影响。结果表明:膜层厚度随电压、氧化时间和电解液组分浓度的增加呈规律性变化;氧气的助烧结作用能促进致密层的生长,随着氧气流量的增加,致密层厚度呈现先增加后减小的规律;KF 105g/L,KOH 85g/L,NaAlO_2 12g/L,电压110V,氧化时间15min,氧气流量为0.010L/s时得到厚度30μm的致密膜层,自腐蚀电位提高至-0.11V,腐蚀电流密度下降至2.1×10^-6A/cm^2,比铝合金基体降低2个数量级以上,表现出良好的耐腐蚀性。     

电流密度对复合氧化法制备涂层结构的影响

对TiO2薄膜涂层的结构、形貌、元素组成、硬度进行了观察和测量,研究了电流密度对复合氧化法(即预氧化和微弧氧化复合处理)制备多孔TiO2涂层的结构和性能的影响.结果表明:电流密度对多孔TiO2涂层的结构和性能有很大影响.随着电流密度的增加,涂层的锐钛矿型TiO2含量减少,金红石型TiO2含量增加,涂层表面微孔孔径增加,凹凸起伏变得明显,显微硬度增加,钙磷原子比也发生了变化.当电流密度为20,40,60,80和100 mA/cm2时,涂层的钙磷摩尔比为1.22,1.60,1.89,2.01,2.12.在40 mA/cm2电流密度下可得到结构和性能较理想的多孔TiO2梯度涂层.     

Effect of Al2O3 layer on improving high-temperature oxidation resistance of siliconized TiAl-based alloy

TiAl-based specimens were siliconized with two different kinds of cementation respectively, one is 23 vol.% Si + 77 vol.% Al₂O₃, and the other is 23 vol.% Si + 77 vol.% ZrO₂. SEM observation showed that a Ti₅Si₃-based layer, in which some Al₂O₃ particles dispersed, formed on the surface after siliconization. Further observation showed that an extra outer Al₂O₃ layer existed on the surface of specimens siliconized with 23 vol.% Si + 77 vol.% Al₂O₃, while no such Al₂O₃ layer was found in specimens siliconized with 23 vol.% Si + 77 vol.% ZrO₂. The cyclic oxidation test performed at 900 °C shows that the oxidation resistance was significantly improved by siliconizing. By comparison, the specimens that siliconized with 23 vol.% Si + 77 vol.% Al₂O₃ exhibits a better oxidation resistance than that with 23 vol.% Si + 77 vol.% ZrO₂. It was deduced that the extra outer Al₂O₃ layer is beneficial to the oxidation resistance of siliconized TiAl-based alloy.     

铝合金表面微弧氧化-黑化一体化技术研究

利用交流电源,通过控制电解液组成及其浓度,在恒流条件下实现了铝合金表面微弧氧化-黑化一体化处理.研究显示,钒酸盐对微弧氧化陶瓷膜的黑化效果具有决定性作用.显微硬度及全浸腐蚀测试结果表明:黑色陶瓷膜色泽稳定,具有较高的显微硬度,并能对基体金属提供有效的腐蚀防护.EDX和XRD分析表明,黑色陶瓷膜主要元素组成包括O、Al、Si、V和P,膜中化合物主要以无定形态和/或微晶态形式存在,只发现少量的γ-Al2O3和ε-Al2O3晶体.SEM观察表明,黑色陶瓷膜为较为疏松的单层结构,其表面在微观尺度上粗糙不平,存在较为密集的尺寸为μm量级的微孔,并有明显的高温烧结痕迹和微裂纹.黑色陶瓷膜的微观结构与其形成机制有关.     

Al对GH4169合金冲击性能的影响

研究了Al对GH4169合金晶界相的析出和冲击性能的影响.结果表明,提高Al含量可抑制晶界δ相的析出,促进晶界Laves相、M7C3相和σ相等有害相的析出;随着Al含量的提高,GH4169合金的室温冲击性能明显降低,冲击断口由穿晶型转变为沿晶型.提高Al含量所导致的Laves相等有害脆性相的析出降低了晶界强度,使晶界裂纹更容易萌生和扩展,降低了GH4169合金的冲击韧性.     

Effect of Mo-alloyed layer on oxidation behavior of TiAl-based alloy

A Mo-alloyed layer was prepared on a TiAl-based alloy using plasma surface metallurgy technique. The microstructure and oxidation behavior of the alloyed TiAl were investigated. The surface alloyed layer with a thickness of approx. 40 μm and a gradient concentration distribution was composed of Ti₂MoAl, TiAl and Mo phases. Cycling oxidation test was carried out at 850 °C in air under an atmospheric pressure. The result of the oxidation kinetics test shows that the mass gain of the Mo-alloyed TiAl after exposure for 100 h was less than the value of the untreated TiAl substrate, exhibiting an improved oxidation resistance. The Al₂O₃-rich mixed oxide scale formed on the alloyed TiAl is supposed to be the main reason of the beneficial effect on the improvement of oxidation resistance for TiAl-based alloy.     

Thermal-driven gigantic enhancement in critical current density of high-entropy alloy superconductors

The high-entropy alloy(HEA)superconductor,Ta1/6Nb2/6Hf1/6Zr1/6Ti1/6(Ta-Nb-Hf-Zr-Ti),is systematically studied to examine changes in superconducting critical properties,critical temperature(Tc),critical cur-rent density(Jc),and upper critical field(Hc2),concerning thermal treatment conditions.Annealing condi-tion affects Jc more significantly than Tc and Hc2,with a large improvement of flux pinning force density(Fp).The Jc of bare sample is reduced to 10 A cm-2 at an applied magnetic field of approximately 1.5 T,whereas the sample annealed at 550 ℃ for 12 h exhibits Jc＞100 kA cm-2 up to around 4 T.Furthermore,the Vickers hardness(HVIT)of the Ta-Nb-Hf-Zr-Ti HEA superconductor notably increases from～384 to 528 HVIT following a 24-h annealing at 500 ℃.These results demonstrate that thermal annealing is a powerful process to optimize both the superconducting and mechanical properties of high-entropy alloy superconductors.     

Al元素对Mn-Cu基阻尼合金耐蚀性能的影响

用干湿循环增重法、极化实验研究了Al含量对Mn-Cu基阻尼合金在0.5%NaCl溶液中耐腐蚀性能的影响,并利用SEM、EDS、XRD等手段对Al元素的影响机理进行了分析。结果表明,Al元素的添加使材料的自腐蚀电位(Ecorr)提高,腐蚀电流密度(Icorr)降低,合金的耐蚀性增加;另一方面,含Al元素的Mn-Cu合金腐蚀产物中Al2O3与Cu2O、Mn3O4、Mn2O3协同作用,使腐蚀层结构致密化,有效阻碍了Cl-向基体的扩散,使材料的耐腐蚀性能提高。     

Effect of short-time thermal oxidation on the surface of Al−Li−Cu−Mg alloy (8090) sheet

The oxidation behaviour of 8090 Al−Li alloy sheet was studied after exposure for short times (<5 min) in laboratory air, moist air, moist argon and hydrogen at 530°C. Oxidation was greater at grain boundaries in hydrogen but not in air. Sites of rapid local oxidation (number density 9 to 8 × 10³ cm⁻²) were associated with insoluble particles. Four types of growth morphology were identified with these sites. Some growths believed to be spinel, were 10 to 25 μm diameter and grew to ≈1 mm in height at 2μm sec⁻¹. Pits beneath these growths were ≈25 μm diameter and 10 to 20 μm deep. A qualitative model is proposed for rapid oxidation in Al−Li alloys and the effect of these sites on weight gain measurements, surface contamination and mechanical properties is discussed.     

LY12铝合金微弧氧化陶瓷层的结构和性能

分析了LY12铝合金微弧氧化陶瓷膜的形貌、组成和结构,研究了氧化膜的硬度、与基体的结合强度以及在油润滑和干摩擦这两种条件下的摩擦学行为.结果表明,铝合金微弧氧化膜可分为疏松层和致密层,疏松层由α-Al2O3、γ-Al2O3以及Al-Si-O相组成,致密层由α-Al2O3和γ-Al2O3组成,致密层中α-Al2O3的含量远远高于疏松层.从表层到基体,微弧氧化膜的断面显微硬度先增大后减 小.微弧氧化膜与铝合金基体结合紧密.随着膜厚度的增加,氧化膜的临界载荷线性增加.氧化膜具有优良的抗磨性能,油润滑条件下的摩擦系数仅为干摩擦下的1/10.     

磁控溅射镀Al对NiCrAlY合金层循环氧化性能的影响

通过磁控溅射手段在NiCrAlY合金表面成功制备了1层Al膜,并比较了镀Al粘结层和不镀Al粘结层在1200℃循环氧化的性能.结果表明,磁控溅射镀Al,制得表面Al膜厚度在2μm左右,NiCrAlY合金层内部的组分并无变化.这层Al膜有助于在表面形成1层分布连续、排列紧密的α-Al_2O_3层,降低了合金层的循环氧化增重速率,延长了涂层开裂脱落时间,使NiCrAlY合金表现出了比较好的抗循环氧化性能.     

电流密度对Sm-Fe电沉积膜显微组织及性能的影响

在室温下的水溶液体系中,采用恒流电沉积技术在Cu基体上制备了Sm-Fe合金薄膜。研究了电流密度对沉积膜层的表面形貌、厚度、元素含量以及物相组成的影响,并测试了制备出的Sm-Fe合金膜的磁性能。结果表明,银灰色的沉积膜由金属Sm、Fe及少量的O组成;随着电流密度的增加,膜层中Sm含量呈现先上升后下降的趋势;而Sm含量越多,膜层的表面越平整光亮;沉积膜主要由Sm Fe12、Sm3Fe5O12等化合物组成,电流密度影响了膜层中物相组成的含量,进而影响了膜层的磁性能。     

Al对V-Fe-Ti三元贮氢合金电化学性能的影响

研究了V2.46TiFe0.54Alx(x=0～0.4)贮氢合金的相结构及其电化学性能.XRD分析表明,所有合金均由单一的BCC相结构组成;随Al含量的增加,BCC相的晶格常数逐渐增大.电化学测试结果显示,所有合金电极的放电容量随循环次数的增加均显著降低.由线性极化曲线可以看出,Al基本上对交换电流密度没有影响.经恒电位放电曲线分析表明,氢在合金电极中的扩散系数随Al含量的增加而增大.Al加入后,合金的高倍率放电性能也得到了一定改善.     

Development of Al2O3 scale during oxidation of a wrought nickel-base alloy

Oxidation exposures consisting of 1 min to 1000 h at 950–1150 °C in still air were used to study the development of surface scale on an Ni-16Cr-4.5Al-4Fe-0.04C-0.01Y alloy. Growth kinetics of the oxide scale were studied thermogravimetrically. Scanning electron microscopy and thin-foil analytical electron microscopy combined with energy dispersive X-ray spectroscopy as well as X-ray diffraction were used to characterize the morphology, structure and composition of oxide scale. After a primary stage of rapid kinetics, oxide growth followed a parabolic rate law with an activation energy of about 400 kJ mol^–1. During primary oxidation, the alloy developed an inner layer of Ni(Al, Cr)₂O₄ spinel and the outer scale contained discrete particles of NiO and Cr₂O₃. When steady-state conditions were established, the inner spinel was replaced by a yttrium-modified layer of -Al₂O₃. Under steady-state conditions, oxide growth appeared to be controlled at least partially by outward diffusion of aluminium as indicated by the effect of exposure time on its concentration in the outer scale. Near the oxide-metal interface, yttrium was found to segregate to grain boundaries of -Al₂O₃. Experimental results suggested that yttrium maintained a fine-grained structure of -Al₂O₃ of improved elevated temperature mechanical strength.Haynes is a registered trademark of Haynes International Co.     

Effects of electrolyte concentration and current density on the properties of electro-deposited NiFeW alloy coatings

NiWP alloy coatings were prepared by electrodeposition, and the effects of ferrous chloride (\(\hbox {FeCl}_{2})\), sodium tungstate (\(\hbox {Na}_{2}\hbox {WO}_{4})\) and current density (\(D_{\mathrm{K}}\)) on the properties of the coatings were studied. The results show that upon increasing the concentration of \(\hbox {FeCl}_{2}\), initially the Fe content of the coating increased and then tended to be stable; the deposition rate and microhardness of coating decreased when the cathodic current efficiency (\(\eta \)) initially increased and then decreased; and for a \(\hbox {FeCl}_{2}\) concentration of \(3.6\, \hbox {g\,l}^{-1}\), the cathodic current efficiency reached its maximum of 74.23%. Upon increasing the concentration of \(\hbox {Na}_{2}\hbox {WO}_{4}\), the W content and microhardness of the coatings increased; the deposition rate and the cathode current efficiency initially increased and then decreased. The cathodic current efficiency reached the maximum value of 70.33% with a \(\hbox {Na}_{2}\hbox {WO}_{4}\) concentration of 50 g \(\hbox {l}^{-1}\), whereas the deposition rate is maximum at 8.67 \(\upmu \hbox {m}\,\hbox {h}^{-1}\) with a \(\hbox {Na}_{2}\hbox {WO}_{4}\) concentration of \(40\, \hbox {g\,l}^{-1}\). Upon increasing the \(D_{\mathrm{K}}\), the deposition rate, microhardness, Fe and W content of the coatings increased, the cathodic current efficiency increases first increased and then decreased. When \(D_{\mathrm{K}}\) was 4 A dm\(^{-2}\), the current efficiency reached the maximum of 73.64%.     

Effect of internal oxidation on the mechanical properties of a Cu-Co-Si alloy

The mechanical properties of an internally oxidized Cu-Co-Si alloy of wire form was studied by torsional deformation. It is found that as a result of the internal oxidation the ageing heat-treatments lead to the formation of regions with cylindrical symmetry which have significantly different mechanical properties.