钛合金微等离子体氧化陶瓷膜结构与耐酸腐蚀

在铝酸钠溶液中,利用微等离子体氧化技术,在TC4钛合金表面原位生长复合氧化物陶瓷膜,研究了陶瓷膜的相组成、形貌和陶瓷膜对钛合金耐酸腐蚀的影响。陶瓷膜由Al2TiO5,α-Al2O3和金红石型TiO2构成;整个膜层由致密层和疏松层组成。在盐酸和硫酸中陶瓷膜使得钛合金耐酸腐蚀特性提高了5倍左右。带有陶瓷膜的钛合金在硝酸中的腐蚀速率为膜层的溶解速率。     

超音速火焰喷涂制备Fe基非晶合金涂层的组织与腐蚀性能研究

采用超音速火焰喷涂技术制备了Fe基非晶涂层,通过激光粒度分析仪、X射线衍射仪、扫描电子显微镜等测试技术对Fe基合金粉末以及获得的Fe基涂层的形貌和显微组织结构进行了研究,结果表明,采用合适的喷涂工艺可以获得非晶态的Fe基合金涂层。Fe基非晶合金涂层的耐腐蚀性实验表明,获得的非晶合金涂层具有优异的耐腐蚀性。     

Cyclic oxidation behaviour of plasma sprayed metallic coatings

High temperature Co- and Ni-based metallic coatings of various compositions were applied on SS-310 samples using plasma spray technique. The coated samples were exposed to air under cyclic conditions at 900°C for upto 100?h. Adhesion of coatings was measured using standard ASTM C 633-79 method. Scanning electron microscopy coupled with energy dispersive X-ray spectroscopy was used to determine the surface morphology and microchemical constitution of coatings. X-ray diffraction was used to identify different phases formed during oxidation. Experimental results indicated that high temperature oxidation of SS-310 alloy was greatly reduced by all coatings. The plasma sprayed metallic coatings on SS-310 alloy performed better than that of bare SS-310 under the selected test conditions. Moreover, when compared among the selected metallic coatings used in the study, the Co-based coatings with higher Cr concentration exhibited superior performance compared to Ni-based coating with lower Cr concentration during the reported cyclic exposure.     

非晶陶瓷涂层对耐高温液锌涂层耐腐蚀性能的影响

热镀锌技术是钢铁材料表层最为有效的防腐蚀手段。为进一步提高耐锌蚀涂层的使用寿命,采用等离子喷涂技术在熔锌装备表面制备了多级耐锌蚀复合涂层及非晶陶瓷涂层,并利用XRD和SEM对其物相组成、结构及形貌进行了研究。结果表明,非晶陶瓷涂层与熔融锌液存在着不浸润,但耐锌蚀涂层仍然会被腐蚀,镀锌装备内部由于存在温度差使得熔融锌液会进行上下、左右的流动,对非晶层会产生冲刷作用,长时间的冲刷会使非晶层变薄,直至消失。非晶陶瓷涂层的制备在一定程度上降低了加热管的导热性,但可以通过加大功率来进行弥补,封孔后的耐锌蚀涂层的热震性能提高了6倍,使用寿命是原来的2.2倍,延长寿命效果显著。     

AZ91D镁合金表面电沉积n-ZrO2/Ni复合镀层及耐蚀性研究

在AZ91D镁合金表面化学镀Ni-P的基础上电沉积n-ZrO2/Ni复合镀层和纯Ni电镀层,并对其表面形貌、截面形貌和耐蚀性进行了对比分析。结果表明AZ91D镁合金表面电沉积纳米复合镀层比纯镍镀层组织更细小,镀层更致密、平整。n-ZrO2/Ni复合镀层具有明显的钝化区,具有良好耐蚀性。     

TiAl合金表面激光重熔热障涂层组织及抗高温氧化性能

为了进一步提高TiAl合金表面等离子喷涂ZrO2-7%(质量分数)Y203热障陶瓷涂层的性能,采用激光重熔工艺对涂层进行处理,研究了激光重熔对涂层微观组织和抗高温氧化性能的影响.用扫描电镜(SEM)分析了涂层形貌和微观结构,同时对其抗高温(850℃)氧化性能进行了考察.结果表明,等离子喷涂热障陶瓷涂层呈典型的层状堆积特征,有一定的孔隙且分布有微裂纹;经过激光重熔处理后,陶瓷涂层片层状组织得以消失,致密性提高,获得了基本没有裂纹等缺陷的重熔层;整个重熔层包括界面没有明显特征的平面晶和上部沿热流方向生长的柱状晶组织.等离子喷涂热障涂层具有较好的抗高温氧化性能,经过激光重熔后可进一步提高其抗高温氧化能力.     

Structure and corrosion resistance of nickel coatings containing tungsten and silicon powders

Ni + W + Si coatings were prepared by nickel deposition from a bath containing a suspension of tungsten and silicon powders. These coatings were obtained at galvanostatic conditions, at the current density of j_dep = − 0.100 A cm^− 2 and at the temperature of 338 K. For determination of the influence of phase composition and surface morphology of these coatings on changes in the corrosion resistance, these coatings were modified in an argon atmosphere by thermal treatment at 1373 K during 1 h. A scanning electron microscope was used for surface morphology characterization of the coatings. The chemical composition of the coatings was determined by EDS and phase composition investigations were conducted by X-ray diffraction. It was found that the as-deposited coatings consist of a three-phase structure, i.e., nickel, tungsten and silicon. The phase composition for the Ni + W + Si coatings after thermal treatment is markedly different. The main peaks corresponding to Ni and W coexist with the new phases: NiW, NiWSi and a solid solution of W in Ni.Electrochemical corrosion resistance investigations were carried out in 5 M KOH, using potentiodynamic and electrochemical impedance spectroscopy (EIS) methods. On the basis of these investigations it was found that the Ni + W + Si coatings after thermal treatment are more corrosion resistant in alkaline solution than the as-deposited coatings. The reasons for this are a reduction in the amount of free nickel and tungsten, the presence of new phases (in particular polymetallic silicides), and a decrease of the active surface area of the coatings after thermal treatment.     

铝合金表面激光熔覆铜镍合金涂层的组织、硬度与耐蚀特性研究

为提升铝合金材料的耐蚀性能,探究铝合金与合金熔覆层间的结合机理,本文利用激光熔覆技术在5083铝合金表面制备了不同Ni含量的铜镍合金熔覆层,并利用扫描电子显微镜、X射线衍射分析、硬度测试与电化学性能测试技术,分析了不同Ni含量的铜镍合金熔覆层相组成与组织形貌、铜镍合金熔覆层与铝合金基体的界面组织形貌,绘制了铝元素扩散曲线,分析了海水腐蚀过程中铜镍合金熔覆层的极化曲线。实验结果表明：所制备的铜镍合金熔覆层形貌良好无缺陷,熔覆层由网络状枝晶组成。对合金熔覆层进行XRD分析发现熔覆层主要由AlNi₃与CuNi两相组成。结合SEM、EDS分析,发现合金熔覆层的网络状枝晶为富铝相,即AlNi₃,晶间相为CuNi相。在硬度测试中,由于AlNi₃硬质相的生成,熔覆层硬度得到了提升且随着铝的向上扩散呈现一定的规律,电化学检测结果表明,铜镍合金熔覆层具有比5083铝合金更高的自腐蚀电位和较小的自腐蚀电流密度,可以有效提升5083铝合金在海水环境中的耐蚀性。     

二元配合物中电镀锌镍合金的结构与抗腐蚀性

为深入了解碱性锌酸盐体系的工艺参数对锌镍合金镀层结构和耐蚀性的影响,在以四乙烯五胺(TEPA)为镍离子主络合剂、三乙醇胺(TEA)为辅助络合剂的碱性镀液中电沉积制备了锌镍合金镀层,利用电子能谱、X射线衍射、极化曲线和电化学阻抗谱等方法表征镀层的组成结构和在氯化钠溶液中的耐腐蚀性.结果表明:镀层含镍原子数分数11.54%~20.12%,为γ-Ni2Zn11+纯Zn两相结构(低含镍原子数分数时)或单一γ相结构(较高含镍原子数分数时),γ相晶粒在(600)方向上具有不同程度的择优取向性;随着镀液中镍原子数分数的提高,镀层的腐蚀电位正移,阻抗增加,耐蚀性提高;当电流密度为2 A/dm2时,镀层的腐蚀电位和电荷传递电阻最高,耐蚀性最好.     

Enhancement of oxidation and wear resistance of Fe-based amorphous coatings by surface modification of feedstock powders

Surface oxidation of the in-flight powders during the preparation of amorphous coatings in high velocity oxygen fuel process causes the formation of oxygen-rich intersplat regions. These regions are brittle in nature and can dramatically deteriorate the mechanical performance of the coatings. To solve this problem, the starting FeCrMoCBY amorphous feedstock powders were modified by electroless plating a thin layer of Ni–W–P amorphous phase. It was found that the covering of the Ni–W–P layer can significantly reduce the oxygen content in the resultant Fe-based amorphous coatings. The wear resistance of the coatings with and without the modification of Ni–W–P thin layer was comparatively studied by ball-on-disk wear tests against Si₃N₄ counterpart in air. It revealed that the wear of two types of coatings follows the same oxidation wear mechanism but the modified coating exhibits much better wear resistance due to the improved oxidation resistance.     

Evaluation of hot corrosion resistance of HVOF coatings on a Ni-based superalloy in molten salt environment

High-velocity oxy-fuel (HVOF) has the advantage of being a continuous and most convenient process for applying coatings to industrial installations at site. In this study, Cr₃C₂–NiCr, NiCrBSi, Stellite-6 and Ni–20Cr coatings were deposited on a Ni-based superalloy (19.5Cr–3Fe–0.3Ti–0.1C–balance Ni) using an HVOF process. Hot corrosion studies were performed on bare as well as coated superalloy specimens after exposure to a molten salt environment at 900 °C under cyclic conditions. The thermogravimetric technique was used to establish the kinetics of corrosion. XRD, SEM/EDAX and EPMA techniques were used to analyse the corrosion products. The hot corrosion resistance of all the coatings were superior to bare superalloy. Among the coatings studied, the Ni–20Cr coated superalloy imparted maximum hot corrosion resistance, whereas the Stellite-6 coated indicated minimum resistance. The hot corrosion resistance of all coatings may be attributed to the formation of oxides and spinels of nickel, chromium or cobalt.     

Electrodeposition and mechanical and corrosion resistance properties of Ni-W/SiC nanocomposite coatings

Ni-W/SiC nanocomposite coatings with various contents of SiC nano-particulates were prepared by electrodeposition in Ni-W plating bath containing SiC particulates. The influences of the SiC nano-particulates concentration, current density and stirring rate of the plating bath on the composition of the nanocomposite coatings were investigated. The surface morphologies of the Ni-W alloy and Ni-W/SiC nanocomposite coating were observed using a scanning electron microscope (SEM). The morphology of Ni-W/SiC nanocomposite coating is smoother than that of Ni-W alloy coating. The microhardness of composite coatings increases with the increasing content of the SiC nano-particulates in the coatings. The corrosion behavior of Ni-W alloy and Ni-W/SiC nanocomposite coatings was evaluated by the anodic polarization curves in 0.5 mol/L NaCl solution at room temperature. It shows that Ni-W/SiC nanocomposite coating has better corrosion resistance than the Ni-W alloy coating.     

Deposition and corrosion behavior of silicate conversion coatings on aluminum alloy 2024

Potassium silicate was deposited on AA2024 aluminum alloy as environmentally friendly conversion coatings and its corrosion behavior were examined by means of electrochemical impedance spectroscopy, potentiodynamic polarization and surfaces techniques. Potentiodynamic polarization curves show significant decrease in corrosion current density of silicate coated aluminum in NaCl solution. The corrosion resistance was increased with increasing silicate concentration of coating baths. The results indicated that the coating applied from 3 molar silicate baths is more uniform and continuous. The X‐ray diffraction (XRD) and energy discharge spectroscopy (EDS) spectra confirm the existence of silicate film on the AA2024 surface. The coating performance was evaluated in acidic and basic NaCl solution and the results show the stability of silicate conversion coating in these solutions.     

纳米粉体制备8YSZ电解质工艺性能研究

实验研究了纳米粉体制备8YSZ电解质的固相烧结过程。根据阿基米德原理测瓷体密度；通过测定烧结前后瓷片尺寸，求出烧结线收缩；采用四端电极法测瓷体的电导率；使用扫描电子显微镜(SEM)观测样品微观形貌，并探讨了YSZ纳米粉体烧结的动力学过程。由于纳米颗粒尺寸较细、粒度分布均匀、无硬团聚和很好的球形度，使得烧结温度大幅度降低。实验表明，最佳烧结温度为1450℃，此时材料致密，相对密度在97％以上；气孔含量少、晶粒均匀，电导率高，1000℃时为0．162Ω^-1cm^-1，是理想的高温电解质材料。     

高强度铸造钛合金的耐空蚀性能

采用不同的试验方法对高强度铸造钛合金的耐空蚀性能进行了探讨研究。结果表明，该合金具有优良的耐空蚀性能，是处于空蚀条件下工作的高速旋转件的理想材料。     

Wear resistance of plasma coatings for a constant work of friction

We analyze the wear resistance of plasma coatings for a constant work of friction. The dependences of the wear resistance of the coatings are obtained for a broad range of loading conditions. It is shown that the minimum sensitivity to loading conditions is exhibited by the molybdenum coatings. It is also established that the wear resistance of the coatings decreases as the amplitude of displacements increases and the cyclic frequency of the tests decreases due to the intensification of fatigue processes on the surfaces. The comparative characteristics of coatings are presented. __________ Translated from Problemy Prochnosti, No. 5, pp. 94–100, September–October, 2007.     

Fatigue of VT20 titanium alloy with vacuum-plasma coatings at high temperatures

We study the influence of vacuum–plasma TiN, (TiAl)N, and (TiC)N coatings on the high-cycle fatigue of VT20 titanium alloy in the temperature range 350–640°C for a loading frequency of 10 kHz. It is shown that, in this temperature range, the fatigue limits of VT20 alloy with the indicated coatings 6 μm in thickness become 15–25% higher than for the material without coating. The possibility of replacement of steel blades with titanium blades with vacuum-plasma coatings is demonstrated. Translated from Problemy Prochnosti, No. 4, pp. 101–107, July–August, 2009.     

Influence of remelting on microstructure,hardness and corrosion behaviour of AlCoCrFeNiTi high entropy alloy

Abstract

High entropy alloys are a newly developed class of alloys, which tend to form a single solid solution or a mixture of solid solutions with simple crystal structures. These alloys possess excellent mechanical properties, thermal stability and corrosion resistance. In the present paper, an AlCoCrFeNiTi high entropy alloy was obtained by induction melting, and the influence of the remelting process on the mechanical and corrosion resistance characteristics of the alloy was investigated. Thus, optical and scanning electron microscopy revealed less phase segregation and a fine dendritic structure for the remelted alloy, while corrosion tests indicated that present alloy, in remelted state, has better corrosion resistance than as cast alloy and stainless steel. The Vickers microhardness measurements demonstrated an improvement of the alloy microhardness by remelting process due to the decrease in phase segregation and the increase in dendrite refinement level.     

电沉积Co-Ni合金镀层结构及硬度的研究

采用氨基磺酸体系电解液电沉积Co-Ni合金，研究了电解液中钴、镍金属离子浓度与合金镍层中钴含量的关系。利用扫描电子显微镜和X射线衍射分析测定了不同钴含量沉积层的微观形貌和晶体结构，同时研究了合金沉积层显微硬度和合金成份的关系及热处理的影响。实验结果表明：电解液中Co^2 /(Co^2 Ni^2 ）在0.1-0.5的范围内时，钴离子的优先共沉积的趋势最强。SEM观察结果和XRD分析测试表明，随着钴镍合金沉积层中钴含量的不断增加，低钴含量合金层粗大的颗粒状结晶逐渐转变为细致、均匀的三角形状结晶，最终又形成中等大小的颗粒状结晶。同时合金层中钴含量的逐渐增加，结构由fcc镍固溶体过渡为fcc的钴固溶体，最后转变为hcp的钴固溶体。并且在形成两个钴固溶体的钴含量范围内（20％－50％和60％－80％），所对应的钴镍合金层的硬度值远大于低钴含量区所具有fcc镍固溶体结构的合金层硬度。     

A novel refractory WMoVCrTa high-entropy alloy possessing fine combination of compressive stress-strain and high hardness properties

Refractory high-entropy alloys (HEAs) possess outstanding mechanical strength at room and high temperature but lack the room temperature ductility. A novel refractory equiatomic powder combination of WMoVCrTa was selected and verified for the feasibility of formation of solid solutions or else bulk-metallic glasses (BMGs) in the alloy based on the Guo et al.’s criteria and mismatch entropy criterion. The powder combination satisfies the above two criteria to crystallize in solid solution phases and inhibit the BMGs. Mechanical alloying characteristics of the powder mixture were determined. The particle size of the powder mixture decreased continuously during initial milling and later increased after 32 h of mechanical alloying. A homogeneous mixture was obtained after milling for 64 h. Crystallite sizes of the constituent elements in the powder mixture decreased continuously on progressive milling. A nanocrystalline powder was obtained by mechanical alloying. The powder milled for 64 h revealed a major BCC1, a minor BCC2 and small unknown phases. The lattice parameters of those BCC1 and BCC2 phases are 3.16 Å and 2.88 Å respectively. The alloy ingots were fabricated from the milled powder by vacuum arc melting technique followed by heat treatment. The ingot crystallizes in three phases such as a major BCC1, a minor BCC2 and a minor laves phase. The lattice parameters of these BCC1 and BCC2 phases are 3.05 Å and 2.85 Å respectively. Thereby, the BCC1 lattice of the milled powder contracts slightly after ingot fabrication. A fine combination of compressive stress and strain of 995 MPa and 6.2% respectively was achieved by the alloy at room temperature. Vickers hardness of the alloy was as high as 773 ± 20HV0.5. The density of the alloy was 11.52 g/cm³. The combination of excellent room temperature stress-strain and high hardness properties can enable the refractory HEA as a potential candidate for structural applications.