Ti活度对Al2O3/AgCuTi/Fe-Ni-Co钎焊接头机械性能和微观组织结构的影响

采用AgCuTi钎料实现了Al₂O₃陶瓷与Fe-Co-Ni合金的钎焊连接,并调查了不同钛含量的钎料对Al₂O₃/AgCuTi/Fe-Ni-Co钎焊接头机械性能和微观组织结构的影响。扫描电子显微镜(SEM), X射线能量色散光谱仪(EDS), X射线衍射仪(XRD)及电子万能试验机用于分析钎焊接头的机械性能和微观组织结构,结果表明:钛含量的增加明显提高AgCuTi钎料与Al₂O₃陶瓷的相互作用,在Al₂O₃/Ag-Cu-Ti界面生成一层由Ti-Al 和 Ti-O化合物组成的反应层。Al₂O₃/AgCuTi/Fe-Ni-Co钎焊接头的抗拉强度随钛含量的增加而增加,当钛含量提高到8wt.%时,抗拉强度达到最大值78Mpa。通过微观组织结构分析发现,采用AgCu4Ti在890℃保温5min的条件下可以获得较好的钎焊接头,典型接头的微观组织结构为Al₂O₃/TiAl+Ti₃O₅/NiTi+Cu₃Ti+Ag(s,s)/Ag(s,s)+Cu(s,s)+(Cu,Ni)/Fe-Ni-Co。采用AgCu8Ti获得的钎焊接头的界面反应层与AgCu4Ti差异不大,但反应层稍微增厚,并伴有TiO和Ti3Al在Al₂O₃/Ag-Cu-Ti界面生成。     

ZrCr梯度界面层对Zr/Al2O3涂层体系抗热震性能影响及机理研究

采用中频磁控溅射和超音速等离子喷涂依次在锆合金(Zr-4)基体表面制备了Zr(84.61 at.%)Cr/Zr(17.39 at.%)Cr/Al₂O₃(ZrCr梯度界面层)和Al₂O₃ (无ZrCr梯度界面层)涂层。利用XRD、SEM和HRTEM等重点分析了ZrCr梯度界面层对Zr-4/Al₂O₃涂层界面微观结构、结合强度和抗热震性能的影响。研究结果表明：通过增设ZrCr梯度界面层,能显著提升Zr-4/ZrCr/Al₂O₃体系结合强度至50.3±2.52 MPa,较Zr-4/Al₂O₃体系结合强度值提升约46%;循环热震条件下,Zr-4/ZrCr/Al₂O₃体系膜基界面完整,与ZrCr梯度界面层能显著提升界面结合强度且喷涂及热震实验过程中ZrCr梯度界面层Cr原子优先形成较致密的Cr₂O₃能进一步有效抑制氧扩散至Zr-4有关;Zr-4/Al₂O₃膜基界面则出现明显开裂甚至剥离行为,其主因是Zr-4/Al₂O₃两者界面热应力集中而导致Zr-4/Al₂O₃界面开裂;HRTEM和EDS线扫描结果证实在Zr-4/Al₂O₃界面开裂处形成的疏松ZrO₂氧化物是后续热震循环中进一步加剧涂层大面积剥落失效的根本原因。     

原位颗粒对近液相线铸造6063铝合金微观组织和耐磨性的影响机理

以CuO-Al作为反应体系,在6063铝合金中原位反应生成Al₂O₃颗粒,采用近液线相铸造的方法制备6063Al-XAl₂O₃(X=0,2,4,6)复合材料。研究原位反应颗粒Al₂O₃与6063铝合金自带的原位结晶颗粒Mg₂Si的形状、尺寸、数量、分布、界面特征等对合金微观组织和耐磨性的影响机理。结果表明,在6063铝合金中原位反应生成尺寸在亚微米级的近球形θ-Al₂O₃颗粒;其(311)晶面与6063铝合金基体(111)晶面成共格界面;6063铝合金中Mg₂Si尺寸大约为100nm,呈条带状,其(02-2)与Al基体(111)晶面属于共格界面。随着Al₂O₃颗粒含量的增加,6063铝基复合材料的晶粒组织形貌由蔷薇状逐渐向等轴晶转变,晶粒尺寸逐渐减小。当Al₂O₃的质量分数为6%时,复合材料组织由等轴晶和细小的柱状晶组成。载荷为50N时,6063铝合金的磨损量为6.72mg,6063-6Al₂O₃复合材料的磨损量为1.63mg,相对于6063铝合金降低75.7%。原位颗粒(Al₂O₃+Mg₂Si)与铝基体都成共格界面,界面之间无污染,界面结合强度高,在磨损过程中,不易从基体中脱落,承当磨损过程中的大部分载荷。原位生成高硬度的Al₂O₃颗粒与原位结晶颗粒Mg₂Si协同作用共同提高复合材料的耐磨性。外加载荷为40N时,随着增强相质量分数的增加,复合材料的磨损机制由粘着磨损转变为磨粒磨损。6063铝合金磨损机制以严重的粘着磨损为主。6063-2Al₂O₃复合材料磨损机制主要以粘着磨损为主,6063-4 Al₂O₃和6063-6Al₂O₃复合材料主要表现为磨粒磨损。     

HOPG上ALD沉积Al2O3介电薄膜的生长行为研究

本文采用原子层沉积(ALD)的方法,选择三甲基铝(TMA)和H₂O₂作为反应前驱体,在高定向热解石墨(HOPG)基体上沉积Al₂O₃。系统研究了反应温度和生长周次对Al₂O₃生长行为的影响。研究表明：受HOPG表面饱和成键的影响,Al₂O₃在衬底表面处形核困难,在生长初期主要表现为台阶处择优生长,其形态为线状结构。当沉积100周次Al₂O₃时,其中在沉积温度为50 °C、150 °C和200 °C时呈现为纳米线状结构,而在100 °C时呈现为非连续薄膜。随着生长周次的增加,不同温度下沉积态Al₂O₃都趋于形成连续薄膜,表明其生长行为发生了由三维岛状生长模式向二维平面生长模式的转变。分析认为,生长模式的转变是由纳米线状结构横向生长造成的;横向生长速率主要受生长温度影响。拉曼结果表明：沉积后的石墨烯层结构未受影响,可保留其原有的优越性能。     

基于磁过滤技术的热障涂层表面Al2O3 覆盖层抗CMAS腐蚀性能

为了提高热障涂层（TBC）的抗沉积物（主要成分为CaO、MgO、Al₂O₃和SiO₂,简称CMAS）腐蚀性能,采用磁过滤阴极真空电弧（FCVA）技术在TBC表面上制备了致密的Al₂O₃覆盖层,比较和分析了Al₂O₃改性TBC和沉积态TBC的润湿行为和抗CMAS腐蚀性能。结果表明：使用FCVA技术制备Al₂O₃覆盖层的过程对7%（质量分数）氧化钇稳定的氧化锆（7YSZ）相的结构无明显影响,且经Al₂O₃改性的TBC综合性能均优于沉积态TBC。在1250 ℃、CMAS腐蚀条件下,Al₂O₃覆盖层有效地限制了熔融CMAS在TBC表面上的扩散行为。同时,Al₂O₃填充了7YSZ柱状晶之间的间隔并且阻碍了熔融CMAS的渗透,证明了FCVA可作为一种制备Al₂O₃涂层的新方法以提高TBC的抗CMAS腐蚀性能,且Al₂O₃涂层及其制备过程对TBC的热震性能均无消极影响。     

CoCrNiAlY涂层制备工艺对组织形态及高温氧化行为的影响

为了研究CoCrNiAlY涂层微观组织结构对高温氧化行为和剥落行为的影响规律,采用激光熔覆技术和等离子喷涂工艺在718高温合金表面制备CoCrNiAlY涂层,观察其微观组织形态。利用XRD和SEM对1150 ℃高温氧化试验样品进行氧化层物相分析和形貌观察。结果表明,激光熔覆制备的CoCrNiAlY涂层中形成了胞状亚结构的等轴晶凝固组织,相对于等离子喷涂制备的CoCrNiAlY涂层结构更致密,具有更优异的抗高温氧化性能。在高温氧化过程中,等离子喷涂CoCrNiAlY涂层生成了以Cr₂O₃结构为主的复合氧化膜。激光熔覆CoCrNiAlY涂层生成Al₂O₃结构的单一氧化膜,而且熔覆层中原位形成的Y₂O₃钉扎作用能有效提高氧化膜的抗剥落性。文中系统分析讨论了两种不同工艺制备的组织形态对高温氧化膜形成机制的影响,激光熔覆涂层在高温下主要是以界面扩散方式形成致密的Al₂O₃膜,等离子喷涂涂层在高温下以界面反应的方式快速形成Cr₂O₃复合氧化膜。     

BN/Al2O3 复合粉末及其聚合物基复合材料的制备与导热性能

采用固-液相共混法制备了多种BN/Al₂O₃复合粉末,通过冻融法和表面修饰法对BN进行了改性处理,改变表面修饰剂类型和摩尔比得到了前驱体和烧结态BN/Al₂O₃复合粉末,并利用机械混合法制备了聚合物基BN/Al₂O₃复合材料,并测试分析了其导热性能。结果表明,经冻融处理的BN分散性和界面相容性明显优于未经冻融处理的BN。多巴胺对BN的改性效果优于聚乙二醇。采用多巴胺作为表面修饰剂且BN与Al(NO₃)₃的摩尔比为1:1时,能够得到纳米Al₂O₃均匀包覆的微米BN粉末,即BN/Al₂O₃微纳复合粉末,其聚合物基复合材料的导热系数可达0.62 W·m^-1·K^-1,是纯聚合物导热系数的3倍,是采用纯微米BN粉末制备的聚合物基复合材料导热系数的1.5倍。在BN表面附着的Al₂O₃可以形成层状热传导通道,能够有效提高聚合物基BN/Al₂O₃复合材料的热导率。     

Al2O3微粉添加量对镁合金微弧氧化膜特性影响研究

为了研究添加Al₂O₃微粉对AZ31A镁合金微弧氧化膜特性影响,在不同浓度Al₂O₃微粉电解液中对其进行了微弧氧化处理。利用扫描电镜(SEM)观察微弧氧化膜形貌,能谱仪(EDS)分析了膜层表面Ca、Mg、O、Al元素分布,X射线衍射仪(XRD)分析了相组成,测定了膜厚、硬度和氧化液中Al₂O₃表面电荷,讨论了掺杂改性机理。结果表明,加入Al₂O₃微粉后,氧化电压随Al₂O₃添加量增加先增加后降低;氧化膜表面孔洞数量和尺寸减小,膜层表面Ca元素分布逐渐减少,成膜效率降低,膜层致密度和表面疏松层硬度提高,氧化膜主要由MgO和MgO₄等相组成。     

铝基表面等离子喷涂Al2O3-TiO2-Ta涂层的制备及防腐性能

采用等离子喷涂技术在铝基表面构建Al₂O₃-TiO₂涂层和Al₂O₃-TiO₂-Ta涂层。由于钽元素的引入,Al₂O₃-TiO₂-Ta涂层表面形貌更均匀、致密。同时钽金属具有极强的耐酸碱特性,因此,Al₂O₃-TiO₂-Ta涂层相对于Al₂O₃-TiO₂涂层具有更强的耐腐蚀性。Tafel曲线结果显示,Al₂O₃-TiO₂涂层使得基体的腐蚀电位仅正移了99.6 mV,Al₂O₃-TiO₂-Ta涂层使得铝基体腐蚀电位正移了208.9 mV。因此,由于耐蚀性极强的Ta金属的掺入,Al₂O₃-TiO₂涂层的防腐性得到了极大的增强,Al₂O₃-TiO₂-Ta涂层有效地防止铝合金腐蚀。     

γ-TiAl合金表面Al2O3/Al复合涂层的抗高温熔盐腐蚀性能研究

采用磁控溅射技术于γ-TiAl合金表面制备Al₂O₃/Al复合涂层。在850 °C下、 100 wt.% Na₂SO₄熔盐中观测Al₂O₃/Al复合涂层的高温腐蚀行为。结果表明,Al₂O₃/Al复合涂层具备由Al₂O₃表层、富Al中间层以及互扩散层组成的梯度结构,因而有效地提高了基体γ-TiAl合金的抗高温腐蚀性能。在腐蚀实验后,涂层试样表面相结构为Al₂O₃,TiO₂和TiAl₃。致密的Al₂O₃/Al复合涂层有效地抑制了O_2-,S_-和Na₊对基体γ-TiAl合金的侵蚀。并且,Al₂O₃/Al复合涂层的梯度结构亦使其表现出了优异的抗开裂和抗剥落性能。     

Comparison of corrosion resistance between Al2O3 and YSZ coatings against high temperature LiCl-Li2O molten salt

In this study, the high-temperature corrosion resistance of plasma-sprayed ceramic oxide coatings has been evaluated in a LiCl-Li₂O molten salt under an oxidizing environment. Al₂O₃ and YSZ coatings were manufactured by atmospheric plasma spraying onto a Ni alloy substrate. Both the plasma-sprayed Al₂O₃ and YSZ coatings had a typical splat quenched microstructure which contained various types of defects, including incompletely filled pores, inter-splat pores and intra-splat microcracks. Corrosion resistance was evaluated by the thickness reduction of the coating as a function of the immersion time in the LiCl-Li₂O molten salt at a temperature of 650 °C. A linear corrosion kinetic was found for the Al₂O₃ coating, while no thickness variation with time occurred for the YSZ coating. The ceramic oxide coatings were reacted with LiCl-Li₂O molten salt to form a porous reaction layer of LiAl, Li₅AlO₄ and LiAl₅O₈ for the Al₂O₃ coating and a dense reaction layer of non-crystalline phase for the YSZ coating. The reaction products were also formed along the inside coating of the porous channel. The superior corrosion resistance of the YSZ coating was attributed to the formation of a dense protective oxide layer of non-crystalline reaction products on the surface and at the inter-splat pores of the coating.     

Sliding Wear Performance of Plasma-Sprayed Al2O3-Cr2O3 Composite Coatings Against Graphite under Severe Conditions

Al₂O₃, Cr₂O₃, and Al₂O₃-Cr₂O₃ composite coatings were produced by plasma spraying. Their tribological properties were evaluated at high load conditions. The average friction coefficients, wear rates, and worn surface temperatures of the coating/graphite pairs were measured. Compared with the single coating/graphite pairs, the friction coefficients of composite coating/graphite pairs are more stable. The corresponding wear rates and worn surface temperatures are lower, which may be conducive to the formation of more effective and stable graphite transfer film on the surface of the coating subjected to abrasion. Especially, 10wt.%Al₂O₃-90wt.%Cr₂O₃ (AC₉₀) composite coating shows better anti-wear performance, which may be attributed to its higher thermal conduction.     

陶瓷壳型面层材料与Ti46Al1B阀门铸件的界面反应

分别采用Al2O3与Y2O3为壳型面层材料,离心铸造了Ti46Al1B(原子分数,%)合金阀门铸件,通过SEM,XRD以及气体分析等方法,确定壳型内表面物相组成、铸件与壳型反应层厚度以及合金的进氧情况,分析了壳型材料与Ti46Al1B合金的反应机理.结果表明,Y203和A120s壳型与合金的反应层厚度分别约为90和170 pm,使用Y203壳型时铸件进氧少,其热力学稳定性好于Al2O3壳型,与热力学计算结果相符.Y2O3壳型比Al2O3壳型更适合铸造Ti46Al1B阀门.     

Oxidation resistance and corrosion behavior of hot-dip aluminized coatings on commercial-purity titanium

Aluminizing is an effective method to protect alloys from oxidation and corrosion. In this article, the microstructure, morphology, phase composition of the aluminized layers and the oxide films were investigated by SEM, EDS and X-ray diffraction. The high temperature oxidation resistance and electrochemical behavior of hot dip aluminizing coatings on commercial-purity titanium had been studied by cyclic oxidation test and potentiodynamic polarization technique. The results show that the reaction between the titanium and the molten aluminum leads to form an aluminum coating which almost has the composition of the aluminum bath. After diffusion annealing at 950 °C for 6 h, the aluminum coating transformed into a composite layer, which was composed of an inner layer and an outer layer. The inner layer was identified as Ti₃Al or Ti₂Al phase, and the outer layer was TiAl₃ and Al₂O₃ phase. The cyclic oxidation treatment at 1000 °C for 51 h shows that the oxidation resistance of the diffused titanium is 13 times more than the bare titanium. And the formation of TiAl₃, θ-Al₂O₃ and compact α-Al₂O₃ at the outer layer was thought to account for the improvement of the oxidation resistance at high temperature. However, the corrosion resistance of the aluminized titanium and the diffused titanium were reduced in 3.5 wt.% NaCl solution. The corrosion resistance of the aluminized titanium was only one third of bare titanium. Moreover, the corrosion resistance of the diffused titanium was far less than bare titanium.     

Noncontaminating plasma arc sprayed crucible coatings for containing molten ceramic oxides

A study was performed to assess the suitability of several plasma arc sprayed coatings applied to graphite crucibles for melt processing AI₂O₃ZrO₂, AI₂O₃ Y₂O₃, and AI₂O₃ ceramics. Coatings of W, Ta over W, and Re over W were evaluated. Pressed compacts of AI₂O₃ ZrO₂, AI2O3Y2O3, and AI₂O₂ were each placed in refractory metal-coated graphite crucibles and heated to 2040,2150, and 2200 ‡, respectively. Compatibility of the coating/ceramic oxide systems was evaluated by optical and scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and combustion chromatography. The Ta over W coating system was chemically nonreactive with all three molten oxides studied.     

Development of a Pre-Oxidation Treatment to Improve the Adhesion between Thermal Barrier Coatings and NiCoCrAlY Bond Coatings

High-temperature coating systems, consisting of a René N5 superalloy, a Ni–23Co–23Cr–19Al–0.2Y (at.%) bond coating (BC), and a yttria (7 wt%)-stabilized zirconia (YSZ) thermal barrier coating (TBC), were thermally cycled to failure for seven different controlled pre-oxidation treatments and one commonly employed industrial pre-oxidation treatment to establish the preferred microstructures of the thermally-grown oxide (TGO) on a NiCoCrAlY bond coating after pre-oxidation. It was found that the failure of the coating system occurred along the TGO/BC interface when the TGO attained a critical thickness, except if a NiAl₂O₄ spinel layer developed contiguous to the TBC/TGO interface. Then, the coating system failed at a smaller TGO thickness along the NiAl₂O₄/α-Al₂O₃ interface. The value for the TGO thickness at failure increased for a larger area fraction of Y-rich oxide pegs at the TGO/BC interface after pre-oxidation. A desired slow-growing oxide layer on the BC surface was promoted when the presence of the oxides NiAl₂O₄, θ-Al₂O₃, Y₃Al₅O₁₂ at the TGO surface after pre-oxidation was avoided. The α-Al₂O₃ layer, which developed adjacent to the BC upon thermal cycling, grew at a low rate if the initial oxide at the onset of oxidation consisted of θ-Al₂O₃ instead of α-Al₂O₃. Based on these results a pre-oxidation treatment is proposed for which the lifetime of the entire coating system during service is enhanced.     

Y2O3 对DZ125合金表面Cr-Al-Y渗层的组织结构及抗氧化性能影响

为进一步提高DZ125合金高温服役性能,通过扩散渗方法在其表面制备了稀土元素Y改性的Cr-Al共渗层,研究了Y₂O₃含量对渗层组织结构及抗高温氧化性能的影响。结果表明：不同条件下制备的Cr-Al-Y渗层均具有三层结构,由外向内依次为：Cr+Ni₃Cr₂外层,Ni₃Cr₂+Al₁₃Co₄中间层,以及Ni₃Al内层。当渗剂中Y₂O₃含量为0%～2%(质量分数,下同)时,渗层的厚度与密度显著增加;当稀土Y₂O₃的添加量过高时(5%),渗层的密度及厚度反而下降。1100℃高温氧化实验表明,Cr-Al-Y渗层显著提高了DZ125合金的抗高温氧化性能。     

γ-TiAl合金定向凝固过程中与氧化钇陶瓷材料的界面反应

研究液态金属冷却定向凝固条件下,Ti-47%Al合金与Y2O3/Al2O3双层结构陶瓷管内层Y2O3的相互作用。分析熔体温度和相互作用时间对界面反应、合金组织和成分的影响。结果表明：虽然Y2O3层受到一定程度的侵蚀和溶解,但Y2O3层有效地阻隔化学稳定性较差的Al2O3外层与TiAl合金熔体接触,避免Al2O3与TiAl之间的化学反应。合金熔体受到一定程度的污染且含有少量夹杂物。在一定保温时间内,合金中的杂质含量（Y和O）和夹杂物（Y2O3）体积分数均随着过热温度的提高而增加,但随着保温时间的进一步延长,杂质含量和夹杂物体积分数趋于恒定值,不再显著变化。     

Microstructure and high temperature oxidation behavior of hot-dip aluminized coating on high silicon ductile iron

High silicon ductile iron was coated by hot-dipping into an Al molten bath. The oxidation behavior of the aluminized alloy and the bare substrate was studied in air at 750 °C. The results showed that the coating layers consisted of three layers, in the sequence of Al, Fe-Al intermetallic and Si pile-up layers from the external topcoat to the substrate. The intermetallic layer was composed of outer FeAl₃ and inner Fe₂Al₅. The outer rod-shaped FeAl₃ dispersed in the aluminum topcoat, while the inner tongue-like Fe₂Al₅ formed in the metallic layer becoming the major phase in the aluminide coating layer. Those three layers of aluminum, Fe₂Al₅ and silicon pile-up layer exhibited hardness of HV 50, HV 1100 and HV 450, respectively. In this study, when the as-coated specimens were examined, Fe-Al-Si compounds could not be found. But the silicon pile-up at the interface between the substrate and the Fe-Al intermetallic layer could be seen in all the as-coated specimens. The graphite nodules were noticed in the substrate. The presence of graphite nodules in the substrate might be markers of hot-dipping. After hot-dipping in Al all the specimens contained graphite nodules in the aluminide layer.The oxidized graphite nodules resulted in cracks propagating in aluminide coating. Even though graphite nodules meant the existence of crack in the aluminide coating, the high temperature oxidation experiments indicated that the aluminide coating could prevent the oxidation of substrate effectively even at 750 °C.