Ti/Ni多层复合材料界面扩散行为研究

针对累积叠轧5道次制备的Ti/Ni多层结构复合材料试样进行热处理,采用光学显微镜和扫描电镜分析方法,对复合材料的显微组织、界面结构和扩散反应层厚度等进行观察分析,结合动力学理论研究了Ti/Ni界面的扩散行为。结果表明:试样经过累积叠轧5道次轧制后,Ti/Ni界面未发生扩散;在(550～750℃)/(0.5～8 h)热处理后,Ti/Ni界面发生扩散,扩散层厚度与保温时间呈幂函数关系,与加热温度呈指数关系;随着热处理温度的升高,Ti-Ni扩散层的生长方式由650℃以下的体扩散控制逐渐转变为晶界扩散控制。通过计算和验证得到采用累积叠轧5道次制备的Ti/Ni多层复合材料的Ti/Ni界面固相反应层生长动力学方程为:y=1.7043×10~4 exp(-78202/RT)t~(1.2009-0.0008T)。     

Ti/Ni多层复合材料界面扩散行为的研究

本文针对累积叠轧5道次制备的Ti/Ni多层结构复合材料试样进行热处理,采用光学显微镜和扫描电镜分析方法,对复合材料的显微组织、界面结构和扩散反应层厚度等进行观察分析,结合动力学理论研究了Ti/Ni界面的扩散行为。研究结果表明：试样经过累积叠轧5道次轧制后,Ti/Ni界面未发生扩散;在(550 ℃-750 ℃)×(0.5 h-8 h)热处理后,Ti/Ni界面发生扩散,扩散层厚度与保温时间呈幂函数关系,与加热温度呈指数关系;随着热处理温度的升高,Ti-Ni扩散层的生长方式由650 ℃以下的体扩散控制逐渐转变为晶界扩散控制。通过计算和验证得到采用累积叠轧5道次制备的Ti/Ni多层复合材料的Ti/Ni界面固相反应层生长动力学方程为：y=1.7043*104*exp(-78202/RT) *t1.2009-0.0008T。     

钛表面沉积Fe-Pd磁性薄膜的研究

采用电弧离子镀设备，以高纯Fe靶和Pd靶为原料，在TA1工业纯钛表面先后沉积Fe，Pd2层单金属薄膜。对样品分别进行700℃～1100℃，保温0．5h～3h的真空退火处理，使Fe膜和Pd膜之间形成扩散层，制备FePd磁性膜。重点研究了Fe，Pd及钛衬底之间的百扩散机制，膜层结构，薄膜的相组成。结果表明：在700℃，0．5h处理后FePd薄膜的合金化较好：在900℃，1h处理后虽有FePd相形成，但基体中的Ti已经扩散至表面：温度高于900℃且保温时间长于1h处理，不利于FePd膜的形成。     

扩散温度对TC4合金表面Cu/Ni复合镀层结构及腐蚀性能的影响

论文采用扩散热处理研究了Cu/Ni/Ti复合镀层不同温度下的扩散行为,分析了扩散层结构,并讨论了扩散过程对镀层结构及腐蚀性能的影响。结果表明：由于Cu/Ni/Ti原子之间的互扩散,形成稳定的扩散层,可以有效提高镀层表面耐蚀性能;随着热扩散温度上升到700℃,膜层结构致密,在扩散层中形成了NixTiy金属间化合物及少量的CuxTiy金属间化合物,镀层表面的耐蚀性最好;温度升高到800℃时,在膜层界面处引发了Kirkendall效应,所形成的Kirkendall空位相互聚集长大,形成裂纹或孔洞,使得镀层疏松多孔,从而低了耐蚀性。     

Ti/Al固相扩散反应行为及其动力学研究（英文）

研究了Ti/Al热处理温度为520~630℃之间不同温度条件下的固相扩散反应,实验选用Ti/Al粉末压坯作为研究TiAl_3金属间化合物反应动力学模型的原始材料,当热处理时间达到46 h条件下,TiAl_3金属间化合物相在Ti/Al界面生成,实验结果显示TiAl_3相沿TiAl_3/Al界面的生长速率明显优于沿Ti/TiAl_3界面的生长速率。此外,建立了TiAl_3固相扩散反应动力学方程,Ti/Al固相扩散反应激活能和动力学指数分别为170.1 k J·mol~(-1)和0.5。通过对不同热处理条件下试样进行成分分析得到,在热处理工艺为590℃/4.5 h条件下,铝完全消耗,而590℃/3.5 h条件下仍有多余的铝剩余,该实验结果与所建立的固相反应扩散动力学模型相一致,表明该模型能够很好地预测Ti/Al材料固相反应的进行状态。     

TiAl合金表面EB-PVD制备热障涂层及高温抗氧化性能

利用EB-PVD技术在Ti Al合金表面制备了扩散铝/YSZ热障涂层。采用SEM、EDS和XRD分析了涂层原始及高温氧化后的微观组织及相组成,并测试了高温氧化性能。结果表明:涂层表面YSZ层为致密柱状晶结构,由非平衡四方相t′-ZrO_2组成。Ti Al合金沉积了扩散铝/YSZ热障涂层后高温氧化性能显著提高,氧化动力学曲线呈对数变化规律,900℃高温氧化时,氧化速率为2.2×10~(-5) mg/cm~2·h。1000℃高温氧化时,氧化速率为1.14×10~(-3) mg/cm~2·h。在高温氧化过程中,粘结层与基体之间发生元素扩散,膜基界面消失。在面层与中间粘结层之间形成了均匀连续的热生长氧化物层TGO。     

钛合金在500℃～650℃下的氧化行为研究

采用XPS试验对Ti811钛合金在500℃～650℃下、50h的氧化行为进行了分析，利用扫描俄歇微探针对氧化后试样表面的氧影响区进行了研究，并对其影响机制进行了探讨。结果表明，温度为550℃时，试样表面生成的氧化膜较致密；温度在500℃～600℃之间时，试样表面氧化膜的厚度随温度的增加的幅度较小，温度高于600℃后迅速增加；而氧缓慢扩散区厚度则在500℃～650℃之间随温度的升高持续增加。     

保温时间对钛-铜扩散连接接头界面组织的影响

在850℃、10 MPa压力下对纯钛和纯铜进行了扩散连接。采用扫描电镜对不同连接时间下接头界面微观组织进行了表征,以研究连接时间对连接界面组织的影响。实验结果表明,当连接时间为30 s时,在钛/铜界面上存在没有完全闭合的微观孔洞,无扩散反应层生成。当连接时间增加到60 s,在接头界面生成了βTi,Ti2Cu,Ti Cu和Ti3Cu4等金属间化合物相,反应层总厚度约2μm。当连接时间增加到90 s,在接头界面产生了βTi,Ti2Cu,Ti Cu,Ti3Cu4,Ti2Cu3和Cu4Ti等金属间化合物,反应层厚度增加约5μm。这说明随着连接时间的增加,由于钛/铜之间互扩散的加剧,反应层不断变厚。     

铸造Ti60氧化形貌的研究

为了研究铸造Ti60的高温氧化形貌,采用熔铸法制备了Ti60合金铸锭,并利用金相显微镜、电子天平、SEM研究了铸态Ti60的金相组织,在不同加热温度保温5 h的氧化增重和表面形貌.结果表明,铸态Ti60的金相组织为针状(α+β)+少量富钕颗粒;在700℃-1 100℃,随着加热温度的升高,铸造Ti60氧化加重,形成氧化钛膜;700℃-900℃,试样增重只有0.110%-0.609%;1 100℃氧化增重严重,达到9.137%;钛的氧化增重为吸氧.铸态Ti60试样表面形貌,700℃氧化钛膜很薄较致密;900℃试样表面有较多的白色颗粒和少量腐蚀坑,表面不致密;1 000℃形成片状和块状TiO2;1 100℃氧化层为厚大块状的TiO2.氧化过程为高温时,氧化膜粗大变得疏松多孔,氧通过氧化膜扩散进基体.     

TiAl/Ti/Nb/GH99扩散连接接头的界面组织结构及接头强度

采用Ti/Nb复合中间层对TiAl与镍基高温合金(GH99)进行扩散连接.采用扫描电镜、电子探针和X射线衍射等手段对连接接头的生成相及界面组织结构进行分析,采用抗剪强度测试对接头的连接强度进行评价.结果表明,GH99/Nb/Ti/TiAl的典型界面结构为GH99/(Ni,Cr)ss/Ni3Nb/Ni6Nb7/Nb/(Ti,Nb)ss/α-Ti+(Ti,Nb)ss/Ti3Al/TiAl.当连接温度为900℃,连接时间为30 min,连接压力为20 MPa时,所得接头抗剪强度最高为273.8 MPa.随着连接温度的升高,界面组织结构及反应层厚度发生变化.当连接温度T>900℃时,界面处生成对接头强度有不利影响的Ni6Nb7反应层;根据试验结果,进一步分析了各反应层的形成过程,揭示了GH99/Nb和Nb/Ti/TiAl的界面扩散反应机制.     

Li4SiO4 氚增殖陶瓷的制备及其与14Cr-ODS钢的腐蚀界面行为

Li₄SiO₄小球与ODS钢的化学相容性对聚变反应器的安全运行具有重要意义。研究了在500、600、700 ℃的氩气环境中保温300 h后ODS钢与小球接触界面组织和成分的变化。结果表明,在600~700 ℃时,Li₄SiO₄小球与ODS钢的界面发生了严重的元素互扩散和反应。在Li₄SiO₄小球表面,由于ODS钢中Fe和Cr的扩散,出现了一层薄薄的反应层,这也导致了密度的增加,破碎负荷从51 N （500 ℃）下降到32 N（700 ℃）。XRD图谱显示,ODS钢表面出现了LiCrO₂和LiFeO₂新相,说明Li₄SiO₄小球中的Li和O原子可以扩散到ODS中,与Fe、Cr元素在高温下发生反应形成腐蚀层。在700 ℃时,腐蚀层可分为2个氧化层。最外层是LiFeO₂和LiCrO₂的混合物,下一层主要是LiFeO₂。在ODS钢的表面,700 ℃/300 h条件下氧扩散系数为2.2×10^-14 cm²/s,这说明ODS钢作为一种包层结构材料,在未来的包层设计中需要一层耐腐蚀涂层。     

Transmission electron microscopy study of the failure mechanism of the diffusion barriers (TiN and TaN) between Al and Cu

Failure mechanisms of transition metal nitride thin film diffusion barriers, such as TiN and TaN (10 nm in thickness), between Al and Cu were investigated by transmission electron microscopy (TEM), scanning transmission electron microscopy, and energy dispersive spectroscopy. After annealing at 450 °C during 30 min, the TiN diffusion barrier initially failed due to an interfacial reaction between TiN and Al forming TiAl3. When the annealing temperature was increased to 500 °C, Cu-Al intermetallic compounds were formed by the interdiffusion of Al and Cu through the diffusion barrier. In the case of the Al/TaN/Cu structure, no interfacial reaction products were observed after annealing up to 550 °C. On the other hand, it failed after annealing at 550 °C due to the inter-diffusion of Cu and Al through the diffusion barrier. TEM also identified Cu to be the rapid diffusing species in both systems. The results are discussed based on the thermodynamic stability of the interface predicted by the ternary phase diagram and the diffusion kinetics of Al and Cu through the diffusion barrier. The results show that both the thermodynamic stability of the diffusion barrier between Al and Cu and the diffusion kinetics of Al and Cu through the diffusion barrier, which are dependent on the microstructure of the diffusion barrier, should be considered carefully when selecting diffusion barrier materials between Al and Cu.     

Diffusion Barrier Selection from Refractory Metals (Zr,Mo and Nb) Via Interdiffusion Investigation for U-Mo RERTR Fuel Alloy

U-Mo alloys are being developed as low enrichment monolithic fuel under the Reduced Enrichment for Research and Test Reactor (RERTR) program. Diffusional interactions between the U-Mo fuel alloy and Al-alloy cladding within the monolithic fuel plate construct necessitate incorporation of a barrier layer. Fundamentally, a diffusion barrier candidate must have good thermal conductivity, high melting point, minimal metallurgical interaction, and good irradiation performance. Refractory metals, Zr, Mo, and Nb are considered based on their physical properties, and the diffusion behavior must be carefully examined first with U-Mo fuel alloy. Solid-to-solid U-10 wt.%Mo versus Mo, Zr, or Nb diffusion couples were assembled and annealed at 600, 700, 800, 900 and 1000 °C for various times. The interdiffusion microstructures and chemical composition were examined via scanning electron microscopy and electron probe microanalysis, respectively. For all three systems, the growth rate of interdiffusion zone were calculated at 1000, 900 and 800 °C under the assumption of parabolic growth, and calculated for lower temperature of 700, 600 and 500 °C according to Arrhenius relationship. The growth rate was determined to be about 10³ times slower for Zr, 10⁵ times slower for Mo and 10⁶ times slower for Nb, than the growth rates reported for the interaction between the U-Mo fuel alloy and pure Al or Al-Si cladding alloys. Zr, however was selected as the barrier metal due to a concern for thermo-mechanical behavior of UMo/Nb interface observed from diffusion couples, and for ductile-to-brittle transition of Mo near room temperature.     

NiCoCrAlY coatings with and without an Al2O3/Al interlayer on an orthorhombic Ti2AlNb-based alloy: Oxidation and interdiffusion behaviors

The mechanism of oxidation protection of NiCoCrAlY overlay coatings on the orthorhombic Ti₂AlNb-based alloy (O alloy) Ti–22Al–26Nb (at.%) is described. While the bare alloy exhibited poor oxidation resistance at 800 °C, adding NiCoCrAlY coatings significantly improved the oxidation resistance. However, serious interdiffusion between the coatings and the substrate resulted in rapid degradation of the coating system. Several reaction layers were formed at the coating/substrate interface by interdiffusion, and non-protective scales mainly of Cr₂O₃ and TiO₂ were formed due to the degradation of the coating. In order to solve this problem, an Al₂O₃/Al interlayer was sandwiched into the coating system as a diffusion barrier. The isothermal and cyclic oxidation protection of the multilayer coating system on the Ti–22Al–26Nb substrate was evaluated at 800 and 900 °C. The results indicated that the interdiffusion was much suppressed, and the duplex coating system demonstrated improved oxidation resistance on the Ti–22Al–26Nb substrate, with a thin and adherent protective α-Al₂O₃ scale forming on the surface.     

High Temperature Performance of an FeAl Laser Coated 9Cr1Mo Steel

The isothermal high temperature corrosion behavior of an FeAl coating, coated on 9Cr1Mo steel through laser surface alloying, was studied in atmospheres of pure oxygen and O₂ + 1 %SO₂. The specimens were tested at 500, 600 and 700 °C for 4–100 h. The mass change of the specimens versus time of exposure was used to study the kinetics of oxidation. The coating degradation through interdiffusion of alloying elements between the surface layer and substrate was investigated by long-term oxidation tests in air. OM, SEM, FESEM, EDS and EPMA analyses were used to study the oxidation behavior of the intermetallic coating. The results showed excellent oxidation/sulfidation resistance of the coated material due to a negligible growth rate of the oxide scale. However, the coating was degraded because of the interdiffusion of Al and Fe atoms between the coating and substrate after prolonged exposure to elevated temperatures.     

Improvement of Oxidation Resistance of γ-TiAl at 900 and 1000 °C Through Hot-dip Aluminizing

Hot-dip aluminizing method and subsequent interdiffusion treatment were used to develop a TiAl₃ coating on Ti–45Al–2Cr–2Nb–0.15B (at.%) alloy. A two-phase coating consisting of an outer pure Al layer and an inner TiAl₃ layer formed on the alloy after the hot-dip and then a single phase TiAl₃ coating was obtained by using interdiffusion treatment. Oxidation of the TiAl₃ coating was conducted at 900 and 1000 °C. Both the interrupt oxidation and the isothermal oxidation tests indicated that the coating provided high protectiveness for the alloy. The coating was stable for at least 300 h during the interrupt oxidation at 900 and 1000 °C, and it was stable for at least 500 h at 1000 °C and 1000 h at 900 °C during the isothermal oxidation. The oxidation behavior of the coating was discussed in detail.     

Development of novel diffusion coatings for 9–12 % Cr ferritic‐martensitic steels

Eventhough 9–12% Cr steels are mechanically designed for power plant applications up to 650 °C, their effective use is limited by the corrosion resistance at this temperature. Therefore, the present paper addresses the development of diffusion coatings on 9% Cr ferritic‐martensitic steels. The difficulty of coating these materials with conventional diffusion processes arises from the temperature limit above which the conversion of the martensite is accelerated and the mechanical properties would be deteriorated. Aluminide coatings consisting of Fe₂Al₅ or FeAl phases were thus developed for deposition temperatures between 650 and 715 °C by the conventional pack cementation technique. As the addition of boron was expected to improve the oxidation properties of the coating, the influence of B on the aluminide coating was investigated. The precedent diffusion of Cr as an interdiffusion barrier before switching to the Al diffusion step was also investigated. As a further technique, the fluidised bed chemical vapour deposition (FBCVD) method allowed the development of Fe₂Al₅ coatings at 550 °C. Furthermore, Si or codiffusion Al‐Si coatings were developed at temperatures as low as 550 °C.     

Effect of intermetallic compounds on heat resistance of hot roll bonded titanium alloy–stainless steel transition joint

The effect of intermetallic compounds on the heat resistance of transition joint was investigated. The experiment of post-weld heat treatment for the hot roll bonded titanium alloy–stainless steel joint using nickels interlayer was carried out, and the interface microstructure evolution due to heat treatment was presented. There was not found significant interdiffusion at stainless steel/nickel interface, when the specimens were heat treated in the temperature range of 600–800 °C for 10 and 30 min, while micro-cracks occurred at the stainless steel/nickel interface heat treated at 700 °C for 30 min. The thickness of intermetallic layers at nickel/titanium alloy interface increased at 600 °C, and micro-cracks occurred at 700 and 800 °C. The micro-cracks occurred between intermetallic layers or between intermetallic layer and nickel interlayer as well. The tensile strength of the transition joint decreased with the increase of heat treatment temperature or holding time.     

The oxidation behavior and mechanical performance of Ti60 alloy with enamel coating

In the present paper, the influence of enamel coating, compared to the traditional TiAlCr coating, on oxidation behavior and oxygen contamination of Ti60 alloy at 700 and 800 °C was studied. A continuous protective alumina scale formed on TiAlCr coating during oxidation at the two temperatures; but a rather heavy interdiffusion layer appeared at the interface of TiAlCr/Ti60 during oxidation at 800 °C. The uniform and dense enamel coating could provide excellent protectiveness to Ti60 due to its thermal chemical stability and good compatibility in terms of thermal expansion coefficient to the substrate Ti60 alloy. According to the microhardness measurement results, there exists a layer of contamination of about 30 μm into the alloy after the enamel was vitrified for 30 min at 900 °C in air; but the depth of oxygen contamination into the alloy changed little after oxidation for 1000 h at 600 °C. The strength and the elongation at ambient temperature of Ti60 alloy with enamel coating decreased about 7.4% and 3.4% in comparison to the original bare alloy, respectively. From the results, the enamel coating could protect Ti60 alloy from oxidation and oxygen embrittlement.     

FABRICATION OF Ti/SiC MMCs BY VACUUM HOT PRESSING WITH AID OF HYDROGEN

1.IntroductionThemechbocalpropertiesofmetaJmatrircomposites(MMCs)arelargelycontrolledbythebounda-rystateofthematrir/fiberiliterfaCe,whichplaysanimport8ntroleinloadtransferinMMCs.TheinterfaCereactionproductsinc0ntinu0usSiCfiberreinforcedtitaulummatrircomp0sitesareusuallybrittleTi5Si3andTiC[1].Accordingt0Reevesetal'swork[z],areactionzoneatreinforcement/matririllterfacewiththicknessofm0rethan1pmresultedinseriousdegradation0ftheinterfaCestrengthandmechanicalpr0perties0fthecomposite.Therefor…