Evaluation of Oxidation of Ti-Al and Ti-Al-Cr Coatings Arc-ion Plated on Ti-60 High-temperature Titanium Alloy

High-temperature titanium alloy for aeroengine compressor applications suffers from high-temperature oxidation and environmental corrosion, which prohibits long-term service of this kind alloy at temperatures above 600℃. In an attempt to tackle this problem, Ti-48Al （at. pct） and Ti-48Al-12Cr （at. pct） protective coatings were plated on the substrate of alloy Ti-60 by arc ion plating （ALP） method. Isothermal and cyclic oxidation tests were performed in static air at elevated temperatures. Phase composition, morphology of the coatings and distribution of elements were investigated by X-ray diffraction （XRD）, scanning electron microscopy （SEM） and energy dispersive X-ray analysis （EDX）. The results showed that the Ti-48Al coating exhibited good isothermal oxidation resistance during exposure at 800℃, but poorer resistance against oxidation at 900℃. By contrast Ti-48Al-12Cr coating demonstrated excellent isothermal oxidation resistance at both temperatures. Cyclic oxidation tests performed at 800℃ indicated that resistance and no spallation of coatings was observed. But both coatings demonstrated good cyclic oxidation at 900℃ only Ti-48Al-12Cr coating demonstrated excellent cyclic oxidation resistance.

High temperature oxidation behavior of Ti(Al,Si)_3 diffusion coating on γ-TiAl by cold spray

A Ti(Al,Si)3 diffusion coating was prepared on γ-TiAl alloy by cold sprayed Al?20Si alloy coating, followed by a heat-treatment. The isothermal and cyclic oxidation tests were conducted at 900 °C for 1000 h and 120 cycles to check the oxidation resistance of the coating. The microstructure and phase transformation of the coating before and after the oxidation were studied by SEM, XRD and EPMA. The results indicate that the diffusion coating shows good oxidation resistance. The mass gain of the diffusion coating is only a quarter of that of bare alloy. After oxidation, the diffusion coating is degraded into three layers: an inner TiAl2 layer, a two-phase intermediate layer composed of a Ti(Al,Si)3 matrix and Si-rich precipitates, and a porous layer because of the inter-diffusion between the coating and substrate.

Influence of Nb Ion Im plantation on Oxidation Resistance of High Tem perature Titaniu m Alloy at 650 ℃

The oxidation rate of a high temperature titanium alloy in air at 650℃ could be decreased significantly by means of ion implantation of 3×10 16 and 3×10 17 ions/cm 2 Nb. The microstructure and alloy elements distribution in the oxidation scale of unimplanted and Nb implanted titanium alloy were investigated by using SEM, XRD and AES. The addition of Nb could reduce the number of point defects and decrease the solubility of oxygen in the alloy substrate. Therefore, the oxidation resistance of the alloy in air at 650℃ is remarkably improved.

High Temperature Oxidation Behavior of NiCrAlY Coating by Arc Ion Plating

A NiCrAlY coating was prepared on the cast Ni-base superalloy K17 using arc ion plating. The coating was uniform, dense and well adhesive to the substrate. The oxidation kinetic curves of the alloy K17 and the coating were obtained. The results indicated that the oxidation resistance of the alloy K17 was evidently improved with NiCrAlY coatings at 900∼1100°C. As oxidation temperature rising, the interdiffusion between the coatings and substrates was enhanced. Ti atoms diffused from the substrate to the surface of coating to form the oxide, which was one of the reasons for the decrement of oxidation resistance. The oxidation resistance of NiCrAlY coating was decreased due to the spalling of pieces of oxide.

Oxidation behavior and mechanism of porous nickel-based alloy between 850 and 1000 °C

The oxidation behavior and mechanism of a porous Ni?Cr?Al?Fe alloy in the temperature range from850to1000°Cwere investigated by optical microscopy,scanning electron microscopy(SEM)and energy dispersive spectroscopy(EDS),X-raydiffraction(XRD)analyses and X-ray photoelectron spectroscopy(XPS).The results show that the oxidation kinetics at950and1000°C of this porous alloy is pseudo-parabolic type.Complex layers composed of external Cr2O3/NiCr2O4and internalα-Al2O3areformed on the surface of the oxidized porous alloys.γ?phases favor the formation of NiO/Cr2O3/NiCr2O4during the initial oxidation.Many fast diffusion paths contribute to the development of the oxide layers.The decrease of the open porosity and the permeabilitywith exposure time extending and temperature increasing can be controlled within a certain range.

Internal Oxidation of Some Pd-40Ag-1RE Alloys

The internal oxidation behavior of Pd-40Ag-1RE (RE = Sm, Eu, Gd, Y) alloy wires has been studied in air at 800 °C 1200°C. The dependence of internal oxidation depth ξ on reaction time t can be expressed as ξ = Ktn, the reaction index n = 0.50 approximately 0.75. The higher the oxidation temperature is, the larger the n value is. It means that the internal oxidation of wire sampls at high temperature deviates from parabola rule observed on plate sample. The activation energies of the studied alloys range over 120 approximately 160 kJ/mol. The internal oxidation process is controlled by the bulk diffusion of oxygen.

Oxidation and tribological properties of anodized Ti45Al8.5Nb alloy

The oxidation performance and tribological properties of the anodized Ti45Al8.5Nb were investigated.Anodization was performed in ethylene glycol containing 0.15 mol/L NH_(4)F.Results showed that the anodized Ti45Al8.5Nb alloy exhibited good resistance against oxidation.After 100 h oxidation at 1000℃,the mass gain of the anodized Ti45Al8.5Nb alloy was only 0.37 mg/cm^(2).This is attributed to the generation of protective oxide scale.On the other hand,the hardness and elastic modulus of the anodized Ti45Al8.5Nb alloy decreased and then increased with the prolonging of thermal exposure due to the generation of the Al_(2)O_(3)-enriched outermost oxide layer.

Effects of tungsten addition on the microstructural stability and properties of Ti-6.5Al-2Sn-4Hf-2Nb-based high temperature titanium alloys

The microstructural evolution,oxidation resistance and mechanical properties of Ti-6.5Al-2Sn-4Hf-2 Nbbased alloys with different contents of tungsten(W)additions ranging from 0 to 4.0 wt.%have been investigated in this study.The addition of W changed the microstructure from Widmanstatten colony of the W-free alloy to basketweave microstructure.After thermal exposure at 650℃ for 1000 h,the retainedβphase became less continuous,and secondaryβnano-particles with high W concentration were precipitated fromαlamellas.Withinαlamellas,the W was found to mainly partitioned into the secondaryβphase and refined the ordered α_(2)-Ti_(3)Al precipitates due to increased solubility of Nb in α_(2) phase.High W addition increased activation energy for oxidation,promoting the formation of more uniform and compact compound oxides,therefore substantially enhanced the oxidation resistance of the alloy.Besides,the W addition also improved the room and high-temperature yield strength without obviously losing plasticity after long-time thermal exposure.The improved mechanical performance was mainly attributed to the introduction of moreα/βinterfaces,the precipitation of secondaryβphase and the refinedα_(2) phase with Nb segregation.

Influences of Alloying Elements on Oxidation Behavior of Steels and Microstructure of Oxide Scales

In order to figure out the oxidation behavior of steels during heating,five micro-alloyed steels were subjected to continuous and isothermal oxidation using the thermo gravimetric analyzer and the Gleeble-3500thermo-mechanical simulator.The microstructure of oxide scales,especially the thickness fractions of Fe2O3,Fe3O4 and FeO layers,was analyzed using the scanning electron microscope（SEM）,electron probe microanalyzer（EPMA）and electron backscattered diffraction（EBSD）techniques.The micro-alloyed steels containing alloying elements（Si,Cr,Ni and Cu）show a higher oxidation resistance compared with the low carbon steel.It is found that alloying elements accumulated at scale/substrate interface during high temperature oxidation.Alloying elements function in two ways in the oxidation of steels：one is enhancing the scale/substrate interface and consequently suppressing the blister of scales;and the other is impeding the outward diffusion of iron cations from substrate to scales,resulting in the decrease of oxidation rate.As the diffusion of iron cations is impeded,the thickness fractions of Fe2O3 and Fe3O4of micro-alloyed steels are more than those of low carbon steels.

DOUBLE GLOW PLASMA SURFACE ALLOYING OF Ti6A14V AND TiAl

In order to improve the wear resistance of titanium alloy Ti6Al4V and high temperature oxidation resistance of intermetallic compound TiAl, the Double Glow Plasma Surface Alloying Technique (DG technique) was applied to modify the surface properties of these materials. Mo, Nb, Cr, Ni were diffused into the substrate materials to form alloyed layers with different properties. This paper shows the microstructure, microhardnesses, distributions of the alloy elements on the alloyed layers. Wear and high temperature oxidation tests were carried out. Test results indicate that the wear resistance of Ti6Al4V and the high temperature oxidation resistance of TiAl were improved significantly.

近α型高温钛合金起燃机理

采用激光氧浓度实验方法,研究激光功率和氧浓度对近α型高温钛合金(TA19合金)燃烧状态的影响,发现合金的起燃温度随激光功率和氧浓度的增加而降低,在200—325 W的激光功率以及21%—60%的氧体积浓度条件下,TA19合金的起燃温度为W27—1595℃,低于合金熔点.通过组织表征揭示保护性氧化层的失效形式,并结合氧化层应力失效模型分析起燃机理:1520℃以上TiO的高蒸气压特性导致表层TiO_(2)下方形成孔隙缺陷,加速TiO_(2)层的热应力失效;且起燃时需要同时满足临界温度条件和瞬时温度变化率条件.在此基础上,将保护性氧化层失效机理与能量方程结合以构建起燃模型;根据实验数据拟合计算得到TA19合金在起燃阶段的反应激活能约为280 kJ/mol,并得出起燃温度随激光功率和氧浓度变化的函数关系为1.2×10^(10)exp(-280000/RT_(ig))c^(1/2)+0.52R_(L)-315=0.该结果对航空发动机复杂气流条件下的阻燃性能研究及其他类型钛合金的起燃温度预测提供理论参考.

TNM钛铝合金高温抗氧化行为研究

TNM(Ti–43Al–4Nb–1Mo–0.1B)钛铝合金具有较低的密度、优异的高温力学性能和较好的高温变形能力,其长期服役温度可达750℃左右,是备受瞩目的新一代航空发动机低压涡轮叶片用材料.选取热暴露温度时间不同的两个热暴露条件对TNM合金在空气中进行氧化实验,采用扫描电子显微镜、能谱仪及X射线光电子能谱分析仪对试样的表面形貌、氧化物组成进行分析,系统研究了TNM合金在不同温度、不同时间热暴露条件下的氧化规律.结果表明,在700℃和760℃下,TNM合金抗氧化级别分别为完全抗氧化和抗氧化等级.700℃下,TNM合金在氧化初期先生成TiO_(2),随后Al_(2)O_(3)逐渐增加,直至覆盖整个样品,在氧化进行200 h时,表面生成的氧化物主要为Al_(2)O_(3),含有少量的MoO_(2)、MoO_(3),能保持较好的抗氧化性;760℃条件下,合金在氧化初期即形成不稳定的Al的氧化物与Ti的氧化物,表面生成的氧化物主要为TiO_(2)和少量的MoO_(2)、MoO_(3)与MoO_(x)的氧化物.

γ-TiAl基合金用Al_(2)O_(3)-SiC-AlPO_(4)复合涂层抗高温氧化性能研究

目的通过表面涂层提高γ-TiAl基合金的抗高温氧化性能。方法采用常规喷涂涂料法在γ-TiAl合金基体上制备Al_(2)O_(3)-SiC-AlPO_(4)磷酸盐复合抗高温氧化涂层。研究γ-TiAl合金和涂层样品在900℃、静态空气条件下的准等温氧化动力学行为。用XRD和SEM/EDS分别对涂层样品氧化前后的物相组成、组织形貌和微区成分进行表征分析;用电子探针(EPMA)分析涂层样品的元素分布情况。结果900℃恒温氧化动力学研究结果表明,γ-TiAl基合金初期氧化速率常数为32.501×10^(-2)mg/(cm^(2)·h^(1/2)),与后期氧化速率常数28.113×10^(-2)mg/(cm^(2)·h^(1/2))基本接近,呈直线规律,不具有抗氧化性能;而Al_(2)O_(3)-SiC-AlPO_(4)磷酸盐复合涂层样品氧化后期氧化速率常数为5.967×10^(-2) mg/(cm^(2)·h^(1/2)),与氧化初期8 h内氧化速率常数23.941×10^(-2) mg/(cm^(2)·h^(1/2))相比,明显降低,遵循典型抛物线规律,具有抗氧化性能。微观分析结果表明,原始涂层与γ-TiAl合金基体结合紧密,涂层主要相组成为Al_(2)O_(3)、SiC、SiO_(2);AlPO_(4)以无定形状态构成涂层连续相。氧化后,AlPO_(4)演变成晶态,形成涂层致密的网络结构;部分基体钛元素扩散进入涂层中疏松部位,氧化后形成TiO_(2)弥散分布在涂层中,填补了涂层疏松部位,使涂层更加致密;在涂层与基体界面2μm区域内形成连续致密Al_(2)O_(3)膜,阻挡了空气中的氧进一步扩散进入基体。结论Al_(2)O_(3)-SiC-AlPO_(4)复合涂层有效降低了γ-TiAl基合金氧化速率,有助于形成保护性Al_(2)O_(3)膜,明显改善了900℃γ-TiAl基合金抗高温氧化性能。

涂层厚度对Cr涂层锆合金包壳高温蒸汽氧化动力学及微观机制的影响

目的研究涂层厚度对Cr涂层锆包壳高温蒸汽氧化行为的影响规律及其微观机制,为耐事故锆包壳表面涂层优化设计提供理论依据。方法以锆合金包壳为基体材料,采用磁控溅射工艺制备纯金属Cr涂层,目标厚度设计值为10、15、20μm 3类。采用高温蒸汽氧化设备开展试验,氧化温度为1200℃,等温氧化时间为500~3000 s,系统研究模拟反应堆失水事故(LOCA)工况下涂层厚度对该材料体系高温蒸汽氧化行为及氧化动力学的影响。试验后,通过X射线衍射仪、场发射扫描电子显微镜及能谱仪等表征各样品氧化膜微结构特征、氧化层厚度、元素分布及物相组成等,基于氧化膜层厚度构建Cr涂层氧化动力学模型,同步探讨涂层原始厚度对其高温蒸汽氧化-失效微观机理的影响。结果涂层厚度为10μm时,其对锆合金基体保护作用有限,等温氧化2000 s时其表面Cr_(2)O_(3)氧化膜和残余Cr涂层已完全丧失保护功能,锆合金基体被连续氧化。涂层厚度为15μm时,第一阶段,生成保护性能较好的Cr_(2)O_(3)氧化膜,Cr涂层的氧化行为满足抛物线规律;第二阶段,Cr涂层的氧化行为发生转变,氧化膜及其残余涂层保护性能衰退,但锆合金基体始终未被氧化。涂层厚度为20μm时,Cr涂层的氧化行为满足抛物线规律,但氧化行为未发生转变,表面氧化膜及残余Cr涂层保护性能较好。结论Cr涂层厚度增加可在一定程度上提升其抗高温蒸汽氧化性能,进而提高反应堆事故工况下燃料包壳抵御事故的能力,从而在一定程度上延长不干预时间。

舰用钛合金及铬涂层抗氧化和腐蚀性能研究

钛合金舰载武器装备长期处于高温及海水飞溅环境,为延长其使用寿命,采用电弧离子镀技术在其表面制备Cr涂层,并研究钛合金及Cr涂层的抗高温氧化和抗盐雾腐蚀性能。结果表明:由于冷热交替作用,650℃循环氧化1 h后,在钛合金表面形成的氧化物和基体上产生裂纹,并形成Ti元素氧化物堆积。电弧离子镀的Cr涂层表面平滑完整,仅发生Cr元素氧化,对基体具有保护作用。盐雾腐蚀720 h后,钛合金表面发生腐蚀并产生剥落区域,而电弧离子镀制备的Cr涂层无腐蚀剥落区域,具有良好的抗盐雾腐蚀性能。

TC4钛合金恒定高温和高低温环境下疲劳性能研究

目的 研究TC4钛合金在恒定高温和高低温环境(25~390℃)的疲劳性能。方法 分别开展恒定高温和高低温环境的疲劳试验及断口分析,研究材料在2种环境下的疲劳性能差异及温度效应机理。结果 当温度从25℃升高至390℃时,TC4钛合金恒定温度的疲劳性能在短寿命段(N<106循环)逐渐降低,疲劳性能在长寿命段(N>106循环)呈非线性的变化趋势,先降低、后升高。通过断口分析发现,氧化现象随着温度升高和试验时间变长越来越明显。同一应力水平下,高低温环境疲劳试验的疲劳寿命介于最高温度和最低温度疲劳试验的疲劳寿命之间。结论 当温度处于25~390℃时,温度和氧化现象同时影响着TC4钛合金的疲劳性能。温度升高使材料的疲劳性能下降,高温环境生成的保护性氧化膜提高了材料的疲劳性能。钛合金的高低温疲劳寿命可以用等效恒定温度的疲劳曲线来预测,并有较好的预测精度。

氧在 Ti-1100 高温钛合金氧化中的扩散规律

测量了Ｔｉ１１００合金在６００～７５０℃氧化１００ｈ后氧化层的厚度和氧化层＼固溶体界面处的氧浓度以及基体富氧层的深度、显微硬度的变化．合金在该温度区间的氧化增重由氧化物的增长和富氧固溶体的形成两部分组成，它们均呈抛物线规律变化．利用扩散方程和氧化物＼固溶体界面处“有效氧浓度”计算出氧在氧化物中的扩散系数是氧在固溶体中的３～６倍．根据富氧层的深度所计算的氧在固溶体中的扩散激活能与扩散系数的线性回归结果具有相当好的一致性．

高速车削钛合金的硬质合金刀具磨损机理研究

使用硬质合金刀具材料进行钛合金(Ti-6Al-4V)的高速干车削试验.采用电子扫描显微镜(SEM)观察刀具的磨损形貌,通过能谱分析(EDS)分析磨损表面的元素分布,并对刀具的主要磨损机理进行了分析.研究结果表明,使用硬质合金刀具材料高速干车削Ti-6Al-4V时,刀具的磨损机理主要为粘结磨损、氧化磨损和扩散磨损.硬质合金刀具的氧化磨损主要发生在刀具前刀具和后刀面的磨损边缘区.由于车削过程中刀具前刀面的切削温度比后刀面的切削温度高,导致刀具前刀面的氧化磨损、粘结磨损和扩散磨损较后刀面严重.

工业纯钛的高温热氧化行为

采用原子力显微镜(AFM)、扫描电镜(SEM)和X射线衍射仪(XRD)研究工业纯钛经600、700和800℃热氧化后硬化层的形貌、粗糙度和相结构,分析热氧化过程中氧原子的扩散机制、渗氧层的形成和氧化膜的分层现象。结果表明:随着氧化时间的延长和温度的升高,硬化层表面粗糙度增大,氧化物颗粒迅速长大,主要物相为TiO2、Ti2O、Ti3O、Ti6O;钛的氧化过程是氧原子通过气相/氧化膜及氧化膜/金属基体的渗透过程;氧化膜随着氧化反应的加剧和自身的分解,其结构和性质发生变化而导致分层现象。