高铌TiAl合金与陶瓷型壳的界面反应

研究了高铌TiAl合金Ti-44Al-8Nb-0.2W-0.1B-0.1Y(at%)分别与Al2O3/ZrO2/Y2O3坩埚的界面反应。测得界面反应层的厚度分别为40,170和20μm。研究中最大的发现在于Ti-44Al-8Nb-0.2W-0.1B-0.1Y(at%)合金在3种坩埚中凝固后显微组织的转变。经测定该合金在3种坩埚中凝固获得的试样中氧含量分别为0.35,0.41和0.11(at%)。由于在合金熔化和凝固过程中,坩埚中的氧元素扩散进入合金基体,较高的氧含量导致合金显微组织发生转变,在与Al2O3和ZrO2坩埚反应的合金中发生了包晶反应。作为对比,选取一种低铌含量的TiAl合金Ti-49.5Al-2Cr-2Nb。经测定在3种坩埚中反应的氧含量分别为0.40,0.63和0.25(at%),但是组织却没有明显的差异。     

Structure Heredity Effect of Mg-10Y Master Alloy in AZ31 Magnesium Alloy

研究了高铌TiAl合金Ti-44Al-8Nb-0.2W-0.1B-0.1Y (at％)分别与Al2O3/ZrO2/Y2O3坩埚的界面反应.测得界面反应层的厚度分别为40,170和20 μm.研究中最大的发现在于Ti-44Al-8Nb-0.2W-0.1B-0.1Y(at％)合金在3种坩埚中凝固后显微组织的转变.经测定该合金在3种坩埚中凝固获得的试样中氧含量分别为0.35,0.41和0.11 (at％).由于在合金熔化和凝固过程中,坩埚中的氧元素扩散进入合金基体,较高的氧含量导致合金显微组织发生转变,在与Al2O3和ZrO2坩埚反应的合金中发生了包晶反应.作为对比,选取一种低铌含量的TiAl合金Ti-49.5Al-2Cr-2Nb.经测定在3种坩埚中反应的氧含量分别为0.40,0.63和0.25 (at％),但是组织却没有明显的差异.     

Ti-47Al-2Cr-2Nb-xTiB_2合金与Al_2O_3陶瓷型壳界面反应的研究

实验室条件下制备了Ti-47Al-2Cr-2Nb-xTiB2(x=0、0.6%、1.0%,体积分数)合金熔体与Al2O3陶瓷型壳的界面反应层。借助SEM、EDS、XRD以及显微硬度测量等手段,对3种TiAl基合金熔体与Al2O3陶瓷型壳的界面反应情况进行了分析和比较。结果表明,TiAl基合金中加入TiB2,能有效减少TiAl基合金熔体与Al2O3陶瓷型壳的界面反应。TiAl基合金与AlO陶瓷型壳间的界面反应是一种不均衡进行的扩散型化学反应,并建立了界面反应的宏观模型。     

电磁场对TiAl合金试样表面粗糙度的影响

研究了电磁场作用下,氧化物陶瓷铸型的种类、粒度和保温功率对Ti50Al合金试样表面粗糙度的影响规律,分析了电磁场作用下表面粗糙度的形成机理.结果表明,在电磁场作用下,在5种氧化物陶瓷材料中所得Ti50Al合金试样的表面粗糙度大小依次为,Ra(Y2O3)＜Ra[ZrO2(Y2O3)]＜Ra[ZrO2(CaO)]＜Ra(CaO)＜Ra(Al2O3);Ti50Al合金试样的表面粗糙度随着耐火材料粒度和保温功率的减小而降低.     

TiAl基合金凝固过程的相选择问题分析

以Ti46Al7Nb2.5Vl.0Cr、Ti47Al7Nb2.5V1.0Cr、Ti48Al7Nb2.5Vl.0Cr、Ti48Al2Cr2Nb、Ti46Al和Ti46Al8Nb等Ti Al基合金为研究对象,进行深过冷非平衡凝固实验,对其显微组织和相组成进行了研究。结果表明,不同Al含量,以及Cr、Nb和V等β相稳定元素对Ti Al基合金具有重要影响。     

TiAl基合金与陶瓷界面反应的研究

借助电子探针微区分析仪、维氏显微硬度计、光学和电子显微镜对TiAl合金与Al2O3,ZrO2以及经CaO稳定的ZrO23种陶瓷型壳的界面反应进行了研究分析。结果表明，这3种材料的化学稳定性依次升高，而经CaO稳定的ZrO2型壳与TiAl反应层的厚度仅为50μm,故可望用作钛铝合金精密铸造型壳面层材料。     

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.     

Ti-47Al-2Cr-2Nb合金熔体与Y_2O_3型壳的界面作用

结合定向凝固工艺要求,研究了不同加热温度和保温时间(1600℃×10min,1600℃×30min和1700℃×10min、1700℃×30min)下,Ti-47Al-2Cr-2Nb合金熔体与Y2O3型壳的界面作用、界面组织形貌、元素分布以及界面生成物的相组成,并讨论了Y2O3型壳用于TiAl基合金铸件定向凝固的可行性。结果表明,相同的保温温度或保温时间下,熔体中的Al元素比Ti元素更易向型壳一侧扩散;同时合金棒表层形成一层几十微米厚的渗透层,1600℃试样表面渗透层是由于合金液对型壳面层材料的浸蚀和热冲击作用,使Y2O3颗粒进入到基体中形成的;而1700℃试样渗透层中在Y2O3颗粒的周围发现含Y、O、Al的灰色相,应为Y2O3与合金液发生反应而形成。     

TiAl基合金熔体与氧化物铸型界面的相互作用

通过实际浇注制取了Ti-48Al—2Cr-2Nb（at％，下同）合金熔体／氧化物铸型界面，继而借助SEM、EPMA和XRD等分析测试手段，对Ti-48Al—2Cr-2Nb合金与氧化物铸型高温反应后的界面组织形貌、元素的分布以及界面生成相的相组成进行了研究，并探讨了Ti-48Al—2Cr-2Nb合金熔体与氧化物铸型间的界面反应机理。结果表明，Ti-48Al—2Cr-2Nb合金熔体与氧化物铸型间发生了一定程度的界面化学反应，但存界而上化学反应并不是均匀进行的，而是在Ti-48Al—2Cr-2Nb金熔体与氧化物铸型紧密结合的区域优先进行。     

Ti50Al和Ti45Al8Nb合金高温初期氧化行为

利用SEM、XPS和AES研究了Ti50Al和Ti45Al8Nb(原子分数,%)合金在900 ℃空气中的初期氧化行为.结果表明:Nb的加入显著提高了合金的抗氧化性.氧化90 min后,Ti50Al合金表面为粗大的富TiO2颗粒,冷却过程中部分表层氧化膜脱落,脱落后内层为多孔、疏松的Ti和Al的混合氧化物(可能有氮化物);Ti45Al8Nb合金表面生成很薄的氧化膜,其外层为细小富Al2O3颗粒,Nb只存在于内层(富TiO2层)和混合层,在外层Al2O3内没有发现,Nb5 取代TiO2中的Ti4 ,降低氧空位浓度从而减慢氧的向内扩散,抑制TiO2的生成,同时促进了外层纯Al2O3层的形成,该层阻碍氧以及合金元素的进一步扩散.     

钛与氧化物陶瓷界面反应研究

借助SEM和差热分析(DTA),研究了纯钛与Y_2O_3、ZrO_3(Y_2O_3,稳定和CaO稳定)陶瓷耐火材料界面反应后金属 侧的显微组织,并测定了纯钛与Y_2O_3,、ZrO_2(Y_2O_3,稳定和CaO稳定)的初始反应温度和反应速率.结果表明,纯钛与 ZrO_2(CaO稳定)反应后的显微组织最粗大,为块状,而与Y_2O_3,反应产物最细小均匀,为条带状;三种陶瓷材料对纯钛 的初始反应温度依次为:1 378℃、1 245℃、1 213℃,反应速率也依次增大.     

用正电子湮没技术研究Cr和Nb对TiAl合金中缺陷和d-d电子相互作用的影响

测量Al,Si,Ti,Cr,Nb等纯元素以及Ti50Al50,Ti50l48Cr2,Ti50Al48Nb2合金的符合正电子湮没辐射多普勒展宽谱和寿命谱,获得金属及合金中d电子和缺陷的信息.结果表明,二元TiAl合金的电子密度和3d电子的信号较低,晶界缺陷的开空间较大.在TiAl合金中加入Cr或Nb,合金中的d-d电子作用增强,基体和晶界处的电子密度均增加.Ti50Al48Cr2合金的多普勒展宽谱的d电子信号高于Ti50Al48Nb2合金.讨论了Cr和Nb对TiAl合金中缺陷和d-d电子相互作用的影响.     

The isothermal and cyclic high temperature oxidation behaviour of Ti–48Al–2Mn–2Nb compared with Ti–48Al–2Cr–2Nb and Ti–48Al–2Cr

The isothermal and cyclic oxidation behaviour of Ti–48Al–2Mn–2Nb (at%) were studied at high temperatures in air in comparison with the intermetallic alloys Ti–48Al–2Cr–2Nb and Ti–48Al–2Cr. Tests were performed in air between 800 and 900°C. At 800°C Ti–48Al–2Mn–2Nb showed an excellent oxidation resistance under isothermal and cyclic conditions, comparable with Ti–48Al–2Cr–2Nb, and superior to Ti–48Al–2Cr. At 900°C the isothermal oxidation rate of Ti–48Al–2Mn–2Nb was similar as found for Ti–48Al–2Cr–2Nb, but much lower as that of Ti–48Al–2Cr. Upon cooling the oxide scale formed on Ti–48Al–2Mn–2Nb was prone to spallation. During the cyclic oxidation at 900°C, a steady state condition is reached for both niobium bearing materials, with a net linear mass loss rate, due to spallation and (re-)growth of the oxide scale. The linear mass loss rate for the Ti–48Al–2Mn–2Nb was higher than that of Ti–48Al–2Cr–2Nb, indicative of a higher susceptibility for spallation. During the initial stage of oxidation of all tested materials a complex multi-phased and multi-layered scale was formed consisting of α-Al₂O₃, TiO₂ (rutile), TiN and Ti₂AlN. After longer exposure times the outer scale was dominated by TiO₂. In case of the niobium containing materials no loss of protectivity of the oxide scale was found during the growth of the outer TiO₂ layer (under isothermal conditions). Two-stage oxidation experiments with isotope tracers were performed to study the oxidation mechanism in more detail.     

溅射TiAlCr涂层对Ti-24Al-14Nb-3V抗氧化性能的影响

研究了溅射Ｔｉ５０Ａｌ１０Ｃｒ及Ｔｉ５０Ａｌ２０Ｃｒ涂层对Ｔｉ２４Ａｌ１４Ｎｂ３Ｖ抗高温氧化性能的影响。结果表明,在８００℃下,Ｔｉ５０Ａｌ１０Ｃｒ及Ｔｉ５０Ａｌ２０Ｃｒ涂层表面由于可形成粘附性良好的Ａｌ２Ｏ３膜,大大改善了Ｔｉ２４Ａｌ１４Ｎｂ３Ｖ的抗高温氧化性能。９００℃时在Ｔｉ５０Ａｌ１０Ｃｒ涂层表面长出大量ＴｉＯ２,导致其氧化增重较大;而在Ｔｉ５０Ａｌ２０Ｃｒ涂层表面生成了连续Ａｌ２Ｏ３,其抗氧化性能良好。然而,由于ＴｉＡｌＣｒ涂层与基体热膨胀系数不同,在循环氧化过程中涂层出现一些裂纹,导致其抗循环氧化性能有所下降。     

废感光胶片制备超细银粉的研究

采用Lu2O3/TiO2/Nb2O5作为ZrO2热障涂层材料的稳定剂,研究Lu2O3/TiO2/Nb2O5共稳定ZRO2(15％ LTNSZ)热障涂层材料在900℃、40 mol％V2O5+60 mol％Na2SO4熔盐中的热腐蚀行为.结果表明:8％YSZ热障涂层材料热腐蚀2h后,t相ZrO2全部相变为m相ZrO2,热腐蚀产物为尺寸较大的YVO4晶体;15％ LTNSZ热障涂层材料热腐蚀20 h后,m相ZrO2的比例仅为5.5％,热腐蚀产物为尺寸较小的LuVO4晶体.与Y2O3稳定剂相比,Lu2O3/TiO2/Nb2O5稳定剂使ZrO2在40 mol％ V2O5+60 mol％ Na2SO4熔盐中的抗热腐蚀性能提高1个量级以上.     

Al2O3/ZrO2(Y2O3)复合材料的可靠性、磨损形态及其切削耐用度

研究了Al2O3和Al2O3/ZrO2(Y2O3)复合刀具材料的Weibull分布、磨损形态及其切削耐用度。用一元线性回归方法确定Al2O3/ZrO2(Y2O3)刀具的耐用度参数,分析切削条件对Al2O3/ZrO2(Y2O3)复合刀具材料寿命的影响。结果表明:Al2O3和含2%(摩尔分数)及3%Y2O3的ZrO2/Al2O3(Al2O3/ZrO2(2Y)及Al2O3/ZrO2(3Y))复合刀具材料Weibull模数的m值分别是5.6、10.2和11.7,说明Al2O3/ZrO2(3Y)陶瓷的可靠性最优;Al2O3/ZrO2(3Y)复合刀具切削40CrMoNiA合金钢的磨损形态主要来自磨粒磨损和粘结磨损,耐用度参数vc、f、ap的指数值分别为1.3、1.69和0.66,陶瓷刀具更适合高速切削,最大影响因素是进给量(f),在最佳切削条件下(vc=140 m/min,ap=0.5 mm和f=0.3 mm/r)切削耐用度为3 h。     

Isothermal oxidation behavior of powder metallurgy beta gamma TiAl–2Nb–2Mo alloy

A new TiAl–2Nb–2Mo beta gamma alloy was synthesized by powder metallurgy process. HIP’ed and vacuum heat treated specimens were isothermally oxidized at 800 °C and 900 °C in air up to 500 h. The TiAl–2Nb–2Mo alloy oxidized parabolically up to 500 h at both 800 °C and 900 °C. The oxides consisted of outer TiO₂ layer, intermediate Al₂O₃ layer, and inner TiO₂ rich mixed layer and the oxidation mechanisms of the alloy were identical at both temperatures. During oxidation, the degradation of lamellar colonies formed a diffusion zone just below the oxide/substrate interface consisting of γ-TiAl matrix and dispersed beta phases which contained high concentration of Nb and Mo. The oxidation rate of the TiAl–2Nb–2Mo alloy is more sensitive to temperature than those of the Ti–48Al–2Nb–2Cr and Ti–48Al–2Nb–2Cr–W alloys.     

高熵合金CrNbTiVZr的微观组织及其在模拟PEMFC环境中腐蚀行为研究

采用真空电弧熔炼和热处理制备了CrNbTiVZr高熵合金,利用XRD、SEM/EDS、动电位与恒电位极化曲线测试及XPS表面分析等方法,研究了高熵合金铸态及退火后的微观组织特征以及合金在模拟PEMFC环境中的电化学腐蚀行为及其钝化膜组成。结果表明,CrNbTiVZr高熵合金的铸态和退火组织均由富集Ti、Nb元素的无序BCC相和富集Cr、V、Zr元素的Laves相组成。铸态和退火合金在模拟PEMFC阴极环境中腐蚀电流密度Icorr均比304SS不锈钢下降一个数量级,具有较好的耐蚀性和稳定性,但在阳极环境中其耐蚀性与304SS相当,其中铸态合金的稳定性较差。合金在阴极环境良好的耐蚀性主要与其表面形成由Cr2O3、Nb2O5、V2O3、Ti2O3及ZrO2组成的致密钝化膜关系密切。     

The solidification path related columnar-to-equiaxed transition in Ti–Al alloys

Columnar-to-Equiaxed Transition (CET) of binary Ti–Al alloys and multi-component Ti–48Al–2Cr–2Nb alloys is studied using Bridgman solidification technique. The effect of aluminum concentration and growth rate on CET is determined. It is found in Ti–46Al and Ti–50Al alloy ingots equiaxed grains develop ahead of the moving solid–liquid interface with a growth rate of 500 μm/s; microstructures in Ti–49Al alloy stay columnar dendrites with the same growth rate. CET in Ti–Al alloys are not only influenced by growth rate, but also by the solidification path that is related to alloying composition. CET in Ti–Al alloys is predicted using the dendritic growth model based on the criterion of growth at marginal stability. According to the calculated results and directionally solidified microstructures, values of the nucleation undercooling for α and β phases are given. The growth rates to avoid CET in Ti–48Al–2Cr–2Nb alloy are suggested.     

The influence of thermal processing route on the microstructure of some TiAl-based alloys

The influence of a range of different continuous cooling rates from the alpha phase field has been investigated in large-grain-sized (∼1500 μm) Ti48Al2Cr2Nb and in grain-refined Ti48Al2Cr2Nb1B alloys. In addition the microstructure of direct laser-fabricated samples of Ti48Al2Nb2Mn has been examined in order to assess the influence of the complex heating cycle and high cooling rate on this alloy. It has been found that the critical cooling rates to obtain a particular structure are higher in grain-refined Ti48Al2Cr2Nb1B than in the alloy without boron (B). The increase in the amount of the lamellar structure during cooling takes place in different manners in the two alloys. The formation of the lamellar structure in laser-treated samples has been found to be very different with the formation of Al-rich gamma regions separating regions with a lamellar structure. The possible factors affecting phase transformations are discussed in terms of the role of grain boundaries and B in solution in the solid state transformations and, in the case of the laser-treated samples, of melting and remelting.