TIG熔敷Ti-Si-C系统在Ti-5Al-2.5Sn表面形成陶瓷涂层的化学反应分析

采用TIG热源在钛合金表面堆焊Ti-SiC和Ti-SiC-C两种体系的粉末,形成表面陶瓷涂层.利用SEM和XRD等分析手段对两种配方陶瓷涂层的微观组织和物相进行了分析,用热力学方法计算了两种系统中各种可能发生的化学反应的Gibbs自由能变化.结果表明,Ti-SiC系统熔敷层的微观组织主要由树枝状的TiC、针棒状和菊花状的Ti₅Si₃相组成,其反应机理为:8Ti+3SiC→3TiC+Ti₅Si₃.Ti-SiC-C系统熔敷层的微观组织除了树枝状的TiC相之外,还有TiSi₂和Ti₃SiC₂,其反应机理为:6Ti+3SiC+C→Ti₃SiC₂+TiSi₂+2TiC.通过对两种系统的微观组织及化学反应分析可得出,在Ti-SiC系统中适当的添加石墨,可生成具有自润滑性能的Ti₃SiC₂相,避免Ti₅Si₃脆性相的生成.     

飞机发动机叶片激光熔覆性能

为了修复飞机发动机叶片（K417G）的铸造缺陷和损伤,采用了500W-IPG光纤激光熔覆系统将镍基合金粉末（RCF-201）熔覆到镍基高温合金K417G基体上.利用显微镜、扫描电子显微镜（SEM）、X射线衍射（XRD）、电子探针（EPMA）和能谱仪（EDS）等分析了堆焊层的组织和成分,用显微硬度计分析了堆焊层硬度分布,用高温蠕变实验机分析了堆焊层高温蠕变性能.试验结果表明,熔覆层从熔合线到表面的组织依次由平面晶、柱状晶和等轴晶组成;熔覆层的组织为亚共晶组织,初晶相为富镍固溶体γ-Ni,共晶组织为γ-Ni+Cr₇C₃+Cr₂₃C₆+（Mo_0.54,Ti_0.46） C;熔覆层的硬度约为650 HV,约是母材硬度（350 HV）的1.86倍;在950℃/235 MPa条件下,激光熔敷试样的蠕变寿命最长约为26.17 h,且断裂位置位于母材.     

激光熔敷对精冲模具寿命的影响

以含有镧铈混合稀土和石墨烯的金属复合粉末作为熔敷材料,对小型齿轮Cr12Mo V精冲模具进行了激光熔敷处理,并对激光熔敷层的显微组织、物相组成以及模具的耐磨损性能和模具寿命进行了分析。分析结果表明,激光熔敷层组织均匀细小,由γ（Ni）相、Ni Ti相、WC相、W₂C相、Co₃W₃C相、Co相和石墨烯组成;激光熔敷处理使模具耐磨性和使用寿命得到明显提高。     

TC4钛合金表面激光熔覆Ni60+Cu/Mo涂层的显微组织和性能

在TC4钛合金表面激光熔覆Ni60A、Ni60CuMo复合粉末,研究Cu和Mo元素对熔覆层显微组织、硬度及耐磨性的影响。结果表明,在相同激光熔覆工艺参数下,Ni60CuMo熔覆层中除含有Ni60A熔覆层所含有的Ti₂Ni、TiNi、TiB₂和TiC相外,还含有Cu_0.81Ni_0.19、Ti₂Cu、MoSi₂等硬质相。在硬质相的作用下,Ni60CuMo熔覆层的显微硬度平均值(HV_0.1)为826,是Ni60A熔覆层硬度的1.2倍。在相同条件下,Ni60CuMo熔覆层的磨损率为3.30×10^-6 mm³/(N·m),约为Ni60A熔覆层磨损率的16.42%,是TC4钛合金基体磨损率的4.23%。添加Cu和Mo能显著提升TC4钛合金表面激光熔覆层的耐磨性。     

TiNiNb钎焊Cf/SiC与TC4接头组织结构

文中在钎焊温度980℃、钎焊时间15 min的条件下,采用Ti_54.8Ni_34.4Nb_10.8（原子分数,%）共晶合金粉末真空钎焊C_f/SiC复合材料与TC4钛合金.用SEM,EDS及差热分析法（DTA）观察测定了钎料组织、成分及熔点,分析了钎焊接头的微观组织结构.结果表明,Ti_54.8Ni_34.4Nb_10.8共晶钎料由Ti₂Ni及Ti（Nb,Ni）化合物组成,实际熔点为935℃.钎焊过程中,Ti和Nb元素与复合材料反应形成TiC和NbC混合反应层;钎料中的镍与TC4中的镍发生互扩散,在TC4钛合金侧形成扩散层;连接层由弥散分布的Ti（Nb,Ni）化合物和Ti₂Ni相组成.C_f/SiC与连接层界面为接头最薄弱环节,此处易形成裂纹.     

铬、钼对耐候钢熔敷金属耐蚀性能和力学性能的影响

通过周浸加速腐蚀试验、锈层微观分析、电化学等方法,研究了铬和钼对耐候钢熔敷金属耐蚀性能和力学性能的影响.结果表明,熔敷金属中铬、钼含量增加,其耐蚀性能提高.钼对耐蚀性的提升优于铬.铬、钼分别以Cr₂O₃,Fe_xCr_3-xO₄,MnFe_xCr_2-xO₄,Mn_1-xFe_xCr₂O₄,NiFe_xCr_2-xO₄和MoO₃形式富集于锈层中,提高锈层致密性,抑制阳极溶解,增强锈层对基体的保护作用,从而提高熔敷金属的耐蚀性能.铬、钼含量增加,熔敷金属强度上升,冲击韧性明显下降.同时,熔敷金属中M-A组元和粒状贝氏体含量增加,针状铁素体含量降低.组织差异是造成熔敷金属强度升高、韧性降低的主要原因.     

CFRP表面激光熔覆TC4 + AlSi10Mg复合涂层的组织与性能

采用激光熔覆技术在碳纤维增强热塑性塑料(carbon fiber reinforced thermoplastics, CFRP)表面成功地制备了TC4 + AlSi10Mg复合涂层. 通过扫描电镜、能谱仪和透射电镜分析了TC4 + AlSi10Mg复合涂层与CFRP基体连接的界面层微观结构、元素成分分布及相组成. 采用纳米压痕仪对复合涂层到基材的硬度变化规律进行测试. 结果表明,通过激光熔覆技术可以快速在CFRP材料表面形成连续的、均匀的TC4 + AlSi10Mg复合涂层. TC4 + AlSi10Mg复合粉末在激光作用下,受热熔化渗透到CFRP基体内部,形成良好的冶金结合,并在碳纤维-树脂-复合涂层之间形成连续的界面层. TC4 + AlSi10Mg复合涂层与CFRP基体连接的界面层相成分为TiC,Ti₃Al,TiS₂和Ti₃AlC相. CFRP基体的平均硬度为10.15 HV,涂层的最高硬度可达1914 HV. 基于试验观察和理论分析,得出CFRP表面激光熔覆TC4 + AlSi10Mg复合涂层主要的界面反应机理为Ti(s) + C(s)→TiC(s),Al(l) + 3Ti(s)→Ti₃Al(s).     

Ti3SiC2含量对Q235B钢表面激光熔覆Fe基耐磨涂层性能的影响

采用激光熔覆技术在Q235B钢表面制备了不同Ti₃SiC₂含量的Fe55/Ti₃SiC₂复合涂层,并利用光学显微镜、扫描电镜、X射线衍射仪、硬度仪、摩擦磨损机和电化学工作站等研究了涂层的显微组织、物相及综合性能。结果表明:由于Ti₃SiC₂的加入及其在高温下分解降低了熔池的换热特性等综合因素,导致Fe55/Ti₃SiC₂复合涂层的晶粒粗化;随着Ti₃SiC₂的添加,Fe55/Ti₃SiC₂复合涂层中形成了Cr₇C₃、SiC、CrC和TiSi等硬质相,组织变得粗大,并且α-Fe相的尺寸粗大及含量增加,而复合涂层中产生的硬质相不足以抵消晶粒粗化以及α-Fe硬度较小而发生软化所降低的硬度,综合导致了复合涂层的硬度下降。Fe55/Ti₃SiC₂复合涂层中形成的金属硅化物TiSi具有良好的抗氧化性能,减小了氧化磨损中因氧化膜脆性和疏松产生的加剧磨损,因此,足以抵消因硬度降低以及摩擦系数增大的影响,使得Ti₃SiC₂添加量为2%的涂层具有最高的耐磨性。     

Ti6Al4V合金激光熔覆Co-Ti3SiC2复合涂层的组织和摩擦学性能

为改善Ti6Al4V合金的摩擦学性能,分别用纯Co、Co-2%Ti₃SiC₂、Co-5%Ti₃SiC₂、Co-8%Ti₃SiC₂混合粉末为原料,在Ti6Al4V合金表面激光熔覆制备复合涂层,利用X射线衍射仪(XRD)、扫描电镜(SEM)以及摩擦磨损试验机分析物相组成、显微组织结构以及在常温下的摩擦学性能。结果表明:所有复合涂层与基体结合良好,伴有少部分微孔。纯Co涂层的主要物相为γ-Co、CoTi、CoTi₂等,而Co-Ti₃SiC₂涂层物相包括γ-Co、CoTi、CoTi₂、TiC、Ti₅Si₃和残留的Ti₃SiC₂。涂层的硬度相对基体提高了1.90~2.15倍,而耐磨性能相应提高了3.02~5.44倍。     

Al/Si比例对TC4合金表面激光熔覆Ti-Al-Si涂层组织与摩擦性能的影响

以不同Al/Si比例的Ti-Al-Si复合粉末为原料,采用激光熔覆技术在TC4合金表面制备Ti-Al-Si涂层,研究了Al/Si比例对涂层物相、微观组织、显微硬度及摩擦磨损性能的影响。结果表明,单道熔覆的涂层中没有发现明显的裂纹及气孔,涂层与基体之间呈现良好的冶金结合。不同Al/Si比例涂层中组织均以熔断的枝晶为主,枝晶的成分主要为α-Ti,增强相为板条状的Ti₅Si₃及Ti₇Al₅Si₁₂,枝晶间主要是TiAl、Ti₃Al、TiAl₃金属间化合物。Si元素含量越高,涂层中原位生成的增强相的含量越多,涂层的显微硬度也比较高,最高可达1194 HV0.1,约为基体的4.1倍,但增强相过多会使涂层的脆性增加,耐磨性降低。Al元素含量较多时,组织细化效果明显,增强相对硬度和耐磨性能的影响比晶粒细化的作用更强。     

Liquid phase surface alloying of CP-titanium with aluminum in an atmosphere of argon and nitrogen

In the present work, surface alloying of CP-titanium with different mixtures of titanium and aluminum powders in a gas mixture of 20% argon and 80% nitrogen was carried out using tungsten inert gas (TIG) process. The microstructures of the alloyed layers were investigated by optical microscope (OM), scanning electron microscope (SEM), and the phases formed were studied by X-ray diffraction analysis. The hardness of these layers was also evaluated using a microhardness machine. The results showed that the surface hardness was significantly enhanced from 175 HV_0.1 for the untreated substrate to more than 1000 HV_0.1 for the alloyed layers, due to the formation of Ti₃Al₂N₂ as well as Ti₃Al and TiN in the modified layers. It was also noticed that the alloyed layers exhibited better wear resistance as compared with the untreated substrate.     

Ti/Al异种合金电弧熔钎焊接头界面断裂行为分析

采用TIG电弧的方法实现了钛合金与铝合金熔钎焊连接,分析了不同焊丝形成的熔钎焊接头的界面组织和断裂特征.结果表明,纯铝接头界面为单一的TiAl3相,裂纹主要沿着TiAl3反应层与焊缝之间的界面扩展.拉伸时首先从坡口拐角启裂,当裂纹扩展至接头反面时,断裂扩展形式转变为从焊缝金属撕裂,接头抗拉强度为139MPa.添加Al-Cu-La焊丝的接头界面结构为TiAl3+ Ti2Al20La双化合物层,拉伸时沿TiAl3反应层与钛合金界面开裂,以界面内的微裂纹为裂纹源并向反应层内扩展,属于准解理断裂,接头抗拉强度达270 MPa.稀土La元素作用下形成的双化合物层是提高接头强度的关键.     

Synthesis of titanium aluminide coatings on aluminum and titanium surfaces by mechanical alloying and subsequent annealing

Intermetallic Ti-Al-based coatings were synthesized by mechanical alloying in a vibratory ball mill and subsequent annealing. A titanium layer was deposited on aluminum specimens and an aluminum layer and aluminum-titanium mixture were deposited on titanium specimens. Under the effect of milling balls, powder particles deposit at the substrates, forming layers that have a very good cohesion with the substrate. During subsequent heating, diffusion layers on the basis of titanium-aluminum phases are synthesized as a result of the chemical interaction between titanium and aluminum. In the case of titanium layer deposited on aluminum, the temperature interval of transformations is 600–650°C; first, a Ti₃Al₅-based phase is formed; then, as diffusion saturation with Al increases, an Al₂Ti-based layer appears; and finally, the Al₃Ti compound is formed. The reaction rates depend on the temperature and the duration of annealing. On titanium with a (Ti + Al) layer deposited on its surface, the Al₃Ti, Al₂Ti, TiAl, and Ti₃Al compounds are formed in a temperature interval of 600–900°C. In the case of deposition a homogeneous aluminum layer on titanium, only Al₃Ti and Ti₃Al phases were observed after annealing.     

Formation of Brittle Phases During Pulsed Current Gas Tungsten Arc Welding of Titanium to Aluminum Alloys

Welding of titanium alloy TA15 to aluminum alloy Al 2024 was conducted by pulsed current gas tungsten arc welding using AlSi12 filler metal. Formation process of phases near the Ti/Al interface was discussed. Titanium and aluminum were partially fusion welded in the upper part while brazed together in the middle and bottom parts of the joint. In the upper part of the joint, intermetallics Ti₃Al + Ti₅Si₃, TiAl + Ti₅Si_3, and TiAl₃ were formed as three layers orderly from the titanium side to the weld metal. In the middle and bottom parts of the joint, intermetallics Ti₅Si₃ and TiAl₃ were formed as two layers near the Ti/Al interface.     

Solid-state hot pressing of elemental aluminum and titanium powders to form TiAl (γ + α2) intermetallic microstructure

The elemental powder metallurgy (EPM) process is used to prepare TiAl-base intermetallics. An EPM process conducted by two-stage solid-state hot pressing was employed to prepare TiAl-base intermetallics and to investigate the resulting microstructural changes. The results showed that the TiAl₃ phase forms in the first stage. During the temperature increase to the second sintering stage, lamellar phases start to precipitate in the TiAl₃ matrix. Further, the TiAl₃ phase transforms to TiAl, and Ti₃Al layers develop in the remaining titanium particles. Meanwhile, the lamellar phases grow into ring-type structures between the TiAl matrix and the Ti₃ Al layers. After the second stage, the remaining titanium particles are fully reacted, and a microstructure of Ti₃Al phases enclosed by fine-grained lamellar rings in the TiAl matrix is developed.     

Ti3SiC2-TiSi2-TiB2熔覆复合材料在氩气退火过程中的相稳定性分析

采用氩弧熔敷法制备了Ti3SiC2-TiSi2-TiB2复合材料,并对其在高温氩气退火过程中的相稳定性进行了分析. 结果表明,Ti3SiC2相在氩气保护和1 450℃高温条件下具有稳定性,而原位合成的含碳的TiSi2(Cx)固溶体相在退火过程中通过原子扩散而发生分解,其转化产物主要为Ti3SiC2及少量的SiC稳定相. 退火后,熔覆样品中Ti3SiC2的体积含量比退火前增加了4.8%. 热力学计算结果表明,样品在退火过程中通过原子扩散引起的反应机制为TiSi2(Cx)→Ti3SiC2+SiC,并提出了Ti3SiC2-TiSi2-TiB2熔覆复合材料在退火过程中的原子扩散反应模型. 退火试验分析结果表明,钨极氩弧熔敷法与高温退火相结合的复合工艺可以提高Ti3SiC2-TiSi2-TiB2熔覆复合材料的整体热稳定性.     

A structural and compositional analysis of a TiO<Subscript>x</Subscript> diffusion barrier for indium tin oxide/Si contacts

We investigated the structural and compositional changes of titanium oxides as a diffusion barrier between indium tin oxide (ITO) and Si under two different Ti oxidation conditions: (1) annealing of the Ti layer deposited on Si in air followed by ITO deposition (Type 1) and (2) annealing in nitrogen after the deposition of ITO/Ti on Si (Type II). The diffusion barrier layer in both samples namely the Ti layer oxidized under different conditions, consisted of two regions: a region composed of a mixture of silicide and titanium oxide near the Si substrate and a titanium oxide region near the ITO layer. However, the titanium oxide in the Type 1 samples was composed of TiO₂ and Ti₂O₃ phases, whereas Ti₂O₃ was dominant in the Type II samples. In addition, the Type I and II samples showed the formation of voids in the middle of the barrier layer and in the region near the ITO layer, respectively. Therefore, the electrical and optical properties of ITO/TiO_x/Si are dependent on the structural and compositional changes of the diffusion barrier layer.     

电弧熔覆Ti-Si金属间化合物表面层的组织与性能

采用在纯钛基体上预敷硅粉,然后进行电弧熔覆的表面处理技术,通过改变焊接电流调整预敷硅粉与纯钛基体的熔化量,制备Ti-Si金属间化合物表面层,使基体获得表面冶金强化.用金相显微镜、扫描电镜和X射线衍射仪,对表面层的微观结构及界面进行了分析研究,并测试了显微硬度分布和耐磨性.结果表明,随着焊接电流增加,表面层的显微组织类型由亚共品到共晶,最后为过共晶.Ti5Si3相使表面层具有较高的硬度,耐磨性比纯钛基体有明显提高.     

Investigation on TIG arc welding–brazing of Ti/Al dissimilar alloys with Al based fillers

Abstract

Dissimilar alloys of Ti–6Al–4V and 5A06 Al were butt joined by Al based fillers using a novel TIG welding process, referred to as keyhole arc welding–brazing. The flow behaviour of weld pool was introduced, which was characterised by the formation of a keyhole under the tungsten electrode. It was found that porosity tended to be produced in the middle of the fusion line, while adding elements prevented its formation. At brazing interface, interfacial reaction at root face was enhanced, and a uniform serrated layer, identified as TiAl₃, was obtained by pure Al fillers. When Al–Cu–La fillers were used, block Ti₂Al₂₀La phases appeared at the interface between the TiAl₃ layer and the brazed seam. Compared to joints brazed by pure Al fillers, the formation of Ti₂Al₂₀La reduced the hardness of the interfacial layer by more than half, while Al₂Cu increased that of the brazed seam by ～50%. The tensile strength of Ti/Al joints reached 270 MPa.     

Pack Cementation Coatings for High-Temperature Oxidation Resistance of AISI 304 Stainless Steel

Aluminum and titanium are deposited on the surface of steel by the pack cementation method to improve its hot-corrosion and high-temperature oxidation resistance. In this research, coatings of aluminum and titanium and a two-step coating of aluminum and titanium were applied on an AISI 304 stainless steel substrate. The coating layers were examined by carrying out scanning electron microscopy (SEM) and x-ray diffraction (XRD). The SEM results showed that the aluminized coating consisted of two layers with a thickness of 450???m each, the titanized coating consisted of two layers with a thickness of 100???m each, and the two-step coatings of Al and Ti consisted of three layers with a thickness of 200???m each. The XRD investigation of the coatings showed that the aluminized coating consisted of Al₂O₃, AlCr₂, FeAl, and Fe₃Al phases; the titanized layers contained TiO₂, Ni₃Ti, FeNi, and Fe₂TiO₅ phases; and the two-step coating contained AlNi, Ti₃Al, and FeAl phases. The uncoated and coated specimens were subjected to isothermal oxidation at 1050?°C for 100?h. The oxidation results revealed that the application of a coating layer increased the oxidation resistance of the coated AISI 304 samples as opposed to the uncoated ones.