自反应火焰喷涂过程中碰撞沉积物的形成及分析

以Ti-B4C-C为反应喷涂体系，基于SHS反应火焰喷涂制备TiC-TiB2复相陶瓷涂层技术，进行粒子与基体碰撞试验，获得了自蔓延反应火焰喷涂粒子与基体碰撞变形后的各种形貌图，通过对飞行粒子结构与粒子变形特点的研究得出：飞行粒子的形态与结构决定了粒子的变形特点，五种形态的碰撞沉积物来自各自对应的飞行粒子；基体预热温度、喷涂距离和喷涂团聚粉粒制备质量对碰撞沉积物的沉积率及扁平化有重要影响：不同变形粒子问的相互作用对涂层组织与性能会造成不同的影响，扁平粒子的薄膜飞溅主要由陶瓷熔滴内的气泡引起。     

碰撞对喷涂陶瓷涂层粒子的影响

通过Ti-B4C-C喷涂体系的自蔓延反应火焰喷涂TiC-TiB2复相陶瓷涂层试验,研究了喷涂过程中处于自蔓延反应状态的飞行粒子与基体的碰撞行为,分析了飞行粒子的反应中间状态及其与基体碰撞变形形态,揭示了碰撞造成粒子自蔓延反应终止的本质原因.结果表明,飞行粒子的自蔓延反应是由表向内进行的,碰撞极大地影响飞行粒子的自蔓延反应进程,由于碰撞压缩弹性波作用、接触物理介质突变和热传导快速凝固等三方面作用导致飞行粒子的自蔓延反应终止.     

Al2O3复相陶瓷涂层的SHS反应火焰喷涂过程

基于自蔓延高温台成技术(SHS)的反应火焰喷椽技术，用氧-乙炔火焰引燃Al-Cuo团聚粉，使之发生自蔓延反应．在钢基表面制备了Al2O3复相陶瓷涂层。通过水淬熄试验截取飞行粒子的中间状态，对经水拎后的粒子及喷涂涂层进行物相与组执分析，从而给出了SHS反应火焰喷涂Al2O3复相陶瓷椽层的基本过程．即各团聚颗粒构成独立的徽小反应单元，经历Al熔化和Cuo分解的反应孕育、Al与Cu2O的飞行反应燃饶、与基体碰撞并继续反应、结构转变与凝固4个阶段，最终形喊Al2O3复相陶瓷馀层。     

反应火焰喷涂TiC/Fe复合涂层组织及形成机理

以TiFe粉和碳的前驱体（石油沥青）为原料通过前驱体碳化复合技术制备了Ti-Fe-C系反应喷涂复合粉末,并用普通火焰喷涂技术制备了TiC/Fe陶瓷金属复合涂层.观测了喷涂粉末、淬熄实验获取的飞行粒子以及涂层的形态、相和组织结构.结果表明：前驱体碳化复合Ti-Fe-C系喷涂粉末有非常紧密的结构;可有效的解决反应喷涂过程中原料粉末分离的问题.在反应火焰喷涂过程中,每一个喷涂粉末颗粒构成独立的微小反应单元,原料之间反应充分.在整个喷涂过程中喷涂粉末经历了熔化扩散、物相形成、碰撞后快速凝固三个阶段.所得涂层由TiC和Ti2O3共生聚集片层和细小TiC颗粒弥散分布于金属基体所形成的内晶型复合强化片层交替叠加而成.     

SHS反应火焰喷涂粒子与基体的碰撞及其数值模拟

以Ti-B4C-C为反应喷涂体系,通过碰撞实验和ANSYS有限元分析方法,研究了反应火焰喷涂TiC-TiB2复相涂层时,喷涂粒子与基体碰撞形成摊片的温度变化情况及其对涂层与基体结合的影响.研究表明,完成自蔓延反应、处于熔融状态的喷涂粒子与基体碰撞形成的摊片各部分温差较大,温度较低,不易使基体表面熔化,难以与基体形成良好结合;自蔓延反应进行中的喷涂粒子与基体碰撞形成的摊片各部分温差较小,温度较高,能较好地实现与基体的结合.模拟结果与实验结果基本吻合.     

SHS反应火焰喷涂粒子与基体的碰撞及其数值模拟

以Ti-B4C-C为反应喷涂体系，通过碰撞实验和ANSYS有限元分析方法，研究了反应火焰喷涂TiC-TiB2复相涂层时，喷涂粒子与基体碰撞形成摊片的温度变化情况及其对涂层与基体结合的影响。研究表明，完成自蔓延反应、处于熔融状态的喷涂粒子与基体碰撞形成的摊片各部分温差较大，温度较低，不易使基体表面熔化，难以与基体形成良好结合；自蔓延反应进行中的喷涂粒子与基体碰撞形成的摊片各部分温差较小，温度较高，能较好地实现与基体的结合。模拟结果与实验结果基本吻合。     

Ti-B4C-C系在火焰喷涂时的SHS过程

以Ti—B4C—C为反应喷涂体系，依托SHS反应火焰喷涂制备TiC—TiB2复相陶瓷涂层技术，通过水淬熄实验，截取了喷涂过程中飞行不同距离的粒子，观测了不同飞行距离下，中间状态反应产物的宏观特征、成分和组织结构及其变化过程，理论探讨了复合粉体在氧．乙炔火焰焰流中的飞行燃烧过程与反应机理。研究表明，中间状态的反应产物按其宏观特征出现了完全熔融的实心陶瓷液滴、完全熔融的空心陶瓷液滴、表面熔融芯部未熔的陶瓷颗粒和完全未熔的陶瓷颗粒4种。其飞行燃烧过程机理是：SHS反应始于钛粉的熔化，对位于火焰焰流芯部的中小尺寸喷涂团聚颗粒，其燃烧合成受扩散和毛细管机制控制，以爆燃方式进行；对位于火焰焰流外围的较大尺寸喷涂团聚颗粒，其燃烧合成受组元熔解析出机制控制。     

Al-CuO系SHS反应火焰喷涂涂层及副产物的形成与转变

采用SHS反应火焰喷涂工艺,在钢基体表面制备了以Al2O3-AlxCuy为主相的复相涂层。通过水淬熄实验,结合SEM和XRD等金相、结构分析测试手段,研究了Al-CuO系反应火焰喷涂过程中,Al-CuO团聚粉粒子的熔化、反应行为及涂层形成过程,阐明了涂层中副产物Cu9Al4和Al2Cu3金属间化合物的形成机理。研究表明:在60mm至150mm的飞行距离当中,CuO受热分解,生成Cu2O、Cu并释放出氧气,至150mm处分解完毕。粒子飞行过程中少量Al与分解产生的Cu2O反应生成少量Al2O3陶瓷相并还原出金属Cu。分解产生及被还原出的Cu与Al在液态下互溶形成合金溶液。喷涂粒子在喷距180mm时撞击基体后,Cu2O与Al充分反应,生成大量Al2O3陶瓷相并还原出金属Cu,其中Cu被液相Al-Cu合金吞并。喷涂后期SHS体系温度下降的过程中,开始发生自蔓延体系的结构转变,Al-Cu合金熔液经复杂的共晶、共析等反应,生成Cu9Al4和Al2Cu3金属间化合物。     

Al-CuO系SHS反应火焰喷涂涂层及副产物的形成与转变

采用SHS反应火焰喷涂工艺。在钢基体表面制备了以Al2O3-AlxCu7为主相的复相涂层。通过水淬熄实验。结合SEM和XRD等金相、结构分析测试手段，研究了Al-CuO系反应火焰喷涂过程中，Al-CuO团聚粉粒子的熔化、反应行为及涂层形成过程，阐明了涂层中副产物Cu9Al4和Al2Cu3金属间化合物的形成机理。研究表明：在60mm至150mm的飞行距离当中。CuO受热分解。生成Cu2O、Cu并释放出氧气，至150mill处分解完毕。粒子飞行过程中少量Al与分解产生的Cu2O反应生成少量Al2O3陶瓷相并还原出金属Cu。分解产生及被还原出的Cu与Al在液态下互溶形成合金溶液。喷涂粒子在喷距180mm时撞击基体后，Cu2O与Al充分反应，生成大量Al2O3陶瓷相并还原出金属Cu。其中Cu被液相Al-Cu合金吞并。喷涂后期SHS体系温度下降的过程中。开始发生自蔓延体系的结构转变，Al-Cu合金熔液经复杂的共晶、共析等反应，生成Cu9Al4和Al2Cu3金属间化合物。     

SHS反应喷涂TiC-TiB2复相陶瓷涂层的热力学分析与实验

基于SHS反应火焰喷涂技术,在钢基表面制备了TiC-TiB2复相陶瓷涂层.通过对SHS火焰喷涂陶瓷涂层反应体系的设计和其热力学计算,给出了SHS反应火焰喷涂TiC-TiB2复相陶瓷涂层的最佳配系.研究得出,当Ti,B4C和C组成的反应体系按1435摩尔比配制时,SHS反应易实现点火,反应绝热温度高,反应速度快,反应产物为TiC0.7N0 3与TiB2二相构成的共晶体,但其特有的共晶层状结构不明显,为交叉复相结构,陶瓷涂层较致密,机械性能较好,陶瓷与钢基体的结合强度可达27.5 MPa,显微硬度HV达15 270 MPa,耐磨性良好.     

涂层结构对Cr2O3涂层组织和性能的影响

采用等离子喷涂技术制备了3种结构的Cr2O3陶瓷涂层，即双层涂层，3层涂层和5层梯度涂层。探讨了涂层结构对涂层组织、抗拉结合强度、抗热震性和耐磨损性能的影响。结果表明，在涂层总厚度相同的条件下，采用多层复合涂层可提高Cr2O3涂层的结合强度、耐磨性和抗热冲击性，其中，5层结构涂层的综合性能最佳。涂层微观组织观察和显微硬度测试结果发现，5层结构涂层从基体到陶瓷层，涂层成分逐渐变化，具有梯度材料的特征。试验表明采用等离子喷涂技术可以制备梯度涂层。     

Plasma Sprayed Coating Using Mullite and Mixed Alumina/Silica Powders

Plasma sprayed ceramic coatings are widely used for thermal barrier coating applications. Commercially available mullite powder particles and a mixture of mechanically alloyed alumina and silica powder particles were used to deposit mullite ceramic coatings by plasma spraying. The coatings were deposited at three different substrate temperatures (room temperature, 300?°C, and 600?°C) on stainless steel substrates. Microstructure and morphology of both powder particles as well as coatings were investigated by using scanning electron microscopy. Phase formation and degree of crystallization of coatings were analyzed by x-ray diffraction. Differential thermal analysis (DTA) was used to study phase transformations in the coatings. Results indicated that the porosity level in the coatings deposited using mullite initial powder particles were lower than those deposited using the mixed initial powder particles. The degree of crystallization of the coatings deposited using the mixed powder particles was higher than that deposited using mullite powder particles at substrate temperatures of 25 and 300?°C. DTA curves of the coatings deposited using the mixed powders showed some transformation of the retained amorphous phase into mullite and alumina. The degree of crystallization of the as sprayed coatings using the mixed powder particles was significantly increased after post deposition heat treatments. The results indicated that the mechanically alloyed mixed powder can be used as initial powder particles for deposition of mullite coatings instead of using mullite powders.     

Calculation of Particle Parameters for Cold Spraying of Metal-Ceramic Mixtures

Formation of metal-ceramic composite coatings by cold spray is one of the major directions in the development and application of the technology. As experiments showed, addition of a hard ceramic component into the mixture can shift the transition from substrate erosion to particles adhesion closer to adhesion. This effect may be induced by ceramic particles which not only erode, but also activate the target surface. Velocity and temperature of particles at their high-velocity impact onto the substrate are governing parameters in particles/substrate interaction. These parameters influence both the process of metal particles deposition and the process of erosion/activation of the substrate surface by ceramic particles. Metallic and ceramic particles collide with each other in the gas stream. These collisions can produce preactivation effect on metal particles by cleaning their surface. The level of activation depends on a typical velocity of collision which is the difference between velocities of metal and ceramic particles. Parameters of metallic and ceramic particles in the gas stream are estimated. Calculations show that components of mixtures with fine abrasive particles have greatly different velocities that influences preactivation of metal particles. At the same time, the substrate surface is activated by fine abrasive particles characterized by a high-impact velocity.     

Combination of electrophoretic deposition and microwave-ignited combustion synthesis for the preparation of ceramic coated intermetallic-based materials

Electrophoretic deposition (EPD) was used to deposit sub-micrometric ZrO₂ particles on metallic powder compacts belonging to the systems Ni + Al and Ti + Al, which were used as deposition electrodes in the EPD cell. After EPD, combustion synthesis (CS) of such reactive electrodes was ignited in a microwave single-mode applicator, operating at a frequency of 2.45 GHz, in order to obtain in a single step the synthesis of the desired intermetallic phase (substrate) and the sintering of the previously deposited ceramic particles (or coating). Experimental results demonstrate that the excess heat released during the formation of nickel and titanium aluminides by CS can be exploited not only to self-sustain and self-propagate the reaction front along the substrate, but also to rapidly sinter the coating obtained by EPD. The innovative procedure here proposed is a promising strategy in order to obtain, in a single step, high temperature intermetallic-based materials, protected by well adhered ceramic coatings.     

Plasma Spray Deposition Enhancement of Titanium Nitride Layer Using Nitrogen-Contained Plasma Irradiation of Titanium Substrate as a Pre-spraying Method

Reactive plasma spray of TiN ceramic coating attracts much attention over the years because of its ability to deposit thick layers on various metal surfaces. However, some mechanical properties of the coating such as its hardness should be improved. In this study, initially a thin layer of titanium nitride was prepared on a titanium substrate during irradiation of titanium substrate by a thermal DC nitrogen-contained plasma jet. Then, during reactive plasma spraying, Ti particles were injected into plasma jet, converted to titanium nitride and huddled on to the substrate. This new hybrid method (primary plasma irradiation and post-reactive plasma spraying) for deposition of TiN coatings would combine the advantages of both plasma-enhanced chemical vapor deposition and reactive plasma spraying methods in part. It resulted in a thick and hard layer of titanium nitride film. Sample produced by this method was analyzed with x-ray diffraction confirming titanium nitride production. Vickers hardness was measured using optical microscopy which was around 1319 H_v300g. To study the cross section of the layer, optical microscopy and scanning electron microscopy (SEM) were used.     

SHS Flame Spraying TiC-TiB2 Multiphase Coatings

SURFACE COATINGS,which can reinforce thesubassembly surface through an additive cover withbetter mechanical property,play more and moreimportant role in the process of re-manufacture of thelapsed equipment or hardware.In recent years,morescientists begin to concentrate on the SHS reactiveFlame spraying,which is the combination ofself-propagating high temperature synthesis andtraditional technology of thermal spraying.In thismethod,it is characteristic of reactive energy betweenreactants…     

Base-metal saturation of refractory carbide coatings produced by enhanced ceramic jets in electrothermally exploded powder spray

Tungsten carbide and tantalum carbide were sprayed onto substrates of mild steel by the electrothermally exploded powder spray (ELTEPS) process. High-speed x-ray radiography revealed that tungsten-carbide jets of molten particles guided inside a nozzle exhibited denser flow than unguided jets at the substrate. The velocity of the jet was approximately 800 m/s at the early stage of jetting. The ceramic coatings obtained from the guided spray consisted of carbides of a few to tens of micrometers in size, which were saturated by the base metal up to the top of the coating. The coatings exhibited diffusion of the sprayed ceramics and base metal at the interface of the deposit and substrate. The enhancement of the jet flow formed a microstructure of the ceramic coating, which was saturated by the base metal even without post heat treatment.