Investigation of Impact Behavior of Cold-Sprayed Large Annealed Copper Particles and Characterization of Coatings

In this research, the large gas-atomized copper powder was selected as the feedstock. Some powder was annealed in a vacuum circumstance to avoid the effect of grain boundaries on the high velocity impact behavior of particles during cold spraying. The annealed Cu powder was deposited by cold spraying with respect to the single impacts and coating deposition under certain gas condition. In addition, the rebounded copper particles were collected for morphology analysis compared to the adhered particles. The results show that the average size of the rebounded particles is apparently increased compared with the starting powder because of the rebounding of larger particles and intensive plastic deformation of the rebounded particles. For the deposited particles, obvious plastic deformation causes a higher hardness to the coating. It is found that the rebounded particles have also experienced large deformation and shear instability at the impact interfaces.     

Thin film coatings of WO<Subscript>3</Subscript> by cold gas dynamic spray: A technical note

Dense and adhesive WO₃ films were prepared on a silicon substrate by the cold gas dynamic spray process (or cold spray). In contrast to standard metallic coatings, there was no sizable crater formation and plastic deformation. However, the aggregation of raw powder particles of a relatively large size was found to be destroyed upon impact on the substrate, forming a highly irregular surface with very fine secondary particles and providing good interlocking powder and void reduction among the particles in the coating. High-resolution images of the substrate interface showed that particles at the interface were more densely packed and that good adhesion was obtained. There fore, the particle bombardment onto the first layer of the coating could provide enhanced adhesion to the substrate mechanically and/or chemically.     

钛合金切削过程氧化膜特性研究

高速切削钛合金时，在加工表面会产生氧化膜，对钛合金的力学性能造成影响。对钛合金Ti-6Al-4V进行单因素车削试验，研究切削表面变形特性并对氧化膜表面进行物相分析。结果表明：切削表面会产生严重塑性变形，变形层的厚度随着进给量的增大而增大，切削表面发生氧化反应，形成氧化膜，表面呈现不同的颜色，其成分主要为Al2O3、锐钛矿型 TiO2 和金红石型 TiO2。     

热氧化TC4静动态力学性能研究

本文选取700 °C/10 h热氧化工艺,对TC4进行热氧化处理。通过准静态压缩,纳米压入及分离式Hopkinson压杆冲击等测试,研究了热氧化对TC4静动态力学性能的影响。此外,借助扫描电镜(SEM)分析了动态冲击后氧化层的形貌。结果表明,热氧化TC4具有较好的静态力学性能和较高的应变率强化效应。氧化层在较低冲击应变率下,能够提高TC4的塑性；而当应变率过大,则会降低其塑性。最后,经过对本构模型修正和试验数据拟合,得到了室温下的热氧化TC4的Johnson-Cook(J-C)本构方程。修正曲线与实验结果对比,两者在塑性平台区吻合较好。     

Al_(0.5)CrCoFeNi高熵合金高温氧化的研究

采用真空电弧炉在氩气保护下熔炼Al0.5Cr Co Fe Ni高熵合金,在不同温度(800~1100℃)下进行100 h的高温氧化实验,测定其氧化动力曲线,采用X射线衍射仪和扫描电镜等方法分析氧化层结构和形貌。结果表明:Al0.5Cr Co Fe Ni高熵合金在800和900℃形成的氧化膜较完整且致密,具有较为优异的抗氧化性能。在1000和1100℃形成的氧化膜较厚,膜内有大量裂纹与孔洞,抗氧化性能较差。氧化初期,界面反应起主导作用,随着氧化膜的生长,扩散过程发挥越来越重要的作用,成为继续氧化的控制因素,以致一种或多种合金元素氧化物在表面析出,形成尖晶石类内层氧化物Ni Cr2O4、Co Cr2O4、Fe(Cr,Al)2O4内氧化层。在高温氧化过程中,N2会参与反应,与Al发生较强反应,生成Al N颗粒,进一步的氧化过程使Al N再次氧化,N2逃逸,留下具有Al N外形的空洞。     

Effects of the substrate temperature on the deposition of thin SiOx films by atmospheric pressure microwave plasma torch (TIA)

The effect of surface temperature on the deposition of silicon oxide (SiO_x) films with a non-thermal microwave axial injection torch (TIA) was investigated in an open air reactor. Argon was used as plasma gas and hexamethyldisiloxane (Si₂O₂C₆H₁₈) as silicon precursor. The parametric study reported here focuses on the influence of the substrate temperature on the morphological and chemical properties of the films deposited in the interval [0 °C–130 °C]. A similar effect of low and high surface temperature on the deposition process and on the microstructure of the deposited films was highlighted. Macroscopically, particles were promptly produced in the gas phase and incorporated to the film, which generates high surface roughness. Microscopically, FTIR results have shown a high carbon contamination of the deposited films at low and high temperatures, resulting in understoichiometric SiO_x films. They have also demonstrated that an optimum growth window for smooth and particle free SiO_x was to keep the surface temperature between 30 and 60 °C. Simple reaction mechanisms for powder formation and continuous silicon oxide thin films growth are suggested for each temperature ranges.     

The Influence of Oxidizing Medium on Structure,Mechanical Properties,and Breakage Pattern of Oxide Films of Zr—1% Nb Alloy under Conditions Simulating Oxidizing Media of WWER and PWR Reactors

This article investigates into the structure, phase composition, mechanical properties, and breakage pattern of oxide films formed on the surface of Zr—1% Nb alloy after corrosion tests in autoclave in water, steam, and water with lithium. Oxidation in water with lithium promotes formation of oxide films with a thickness of more than 100 μm, and, after oxidation in water or steam, the thickness is 5–15 μm. Upon oxidation in water, oxide films are generated with laminar structure: in the substrate, the grains are extended with the thickness of ~80 nm, near film surface the grains are equiaxial with the diameter of ~30 nm. After holding of the specimens in steam the oxide films are comprised mainly extended grains with the thickness of ~95 nm with a minor amount of equiaxial grains, 10%, with a diameter of ~30 nm, after oxidation in water with lithium the mixture of equiaxial and weakly extended nanograins is observed in the film structure. Upon loading of specimens with the structure of equiaxial and weakly extended grains the oxide films are broken due to generation of transversal cracks propagating to basic metal. The oxide films with laminar structure oxidized in water are broken due to exfoliation along the interface between the layers of extended and equiaxial grains. Breakage of films with the structure of equiaxial and weakly extended grains starts at the stage of elastic deformation at a stress of 300 MPa. The highest breakage stresses of 1150 MPa are characteristic for alloy specimens oxidized in steam. Breakage of films with laminar structure after oxidation in water occurs at average stresses of 798 MPa. The cohesive/adhesive strengths of films oxidized in water and steam are nearly the same. In thick alloys, oxide films oxidized in water with lithium, substrate does not open even at loading of 100 N. According to data of Raman spectroscopy, oxide film is mainly comprised of monoclinic phase of zirconium oxide; however, after oxidation in steam at the metal—film interface, a barrier layer of tetragonal phase of zirconium dioxide has been detected that prevents accelerated oxidation.     

Amorphization of ZrO2 + CeO2 Powders Through Mechanical Milling for the Use of Kinetic Spray

The coating formation in a kinetic spray process mainly depends on the impact of inflight particles at a high velocity. The plastic deformation at the impact interface would disrupt the native oxide scale on the particle and the substrate to generate the intimate contact of the atomic structures. Accordingly, it poses a challenge in producing ceramic coating during kinetic spray because of the lack of plasticity of ceramic powders at room temperature. In this study, we proposed to prepare ZrO₂ ceramic coatings using partially amorphized powder with nanometer size in the kinetic spray process. To prepare the powder for the use of the kinetic spray, the amorphization and grain refinement of ZrO₂ powder in mechanical ball milling were studied. The results showed that the amorphization and grain refinement were improved because of the formation of solid solution when the CeO₂ agent was added. Subsequently, a nearly spherical powder was achieved via spray drying using the milled powders. The plasticity of the milled powders was tested in the kinetic spray process using Nitrogen as process gas. A dense ZrO₂-CeO₂ coating with a thickness of 50 μm was formed, whereas spraying milled ZrO₂ powder can only lead to an inhomogeneous dispersion of the destructible particles on the surface of the substrate.     

微纳米陶瓷粉末对粒子行为及复合涂层性能的影响

将微纳米材料应用于热喷涂制备高耐磨、耐蚀的涂层是近年来的研究热点.作者测量了微纳米陶瓷粉末对电弧喷涂中飞行粒子熔化程度、飞行速度及雾化粒子尺寸的影响,观察了喷涂铁基TiB2/Cr3C2/Al2O3粒子的变形过程,分析微纳米陶瓷粉末对粒子行为的影响规律,并对涂层性能进行了测试,发现微纳米粒子增加了金属陶瓷复合涂层的结合强度,改善涂层的韧性,对涂层的耐磨粒磨损性能影响不大,但明显提高涂层的耐冲蚀性能.最后对微纳米陶瓷粉末在喷涂过程中的作用、对粒子行为及涂层性能的影响机理进行了探讨.     

硼砂在制备WCp增强铁基复合材料中的去氧化膜作用机理

通过X-Ray衍射图谱分析，研究硼砂在制备WCp增强铁基复合材料中的去氧化膜作用及原理。结果表明，在增强相碳化鸲颗粒当中加入一定量的硼砂，这些硼砂在高温铁液的热作用下将被熔化，所形成的熔融态的硼砂液可溶解氧化铁等，使固相的氧化铁等变成可以流动的液相。另一方面，无机非金属的硼砂液与碳化鸲颗粒的润湿性较差，而铁液与碳化钨颗粒之间几乎可以完全润湿。所以，当铁液进入到碳化钨颗粒之间时，铁液将把熔融态的硼砂液排挤出去。从而实现去除复合材料组织中氧化膜的目的。     

Metal particle deposition stimulation by surface abrasive treatment in gas dynamic spraying

Processes of supersonic blasting for producing thin metal coatings and of cold spray for producing thick coatings by solid metal particle jets are based on the particle plastic deformation. Extensive plastic deformation of accelerated metal particles at the surface roughness was observed. The possibility of stimulation of metal particle deposition by the substrate and coating blasting by ceramic particles was experimentally confirmed. The process of thick coating creation by the mixed metal-ceramic powder supersonic jet is presented.     

Tribological properties of nanoporous anodic aluminum oxide film

Friction and wear properties of nanostructured anodic aluminum oxide (AAO)) films were studied in relation to contact load and pore size (pore diameter). Uniformly arrayed nanoporous aluminum oxide films (pores of 28 nm, 45 nm, 95 nm, and 200 nm diameter and 60-100 μm thick) were synthesized by anodization. Reciprocating wear tests using 1 mm diameter steel balls as counterpart were carried out for a wide range of load (from 1 mN to 1 N) at ambient environment. The friction coefficient reduced with the increase of load. The friction coefficient decreased by approximately 30% when the load increased by 3 orders of magnitude. The pore density marginally affected the frictional properties of AAO films. The influence of pore size on the friction coefficient was significant at relatively high loads (0.1 N and 1 N) whereas it was negligible at low loads (1 mN and 10 mN). The worn surface of AAO films tested at low loads did not experience tribochemical reaction and exhibited only mild plastic deformation. Dispersed thick smooth films were formed on the worn surface of all samples at relatively high loads whereas only extremely thin smooth film patches were rarely formed at low loads. These thick smooth films were generated by combined influence of tribochemical reaction at the contact interface and plastic deformation of compacted debris particles as evidenced by energy-dispersive spectroscopy analysis. We suggest that these thick films mainly contributed to the decrease of friction regardless of the pore size.     

Fe-Ni-B超细非晶粉表面不同处理后的组成和性能

本文对Fe—Ni—B超细非晶粉表面加以单宁酸和重铬酸钾处理，并采用了XPS和TEM等对处理后超细粉的表面组成和结构进行了分析。结果表明，单宁酸和重铬酸钾处理均可以提高Fe—Ni—B超细非晶粉的饱和磁化强度，但后者的提高幅度远大于前者。原因在于二种表面处理均使超细粉的表面状态发生了有利于饱和磁化强度的变化，在表面形成了复合型氧化物NiFe2O4；而重铬酸钾处理还在超细粉表面形成了致密的Cr2O3层，阻挡了氧原子从表面向体内的扩散，减少了超细粉的氧化态数量，而使其饱和磁化强度得以大大提高。     

Formation of Cold-Sprayed Ceramic Titanium Dioxide Layers on Metal Surfaces

Titanium dioxide (TiO₂) coatings have potential applications in biomedical implants or as photo-catalytic functional systems. Cold spraying is a well-established method for metal on metal coatings. In cold spraying, the required heat for bonding is provided by plastic deformation of the impacting ductile particles. In contrast, few authors have investigated the impact phenomena and layer formation process for spraying brittle ceramic materials on ductile metal surfaces. In this study, the formation of TiO₂ coatings on aluminum, copper, titanium, and steel substrates was investigated by SEM, TEM, XRD, and Raman spectroscopy. The results show that the deposition efficiency depends on spray temperature, powder properties, and in particular on substrate ductility, even for impact of ceramic particles during a second pass over already coated areas. Ceramic particles bond to metallic substrates showing evidence of shear instabilities. High-resolution TEM images revealed no crystal growth or phase transitions at the ceramic/metal interfaces.     

Micro-FAST成形过程中电流大小对颗粒变形的影响

创新性地采用多物理场活化烧结微成形技术(Micro-FAST)制备了316L不锈钢和纯Cu微型齿轮。探讨了电流大小对316L不锈钢和纯Cu粉末体系在烧结过程中颗粒变形的影响。结果表明,在电场、力场和温度场的耦合作用下,升温过程是粉末体系实现致密化的主要过程。由于电塑性效应的影响,粉末体系在致密化过程中表现出的显著特征之一是颗粒的塑性变形。电流越大,颗粒的变形量越大,粉末体系的轴向尺寸减小量越多,最终微型烧结体的相对密度也越大。     

超细WC-Co硬质合金及其磨损性能研究

采用低温化学镀方法在超细WC颗粒表面进行金属钴包覆,烧结包覆后的复合粉体制备新型硬质合金NYG（WC-3%Co）.研究了超细WC-Co硬质合金的力学性能、断口形貌和显微结构,在销盘式磨损试验机上进行干滑动磨损实验.结果表明,在硬质合金烧结过程中,沿WC晶界均匀分布的金属钴不仅起粘结剂作用,也起抑制剂作用阻碍晶粒的长大;新型硬质合金的抗弯强度、断裂韧性、硬度和耐磨性能均得到较大提高;在干滑动摩擦条件下,新型WC-Co硬质合金的失效以塑性变形及细小碳化钨相颗粒脱落为特征.     

锌粉颗粒形状对机械沉积无结晶镀层结构的影响

以球状锌粉和片状锌粉为原始锌粉借助于机械镀工艺制备了无结晶锌防护层，运用光学显微镜（OM）、扫描电子显微镜（SEM）观察了镀层的结构形貌；采用XRD技术分析了镀层的物相组成；采用贴滤纸法进行了镀层的孔隙率测试。研究结果表明，片状锌粉制备的镀层比球状锌粉制备的镀层表面要平滑、光亮。球状锌粉制备的镀层中锌粉颗粒呈紧密堆积，部分锌粉颗粒发生塑性变形；片状锌粉制备的镀层中的锌粉颗粒呈层片状叠加，镀层中锌粉颗粒没有发生明显塑性变形。两种形状锌粉制备的镀层均为锌基多相混合体系，镀层中没有固溶体、化合物等合金相产生，属于锌基复合镀层。锌粉颗粒形状对镀层中颗粒之间的结合机理没有显著影响，两种镀层中锌粉颗粒间均以机械咬合为主。     

纯Fe在Cr粉末中经表面机械研磨处理后的组织与性能

在含有Cr粉末的容器中对Fe进行表面机械研磨处理(SMAT),得到具有一定厚度的纳米晶表层。结果表明,在纳米表层高的扩散性能和高应变速率的剧烈塑性变形条件下,Cr元素被压入和扩散入Fe纳米晶表层。在随后不同温度的退火处理中,Cr元素在纳米表层中进一步扩散和均匀化,在细晶强化和加工硬化作用消失后仍导致退火后Fe表层力学性能的提高。在粉末介质中进行表面机械研磨处理能方便和有效地实现材料的表面改性,应对其应用加以关注。     

Bonding mechanisms of thermally softened metallic powder particles and substrates impacted at high velocity

Thermally softened titanium powder particles were impacted at about 760 m/s onto three substrate materials, i.e., titanium, aluminum, and zirconia, at the same time. In spite of the very different physicochemical properties of these substrate materials, most of particles were bonded to the substrate. However, their microstructures suggested different dynamic deformation behaviors and interface features. On titanium or zirconia substrate, particles showed shear instability and direct metallurgical bonding or metal-ceramic bonding that resulted from the removal of oxide covered on them, while on aluminum, although the particle was not heavily deformed and its oxide remained it was also bonded to the substrate due to the instability of substrate and the removal of aluminum oxide. The results have demonstrated the complex and material dependent nature of bonding formation in kinetic spraying using thermally softened metallic powder particles.     

铜粉处理对涂料导电性能的影响

金属铜粉由于它具有固有的光泽、良好的导电性和低廉的价格，作为导电涂料的填料引起了人们的关注。但铜较活泼，容易被氧化。在贮存和运用过程中，铜粉表面容易形成Cu2O和CuO不导电薄膜，这给铜粉的使用带来了障碍。在铜粉表面包覆硬膜酸是防止铜粉氧化而实施的一种方法，但硬脂酸是一种不导电的有机物，这给制备导电涂料带来了不便。针对以上两种情况，本文探讨了对表面部分氧化的铜粉和包覆有硬脂酸的铜粉的处理方法，以及它们对涂料导电性的影响。