碳钢硅-锆复合预处理工艺研究

目的为解决传统预处理工艺能耗高、环境污染严重的问题,在前期研制的硅烷化和锆化配方的基础上,进一步调整工艺参数,探索将硅烷化和锆化工艺合二为一,优化出性能优良的硅-锆金属预处理工艺。方法通过硫酸铜点滴实验、盐水浸泡实验、电化学极化曲线法测试转化膜的耐蚀性能,采用拉开法测试涂层在金属表面的附着力。使用SEM对转化膜的微观形貌进行表征。结果硅锆处理的最佳工艺参数为:pH=3.5,处理温度20℃,处理时间10 min。极化曲线测试结果表明,经硅锆处理后的碳钢腐蚀电流密度为未处理的1/40,膜层耐蚀性能良好。拉开法测得涂层在基体上的附着力达到11.48 MPa,完全满足一般预处理工艺要求。微观形貌分析显示,硅锆膜属于纳米级无定形型转化膜,膜层均匀、致密,能为金属表面提供有效防护。结论通过调整工艺参数,将硅烷化处理和锆化处理合二为一,获得性能优良的硅-锆复合膜。转化膜的耐蚀性能优良,与涂层附着力良好,满足预处理工艺要求。     

磁控溅射Ti膜对AZ91镁合金耐磨耐蚀性能的影响

目的通过表面镀Ti膜提高AZ91镁合金的耐磨性能。方法通过直流磁控溅射方法在AZ91镁合金表面镀Ti膜,用拉伸实验法在电子万能实验机上测定薄膜的附着强度,用原子力显微镜观察薄膜与基体的界面形貌,并分析不同溅射参数时膜基的结合能力。通过湿摩擦实验分析两种试样的耐磨性能,采用Js M-670l F冷场发射型扫描电子显微镜观测两种试样磨损后的表面形貌。采用动电位极化曲线测试装置测得两试样的极化曲线,从而判定其耐腐蚀能力。结果通过直流磁控溅射方法制备的Ti膜和AZ91镁合金基体的结合能力与溅射时间有关,当溅射时间为6 min时,膜基结合能力最佳,但结合其他两项参数,所制备试样采用的时间应为4 min。AZ91镁合金镀Ti膜后磨损率降低,腐蚀电流降低,腐蚀电位升高。结论直流磁控溅射方法镀Ti膜提高了AZ91镁合金的耐磨耐蚀性能。     

Thickness modulation effect of CeO_2 layer for YBCO films grown by pulsed laser deposition

CeO_2 film plays an essential role in nucleation and growth of YBa_2 Cu_3 O_7-x(YBCO) films. In this work,the dependence of superconducting properties of YBCO on CeO_2 films with different thicknesses was investigated,in order to achieve fabrication of high-performance YBCO coated conductors in industrial scale. The crystalline structure and morphology of CeO2 films with thickness ranging from 21 to 563 nm were systematically characterized by means of X-ray diffraction(XRD), atomic force microscope(AFM) and reflection high-energy electron diffraction(RHEED). Additional focus was addressed on evolution of the surface quality of CeO_2 films with thickness increasing. The results show that at the optimal thickness of 221 nm, CeO_2 film exhibits sharp in-plane and out-of-plane texture with full width of half maximum(FWHM) values of 5.9° and 1.8°, respectively, and smooth surface with a mean root-mean-square(RMS) roughness value as low as 0.6 nm. Combing RHEED and transmission electron microscope(TEM) cross-sectional analysis, it is found that nucleation and growth of CeO_2 films at early stage remain in island growth mode with rougher surface,while further increasing the thickness beyond the optimal thickness leads to weak surface quality, consequently resulting in degradation of superconductor layers deposited subsequently. Eventually, a critical current density(J_c) as high as 4.6×10~6 A·cm^-2(77 K, self-field) is achieved on a YBCO film on a thickness-modulated CeO_2/MgO/Y_2 O_3/Al_2 O_3/C276 architecture, demonstrating the advantages of CeO_2 films as buffer layer in high-throughput manufacture of coated conductors.     

调质结构对Ti-TiN-Zr-ZrN多层膜力学性能影响

采用真空阴极电弧离子镀技术,在TC11钛合金和单晶Si片表面分别沉积不同调制周期、不同R_Ti/TiN:R_Zr/ZrN调制比和不同厚度的Ti-TiN-Zr-ZrN多层膜。用扫描电镜、X射线衍射仪、划痕仪、显微硬度计和应力测试仪分析测试了多层膜的截面形貌、厚度、结合力、硬度和残余应力;重点研究了调制周期、调制比和膜层厚度等调制结构的改变对多层膜残余应力和相关性能的影响。结果表明：增加调制周期,则残余应力降低,结合力和硬度均增大;降低RTi/TiN:RZr/ZrN调制比,则残余应力增大,结合力下降,硬度增加;增大多层膜厚度,则残余应力略有上升,结合力和硬度都提高,当膜层厚度达到7.54μm后,硬度稳定在30Gpa左右。     

Development of a friction energy capacity approach to predict the surface coating endurance under complex oscillating sliding conditions

In the case of surface coatings application it is crucial to establish when the substrate is reached to prevent catastrophic consequences. In this study, a model based on local dissipated energy is developed and related to the friction process. Indeed, the friction dissipated energy is a unique parameter that takes into account the major loading variables which are the pressure, sliding distance and the friction coefficient. To illustrate the approach a sphere/plane (Alumina/TiC) contact is studied under gross slip fretting regime. Considering the contact area extension, the wear depth evolution can be predicted from the cumulated dissipated energy density. Nevertheless, some difference is observed between the predicted and detected surface coating endurance. This has been explained by a coating spalling phenomenon observed below a critical residual coating thickness. Introducing an effective wear coating parameter, the coating endurance is better quantified and finally an effective energy density threshold, associated to a friction energy capacity approach, is introduced to rationalize the coating endurance prediction. The surface treatment lifetime is then simply deduced from an energy ratio between this specific energy capacity and a mean energy density dissipated per fretting cycle. The stability of this approach has been validated under constant and variable sliding conditions and illustrated through an Energy Density–Coating Endurance chart.     

Size dependence of martensite transformation temperature in nanostructured Ni-Mn-Sn ferromagnetic shape memory alloy thin films

In the present study, we report the influence of grain size on structural and phase transformation behaviour of nanostructured Ni-Mn-Sn ferromagnetic shape memory alloy thin films synthesized by dc magnetron sputtering. With increase in substrate temperature, the structural phase changes from austenite with L2₁ cubic crystal structure to martensite with monoclinic structure. In addition, field-induced martensite-austenite transformation is observed in magnetization studies using superconducting quantum interference device magnetometer. The martensitic transformation behaviour of these films depends critically on the microstructure and dimensional constraint. Both, the martensite start temperature (M_s) and austenite finish temperature (A_f) of these nanostructured films decreases with decreasing grain size. The excess free volume associated with grain boundaries has been observed to increase with decrease in grain size which in turn leads to an increase in the number of grain boundaries. It has been proposed that the grain boundaries impose constraints on the growth of the martensite and confine the transformed volume fraction in nanocrystalline structure. A martensite phase nucleated within a grain will be stopped at the grain boundaries acting as obstacles for martensite growth. The investigations revealed that below a critical grain size of 10.8 nm, the austenite phase is observed to be more stable than the martensite phase which leads to the complete suppression of martensitic transformation in these films.     

Study of bactericidal efficiency of magnetron sputtered TiO2 films deposited at varying oxygen partial pressure

TiO₂ thin films have been deposited at different Ar:O₂ gas ratios (20:80,70:30,50:50,and 40:60 in sccm) by rf reactive magnetron sputtering at a constant power of 200 W. The formation of TiO₂ was confirmed by X-ray photoelectron spectroscopy (XPS). The oxygen percentage in the films was found to increase with an increase in oxygen partial pressure during deposition. The oxygen content in the film was estimated from XPS measurement. Band gap of the films was calculated from the UV-Visible transmittance spectra. Increase in oxygen content in the films showed substantial increase in optical band gap from 2.8 eV to 3.78 eV. The Ar:O₂ gas ratio was found to affect the particle size of the films determined by a transmission electron microscope (TEM). The particle size was found to be varying between 10 and 25 nm. The bactericidal efficiency of the deposited films was investigated using Escherichia coli (E. coli) cells under 1 h UV irradiation. The growth of E. coli cells was estimated through the Optical Density measurement by UV-Visible absorbance spectra. The qualitative analysis of the bactericidal efficiency of the deposited films after UV irradiation was observed through SEM. A correlation between the optical band gap, particle size and bactericidal efficiency of the TiO₂ films at different argon:oxygen gas ratio has been studied.     

High density large area hydrogen plasma by hollow cathode plasma array

Hydrogen plasma becomes an alternative to the conventional oxygen plasma in stripping photoresist in the next generation semiconductor processing because the conventional oxygen plasma is known to degrade ultralow dielectric constant films by depleting carbons from the films. An array of hollow cathode plasma is designed to have uniform and high density hydrogen plasma. From many combinations of cavity size and distribution, it is found that cylindrical ceramic cavity with 6 mm inner diameter, 10 mm depth and 30 mm spacing between neighboring cavities shows the widest process window. Nineteen cavities are engraved into the cathode plate of 200 mm diameter. Ceramic cavities are needed to survive against energetic ion bombardment. Dependence of the stripping rate on mixture ratio of N₂/H₂, gas flow rate, chamber pressure and RF power is investigated, and we have found that a stripping rate of more than 260 nm/min with 7% uniformity can be achieved when chamber pressure is 213 Pa, gas flow rate 10000 sccm, N₂/H₂ mixture ratio of 3:7 and RF power 2.5 KW. This high density hydrogen plasma in the order of 10¹¹/cm³can be a very effective method of photoresist stripping in the dual damascene process of copper metal and low-k dielectrics where oxygen plasma cannot be used.     

Microstructural characteristics of the oxide scale formed on 304 stainless steel in oxygenated high temperature water

The microstructural characteristics of oxide scale formed on type 304 stainless steel in oxygenated high temperature water have been investigated. From outer to inner layer, the oxide scale consists of faceted spinel particles, irregularly shaped hematite particles and a compact layer of nano-sized spinels. Some outmost spinels formed on top of other particles are depleted in Cr, while the hematite particles tightly embedded into the inner layer contain more Cr in the inner than in the outer part. The inner nano-sized oxide grow inwards directly from the bottom of outer particles. The related oxidation mechanism is discussed.     

Laser chemical vapor deposition of titanium nitride films with tetrakis (diethylamido) titanium and ammonia system

Wide-area and thick titanium nitride (TiN_x) films were prepared on Al₂O₃ substrate by laser chemical vapor deposition (LCVD) using tetrakis (diethylamido) titanium (TDEAT) and ammonia (NH₃) as source materials. Effects of laser power (P_L) and pre-heating temperature (T_pre) on the composition, microstructure and deposition rate of TiN_x films were investigated. (111) and (200) oriented TiN_x films in a single phase were obtained. The lattice parameter and N to Ti ratio of the TiN_x films slightly increased with increasing P_L and was close to stoichiometric at P_L > 150 W. TiN_x films had a cauliflower-like surface and columnar cross section. The deposition rate of TiN_x films increased from 42 to 90 µm/h at a depositing area of 10 mm by 10 mm substrate, decreasing with increasing P_L and T_pre. The highest volume deposition rate of TiN_x films was about 10² to 10⁵ times greater than those of previous LCVD using Nd:YAG laser, argon ion laser and excimer laser.