2018 Vol. 38, No. 2

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2018, 38(2): .
Research Process in Plasma Spray Physical Vapor Deposited Thermal Barrier Coatings
Jia SHI, Liangliang WEI, Baopeng ZHANG, Lihua GAO, Hongbo GUO, Shengkai GONG, Huibin XU
2018, 38(2): 1-9.
Plasma spray physical vapor deposition (PS-PVD) is a newly developed processing technology for advanced functional coatings and films. PS-PVD is featured with the advantages of plasma spray (PS) and physical vapor deposition (PVD) and can be used for high efficient co-deposition of vapor phases, liquid droplets and solid particles, with the capability of highly flexibility in building up various microstructure architectures. Besides, uniform deposition of the coatings or films can be achieved by this technology even on the non-line-of-sight areas of those components with complex geometry. Owing to the above merits, PS-PVD shows very promising potential in the fields of thermal barrier coatings (TBCs), environmental barrier coatings (EBCs), super-hard and wear-resistant coatings or films, oxygen permeable membranes and electrode membranes. Further, PS-PVD is recognized as the processing technology for advanced TBCs in the future. In this paper, physical principles and recent research progress in preparation and deposition mechanisms of PS-PVD TBCs are briefly introduced and summarized. The future development trends of PS-PVD in new thermal barrier coatings are prospected.
Novel Ceramic Materials for Thermal Barrier Coatings
Zhaolu XUE, Hongbo GUO, Shengkai GONG, Huibin XU
2018, 38(2): 10-20.
Thermal barrier coatings (TBCs) are the key technologies for hot-components in advanced gas turbine and land-based engines. Yttria stalized zirconia (YSZ) is now extensively used as ceramic topcoat in TBC system. However, YSZ cannot be used for next generation aircraft engines due to its limitation in high-temperature capabilities and thermal barrier performances. In this paper, recent research progress of several novel TBC ceramic candidates covering multiple oxide co-doped zirconia, A2B2O7-type compounds, magnetoplumbite compounds, garnet-type compounds, perovskites and other new oxides ceramics is overviewed. And the development tendencies and challenges of ultra-high temperature TBC materials for future applications are prospected.
High Temperature Protective Bond Coats:Development and Effect of Reactive Element
Zebin BAO, Chengyang JIANG, Shenglong ZHU, Fuhui WANG
2018, 38(2): 21-31.
High temperature protective coatings, mostly metal-based, are widely utilized for protecting key components (such as gas turbine blades) serving in areo- or land-based turbine engines. By forming a slow-growing dense oxide scale (Al2O3, Cr2O3 and SiO2 etc.), these coatings offer reliable protection, and prevent the underlying substrate alloy from aggressive invasion at high temperature. The paper reviews the developing history of bond coats, mainly aluminide diffusion coating and MCrAlY overlay. Modification of these coatings has been mainly related to increasing Al content for achieving a proper distribution, while the refrainment of element inter-diffusion between coating and substrate alloy is a worrying concern. Then, the attention is transferred to reactive element effects (REEs), including how REE was observed in history, mechanisms explaining REE and recent investigations on the doping-effect of RE. In summary, the challenges to achieve an ideal protective metal coating are presented, in which the possible solutions to overcome these challenges are mentioned.
Service Environment Simulation Test Method of Thermal Barrier Coatings
Jundong SHI, Qing HE
2018, 38(2): 32-42.
Research of thermal barrier coatings (TBCs) is extremely challenging to the poor service conditions, failure mechanism with multi-coupling factors and its own complex multi-interface poly-phase characteristics. The performance of TBCs is mainly determined by its special composition and microstructure, and it is degraded due to the temperature, time, environment and other factors in service. The evaluation of service performance of TBCs is a necessary way to improve coating performance and develop new coatings. In order to rationally evaluate the life of the coatings and to further study the evolution of coating structure and properties, different simulated service environment test devices are established. These test devices have different heat sources, such as furnace, flame, infrared lamp and laser, etc., which coupled the function with rapid temperature rise and down, temperature gradient, corrosion and CMAS deposition simulation, even the alternating load simulation, and then the low-cost, flexible and controllable testing means and methods are obtained for revealing failure mechanism of TBCs, improving the coating material and process and fast evaluation of durability of the coatings.
Failure and Protection of Thermal Barrier Coating under CMAS Attack
Shanjie YANG, Hui PENG, Hongbo GUO
2018, 38(2): 43-51.
Along with the increase of operating temperature of aero-engine, thermal barrier coatings (TBCs) used in the engine are highly susceptible to the attack of glassy silicate deposits, the chemical composition of which is mostly CaO-MgO-Al2O3-SiO2 (CMAS). The deposition of CMAS on TBCs tends to cause blocking of cooling holes in turbine blades, which results in decrease of cooling efficiency, change of temperature and stress distribution in blades. On the other hand, the durability of TBCs is significantly reduced due to the CMAS deposition. It is very important to make the strategy to constrain the absorption and infiltration of glassy CMAS on TBCs at high temperature to ensure the development of advanced aero-engine. In this paper, the failure mechanisms of TBCs which are thermochemistry, densification and phase transformation caused by CMAS are summarized, and the solutions to CMAS, such as coating structure optimization, adding permeability barrier layer and sacrificial layer are briefly overviewed.
Electrodeposition of NiCrAl(Y) Coatings with High Contents of Cr and Al and Their Oxidation Resistance
Huijuan ZHEN, Lixi TIAN, Zhihong DONG, Xiao PENG
2018, 38(2): 52-58.
NiCrAlY coatings have been widely employed as the coatings to risist high temperature oxidation, hot corrosion and also the bond coat (BC) under thermal barrier coatings (TBCs). High quality NiCrAlY coatings are currently always manufactured by means of physical vapor deposition (PVD). This work prepared new NiCrAl nanocomposite coatings through electrodeposition of Ni into a porous CrAl nanoparticle layer pre-deposited electrophoretically on a metallic substrate. Microstructural observation shows that the as-deposited NiCrAl coatings, where the CrAl nanoparticles with the maximum mass percentage reaching 35 are uniformly dispersed, are dense and well bonded to the substrate. Oxidation in air at 1000 ℃ shows that the NiCrAl coatings can " smartly” grow a protective scale of either Cr2O3 or Al2O3, depending on the ratio of the content of Cr to Al which can be controlled during electrophoretic deposition. In the meantime, no spallation occurs even though the coatings oxidized for hundreds of hours.It is implying that the NiCrAl coatings are as good as the NiCrAlY coatings prepared by PVD in resistance to high temperature oxidation. This work paves a new way for manufacturing high quality NiCrAl(Y) coatings employed as overlay coat and BC, through electrodeposition with the merits of ease of fabrication and low cost as well as high efficiency.
Application Potential of 4D Printing Technology in Development of Aircraft
Yadong SU, Xiangming WANG, Bin WU, Fuyu WANG, Jiaxing WANG, Bendong XING
2018, 38(2): 59-69.
4D printing is a new developing technology that has been developed rapidly in recent years. It is of great significance for the development of intelligent structure of aeronautical and aerospace equipments. This paper discusses the development process and the demand for the multifunctional structure of the fighter, and explains the important functions of 4D printing in the realization of aircraft functions integration, explores the definition of 4D printing, special materials, processing equipment and structure characteristics. The application potential of 4D printing in intelligent variant structure, the new generation of thermal protection technology and the new stealth technology are also discussed. The development proposals of 4D printing in technical maturity, key technical breakthrough and discipline integration are given.
Research Progress and Application Perspectives of 4D Printing
Ya'nan WANG, Fanghui WANG, Zhongming WANG, Jianjun LIU, Hong ZHU
2018, 38(2): 70-76.
4D printing technology has attracted people's attention since it came up in 2013. 4D printing is a kind of new manufacturing technology which is based on 3D printing and smart materials. In other word, 4D printing is evolved from 3D printing and aimed at the improvement of structure, property and function. 4D printing predicts that the self-assembly, multifunction and self-healing can be achieved. This paper reviews the whole research progress of 4D printing in time sequence, and summarizes the achievements of this technology in material science, manufacturing industry, bioengineering and medical science. In addition, the application perspectives in this field are also discussed.
Research Progress on Laser Assisted Machining
Yingxin ZHANG, Libao AN
2018, 38(2): 77-85.
This paper reviews the recent research progress on laser assisted machining technology. On the experimental research aspect, the technical characteristics of various processes including laser assisted turning, milling, drilling, and grinding have been summarized, and the effects of laser and cutting parameters on machining quality have been stated. Investigations show that properly increasing laser power and decreasing cutting speed and feed rate within limits is propitious to fully soften the workpiece material in the cutting zone, and therefore improves the machinability of the workpiece material and enhances the machining efficiency and quality. Current simulation research on laser assisted machining is mainly focused on the cutting temperature field and machining process. By establishing the model of temperature field, the best temperature range for removing workpiece material can be predicted and the cutting parameters can be optimized. Cutting process simulation discusses the influence of physical quantities in machining such as stress, strain, and temperature, providing a basis for controlling the quality of the machined surface in real operations. In the future, the study on machining mechanism, processing techniques and simulation for optimization should be strengthened, and the data base for laser assisted machining processes should be found, in order to promote the industrial application of the technology.
Research Progress on Preforms of C/C Composites
Le SUN, Cheng WANG, Xiaofei LI, Heng LI, Mengyuan YE, Chong AN
2018, 38(2): 86-95.
Carbon/carbon (C/C) composites are important fundamental thermal-structure materials in aeronautic and astronautic fields. One of the most primary basic technologies of C/C composites is the manufacture of carbon fiber preforms which determines the performances of C/C composites. In this paper, the preforms including needle-punched felt, fine weave pierced and axial carbon rod weave fabric are introduced, and the process, properties and applications of those preforms are compared. Due to the low cost and homogeneous ablation, needle-punched felt preforms are extensively used in solid rocket motor nozzle and aircraft brake disc. Fine weave pierced preforms are applied in SRM because of high fiber volume content, short densification cycle and low ablative rate. With the excellent ablative rate attributed to more than 70% fiber perpendicular to the gas flow direction, axial carbon rod weave fabric is used in large SRM. For the domestic research status of preforms, it is suggested that the research involving the effect of pore structure and fiber distribution on mechanical, thermal physics properties and the subsequent densification of C/C composites should be further enhanced in order to promote the performance of C/C composite material.
Strain Study of Nb-Si{001} Interface Based on Geometric Phase Analysis
Xu LI, Lingling REN, Sitian GAO, Liqi ZHOU, Xingfu TAO
2018, 38(2): 96-103.
High resolution electron microscopy imaging and geometric phase analysis were employed to study the microstructure and strain states of Nb/Si interface prepared at different sputtering pressures. The results show that the surface of Nb thin film consists of petals-shape lamellas with random morphological distribution and no obvious characteristic orientation. The size of the lamella increases and the density of the lamella decreases with the increase of deposition pressure; meanwhile, a large number of pores appear on the surface of Nb film and a mixed layer of Nb and Si is generated between Nb film and Si substrate. When Nb films were deposited at 0.65, 0.85 Pa and 1 Pa, the strain values of εxx were respectively –0.16%, –0.30% and 0.42%; the strain values of εyy were respectively –1.23%, –0.31% and 0.26%.The strain states of Si substrate are tremendously influenced by the disposition pressure. The strain states of Si substrate are mainly produced by the effect of the interfacial mixed layer and Nb thin film. A large number of structure defects are generated in the mixed layer of Nb and Si, which produces intrinsic stress in the mixed layer, and further results in the formation of strain in Si substrate.
Preparation and Wave-absorbing Performance of Retinyl Schiff Base Salts Coordinated with Rare Earth La3+ and Ce3+ Ions
Huteng LIU, Kesheng ZHOU, Lianwen DENG, Sheng LIU, Longhui HE, Lingling YAO
2018, 38(2): 104-109.
With vitamin A acetate as raw material, ethylenediamine retinyl Schiff base salts coordinated with rare earth ion La3+, Ce3+ were synthesized, and the structure of the products was characterized by FT-IR and Raman spectra. The electromagnetic parameters in the frequency range of 2-18 GHz were measured by microwave vector network analyzer, its reflectivity was calculated, and the main factors and mechanism that affect the wave-absorbing performance of rare retinyl Schiff base salts were discussed. The results show that the coordination bond is formed by the rare earth ions and Schiff base. The reflectivity of Schiff base coordinated with La3+ ion is –16 dB at 12.9 GHz (bandwidth with reflectivity better than –10 dB is 3.1 GHz), the reflectivity of Schiff base coordinated with Ce3+ ion is –18.8 dB at 12.7 GHz (bandwidth with reflectivity better than –10 dB is 3.4 GHz). Microwave absorption performances of the both are superior to the wave-absorbing performance of Schiff base coordinated with non-rare earth ions.
Effect of Different Stress Levels on Fatigue Residual Stiffness of Carbon Fiber Reinforced Composite
Shuang QIU, Jinyu ZHOU
2018, 38(2): 110-117.
In order to study the fatigue behavior of carbon fiber reinforced composite and the effect of stress level on its fatigue residual stiffness, monotonic tension tests and fatigue tests were conducted and the fracture morphology of carbon fiber composite was observed by using scanning electron microscope (SEM). The results show that the fatigue performance of carbon fiber reinforced composite is good at room temperature, and the cycle time is more than 106 under 48% ultimate tensile strength. The decline rate of its residual stiffness is different under different stress levels. In the early stage of the fatigue, the decline rate of residual stiffness is relatively lower under high stress level, while it is higher under low stress level. In addition, the boundary characteristics of residual stiffness is also different under different stress levels. The boundaries under low stress are significant, while the boundaries under high stress are obscure. The results of fracture analysis show that with the decrease of stress level, the fatigue failure mode is complicated. Under high stress, the fracture of the fiber cluster is the main feature, while at low stress level the fatigue failure mode includes fiber and matrix fracture, interfacial debonding and fiber pull-out, etc.
Finite Element Model of X-cor Sandwich Structure
Hangying SHAN, Jun XIAO, Qiyi CHU
2018, 38(2): 118-125.
Referring to the mode of Z-pin pre-processing, three kinds of finite element method models including assembled, combined and separated model are introduced. Applicability, advantage and disadvantage of the models are presented, which provide the references for the designers to use finite element method. On the basis of Z-pin bridging law by pullout test and Z-pin pulled out from foam test, separated model of X-cor sandwich structure for finite element analysis is introduced. Double spring coupling elements are introduced to reveal microscopic mechanism of interaction between Z-pin, foam and face-sheets in separated model. The spring parallel to Z-pin interface simulates the relative slip and analyzes the adhesive stress of interface, the spring perpendicular to Z-pin interface simulates the transverse elastic supporting of foam to Z-pin buckling. The finite element simulation on mechanical behavior and interface failure of X-cor sandwich structure are realized.