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81.
《Ceramics International》2022,48(4):5229-5238
The uneven growth of thermally grown oxides (TGOs) in thermal barrier coating systems is an important cause of cracking failure at the coating interface in high-temperature environments. The doping of rare earth elements in the bonding layer can effectively inhibit the formation of spinel oxides in the TGO and improve the high-temperature oxidation resistance of the coating. However, a single rare earth element has a limited effect on inhibiting TGO failure. In this study, a NiCoCrAlYHf coating was prepared using a supersonic flame spraying (HVOF) technique. The effects of HfO2 doping on the high-temperature oxidation behaviour of the coatings and diffusion behaviour of metallic elements in the coatings were investigated at 1100 °C. The results showed that the nano-sized HfO2 filled the pores between the powder particles and improved the hardness of the coating. During the high-temperature oxidation process, the oxides formed by Hf and Y had a large size and low solubility, which effectively blocked the diffusion of Al. This slowed the generation of spinel oxides, effectively inhibited the growth of the TGO, it inhibits the initiation and propagation of cracks within the coating, reduces damage to the coating from tensile and compressive stresses at the interface, and improved the high-temperature oxidation resistance of the coating. 相似文献
82.
《Ceramics International》2022,48(1):179-189
Combined stir casting and squeeze casting processes were used to fabricate Al5083 matrix composites reinforced with 20, 25, and 30 wt% SiCp. The microstructure, mechanical properties and wear behavior of the composites fabricated by combined stir casting and squeeze casting were compared with those fabricated by stir casting. The results revealed that the combined casting method improved the distribution of SiC particles through the reduction of the agglomeration of SiC particle and reduced the porosities of the samples from 2.32% to 1.29% in the sample containing 30 wt% SiC. These modifications led to the enhancement of mechanical properties i.e. increased the hardness to 85 BHN and the compressive strength to 350 MPa for the sample containing 30 wt% SiC fabricated by the combined casting method. In addition, the wear resistance of the samples fabricated by the combined casting method improved because of the reduced size of the wear debris as well as the smaller worn region. The dominant wear mechanism of all the composite samples fabricated by both methods was the delamination of the tribological layer while adhesion wear was dominant in the monolithic Al alloy. 相似文献
83.
采用化学镀方法在钕铁硼表面分别制备Ni-P合金镀层、Ni-Mo-P合金镀层、Ni-P/PTFE复合镀层和Ni-Mo-P/PTFE复合镀层,并研究了不同化学镀层在模拟海洋大气环境中的腐蚀行为。结果表明:Ni-P合金镀层、Ni-Mo-P合金镀层、Ni-P/PTFE复合镀层和Ni-Mo-P/PTFE复合镀层都完整覆盖钕铁硼表面,它们的粗糙度差别不大,在模拟海洋大气环境中的腐蚀失重都低于钕铁硼的腐蚀失重,容抗弧半径增大且电荷转移电阻有不同程度的提高。与Ni-P合金镀层和Ni-Mo-P合金镀层相比,Ni-P/PTFE复合镀层和Ni-Mo-P/PTFE复合镀层具有优良的耐腐蚀性能,原因在于PTFE颗粒较均匀的沉积在镀层表面增加一道屏蔽层,也起到阻碍腐蚀介质渗透腐蚀的作用。尤其是Ni-Mo-P/PTFE复合镀层,其表面更致密,PTFE颗粒沉积更均匀,能更有效延缓腐蚀介质与钕铁硼接触,显著提高钕铁硼在模拟海洋大气环境中的耐腐蚀性能。 相似文献
84.
《Journal of the European Ceramic Society》2022,42(11):4479-4492
ZrB2-MeC and ZrB2-19 vol% SiC-MexCy where Me=Cr, Mo, W were obtained by pressureless sintering. The capability to promote densification of ZrB2 and ZrB2-SiC matrices is the highest for WC and lowest for Cr3C2. The interaction between the components results in the formation of new phases, such as MeB (MoB, CrB, WB), a solid solution based on ZrC, and a solid solution based on ZrB2. The addition of Cr3C2 decreases the mechanical properties. On the other hand, the addition of Mo2C or WC to ZrB2-19 vol% SiC composite ceramics leads increased mechanical properties. Long-term oxidation of ceramics at 1500 °C for 50 h showed that, in binary ZrB2-MexCy, a protective oxide scale does not form on the surface thus leading to the destruction of the composite. On the contrary, triple composites showed high oxidation resistance, due to the formation of dense oxide scale on the surface, with ZrB2-SiC-Mo2C displaying the best performance. 相似文献
85.
《Journal of the European Ceramic Society》2022,42(1):43-51
Poor antioxidant and thermal-shock capacities of C/C composites thermal barrier coating (TBC) caused by cracking and shedding of coatings has been a major obstacle blocking the development of C/C composites. Herein, in-situ growth of whisker reinforced silicon carbide transition layer and inter-embedding mechanism of multi-gradient coatings were brought into the design of TBC to enhance the antioxidant and thermal-shock capacities. A three-layer gradient coating SiC-SiCw/ZrB2-SiC/ZrSiO4-aluminosilicate glass (ZAG) from inside to outside, in which ZrB2-SiC/ZAG serve as oxygen barrier layers with self-healing ability and SiC-SiCw provides thermal stress buffering and bonding against cracking and shedding of coatings, is designed. The ZAG mainly forms a dense oxygen blocking frontier with self-healing ability through fluidized glass, while the ZrB2-SiC can react actively with infiltrated oxygen in a way of self-sacrifice, preventing oxygen erosion to C/C matrix and SiC-SiCw transition layer. As a result, the collaborative work among layers endows this coating with excellent high temperature service performance. This work provides a new insight for the design of excellent TBC. 相似文献
86.
《Ceramics International》2022,48(14):20041-20052
The growing demand for radiation-resistant optical glasses for space and nuclear radiation applications has attracted significant research interest. However, radiation-resistant fluorophosphate glasses have been poorly studied. In this work, we report on the tailoring and performance of radiation-resistant fluorophosphate glasses that contained cerium through codoping with Sb2O3 and Bi2O3. The physical properties, optical properties, microstructure, and defects of fluorophosphate glasses were investigated using transmittance measurements, absorption measurements, as well as Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and electron paramagnetic resonance (EPR) spectroscopy. The results showed that the radiation resistance of all codoped fluorophosphate glasses was better than the undoped cerium-containing fluorophosphate glasses after 10–250 krad(Si) irradiation. Especially in glasses doped with Bi2O3, the optical density increment at 385 nm was only 0.1482 after 250 krad(Si) irradiation. The CeO2 prevented the development of phosphate-related oxygen hole center (POHC) defects, whereas further codoping with Bi2O3 suppressed the formation of oxygen hole center (OHC) and POEC defects, reducing the breaking of phosphate chains caused by CeO2. Bi3+ is more likely than Sb3+ to change the valence, affecting the transition equilibrium of intrinsic defects and reducing the concentration of defects produced by irradiation. When codoping with Sb2O3 and Bi2O3, Bi2O3 does not enhance radiation resistance owing to the scission effect of Sb2O3 on the phosphate chain, which is not conducive to the radiation resistance of glasses. This indicates that the cerium-containing fluorophosphate glasses doped with Bi2O3 can effectively suppress the defects caused by irradiation and improve the radiation resistance of the glasses. 相似文献
87.
88.
Mozhgan Shahmirzaee Ahmad Iran Nejhad Amir Masoud Arabi 《Particulate Science and Technology》2019,37(1):110-117
ZnAl2O4 and ZnO nanostructure particles and in situ crystallization of zinc aluminate and zinc oxide coating layers on sintered α-Al2O3 and γ-Al2O3 granules by the microwave-assisted combustion method were investigated. For powders, the effects of solution pH value and for coated samples the influence of support type on the structure, microstructure, and photocatalytic activity of powders were studied. Results showed that variation of synthesis pH value caused to considerable change in agglomeration, specific surface area, obtaining up to 88 and 92% yields for zinc aluminate and zinc oxide nanoparticles, respectively. γ-alumina granules were more appropriate supports than the α-alumina ones because of the better photocatalytic activities and lower extent of the attritions for both zinc aluminate and zinc oxide coating layers. 相似文献
89.
The different types of metal powder used for selective laser melting(SLM) process would cause distinct corrosion behavior due to the uniformity of the obtained microstructure.The SLM-produced Ti–5Cu alloy using atomized Ti–5Cu metal powder(SLMed Ti–5Cu) in this work reveals a relatively uniform microstructure with overwhelming acicular α/α′ phase and shows great advantages on corrosion resistance compared with the SLM-produced Ti–5Cu alloy using the mixture powder(SLMedM Ti–5Cu).The effect of the micro-galvanic cells decreases due to the undetectable Ti_2Cu phase in the microstructure of the SLMed Ti–5Cu.An apparent passivation behavior was observed for SLMed Ti–5Cu instead of severe pitting phenomenon for the SLMed-M Ti–5Cu.The charge transfer resistance of SLMed Ti–5Cu in this work is 10.09 ± 2.63 MΩ cm~2, which is significantly higher than that of SLMed-M Ti–5Cu(4.76 MΩ cm~2).The above result indicates the atomized Ti–5Cu powder plays an important role in the formation of the uniform microstructure of SLMed product, thereby enhancing its corrosion resistance in Hank's solution at 37 ℃. 相似文献
90.
MCrAlY coatings are widely used to provide protection of hot component in modern gas turbine engines against high‐temperature oxidation and hot corrosion. Coating‐substrate interface, where the substrate is only partially covered by the ?coatings, is vulnerable to the hot corrosion attack. The accelerated degradation at the coating‐substrate interface can cause fast spallation of the coating, leading to the early failure of the gas turbine components. In this paper, MCrAlY powder was deposited on IN792 disks by high‐velocity oxygen‐fuel spraying. The hot corrosion behavior of the coated sample was investigated using (0.8Na, 0.2K)2SO 4 salt deposition at 900°C in lab air. Results showed a minor attack in the coating center, however, an accelerated corrosion attack at the coating‐substrate interface. The fast growth of corrosion products from substrate caused large local volume expansions at the coating‐substrate interface, resulting in an early coating spallation. 相似文献