共查询到20条相似文献,搜索用时 23 毫秒
1.
采用真空电弧熔炼制备了Al0.5Nb1.5TiV2Zr0.5高熵合金,并研究了其微观组织、密度及力学性能。结果表明,Al0.5Nb1.5TiV2Zr0.5合金由为90.6%(体积分数)的体心立方相和9.4%(体积分数)的C14-Laves第二相组成。合金基体相富含Ti和V,第二相富含Al和Zr。合金的密度为6284 kg/m3,维氏硬度为5197.9 MPa。合金的屈服强度随温度升高而降低,由室温下1082.9 MPa降低到1073 K下的645.0MPa。压缩应变由室温下的27.20%降低到873 K下的14.94%,这与合金中原子间的相互作用力随温度升高而降低有关。在1073 K时合金应变超过50%,表现出良好的塑性而未发生断裂。压缩测试结果表明,合金韧脆转变温度在873~1073 K之间。 相似文献
2.
Y3Al5O12 and ZrO2-Y2O3 (8 mol% YSZ) coatings for potential application as thermal barrier coatings were prepared by combustion spray pyrolysis. Thermal cycling of as deposited coatings on stainless steel and FeCrAlY bond coat substrates was carried out at 1000 °C and 1200 °C to determine the thermal fatigue response. Structural and morphological studies on Y3Al5O12 and 8 mol% YSZ coatings before and after thermal cycling have been carried out. It has been noted that the coatings on FeCrAlY substrates remain intact after 50 cycles between room temperature and 1200 °C, whereas the coatings on stainless steel show some minor damage such as peeling off near the periphery after 50 cycles at 1000 °C. Thermal diffusivity values of Y3Al5O12 and 8 mol% YSZ films were measured by using photo thermal deflection spectroscopy and the values are lower than those of coatings produced by conventional techniques such as EBPVD and APS. 相似文献
3.
Increased turbine inlet temperature in advanced turbines has promoted the development of thermal barrier coating (TBC) materials with high-temperature capability. In this paper, BaLa2Ti3O10 (BLT) was produced by solid-state reaction of BaCO3, TiO2 and La2O3 at 1500 °C for 48 h. BLT showed phase stability between room temperature and 1400 °C. BLT revealed a linearly increasing thermal expansion coefficient with increasing temperature up to 1200 °C and the coefficients of thermal expansion (CTEs) are in the range of 1 × 10− 5–12.5 × 10− 6 K− 1, which are comparable to those of 7YSZ. BLT coatings with stoichiometric composition were produced by atmospheric plasma spraying. The coating contained segmentation cracks and had a porosity of around 13%. The microhardness for the BLT coating is 3.9–4.5 GPa. The thermo-physical properties of the sprayed coating were investigated. The thermal conductivity at 1200 °C is about 0.7 W/mK, exhibiting a very promising potential in improving the thermal insulation property of TBC. Thermal cycling result showed that the BLT TBC had a lifetime of more than 1100 cycles of about 200 h at 1100 °C. The failure of the coating occurred by cracking at the thermally grown oxide (TGO) layer due to severe oxidation of bond coat. Based on the above merits, BLT could be considered as a promising material for TBC applications. 相似文献
4.
采用固-液相共混法制备了多种BN/Al2O3复合粉末,通过冻融法和表面修饰法对BN进行了改性处理,改变表面修饰剂类型和摩尔比得到了前驱体和烧结态BN/Al2O3复合粉末,并利用机械混合法制备了聚合物基BN/Al2O3复合材料,并测试分析了其导热性能。结果表明,经冻融处理的BN分散性和界面相容性明显优于未经冻融处理的BN。多巴胺对BN的改性效果优于聚乙二醇。采用多巴胺作为表面修饰剂且BN与Al(NO3)3的摩尔比为1:1时,能够得到纳米Al2O3均匀包覆的微米BN粉末,即BN/Al2O3微纳复合粉末,其聚合物基复合材料的导热系数可达0.62 W·m-1·K-1,是纯聚合物导热系数的3倍,是采用纯微米BN粉末制备的聚合物基复合材料导热系数的1.5倍。在BN表面附着的Al2O3可以形成层状热传导通道,能够有效提高聚合物基BN/Al2O3复合材料的热导率。 相似文献
5.
Jeong-Hun JuKwang-Sun Ryu 《Journal of Alloys and Compounds》2011,509(30):7985-7992
The core-shell structure cathode material Li(Ni0.8Co0.15Al0.05)0.8(Ni0.5Mn0.5)0.2O2 (LNCANMO) was synthesized via a co-precipitation method. Its applicability as a cathode material for lithium ion batteries was investigated. The core-shell particle consists of LiNi0.8Co0.15Al0.05O2 (LNCAO) as the core and a LiNi0.5Mn0.5O2 as the shell. The thickness of the LiNi0.5Mn0.5O2 layer is approximately 1.25 μm, as estimated by field emission scanning electron microscopy (FE-SEM). The cycling behavior between 2.8 and 4.3 V at a current rate of 18 mA g−1 shows a reversible capacity of about 195 mAh g−1 with little capacity loss after 50 cycles. High-rate capability testing shows that even at a rate of 5 C, a stable capacity of approximately 127 mAh g−1 is retained. In contrast, the capacity of LNCAO rapidly decreases in cyclic and high rate tests. The observed higher current rate capability and cycle stability of LNCANMO can be attributed to the lower impedance including charge transfer resistance and surface film resistance. Differential scanning calorimetry (DSC) indicates that LNCANMO had a much improved oxygen evolution onset temperature of approximately 251 °C, and a much lower level of exothermic-heat release compared to LNCAO. The improved thermal stability of the LNCANMO can be ascribed to the thermally stable outer shell of LiNi0.5Mn0.5O2, which suppresses oxygen release from the host lattice and not directly come into contact with the electrolyte solution. In particular, LNCANMO is shown to exhibit improved electrochemical performance and is a safe material for use as an electrode for lithium ion batteries. 相似文献
6.
Gamil A. El-Shobaky Awad I. AhmedHassan M.A. Hassan Shaymaa E. El-Shafey 《Journal of Alloys and Compounds》2011,509(4):1314-1321
The effects of K2O and Li2O-doping (0.5, 0.75 and 1.5 mol%) of Fe2O3/Cr2O3 system on its surface and the catalytic properties were investigated. Pure and differently doped solids were calcined in air at 400-600 °C. The formula of the un-doped calcined solid was 0.85Fe2O3:0.15Cr2O3. The techniques employed were TGA, DTA, XRD, N2 adsorption at −196 °C and catalytic oxidation of CO oxidation by O2 at 200-300 °C. The results revealed that DTA curves of pure mixed solids consisted of one endothermic peak and two exothermic peaks. Pure and doped mixed solids calcined at 400 °C are amorphous in nature and turned to α-Fe2O3 upon heating at 500 and 600 °C. K2O and Li2O doping conducted at 500 or 600 °C modified the degree of crystallinity and crystallite size of all phases present which consisted of a mixture of nanocrystalline α- and γ-Fe2O3 together with K2FeO4 and LiFe5O8 phases. However, the heavily Li2O-doped sample consisted only of LiFe5O8 phase. The specific surface area of the system investigated decreased to an extent proportional to the amount of K2O and Li2O added. On the other hand, the catalytic activity was found to increase by increasing the amount of K2O and Li2O added. The maximum increase in the catalytic activity, expressed as the reaction rate constant (k) measured at 200 °C, attained 30.8% and 26.5% for K2O and Li2O doping, respectively. The doping process did not modify the activation energy of the catalyzed reaction but rather increased the concentration of the active sites without changing their energetic nature. 相似文献
7.
The starting materials of Al2O3, TiO2, ZrO2 and CeO2 nanoparticles were agglomerated into sprayable feedstock powders and plasma sprayed to form nanostructured coatings. There were net structures and fused structures in plasma sprayed nanostructured Al2O3–13 wt.%TiO2 coatings. The net structures were derived from partially melted feedstock powders and the fused structures were derived from fully melted feedstock powders. The nanostructured Al2O3–13 wt.%TiO2 coatings possessed higher hardness, bonding strength and crack growth resistance than conventional Metco 130 coatings which were mainly composed of lamellar fused structures. The higher toughness and strength of nanostructured Al2O3–13 wt.%TiO2 coatings were mainly related to the obtained net structures. 相似文献
8.
Kong Xiangrong Zang Jun Yang Xiaowei Zeng Yanwei 《Journal of Alloys and Compounds》2008,464(1-2):418-421
In the atmosphere of N2, low cost paraffin slices were refined and then successfully utilized as a solvent instead of the expensive high-carbon alkanes or alkenes like 1-octadecene to synthesize Zn0.5Fe2.5O4 nanocrystals at 320 °C. In the experiments, the precursor solutions of ferric and zinc oleates were stoichiometrically prepared and injected by two-step operations into the hot solvent, together with controlled amounts of ethanol to tailor their thermal decomposition performances. The synthesized Zn0.5Fe2.5O4 nanocrystals were characterized by XRD and FESEM, having uniform morphology and a quasi-monodisperse size distribution with a mean value 25 nm and a standard deviation of ±12.3%. The formation and structural characteristics of Zn0.5Fe2.5O4 nanocrystals are attributed to the catalysing function of ethanol and the effective separation of nucleation and growth of nanocrystals via the two-step injections of reactive precursors. 相似文献
9.
Crystalline γ-AlO(OH) was synthesized by the precipitation of sodium aluminate and oxalic acids in aqueous solution. And then γ-AlO(OH) was successfully transferred to γ-Al2O3 after subsequent high temperature heat treatment. The effects of reaction conditions on formation of γ-AlO(OH) and γ-Al2O3 were further investigated in detail. The XRD analysis shows that the complete formation of crystalline γ-Al2O3 is at pH 8–9, reaction temperature of 93–96 °C and calcination temperature of higher than 400 °C. The product of γ-Al2O3 contains impurity, including iron, calcium and silicon ion with a low content of about 0.01% and has large specific surface area and high pore volume of 269.9 m2/g and 0.57 mL/g, which can be applied in catalysts and catalyst supports. 相似文献
10.
P.T.A. Santos A.C.F.M. Costa R.H.G.A. Kiminami H.M.C. Andrade H.L. Lira L. Gama 《Journal of Alloys and Compounds》2009,483(1-2):399
The aim of this work was to study the NiFe2O4 spinel catalyst obtained by combustion reaction in the preferential oxidation of carbon monoxide reaction to conversion reactants H2, CO and O2 and to conversion products CH4, H2O and CO2. The powders were prepared according to propellants chemical concept and characterized by XRD, TEM and catalytic tests. The XRD pattern shows the characteristic peaks of the spinel phase. The particle size calculated by TEM was 10.7 nm. The catalyst proved to be more selective to reagents for conversion into O2 (89.5%) at 350 °C. 相似文献
11.
Production of nanoscale Ba(Zn1/3Nb2/3)O3 microwave dielectric ceramics by polymerised complex method
Ba(Zn1/3Nb2/3)O3 nanoparticles have been synthesized by a polymerised complex method by using precursor materials of barium nitrate, zinc acetate, niobium oxide, hydrofluoric acid and citric acid. Thermal decomposition characteristics and crystallization behavior of the powders were investigated by the thermogravimetric and differential thermal analysis, X-ray diffractometer and Fourier transform infrared spectroscopy. Ba(Zn1/3Nb2/3)O3 phase started to form at low temperature of 400 °C and, single phase Ba(Zn1/3Nb2/3)O3 perovskite structure was obtained at 1000 °C. Microstructural investigation revealed that the major particle size of Ba(Zn1/3Nb2/3)O3 nanoparticles were in the range of 80–110 nm with spherical morphology and homogeneous size distribution. But the powders also contained some agglomeration. 相似文献
12.
Won-Hee Lee Hyung-Jun Kim Dong-Won Lee Min-Goon Jeong Dae-Soon Lim Song-Min Nam 《Surface & coatings technology》2012,206(22):4679-4684
We attempted the room-temperature fabrication of Al2O3-based nanodiamond (ND) composite coating films on glass substrates by an aerosol deposition (AD) process to improve the anti-scratch and anti-smudge properties of the films. Submicron Al2O3 powder capable of fabricating transparent hard coating films was used as a base material for the starting powders, and ND treated by 1H,1H,2H,2H-perfluorooctyltriethoxysilane (PFOTES) was added to the Al2O3 to increase the hydrophobicity and anti-wear properties. The ND powder treated by PFOTES was mixed with the Al2O3 powder by ball milling to ratios of 0.01 wt.%, 0.03 wt.%, and 0.05 wt.% ND. The water contact angle (CA) of the Al2O3-ND composite coating films was increased as the ND ratio increased, and the maximum water CA among all the films was 110°. In contrast to the water CA, the Al2O3-ND composite coating films showed low transmittance values of below 50% at a wavelength of 550 nm due to the strong agglomeration of ND. To prevent the agglomeration of ND, the starting powders were mixed by attrition milling. As a result, Al2O3-ND composite coating films were produced that showed high transmittance values of close to 80%, even though the starting powder included 1.0 wt.% ND. In addition, the Al2O3-ND composite coating films had a high water CA of 109° and superior anti-wear properties compared to those of glass substrates. 相似文献
13.
Bulk WC-Al2O3 composites prepared by spark plasma sintering 总被引:1,自引:0,他引:1
Donghai ZhengXiaoqiang Li Xuan AiChao Yang Yuanyuan Li 《International Journal of Refractory Metals and Hard Materials》2012,30(1):51-56
WC and WC-Al2O3 materials without metallic binder addition were densified by spark plasma sintering in the range of 1800-1900 °C. The densification behavior, phase constitution, microstructure and mechanical properties of pure WC and WC-Al2O3 composite were investigated. The addition of Al2O3 facilitates sintering and increases the fracture toughness of the composites to a certain extent. An interesting phenomenon is found that a proper content of Al2O3 additive helps to limit the formation of W2C phase in sintered WC materials. The pure WC specimen possesses a hardness (HV10) of 25.71 GPa, fracture toughness of 4.54 MPa·m1/2, and transverse fracture strength of 862 MPa, while those of WC-6.8 vol.% Al2O3 composites are 24.48 GPa, 6.01 MPa·m1/2, and 1245 MPa respectively. The higher fracture toughness and transverse fracture strength of WC-6.8 vol.% Al2O3 are thought to result from the reduction of W2C phase, the crack-bridging by Al2O3 particles and the local change in fracture mode from intergranular to transgranular. 相似文献
14.
Al2O3, Al2O3-Cr2O3 and Cr2O3 coatings were deposited by atmospheric plasma spraying. Phase composition of powders and as-sprayed coatings was determined by X-ray diffraction. Electron probe microanalyzer was employed to investigate the polished and fractured surface morphologies of the coatings. Mechanical properties including microhardness, fracture toughness and bending strength were evaluated. The results indicate that the addition of Cr2O3 is conducive to the stabilization of α-Al2O3. Compared with the pure Al2O3 and Cr2O3 coatings, Al2O3-Cr2O3 composite coatings show lower porosities and denser structures. Heterogeneous nucleation of α-Al2O3 occurs over the isostructural Cr2O3 lamellae and partial solid solution of Al2O3 and Cr2O3 might be occurring as well. Furthermore, grain refining and solid solution strengthening facilitate the mechanical property enhancement of Al2O3-Cr2O3 composite coatings. 相似文献
15.
Wen-Fang PengShao-Yu Zou Guan-Xi LiuQuan-Lan Xiao Rui ZhangLi-Juan Xie Li-Wei CaoJian-Xin Meng Ying-Liang Liu 《Journal of Alloys and Compounds》2011,509(23):6673-6676
The CaSc2O4:Ce3+ nano-phosphors were successfully prepared by a single-step combustion method at an ignition temperature as low as 200 °C in a closed autoclave using glycine as a fuel and PEG4000 as a dispersant. The samples were characterized by X-ray diffraction (XRD), photoluminescence (PL) spectroscopy, scanning electron microscopy (SEM) and transmission electron microscope (TEM). The results revealed that CaSc2O4:Ce3+ nano-phosphors can be conveniently prepared at an ignition temperature as low as 200 °C, which was much lower than that in the ordinary combustion methods. The optimized ignition temperature was 220 °C. The CaSc2O4:Ce3+ nano-phosphors give a uniform particle size in the range of 15-20 nm. The low ignition temperature and the addition of PEG4000 dispersant play important roles in the formation of small sized nanoparticles. The as-prepared nano-phosphors were incompact aggregates, but highly dispersed nano-phosphors can be obtained after further ultrasonic treatment. The CaSc2O4:Ce3+ nano-phosphors give satisfactory luminescence characteristic benefiting from the closed circumstance, in which cerium atoms can be isolated from the oxidizing atmosphere and non-fluorescent Ce4+ ions can be ruled out. The present highly dispersed CaSc2O4:Ce3+ nano-phosphors with efficient fluorescence are promising in the field of biological labeling, and the present low temperature combustion method is facile and convenient and can be applied as a universal process for preparing non-aggregate oxide nano-phosphors, especially those being sensitive to air at high temperature. 相似文献
16.
Piezoelectric and dielectric properties of Dy2O3-doped (Bi0.5Na0.5)0.94Ba0.06TiO3 lead-free ceramics
Chen Zhi-hui Ding Jian-ning Mei LinYuan Ning-yi Zhu Yuan-yuan 《Journal of Alloys and Compounds》2011,509(2):482-485
(Bi0.5Na0.5)0.94Ba0.06TiO3 + x wt% Dy2O3 with x = 0-0.3 ceramics were synthesized by conventional solid-state processes. The effects of Dy2O3 on the microstructure, the piezoelectric and dielectric properties were investigated. X-ray diffraction pattern confirmed that the coexistence of tetragonal and rhombohedral phases in the (Bi0.5Na0.5)0.94Ba0.06TiO3 composition was not changed by adding 0.05-0.3 wt% Dy2O3. SEM images indicate that all the ceramics have pore-free microstructures with high density, and that doping of Dy2O3 inhibits the grain growth of the ceramics. The addition of Dy2O3 shows the double effects on decreasing the piezoelectric and dielectric properties for 0 < x < 0.15 when Dy3+ ions substitute B-site Ti4+ ions, and increasing the properties for 0.15 < x < 0.3 when Dy3+ ions enters into A-site of the perovskite structure. The optimum electric properties of piezoelectric constant d33 = 170 pC/N and the dielectric constant ?r = 1900 (at a frequency of 1 kHz) are obtained at x = 0.3. 相似文献
17.
M.A. Khaghani-DehaghaniR. Ebrahimi-Kahrizsangi N. SetoudehB. Nasiri-Tabrizi 《International Journal of Refractory Metals and Hard Materials》2011,29(2):244-249
Alumina-titanium diboride nanocomposite (Al2O3-TiB2) was produced using mixtures of titanium dioxide, acid boric and pure aluminum as raw materials via mechanochemical process. The phase transformation and structural characterization during mechanochemical process were utilized by X-ray diffractometry (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), and thermogravimetric analyses (TG-DTA) techniques. A thermodynamic appraisal showed that the reaction between TiO2, B2O3 and Al is highly exothermic and should be self-sustaining. XRD analyses exhibited that the Al2O3-TiB2 nanocomposite was formed after 1.5 h milling time. The results indicate that increasing milling time up to 40 h had no significant effect other than refining the crystallite size. 相似文献
18.
以氧化铝粉末为基体,添加具有粘结性和一定陶瓷产率的硅树脂粉末,通过干压成型和无压烧结制备出氧化铝基陶瓷型芯,重点研究了硅树脂添加量对氧化铝基陶瓷型芯性能的影响。结果表明:硅树脂在裂解过程中会形成二氧化硅,二氧化硅与氧化铝基体发生反应形成新相莫来石。由于硅树脂在交联和裂解过程中会释放大量气体,导致烧结体失重,且气体的逸出会抑制由烧结引起的收缩,因此,随着硅树脂添加量增加,产生的气体量增加,烧结体的失重率增加,收缩率降低。硅树脂含量的增加使得烧结体的气孔率变大和体积密度减小,烧结体的室温抗弯强度逐渐减小。硅树脂的添加虽然降低了其室温强度,但是保证了陶瓷型芯的尺寸精度。 相似文献
19.
Cagri Tekmen Yoshiki Tsunekawa Masahiro Okumiya 《Surface & coatings technology》2008,202(17):4170-4175
In-situ plasma spraying (IPS) is a promising process to fabricate composite coatings with in-situ formed thermodynamically stable phases. In the present study, mechanically alloyed Al-12Si, B2O3 and TiO2 powder was deposited onto an aluminum substrate using atmospheric plasma spraying (APS). It has been observed that, during the coating process, TiB2 and Al2O3 are in-situ formed through the reaction between starting powders and finely dispersed in hypereutectic Al-Si matrix alloy. Also, obtained results demonstrate that in-situ reaction intensity strongly depends on spray conditions. 相似文献
20.
Mechanical properties and wear rates of Al2O3-13 wt.% TiO2 (AT-13) and Al2O3-43 wt.% TiO2 (AT-43) coatings obtained by flame and atmospheric plasma spraying were studied. The feed stock was either ceramic cords or powders. Results show that the wear resistance of AT-13 coatings is higher than that of AT-43 and it seems that the effect of hardness on wear resistance is more important than that of toughness. Additionally, it was established that, according to conditions used to elaborate coatings and the sliding tribological test chosen, spray processes do not seem to have an important effect on the wear resistance of these coatings. 相似文献