黏结相含量对超音速火焰喷涂TiB_2-Ni涂层组织和性能的影响

以机械合金化工艺制备的TiB2-40Ni和TiB2-50Ni粉末为原料,利用超音速火焰喷涂沉积不同TiB2-Ni涂层,采用扫描电镜、X射线衍射仪研究了涂层的组织和相结构,运用压痕法测定了涂层的显微硬度,通过水淬法测试涂层的抗热震性能,并研究涂层的耐熔融铝硅腐蚀性能。结果表明,TiB2-40Ni和TiB2-50Ni涂层致密,孔隙率分别为1.25%和0.12%;涂层的主要物相为TiB2和Ni;显微硬度值分别为(643.5±56.8)HV0.3与(597.9±36.1)HV0.3;涂层均具有较好的抗热震性能,其中以TiB2-50Ni涂层最佳;经过120h熔融铝硅腐蚀后发现,两种涂层均具有良好的抗熔融铝硅腐蚀性能,TiB2-50Ni涂层试样具有最好的耐腐蚀性能。     

Q235钢表面热喷涂TiB2-50Ni金属陶瓷层的组织结构和性能

目前,对超音速火焰喷涂TiB2增强金属基复合涂层的耐磨性有一定研究,但对其抗热震性能和耐熔融金属腐蚀性能的报道较少.采用机械球磨制备了TiB2-50Ni金属陶瓷复合粉末,通过超音速火焰喷涂技术在Q235钢表面制备TiB2-50Ni金属陶瓷涂层.采用扫描电镜和X射线衍射技术分析了涂层的微观组织和物相,采用HVS-1000显微硬度计测试涂层的硬度值,采用水淬法测试涂层的抗热震性能,并研究了涂层的耐熔融Al-12.07％Si合金腐蚀性及耐磨损性能.结果表明:TiB2-50Ni涂层具有层状结构,组织致密;TiB2-50Ni涂层的主要物相为TiB2和Ni,与喷涂粉末的相同;涂层的硬度值为(348±37) HV3N;涂层与基体结合良好,耐蚀性良好,经60 h的熔融Al-12.07％Si腐蚀后,磨损失重量是Q235低碳钢的1/4;涂层抗热震性能良好,耐磨性较基体明显提高.     

超音速火焰喷涂TiB2-50Co涂层及其性能

在322、402和462 L/min 3种氧气流量条件下采用超音速火焰喷涂技术制备了3种TiB₂-50Co涂层,通过SEM和XRD对涂层的微观组织和物相结构进行分析,测试其硬度,采用水淬法测试涂层的抗热震性能,并研究了涂层的耐熔融铝硅(Al-12.07wt%Si)合金腐蚀和耐磨粒磨损性能.研究结果表明:3种TiB₂-50Co涂层的物相均为TiB₂和Co;3种涂层的组织均致密,其中以氧气流量为322 L/min条件下制备的涂层试样最致密,其孔隙率最低(1.76%),涂层硬度值最高,达到(558±90) HV_0.3;氧气流量为462 L/min条件下制备的涂层抗热震性能最差,涂层截面出现明显裂纹;在熔融Al-12.07wt%Si合金中腐蚀60 h后,3种涂层均具有良好的耐熔融Al-12.07wt%Si腐蚀性能;在载荷为6 N的条件下,3种涂层均具有良好的耐磨损性能,以氧气流量为322 L/min条件下制备的涂层试样最佳.     

电弧喷涂含TiB2金属陶瓷复合涂层的性能

为了减少磨损给生产所带来的经济损失,利用电弧喷涂含TiB2的粉芯线材来制备含TiB2陶瓷的涂层,并对涂层的结合强度、硬度、抗热震性和耐磨粒磨损性能等进行了测试,利用金相显微镜、X-射线衍射仪、扫描电子显微镜等对涂层进行测试分析,研究涂层磨损机理.研究结果表明,涂层结合强度达到49MPa,显微硬度达887HV,具有良好的抗热震性能,耐磨粒磨损性能比基体Q235钢提高了4.5倍.研制的涂层具有极大的实际应用和推广价值.     

重力分离SHS法制备钢管Al2O3内衬耐热耐磨涂层的研究

采用重力分离SHS制备了钢管内衬Al2O3涂层,进行了力学、抗热震、耐蚀等性能测试,研究了管径、装料密度及不同含量SiO2、CrO3添加剂对涂层组织与性能的影响。研究结果表明,涂层主要物相结构为α-Al2O3+FeAl2O4相,添加剂SiO2和CrO3不改变涂层的主要相组成。反应过程中熔融金属Fe在钢管基体和内衬陶瓷层之间形成了一层金属过渡层。当添加2%SiO2+6%CrO3时,涂层孔隙率最小,硬度最大,抗热震性能最好,耐蚀性也较好,具有良好的综合性能。实验条件下,管径25cm、装料密度1.5g/cm3的内衬涂层硬度为1917HV,孔隙率为9.0%。     

Al2O3梯度涂层的制备及性能研究

为了克服无梯度陶瓷涂层中应力集中、易产生裂纹的缺陷,以提高涂层的结合强度,采用等离子喷涂方法制备了NiAl-Al-2O-3梯度陶瓷涂层,并对涂层的组织分布、结合强度、显微硬度和抗热震性进行了研究.结果表明,梯度涂层的组织表现出宏观的不均匀性和微观的连续性分布特征,NiAl过渡层的引入可有效地改善涂层的质量.本梯度涂层中Al-2O-3含量为80%时,涂层的显微硬度最高(达620 HV).涂层成分的梯度化有利于涂层的结合强度和抗热震性能的提高.     

铜合金表面热喷涂(焊)涂层组织及性能研究

采用等离子喷涂工艺在纯铜表面分别制备了NiCrCoAlY、Cr3C2-NiCr两种涂层,采用等离子喷焊工艺制备了Ni60喷焊层,并分别进行了显微形貌、显微硬度、耐磨性能及热震性能分析。结果表明,等离子喷涂层主要为机械咬合,其次是微区冶金结合和化学键结合,而等离子喷焊层与基体形成良好的冶金结合,其结合强度相对较高。Cr3C2-NiCr涂层硬度高达534 HV,耐磨性能最优,而NiCrCoAlY涂层硬度为352 HV,耐磨性能较好,且抗热震性能优异;Ni60焊层熔合区硬度为154 HV,焊层中部高达606 HV,随后缓慢降低至平稳。     

超音速火焰喷涂CoCrAlYTa-10%Al_2O_3涂层的组织与性能

采用超音速火焰(HVOF)喷涂技术在Q235钢基体上制备了CoCrAlYTa-10%Al_2O_3涂层,利用光学显微镜(OM)、扫描电子显微镜(SEM)、能谱仪(EDS)、X射线衍射仪(XRD)、显微硬度计等研究了涂层的微观组织形貌、物相组成以及显微硬度。结果表明:涂层组织致密且分布均匀,孔隙率为0.44%;涂层主要由浅灰色钴基固溶体、深灰色铬基固溶体、白色球状富钽固溶体以及黑色Al_2O_3组成,其中Al_2O_3来自于喂料的原始组成和CoCrAlYTa合金中铝的氧化;涂层硬度为580630HV0.3,大约是Q235钢基体硬度(200HV0.3)的3倍,涂层具有良好的力学性能。     

超音频感应熔覆钴基涂层的组织与摩擦磨损性能

为提高45钢的摩擦磨损性能,采用超音频感应熔覆技术在45钢基体上制备Co基合金涂层,研究涂层的微观组织形貌、物相组成、显微硬度以及摩擦磨损性能.结果 表明:Co基合金涂层与基体冶金结合,涂层内无孔洞、裂纹等缺陷;涂层物相组成复杂,主要由γ-Co、γ-(Fe,Ni)、Cr23C6、Cr7C3、Co7W6以及金属间化合物Co3Fe7和FeNi3组成;钴基合金涂层的显微硬度约为573.1 HV0.2N,是基体45钢(215.0 HV0.2N)的2.67倍;在室温干摩擦条件下,钴基合金涂层的摩擦磨损性能优于45钢基体,其磨损形式为轻微的磨粒磨损和黏着磨损.     

304不锈钢激光熔覆搭接率对CoCrW涂层组织与耐磨及耐腐蚀性能的影响

利用光纤激光器在304不锈钢表面制备CoCrW合金熔覆涂层,改善其表面耐磨损及耐蚀性能.使用OM、SEM、XRD、EDS、显微硬度计、MMG-500三体磨损试验机和CS310电化学工作站分析不同搭接率对涂层组织、硬度、耐磨及耐蚀性能的影响,并寻求合适的搭接率,以期获得性能较优的激光熔覆涂层.研究结果表明:30％搭接率下的涂层无明显缺陷,从顶部到底部依次是等轴晶、柱状晶、平面晶,这些晶体主要由fcc结构的γ-Co相形成的晶核以及部分Cr7C3、(Co,Cr)23 C6等相形成的晶界组成.因此适宜搭接率为30％,该参数下涂层显微硬度达到450HV,约为基体显微硬度(210HV)的2.1倍;涂层磨损量为12.71 mg,约为基体(63.06 mg)的20％;涂层平均摩擦系数约为0.4,是基体平均摩擦系数(0.65)的60％;涂层自腐蚀电位为-889 mV,基体自腐蚀电位为-998 mV;涂层自腐蚀电流密度为5.7μA/cm2,约为基体自腐蚀电流密度(38.9μA/cm2)的14％.合适的涂层材料及激光熔覆工艺参数可使304不锈钢涂层腐蚀倾向更小,使显微硬度、耐磨损性能及耐蚀性显著提高.     

High oxygen pressure synthesis of new copper oxide superconductors

The unique coordination of the copper ions in +1, +2, and +3 oxidation states, which are stable in a range of oxygen partial pressure. 10^–6<P(O₂)< 10³ atm, makes possible the formation of a wide variety of distinct structures. By controlling the oxygen pressure during the synthesis and annealing, the distribution of metal and oxygen ions can be modified on an atomic scale to optimize the structural and electronic properties. We present several examples of compounds for which the critical structural elements for superconductivity, i.e., the perfectly ordered CuO₂ planes, have been obtained and doped with holes by means of high oxygen pressure,P(O₂)>1 atm. These materials, La₂CuO₄₊ , La_2–x Ca _x CuO₄, and YSr_2–x La _x Cu₃O₇₊ , offer a unique opportunity to study the relationship between superconductivity and structural, magnetic, and chemical properties.     

Use of oxygen isotope to study the transport mechanism during high temperature oxide scale growth

Abstract

The examination of high temperature (HT) oxide scale growth mechanisms was performed using secondary ion mass spectrometry (SIMS) and secondary neutral mass spectrometry (SNMS), in conjunction with ¹⁶O₂/¹⁸O₂ HT oxidation experiments. Cr₂O₃, NiO, ZrO₂ and Al₂O₃ were studied because they constitute excellent representative thermally grown oxide scales: they grow by cationic diffusion (Cr₂O₃, NiO), anionic diffusion (ZrO₂) or mixed anionic-cationic diffusion (Al₂O₃). The oxidation tests were performed first in ¹⁶O₂ and subsequently in ¹⁸O₂ at several temperatures (600–1000°C for NiO, 600°C for ZrO₂, 1000°C for Cr₂O₃ and 1100°C for Al₂O₃). The oxygen isotope distribution observed by SIMS and SNMS profiles are discussed and related with the HT oxidation mechanisms proposed in the literature.     

Characterization of high quality tantalum pentoxide film synthesized by oxygen plasma enhanced pulsed laser deposition

Tantalum pentoxide films were deposited on BK7 glass substrates using oxygen plasma enhanced pulsed laser deposition (OPE-PLD). X-ray diffraction, atomic force microscopy, ultraviolet–visible–near infrared scanning spectrophotometry, and spectroscopic ellipsometry were used to characterize the crystallinity, microscopic morphology and optical properties of films. Results show that the film roughness increased with the increase of oxygen pressure, and decreased with the application of OPE. Meanwhile the use of oxygen plasma in a 2 Pa O₂ pressure resulted in the transmittance of the thin film of 91.8% at its peak position (the transmittance of bare substrate). Moreover, the root-mean-square roughness as low as 0.736 nm, and refractive index of 2.18 at 633 nm wavelength, close to the refractive index of bulk Ta₂O₅ (~ 2.20 at 633 nm wavelength), were obtained.     

Observation of weakly adsorbed oxygen on Y5Ba6Cu11Oy

We observed, for the first time, adsorption of weakly bonded oxygen at low temperature (<-250°C) by a Y₅Ba₆Cu₁₁O _y sample, using thermogravimetric analysis. The resulting oxygen enriched phase in the surface layers may be attributed to the observation of a superconductivity-like transition at above 200 K.     

On the oxygen isotope shift in La2?xSrxCuO4

The anomalous oxygen isotope shift observed in the high-temperature superconductors La_2–xSr_xCuO₄ and La_2–xBa_xCuO₄ is discussed within the model of superconductivity in which the apex oxygen vibrations play the major role in the pairing mechanism. We show that the dependence of both the critical temperature and its isotope shifts on the doping level is consistently described within this model. The anomaly occurring in the isotope shift between x = 0.11 andx=0.15 is traced back to the oxygen mass exponent associated with the apex oxygen frequency.     

Effect of oxygen content on the electrical properties of YBa2Cu3O7−x single crystals

The effect of oxygen content in the single crystals of high-temperature superconductor YBa₂Cu₃O_7−x on the electrical resistivity, the Hall effect in the plane perpendicular to thec axis and the energy gap Δ, measured with tunnelling electron microscope, has been studied. The distribution of the gap along the surface of the crystal was also studied. The results of the study on the relationship between the magnitude of the energy gap Δ and the superconducting transition temperatureT _c of single crystals with various oxygen contents are approximated by the linear dependence 2Δ_av=4·4kT _c .     

Optimization of annealing temperature for YBa2Cu3O7 thin films post-annealed at a low oxygen partial pressure

Post-annealing of YBa₂Cu₃O₇ (YBCO) thin films is usually performed at 850–900°C in atmospheric-pressure oxygen. In this study, coevaporated YBCO films on LaAlO₃ were post-annealed in an oxygen partial pressure of 29 Pa at temperatures in the range 700–825°C. Zero resistance transition temperatures were 89–90 K. Both d.c. (room-temperature resistance and critical-current density) and a.c. parameters (extracted from eddy-current response measurements at 25 MHz) were monitored. The optimum temperature is close to 750°C, which is on the YBCO thermodynamic stability line at this low oxygen partial pressure.     

Conversion of a plasma enhanced chemical vapor deposited silicon-carbon-nitride thin film at ultra-low temperature by oxygen plasma

In this work we present an ultra-low temperature method for the oxidation of an amorphous silicon-carbide-nitride (SiCN) material. The SiCN is deposited on silicon substrates by plasma enhanced chemical vapor deposition using CH₄, SiH₄, and N₂ chemistry. The physical and chemical properties are characterized for the as-deposited SiCN and post-oxidized films are discussed. The SiCN film is exposed to oxygen plasma, where it undergoes a chemical transformation into a binary SiO₂ material system. A 1.7 nm/min oxidation rate is typical for this process and compares favorably to oxidation methods utilizing much higher temperatures. The substrate temperature remains extremely low throughout the oxidation process, T_s < 200 °C. Changes in film stress, optical constants, film thickness, surface roughness, and film density are measured. Chemical analysis by X-ray photoelectron spectroscopy is reported for both the as-deposited and oxidized film and confirms the resultant film to be the chemical equivalent of thermally grown SiO₂. We discuss applications specifically targeted to the conversion of SiCN to SiO₂.     

Oxygen permeation through perovskite membranes and the improvement of oxygen flux by surface modification

Abstract

BSCF hollow fiber membranes possessing an asymmetric layered structure were prepared using a modified phase inversion process followed by subsequent sintering at temperatures from 1100 to 1175 ?C. The fibers were characterized by SEM, and tested for air separation at ambient pressure and temperatures between 650 and 950 ?C. Although the prepared hollow fibers resulted in self-supported asymmetric substrate with a very thin densified perovskite layer for mixed conduction, O₂ permeation was controlled by surface O₂ exchange kinetics rather than bulk diffusion. In order to improve O₂ flux, surface modification was carried out by the attachment of Pt particles on the surface of the hollow fiber. The maximum O₂ flux measured for pure perovskite hollow fiber was 0.0268 mol m^?2 s^-1 at 950 ?C whilst O₂ fluxes increased up to 25% after the surface modification using Pt micro-particles.     

Oxygen permeation through perovskite membranes and the improvement of oxygen flux by surface modification

BSCF hollow fiber membranes possessing an asymmetric layered structure were prepared using a modified phase inversion process followed by subsequent sintering at temperatures from 1100 to 1175 °C. The fibers were characterized by SEM, and tested for air separation at ambient pressure and temperatures between 650 and 950 °C. Although the prepared hollow fibers resulted in self-supported asymmetric substrate with a very thin densified perovskite layer for mixed conduction, O₂ permeation was controlled by surface O₂ exchange kinetics rather than bulk diffusion. In order to improve O₂ flux, surface modification was carried out by the attachment of Pt particles on the surface of the hollow fiber. The maximum O₂ flux measured for pure perovskite hollow fiber was 0.0268 mol m⁻² s⁻¹ at 950 °C whilst O₂ fluxes increased up to 25% after the surface modification using Pt micro-particles.