一种可内生Al2O3扩散障的δ-Ni2Al3-Cr2O3/ Ni-Cr2O3涂层体系

通过对Ni-Cr₂O₃复合镀层620 ℃部分渗铝制备了δ-Ni₂Al₃-Cr₂O₃/Ni-Cr₂O₃涂层体系。Cr₂O₃颗粒在渗铝的过程中和Al反应生成更为稳定的Al₂O₃。1000 ℃恒温氧化20 h后发现,铝化物涂层和复合镀层内掺杂的Cr₂O₃颗粒完全转化为Al₂O₃,并在铝化物涂层/Ni镀层界面自发形成了一层Al₂O₃富集层,该富集层起扩散障作用,阻碍铝化物涂层因互扩散所致的退化。     

传感器用离子镀Cr/AlCr(Si)N涂层的组织和反射率

以Ni-11Cr合金作为基材,采用多弧离子镀工艺在其表面制备Cr/AlCrN与Cr/AlCrSiN涂层,并对其在700~900 ℃温度下进行真空热处理,研究热处理温度及Si元素对Cr/AlCr(Si)N涂层组织和红外反射率的影响。结果表明:真空热处理后两涂层形成了Cr₂O₃与Al₂CrO₃的特征峰,900 ℃热处理后,氧化物晶体结构特征衍射峰明显增加。两种涂层的组织呈柱状形态,在Cr/AlCrN涂层中存在许多hcp-CrN纳米晶;Cr/AlCrSiN涂层中形成了粒径尺寸均匀的hcp-AlN纳米晶。真空热处理温度越高,两个涂层红外稳定反射率越大,Ni扩散系数和热处理温度之间呈现单调增加的变化趋势,Cr/AlCrN涂层具有更优异的低红外稳定反射率,Cr/AlCrSiN涂层具备高的红外稳定反射率。     

纳米Al2O3掺杂酚醛/环氧复合涂层的耐腐蚀性能

以酚醛树脂(PF)改性环氧树脂(EP)为基体,将硅烷改性的纳米Al₂O₃掺杂其中,制备了纳米Al₂O₃-PF/EP复合涂层。利用红外光谱仪(FTIR)、接触角测量仪和电化学阻抗谱(EIS)等测试方法对复合涂层进行了表征。结果表明：硅烷改性的纳米Al₂O₃和PF与EP之间发生了化学反应,酚醛固化涂层的抗渗透性和交联密度提高;纳米Al₂O₃-PF/EP复合涂层的耐腐蚀性能优于EP涂层和PF/EP涂层,且掺杂3%(质量分数)纳米Al₂O₃的PF/EP复合涂层,其耐腐蚀性能最优;硅烷改性的纳米Al₂O₃与PF/EP之间的分散性和稳定性提高,涂层变得更致密,阻碍了腐蚀性介质的扩散,从而提高复合涂层的耐腐蚀性能。     

镍基单晶高温合金N5及其纳米晶涂层在900℃下O2和O2+20%H2O气氛中的氧化行为

以镍基单晶高温合金N5为基体,采用磁控溅射技术在基体表面沉积与其成分相同的纳米晶涂层,并对比研究合金及其纳米晶涂层在900℃下O₂和O₂+20%(体积分数) H₂O气氛中的氧化行为。结果表明,水蒸气加快了合金和涂层的氧化速率,促进合金表面氧化膜的剥落,并且影响了氧化膜的组成和结构。在O₂和O₂+H₂O环境中,合金表面氧化膜都由外层NiO、中间层NiAl₂O₄和内层Al₂O₃组成;但在O₂+H₂O环境中,合金氧化速率较大,外层氧化膜发生剥落。纳米晶涂层显著提高了合金的抗高温氧化性能,在O₂气氛中表面形成Al₂O₃,而在O₂+H₂O气氛中表面氧化膜主要为NiAl₂O₄。同时,纳米...     

LaMgAl11O19热障涂层退火过程残余热应力分布及涂层热稳定性的数值模拟

目的 研究退火过程中La Mg Al₁₁O₁₉热障涂层内部残余热应力的分布情况及其对热障涂层热稳定性的影响机理。方法 基于等离子喷涂制备的La Mg Al₁₁O₁₉/YSZ双热障涂层物理模型,采用Abaqus建立数值仿真模型,通过温度位移耦合计算,系统分析不同退火温度下LaMgAl₁₁O₁₉热障涂层内部残余热应力的分布情况。通过扫描电镜,观察退火前后涂层表面及断面的微观组织形貌。根据数值模拟结果及涂层SEM图像,分析残余热应力对LaMgAl₁₁O₁₉热障涂层热稳定性的影响,探究引起涂层裂纹损伤失效的影响因素。结果 数值模拟结果显示,La Mg Al₁₁O₁₉热障涂层内部的残余热应力以径向应力为主,其值远大于轴向应力及剪切应力。退火中,径向残余热应力在径向距离0～2.4mm内缓慢增长到最大值,而在x=2.4mm至径向边缘范围内急剧降低。退火后,在涂层径向边缘位置出现应力集...     

Al2O3/TiB2/Al复合材料的微观结构和高温力学性能

以细雾化铝粉和TiB₂颗粒为原料,通过粉末冶金和热轧制制备微米TiB₂和纳米Al₂O₃颗粒增强铝基复合材料。室温时,由于TiB₂和Al₂O₃的综合强化作用,Al₂O₃/TiB₂/Al复合材料的屈服强度和抗拉强度分别为258.7 MPa和279.3 MPa,测试温度升至350℃时,TiB₂颗粒的增强效果显著减弱,原位纳米Al₂O₃颗粒与位错的交互作用使得复合材料的屈服强度和抗拉强度达到98.2MPa和122.5 MPa。经350℃退火1000 h后,由于纳米Al₂O₃对晶界的钉扎作用抑制晶粒长大,强度和硬度未发生显著的降低。     

TiAl合金表面热障涂层的高温抗氧化性能研究

利用大气等离子喷涂技术(APS)在TiAl合金基体表面制备TiAl₃/Al₂O₃-13TiO₂纳米热障涂层。采用SEM、EDS和XRD技术分析纳米热障涂层在氧化前后的微观组织及相组成,并对其在950℃下的抗氧化性能进行测试。结果表明,TiAl合金表面制备TiAl₃/Al₂O₃-13TiO₂纳米热障涂层后高温抗氧化性能显著提高,氧化动力学曲线呈对数变化规律,950℃高温氧化时,氧化速率常数为3.7×10^-3 mg²·cm⁴/s。在高温氧化过程中,TiAl₃粘结层与TiAl合金基体之间发生元素扩散,TiAl合金基体与粘结层之间界面消失。在陶瓷层与粘结层之间形成均匀连续的热生长氧化物层(TGO),在TiAl₃粘结层完全降解为TiAl₂相和三元Ti-Al-O化合物后,TGO对陶瓷层和粘结层仍...     

(NiCoCrAlYSiB+AlSiY)复合涂层热腐蚀行为的研究

采用电弧离子镀（AIP）技术在镍基单晶高温合金基体上制备了NiCoCrAlYSiB涂层（普通涂层）和（Ni-CoCrAlYSiB+AlSiY）复合涂层,研究了高温合金基体与2种涂层分别在900和700℃下的涂盐（Na₂SO₄+K₂SO₄和Na₂SO₄+NaCl）热腐蚀行为.结果表明:高温（900℃）热腐蚀条件下,基体合金表面主要生成NiO;普通涂层表面主要生成Cr₂O₃,而且涂层内部出现内氧化和内硫化现象;复合涂层表面主要生成Al₂O₃,外层出现程度较轻的内氧化,涂层表层Al含量仍然较高,维持表面Al₂O₃膜的形成和修复.低温（700℃）热腐蚀条件下,基体合金表面主要生成NiO;普通涂层表面主要生成Cr₂O₃,涂层内部出现严重的内氧化;复合涂层表面也出现了内氧化,高Cr的内层未受腐蚀,有助于提高涂层的抗腐蚀性能.     

Fe基非晶/纳米晶涂层的微结构及其在H2O2溶液中的腐蚀性能

为研究强氧化环境中,显微结构和相组成对Fe基非晶/纳米晶复合涂层的腐蚀腐蚀性能的影响,采用大气等离子喷涂(APS)技术,在1Cr18Ni9Ti不锈钢基体上喷涂制得具有不同微结构和相组成的Fe基非晶/纳米晶的复合涂层。采用XRD、SEM、TEM和DSC等检测方法对涂层的组织和相组成、晶化行为、晶化程度、内部的孔隙等微观结构进行表征。采用电化学法研究具有不同微结构和相组成的涂层在30%H₂O₂ (质量分数,下同)溶液中的腐蚀行为,探讨Fe基非晶/纳米晶复合涂层在强氧化环境中的腐蚀机理。研究表明,Mo₃Si和Fe₅Si₃相的形成使得涂层耐腐蚀性能明显降低。     

(NiCoCrAlYSiB+AlSiY)复合涂层热腐蚀行为的研究

采用电弧离子镀（AIP）技术在镍基单晶高温合金基体上制备了NiCoCrAlYSiB涂层（普通涂层）和（Ni-COCrAlYSiB+AlSiY）复合涂层,研究了高温合金基体与2种涂层分别在900和700℃下的涂盐（Na₂SO₄+K₂SO₄和Na₂SO₄+NaCl）热腐蚀行为.结果表明:高温（900℃）热腐蚀条件下,基体合金表面主要生成NiO;普通涂层表面上要生成Cr₂O₃,而且涂层内部出现内氧化和内硫化现象;复合涂层表面主要生成Al₂O₃,外层出现程度较轻的内氧化,涂层表层Al含量仍然较高,维持表面Al₂O₃膜的形成和修复.低温（700℃）热腐蚀条件下,基体合金表面主要生成NiO;普通涂层表面主要生成Cr₂O₃,涂层内部出现严重的内氧化;复合涂层表面也出现了内氧化,高Cr的内层未受腐蚀,有助于提高涂层的抗腐蚀性能.     

The Impact of Annealing Temperature on the Optical Performance of Cr-Cr2O3 Produced by Plasma Spraying as Solar Energy Selective Absorber Coating

A series of selective solar absorber coatings of Cr-Cr2O3 were deposited in different content on stainless steel by plasma spraying.The samples were annealed at different temperatures.The optical performance(both the solar absorptance and the thermal emittance)were studied by spectrophotometry.The surface morphology,the structure and the surface roughness were investigated by scanning electron microscopy(SEM),X-ray diffraction(XRD),and roughmeter respectively.The results show that,as the content of Cr increased,the solar absorptance(α)decreased greatly,from 0.91 to 0.84.Meanwhile,the thermal emittance(ε) decreased more greatly,from 0.86 to about 0.64.The ratio between the solar absorptance and the thermal emittance increased from 1.06 to 1.31.Annealing had a great impact on the optical performance.Annealing temperature is an important element.But its influence was a little complex.To pure Cr coating,annealing at 500℃ was a perfect chosen,where the ratio between the solar absorptance and the thermal emittance was highest of 1.46.     

Enhancing High-Temperature Strength and Thermal Stability of Al_2O_3/Al Composites by High-Temperature Pre-treatment of Ultrafine Al Powders

Amorphous Al_2 O_3-reinforced Al composite(am-Al_2 O_3/Al) compacted from ultrafine Al powders for high-temperature usages confronts with drawbacks because crystallization of am-Al_2 O_3 at high temperatures will result in serious strength loss.Aiming at this unsolved problem,in this study,high-temperature Al materials with enhanced thermal stability were developed through introducing more thermally stable nano-sized particles via high-temperature pre-treatment of ultrafine A1 powders.It was found that the pre-treatment at ≤550℃ could introduce a few Al_2 O_3 in the Al matrix and increase the strength of the composites,but the strength was still below that of am-Al_2 O_3/Al because without being pinned firmly,grain boundaries(GBs) were softened at high temperature and intergranular fracture happened.When the pre-treatment was carried out at 600℃,nitridation and oxidation processes happened simultaneously,producing large numbers of intergranular(AlN+γ-Al_2 O_3) particles.GB sliding and intergranular fracture were suppressed;therefore,higher strength than that of am-Al_2 O_3/Al was realized.Furthermore,the(AIN+γ-Al_2 O_3)/Al exhibited more superior thermal stability compared to amAl_2 O_3/Al for annealing treatment at 580℃ for 8 h.Therefore,an effective way to fabricate high-temperature Al composite with enhanced thermal stability was developed in this study.     

NiCrAlY/Al-Al2O3/Ti2AlNb高温抗氧化和力学性能研究

采用电弧离子镀技水在NiCrAlY涂层与O相Ti₂AlNb合金之间沉积不同Al:Al₂O₃比例的Al-Al₂O₃薄膜作为扩散阻挡层.研究了900℃下恒温氧化500 h后NiCrAlY/Al-Al₂O₃/Ti₂AlNb体系中Al-Al₂O₃层阻挡合金元素互扩散的行为,以及对涂层氧化动力学曲线的影响.结果表明,没有添加扩散阻挡层的NiCrAlY/Ti₂AlNb体系,涂层和基体之间的元素互扩散十分严重,涂层丧失抗氧化能力;而添加扩散阻挡层的材料体系,涂层和基体之间的元素互扩散受到抑制,涂层的长期抗高温氧化性能得到提高.对于3Al-Al₂O₃,1Al-Al₂O₃和0Al-Al₂O₃ 3种扩散阻挡层,综合比较材料体系的抗氧化性能、阻挡层阻挡涂层和基体元素互扩散能力、以及涂层和基体之间结合力,当1Al-Al₂O₃薄膜作为扩散阻挡层时,材料性能最优异.同时,本文利用扩散阻挡系数简洁定量地表示出不同Al:Al₂O₃比例阻挡层的阻挡扩散能力.     

Fabrication of carbon-coated cobalt nanoparticles by the catalytic method

A mass of carbon-coated cobalt nanoparticles were successfully synthesized by chemical vapor deposition of methane over Co/Al catalyst at 650 °C. The phases found in the as-prepared carbon-coated nanoparticles were fcc-Co. The diameter of these nanoparticles with 2–10 nm carbon coating shell was in the range of 5–80 nm. However, it is well-known that the Co nanoparticles are suitable for carbon nanotube synthesis, such as Co/Al₂O₃ and Co/SiO₂ catalysts. Here, we speculated that the formation mechanism of carbon-coated cobalt nanoparticles might due to that the formation of carbon nanotubes was inhibited by the catalyst supporter of Al. Compared with Al₂O₃ and SiO₂, Al possesses very low melting point (660 °C), very high diffusion coefficient and thermal conductivity, thus the isotropic precipitation of carbon species on the surface of cobalt particles took place, favoring the formation of carbon-coated Co nanoparticles.     

A comparative research on physical and mechanical properties of (Ti, Al)N and (Cr, Al)N PVD coatings with high Al content

Arc ion plating (Ti_0.34, Al_0.66)N and (Cr_0.28, Al_0.72)N coatings are deposited onto cemented carbide substrates at 350 °C. The crystal structure and microstructure of the deposited coatings are characterized by means of X-ray diffraction (XRD), electron probe microanalysis (EPMA), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). XRD examination indicates that both (Ti_0.34, Al_0.66)N and (Cr_0.28, Al_0.72)N coatings are of fcc structure. The atomic ratios of Al against Ti (Cr) for the two coatings are approximately close to those of the alloy targets according to EPMA measurement. In accordance with SEM observation, the fractured cross-section of the (Cr_0.28, Al_0.72)N coating is composed of columnar crystallites repeatedly interrupted by a renucleation process. Based on SEM and TEM methods, the cross-sectional fracture of (Ti_0.34, Al_0.66)N coating is found to show nano-crystalline feature without appearance of the columnar structure. (Cr_0.28, Al_0.72)N coating exhibits better wear resistance, approximately equal adhesion with the substrate, but lower nano-hardness compared with (Ti_0.55, Al_0.45)N coating.     

Properties of copper matrix reinforced with various size and amount of Al2O3 particles

Copper matrix was reinforced with Al₂O₃ particles of different size and amount by internal oxidation and mechanical alloying accomplished using high-energy ball milling in air. The inert gas-atomised prealloyed copper powder containing 1 wt.% Al as well as a mixture of electrolytic copper powder and 3 wt.% commercial Al₂O₃ powder served as starting materials. Milling of Cu-1 wt.% Al prealloyed powder promoted formation of fine dispersed particles (1.9 wt.% Al₂O₃, approximately 100 nm in size) by internal oxidation. During milling of Cu-3 wt.% Al₂O₃ powder mixture the uniform distribution of commercial Al₂O₃ particles has been obtained. Following milling, powders were treated in hydrogen at 400 °C for 1 h in order to eliminate copper oxides formed at the surface during milling. Compaction was executed by hot-pressing. Compacts processed from 5 to 20 h-milled powders were additionally subjected to high-temperature exposure at 800 °C in order to examine their thermal stability and electrical conductivity. Compacts of Cu-1 wt.% Al prealloyed powders with finer Al₂O₃ particles and smaller grain size exhibited higher microhardness than compacts of Cu-3 wt.% Al₂O₃ powder mixture. This indicates that nano-sized Al₂O₃ particles act as a stronger reinforcing parameter of the copper matrix than micro-sized commercial Al₂O₃ particles. Improved thermal stability of Cu-1 wt.% Al compacts compared to Cu-3 wt.% Al₂O₃ compacts implies that nano-sized Al₂O₃ particles act more efficiently as barriers obstructing grain growth than micro-sized particles. Contrary, the lower electrical conductivity of Cu-1 wt.% Al compacts is the result of higher electron scatter caused by nano-sized Al₂O₃ particles.     

激光重熔对Al2O3-40% TiO2等离子喷涂层耐冲蚀性能的影响

利用等离子喷涂方法制备Al₂O₃-40% TiO₂涂层,对涂层进行激光重熔处理.分别对等离子喷涂层和激光重熔涂层进行耐冲蚀磨损性能试验,研究了激光重熔对Al₂O₃-40% TiO₂等离子喷涂层耐冲蚀性能的影响.结果表明,激光重熔消除了Al₂O₃-40% TiO₂等离子喷涂层的层状结构,使得等离子喷涂层中γ-Al₂O₃转变为α-Al₂O₃,形成了α-Al₂O₃+TiAl₂O₅稳定结构.激光重熔后的涂层组织致密均匀、硬度高,具有冶金结合特征,使得耐冲蚀性能得到极大提高,其磨损特征为冲蚀粒子冲击作用下产生的裂纹、破碎与块状剥落.     

Fabrication of Bulk (Fe,Cr)_3Al/Al_2O_3 Intermetallic Matrix Nanocomposite Through Mechanical Alloying and Sintering

In the present study,(Fe,Cr)_3Al/20 vol% Al_2O_3 nanocomposite was prepared through mechanochemical reactions during ball milling and successfully bulked using a combination of cold isostatic press and sintering at 1400 ℃ for 1 h. Two processing approaches were utilized to produce(Fe,Cr)_3Al/Al_2O_3 nanocomposite: The first was milling of Fe, Cr,Al and Fe_2O_3, while the second one was milling of Fe, Cr, Al and Cr_2O_3, both in stoichiometric condition, to synthesize(Fe,Cr)_3Al/20 vol% Al_2O_3. Structural changes of powder particles during mechanical alloying were studied by X-ray diffraction. The microstructure and the morphology of powder particles and bulk samples were also studied by scanning electron microscopy and transmission electron microscopy. Microstructural analysis showed that mechanochemical reactions took place during milling, and nanometric Al_2O_3 was uniformly distributed in the matrix. The results also showed that the second approach required a considerably higher milling time to produce(Fe,Cr)_3Al/Al_2O_3 nanocomposite, as compared to the first one. For this reason, bulk samples were produced from the synthesized nanocomposite in the first approach. The microstructure of the sintered samples consisted of a network structure of(Fe,Cr)_3Al and Al_2O_3 phases with superior mechanical properties.     

Characteristics and properties of surface coated nano-TiO2

Nano-TiO₂ was coated with Al₂O₃, SiO₂ and silane coupling agent by chemical liquid deposition. The coating was characterized by Raman spectroscopy, XRD, TEM and FT-IR. The coating content and anti-ultraviolet capacity of nano-TiO₂ were measured by XRF and UV-vis spectrometer. The results show that dense coatings containing 5% Al₂O₃ or SiO₂ can be obtained by mixing slurry at pH 10, adding coating reagent and neutralization reagent into the slurry for 60 min at 85–95 °C, and finally aging for 120 min. Noncrystal SiO₂ was coated on the surface of nano-TiO₂ to form silica gel polymer with a Ti—O—Si bond, while aluminum compound exists in the form of AlOOH and part Al(OH)₃. The integrated dense film can shield photocatalysis effectively. The inorganic coating film can increase the wettability for xylene and stability in water. The surface modification of nano-TiO₂ will not impair its ability for anti-ultraviolet radiation, and more short band ultraviolet radiation can be absorbed. In addition, the optimal coating amount of silane coupling agent should be less than 3% and the best wettability for xylene can be reached when the amount is 1.2%.