Mo-MoSi2梯度材料的粉末渗硅法制备

采用粉末Si覆盖在金属Mo的表面,以高频电源为加热热源,使Si在Mo基体中进行高温扩散,制备了MoMoSi2梯度材料,研究了渗硅温度、渗硅时间对Mo-MoSi2梯度层特征的影响。利用X射线衍射、扫描电镜、能谱等对梯度层的物相、形貌、结构等进行了检测和分析,其结果表明:在1 350℃下,渗硅时间延长至300min,试样表面层可以获得纯MoSi2相,Mo-MoSi2梯度层结构致密,厚度可达到350μm,其物相依次为MoSi2、Mo5Si3、MoSi3、Mo。     

SiB6-MoSi2复合涂层显微结构及抗氧化性能的研究

采用脉冲电弧放电法在SiC-C/C复合材料表面制备硼化硅和硅化钼的复相(SiB6-MoSi2)抗氧化涂层.借助X射线衍射、扫描电子显微镜对复合涂层的晶相组成、显微结构和抗氧化性能进行了表征与测试.研究了不同晶相组成(m[MoSi2]/m[SiB6]=Cp)对SiB6-MoSi2涂层显微结构的影响.结果表明:当晶相组成m[MoSi2]/m[SiB6]=1∶4时,制备的涂层致密均匀,在1 773K氧化156h后失重仅为2.12%,复合涂层氧化失效是由于长时间氧化后涂层挥发变薄,不能及时有效的愈合气相(CO和CO2)的逸出产生的氧化孔洞等缺陷导致的.     

Al-Si合金Al2O3-ZrO2微弧氧化层生长及性能测试

针对单一Al2O3微弧氧化层不能满足基体Al-Si合金使用要求的问题,采用微弧氧化法在Al-Si合金表面制备了Al2O3-ZrO2复合陶瓷层,研究了涂层的组成、结构及生长过程;测试了涂层的隔热温度.研究结果表明：在Al-Si合金试样表面微弧氧化30 min后,涂层的表面形成＂火山喷射状＂组织形貌,截面由疏松层、致密层、过渡层组成;涂层由-αAl2O3,γ-Al2O3,m-ZrO2和t-ZrO2组成,t-ZrO2为涂层的主晶相,膜层的生长分为匀速生长阶段和缓慢生长阶段;膜层隔热温度可达30℃.     

低膨胀IN909合金650℃的氧化行为

IN909低膨胀高温合金具有较低的热膨胀系数和高的综合力学性能,但由于合金不含Cr,其抗氧化性能较差,因此,在高温使用时需采用氧化涂层.为进一步提高合金的抗氧化性能,采用扫描电镜（SEM）和能谱分析（EDX）方法,研究了低膨胀IN909合金在650℃的氧化行为,结果显示IN909合金的氧化质量增加分段遵循抛物线规律,氧化由晶界开始,形成Nb、Ti、Si等元素的晶界氧化物;Fe置换氧化物中的Nb、Ti、Si,形成外层Fe的氧化物.氧化过程中,Fe由基体向合金表面扩散,Nb和Ti由氧化过渡层向基体扩散.Nb和Ti在基体前沿的富集形成ε相大量析出的薄层,可有效地阻碍Fe元素的进一步扩散,降低氧化速率.     

TA1表面制备Ni/Al涂层的反应扩渗及抗氧化行为

为了提高纯钛的高温抗氧化性能,采用电弧喷涂和等离子喷涂方法在纯钛表面制备Ni/Al涂层.对试件进行900 ℃×5 h热处理后,再进行900 ℃×40 h连续氧化实验,探索其高温抗氧化行为.结果表明,经过表面改性处理的Ni/Al涂层可以显著提高纯钛的高温抗氧化性.在热处理过程中Ni/Al涂层中的Al发生熔化扩散并与Ni和Ti形成以NiAl与TiAl₃相为主的扩散层.在氧化过程中Ni/Al涂层表面形成连续且致密的α-Al₂O₃,同时表面扩散层中的富铝相可为涂层表面提供充足的Al元素,进而对纯钛基体提供有效的高温抗氧化保护作用.     

TiAl合金电弧喷涂Al涂层的高温氧化性能

为了提升TiAl合金的高温抗氧化能力,采用电弧喷涂工艺在TiAl合金表面制备了纯铝涂层,并分别在900℃和1 000℃进行了恒温氧化试验.通过绘制氧化动力学曲线,对比了有无涂层试样的抗氧化性能.运用SEM、EDS、EPMA和XRD分析其氧化前后涂层的微观形貌、成分组成、元素分布和相组成.结果表明：纯铝涂层均匀致密、无裂纹.在900℃空气中氧化100 h后,涂层表面形成了致密的Al₂O₃氧化膜,次表层为TiAl₃相,扩散层为TiAl₂相.在1 000℃空气中氧化100 h后,涂层表面氧化膜由Al₂O₃和少量TiO₂组成,次表层为TiAl₃相,扩散层为TiAl₂相.电弧喷涂铝涂层提高了TiAl合金的高温抗氧化能力.     

TA1表面制备Ni/Al涂层的反应扩渗及抗氧化行为

为了提高纯钛的高温抗氧化性能,采用电弧喷涂和等离子喷涂方法在纯钛表面制备Ni/Al涂层.对试件进行900℃×5 h热处理后,再进行900℃×40 h连续氧化实验,探索其高温抗氧化行为.结果表明,经过表面改性处理的Ni/Al涂层可以显著提高纯钛的高温抗氧化性.在热处理过程中Ni/Al涂层中的Al发生熔化扩散并与Ni和Ti形成以NiAl与TiAl_3相为主的扩散层.在氧化过程中Ni/Al涂层表面形成连续且致密的α-Al_2O_3,同时表面扩散层中的富铝相可为涂层表面提供充足的Al元素,进而对纯钛基体提供有效的高温抗氧化保护作用.     

TC4热浸铝高温氧化性能的研究

通过热浸铝和扩散退火在TC4合金表面制备钛铝合金复合涂层,研究该涂层在850℃和900℃的长时间高温氧化行为。利用扫描电镜(SEM)、X射线衍射仪(XRD)等技术手段,分析复合涂层在高温氧化前后的微观组织。研究结果显示,复合涂层分为中间层和扩散层,扩散层主要相是TiAl_3和少量Al_2O_3;热浸铝有效提高基体的高温氧化性,850℃循环氧化后试样表面形成一层Al_2O_3保护层,900℃循环氧化后试样表面形成一层由Al_2O_3和TiO_2组成的混合氧化物层。     

激光重熔制备TA1表面Ni/Al复合抗高温氧化涂层

为了提高纯钛的高温抗氧化性能,采用电弧喷涂和等离子喷涂方法在纯钛表面制备Ni/Al复合涂层.利用激光重熔使得Ni层与Al层发生冶金反应,对试件进行800℃×40 h连续氧化.根据生成的金属间化合物特征研究纯钛的高温抗氧化行为.结果表明,经过表面改性处理后Ni/Al复合涂层可以显著提高纯钛的高温抗氧化性能.在激光重熔过程中Ni/Al复合涂层中的Al发生熔化扩散并与Ni形成以Ni_2Al_3相为主的扩散层.在氧化过程中Ni/Al复合涂层表面形成连续且致密的α-Al_2O_3氧化膜与大量NiAl相,表面扩散层中的富铝相可为表面提供充足的Al元素,进而对纯钛基体提供有效的高温抗氧化保护作用.     

纯铜热喷涂扩散渗铝层的显微组织

铜铝合金具有很好的抗高温氧化性能.在纯铜表面分别电 弧喷涂15mm和25mm厚的铝涂层,经900?℃保温4?h的扩散处理后获得19mm和36mm厚的铜铝合金渗层.主要针对渗层显微组织、渗层内的成分分布以及渗层的物相构成进行观察与测定.分析结果表明：渗层由表面层和内层两部分组成,层间结合良好.在加热处理过程中,铝涂层发生熔化,基体中的铜原子进入铝熔体形成表面渗层,表面渗层中遗留了原涂层的氧化物和孔洞.铝原子向铜基体的扩散形成组织紧密的内扩散层.内、外渗层都由金属间化合物Cu₉Al₄与αCu固溶体二相结构组成.在同样的扩散处理条件下,试件喷涂的铝涂层越厚,形成的渗层厚度越大,渗层中平均     

Effect of relative density on cyclic oxidation resistance properties of MoSi2

MoSi2 powders were fabricated respectively by mechanical alloying technique and sintering at different temperatures to prepare materials with different relative densities. The relative oxidation behavior of all MoSi2 materials at 1 473 K was investigated by TGA,SEM and XRD. The results show that the ＂pesting＂ is not found in all materials after being oxidized for 480 h. The density has no essential relation to the ＂pesting＂. The oxidation curve of specimens with lower density shows two-step oxidation kinetics. Both the first stage （0-1 h） and the second stage （1-480 h） nearly obey linear kinetics,but the oxidation rates are obviously different. The oxidation kinetics of MoSi2 with higher relative density nearly follows parabolic law. The mass gains of MoSi2 with the lowest relative density （78.6%） and the highest relative density （94.8%） are increased by 10.390 and 0.135 mg/cm^2,respectively. The oxide scale of materials with lower densities is non-protective and makes the oxygen diffusion easy. A dense scale in the material with higher density is formed,which acts as a diffusion barrier to the oxygen atoms to penetrate into the matrix,showing much better high temperature oxidation resistance. The phases distribution of oxidation scale from the outside to the inside is SiO2→Mo5Si3→MoSi2.     

Cyclil Oxidation Behaviors of MoSi2 with Different Relative Density

The influence of different relative density on the cyclic oxidation behaviors of MoSi2 at 1 273 K were studied. "Pesting" was not found in all MoSi2 materials after being oxidized for 480 h. All samples exhibited continuous mass gain during the oxidation process. The mass gains of MoSi2 with the lowest relative density (78.6%) and the highest relative density (94.8%) are increased by 8.15 mg·cm2 and 3.48 mg·cm-2, respectively. The surface of the material with lower relative density formed a loose, porous and discontinuous oxidation scale, which accelerated oxygen diffusion and aggravated the oxidation process. However, a dense scale in the material with higher relative density is formed, which acts a diffusion barrier to the oxygen atoms penetrating into the matrix. The high temperature oxidation resistance of MoSi2 can be improved by increasing its relative density.     

Nb质量分数对Al⁃15Si⁃xNb涂层组织与耐蚀性能的影响

以Al?15Si?xNb涂层为研究对象,探究了Nb质量分数对涂层显微组织结构和耐蚀性能的影响规律。采用金相显微镜观察涂层的组织形貌,运用XRD分析涂层的物相组成,应用电化学实验方法（包括开路电位、阻抗谱、极化曲线）表征并讨论了涂层在质量分数为3.5%的NaCl溶液中的腐蚀行为。结果表明,Al?15Si?xNb涂层主要由α?Al、初生Si、共晶Si组成,在涂层中加入Nb元素后生成少量的NbAl₃相和Nb₅Si₃相;Nb元素的加入促进异质形核,较明显地改变涂层的组织分布;Al?15Si?10Nb涂层中的组织更细小且分布更均匀,均匀分布的α?Al、初生Si和共晶Si构成众多均匀分布的腐蚀微电池,促进α?Al阳极反应,使涂层表面生成的Al₂O₃氧化膜更加连续;Al?15Si?xNb涂层的极化曲线具有类钝化特征,其中Nb质量分数为10%时涂层的自腐蚀电位和点蚀电位较高,产物膜电阻较大,维钝电流密度较低,具有更好的耐腐蚀性能。     

硅烷CVD法在钢基体表面生成硅扩散涂层

采用硅烷(SiH4)直接分解的化学气相沉积技术(CVD),在钢基体表面生成硅扩散涂层.X射线衍射(XRD)分析表明硅扩散涂层的主要成分是铁的硅化物FeSi.用扫描电子显微镜(SEM)对其形貌进行表征,发现涂层颗粒之间相互紧密粘结.金相照片显示,涂层与基体之间没有明显的界面,形成良好的扩散结合.     

Influence of potential on structure and properties of microarc oxidation coating on Mg alloy

In order to obtain optimizing microarc oxidation coating on Mg alloy from a friendly-enviormental electrolyte free of Cr6 and PO43-, constant potential regime was applied to produce it. The influence of potential on the morphology, composition, structure and other properties, such as microhardness and corrosion resistance were investigated by scanning electron microscopy (SEM), energy dispersive spectroscope (EDS), X-ray diffraction (XRD), hardness tester and electrochemical method. The results clearly show that oxidation potential plays an important role in the formation of coating's structure and properties. The microarc oxidation coating is smooth and white, which consists of two layers. The external layer is loose and porous and enriched in Al and Si. Moreover, its content of Al and Si increases with the increasing operated potential. While the inner layer is compact and the content of Al and Si are lower than that of the external layer. The coating is composed of several phases and the major phases are MgA12O4 and MgO, and the minor phases are Al2O3 and SiO2 when the potential is higher. The microhardness of coating is obtained the maximum at the potential of 45 V, so does the corrosion resistance.     

加热扩散对电弧喷涂Al涂层的影响

为了提高Al涂层的抗高温氧化性及硬度,采用电弧喷涂方法在Q235碳钢基体上制备了Al涂层.结果表明,经过加热扩散处理后Al涂层和基体之间形成了扩散层.涂层厚度、加热温度与加热时间对扩散层具有一定影响.当加热温度为800℃和900℃时,Al涂层主要形成相为Fe Al、Fe Al2、Fe Al3和Fe2Al5.经过加热扩散处理后Al涂层具有优良的抗高温氧化性,且平均硬度相比未经加热扩散处理的Al涂层提高了10倍以上,利用扩散系数求出的扩散层深度与实际扩散层深度相近.     

Influence of potential on structure and properties of microarc oxidation coating on Mg alloy

In order to obtain optimizing microarc oxidation coating on Mg alloy from a friendly-enviormental electrolyte free of Cr⁶⁺ and PO ₄ ³⁻ , constant potential regime was applied to produce it. The influence of potential on the morphology, composition, structure and other properties, such as microhardness and corrosion resistance were investigated by scanning electron microscopy (SEM), energy dispersive spectroscope (EDS), X-ray diffraction (XRD), hardness tester and electrochemical method. The results clearly show that oxidation potential plays an important role in the formation of coating’s structure and properties. The microarc oxidation coating is smooth and white, which consists of two layers. The external layer is loose and porous and enriched in Al and Si. Moreover, its content of Al and Si increases with the increasing operated potential. While the inner layer is compact and the content of Al and Si are lower than that of the external layer. The coating is composed of several phases and the major phases are MgAl₂O₄ and MgO, and the minor phases are Al₂O₃ and SiO₂ when the potential is higher. The microhardness of coating is obtained the maximum at the potential of 45 V, so does the corrosion resistance.