石墨表面化学气相沉积SiC及C涂层的制备

以C3H8和CH3SiCl3（MTS）为先驱体原料,用化学气相沉积法在石墨基体表面分别制备了C涂层、SiC涂层。采用X射线衍射仪和扫描电镜分析了两种涂层的成分和表面微观形貌,研究了温度和气体流量对涂层微观形貌的影响。结果表明,当C3H8＋N2流量为140 L/h,沉积温度为1300℃时,石墨基体表面可获得致密度较高的C涂层,而且涂层比较平整、均匀,而流量为160 L/h时涂层比较粗糙。当MTS＋H2流量为60 L/h、沉积温度1100℃时在石墨基体表面可以形成致密的SiC涂层,1300℃时生长的SiC晶体形貌发生改变,涂层厚度增加,表面有较多圆形凸起。当MTS-H2气体流量增大可使SiC涂层晶粒尺寸增大,但大流量易产生涂层剥落。采用C和SiC共沉积涂层作过渡层,涂层与石墨基体界面结合增强;SiC涂层与石墨基体之间存在厚度较大的过渡区域,过渡区域平均厚度约2μm。     

原位生长碳纳米管及其在SiC_f/SiC复合材料中的应用

采用碳纳米管改善纤维与基体间的界面结合,同时利用碳纳米管自身的优异性能对碳化硅纤维增强碳化硅复合材料(SiCf/SiC)进行二次增强。通过化学气相沉积工艺(CVD)在SiC纤维编织件内原位生长碳纳米管,优化碳纳米管原位生长过程中的碳源流量、反应温度和反应时间等工艺参数,对碳纳米管的原位生长工艺及机理进行系统分析,并结合先驱体浸渍裂解工艺(PIP)制备CNTs-SiCf/SiC复合材料,探讨原位生长碳纳米管的引入对复合材料力学性能的影响。结果表明,优化后的工艺参数如下:反应温度750℃,C2H2、H2和N2流量比1/1/3,C2H2流量100~150 mL/min,反应时间60 min;碳纳米管的引入使SiCf/SiC复合材料的弯曲强度、弯曲模量和断裂韧性分别提高了16.3%、90.4%和106.3%。     

气体流量对LPCVD ZrC涂层结构和沉积机理的影响

利用低压化学气相沉积(LPCVD)工艺,采用Zr-Br2-C3H6-H2-Ar反应体系,在1200℃下,于石墨基底表面制备了ZrC涂层。研究了气体流量对ZrC涂层微观形貌和沉积机理的影响。结果表明,随着气体流量由200 mL/min向1000 mL/min增大,涂层的沉积速率先增大后减小,在800 mL/min时达到极值,极大值为3.37×10-3g·cm-2·h-1。同时,涂层的择优取向发生了明显的变化,在600~800 mL/min范围内,涂层具有稳定且强烈的(200)晶面择优取向。XPS分析结果表明,沉积产物中的C/Zr比也随气体流量的增大,相应的由0.85快速地升高到1.49。当气体流量为200 mL/min时,涂层致密光滑,ZrC晶粒具有典型的等轴晶结构特征;当气体流量为400~800 mL/min时,涂层光滑平坦,ZrC晶粒具有规则的四面体结构;当气体流量为1000 mL/min时,涂层表面存在着大量不规则的岛状、弓状颗粒。基底表面边界层厚度的变化是影响涂层沉积过程的主要因素。     

温度对CVD-TaC涂层组成、形貌与结构的影响

利用TaCl5-C3H6-H2-Ar反应体系,用化学气相沉积法(CVD)成功地在C/C复合材料表面沉积TaC涂层及C-TaC复合涂层.研究了温度对TaC涂层的相组成和表面形貌的影响以及CVD-TaC涂层的沉积机理.结果表明:在1373～1673 K温度范围内能够在C/C复合材料表面制备碳化钽涂层,它由TaC和游离碳组成.提高沉积温度和H2/C3H6的流量比,TaC涂层中游离碳的含量减少;随着沉积温度的升高,TaC涂层的颗粒尺寸增大,均匀程度下降;在1 573 K时颗粒间出现明显的烧结界面,结构致密无裂纹.制备出成分波动的C-TaC复合涂层,该涂层与基体间具有良好的机械相容性.分析了低应力、无裂纹TaC复合涂层的形成机制.     

C/C复合材料表面原位生长SiC_w的工艺

以三氯甲基硅烷(CH3SiCl3,MTS)为先驱体原料,采用化学气相沉积法在C/C复合材料基体上原位生长碳化硅晶须,研究稀释气体流量、催化剂以及沉积温度对碳化硅晶须生长的影响。结果表明:有催化剂存在时可以制备具有较高长径比的SiCw,无催化剂制备的SiC主要以短棒状或球状SiC为主;随着稀释气体流量或者沉积温度的增加,SiCw的产率是先增加、后减少,在1 100℃、载气和稀释气体流量均为100 mL/min时,制备的碳化硅晶须的产率最高,晶须质量最好。     

以HMDS为前驱体沉积SiC涂层的研究

以六甲基二硅胺烷(HMDS)作为硅源和碳源,H2为载气,Ar为稀释气体,前驱体由载气通过鼓泡法带入反应室,通过等温化学气相渗透法(Isothermal Chemical vapor Infiltration,ICVI)在SiC纤维表面沉积SiC涂层.通过控制沉积温度来控制涂层的表面形貌、厚度.研究表明,在1100℃沉积的涂层中开始有β-SiC晶相析出,适当降低沉积温度至950℃可以防止残余碳在反应室的富集,在950℃时SiC的沉积厚度与沉积时间呈近线性关系.     

化学气相沉积方法制备定向W涂层研究

采用化学气相沉积方法在钼基体上制备了具有[110]择优取向的W涂层,采用SEM、XRD、EBSD方法分析了涂层性能,研究表明涂层致密,法向偏离[110]晶向8°范围的晶粒占涂层面积的比例为85.32%,10°范围内[110]晶粒占全部面积的96.86%,[110]择优取向的生成受气体流量H2/Cl2,反应室压强及沉积温度的影响;对截面织构研究表明涂层形成机制为竞争生长机制。在室温～1400℃～室温20次热循环后涂层界面存在互扩散形成的孔洞,但是涂层结合良好。     

Fabrication of PyC/SiC Compound Coating on Carbon Fiber Preform and Its Effect on the Properties of Cf/Al Composite

为改善碳纤维与熔融铝合金间的润湿性、减小界面反应程度,采用化学气相沉积（CVD）法在碳纤维预制体表面沉积制备了PyC/SiC复合涂层,利用真空吸渗挤压浸渗工艺制备了Cf/Al复合材料。研究了沉积参数对碳纤维表面涂层的影响,并通过复合材料微观组织分析及材料机械性能测试来反映涂层对Cf/Al复合材料的浸渗质量和性能的影响规律。结果表明：沉积温度对涂层沉积速率影响较大,通过选择合适的沉积温度或者沉积时间,可在碳纤维表面得到厚度均匀的PyC/SiC复合涂层。碳纤维预制体表面涂层的存在可使其与基体合金润湿性良好、界面结合强度适中,形成合适的界面结合状态,有效提高浸渗质量和复合材料性能;并且当PyC涂层、SiC涂层厚度分别为0.068、0.257 μm时,复合材料性能改善效果最佳     

原位生长碳纳米管对化学气相沉积SiC涂层的影响

以碳/碳复合材料为基体,MTS为先驱体原料,采用化学气相沉积法在复合材料表面制备CNT-SiC/SiC复合涂层;研究原位生长的碳纳米管(CNTs)对SiC沉积速度和微观形貌的影响。结果表明:CNTs加快SiC的沉积,涂层的平均质量增加速率提高5%,提高沉积的均匀性,且晶粒更细小;经1 100℃恒温氧化10 h后,单一SiC涂层、CNT-SiC/SiC涂层的质量损失率分别为41.11%和34.32%;经(1 100℃,3 min)(室温,3 min)热循环15次后,单一SiC涂层和CNT-SiC/SiC涂层的质量损失率分别为33.17%和30.25%,部分区域涂层脱落及涂层表面形成的气孔是涂层试样质量损失的主要原因。     

CH3SiCl3-H2前驱体化学气相沉积法制备SiC涂层

目的 在石墨基座表面制备碳化硅(SiC)涂层,提高其抗氧化性和耐蚀性。方法 采用化学气相沉积(CVD)法在高纯石墨基体表面制备SiC涂层,结合热力学分析、SEM、XRD等分析测试方法,分析了SiC沉积过程中气相平衡组成在不同H₂/MTS物质的量比时随温度变化的关系,研究了工艺参数对涂层沉积速率和组织形貌的影响,探讨了SiC涂层择优取向的形成机制。结果 随着沉积温度升高,SiC沉积过程中主要含碳和含硅中间产物发生转变(CH₄→C₂H₂,SiHCl₃、SiCl₄→SiCl₂)。涂层沉积速率随温度升高而快速增大,受表面化学反应控制,此时β-SiC易沿着(111)晶面生长,从而形成<111>择优取向。随着沉积温度升高,涂层平均晶粒尺寸增大,同时晶粒尺寸的差异性增强,导致涂层表面粗糙度增大。当H₂/MTS物质的量比较大时,单位体积内的MTS浓度降低,进而导致涂层沉积速率下降;随着H₂/MT...     

Experimental design in the deposition of BN interface coatings on SiC fibers by chemical vapor deposition

Boron Nitride (BN) coatings deposited by chemical vapor deposition (CVD) have been increasingly used as an interface material for SiC/SiC composites. In this work, the CVD of BN was investigated using a statistical design of experiments (DOE) approach. In order to determine the most significant parameters for the process a two-level screening design (Plackett-Burman) was employed. The deposition pressure, gas mixture dilution factor, deposition time, and the reaction gas flow ratios were found to be the most significant factors that influenced coating thickness. To optimize the deposition process, a three-level surface response design (Box-Behnken) was used with the aim of producing a predictive mathematical model of the process. The generated response surface modeling (RSM) showed that deposition time had the greatest effect on coating thickness while, temperature-time and temperature-NH₃/BCl₃ interactions may be large at low/high NH₃/BCl₃ ratios and high deposition time, respectively. Tensile strength was strongly influenced by the deposition temperature and deposition time. The response model showed the dependence of tensile strength on coating thickness, NH₃/BCl₃ gas flow ratios and time. The model interaction plots suggested a dependence of temperature-gas flow ratio on tensile strengths of BN coated SiC fibers.     

铝合金表面等离子喷涂Al2O3-3%TiO2复合涂层工艺参数优化的研究

目的 通过优化等离子喷涂工艺参数，提高铝合金表面等离子喷涂Al2O3-3%TiO2复合陶瓷涂层的结合强度和涂层表截面硬度。方法 用正交试验法，对影响喷涂涂层结合强度和硬度的4个关键喷涂参数进行优化，分别得到喷涂粘结底层Ni-5Al和工作表层Al2O3-3%TiO2的最佳优化参数。结果 通过正交试验确定影响Ni-5Al涂层综合指标的因素由主到次是喷涂电流、喷涂距离、辅气流量、主气流量，最优水平数为2、3、2、1；影响Al2O3-3%TiO2涂层综合指标的因素由主到次是喷距、辅气流量、电流、主气流量，最优水平数为2、3、2、1。Ni-5Al涂层的最佳喷涂工艺参数为：喷涂距离120 mm，喷涂电流520 A，主气流量42 L/min，辅气流量7.5 L/min。Al2O3-3%TiO2复合涂层最佳喷涂工艺参数为：喷涂距离90 mm，喷涂电流530 A，主气流量46 L/min，辅气流量7.8 L/min。最佳工艺下制备的Ni-5Al底层与基体的结合强度为25.2 MPa，Al2O3-3%TiO2复合涂层与Ni-5Al底层的结合强度为17.8 MPa，且其截面硬度在1000HV0.5以上。结论 对喷涂工艺参数进行优化可以得到质量高且稳定的Al2O3-3%TiO2复合喷涂涂层，与非最佳工艺参数喷涂涂层相比，各指标均有较大提高。     

金刚石粉体表面CVD法镀钨的工艺研究

目的增强金刚石与基体的界面结合能力。方法首先对金刚石粉体进行"除有机物→除油→粗化→烘干"处理。采用自制化学气相沉积装置,研究了以H_2和WF_6为反应气体在金刚石表面CVD法镀覆钨工艺。使用扫描电镜(SEM)、能谱(EDS)、X射线衍射(XRD)、透射电镜(SEM)等检测方法,分析了金刚石粉体镀层钨的微观形貌、成分、组织结构,对镀层包覆金刚石粉体相关性能进行了初步测试。结果在粒径约为223.6mm的金刚石表面获得均匀致密镀覆层的最佳工艺参数为:沉积温度670℃,沉积时间2 min,H_2通入量1 L/min,WF_6消耗量2 g/min。沉积温度为580℃时,获得的均匀致密钨镀层的厚度为150 nm,且镀层杂质含量较少。将镀覆钨的金刚石和普通金刚石分别与铜粉热压烧结后进行抗弯强度测试,结果显示含镀覆钨的金刚石试样抗弯强度提高了38.6%。加入镀钨金刚石压块的热膨胀系数比加入普通金刚石的有所降低,并且加入的镀钨金刚石粉体越多,压块的热膨胀系数越低。结论镀钨后的金刚石颗粒的表面性能得到改善,与基体的结合能力得到提高。     

钨丝-CVD钨复合材料制备及性能分析

采用自制实验装置,通过化学气相沉积钨过程中间断缠绕钨丝,得到钨丝-CVD钨复合材料。测试分析了材料的密度、成分及显微硬度;通过压溃试验计算出钨复合材料的压溃强度,通过拉伸试验和三点弯曲试验分别绘出拉伸和弯曲曲线。实验结果表明,化学反应温度控制在550℃,WF6和H2流量分别控制在2 g/min和1 L/min时,可得到没有孔洞的致密涂层。与相同工艺条件下不缠钨丝CVD钨样品相比,钨丝-CVD钨复合材料仍具有较高的纯度、致密度,显微硬度大致相同,而压溃强度、抗拉强度和抗弯强度大大提高。     

Effects of Growth Parameters on the Morphology of CNTs/Cu Composite Powder Prepared Using Cr/Cu Catalyst by Chemical Vapor Deposition

采用化学共沉淀法制备了Cr/Cu复合粉体催化剂,并用化学气象沉淀法（CVD）原位合成CNTs/Cu复合粉末。利用SEM, TEM和Raman光谱分别对其微观形貌和结构进行表征。结果表明：采用化学气相沉淀法,使用10 wt%Cr/Cu 的催化剂,在混合气体(Ar/H2/C2H4) 流量2450/300 mL/min下,于1073 K 温度生长30 min,可以得到优质、结晶良好的 CNTs/Cu 复合粉末     

Structural characteristics and formation mechanisms of crack-free multilayer TaC/SiC coatings on carbon-carbon composites

In order to improve high temperature （over 2 273 K） ablation resistance, TaC and TaC/SiC composite coatings were deposited on carbon-carbon composites by CVD method utilizing reactive TaCl2-C3H6-H2-Ar and TaCl5-C3H6-CH3SiCl3-H2-Ar systems respectively. The structure and morphology of these coatings were analyzed by XRD and SEM. The results show that the double carbide coatings have good chemical compatibility during preparation. Two distinctive composition gradients are developed and used to produce multilayer TaC/SiC coatings with low internal stress, free crack and good resistant to thermal shock. A transition layer consisting of either C-TaC or C-SiC formed between the coating and the C/C matrix can reduce the residual stress effectively. The processing parameters were optimized and the possible growth mechanisms for these coatings were proposed. A designing methodology to prepare high performance multilayer TaC/SiC composite coatings was developed.     

等离子喷涂AlSi-ployester封严涂层工艺优化研究

采用AlSi-ployester粉末和PARXAIR-3710等离子喷涂系统制备封严涂层.为使AlSi-ployester等离子喷涂涂层获得优良的涂层性能,选择涂层结合强度为判据,通过正交试验对AlSi-ployester等离子喷涂工艺进行了优化.利用扫描电镜,Axio lmager.A lm金相图像分析系统等手段对涂层形貌和孔隙率进行分析,同时对涂层的硬度、抗热震性能进行了测试.确定优化后的工艺参数为:电弧电流790A.主气流量62.7 L/min,辅气流量5 L/min,喷涂距离100mm.结果表明,电弧电流、主气流量、辅气流量、喷涂距离对AlSi-ployester涂层结合强度具有不同的影响,在优化的喷涂工艺参数条件下,AlSi-ployester涂层结合强度可达6.9MPa,具有较好的硬度和热震性能,可为今后等离子喷涂系统工艺参数的选定提供参考.     

有无外磁场下铁在H_2SO_4 K_2Cr_2O_7溶液中的电化学状态和阴极极化行为

在[H_2SO_4]为0.1～2mol/L,[K_2Cr_2O_7]为0.01～0.4mol/L的范围内,研究了Fe/H_2SO_4 K_2Cr_2O_7系统的电化学状态和阴极极化行为,讨论了[H_2SO_4]、[K_2Cr_2O_7]和[H_2SO_4]/[K_2Cr_2O_7]比值与Fe的电化学状态的关系。分析了所出现的五种类型阴极极化曲线和外磁场对阴极过程的影响。     

Preparation of TiAl3-Al composite coating by cold spraying

TiAl₃-Al coating was deposited on orthorhombic Ti₂AlNb alloy substrate by cold spraying with the mixture of pure Al and Ti as the feedstock powder at a fixed molar ratio of 3:1 when the spraying distance, gas temperature and gas pressure for the process were 10 mm, 250 °C and 1.8 MPa, respectively. The as-sprayed coating was then subjected to heat treatment at 630 °C in argon atmosphere for 5 h at a heating rate of 3 °C/min and an argon gas flow rate of 40 mL/min. The obtained TiAl₃-Al composite coating is about 212 μm with a density of 3.16 g/cm³ and a porosity of 14.69% in general. The microhardness and bonding strength for the composite coating are HV525 and 27.12 MPa.     

Investigation on the Electrical Properties of Vacuum Cold Sprayed SiC-MoSi2 Coatings at Elevated Temperatures

SiC-MoSi₂ composite powders was prepared by wet milling with MoSi₂ powders and SiC loose grinding ball in alcohol solution. Vacuum cold spray (VCS) process was used to deposit SiC-MoSi₂ electric conducting composite coatings. The microstructure of the VCS SiC-MoSi₂ composite coatings were characterized by scanning electron microscopy. The electrical resistance of the coatings was measured using a four-point probe method. The effects of the deposition parameters on the electrical resistivity of the composite coatings were investigated. The electrical properties of the coatings at elevated temperatures in air and Ar gas atmospheres were also explored. The results show that the electrical resistivity of SiC-MoSi₂ coatings decreases with increasing He gas flow rates ranged from 3 to 6 L/min. The electrical resistivity increases with the increase in heat treatment temperature due to “pesting” behavior of MoSi_2. The electric conductive property of the VCS SiC-MoSi₂ coating is significantly improved after heat treatment at 1000 °C for 3 h in Ar protective atmosphere without oxidation. A minimum resistivity of the heat treated coating is 0.16 Ω · cm.