PROCESS AND PROPERTIES OF ELECTROLESS PLATING RE-Ni-B-SiC COMPOSITE COATINGS

Technology and properties of electroless composite RE-Ni-B-SiC coatings have been investigated.Results show that stabilizer plys a decisive role in electroless composite Ni-B-SiC,the addition of appropriate quantity of RE(rare earth) into the Ni-B-SiC bath not only increases SiC content in composite coatings,their hardness and wear resistance but also improves crystalline fineness,Wear resistance increases with the increase of SiC.Hardness and wear resistance of composite coatings reach peak values a fter heat treatment at 4OO and 500℃ for 1h respectively.

Oxidation behavior of oxidation protective coatings for C/C-SiC composites at 1500 ℃

Porous carbon/carbon preforms were infiltrated with melted silicon to form C/C-SiC composites. Three-layer Si-Mo coating prepared by slurry painting and SiC/Si-Mo multilayer coating prepared by chemical vapor deposition(CVD) alternated with slurry painting were applied on C/C-SiC composites, respectively. The oxidation of three samples at 1 500 ℃ was compared. The results show that the C/C-SiC substrate is distorted quickly. Three-layer Si-Mo coating is out of service soon due to the formation of many bubbles on surface. The mass loss of coated sample is 0.76% after 1 h oxidation. The sample with SiC/Si-Mo multilayer coating gains mass even after 105 h oxidation. SiC/Si-Mo multilayer coating can provide longtime protection for C/C-SiC composites and has excellent thermal shock resistance. This is attributed to the combination of dense SiC layer and porous Si-Mo layer. Dense SiC layer plays the dual role of physical and chemical barrier, and resists the oxidation of porous Si-Mo layer. Porous Si-Mo layer improves the thermal shock resistance of the coating.

Preparation and characterization of molybdenum powders with copper coating by the electroless plating technique

Molybdenum powders with a diameter of approximately 3 μn were coated with copper using the electroless plating technique in the pH 12.5-13 and temperature range of 55-75℃. The optimization of the electroless copper bath was evaluated through the combination of process parameters like pH and temperature. The optimized values ofpH and temperature were found to be 12.5 and 60℃, respectively, which attributes to the bright maroon color of the coating with an increase in weight of 46%. The uncoated and coated powders were subjected to microstructural studies using scanning electron microscope （SEM） and the phases were analyzed using X-my diffrction （XRD）. An attempt was made to understand the growth mechanism of the coating. The diffusion-shrinkage autocatalytic model was suggested for copper growth on the molybdenum surface.

Processing and properties of 2D SiC/SiC composites by precursor infiltration and pyrolysis

Two-dimensional plain-weave silicon carbide fiber fabric reinforced silicon carbide(2D-SiC/SiC)composites were molded by stacking method and densified through precursor infiltration and pyrolysis(PIP)process.SiC coating was deposited as the fiber/matrix interphase layer by chemical vapor deposition(CVD)technique.Fiber/matrix debonding and relatively long fiber pullouts were observed on the fracture surfaces.Additionally,the flexural strength and elastic modulus of the composites with and without fiber/matrix interphase layer were investigated using three-point bending test and single-edge notched beam test.The results show that the fiber fraction and the porosity of 2D-SiC/SiC composites with and without coating are 27.2%(volume fraction)and 11.1%,and 40.7%(volume fraction)and 7.5%,respectively.And the flexural strength and elastic modulus of 2D-SiC/SiC composites with and without coating are 363.3 MPa and 127.8 GPa,and 180.2 MPa and 97.2 GPa,respectively.With a proper thickness,the coating can effectively adjust the fiber/matrix interface,thus causing a dramatic increase in the mechanical properties of the composites.

Ablation behavior of(ZrC/SiC)_(3)alternate coating prepared on sharp leading edge C/C composites by CVD

A(ZrC/SiC)_(3)alternate coating was deposited on sharp leading edge(SLE)C/C composites by chemical vapor deposition(CVD).The ablation behavior was examined via oxyacetylene torch with heat flux of 2.38 MW/m^2.The results indicated that the alternate coating exhibited great ablation resistance,providing an effective protection for C/C composites.In initial rapid heating stage,the(ZrC/SiC)_(3) alternate coating can relieve thermal stress,avoiding the peeling of coating and keeping an intact coating structure.In subsequent ablation,the Si C layers in central region were consumed rapidly,leaving layered interspaces.Three stacked ZrO_(2) layers were reserved with the assistance of the release of thermal stress by interspaces,offering a great anti-scouring effect.In transition and border regions,the alternate Si C layers can delay oxygen erosion of inner coating and C/C substrate by the formation of SiO_(2).It is believed that the results would be helpful for the design and application of anti-ablation coatings on SLE C/C composites.

SiC/Cu-Al复合材料无压浸渍制备工艺的研究

利用化学镀法在SiC颗粒表面包覆Cu层制备了SiC/Cu复合粉体,然后将其压制成预制体并在熔融铝液中无压浸渍,制出了SiC/Cu-Al复合材料。研究了浸渍温度和时间对所制SiC/Cu-Al复合材料浸渍效果的影响。结果表明:SiC颗粒表面的Cu包覆层分布均匀;在800℃、保温2 h条件下制备的SiC/Cu-Al复合材料显微组织致密;在700～900℃的浸渍温度范围内,铝的浸渍深度随着浸渍温度的升高先增加后减小;随着浸渍时间的延长,复合材料的显微组织越来越致密;Cu包覆层有效地改善了SiC颗粒与铝熔体间的润湿性,抑制了Al4C3脆性相的生成。

Mg_2B_2O_5晶须增强AZ91D镁基复合材料表面Ni-P-SiC化学镀层的耐蚀性与SiC含量的关系

有关Ni-P-Si C复合镀层耐蚀性的研究不多。为此,在Mg2B2O5晶须增强AZ91D镁基复合材料表面化学镀Ni-P-Si C层。采用扫描电镜(SEM)、电子探针(EPMA)、电化学方法研究了镀液中纳米Si C含量对镀层表面形貌、成分、耐蚀性、结合力的影响。结果表明:纳米Si C颗粒的加入细化了镀层晶粒,造成了镀层疏松,随着镀液中Si C浓度的增加,复合镀层的耐蚀性逐渐降低,但对基体仍有保护作用,Si C浓度为2 g/L时耐蚀性较佳,且镀层与基体结合良好。

CVD-PyC界面层和SiC涂层厚度数学计算模型的建立与验证

建立了合适的化学气相沉积碳界面层厚度数学计算模型和SiC涂层厚度数学计算模型,并通过工艺实验对该模型进行了验证。结合实验结果分析,发现通过该模型计算出的化学气相沉积碳界面层厚度和SiC涂层厚度与SEM照片分析结果基本接近,因此可利用上述模型估算出C/SiC复合材料产品的化学气相沉积碳界面层厚度和SiC涂层厚度,快速评估C/SiC复合材料产品化学气相沉积质量能否满足实际工况使用要求。

CVD沉积工艺对SiC涂层结晶度与耐腐蚀性能的影响

通过化学气相沉积(CVD)SiC涂层来提高SiC_(f)/SiC复合材料的耐腐蚀性能,本文以CH_(3)SiCl_(3)(MTS)为源气体,在反应烧结SiC基体上制备SiC涂层,控制沉积温度、炉压及H_(2)/MTS摩尔比等工艺参数,通过X射线衍射实验(XRD)得到不同工艺条件下生成的碳化硅涂层的物相组成和结晶度,通过高温水腐蚀实验检测涂层的耐腐蚀性,并利用扫描电子显微镜(SEM)观察腐蚀前后的表面形貌。结果表明:当沉积时间为8 h,沉积温度从1050℃到1250℃,β-SiC涂层表面平整性提高,沉积厚度由12.97μm急剧增加至71.10μm,SiC晶粒尺寸逐渐增大,最终呈金字塔状;碳化硅涂层腐蚀60 d后,表面呈现针状结构,1250℃下沉积的SiC涂层耐腐蚀性能较好;β-SiC涂层的晶粒尺寸随沉积炉压的增大而增大,结晶度随沉积炉压增大而减小,在200 Pa以下,获得的β-SiC晶粒的结晶度最高(81.08%)、晶粒尺寸最小(13.7 nm);随着H_(2)/MTS摩尔比增加,β-SiC晶粒结晶度迅速下降,当H_(2)/MTS=6.5时,结晶度最高(95.91%)。

镀液中SiC含量和粒径对Ni-P-SiC复合化学镀层性能的影响

采用化学镀方法制备了Ni P SiC复合镀层 ,系统研究了镀液中SiC含量和粒径对镀层结构及显微硬度的影响。结果表明 ,镀层中SiC析出量随镀液中SiC含量的增加而增加 ,在SiC含量一定的情况下 ,当SiC粒径为 7.0 μm时 ,析出量最大 ;镀液中SiC的含量和粒度对原始镀层的硬度影响不大 ,但对 4 0

铝合金表面化学镀Ni-Co-P/SiC复合镀层的组织与性能研究

通过化学镀的方法,在铝合金表面成功地制备了Ni-Co-P/SiC复合镀层。对复合镀层的表面形貌、化学成分、晶态结构、硬度进行了表征分析,通过电化学测试对其耐腐蚀性进行了研究。结果表明:SiC纳米微粒起到了提高Ni-Co-P合金镀层硬度的作用,向镀液中加入12 g/L SiC纳米微粒时,复合镀层的硬度达到最大值524HV;Ni-Co-P/SiC复合镀层能增强铝合金材料的耐蚀性能,镀液中SiC微粒的质量浓度为9 g/L时,复合镀层的耐腐蚀性相对最好。

Ni-SiC和Ni-SiO_2复合镀层性能的研究

对Ni SiC、Ni SiO2 复合镀层在 5 %NaCl+0 .5 %H2 O2 溶液中的腐蚀性能 ,80 0℃高温下的抗氧化性能以及导热性能进行了研究。并利用扫描电镜 (SEM)对镀层微观组织形貌进行了观察和分析。实验结果表明 :与Ni SiC复合镀层比较 ,Ni SiO2 复合镀层在 5 %NaCl+0 .5 % /H2 O2 溶液中以及在 80 0℃高温环境中 ,均表现出较好的耐蚀和抗氧化能力 ;而Ni SiC复合镀层的导热性则明显强于Ni SiO2 ,两者的导热系数随时间延长均略有减少。文中对产生这些性能差异的原因进行了初步的探讨与分析。

SiC粉体化学镀铜工艺研究

介绍了SiC粉体的敏化、活化及其碱性化学镀铜的工艺配方.分别对镀液稳定性的影响因素和各工艺条件对镀速的影响进行了研究.结果表明,SiC粉体颗粒越细、镀液pH增大、温度升高,都容易导致镀液分解;增加甲醛含量,可以提高镀速,但是镀液稳定性下降;适宜的络合剂,可以提高镀层质量,保持镀液稳定,但络合剂含量增加,镀速降低.得出了最佳的工艺条件:φ(甲醛)10～20 mL/L,ρ(络合剂)50～70 g/L,温度15～35 ℃, pH 12.5 ～13.碱性化学镀铜后的SiC-Cu复合粉体及其于1 050 ℃热处理后的X-射线衍射分析表明,镀层中含Cu、SiC 和Cu2O,且Cu呈结晶态;铜镀层在高温下与SiC粉体能够较好共存,无脱落现象.扫描电镜照片显示,SiC-Cu复合粉体分散性良好,镀层表面平滑、均匀,并有细小的金属胞状颗粒随机堆积而成.

化学复合镀制备Ni-P-SiC包覆立方氮化硼的机理研究

采用化学复合镀方法,制备了Ni-P-SiC包覆cBN磨料,通过SEM、EDX和XRD方法对制备的磨料进行了表征。分析了复合镀层的表面形貌、元素组成和物相结构,研究了复合镀层的沉积机理与胞状物的生长过程。SiC微粒与镀层的结合方式可能有三种,只有SiC微粒在镀液中完全被活化,才有可能被Ni-P合金牢固包覆,不至于被流动的镀液冲刷下来。

化学镀Ni-P-SiC镀层的微观组织结构特征

对化学镀Ni P SiC复合镀层的微观组织结构特征进行了研究 ,结果表明 ,SiC微粒弥散分布在复合镀层中 ,Ni P合金主要作为粘结金属包络着SiC微粒 ,两者之间存在电子转移 ,发生了界面反应 ,反应扩散层为 10 - 1nm级 ,界面结合紧密 ,无孔隙和裂纹等缺陷。元素存在形态主要表现为Ni和P以单质的形式存在 ,Si以共价健SiC的形式存在 ,Ni

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。

电刷镀纳米Ni-P-SiC复合镀层性能的研究

纳米微粒加入镀液可提高镀层的性能,用电刷镀方法制备了纳米SiC/NiP复合镀层,测试了纳米SiC微粒添加量对复合镀层的硬度、耐磨性的影响,探讨了纳米SiC微粒复合镀层的强化机制及NiP晶化过程中的强化作用。结果表明,采用电刷镀制备工艺,能在一定程度上改善纳米微粒在镀液中的分散均匀性并能提高复合镀层性能。在NiP合金镀液中适量添加纳米SiC微粒(7～10g/L),纳米SiC微粒在形成复合镀层时能起到硬质点的强化作用,同时在NiP晶化过程中还能在细化晶粒中起到再强化作用。不仅能使镀层硬度提高1.5～1.8倍,还能提高其耐磨性。

SiC涂层化学气相沉积过程的数值模拟

根据化学气相沉积法的工艺特点,对C/C复合材料SiC涂层的制备过程进行了数学建模和有限元模拟,得出了反应器内以及试样表面反应物浓度的变化规律,并且获得了反应器内反应物浓度与沉积产物间的关系.结合实验分析,验证了SiC涂层晶粒尺寸的变化和沉积形貌的演变是由于反应气体浓度分布随位置变化造成的:沿着反应气体流动的方向,反应物浓度逐渐降低,沉积得到的SiC晶粒尺寸逐渐减小,沉积形貌由堆积岛状到颗粒状再到晶须状逐级演变.

碳纤维表面化学复合镀Ni-P-SiC镀层的形貌及性能

为了同时改善碳纤维与金属铝基体之间的润湿性和分散性,采用化学复合镀的方法在碳纤维上制备Ni-P-SiC复合镀层。通过扫描电子显微镜观察镀层表面和截面形貌,通过单纤维电子强力测试仪分析Ni-P镀层和Ni-P-SiC镀层力学性能,采用同步热分析仪分析Ni-P镀层和Ni-P-SiC镀层的氧化性能。结果表明:Ni-P-SiC镀层的抗拉强度比Ni-P镀层的抗拉强度稍低,但Ni-P-SiC镀层的形状参数m对比Ni-P的形状参数m提高了8.45%,材料的可靠性提高;对比出现最大放热峰的温度,Ni-P-SiC镀层比Ni-P镀层的出现温度高130℃,Ni-P-SiC镀层的抗氧化性明显提高;通过Ni-P-SiC镀层改性后的碳纤维在铝基中分散性明显提高,减少了碳纤维的聚集。Ni-P-SiC镀层有效解决了高温条件下碳纤维与铝基复合的难题。

AZ91D镁合金表面化学镀Ni-P-SiC复合镀层的结构与性能

采用化学复合镀的方法在AZ91D镁合金表面制备了Ni-P-SiC复合镀层,对其组织与相结构进行了SEM及XRD分析,并进行了电化学与磨损试验。结果表明:制备得到了均匀、致密、无明显缺陷的Ni-P-SiC复合镀层,SiC颗粒在镀层中分布均匀;复合镀层为非晶态结构,硬度高达643HV;复合镀层具有明显的钝化区,耐腐蚀性能优异,其耐磨性明显优于NiP镀层的。