NiCrBSi超音速火焰喷涂层的电化学腐蚀机制

采用超音速火焰喷涂方法在普通碳钢表面制备了NicrBsi合金涂层，然后将涂层在利用冰醋酸调整pH值到3的3．5％NaCl(质量分数)溶液中进行全浸泡试验．应用化学成分分析、电子探针分析方法分析了涂层腐蚀后的成分变化和分布，用高频等离子体发射光谱仪分析了腐蚀液中的离子存在情况，用X射线能谱分析了腐蚀产物，用扫描电镜观察了涂层腐蚀后的形貌．结果发现：NiCrBSi合金涂层没有发生成分选择性腐蚀；涂层的腐蚀包括表面宏观均匀腐蚀和腐蚀介质侵入涂层内部引发的腐蚀，后者起关键作用；腐蚀首先在涂层表面存在未熔颗粒及孔隙、夹杂和微裂纹的局部阳极区发生，随后沿孔隙、夹杂、微裂纹、层状组织等形成的阳极通道扩展；涂层的主要失效形式是片状或层状剥离；调整喷涂工艺参数以降低涂层的电化学不均匀性或进行封孔处理有助于提高涂层的耐蚀性能．     

超音速火焰喷涂Cr_3C_2-NiCr涂层的冲蚀磨损特性

实验研究了燃气流量、氧气流量和喷涂距离对超音速火焰 (HVOF)喷涂Cr3C2 NiCr涂层冲蚀磨损性能的影响 ,在对不同角度冲蚀后涂层表面和横截面结构分析的基础上 ,探讨了其冲蚀磨损失效机制 .结果表明 :Cr3C2 NiCr涂层的冲蚀磨损呈现脆性材料的冲蚀磨损特征 ,在 90°冲蚀率最大 ;磨料冲击引起的裂纹沿涂层内粒子界面萌生、扩展并最终导致粒子剥落 ,是涂层主要的冲蚀磨损机制 .     

HVOF制备的Ni60/WC-10Co4Cr涂层组织和滑动磨损性能研究

为了降低超音速火焰(HVOF)喷涂金属陶瓷涂层的材料和加工成本,使其在更大范围内替代会给环境带来严重污染的电镀硬铬(EHC)涂层,本文将不同比例的Ni60与WC-10Co4Cr相混合,并采用HVOF喷涂工艺分别制备了5种金属陶瓷复合涂层.研究了这些涂层的显微组织、基本性能和滑动磨损性能,并将其与EHC涂层进行对比.结果表明:所有HVOF喷涂工艺制备的Ni60/WC-10Co4Cr涂层都很致密(孔隙率小于1%),随着WC-10Co4Cr比例的增加,Ni60/WC-10Co4Cr涂层的硬度从688.3 HV0.3增加到1 203.4HV0.3,磨损率由2.75×10~(-5) mm~3/N·m降低到7.29×10~(-7) mm~3/N·m.并且,所有HVOF喷涂工艺制备的涂层和与其配对的摩擦副的磨损率以及磨擦系数均低于EHC涂层,表现出良好的抗滑动磨损性能.     

表面熔融粒子结构对超音速火焰喷涂层结合性能的影响

探讨了在超音速火焰喷涂（HVOF）过程中所形成的表面金属层熔化而芯部陶瓷相不熔化的表面熔融粒子结构。研究了这种粒子结构对HVOF涂层结合性能的影响规律,发在态颗粒的密度及体积分数与结合强度有直接的对应关系。提出了综合考虑固态粒子密度、体积分数及速度,表征半熔结构状态对涂层结合性能影响的有效固相质量和有效固相动能两个参量。有效固相质量定义为固态粒子密度和其体积分数平方的乘积,有效固相动能定义为有效固相质量与粒子速度平方的乘积。试验结果表明,涂层的结合强度随这两个参量的增加而增加。     

超音速火焰喷涂制备双峰WC-12Co涂层组织性能研究

采用JP-8000型超音速火焰(HVOF)喷涂设备,在低碳钢基体上制备了双峰WC-12Co涂层,测试了涂层的结合强度、显微硬度、气孔率以及抗磨粒磨损性能.并利用XRD对喷涂粉末及涂层进行了相结构分析,用扫描电子显微镜对喷涂粉末、磨粒磨损后的涂层表面形貌进行了观察.结果表明:在喷涂过程中,仅有很少量的WC粒子发生氧化脱碳...     

Effects of surface modification on isothermal oxidation behavior of HVOF-sprayed NiCrAlY coatings

NiCrAlY coatings were deposited on Ni-based superalloy by high-velocity oxygen-fuel spraying (HVOF). Surface modification by means of grit-blasted, shot-peened and ground methods was used in order to study the effect of surface conditions on the isothermal oxidation behavior of HVOF-sprayed NiCrAlY coatings at 1050 ℃. The results showed that surface modification had an obvious effect on the isothermal oxidation behavior of the coatings. There was a large decrease in growth rate compared with the as-sprayed coating. The scale formed on the grit-blasted and shot-peened coatings was a mixture of Al₂O₃ and NiCr₂O₄, while the oxide formed on the ground coating was composed mainly of Al2O3. After surface modification, the content of NiCr₂O₄ spinels decreased compared with the as-sprayed coating.     

超音速火焰喷涂WC-12Co涂层的滑动磨损特性

利用超音速火焰喷涂工艺在铜基复合材料表面制备WC-12Co涂层. 分析了涂层的微观结构、相组成和含量以及表面和截面硬度,并对涂层的摩擦磨损性能进行测试. 结果表明:涂层组织和截面硬度分布均匀,耐磨性好,摩擦过程中会形成两种摩擦膜. 磨损率随载荷增加而呈增大趋势,随转速的增加呈先减小后增大的趋势. 涂层最适用的环境为300 ~500 r· min-1和2~3 N,磨损率与滑动速度间的回归方程满足一元二次函数;磨损率与载荷间的回归方程满足指数方程.     

Effects of surface modification on isothermal oxidation behavior of HVOF-sprayed NiCrA1Y coatings

NiCrAlY coatings were deposited on Ni-based superalloy by high-velocity oxygen-fuel spraying(HVOF).Surface modification by means of grit-blasted,shot-peened and ground methods was used in order to study the effect of surface conditions on the isothermal oxidation behavior of HVOF-sprayed NiCrAlY coatings at 1 050℃.The results showed that surface modification had an obvious effect on the isothermal oxidation behavior of the coatings.There was a large decrease in growth rate compared with the as-sprayed co...     

Effects of surface modification on thermal cycling lifetime of thermal barrier coatings with HVOF NiCrAlY bond coat

NiCrAlY bond coat was prepared by HVOF (high-velocity oxygen fuel) spray on nickel-based superalloy. Surface treatments like grit-blasting, shot-peening and vacuum treatment methods were carried out in order to study the effects of surface modification on thermal cycling lifetime of TBCs. The surface-modified TBCs exhibited better thermal shock resistance. Failure of TBCs with the as-sprayed bond coat occurred within the top coat and at the interface between spinels and the top coat, while that of after shot-peening, grit-blasting and vacuum treatment occurred mainly within the top coat. TGO (thermally grown oxide) formed on as-sprayed bond coat was composed of a Ni(Al,Cr)2O4 spinels outer layer and a Al2O3 inner layer. But, a continuous and uniform Al2O3 formed after surface modification . Formation of the mixed oxides (spinels) on the as-sprayed bond coat accelerated the failure of TBCs.     

Characterization of MCrAlY/nano-Al2O3 nanocomposite powder produced by high-energy mechanical milling as feedstock for high-velocity oxygen fuel spraying deposition

Al2O3 nanoparticles and MCrAlY/nano-Al2O3 nanocomposite powder (M = Ni, Co, or NiCo) were produced using high-energy ball milling. The MCrAlY/nano-Al2O3 coating was deposited by selecting an optimum nanocomposite powder as feedstock for high-velocity oxy-gen fuel thermal spraying. The morphological and microstructural examinations of the Al2O3 nanoparticles and the commercial MCrAlY and MCrAlY/nano-Al2O3 nanocomposite powders were investigated using X-ray diffraction analysis, field-emission scanning electron microscopy coupled with electron dispersed spectroscopy, and transmission electron microscopy. The structural investigations and Williamson–Hall res-ults demonstrated that the ball-milled Al2O3 powder after 48 h has the smallest crystallite size and the highest amount of lattice strain among the as-received and ball-milled Al2O3 owing to its optimal nanocrystalline structure. In the case of developing MCrAlY/nano-Al2O3 nanocompos-ite powder, the particle size of the nanocomposite powders decreased with increasing mechanical-milling duration of the powder mixture.