Microstructure and electrical characteristics of Ni-Cr thin films

Microstructure of thin films of different compositions of Ni-Cr alloy, over the range from 40 wt.% to 80 wt.% Ni, deposited on silicon nitride coated GaAs substrates, is investigated under Transmission Electron Microscope (TEM) in as-deposited and annealed conditions. The procedure of wet etching vias through GaAs substrates is used for preparing samples for TEM. Microstructures of as-deposited films of different Ni-Cr alloys are related to the nature of the parent alloy in the binary phase diagram. The microstructural transformations in annealed films of single and two-phase alloy materials are interpreted based on the comparison of TEM micrographs in conjunction with the X-ray diffraction and electron diffraction data. The changes in the electrical characteristics such as resistivity and temperature coefficient of resistance (TCR) of the films in relation to the microstructural transformations are discussed. The effect of superimposing a polyimide layer on the TCR of Ni-Cr films is also discussed.     

石墨及碳化物对高镍铬无限冷硬铸铁轧辊耐磨性的影响

本文研究了具有不同石墨和碳化物含量的高镍铬无限冷硬铸铁轧辊材料在滚动摩擦和干滑动摩擦条件下的摩擦学特性，考察了高镍铬无限冷硬铸铁中石墨和碳化物数量、分布对其摩擦学特性的影响。研究结果表明，组织中的石墨和碳化物数量、形态和分布对材料的耐磨性有较大影响。石墨含量在低于9．21％时，增加石墨量并适当减少碳化物量可以提高材料的耐磨性；呈均匀分布的长片状石墨和连续网状分布的碳化物对提高高镍铬无限冷硬铸铁轧辊的耐磨性有显著意义。     

The Response of Alloys to Erosion-Corrosion at High Temperatures

Pure nickel, Ni-20Cr and Ni-30Cr alloys wereexposed to conditions of erosion and corrosionsimultaneously at 700°C and 800°C. The exposureswere made using normal impact of an air stream loadedwith 20-m alumina. The alumina particles flowed at therate of 400 mg per min and the velocities used were 75m/s and 125 m/s. The reaction kinetics were measureddiscontinuously by interrupting the exposure and measuring the weight loss. The specimens wereexamined using SEM-EDAX both on the surface and incross-section. Under simple oxidation, the alloyspecimens developed a thin protective layer of chromia. Under erosion-corrosion conditions, thisprotective scale was prevented from forming and thealloys were found to undergo aggressive attack at a ratethat was the same as that experienced for pure nickel, the surface oxides were identified asCr₂O₃ and NiO. It is proposedthat, under erosion corrosion, the erosive streamprevents the formation of a continuous layer of chromiaby removing the oxide faster than it can spread laterally. The specimen issaid to be in a state of erosion-maintained transientoxidation. This mechanism implies that it would bedifficult for protective scales to form in the presence of erosion and the oxidation behavior of analloy cannot be used as a guide to its resistance toerosion-corrosion.     

Characterization of oxide structures formed on nickel-chromium alloy during low pressure oxidation at 500–600°C

Low pressure oxidation studies of Ni-18%Cr alloy were carried out at temperatures of 500–600°C for very brief periods. Detailed XPS, AES, SEM, and TEM studies identified four stages in the initial oxidation. These are: (1) formation of a mixed nickel-chromium oxide overlayer; (2) growth of submicron-sized oxide nodules; (3) development of dark hole-like patches on the surface; and (4) growth of second generation oxide nodules. Both types of nodules consist primarily of a nickel structure depleted in oxygen. Their formation appears to result from a very rapid outward movement of nickel from localized defects in the metal. The dark patches result from the presence of a chromium oxide-rich underlayer, which appears to form by a lateral migration of chromium from adjacent oxide/metal interface regions and from grain boundaries.     

锅炉受热面NiCr涂层抗高温热腐蚀机制与性能的研究

针对电站锅炉受热面高温腐蚀的影响,通过采用电弧喷涂工艺,研究了Q235钢板表面电弧喷涂PS45、FeCrAl、4Cr13合金涂层后在高温条件下的热腐蚀机制与性能.热腐蚀动力学试验和分析结果显示,在700℃下腐蚀77 h、Na2SO4+K2SO4盐膜量为3~4 mg/cm2的试验条件下,测试得到的PS45、FeCrAl、4Cr13合金涂层的热腐蚀速度分别为υ=0.38t-0.59、υ=1.35t-0.12和υ=1.79t-0.23.涂层表面的成分和组织分析结果表明,Q235钢板表面的PS45涂层之所以表现出比FeCrAl、4Cr13涂层更高的抗热腐蚀(Na2SO4/K2SO4)性能,其原因在于PS45镍基合金中含有最多的Cr,涂层表面的Cr2O3膜层具有较高的连续性、致密性和稳定性.     

锅炉受热面NiCr涂层抗高温热腐蚀机制与性能的研究

针对电站锅炉受热面高温腐蚀的影响,通过采用电弧喷涂工艺,研究了Q235钢板表面电弧喷涂PS45、FeCrAl、4Cr13合金涂层后在高温条件下的热腐蚀机制与性能.热腐蚀动力学试验和分析结果显示,在700℃下腐蚀77 h、Na2SO4＋K2SO4盐膜量为3-4 mg/cm2的试验条件下,测试得到的PS45、FeCrAl、4Cr13合金涂层的热腐蚀速度分别为υ=0.38t-0.59、υ=1.35t-0.12和υ=1.79t-0.23.涂层表面的成分和组织分析结果表明,Q235钢板表面的PS45涂层之所以表现出比FeCrAl、4Cr13涂层更高的抗热腐蚀（Na2SO4/K2SO4）性能,其原因在于PS45镍基合金中含有最多的Cr,涂层表面的Cr2O3膜层具有较高的连续性、致密性和稳定性.     

离子注入Y~ 对Ni30Cr定向凝固合金氧化行为的影响

利用热重分析(TGA)、扫描电镜、能谱分析、电子探针及X射线衍射等技术研究了离子注入1×10~17Y~ /cm~2对Ni30Cr定向凝固合金1000℃恒温氧化行为的影响。合金的横向和纵向虽具有不同的显微结构,但氧化行为相似。注入Y~ 降低了合金的氧化速率约1～2倍,细化了氧化膜晶粒,抑制了晶界优先氧化及内氧化现象的发生,减少了界面空洞,增强了膜的粘附性。产生上述结果的原因在于注入Y~ 改变了合金的氧化机制,未注Y~ 合金的氧化膜主要靠铬向外扩散生长,注Y~ 合金则主要靠氧向内扩散生长。     

Chloridation-oxidation of Fe-Cr and Ni-Cr alloys at 800°C

The chloridation-oxidation behavior of Fe-Cr (0–25 wt. %Cr) and Ni-Cr (0–20 wt.%Cr) alloys was studied at 800°C in three different H₂-HCl-H₂O() environments. In a low-HCI and low-H₂O() environment, where Cr₂O₃ is thermodynamically stable, the corrosion resistance of the Fe-Cr alloys increased with increasing Cr content in the alloys. In a high-HCl and high-H₂O() environment, where FeCr₂O₄ is stable and CrCl₂ is metastable, the corrosion resistance of the Fe-Cr alloys depended similarly on the Cr content. Low-Cr-Fe-Cr alloys exhibited large weight losses, while Fe-Cr alloys with higher than 19 wt. %Cr showed good corrosion resistance. In an environment of high-HCl in the absence of H₂O(), the evaporative corrosion rate was fast and limited by gas phase diffusion, and independent of the Cr content in the Fe-Cr alloys. Ni and Ni-Cr alloys generally showed good corrosion resistance in the environments of high H₂O() because of the low NiCl₂ vapor pressure and formation of a protective Cr₂O₃ scale. However, in the environment of high HCl in the absence of H₂O(), selective formation and evaporation of CrCl₂ occur, which results in Cr depletion and networks of voids for even a high-Cr Ni-Cr alloy.     

Ni-Cr/BN混合粉末在石墨舟中烧结时的碳化和粉化行为

采用扫描电镜、X射线衍射、差示热分析(DTA)等方法对Ni-Cr／BN混合粉末在1250℃烧结时发生的碳化和粉化行为进行了分析,借用Grabke的模型探讨了这种现象产生的原因和机理,并进行了碳化动力学的讨论,提出了预防产生这种现象的措施。     

Sliding wear behaviors of electrodeposited Ni composite coatings containing micrometer and nanometer Cr particles

Micrometer and nanometer Cr particles were co-deposited with Ni by electroplating from a nickel sulfate bath containing a certain content of Cr particles. Cr microparticles are in a size range of 1-5 (m and Cr nanoparticles have an average size of 40 nm. The friction and the wear performance of the co-deposited Ni-Cr composite coatings were comparatively evaluated by sliding against Si3N4 ceramic balls under non-lubricated conditions. It is found that the incorporation of Cr particles enhances the microhardness and wear resistance of Ni coatings. The wear resistance of Ni composite coating containing Cr nanoparticles is higher than that of the Ni composite coating containing Cr microparticles with a comparable Cr particle content. The co-deposition of smaller nanometer Cr particles with Ni effectively reduces the size of Ni crystals and significantly increases the hardness of the composite coatings due to grain-refinement strengthening and dispersion-strengthening, resulting in a significant improvement of wear resistance of the Ni-Cr nanocomposite coatings.