原位合成Cr7C3激光熔覆陶瓷涂层的显微组织及腐蚀性能

采用激光熔覆技术在Q235钢表面原位合成了Cr7C3陶瓷熔覆层,并采用光学显微镜、X射线衍射仪、扫描电子显微镜及静态浸泡法结合极化曲线分析,对熔覆层的显微组织及耐腐蚀性能进行研究。结果表明,熔覆层表面平整、无裂纹、无孔洞且与基体呈冶金结合,陶瓷Cr7C3形状多为条状和块状;熔覆层腐蚀电流密度约为基材的1/2,表明其具有良好的耐腐蚀性能。     

氨分解气氛保护下钎焊金刚石界面微观组织分析

为探索钎焊金刚石工具的大批量生产工艺,在氨分解气氛保护环境下于连续式网带炉中用Ni-Cr合金做钎料进行了金刚石的钎焊试验和钎焊磨盘的磨削试验. 用扫描电镜观察了钎焊后金刚石磨粒的微观组织形貌;用X射线能谱仪对深腐蚀后的金刚石磨粒表面进行了能谱分析,结合X射线衍射仪对磨粒表面生成物进行了物相鉴定;用三维视频显微镜观察和分析了金刚石磨盘磨削花岗岩时磨粒脱落情况. 结果表明,氨分解气氛保护钎焊金刚石,金刚石与钎料界面发生了化学冶金反应,生成了柱状碳化物,磨粒获得了较高的结合强度,磨削花岗岩50 m,磨粒脱落率仅为2.2%,略高于真空钎焊磨盘.     

Ni-Cr合金真空钎焊金刚石界面反应的热力学与动力学分析

采用Ni-Cr合金钎料，适当控制钎焊工艺，实现了金刚石与钢基体的高强度连接。采用扫描电子显微镜(SEM)和能谱仪(EDS)及X射线衍射结构分析了真空加热条件下，Ni-Cr合金钎料与金刚石之间的界面反应，探讨了钎料与金刚石界面处碳化物的形成机理。结果表明，Ni-Cr合金钎料中的Cr和少量Si在金刚石表面富集并与金刚石中的C发生反应生成Cr7C3、Cr3C2碳化物，其中Cr7C3呈笋状生长，Cr3C2呈片状，可能有少量SiC生成。金刚石与钎料的界面形成了金刚石＼SiC、Cr3C2＼Cr7C3钎料的梯度材料，实现了Ni-Cr合金与金刚石的冶金结合。     

CuCrZr合金表面等离子喷涂Cr3C2-NiCr及NiAl/Cr3C2-NiCr涂层的结合性能

在CuCrZr合金表面等离子喷涂Cr3C2-NiCr涂层、NiAl/Cr3C2-NiCr复合涂层.测试涂层与基体间的结合强度及涂层的热震性能,结合SEM,EDS和XRD等分析涂层物相变化,探讨涂层的结合机理.结果表明,涂层的结合强度均较高;Ni-Al发生放热反应,生成Al4Ni3,Al3Ni2,AlNi3,剩余的铝与铜反应生成Cu3Al2,CuAl2,CuAl,局部区域形成微冶金结合;二种涂层均以机械锚合为主,在参数适合且基体相同的情况下,涂层结合强度取决于涂层材料的力学性能;相同试验条件下,NiAl/Cr3C2-NiCr复合涂层的热震性能优于Cr3C2-NiCr涂层.     

Cr3C2/Ni3Al表面耐磨堆焊材料的焊接性

Cr3 C2/Ni3 Al复合材料是一种极具潜力的高温表面耐磨堆焊材料,焊接性对于该材料的推广应用至关重要.将真空烧结制得的Cr3 C2-NiAl-Ni焊条堆焊于碳钢和耐热钢表面,可形成无焊接裂纹的Cr3 C2/Ni3Al复合材料堆焊层,表明Cr3 C2/Ni3 Al复合材料具有良好的焊接性,适于作为铁基材料表面耐磨堆焊材料推广应用.分析认为,Cr3 C2/Ni3 Al复合材料具有良好焊接性的原因在于:(1)焊接过程中,Cr3 C2发生溶解再析出,熔池中的C优先被氧化,保护了Al的氧化.(2)从铁基材料基材中扩散入到焊层中的Fe元素和Cr3 C2溶解而固溶于焊层中的Cr元素有效地改善了Ni3 Al基体的焊接性.     

激光扫描速率对NiCr/Cr3C2涂层微结构与耐磨性的影响

采用激光熔覆技术在3种扫描速率下制备了NiCr/Cr₃C₂复合涂层,分别采用扫描电镜(SEM)、X射线衍射仪(XRD)、显微维氏硬度计、摩擦磨损试验机表征了熔覆层的组织形貌、硬度与摩擦磨损性能。结果表明,激光扫描速率从2 mm/s升至4 mm/s时,熔覆层组织从以树枝晶为主转变为以等轴晶为主,缺陷由气孔转变为大尺寸间隙与裂纹。扫描速率低于3 mm/s时,Cr₃C₂熔化分解导致熔覆层主要含有Cr₇C₃,随着激光扫描速率增加,Cr₃C₂熔化程度降低,熔覆层以Cr₇C₃与Cr₃C₂为主。因此,随着激光扫描速率从2 mm/s升高至4 mm/s,熔覆层硬度从400 HV0.3提升至780 HV0.3。不同激光扫描速率下熔覆层磨损均以磨粒磨损为主,但是由于结构致密和硬度较高,3 mm/s涂层磨损量最小,耐磨性最好。     

Cr3C2对镍基碳化钨激光熔覆层组织与性能的影响

研究了不同Cr3C2加入量对镍基碳化钨熔覆层显微组织、横截面微观硬度、耐蚀性及耐磨性的影响。结果表明,Cr3C2使熔覆层质量得到改善,涂层中花状、鱼骨状枝晶组织基本消失,组织主要由浅白色块状、黑色不规则块状、浅黑色菱角状组织以及未熔WC颗粒组成。当Cr3C2加入量为10%时,组织中裂纹、气孔等缺陷基本清除,未发现WC的聚集和桥接,熔覆层显微硬度及耐蚀性均有所提高,硬度分布更加均匀。干滑动摩擦摩损试验时,熔覆层表面磨粒磨损特征的犁沟相对较浅,没有WC粒子脱落现象。     

HVOF喷涂Cr3C2-NiCr涂层的磨粒磨损性能

探讨了氧气流量、燃气流量和喷涂距离三个喷涂工艺参数对ＨＶＯＦ喷涂Ｃｒ３Ｃ２－ＮｉＣｒ涂层硬度和磨粒磨损性能的影响。结果表明,燃气流量、氧气流量和喷涂距离对涂层的显微硬度和磨粒磨损性能的规律有所不同。在较高的燃气流量、适中的氧气流量和喷涂距离条件下,涂层具有较高的显微硬度;而氧气流量和燃气流量对涂层的磨粒磨损性能影响较大,适中的燃气流量条件下,涂层的磨粒磨损失重量较低,高的氧气流量条件下,磨损失重量     

铸铁轧辊表面Cr3C2-NiCr涂层的显微组织

研究分析了铸铁轧辊表面等离子喷涂Cr3C2-25NiCr复合涂层的组织结构。结果表明,Cr3C2-25NiCr涂层具有典型的层状结构;涂层质量较好,组织相对紧密,与基体结合尚可;由EDS和涂层物相分析可知,涂层与基体间没有发生元素扩散现象,涂层与基体呈机械结合。     

铬锆铜表面等离子喷涂Cr3C2p/NiCr涂层的组织与性能

采用等离子喷涂技术在铬锆铜(CrZrCu)基体表面制备了Cr3C2 p/NiCr涂层。利用X射线衍射仪(XRD)、扫描电镜(SEM)等仪器研究了涂层的显微组织及结构,采用磨粒磨损试验机对Cr3C2 p/NiCr涂层与电镀NiCo层的磨损性能进行了测试比较。结果表明:涂层组织呈片层状结构,在NiCr合金片层上分布着未熔的Cr3C2和Cr7C3、Cr2Ni3、CrNi析出相。与电镀Ni-Co镀层相比,Cr3C2 p/NiCr涂层具有较高的硬度和耐磨粒磨损性能,其磨损量仅为电镀层的35%。     

Ni-Cr合金真空钎焊金刚石的碳化物生长及位向关系

采用Ni-Cr合金在不同温度下进行钎焊单晶金刚石磨粒试验,使用SEM、EDS和XRD对Ni-Cr合金钎焊金刚石的碳化物生长及形貌进行分析.结果表明:真空钎焊过程中,在Ni-Cr合金完全熔化前,在合金前端有碳化物开始形核,并生成排列整齐的Cr_3C_2和无序的SiC,Cr_3C_2的生长方向与金刚石的外露晶面有一定的位向关系;合金完全熔化后,在金刚石表面生成两层碳化物,内层为排列整齐的Cr_3C_2,外层为无序的Cr_7C_3.     

Ni-Cr合金钎料激光钎焊金刚石磨粒界面显微结构及形成机理

本文采用Ni-Cr合金钎料,在Ar气保护条件下,对金刚石磨粒进行了激光钎焊试验研究。采用扫描电镜(SEM)和能谱仪(EDS)及X射线衍射仪(XRD)分析金刚石磨粒与Ni-Cr钎料结合界面的组织结构与物相组成,并研究了钎料与金刚石界面处碳化物的形成机理。测试结果表明,激光钎焊过程中在金刚石表面附近形成的富Cr层与金刚石表面的C元素反应生成碳化物Cr3C2,通过反应热力学与动力学分析显示界面反应产物可以依靠置换反应形成,使金刚石磨粒与钎料实现了牢固结合。     

TiNi-V共晶钎料钎焊Si3N4陶瓷接头界面结构及性能

采用真空电弧熔炼技术制备了TiNi-V高温共晶钎料合金,研究了该钎料在Si3N4陶瓷表面的铺展行为．随后采用TiNi—V钎料实现了Si3N4陶瓷的钎焊连接,利用SEM,EDS以及XRD等分析方法,确定了接头的典型界面结构为：Si3N4／TiN＋Ti-si化合物／NiV．重点研究了钎焊温度对接头界面结构及力学性能的影响．结果表明,随着钎焊温度的升高,熔融钎料与Si3N4陶瓷反应程度增加,导致钎缝中TiN＋Ti-Si化合物层厚度不断增加,且在接头残余应力的作用下形成了大量显微裂纹,降低了接头性能．当钎焊温度为1200℃,钎焊时间为10min时,接头室温抗剪强度达到最大为28MPa．断口分析显示接头断裂于TiN＋Ti-Si化合物层为脆性断裂．     

Effect of Cr7C3 on the mechanical, thermal, and electrical properties of Cr2AlC

In this work, phase pure Cr₂AlC and impure Cr₂AlC with Cr₇C₃ have been fabricated to investigate the mechanical, thermal, and electrical properties. The thermal expansion coefficient is determined as 1.25 × 10⁻⁵ K⁻¹ in the temperature range of 25-1200 °C. The thermal conductivity of the Cr₂AlC is 15.73 W/m K when it is measured at 200 °C. With increasing temperature from 25 °C to 900 °C, the electrical conductivity of Cr₂AlC decreases from 1.8 × 10⁶ Ω⁻¹ m⁻¹ to 5.6 × 10⁵ Ω⁻¹ m⁻¹. For the impure phase of Cr₇C₃, it has a strengthening and embrittlement effect on the bulk Cr₂AlC. And the Cr₂AlC with Cr₇C₃ would result in a lower high-temperature thermal expansion coefficient, thermal conductivity, specific heat capacity and electrical conductivity.     

Co-Nb-Pd-Ni-V钎料真空钎焊Cf/SiC复合材料的接头组织与性能

采用自行设计的Co-Nb-Pd-Ni-V高温活性钎料对碳纤维增强碳化硅（C_f/SiC）复合材料进行钎焊连接,钎焊温度为1 200 ~ 1 320 ℃,钎焊时间固定为10 min. 结果表明,钎料中的V和Nb元素同时发挥反应活性,与C_f/SiC复合材料发生界面反应,在陶瓷界面形成了VC和NbC双层界面反应层. 当钎焊参数为1 280 ℃/10 min,典型的接头组织为（VC/NbC）双界面反应层/（Co,Ni）₂Si + CoSi + NbC + Pd₂Si/（NbC/VC）双界面反应层. 在此参数下获得的接头性能最佳,其中室温三点弯曲强度为61.0 MPa,在900和1 000 ℃下测得的强度均高于其室温强度,分别为83.2和87.7 MPa. 接头中的NbC和Pd₂Si高熔点物相弥散分布在钎缝内部,大大提高了接头的高温性能.     

Cyclic oxidation behaviour of Ti3Al-based alloy with Ni-Cr protective layer

The influence of a thin 80Ni-20Cr (at.%) protective coating on the cyclic oxidation of a Ti-24Al-11Nb (at.%) alloy based on Ti₃Al at 600 and 900 °C in air was investigated using scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS) and X-ray diffraction analysis (XRD). The results of the oxidation tests showed that deposited Ni-Cr layer provides an improved oxidation resistance due to the formation of protective oxide scale which barriers the outward Ti diffusion into the scale. In some extent surface formation of the nitride layer also prevents diffusion of alloying elements from the matrix. Although oxidation at 900 °C is faster than that at 600 °C, a remarkable reduction in mass gain of the alloy with protective coating was observed. The thickness of oxide scale on the coated samples is approximately two times less than that formed on the uncoated samples treated under the same exposure conditions (120 h).     

Sulfidation properties of Cr23C6 at 1073 K in H2S-H2 atmospheres of 103.5−10−6 Pa sulfur pressure

The sulfidation behavior of chromium carbide, Cr₂₃C₆, was investigated in H₂S-H₂ gas mixtures over a sulfur partial pressure range of 10^3.5–10^–6 Pa at 1073 K using thermogravimetry, optical and scanning electron microscopy, X-ray diffraction analysis, and electron-probe microanalysis. The kinetics were rapid for short time periods and followed a linear rate law at low sulfur pressures, whereas sulfidation tends to obey a parabolic rate law at high pressures. Sulfidation rates decreased with increasing carbon content in the carbide. Surface morphologies could be divided into three groups: (I) at high sulfur pressures, petal-like. crystals (Cr₂S₃); (II) at intermediate pressures, a twinlike structure (Cr₃S₄); (III) and at low pressures, a flat surface with numerous hexagonal pits (Cr_1–xS). The scale consisted of two distinct layers: an external scale with a single or multilayer structure and an inner scale with a mixture of Cr_1–xS, Cr₃C₂, and Cr₇C₃. These higher carbides, Cr₃C₂ and Cr₇C₃, may be formed by the sulfidation-carburization of Cr₂₃C₆. Pt-marker experiments indicated that the external scale grew by chromium diffusion and that sulfur migration played an important role in the growth of the inner scale.     

Microstructure and properties of Cr3C2-modified nickel-based alloy coating deposited by plasma transferred arc process

The nickel-based alloy with 30 wt.% chromic carbide (Cr₃C₂) particles has been deposited on Q235-carbon steel (including 0.12 wt.% C) using plasma transferred arc (PTA) welding machine. The microstructure and properties of the deposited coatings were investigated using optical microscope, scanning electron microscope (SEM) equiped with X-ray energy spectrometer (EDS), X-ray diffraction (XRD), transmission electron microscopy (TEM), microhardness testes, and sliding wear test. It was found that the γ(Ni, Fe), M₇(C,B)₃, Ni₄B₃, and (Cr,Fe)₂B phases existed in the Cr₃C₂-free nickel-based alloy coating obtained by PTA process. The typical hypoeutectic structure and composition segregation in the solid solution could be found clearly. The addition of 30 wt.% Cr₃C₂ particles led to the existing of Cr₃C₂ phase and the microstructure changing from hypoeutectic structure into hypereutectic structure. The composition segregation in the solid solution could not be found clearly. The average microhardness of the Cr₃C₂-free nickel-based alloy coating increased by 450-500 HV after the addition of 30 wt.% Cr₃C₂ particles. The partial dissolution of Cr₃C₂ particles led to the enrichment of carbon and chromium in the melten pool, and hence caused the formation of more chromium-rich carbides after the solidification process. The undissolved Cr₃C₂ particles and the increasing of chromium-rich carbides was beneficial to enhance the hardness and wear resistance of the Cr₃C₂-modified nickel-based alloy coating deposited by PTA process.     

Microstructure,adhesion and growth kinetics of protective scales on metals and alloys

Currentunderstanding of the complex interrelationships among growth kinetics, microstructure, and adhesion of protective Cr₂O₃ and Al₂O₃ scales is critically reviewed. Similarities and differences in the behavior of these two systems are highlighted. The morphology of the alloy-scale interface appears to be a critical factor. Recent ideas are advanced to interpret the effect of oxygen-active elements on the development of a tortuous interface conducive to improved scale tenacity.This work was supported by the Director, Office of Energy Research, Office of Basic Energy Sciences, Materials Sciences Division of the U.S. Department of Energy under Contract No. DE-AC03-76SF00098.Deceased.on leave to Industrial Materials Research Institute, NRC, Montreal, Quebec, H4C 2K3 Canada.     

激光熔覆Ni3Al/Cr3C2复合材料耐磨性能研究

采用激光熔覆技术在304不锈钢基板上制备了Ni_3Al合金和Ni_3Al/Cr_3C_2(25%,质量分数)复合材料耐磨涂层,分析了Ni_3Al合金和Ni_3Al/Cr_3C_2熔覆层的显微组织、硬度和耐磨性能。结果表明,Ni_3Al/Cr_3C_2熔覆层显微组织由基体γ'-Ni_3Al相和原位自生M_7C_3(M=Cr,Fe)型碳化物组成,且细小M_7C_3弥散分布于γ'-Ni_3Al基体。与Ni_3Al合金熔覆层相比较,Ni_3Al/Cr_3C_2熔覆层显微硬度提高了约4000 MPa。650℃时,Ni_3Al/Cr_3C_2熔覆层磨损量仅为对比材料蠕墨铸铁的28%左右,表明Ni_3Al/Cr_3C_2复合材料熔覆层具有良好的耐磨性能。