WC-氧化石墨烯/Ni复合熔覆层的制备及形成机制

采用真空熔覆技术制备了WC-氧化石墨烯(GO)/Ni复合熔覆层,运用扫描电镜、能谱仪、X射线衍射仪观察并分析在不同温度下熔覆层内显微形貌的变化与物相组成。结果表明:在ZG45表面制备了组织致密、与基体形成良好冶金熔合的WC-GO/Ni复合熔覆层;熔覆层的微观结构组成从表面至基体依次是约1.5 mm厚的复合层、360 μm左右的过渡层、50 μm左右的扩散熔合层和100 μm左右的扩散影响层,其主要组成相有Cr₇C₃、FeNi₃、WC、Cr₂₃C₆、Ni₃Si、C、Fe₇W₆、γ-Ni固溶体等,FeNi₃、Fe₇W₆分散在冶金熔合带,扩散影响区主要组织为珠光体;复合区的物相尺寸小于界面区的物相尺寸,熔覆层形成过程中复合区的金属颗粒变化先于界面区,凝固时熔化不完全的颗粒表面长出团簇物(Cr₇C₃/Cr₂₃C₆),随着保温长大逐渐变成针状物镶嵌在Ni基固溶体中。      

类表面织构化镍基复合涂层的摩擦磨损性能

在低碳钢表面添加质量分数为20%的WC和6%的石墨颗粒,采用真空熔覆方法制备出具有类织构切面形貌的镍基合金(Ni0)复合涂层,研究了复合涂层的显微组织形貌及形成机理、相组成以及干摩擦条件下的摩擦磨损性能,并与镍基合金(Ni0)、碳化钨增强镍基合金(Ni0+20%WC)、石墨改性镍基合金(Ni0+6%石墨)三种涂层进行了比较。结果表明,WC呈不连续的三维网状分布在镍基合金基体中,镍基合金主要由基体相γ-Ni,铬化物硬质相CrB、Cr7C3、Cr23C6和共晶相Ni3B、Ni3Si构成;WC和石墨的单独加入都能提高复合涂层的摩擦磨损性能,类织构组织复合熔覆层的摩擦磨损性能优于相同组成的硬质颗粒单独弥散分布的复合熔覆层;在WC和镍基合金基体组成的类织构形貌结构和石墨润滑相的共同影响下,复合涂层比单一镍基合金涂层的耐磨性提高大约9.6倍。     

Cr7C3 / Ni3Al 复合材料制备过程中碳化铬的溶解再析出行为

将真空常压烧结方法制得的Cr₃C₂-Ni₂Al 复合焊丝堆焊于碳钢表面。分析表明, 在堆焊过程中, 利用氩弧物理热和Ni-Al 反应热, Ni 与Al 化合反应生成Ni₃Al 金属间化合物, Cr₃C₂ 则发生分解, 除少部分[ C]与[Cr ]固溶于Ni₃Al 基体中外, 大部分反应析出更稳定的Cr₇C₃ 相, 其尺寸取决于堆焊层中不同区域的冷却环境,较为均匀地分布于Ni₃Al 基体中。由于Cr 在Ni₃Al 中的固溶度远大于C , 加之Cr₃C₂ 转化为Cr₇C₃ 也造成部分富余的C , 结果造成在该Ni₃Al 表面强化材料焊层中形成石墨相, 其密度轻、熔点高, 主要偏聚于焊层表层。Cr₇C₃ / Ni₃Al 复合材料的室温、高温硬度远高于传统高温耐磨材料Stellite 合金, 该材料有望成为一种新型的高温耐磨表面强化材料。      

Ni-Co/WC-Graphite复合熔覆层的组织与三点弯曲行为

采用真空熔覆技术制备了Ni-Co/WC-Graphite(G)复合熔覆层,采用SEM、XRD等分析了微观组织及相组成,利用三点弯曲研究了复合熔覆层的弯曲行为,并分析了断口形貌特征、微区元素分析与断裂机制。结果表明:整个Ni-Co/WC-G熔覆层包括复合层区、过渡层区、扩散冶金熔合带以及热影响扩散区,复合层区呈现三维织构组织特征,主要组成相有Cr_7C_3、Cr_(23)C_6、Ni_3Si、CrB、WC、C和γ-Ni-Co固溶体,扩散影响区主要组织为珠光体,扩散冶金熔合带及过渡层主要组成相为镍钴基合金固溶体及金属间化合物;具有复合熔覆层试样的三点弯曲载荷-位移曲线初始呈线性变化,而后曲线斜率逐渐减小,在达到载荷峰值时Ni-Co/WC-G复合熔覆层在承受压应力时溃裂,而在承受拉应力时断裂,由于过渡层、扩散冶金带以及热影响扩散区的存在,使载荷在熔覆层失效后仍在一定范围内缓慢增加,熔覆层区断口形貌呈沿晶或穿晶特征,基体侧的热影响扩散区呈扇形解理断裂特征,远离界面的基体区域为具有大量韧窝的韧性断裂。     

熔覆温度对真空熔覆WC增强镍基合金层组织及性能的影响

为了在保证良好力学性能的前提下提高45钢的表面质量,采用真空熔覆技术以不同熔覆温度在45钢表面制备WC增强镍基合金熔覆层。利用扫描电镜分析熔覆层组织形貌以及过渡层结合情况;通过硬度测试和磨损试验分析熔覆温度对熔覆层性能的影响。结果表明:随着熔覆温度的升高,熔覆试样过渡层逐渐增厚但整体变化不大,都大于30μm,满足冶金需求;熔覆温度过高时,WC分解严重,熔覆层耐磨性大大降低;熔覆温度为1 225℃时,得到的WC增强镍基合金效果良好,熔覆层洛氏硬度接近40 HRC,对母材强化作用明显,可显著提高其耐磨性。     

WC含量对真空熔覆镍基合金涂层组织及性能的影响

为了强化45钢表面性能,在45钢表面于1 225℃下通过真空熔覆制备了WC颗粒增强的镍基合金涂层,利用SEM观察了熔覆层组织形貌,结合EDS分析了各元素扩散情况及WC含量对过渡层结合情况的影响,通过硬度测试和磨损试验,研究了不同WC含量对熔覆层性能的影响。结果表明:熔覆过程中元素互扩散使母材与熔覆层达到冶金结合,同时WC颗粒发生沉降;当WC含量低于20%时,WC颗粒偏聚在母材过渡层附近,且颗粒越大,越靠近母材侧;随着WC含量逐渐增加,颗粒之间相互支撑形成骨架可减少沉降,使分布逐渐趋于均匀,但当WC含量过多时,WC聚集形成熔池使熔覆层中气孔率提高;WC含量达到40%时,出现大量分布在WC颗粒之间或周围的空洞,同时,WC的加入可大大提高材料的耐磨性;当WC含量为30%时,平均磨损失重约为21.5 mg,仅为母材的15%左右。将WC颗粒增强的镍基合金熔覆于45钢表面,在保证母材基本性能的同时可显著提高45钢的表面硬度及耐磨性。加入30%WC既能保证涂层与母材良好的冶金结合,又能显著提高其表面耐磨性,具有一定的研究价值。     

激光熔覆镍基无磁合金涂层的耐磨性能

无磁不锈钢耐磨性差,采用激光熔覆技术在304无磁不锈钢表面制备了3种无磁耐磨涂层,对熔覆层的显微组织、硬度、相组成和摩擦磨损性能进行了测试与分析。结果表明:无磁镍基合金熔覆层的显微硬度为393HV,比不锈钢基体提高了约60%,无磁镍基合金粉末与WC颗粒以体积比为2∶1混合的熔覆层与以3∶1混合的熔覆层的硬度均为520 HV,较基体提高了1倍;无磁合金熔覆层的抗磨损能力是不锈钢基体的2.88倍,而镍基合金粉末与WC颗粒体积比为2∶1和3∶1的混合熔覆层的抗磨损能力均为基体的6.45倍。     

激光熔覆添加碳化钨的镍基合金层的组织和硬度研究

为促进激光熔覆在金属材料表面改性中的进一步应用,利用光学显微镜、扫描电镜、显微硬度计和电子探针微区成分分析,研究了Q235钢基体上激光熔覆添加有WC的Ni基合金层的特性及其演变,讨论了熔覆层合金成分和显微硬度的变化规律,力求得到熔覆粉的最佳WC含量.结果表明,当添加WC低于30%(质量分数)时,激光熔覆不出现裂纹;而当WC质量分数增加到30%(质量分数)时,熔覆层平均硬度增加,出现裂纹.在熔覆层中WC完全熔化并溶解,凝固组织主要由枝晶和枝晶间共晶组成,熔覆层呈胞状或条带状快凝亚稳的两相组织.     

热轧45钢表面Ni60-WC涂层的高频感应熔覆及其电接触强化前后的性能

为了降低WC增强镍基合涂层的制备成本,提高其表面性能,采用高频感应熔覆技术在热轧45钢表面制备Ni60-WC合金层,并对熔覆层进行电接触强化。采用光学显微镜、X射线衍射仪及显微硬度计分析了熔覆层电接触强化前后的形貌、相结构及显微硬度;采用滚动疲劳接触磨损试验研究了熔覆层电接触强化前后的耐磨性。结果表明:热轧态45钢感应熔覆层组织较为致密,但存在孔洞、夹生缺陷;熔覆层电接触强化后组织更加致密,孔洞减少,夹生层重新熔合,热影响区减小;熔覆层电接触强化前后的相结构相同,均由WC,W2C,Cr23C6,Cr7C3,Fe Ni,Ni3Fe等相组成;熔覆层电接触强化后的显微硬度和耐磨性较电接触强化前大幅提高,熔覆层电接触强化后抗疲劳磨损性能大幅提高且远高于淬火态45钢的。     

Ti6Al4V合金激光熔覆γ-NiCrAlTi/TiC复合层的组织与摩擦学性能

为提高Ti6Al4V合金的摩擦学性能,以NiCr-Cr₃C₂金属陶瓷粉末为涂覆材料,采用激光熔覆技术在Ti6Al4V表面制备以TiC为增强相、γ-NiCrAlTi固溶体为增韧相的熔覆层。采用X射线衍射仪（XRD）、扫描电镜（SEM）、能谱仪（EDS）分析了熔覆层的物相组成及显微组织,测试了熔覆层沿层深方向的硬度分布,分别在室温（24℃）,300,600℃测试了熔覆层和Ti6Al4V合金基体的干滑动磨损性能。结果表明:熔覆层的平均硬度约1 100HV_{2 N},约为基体的3倍;室温时,由于高硬度增强相TiC和增韧相γ-NiCrAlTi固溶体的综合效应,激光熔覆γ-NiCrAlTi/TiC复合层的摩擦系数和磨损率比Ti6Al4V合金基体的显著降低,熔覆层具有较好的耐磨减摩性能,磨损机理主要为黏着磨损;300,600℃时,熔覆层被氧化,耐磨性减弱,磨损机理主要为黏着磨损和塑性变形。     

Microstructure characteristics of Ni-based WC composite coatings by laser induction hybrid rapid cladding

To avoid low cladding rate and cracks of cladding layer, laser induction hybrid rapid cladding (LIHRC) has been put forward in the paper. The microstructure characteristics of Ni-based WC composite coatings at the different laser scanning speed were investigated. For low laser scanning speed, the growth of γ-nickel was characterized by coarse columnar dendrites and eutectics, blocky W₂C + Fe₃W₃C carbides, and bar-like (W, Cr, Ni)₂₃C₆ carbides were formed. With increasing laser scanning speed, the growth of γ-nickel presented the fine dendrites and eutectics, the only blocky mixed carbides were precipitated and identified as W₂C + FeW₃C + W₆C_2.54 carbides. With further increasing laser scanning speed, the growth of γ-nickel was characterized by cellular crystals and eutectics, the only blocky carbides were identified as W₂C + W₆C_2.54. Moreover, experimental results showed that the efficiency of LIHRC was increased much four times higher than that of laser cladding without preheating, ceramic–metal composite coatings detected were free of cracks and had a good metallurgical bonding with substrate.     

稀土对真空熔覆Ni基/WC涂层组织结构的影响

以往对稀土Ce La影响真空熔覆Ni基/WC涂层的探讨较少.采用真空熔覆的方法在45钢上获得添加有稀土的Ni基/WC复合涂层,借助X射线衍射、SEM及EDX研究了涂层的显微组织、化学成分和相结构.结果表明:稀土的加入改善了真空熔覆Ni基/WC复合涂层的组织,消除了针状相,使组织更加均匀致密;稀土还降低了Ni基/WC涂层各组成相中Fe元素的含量,减缓了Fe原子对Ni基合金涂层的"稀释"作用;稀土还使真空熔覆Ni基/WC涂层的(Ni,Fe)固溶体基体部分转变成了(Ni,Cr,Fe)固溶体基体,并析出了新的第二相NiB.     

抑制剂对WC-Co硬质合金涂层性能的影响

利用原位还原碳化反应合成的超细WC-12Co复合粉末作为原料, 分别添加1.0wt%晶粒长大抑制剂即VC、Cr₃C₂和NbC, 经团聚造粒和超音速火焰(HVOF)喷涂制备了超细结构的硬质合金涂层。研究了不同晶粒长大抑制剂对涂层的显微组织结构、物相、硬度、耐磨性能和耐蚀性能的影响。结果表明, 与未添加晶粒长大抑制剂涂层相比, 添加1.0wt% VC或Cr₃C₂制备的硬质合金涂层中WC颗粒的平均尺寸降低了约49%, 涂层硬度明显提高, 磨损速率降低了约52%~55%。添加1.0wt% NbC对制备涂层中WC颗粒尺寸的抑制作用不明显, Co粘结相中由于形成了(W, Nb)C化合物, 其耐蚀性获得显著提高, 但该化合物脆性大, 导致涂层耐磨性不及添加VC和Cr₃C₂制备的涂层。     

Interfacial microstructure and strength of partial transient liquid-phase bonding of silicon nitride with Ti/Ni multi-interlayer

Partial transient liquid-phase bonding (PTLP bonding) of silicon nitride (Si₃N₄) ceramic has been performed using Ti/Ni multi-interlayer in vacuum at 1273–1423 K. Interfacial microstructures were examined by scanning electron microscope, electron probe micro-analysis, and X-ray diffraction. The joint strength has been measured by four-point bending tests from room temperature up to 1000 °C. Interfacial structure of Si₃N₄/TiN/Ti₅Si₃ + Ti₅Si₄ + Ni₃Si/(NiTi)/Ni₃Ti/Ni is formed after bonding process. The NiTi layer is gradually consumed with simultaneous growth of the reaction layer and the Ni₃Ti layer. The room temperature joint strength is significantly affected by the reaction layer thickness, whereas the elevated temperature joint strength significantly depends on whether the low melting point NiTi layer exists in the joint. The joint strength of more than 100 MPa is retained up to 800 °C as the NiTi layer is completely consumed. A model is proposed to optimize the PTLP bonding parameters for optimizing joint strength at both room temperature and elevated temperature.     

Nickel Enriched Diffusion Layers on a NiAl Alloy

The intermetallic phase NiAl is a perspective material for high-temperature and shape memory effect applications. Formation of Ni₅Al₃, Ni₂Al, Ni₃Al phases which influence the extent of martensitic transformation in NiAl have been studied up to now with controversial results. We have investigated (using SEM and local elemental analyses) the microstructure of nickel enriched surface layers on a Al-79 wt.% Ni alloy. The layers were prepared by diffusion annealing and subsequently given two different heat treatments: at 930°C outside the Ni₅Al₃ region and at 500°C within the Ni₅Al₃ region of the phase diagram. In the specimen which was only diffusion annealed separate islands of Ni₅Al₃ phase elongated in the direction of the concentration gradient could be recognized within the nickel enriched surface layer. In the samples additionally annealed at 500°C, a well defined continuous layer of the Ni₅Al₃ phase situated 0.4 mm below the specimen surface was found. In the samples annealed at 930°C, isolated Ni₃Al precipitates were observed. Their number and size gradually increased with increasing nickel content.     

Ni60A+20WC于水刀喷嘴耐磨层的应用工艺

采用高频感应熔覆技术以提高高压水刀喷嘴的耐磨性能,本实验选用304不锈钢板作为基体材料,Ni60A+20%WC合金粉末作为熔覆层材料;分别采用高频感应加热设备、电火花成型机和小孔机对试件进行加热、熔覆并加工到规定尺寸.采用扫描电子显微镜观察试件的微观组织,发现涂层和基体之间产生了扩散层;采用X射线衍射仪分析涂层相结构,涂层中存在的强化相有WC、Fe_3Ni_2、W2C、Cr_3C_2、Cr_2Ni_3等;摩擦学性能测试实验表明涂层材料大大提高了水刀喷嘴的耐磨性;显微硬度实验表明WC极大地提高了涂层的硬度,其平均值约为1 000 HV0.1,基体约为190 HV0.1.在水刀喷嘴内孔成功制备了WC增强Ni基熔覆层,该熔覆层光滑平整,表面无明显缺陷,与基体实现冶金结合,性能优异.     

Microstructural evolution of Alloy 690 during sensitization at 700 °C

A structural characterization of sensitized Alloy 690 has been carried out. Alloy 690 was solution annealed (SA; 1100 °C for 30 min, water quenched, WQ) and sensitized at 700 °C for 5, 12, 24, 36, 48 and 72 h, followed by water quenched. Techniques employed included scanning electron microscope (SEM), transmission electron microscopy (TEM), X-ray diffraction and corrosion weight-loss tests. It was found that the cubic Cr_0.19Fe_0.7Ni_0.11 phase was the main component in all the conditions. In addition, a grain refinement was observed when the aging time was increased; but after 48 h of aging, a discrete, semicontinuous network of Cr₂₃C₆ precipitates was detected by X-ray diffraction, in addition to the NiCrO₄, Ni₉S₈ and (Fe,Ni)₉S₈ phases found by TEM at the grain boundaries, making this alloy more susceptible to intergranular attack (IGA). After 72 h of aging, chromium continues diffusing, “back-filling” the prior depletion profile, recovering the IGA resistance.     

Microstructure of Al2O3 nanocrystalline/cobalt-based alloy composite coatings by laser deposition

Composite coatings, made of nano-Al₂O₃/cobalt-based alloy, produced by a 5-kW CO₂ laser on Ni-based superalloy were investigated. The coatings were examined to reveal their microstructure using optical microscope, scanning electron microscope, transmission electron microscope and X-ray diffraction instrument. The results showed that some equilibrium or non-equilibrium phases, such as γ-Co, Cr₂₃C₆, CoAl₂O₄, Al₂O₃ and ε-Co existed in the coatings. Fine and short dendritic microstructure and columnar to equiaxed transition occurred by adding nano-Al₂O₃ particle. With the increase of nano-materials (1%, mass fraction), fully equiaxed crystallization appeared. These were contributed to that nano-Al₂O₃ particles acted as new nucleation site and rapid solidification of the melted pool. The results also showed inhomogeneous dispersion of nano-Al₂O₃ that resulted in the formation of ε-Co phase in the coatings. The sub-microstructure of the clad was stacking fault. The mechanism of formation of equiaxed grains was also analyzed.     

镍基高温合金定向凝固用陶瓷型壳粘砂反应

以合金表面粘砂比例和粗糙度为优化指标,采用多指标正交实验设计方法,通过极差分析研究了定向凝固用陶瓷型壳面层粒度配比和Cr₂O₃添加剂对铸件表面质量的影响。结果表明,铸件表面粘砂层的主要成分为Al₂O₃以及少量Cr、Ni等合金元素;调整陶瓷型壳面层的粒度级配能降低陶瓷型壳面层的孔隙率,使型壳面层形成致密的结构,从而减少在定向凝固过程中合金液向陶瓷型壳面层的渗入、减少铸件表面的物理粘砂;Cr₂O₃添加剂与型壳中的Al₂O₃反应生成的二元化合物Al₂O₃-Cr₂O₃或Al₂O₃-SiO₂-Cr₂O₃三元系产物,抑制了合金中的活性元素(Ni、Ti、Al等)与型壳中游离的SiO₂反应,从而减少铸件表面的化学粘砂、提高铸件的表面质量。