Microstructure of Ni–Al powder and Ni–Al composite coatings prepared by twin-wire arc spraying

Ni–Al powder and Ni–Al composite coatings were fabricated by twin-wire arc spraying (TWAS). The microstructures of Ni-5wt%Al powder and Ni-20wt%Al powder were characterized by scanning electronic microscopy (SEM) and energy dispersive spectroscopy (EDS). The results showed that the obtained particle size ranged from 5 to 50 μm. The morphology of the Ni–Al powder showed that molten particles were composed of Ni solid solution, NiAl, Ni₃Al, Al₂O₃, and NiO. The Ni–Al phase and a small amount of Al₂O₃ particles changed the composition of the coating. The microstructures of the twin-wire-arc-sprayed Ni–Al composite coatings were characterized by SEM, EDS, X-ray diffraction (XRD), and transmission electron microscopy (TEM). The results showed that the main phase of the Ni-5wt%Al coating consisted of Ni solid solution and NiAl in addition to a small amount of Al₂O₃. The main phase of the Ni-20wt%Al coating mainly consisted of Ni solid solution, NiAl, and Ni₃Al in addition to a small amount of Al and Al₂O₃, and NiAl and Ni₃Al intermetallic compounds effectively further improved the final wear property of the coatings. TEM analysis indicated that fine spherical NiAl₃ precipitates and a Ni–Al–O amorphous phase formed in the matrix of the Ni solid solution in the original state.     

Preparation and properties of the Ni-Al/Fe-Al intermetallics composite coating produced by plasma cladding

A novel approach to produce an intermetallic composite coating was put forward. The microstructure, microhardness, and dry-sliding wear behavior of the composite coating were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrum (EDS) analysis, microhardness test, and ball-on-disc wear experiment. XRD results indicate that some new phases FeAl, Fe_0.23Ni_0.77Al, and Ni₃Al exit in the composite coating with the Al₂O₃ addition. SEM results show that the coating is bonded with carbon steel metallurgically and exhibits typical rapid directional solidification structures. The Cr₇C₃ carbide and intermetallic compounds co-reinforced composite coating has a high average hardness and exhibits an excellent wear resistance under dry-sliding wear test compared with the Cr₇C₃ carbide-reinforced composite coating. The formation mechanism of the intermetallic compounds was also investigated.     

铝合金表面机械球磨Ni-Al-Mo复合涂层的制备及其摩擦特性研究

通过机械球磨方法在铝合金表面制备了Ni-Al-Mo复合涂层,对涂层微观组织、组成成分和摩擦学性能等进行了分析.结果表明:经过7 h机械球磨制备的Ni-Al-Mo复合涂层内元素均匀分布;550℃退火后涂层中均有Al3 Ni金属间化合物新相生成;复合涂层中Al3 Ni和Mo的存在使得涂层硬度高于铝合金基体和Ni-Al涂层,...     

Characterization and wear behavior of WC-0.8Co coating on cast steel rolls by electro-spark deposition

To prepare high wear resistance and high hardness coatings, electro-spark deposition was adopted for depositing an electrode of a mixture of 92wt%WC+8wt%Co on a cast steel roll substrate. The coating was characterized by classical X-ray diffractometer (XRD) and scanning electron microscopy (SEM) with energy dispersive X-ray analysis (EDX). The results indicate that the coating shows nanosized particulate structure and dendritic structure including columnar structure and equiaxed structure. The primary phases of the coating contain Fe₃W₃C, Co₃W₃C, Fe₂C and Si₂W. The coating has a low friction coefficient of 0.13, its average wear-resistance is 3.3 times that of the cast steel roll substrate and the main mechanism is abrasive wear. The maximum microhardness value of the coating is about 1573.9 Hv_0.3. The study reveals that the electro-spark deposition process has the characteristic of better coating quality and the coating has higher wear resistance and hardness.     

不同pH值环境中镍铝青铜冷喷涂涂层腐蚀磨损性能

镍铝青铜合金是铸造大型舰艇螺旋桨的主要材料,海洋污损生物在合金表面附着引起的pH值变化会加速镍铝青铜合金的腐蚀磨损,威胁到舰艇安全航行.采用冷喷涂技术制备了较为致密的镍铝青铜涂层,厚度约300μm,利用扫描电镜、光学显微镜观察了涂层的微观形貌,重点研究了涂层在pH值分别为3、7和11,质量分数为3.5%的NaCl溶液中的电化学腐蚀性能和腐蚀磨损行为.实验结果表明:pH值为3的环境中,镍铝青铜基体发生了选相腐蚀,表面疲劳裂纹主要分布在富Cu的α相上,涂层上的犁削沟槽加深发生了磨粒磨损,涂层耐腐蚀性能优于基体;pH值为7的环境中,基体发生了黏着磨损,表面有片层状金属剥落,涂层中的孔隙收容了大量磨屑避免了剧烈的三体摩擦,表面犁削沟槽较浅,涂层致钝电位高于基体,耐腐蚀性能变差.pH值为11的环境中,基体发生了表面疲劳磨损,涂层磨痕上有较深的犁削沟槽,沟槽内有微裂纹,涂层耐腐蚀性能优于基体.总体来说,在不同pH值环境中,涂层由于在冷喷涂过程中发生了冷加工硬化并且涂层上的孔隙收容了磨屑,导致涂层的耐腐蚀磨损性能增强.     

堆焊Mo-Cr-Fe-B合金覆层的组织及性能研究

采用自制Mo-Cr-Fe-B系药芯焊丝通过堆焊法在Q235钢基体表面制备覆层。借助光学显微镜、SEM、XRD、EDS、显微硬度计、磨损试验机等对覆层及结合界面的组织结构、物相、硬度分布及耐磨性进行了表征与分析,并研究了覆层堆焊成型的反应过程。结果表明,覆层主要由Mo_2FeB_2、M_3B_2(M:Mo、Cr、Fe)、Fe_2B、Fe(Cr、Mo)等相组成,覆层与钢基体结合良好,在覆层-钢基体界面结合处有元素的扩散,覆层硬度最高可达980HV0.5且耐磨性良好。     

High-temperature oxidation resistance of ceramic coatings on titanium alloy by micro-arc oxidation in aluminate solution

Ceramic coatings with aluminum titanuate (Al₂TiO₅) were prepared on Ti–6Al–4V alloy using pulsed bi-polar Micro-arc Oxidation (MAO). The micromorphology and phase composition of the micro-arc-oxidition ceramic coatings on the titanium alloy were characterized by X-ray powder diffraction (XRD), and scanning electron microscopy (SEM) respectively. The results revealed that the distinct discharge channels and pores on the surface of the micro-arc-oxidition coatings appeared, and these channels were connected in the molten state. The electrolyte concentration was inversely proportional to the coating hardness; additionally, the coating prepared with sodium aluminate and sodium hypophosphite concentrations of 4 ?g/L and 0.5 ?g/L, respectively, was the most refined after high-temperature sintering, and it was demonstrated to better prevent oxidation. Increasing the electrolyte concentration coincided with fluctuating coating thermal shock resistance. The thermal shock resistance of the coating respectively prepared with sodium aluminate, and the sodium hypophosphite concentrations of 4 ?g/L and 0.5 ?g/L was the highest. Additionally, the high-concentration coatings performed significantly better than the low-concentration coatings. The oxidation resistance of the coating samples was also significantly higher than that of the TC4 titanium alloy substrate. The adhesion strength between the coatings and the substrate with and without the sealing treatment was measured by tensile tests. Then, the high-temperature oxidation performance of the coating samples with and without the sealing treatment was investigated by conducting a high-temperature oxidation experiment at a calcinating temperature of 500 ?°C. The results indicate that the adhesion strength between the coatings and substrate was high for the as-prepared and sealed micro-arc oxidation samples regardless of whether they were calcined. The high-temperature oxidation mass increase curves for the sealed and unsealed coating samples calcined at 500 ?°C for 500 ?h revealed that the high-temperature-oxidation-induced mass increase of the coating samples sealed with a sodium silicate solution was much lower than that of the titanium alloy substrate. Thus, the sealing treatment significantly improved the high-temperature oxidation resistance of the TC4 titanium alloy. Lastly, the high-temperature oxidation behavior at 500 ?°C was analyzed and discussed.     

High-temperature frictional wear behavior of MCrAlY-based coatings deposited by atmosphere plasma spraying

Al₂O₃-Cr₂O₃/NiCoCrAlYTa coatings were prepared via atmosphere plasma spraying (APS). The microstructure and phase composition of the coatings were analyzed by X-ray diffraction (XRD), scanning electron microscopy (SEM), laser confocal scanning microscopy (LSCM), and transmission electron microscopy (TEM). The dry frictional wear behavior of the coatings at 500℃ in static air was investigated and compared with that of 0Cr25Ni20 steel. The results show that the coatings comprise the slatted layers of oxide phases, unmelted particles, and pores. The hot abrasive resistance of the coatings is enhanced compared to that of 0Cr25Ni20, and their mass loss is approximately one-fifteenth that of 0Cr25Ni20 steel. The main wear failure mechanisms of the coatings are abrasive wear, fatigue wear, and adhesive wear.     

氩弧熔敷原位自生WC复合涂层组织及耐磨性

为提高采煤机中截齿的耐磨性能,利用氩弧熔敷技术,在35CrMnSi钢表面制备WC增强Ni基复合涂层。利用OM、SEM、XRD和EDS分析复合涂层的显微组织,采用显微维氏硬度仪测试复合涂层的显微硬度,并测试涂层在室温磨损条件下的耐磨性能。结果表明：氩弧熔敷涂层组织均匀致密,熔敷涂层与基体呈冶金结合,主要由WC、W：C、T—Ni、（Fe,Cr）23,C6等物相组成;WC颗粒呈弥散分布,颗粒尺寸为1txm;熔敷涂层可以改善基体的表面硬度,最高显微硬度可达12．6GPa;熔敷涂层在室温冲击磨粒磨损实验条件下,具有优异的耐磨性,磨损机制主要是磨粒磨桶．其耐磨性较35CrMnSi基体提高近12倍。     

Cr3C2-NiCr涂层磨料磨损行为

采用橡胶轮磨损实验机 ,对三种类型粉末制备的 HVOF Cr3 C2 - 2 5 % Ni Cr涂层进行了磨料磨损实验 ,研究了涂层的磨损特性和喷涂工艺条件、粉末制备工艺对涂层磨损速率的影响。在运用扫描电镜对涂层结构和磨损表面观察分析的基础上 ,结合涂层结构和橡胶轮磨料磨损的特征 ,探讨了该涂层的磨料磨损失效行为。     

Bonding characteristics of the Al2O3-metal composite coating fabricated onto carbon steel by combustion synthesis

The fabrication of an alumina-metal composite coating onto a carbon steel substrate by using a self-propagating high-temperature synthesis technique was demonstrated. The effects of the type and thickness of the pre-coated layer on the binding structure and surface quality of the coating were systematically investigated. The macrostructure, phase composition, and bonding interface between the coating and the substrate were investigated by scanning electronic microscopy (SEM), X-ray diffraction (XRD), and energy-dispersive X-ray spectrometry (EDS). The diffraction patterns indicated that the coating essentially consisted of α-Al₂O₃, Fe(Cr), and FeO·Al₂O₃. With an increase in the thickness of the pre-coated working layer, the coating became more smooth and compact. The transition layer played an important role in enhancing the binding between the coating and the substrate. When the pre-coated working layer was 10 mm and the pre-coated transition layer was 1 mm, a compact structure and metallurgical bonding with the substrate were obtained. Thermal shock test results indicated that the ceramic coating exhibited good thermal shock resistance when the sample was rapidly quenched from 800°C to room temperature by plunging into water.     

Microstructure characteristics of Ni/WC composite cladding coatings

A multilayer tungsten carbide particle (WCp)-reinforced Ni-based alloy coating was fabricated on a steel substrate using vacuum cladding technology. The morphology, microstructure, and formation mechanism of the coating were studied and discussed in different zones. The microstructure morphology and phase composition were investigated by scanning electron microscopy, optical microscopy, X-ray diffraction, and energy-dispersive X-ray spectroscopy. In the results, the coating presents a dense and homogeneous microstructure with few pores and is free from cracks. The whole coating shows a multilayer structure, including composite, transition, fusion, and diffusion-affected layers. Metallurgical bonding was achieved between the coating and substrate because of the formation of the fusion and diffusion-affected layers. The Ni-based alloy is mainly composed of γ-Ni solid solution with finely dispersed Cr₇C₃/Cr₂₃C₆, CrB, and Ni+Ni₃Si. WC particles in the composite layer distribute evenly in areas among initial Ni-based alloying particles, forming a special three-dimensional reticular microstructure. The macrohardness of the coating is HRC 55, which is remarkably improved compared to that of the substrate. The microhardness increases gradually from the substrate to the composite zone, whereas the microhardness remains almost unchanged in the transition and composite zones.     

高铝铜合金激光熔敷层高载荷干摩擦下的摩擦磨损特性

采用激光熔覆技术在45#钢基体上制备高铝铜合金涂层,对涂层进行较高载荷下的干摩擦磨损实验研究,测定不同载荷下涂层的摩擦系数,观察涂层的磨损形貌,测量涂层不同载荷下的磨损失重量,探讨涂层的磨损机理。结果表明:随外加载荷的增加,激光熔覆层的摩擦因数变化很小,其值在0.65～0.83,具有很好的摩擦稳定性,磨损量随载荷的增加逐渐增大,但不同载荷下涂层的磨损机理不同,在100N的较低载荷下,涂层以磨粒磨损和刮擦磨损为主,随载荷增加到200、300N时,磨损失重的主要原因是切削磨损和磨粒磨损,当载荷超过400N时,涂层的磨损形式则以磨粒磨损、粘着磨损和剥落磨损的复合磨损形式体现.     

Microstructure and high-temperature wear properties of in situ TiC composite coatings by plasma transferred arc surface alloying on gray cast iron

In this work, an in situ synthesized TiC-reinforced metal matrix composite (MMC) coating of approximately 350–400μm thick-ness was fabricated on a gray cast iron (GCI) substrate by plasma transferred arc (PTA) surface alloying of Ti–Fe alloy powder. Microhard-ness tests showed that the surface hardness increased approximately four-fold after the alloying treatment. The microstructure of the MMC coating was mainly composed of residual austenite, acicular martensite, and eutectic ledeburite. Scanning electron microscopy (SEM) and X-ray diffraction analyzes revealed that the in situ TiC particles, which were formed by direct reaction of Ti with carbon originally contained in the GCI, was uniformly distributed at the boundary of residual austenite in the alloying zone. Pin-on-disc high-temperature wear tests were performed on samples both with and without the MMC coating at room temperature and at elevated temperatures (473 K and 623 K), and the wear behavior and mechanism were investigated. The results showed that, after the PTA alloying treatment, the wear resistance of the sam-ples improved significantly. On the basis of our analysis of the composite coatings by optical microscopy, SEM with energy-dispersive X-ray spectroscopy, and microhardness measurements, we attributed this improvement of wear resistance to the transformation of the microstruc-ture and to the presence of TiC particles.     

化学沉积法制备Ni-P-SiC(C)复合镀层的研究

选择廉价的SiC和石C颗粒作为复合镀层添加物，用化学沉积法在碳钢表面制度Ni-P-SiC(C)复合镀层，研究了复合镀层的制备工艺，镀液配方以及复合镀层的性能等，结果显示：风表面开成的复合镀层厚薄均一，SiC和石墨C颗粒在镀层中分布均匀，镀层开成速度理想，表明本文采用的工艺技术合理可行，与单一的Ni-P镀层相比，Ni-P-SiC和Ni-P-C复镀层耐磨性能均有不同程度的提高，而将2种不同性能的SiC和C颗粒同时加入槽液，形成的Ni-P-SiC－C复合镀层具有最优异的耐磨性能。     

Role of surfactants on particle deposition,wear, and corrosion behavior of TaC particle incorporated electroless nickel-phosphorus coating

The coatings prepared by incorporating submicron-sized TaC particles while depositing Ni and P atoms on the steel substrate via electroless method showed mixed results of surface finishing, microstructural properties, mechanical, tribological, and corrosion behavior with the addition of various surfactants during the coating process. The surfactant sodium dodecyl sulfate (SDS) enhanced the microhardness when added during the coating process of Ni–P–TaC composite, whereas the cetyltrimethyl ammonium bromide (CTAB) lowered the microhardness as compared to the surfactant-free coating. Moreover, the TaC particle incorporation was hindered by the surfactants CTAB and Triton X-100. An excellent wear resistance behavior has been observed in the surfactant-free Ni–P–TaC coating in comparison to particle-free Ni–P coating. The Ni–P–TaC coatings showed the dependency of wear behavior on the material properties of the counter sliding surface although this dependency has not been observed in Ni–P coatings. The wear damage in Ni–P coating is immense irrespective of the properties of counter-sliding materials. Various surfactant-used Ni–P–TaC coating surfaces deteriorated much more due to corrosion than surfactant-free Ni–P–TaC coating. Among the various surfactants, the CTAB used Ni–P–TaC coating showed weak corrosion resistance.     

HVOF制备亚微米结构WC-12Co涂层性能研究

采用超音速火焰(HVOF)喷涂工艺制备了亚微米结构WC-12Co涂层,测试了这种亚微米涂层的结合强度、显微硬度及抗磨粒磨损性能,并利用XRD对喷涂粉末及涂层进行相结构分析,用扫描电子显微镜对喷涂粉末、磨粒磨损前后的涂层表面形貌进行观察.研究结果表明:喷涂过程中,亚微米结构WC粒子没有明显的脱碳分解发生,涂层组织结构致密,其显微硬度平均值高达HV1105;在相同的试验条件下,16Mn钢的磨粒磨损量是亚微米WC-12Co涂层的7.8倍,这表明亚微米结构涂层具有优异的抗磨粒磨损性能.     

注塑模零件电刷镀纳米镀层的耐磨性能研究

利用电刷镀技术制备了含纳米SiO2和石墨粉的非晶态Ni-P合金复合镀层，并对其摩擦磨损性能进行了研究。研究表明，当纳米粉体在基质镀液中分散良好时，该复合镀层具有较高的显微硬度，较好的耐磨性及减摩性；当分散不良时，镀层的各项性能未见明显改善。模具试验表明，复合镀层有效地降低了干摩擦状态下注塑模推管与摩擦件的表面划伤与金属转移。     

Oxidation and interdiffusion behavior of a germanium-modified silicide coating on an Nb-Si-based alloy

To investigate the interdiffusion behavior of Ge-modified silicide coatings on an Nb-Si-based alloy substrate, the coating was oxidized at 1250℃ for 5, 10, 20, 50, or 100 h. The interfacial diffusion between the (Nb,X)(Si,Ge)₂ (X=Ti, Cr, Hf) coating and the Nb-Si based alloy was also examined. The transitional layer is composed of (Ti,Nb)₅(Si,Ge)₄ and a small amount of (Nb,X)₅(Si,Ge)₃. With increasing oxidation time, the thickness of the transitional layer increases because of the diffusion of Si from the outer layer to the substrate, which obeys a parabolic rate law. The parabolic growth rate constant of the transitional layer under oxidation conditions is 2.018 μm·h-1/2. Moreover, the interdiffusion coefficients of Si in the transitional layer were determined from the interdiffusion fluxes calculated directly from experimental concentration profiles.     

TiC/Fe cermet coating by plasma cladding using asphalt as carbonaceous precursor

A new Ti-Fe-C compound powder for plasma cladding was prepared by heating a mixture powder of ferrotitanium and asphalt pyrolyzed as carbonaceous precursor. The carbon by the pyrolysis of the asphalt acts as a reactive constituent as well as a binder in the compound powder. TiC/Fe cermet coatings were prepared by plasma cladding with the compound powder. Results show that the Ti-Fe-C compound powder has a very tight structure, which can avoid the problem that reactive constituent particles are separated during cladding. The TiC/Fe cermet coating presents a typical morphology of plasma cladding coatings with two different laminated layers: one is the composite layers in which the round fine TiC particles (<500nm) are dispersed within a Fe matrix, the other is the paragentic layers of TiC and Ti₂O₃. The coating shows high hardness and excellent wear resistance. The surface hardness of the coating is 68±5(HR30N). In the same fretting conditions, the wear area of Ni60 coating is about 11 times as much as the TiC/Fe cermet coating.