Effect of microstructure and chemical composition of hardfacing alloy on abrasive wear behavior

Hardfacing, a surface modification technique, is used to rebuild the surface of a workpiece. The economic success of the process depends on selective application of hardfacing material and its chemical composition for a particular application. In this context, three hardfacing electrodes having different chemical compositions have been selected and their abrasive wear responses was compared with that of mild steel. The emphasis has been made to realize the effect of microstructure and chemical composition on the wear response of the hardfacing material with respect to mild steel. It has been observed that the wear rate of hardfacing alloys is lower than that of mild steel. The hardfacing alloy having the highest chromium content exhibits the lowest wear rate.     

New attachment for controlling gas flow in the HVOF process

During the decade, the high-velocity oxyfuel (HVOF) process proved to be a technological alternative to the many conventional thermal spray processes. It would be very advantageous to design a nozzle that provides improved performance in the areas of deposition efficiency, particle in-flight oxidation, and flexibility to allow deposition of ceramic coatings. Based on a numerical analysis, a new attachment to a standard HVOF torch was modeled, designed, tested, and used to produce thermal spray coatings according to the industrial needs mentioned above. Performance of the attachment was investigated by spraying several coating materials including metal and ceramic powders. Particle conditions and spatial distribution, as well as gas phase composition, corresponding to the new attachment and the standard HVOF gun, were compared. The attachment provides better particle spatial distribution, combined with higher particle velocity and temperature. The original version of this article was published as part of the ASM Proceedings, Thermal Spray 2003: Advancing the Science and Applying the Technology, International Thermal Spray Conference (Orlando, FL), 5–8 May, 2003, Basil R. Marple and Christian Moreau, Ed., ASM International, 2003.     

板坯连铸结晶器Co基合金涂层抗冷热疲劳性能研究

采用HVOF对板坯连铸结晶器窄边CrZrCu板喷涂C0基合金涂层，与电镀Co—Ni镀层进行对比分析。结果表明：450℃下进行冷热疲劳试验，Co基合金涂层经过113次后，涂层还保持完好无损，未出现任何缺陷，而电镀镀层只能承受37．8次；800℃时，Co基合金涂层经过29．4次冷热疲劳后，有3l％的涂层剥落，而电镀层只能承受21．4次。这说明HVOF涂层具有非常高的抗冷热疲劳性能。     

超音速火焰喷涂涂层抗高温氧化和耐冲蚀性能

采用超音速火焰喷涂（HVOF）技术喷涂WC涂层，并对其抗高温氧化和耐冲蚀性能进行测定。试验结果显示，与基体1Cr12W1MoV比较，HVOF制备的WC-17Co、WC-12Co、NiCrBSi＋35WC涂层具有非常良好的抗高温氧化和耐冲蚀性能。其中WC-17Co涂层在任何冲蚀角度下均表现出优良的抗冲蚀能力，是一种理想的汽轮机高压部件防护涂层。     

铜基体超音速火焰喷涂碳化物涂层界面研究

使用扫描电子显微镜及透射电子显微镜，对铜基体超音速火焰喷涂（HVOF）碳化物涂层的形成过程，组织结构和界面形态进行了研究。结果表明，HVOF涂层界面显微组织非常复杂，存在纳米晶，非晶和大量位错孢，非晶是粘结相在喷涂中受热，骤冷形成的，而涂层中的纳米晶来自半熔碳化物的破碎。     

超音速热喷涂316L合金涂层在实际炼油环境中的冲蚀行为

利用超音速热喷涂技术在碳钢基体上制备出了316L合金涂层，研究了该涂层在实际炼油环境中的冲蚀行为。结果表明：超音速热喷涂316L合金涂层在实际炼油环境中具有非常好的抗冲蚀性能，长期现场挂片后涂层仍保持完整，仅表面有轻微的冲蚀痕迹，涂层表面形成的保护性氧化膜、涂层金属自身良好的耐蚀性以及涂层较高的硬度是其具有优异抗冲蚀性能的主要原因。     

Friction and wear properties of high-velocity oxygen fuel sprayed WC-17Co coating under rotational fretting conditions

Rotational fretting which exist in many engineering applications has incurred enormous economic loss. Thus, accessible methods are urgently needed to alleviate or eliminate damage by rotational fretting. Surface engineering is an effective approach that is successfully adopted to enhance the ability of components to resist the fretting damage. In this paper, using a high-velocity oxygen fuel sprayed(HVOF) technique WC-17 Co coating is deposited on an LZ50 steel surface to study its properties through Vickers hardness testing, scanning electric microscope(SEM), energy dispersive X-ray spectroscopy(EDX), and X-ray diffractrometry(XRD). Rotational fretting wear tests are conducted under normal load varied from 10 N to 50 N, and angular displacement amplitudes vary from 0.125° to 1°. Wear scars are examined using SEM, EDX, optical microscopy(OM), and surface topography. The experimental results reveal that the WC-17 Co coating adjusted the boundary between the partial slip regime(PSR) and the slip regime(SR) to the direction of smaller amplitude displacement. As a result, the coefficients of friction are consistently lower than the substrate's coefficients of friction both in the PSR and SR. The damage to the coating in the PSR is very slight. In the SR, the coating exhibits higher debris removal efficiency and load-carrying capacity. The bulge is not found for the coating due to the coating's higher hardness to restrain plastic flow. This research could provide experimental bases for promoting industrial application of WC-17 Co coating in prevention of rotational fretting wear.     

工业汽轮机阀杆超音速火焰喷涂的研究

采用超音速火焰喷涂球形烧结态Cr3C2-25%NiCr复合粉末制备高温耐磨损涂层,分析了涂层的显微组织结构,测试了涂层的结合强度、硬度和耐磨性能,结果表明：涂层中以Cr3C2为主的颗粒增强相弥散分布在NiCr固溶体中,涂层的显微硬度比基体(2Cr12MoV)提高了3倍多,摩擦磨损性能也有明显提高。     

CoCrAlYTaCSi涂层和ZL101铸铝合金的气蚀性能研究

目的对比研究两种材料在RP-3航空煤油和去离子水中的耐气蚀性能,分析材料的气蚀机理以及介质的理化性质对其的影响机制,探讨用去离子水代替航空煤油以便快速筛选航空用耐气蚀材料的可行性。方法采用超音速火焰喷涂技术在铸铝合金(ZL101)表面均匀喷涂CoCrAlYTaCSi涂层。使用X射线衍射仪分析喷涂粉末、涂层和基体材料的物相组成。使用扫描电镜及其自带能谱仪分析材料气蚀前后的形貌以及元素分布。采用纳米压痕仪检测材料的力学性能。使用超声波振动气蚀试验机表征涂层及铸铝合金在航空煤油和去离子水中的气蚀性能。综合考虑两种材料气蚀后的平均侵蚀深度、形貌以及两种液体介质的理化性能,分析相应气蚀机理。结果 CoCrAlYTaCSi涂层主要由AlCo、Al_(80)Cr_(20)、Al_(45)Cr_7等物相组成,且分布均匀;铸铝合金主要由Al和Al_9Si相组成,增强相主要沿晶界分布。涂层的纳米硬度和弹性模量分别约是铸铝的6倍和2倍。气蚀中,铸铝合金晶粒内部的Al最先被损坏,加剧了气蚀进程;而CoCrAlYTaCSi涂层由于物相分布均匀、力学性能优异,所以损坏程度远轻于铸铝合金,在水和航空煤油中的平均侵蚀深度分别仅约为铸铝合金的2%和1%。两种材料在航空煤油中的平均侵蚀深度都比在水中的小。结论 CoCrAlYTaCSi涂层的物相分布均匀,具有较高的致密度、硬度和弹性模量,其在两种介质中均显示出更高的气蚀抵抗力。但材料在两种液体中的气蚀机理并不相同,导致在航空煤油介质中,CoCrAlYTaCSi涂层显示出更加优异的抗气蚀性能。     

钛合金表面粗化对WC-17Co涂层结合性能的影响

研究Ti-6Al-4V合金表面不同粗糙度对超音速火焰喷涂(HVOF)碳化钨(WC-17Co)涂层结合性能的影响. 采用不同喷砂工艺对钛合金表面进行粗化预处理,得到1,2和3号试样的表面粗糙度分别为22.003,20.845和14.765 μm. 利用超音速火焰喷涂技术在粗化后的钛合金表面制备WC-17Co涂层,厚度为0.3 mm. 对WC-17Co/Ti-6Al-4V试样进行三点弯曲试验,利用扫描电镜观察界面形貌. 结果表明,3号试样的界面裂纹扩展最严重并引起了部分涂层脱落,2号试样结合最好;采用四点弯曲法测试涂层与基体的结合界面的断裂能量释放率分别为239.7,259.0和200.1 J/m2.