丝电爆炸喷涂方法用于管内壁钼涂层的制备

开发一种管内壁连续丝电爆炸喷涂装置,在不锈钢管内进行钼丝的电爆炸喷涂试验,分析不同能量密度下涂层的表面形貌以及与基体的结合形态.结果表明,涂层主要是由爆炸产物中熔融液滴直接撞击基体表面形成.随着能量密度的提高,涂层由液相堆积层向液相喷涂层转变;进一步增大能量密度E,当E>350 J/mm3时,熔融金属粒子尺寸减小,温度增高,冲击速度变大,从而获得表面平整喷涂层,该类型涂层与基体结合强度高,但爆炸产物中的气相粒子份额增多,涂层的沉积率降低.     

电爆喷涂方法的研究进展

电爆喷涂是一种新兴的热喷涂方法,它是利用高电压对喷涂材料脉冲放电,瞬时大电流将其加热并发生爆炸,产生高温粒子伴随冲击波喷射到基体表面形成涂层。其特点是喷射粒子速度高,设备尺寸小,适用于孔腔内壁喷涂。本文综述了电爆喷涂方法的发展现状,其经历了自由、定向和约束电爆喷涂。自由喷涂的电极直接接触,烧损严重,并对管径有限制,仅用于小直径管/孔内壁;定向喷涂的约束腔常用陶瓷材料,在爆炸冲击时易破裂或烧蚀;约束喷涂采用消融材料制作约束腔,气体放电导入电流,使这些问题得以解决。其次,阐述了该方法制备的涂层特性,即涂层与基体呈冶金结合,形成了超细晶、纳米晶结构的致密涂层,且具有良好的耐磨和抗腐蚀性及较高的硬度;给出了过程参数与涂层的关系,能量密度和喷涂距离是影响涂层性能的主要因素。最后分析了将来需要研究的问题,展望了电爆喷涂方法的发展趋势。     

钛及钛合金表面金属电沉积的预处理问题

分别采用大气等离子喷涂APS和带延长Laval喷嘴的大气等离子喷涂制备了Al2O3-3%TiO2涂层,对涂层的相组成、显微结构、结合强度、显微硬度等进行了评价,并和常规大气等离子喷涂氧化铝涂层的性能进行了对比,根据粒子在焰流中的特征对涂层性能差异进行了讨论。结果表明,两种Al2O3-3%TiO2涂层均以γ-Al2O3为主,其中还含有少量的α-Al2O3和微晶或非晶。带Laval喷嘴APS所制备涂层的孔隙率、显微硬度和结合强度均明显劣于普通APS涂层,但前者涂层的沉积率达到70%,明显高于后者,大大降低了涂层的生成成本。粒子特征分析表明,延长的Laval喷嘴降低了粒子在等离子焰流中的速度,延长了粒子在焰流中的停留时间,从而使涂层的结合强度和致密度降低,而使涂层沉积率有明显升高。     

砂质涂料离心喷涂的研究

离心喷涂砂质涂料是连续供给的砂质涂料在高速旋转的特制离心头中细分成微滴，并借助于离心力作用飞出，在已预热至220℃左右的金属铸型内壁上均匀堆积形成涂层。与喷枪喷涂相比，可以使涂料的含水比例降低，金属铸型的冷却速度减小，从而使金属铸型的预热温度降低；离心头和金属铸型的同轴反向双重旋转，使涂层更加均匀。离心喷涂方法可以用于大型轧辊离心铸造，以及大直径金属管件内壁防腐、耐热、耐磨涂层的生成。     

管内壁的粉末电爆喷涂工艺

开发了小口径管内壁连续送粉电爆喷涂设备,适用于内径最小为Φ50 mm的管内壁涂层的制备。使用多种粒径的Ni60A合金粉末进行了电爆喷涂试验,分析粉末粒径对涂层形成的影响。结果表明:在本试验参数范围内,粉末粒径越小、电压越高,电爆过程中能量沉积越多,获得的涂层结合强度越高。在加热阶段,放电回路中会产生旁路电流,该电流阻碍了能量向粉末上沉积。通过减小粉末粒径或增大初始充电电压可延迟旁路电流的发生,增加粉末上的能量沉积率。     

连续退火炉炉辊结瘤原因及涂层炉辊的应用

在冷轧连续退火机组生产带钢的过程中，退火炉炉辊表面常常结瘤，影响其使用寿命和带钢的表面质量。为此，通过金相检验、能谱分析等研究了炉辊结瘤的原因，并通过模拟试验进行了验证。结果表明：炉辊结瘤主要是Mn和Fe的氧化物。在生产过程中，带钢进入退火炉时合金元素发生选择性氧化，其表面形成不稳定的Mn氧化物，与炉辊发生化学反应产生结瘤的基础层。炉辊涂层具有抑制Fe氧化物结瘤的作用，但如果Mn氧化物富集厚度超过炉辊涂层元素的扩散范围，涂层抑制Fe氧化物结瘤的作用将消失。此外，简述了涂层炉辊的优缺点和应用。     

腔内约束电热爆喷涂涂层的形成

在内径为7 mm的聚乙烯爆炸腔进行钼丝的电热爆喷涂试验,用扫描电镜观察涂层的表面和截面形貌、涂层厚度,分析涂层与基体的结合情况.结果表明,爆炸腔内钼丝的爆炸产物在基体上会形成一个喷涂圆面,由中心涂层区和外围粘结层组成.中心涂层区在喷涂距离5～8 mm时,所得涂层致密、厚度均匀,与基体结合良好,局部界面附近存在元素扩散现象;外围粘结层随喷涂距离的增大而消失.大面积喷涂层可由单个喷涂圆面的合理搭接来形成,通过多次喷涂可增加涂层的厚度.     

内孔电弧热喷涂装置及涂层结构的研究

为了实现给铝制发动机缸体内壁喷涂铁基耐磨涂层,设计并制造一种新型的适合直径80 mm及以上内孔的电弧喷涂装置。利用所设计的喷涂装置,采用08Mn2Si作为喷涂丝材,分别选用不同的电流和不同的喷涂距离进行喷涂,通过对涂层微观组织比较分析得出,采用电流70 A和喷涂距离70 mm时,完全可以满足对直径80 mm及以上内孔的喷涂,进而对涂层结构研究时发现,在涂层中具有大量铁基氧化物,涂层结合界面上没有大的氧化物、孔隙及夹杂,涂层结合强度高且涂层组织结构由外部到内部基本一致。     

热喷涂汽车发动机气缸内壁涂层的研究进展

为了达到越来越苛刻的内燃机排放标准,减轻车身重量以降低燃油消耗是近年来车辆行业的重要发展方向之一。采用热喷涂方法在铝合金或铸铁气缸内壁喷涂减摩、耐磨并耐腐蚀的涂层代替传统铸铁缸套具有广阔的应用前景。首先介绍制备气缸内壁涂层的工艺流程,主要阐述现有制备气缸涂层的超音速火焰喷涂、电弧喷涂、大气等离子喷涂和等离子转移弧线材喷涂等工艺的原理,对不同热喷涂工艺特点进行了总结,阐明不同热喷涂方法获得的涂层结构特点。通过列举国内外车辆制造商先进热喷涂涂层的应用实例,进一步分析各类涂层的优缺点。最后提出优化喷涂参数、开发新型喷涂材料、控制涂层内应力和应对未来生物燃料是汽车气缸涂层的下一步研究方向。     

锅炉“四管”用耐磨耐蚀涂层研究进展

总结了锅炉"四管"失效的形式和机理.热腐蚀和高温冲蚀磨损是锅炉"四管"失效的主要原因,采用热喷涂金属涂层、陶瓷涂层及金属陶瓷复合涂层等可以有效控制热腐蚀和高温冲蚀磨损.目前制备高性能涂层常用的方法有等离子喷涂、电弧喷涂、超音速火焰喷涂等.详细介绍了高镍铬合金涂层的研究状况和喷涂工艺的特点,最后展望了纳米结构涂层在该领域的研究进展和应用前景.     

喷嘴形状对Al2O3-3TiO2粒子扁平化及其涂层性能的影响*

采用SprayWatch在线监测系统测量了F6大气等离子喷枪在不同喷嘴条件下产生的等离子射流中Al2O3-3TiO2粒子的温度和速度。利用201不锈钢和Q235钢作为基体,分别用来收集粒子和制备涂层。分析了不同喷嘴对飞行粒子温度和速度的影响,并通过扫描电镜(SEM)对扁平粒子的铺展程度和涂层显微组织进行了分析,并对比了涂层的结合强度、显微硬度和磨损失重量的差异。结果表明:在相同的测量位置,圆柱形喷嘴喷出粒子的速度比Laval喷嘴条件下的高出一倍,但是温度比Laval喷嘴条件下略低。圆柱形喷嘴获得的扁平粒子比Laval喷嘴获得的扁平粒子铺展程度要大;圆柱形喷嘴获得的涂层的孔隙率及磨损失重量比Laval喷嘴制备的小,其涂层的结合强度、显微硬度均高于Laval喷嘴制备的涂层。     

Optical Diagnostics Study of Gas Particle Transport Phenomena in Cold Gas Dynamic Spraying and Comparison with Model Predictions

Cold gas dynamic spraying (CGDS), a relatively new thermal spraying technique has drawn a lot of attention due to its inherent capability to deposit a wide range of materials at relatively low-operating temperatures. A De Laval nozzle, used to accelerate the powder particles, is the key component of the coating equipment. Knowledge concerning the nozzle design and effect of process parameters is essential to understand the coating process and to enable selection of appropriate parameters for enhanced coating properties. The present work employs a one-dimensional isentropic gas flow model in conjunction with a particle acceleration model to calculate particle velocities. A laser illumination-based optical diagnostic system is used for validation studies to determine the particle velocity at the nozzle exit for a wide range of process and feedstock parameters such as stagnation temperature, stagnation pressure, powder feed rate, particle size and density. The relative influence of process and feedstock parameters on particle velocity is presented in this work.     

低温爆炸喷涂WC涂层的理论与试验研究

为解决爆炸喷涂过程中WC颗粒由于高温导致的脱碳问题,本文设计了一种带有拉瓦尔喷管的爆炸喷涂装置,利用该装置进行了爆炸喷涂WC涂层的理论和试验研究。基于等熵流的数值计算结果表明,喷管可以有效降低载气的温度,并可将WC颗粒加速至1000m/s以上。利用压力传感器测试了喷管入口和出口处的压力,计算了气流马赫数。在喷管出口处采用激光遮挡法测试了粒子的速度,测试结果与理论计算结果具有较好的一致性。采用扫描电镜、金相显微镜和XRD对碳化钨颗粒、涂层进行了表征,结果表明喷管的使用可以有效避免脱碳现象。该研究为解决爆炸喷涂碳化钨过程中的脱碳问题提供了一种新思路。     

The influence of nozzle design on HVOF exit gas velocity and coating microstructure

A simple device was constructed for determining a value for the average combustion gas velocity at the exit plane of a high-velocity oxyfuel gun. This device was used to measure the velocities of a standard factory-made barrel nozzle and a specially designed de Laval nozzle as a function of the fuel/oxygen ratio and the total mass flow rate. The Mach number of the de Laval nozzle was 1.42. The maximum combustion gas exit velocities determined for the standard and the de Laval nozzles were 1100 and 1550 m/s, respectively. The maximum velocity depends on the fuel/oxygen ratio but is independent of the total flow rate. The effect of increased combustion gas velocity on coating quality is demonstrated.     

多功能微弧等离子喷涂技术

根据空气动力学和等离子喷涂理论,按照"一专多能"的设计指导思想,采用IGBT逆变技术、微电脑控制技术、软开关变换技术、拉瓦尔喷嘴和中心轴向送粉等,设计了多功能微弧等离子喷涂系统,且具有体积小、重量轻、抗干扰强、控制精确、喷涂粒子速度高、粉末沉积效率高等特点,可制备各种金属合金、金属陶瓷以及氧化物涂层.通过试验测定,多功能微弧等离子喷涂制备的纳米结构Al2O3 13%TiO2涂层的结合强度、显微硬度等性能优于9M等离子喷涂制备的纳米结构的Al2O3 13%TiO2涂层,这表明通过改进电源设计、喷枪结构设计、送粉方式等,低功率多功能微弧等离子喷涂能够与大功率等离子叶涂性能相当甚至更优异性能的涂层.     

Fluid dynamic study of direct current plasma jets for plasma spraying applications

Recently, direct current (dc) plasma torches equipped with converging-diverging (Laval) nozzles, instead of standard cylindrical ones, have been shown to present several advantages for both vacuum and atmospheric plasma spraying, such as diminishing the gradients of temperature and velocity and reducing the turbulence intensity in the jet fringes. The present study was concerned with the diagnostics of the plasma jets produced by three nozzles of various contours: a standard cylindrical anode and a Mach 2.5 and Mach 3 Laval nozzle. Emission spectroscopy (absolute intensity) and enthalpy probe techniques were used to measure temperature and velocity fields. Special attention was given to the effects of spray chamber pressure on flow regime inside the nozzles and to the distribution of the temperature and velocity fields in the plasma jet. Results showed that under the chamber pressure conditions used (vacuum), for which Laval nozzles originally were designed, the generated plasma jets had greater centerline velocities and larger high temperature zones compared to standard cylindrical nozzles. The results showed significant improvement in the deposition efficiency by using nozzles with these computed contours.     

Crystallization Evolution of Cold-Sprayed Pure Ni Coatings

Cold spraying is a coating technology on the basis of aerodynamics and high-speed impact dynamics. Spray particles (usually 1-50 μm in diameter) are accelerated to high velocity (typically 300-1200 m/s) by a high-speed gas (preheated air, nitrogen, or helium) flow that is generated through a convergent-divergent de Laval type nozzle. The coating forms through the intensive plastic deformation of particles impacting on the substrate at temperatures well below the melting point of the spray material. In the present paper, the main processing parameters affecting the crystallization behavior of pure Ni cold spray deposits on IN718 alloy are described. Various experimental conditions have been analyzed: gas temperature and pressure, nozzle to substrate distance. In particular, the study deals with those conditions leading to a strong grain refinement, with an acceptable level of the deposits mechanical properties. In precise spray conditions, a shift toward amorphous phases has been observed and studied. A systematic analysis of microstructural evolution, performed through TEM observations, as a function of processing parameters is presented.     

Development of high quality thermal spraying process by shielding control

Abstract

The shielding controlled plasma spraying process was investigated to improve corrosion resistance of metal surfaces. In this process, a shielding nozzle that covered only spraying area was attached in front of the tip of a commercial plasma spray gun nozzle, and the environment surrounding the plasma jet was controlled by nitrogen flow. When the oxygen concentration in the shielding nozzle was maintained at 0·5%, the metal oxide contents in CoNiCrAlY coating and the porosity of the coating reduced to 0·2 and 0·3% at optimal spray particle size respectively. The corrosion potential in an acid solution including chloride ions was almost constant for 1000 h for CoNiCrAlY coating deposited by shielding controlled plasma spraying. On the other hand, those obtained by atmospheric plasma spraying process decreased in the corrosion potential largely after 10 h. Thus, it can be concluded that the shielding controlled plasma spraying process improves the corrosion resistance of the metal.     

吸波涂层精准厚度涂装工艺研究

目的降低涂层厚度波动范围,提高吸波性能的稳定性。方法通过资料分析,选用空气辅助无气喷涂工艺,综合空气喷涂和无气喷涂工艺的优点,改进喷嘴,实现喷雾流量和雾化幅度等工艺参数的精确控制。进行喷涂参数优化试验和吸波性能检测,获得最佳喷涂工艺。结果采用空气辅助无气喷涂工艺和改进的喷嘴,调节喷幅在5~30 mm,采用5次喷涂,每次喷涂20~24 min,获得的吸波涂层表面平整,没有直径大于50μm的颗粒。喷涂的2 mm厚涂层单位面积厚度的偏差从200μm降低到60μm以下,吸波性能从5 d B降到2 d B以下。结论研制出的吸波涂层精准厚度涂装工艺,可根据涂装基准面的形态和结构选择不同喷幅的喷嘴调节雾化,实现厚涂层吸波涂料的均匀喷涂,大幅度提高吸波涂层的涂装质量。     

Nozzle developments for thermal spray at very low pressure

Very low pressure plasma spraying has been the object of numerous studies for the past years. However, numerical simulations and experiments revealed some difficulties such as the presence of successive expansions and constrictions of the plasma jet that have an influence on the deposition efficiency and on the coating structure. Optimization of the plasma gun is thus required and the use of bell-contoured De Laval nozzle extensions seems particularly promising. In this paper, new developments concerning the use of an in-house bell-contoured nozzle extension are presented, and both numerical calculations and experiments were performed. This article was originally published inBuilding on 100 Years of Success, Proceedings of the 2006 International Thermal Spray Conference (Seattle, WA), May 15–18, 2006, B.R. Marple, M.M. Hyland, Y.-Ch. Lau, R.S. Lima, and J. Voyer, Ed., ASM International, Materials Park, OH, 2006.