液体燃料-空气/氧气混合助燃超音速火焰喷涂枪的研制

采用枪内混气方式,设计研制了一种采用炽热体作为稳焰器的液体燃料-空气/氧气混合助燃超音速火焰喷涂枪.用SprayWatch热喷涂监测系统测试喷涂枪焰流出口速度和温度,并研究喷涂工艺对WC-12Co涂层组织和性能的影响.结果表明,喷涂枪焰流出口速度超过1300m/s,焰流温度可在2302～3410K之间进行精确调节,精度达到±50K;提高空气/氧气比,涂层中WC保留率明显提高,使涂层硬度比氧气助燃时得到明显提高;采用空气助燃进行喷涂,可以得到厚度超过5mm的WC-12Co涂层.     

超音速火焰喷涂的火焰速度特性

本文介绍了超音速火焰喷涂系统的火焰特性。试验结果表明在使用氧气和丙烷燃气时．可在较大的压力和流量范围内,获得超音速火焰。喷枪出口火焰的速度可达1500m／s以上。根据火焰射流照片中的马赫锥角来计算马赫数,并依据火焰的其它参数估算出火焰的速度。     

氧气-空气混合助燃超音速火焰喷涂WC-Co涂层性能研究

采用液体燃料氧气-空气混合助燃超音速火焰喷涂(HVO/AF)工艺在45钢表面制备WC-Co涂层,采用扫描电镜(SEM)、X射线衍射(XRD)表征了涂层的微观结构及相组成,并对涂层的孔隙率、显微硬度和结合强度进行了分析.研究结果表明,采用液体燃料氧气-空气混合助燃超音速火焰喷涂制备的涂层均具有较好的性能,超音速火焰喷涂氧气与空气混合比例对涂层的性能影响较大,采用HVO/AF喷涂技术能有效地抑制WC的氧化和分解,降低了涂层的孔隙率,提高了WC-Co涂层的硬度和结合强度等性能.涂层质量要好于传统的氧气助燃超音速火焰喷涂.     

超音速火焰喷涂枪的研究

利用理论分析与实验相结合的方法,在比较和借鉴国外相近喷枪的基础上,对喷枪结构参数进行了选择,对喷枪的实际性能进行了估算。将在此基础上设计出的喷枪进行点火试验,得到的实测值与估算值吻合得很好。这证明了喷枪的结构设计合理,性能的估算比较准确,从而为设计和改进喷枪结构,提高喷枪的性能提供了可靠的理论依据。     

超音速火焰喷涂气固两相流的数值模拟

从两相流的基本理论和输运方程出发,建立超音速火焰喷涂过程的气固两相流场的数学模型,以FLUENT软件为计算平台,采用k-ε湍流模型模拟湍流流动,采用非预混燃烧模型设置反应过程,模拟气态流场的流动特性,研究喷涂过程中燃烧反应、燃烧物质含量比等参数对气态流场的影响;采用离散相模型中颗粒随机跟踪轨道模型计算喷涂颗粒的动力学飞行行为,研究颗粒大小与颗粒注射速度对颗粒动力学行为的影响,为以后喷涂工艺参数的选取和FLUENT在喷涂模拟中的广泛应用提供有用信息.结果表明:当煤油与氧气含量比为3时,焰流速度与温度场最好;随颗粒直径的增大,颗粒的加速度减小;速度为25 m/s以上的颗粒出现了与壁面的撞击行为.     

超音速火焰喷涂及涂层性能简介

本文简要介绍了超音速火焰喷擦的原理、发展状态；比较了超音速火焰喷涂层、等离子喷涂层，爆炸喷涂层、自熔合金喷熔层以及电镀硬铬层的硬度和耐磨损性能；介绍了超音速火焰喷涂层的部份应用实例及其应用效果。     

超音速火焰喷涂流场有限元分析

在液体火箭发动机原理的基础上,建立了超音速火焰喷涂过程全流场分析模型,对KY-HVO(A)F多功能超音速火焰喷涂系统进行了流场分析,得到了HVOF与HVAF两种状态下燃气的速度、温度分布,分别体现了燃气欠膨胀与过膨胀的特点。在HVOF状态计算结果中有8个马赫锥而实际焰流照片中有8～9个马赫锥,所处位置基本对应,可以合理解释喷涂过程的激波现象,不同截面上的速度分布,体现了燃气速度在径向截面上的自模特性。     

超音速火焰喷涂WC-CrNi涂层的滑动磨损特性研究

采用超音速火焰喷涂技术制备WC-CrNi涂层,研究了自配副磨损和三体磨损条件下,涂层的滑动磨损性能,并分析了涂层磨损前后的形貌及成分变化。结果表明:WC-CrNi涂层组织致密、结构均匀;两种磨损条件下,涂层的摩擦系数相差较大,三体磨损时,涂层损伤严重,由于配副接触面间第三体存在增加了摩擦阻力,使得摩擦系数稳定性变差;涂层在两种磨损条件下的磨损机制有所不同,自配副时的磨损机制为WC层状剥离,三体磨损下则以微切削并伴随塑性变形为主。     

超音速火焰喷涂FeCrSiB涂层的腐蚀行为

采用超音速火焰(high velocity oxygen fuel,HVOF)喷涂技术在Q235钢基体上制备了FeCrSiB合金涂层.利用X射线衍射仪、扫描电子显微镜、电化学工作站等设备对涂层的显微组织结构和耐腐蚀性进行了研究.结果表明,采用HVOF喷涂技术制备的FeCrSiB涂层结构致密,孔隙率为0.65%,与基体结合良好.FeCrSiB涂层在3.5%NaCl溶液、1 mol/L HCl溶液和1 mol/L NaOH溶液中都经历了活性溶解-钝化-过钝化的过程,且该涂层在3.5%NaCl溶液和1 mol/L HCl溶液中的耐腐蚀性能要优于镀铬层,在1 mol/L NaOH溶液中的耐腐蚀性能低于镀铬层.     

TiAlNb intermetallic compound coating prepared by high velocity oxy-fuel spraying

Ti_28.35Al_63.4Nb_8.25 (at.%) intermetallic compound coatings were sprayed onto 316 L stainless steel substrates by HVOF processes using various parameters. By varying the grit blasting pressure between 0.11 and 0.55 MPa, the effects of substrate roughness on the adhesion of TiAlNb thermal sprayed coatings were investigated. The microstructure, porosity and microhardness of the coatings were characterized by SEM, XRD, Image Analysis and Vickers hardness analysis. The tensile adhesion test (TAT) specified by ASTM C 633-79 was used to measure the tensile bonding strength of the coating. The results show that the coatings with substrate roughness of 8.33 μm displayed the best combined strength. TiAlNb coatings had a lamellar microstructure with different spraying parameters. The porosity, bonding strength, microhardness of coatings were assessed in relation to the spraying processes. The thickness of bond coat on the bond strength of coatings was also discussed.     

不同燃料超音速火焰喷涂NiCr-Cr3C2涂层

采用超音速火焰喷涂工艺在20CrMo钢圆片上成功制备25%NiCr-Cr3C2金属陶瓷涂层,研究了不同燃料对喷涂层组织性能的影响。结果表明,以丙烷为主要燃料所得喷涂层的组织不均匀,存在典型的层状结构,孔隙率约为3.2%,显微硬度仅为836 HV,涂层断裂韧性KIC为2.08 MPa.m3/2;以煤油为主要燃料所得喷涂层的组织分布均匀,细小致密,孔隙率约为2.4%,显微硬度可达1045 HV,涂层断裂韧性KIC为2.56 MPa.m3/2。前者的组成相为Ni(Cr)固溶体、Cr3C2和微量NiCrO4;后者的组成相除Ni(Cr)固溶体和Cr3C2外,还有Cr7C3、Cr23C6和Ni(Cr)相出现。     

Molybdenum based amorphous and nanocrystalline coatings prepared by high velocity oxy-fuel spraying

The high velocity oxy-fuel(HVOF) based thermal spray process has developed as a potential advantageous approach for fabricating various kinds of functional coatings.In this article,the coatings of Mo-based alloy were synthesized using the HVOF process.The microstructure and the mechanical properties of the HVOF-processed coatings were investigated using SEM,TEM,XRD,and hardness and wear tests.Annealing treatment was applied to the as-sprayed coatings to develop the microstructure and its effect on the microstructure and mechanical properties of the coatings was examined.It is found that the HVOF-processed Mo-based alloy coatings are comprised of an amorphous splat matrix embedded with nano-sized crystalline particles.Annealing at temperatures over 950 ℃ results into crystallization of the amorphous matrix.The mechanical properties of the as-sprayed coatings are enhanced with annealing temperature up to 750 ℃ and from 950 to 1050 ℃,keeps constant between 750 and 950 ℃,and reduce over 1050 ℃.The change of the mechanical property with the microstructure was illustrated in the study.     

超音速火焰喷涂合成TiC-Ni涂层滑动磨损性能研究

采用二次正交回归试验方法得到了喷涂工艺参数与反应超音速喷涂合成涂层滑动磨损性能的定量关系,研究了涂层的磨损失效机制,并分析了氧气流量、燃气流量和喷涂距离对超音速火焰喷涂合成TiC-Ni涂层滑动磨损性能的影响。结果表明：涂层的磨损机制以粘结相的优先磨损以及硬质相的剥落引起的磨粒磨损为主。氧气流量、燃气流量和喷涂距离对涂层滑动磨损性能有较大影响。适中的氧气流量、燃气流量有利于获得耐磨性较好的涂层,喷涂距离较小时,涂层的磨损失重量变化不明显．喷涂距离较大时,失重量较高。     

HVOF喷涂Fe-Cr基涂层中非晶与纳米晶形成的研究

采用多元Fe基合金（含Cr、Si、Mn、B等）作为喷涂粉末,用超音速火焰（HVOF）喷涂法在不锈钢基体上制备厚度约200μm的Fe-Cr基涂层.用X射线衍射、扫描电镜、透射电镜、差示扫描量热仪（DSC）对涂层的组织结构特征进行了研究.涂层由于熔融和半熔化状态的液滴的连续堆积而成层状,由Fe基非晶、纳米晶及硼化物组成,纳米晶尺寸约为10-30nm.DSC分析表明非晶的晶化温度约为605℃.非晶的形成是由于喷涂液滴快的冷却速度及合适的粉末成分;非晶由于后续熔融液滴的堆积对前涂层产生退火效应,以非均匀形核的方式分别在非晶内部和非晶与硼化物的界面形成.     

超音速火焰喷涂CoCrW涂层的高温抗氧化性能

采用超音速火焰喷涂工艺制备了CoCrW涂层，用增重法测试了涂层的高温抗氧化性能。试验结果表明，在氧化性气氛下，涂层在850℃以下或经过较短时间处理时，涂层氧化增重较少，而经850℃以上处理或经过较长时间处理时，涂层氧化增重明显，而且，处理后涂层的X射线衍射结果也证明在涂层中出现了铬和钴的氧化物。可见，CoCrW涂层的稳定使用温度应控制在850℃以下。     

Oxidation of stainless steel in the high velocity oxy-fuel process

The high velocity oxy-fuel (HVOF) spray process has been primarily used for the application of wear-resistant coatings and, with the introduction of new, more powerful systems, is being increasingly considered for producing corrosion-resistant coatings. In this study, the influence of various spray parameters for the JP-5000 and Diamond Jet (DJ) Hybrid systems on the oxidation of stainless steel 316L is characterized. Experimental results reveal that coating oxygen contents of less than 1 wt.% can be more easily attained with the JP-5000 than the DJ Hybrid systems because of the former’s design. In both cases, however, the low particle temperatures necessary for low oxygen content coatings may impair bond and cohesive strength. Heat treating the coatings after processing reduces hardness, metallurgically enhances bond strength, and enables the spheroidization of oxide layers surrounding unmelted particles. An empirical model describing oxidation in the thermal spray process was expanded to explain the oxidation in the HVOF spraying of stainless steel. It was concluded that for these oxygen-sensitive materials, maintaining a relatively low particle temperature throughout the spray process minimizes oxygen pickup by preventing an autocatalytic oxidation process and particle fragmentation upon impact. For the DJ Hybrid systems, understoichiometric fuel settings are selected, whereas for the JP-5000, oxygen-rich mixtures are preferred.     

Studies of Fe-40Al coatings obtained by high velocity oxy-fuel

Interesting properties that intermetallics possess have made them to be promising materials to be used either as bulk materials or as coatings, both at medium or elevated temperature environments. This group of materials possesses a long-range order, which can be kept by some intermetallics until their melting point, which is the main reason why they possess a good stability at high temperatures. Some other properties can be summarized as follows: high thermal conductivity; low density; great strength, particularly at high temperatures; good oxidation resistance at high temperatures (because of the formation of oxide films); low ductility, brittle fracture at room temperature.FeAl coatings from powder of nominal composition Fe-40Al-0.05 Zr (at.%) with 50 ppm B and 1 wt.% Y₂O₃ have been prepared using high velocity oxy-fuel (HVOF) technique. Several standard spraying conditions have been assessed; some parameter variations from those standards intend to find optimal spraying conditions. The characterization has been carried out by DRX, EDS and Scanning Electron Microscopy. The results conclude that a major intermetallic FeAl phase has been obtained.Microhardness and wear properties have been evaluated for those coatings obtained with optimal conditions. Compared to room temperature sliding wear behaviour, the friction coefficient is reduced when the test is performed at 400 °C.     

Configuration optimization of high velocity arc spraying gun

In order to improve the in-flight characteristics of the atomizing droplets during high velocity wire arc spraying (HVAS), some changes have been operated on the original design of the HVAS gun configuration. A comparative study was carried out to investigate the microstructure and properties of the coatings produced by the original design spraying gun and the modified one, using 3Cr13 wires of 3 mm in diameter. The characteristics of their jets were examined during spraying. The results indicate that, the included angle between the two wires and the distance from the nozzle to the meeting point of the two vires may have a strong influence on the characteristics of the in-flight droplets and then the coatings. The jet divergence is found to be lower than that of the original one (about 12° against 25°). By modified gun, the adhesion strength, the microhardness and porosity of the coating deposited by modified gun are increased by 39% and 9% respectively. And the porosity of the coatings is decreased by 57%.     

Numerical modeling of in-flight characteristics of inconel 625 particles during high-velocity oxy-fuel thermal spraying

A computational fluid dynamics (CFD) model is developed to predict particle dynamic behavior in a high-velocity oxyfuel (HVOF) thermal spray gun in which premixed oxygen and propylene are burnt in a combustion chamber linked to a long, parallel-sided nozzle. The particle transport equations are solved in a Lagrangian manner and coupled with the two-dimensional, axisymmetric, steady state, chemically reacting, turbulent gas flow. Within the particle transport model, the total flow of the particle phase is modeled by tracking a small number of particles through the continuum gas flow, and each of these individual particles is tracked independently through the continuous phase. Three different combustion chamber designs were modeled, and the in-flight particle characteristics of Inconel were 625 studied. Results are presented to show the effect of process parameters, such as particle injection speed and location, total gas flow rate, fuel-to-oxygen gas ratio, and particle size on the particle dynamic behavior for a parallel-sided, 12 mm long combustion chamber. The results indicate that the momentum and heat transfer to particles are primarily influenced by total gas flow. The 12 mm long chamber can achieve an optimum performance for Inconel 625 powder particles ranging in diameter from 20 to 40 μm. At a particular spraying distance, an optimal size of particles is observed with respect to particle temperature. The effect of different combustion chamber dimensions on particle dynamics was also investigated. The results obtained for both a 22 mm long chamber and also one with a conical, converging design are compared with the baseline data for the 12 mm chamber.