焊接工艺——熔焊

Ti-Si对SiCq／Al基复合材料等离子弧原位焊接性能的影响;等离子熔射过程中射流与粒子流的加热效应;铝合金变极性等离子焊接电弧产热机理;手工自蔓延焊接技术;GMAW-P脉冲焊接参数对焊缝成形影响的分析;     

焊接工艺——熔焊

Ti-Si对SiCq／Al基复合材料等离子弧原位焊接性能的影响;等离子熔射过程中射流与粒子流的加热效应;铝合金变极性等离子焊接电弧产热机理;手工自蔓延焊接技术;GMAW-P脉冲焊接参数对焊缝成形影响的分析;     

面向等离子熔射成形技术的粉末飞行特性数值分析

粉末在射流场中飞行特性是影响熔射成形件质量的重要因素。通过所建立的粉末与射流相互作用的动量和能量传递方程，应用有限差分法，模拟计算和分析了粉末速度与温度分布规律及其对成形件质量的影响。结果表明：①粒径及密度越小，加(减)速度越快，而到达原模时的速度则不同；②热传导性越差，粒径越大，极值温度则越小，且逐渐向原模方向偏移；③粉末的力学行为和加热特性的匹配，可进一步提高熔射成形件质量。模拟结果为实现熔射成形质量控制及参数优化，提供了理论依据。     

等离子熔射过程数据挖掘技术及智能控制策略

结合图像处理与模式识别技术提取等离子射流的形态特征,采用射流狭长度对其进行表征.采用数据挖掘技术将等离子弧电流、电压参数和射流狭长度特征进行聚类分析,构造对等离子熔射过程中射流发生子系统进行智能化控制的知识库.根据涂层的残余应力、孔隙率和硬度等主要性能参数以及微观组织结构对分类结果进行质量评判,生成工艺参数到最佳分类的推理规则集,从而实现了对工艺参数—射流形态—涂层性能之间关联关系的研究.基于规则库监督多模型自适应控制系统结构,提出了一种等离子射流发生子系统的智能化控制策略.     

等离子熔射皮膜破坏温度场诊断

应用红外热像仪获取等离子熔射过程中基体与皮膜发生破坏时的温度场,对比分析皮膜破坏发生区域.然后从通过破坏区域的直线上的温度变化曲线,深入分析该区域的温度波动.实验结果表明:皮膜破坏一般发生在预热后基体温度较高区域和温度较高区域向临近温度偏低区域过渡部位;温度曲线中,皮膜破坏区域对应的温度极大值要高于临近区域平均温度30℃～50℃或者更高.实验结果为等离子熔射过程中皮膜温度监控确定了皮膜破坏预警信息和核心目标监控区域.     

新型大气长层流等离子体喷涂方法和研究进展

介绍了一种新型大气等离子喷涂方法,该方法采用特殊内通道结构的直流非转移电弧等离子发生器,可以直接在大气条件下获得长度100～1000 mm之间变化的等离子射流。在大气条件下,等离子射流的流动特性具有"长、直、准"的层流或类层流状态,工作时噪音小于80 dB。在工作参数范围内,等离子射流的长度在固定总气流量条件下可以随输出功率的增加而增长;射流的长度在固定输出功率的条件下随总气流量的增加而减小。当使用在大气等离子喷涂技术中时,会为飞行粉末颗粒带来超长的加热和加速过程。文中详细介绍了大气层流等离子喷涂技术的研究历史和研究现状,以及研究团队利用该新型技术制备的6种涂层的显微结构、颗粒的飞行和加热特点,并对比了目前其他大气等离子喷涂技术的结果。结果表明,文中介绍的方法在最低的输出功率和气流量条件下,为金属和陶瓷颗粒提供了超长的飞行和加热条件,表现为较低的颗粒飞行速度和超高的颗粒表面温度。可以在不同的射流长度或喷涂距离下,获得不同的颗粒熔化状态或涂层结构,并发现可以直接在大气条件下获得大规模气液共沉积的涂层。     

等离子熔射皮膜温度分布在线监控与过程诊断

采用红外测温仪与热像仪相结合的现场红外诊断方法对等离子熔射过程中基体/皮膜温度进行在线监控与过程诊断,分析了皮膜温度的变化规律,并对皮膜破坏现象进行诊断.试验结果表明:皮膜破坏一般发生在预热后基体表面温度较高区域及其与临近温度偏低区域之间的过渡区域;温度曲线中皮膜破坏区域对应的温度极大值要比临近区域平均温度高30～50℃,甚至更高.因此该方法为等离子熔射成形质量控制提供了一种可行途径,同时试验结果也为皮膜温度监控确定了皮膜破坏预警信息与核心监控区域.     

喷嘴出口直径对冷喷涂射流流场及基板最佳位置影响的数值分析

冷喷涂过程中,喷嘴出口后射流流场的波系结构对粒子冲击基板时的速度有很大影响.利用CFD软件Fluent对不同出口直径的喷嘴后单相自由射流和两相冲击射流流场进行了模拟计算.结果表明,喷嘴出口直径对冷喷涂射流流场及粒子冲击速度会产生一定的影响;在喷嘴出口与基板之间存在一个最佳距离使得粒子能够获得较大的冲击速度,该最佳距离会随喷嘴出口直径的增加而线性增加.     

多喷嘴射流泵流场的数值模拟与PIV测量

为研究多喷嘴射流泵性能和内部流场特征,设计了不同结构的多喷嘴射流泵试验模型.采用k-ε湍流模型和壁面函数法对不同参数下的多喷嘴射流泵进行了数值模拟,模拟结果表明,喷嘴数和喷嘴角度及喉嘴距对射流泵工作性能影响较大;在吸入室及喉管入口处湍动能较大.利用PIV系统对不同结构射流泵内部流场进行了三维测量,获得了射流泵对称面流场的速度矢量和湍动能等值线图.试验结果表明,其速度梯度衰减得愈快,工作流体和被吸流体混合距离越短.验证了多喷嘴射流泵可缩短喉管长度.测量结果证明数值模拟的正确性,为多喷嘴射流泵理论研究和合理设计提供了理论依据.     

电磁制动下钢液射流及钢-渣界面波动行为的数值模拟

建立了描述全幅一段电磁制动作用下结晶器内钢液射流及钢-渣界面波动行为的数学模型,采用数值模拟方法研究了不同电磁参数对结晶器内钢液射流及其引起的钢-渣界面波动行为的影响,分析了磁感应强度及水平磁极与浸入式水口之间距离变化对结晶器内钢液射流行为和钢-渣界面波动行为的影响。结果表明,当全幅一段电磁制动稳恒磁场同时覆盖射流冲击区域、上返流和下返流区域时(D=20mm),电磁制动的施加可以有效控制钢液射流结构,降低上返流和下返流钢液流速,稳定钢-渣界面波动;当电磁制动水平磁极与浸入式水口垂直距离较远时(D=220mm),增大磁感应强度不能对结晶器内上返流区域钢液流速进行抑制,不利于钢-渣界面波动的稳定,增大卷渣发生几率。     

Diagnostics in plasma spraying techniques

The paper presents three innovative diagnostics for application to the plasma spraying process. With plasma computer tomography, the plasma jet is investigated by recording its radiation under several directions. The laser-based particle shape imaging technique is applied for determining dynamic and geometric parameters of spray particles within the plasma jet. The particle flux imaging method, which allows the characterisation of the total process except the formation of the coating, can be used for process monitoring and quality control.     

大气等离子射流中粒子飞行行为的试验测量

为考察等离子熔射中粉末的飞行过程,应用芬兰Oseir公司等离子喷涂在线监测和分析设备SprayWatch对射流中粒子的温度、飞行速度和粒子流量进行了测量,探讨了等离子弧电压、电流、功率以及送粉量等参数对粒子飞行状态的影响.结果表明:同等功率下,电流对粒子速度的影响高于电压,电压对粒子流量的影响高于电流,电压、电流对粒子温度则呈现交替重要的影响;在电流400A、电压50V下粒子流量随送粉量的增加呈现低-高-低的"山峦"状变化,反映了粒子飞行路径和分布的变化.     

基于响应曲面法的Ar-N2 等离子射流特性研究

目的研究等离子射流特性,提高射流品质,为工程实践提供支撑。方法通过响应曲面法,以粒子速度和温度为指标反映射流特性的变化,采用Box-Behnken-Design(BBD)设计分析电流(I)、主气流量(Q)以及次级气比例(C)对于射流特性的影响规律及其相互作用关系。结果对粒子速度的影响因素排序为Q_(Ar)IC,对粒子温度的影响因素排序为IQ_(Ar)C。该喷嘴下实现最佳加热效应的参数为:主气流量80 L/min、电流450 A、次级气比例22.5%。实现射流最佳加速效应的离子气及电参数为:主气流量140 L/min、次级气比例15%、电流400 A。在射流最佳加速效应对应参数下制备的AT40涂层均匀致密、孔隙少。结论运用响应曲面法分析和解决等离子射流特性影响问题具有科学性和可操作性,能够有效指导涂层制备。     

Numerical Modelling of Ar-N<Subscript>2</Subscript> Plasma Jet Impinging on a Flat Substrate

Substrate heating in the plasma spray process is one of the important parameters, which affects the microstructure of coatings and bonding between coating and substrate. In this study, a three-dimensional numerical model is developed to study the thermal exchange between the plasma jet and the substrate. The plasma jet temperature and velocity distributions and thermal flux to the substrate surface are predicted. The effects of arc current, gas flow rate, and stand-off distance on the temperature and velocity fields of the impinging plasma jet and thermal flux to the substrate are clarified. Results indicate that the three-dimensional effect has a very weak influence on the substrate heating. The air entrainment is compared for different cases. The present model is validated by comparing the present results with previous predictions and measurements. The temperature distributions in the substrate for different stand-off distances are predicted.     

等离子体喷涂中颗粒加热过程数值模拟

目的研究颗粒在等离子体喷涂中的加热过程及影响因素。方法使用Fluent软件对处于等离子射流中颗粒的加热过程与状态进行求解计算,根据计算结果分析了喷距、颗粒直径与颗粒材料对颗粒加热状况与内部温度梯度的影响。结果对于不同的喷距,在颗粒升温过程中,颗粒表面温度高于中心温度;在颗粒降温过程中,颗粒表面温度低于中心温度,并且降温过程中的表面-中心温差远小于升温过程中的表面-中心温差。在颗粒升温过程中,其内部存在不同的加热阶段。对于不同的直径,虽然大颗粒比小颗粒能进入射流中心更深的位置,但小颗粒的加热效果更好。表面-中心温差随着颗粒直径的增大而增大,三种不同直径的颗粒的表面-中心温差变化曲线都表现出相似的趋势。对于不同材料的颗粒,热导率越低的颗粒,其表面-中心温差越高,越难以完全熔化。结论喷距、颗粒直径与颗粒材料对颗粒加热状况和内部温度梯度有很大的影响,该模拟结果能为分析颗粒与等离子体之间的传热提供参考。     

低压条件下的等离子射流特性分析

低压等离子喷涂由于具有特殊的射流特性,以及可以沉积组织均匀的特殊结构涂层而备受关注.涂层的形成受到等离子射流特性的影响,比如焓值、温度、速度等.研究中利用热焓探针技术在环境压力为3 kPa的条件下,测量了Ar-H₂等离子体不同轴向位置射流中心的焓值和压力,并且进一步计算了射流的温度和速度,以及表征等离子体对粉体加热能力的努森数.结果表明,等离子射流在距离喷嘴出口12.5 mm处的温度为11 000 K;400 mm处降为7 000 K;等离子射流速度在喷嘴出口处25 mm左右达到最大值,约为2 000 m/s;喷嘴外部等离子射流的努森数处于过渡区,对粉体的加热能力较低.     

Diagnostics and modeling of an argon/helium plasma spray process

The natural instability of the are in direct current (DC) plasma torches used in spray processing is one of the most important causes for variations in heating of sprayed particles, leading to inconsistencies in the final coating quality. A relatively simple diagnostic system has been set up to monitor the plasma jet instability, as well as some important process characteristics. Effects of the operating parameters and the anode condition on properties of plasma jets, particle properties, and coatings have been measured. These results show that the inconsistency caused by the jet instability influences the plasma spray process in several ways. The coating porosity and the deposition efficiency can be correlated to an average jet length obtained from a series of high speed images. Selected frequency peaks in the power spectrum of the acoustic signal are correlated with the average jet length, and these results are used to derive a simple control scheme, which adopts a fuzzy look-up model indicating the condition of the anode. Increasing the are current is the most effective way to counteract the negative effects of anode erosion.     

Effect of plasma spray operating conditions on plasma jet characteristics and coating properties

Using statistical design of experiments, the arc current, total gas flow rate, percent secondary gas (He), and powder feed rate have been varied to assess the torch behavior and establish its correlation to coating properties. The torch response includes arc voltage drop, torch efficiency, and plasma jet geometry. High-speed images of the luminous plasma jet for each operating condition have been acquired with a LaserStrobeℳ videocamera, and image analysis has been used to quantify the jet length and jet fluctuations as additional torch responses. Porosity and unmelted particles, which are determined using image analysis of a micrograph of a NiAl coating cross section, were selected as principal coating characteristics. These findings are expected to be useful for optimization of new spray processes and for evaluation of new torch designs.     

Behavior of Ni-Al particles in argon: Helium plasma jets

To better understand the plasma spray coating process, an experimental study of the interaction between a subsonic thermal plasma jet and injected nickel- aluminum particles was performed. The velocity, temperature, and composition of the argon/helium gas flow field was mapped using an enthalpy probe/mass spectrometer system. The sprayed particle flow field was examined by simultaneously measuring the size, velocity, and temperature of individual particles. Particle and gas temperatures were compared at the nominal substrate stand- off distance and axially along the median particle trajectory. Temperature and velocity differences between the particle and the gas surrounding it are shown to vary substantially depending on the trajectory of the particles. On the median trajectory, the average particle is transferring heat and momentum back to the plasma by the time it reaches the substrate. Because the exchange of heat and momentum is highly dependent on the particle residence time in the core of the plasma, the condition of particles at the substrate can be optimized by controlling the particle trajectory through the plasma.