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.     

等离子熔射制模过程中工艺参数的实验研究

开展了等离子熔射制模过程中主要工艺参数对熔射层质量影响规律的实验研究。通过改变等离子熔射过程中的工艺参数，得出熔射功率：熔射扫描间距和熔射扫描速度等主要工艺参数对等离子熔射层残余应力、孔隙率的影响规律，从而为建立合理的等离子熔射制模工艺提供了依据。     

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.     

等离子熔射成形法制造陶瓷零件基础研究

提出用等离子熔射成形法制造陶瓷零件的设想，论述该成形方法的基本原理与步骤。以Al2O3·TiO2粉末为例．用实验证实上述设想可行性．并讨论与之相关的问题.     

基于等离子熔射成形的快速制模实验研究

研究了等离子喷涂法快速制作具有复杂、精密图案的模具型腔的新工艺 ,获得了满意的实验结果 ,分析了制作过程中的主要影响因素。     

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.     

铁基合金粉末等离子熔射成形制件的氧化处理

针对铁基合金粉末等离子熔射成形制件表面耐腐蚀性差的问题,结合其成分及微观结构的特点,着重研究了该类零件的氧化处理工艺,并讨论了相关问题。     

基于多层ANN的机器人等离子熔射智能化模型

分析了机器人等离子熔射过程的神经网络模型的实现方法,基于多层人工神经网络(antificial neural network,ANN)建立了等离子熔射过程的智能化模型.基于该模型,系统研究了等离子弧电流、熔射距离、机器人扫描间距和速度对主要涂层性能参数-残余应力和孔隙率的影响规律,并通过试验数据库的学习对涂层性能参数进行预测.结果表明,模型预测结果与试验结果有着很好的吻合,解决了工艺试验结果中仅有离散数据且难以全面反映等离子熔射工艺参数一涂层性能之间复杂非线性关系的难题.

Abstract：

The implementation of multi-layer artificial neural networks (ANNs) in robotic plasma spraying was discussed and an intelligent process model was constructed to fully describe the relationships between process parameters and coating properties. Influences of plasma arc current, spray distance, robot scanning space and scanning velocity on coating properties, i.e. residual stress and porosity, were systematically studied based on the present model. Prediction can be effectively carried out after the learning of the experimental database. Theoretical analysis shows the prediction results agree well with the experiments. It is favorable to fully investigate the complex and nonlinear relationships between processing parameters and coating properties as well as to overcome the limited information indicated by the discrete variable in the processing results.     

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。     

等离子熔射快速制造摩托车护罩覆盖件硬模的研究

概述了快速制模技术的几种应用形式，介绍了等离子熔射快速制造金属硬模具的工艺方法，并试制了摩托车护罩覆盖件模具进行注射试验。试验结果表明，该方法制作的模具具有表面硬度高、质量好、工艺简单等特点，适用于汽车、摩托车行业的模具快速制造及新产品试制。     

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.     

On the reproducibility of air plasma spray process and control of particle state

Controlling particle state is important to not only achieve the required microstructure and properties in coatings but also to clearly isolate and understand the role of other clusters of variables (such as the various substrate and deposition conditions) on the aforementioned attributes. This is important to design coatings for high performance applications and in the ongoing efforts toward achieving prime reliance. This study examines the variability in particle state and explores a few strategies to control them for improved reproducibility with the aid of in-flight particle and plume sensors. The particle state can be controlled by controlling the torch parameters or by directly controlling the particle state itself via feedback from particle and plume sensors such as DPV 2000 (Tecnar Automation Ltd, Quebec, Canada) and torch diagnostic system-spray plume trajectory sensor (TDS-SPT) (Inflight Ltd, Idaho Falls, ID). There exist at least a few control protocols to control the particle state (predominantly temperature and velocity) with judicious choice of critical parameters. In the present case particle state has been controlled by varying the critical torch parameters (primary gas flow and arc current) in a narrow range using 8% YSZ of angular morphology (fused and crushed) with 10–75 μm size distributions in conjunction with a N₂-H₂ laminar (nonswirl) plasma. Two important results emerge: (a) The particle state resulting from averaged individual particle measurements (DPV 2000) is surprisingly stable with variability in T<1% and variability in V of <4%. Ensemble approaches yield a somewhat higher variability (5% in temperature). Despite this the variability in basic coating attributes such as a thickness and weight is surprisingly large. (b) Applying a much simpler control strategy to only control the particle injection and hence the particle trajectory results in reduced variability in coating attributes. 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.     

New developments in cold spray based on higher gas and particle temperatures

In cold spraying, bonding is associated with shear instabilities caused by high strain rate deformation during the impact. It is well known that bonding occurs when the impact velocity of an impacting particle exceeds a critical value. This critical velocity depends not only on the type of spray material, but also on the powder quality, the particle size, and the particle impact temperature. Up to now, optimization of cold spraying mainly focused on increasing the particle velocity. The new approach presented in this contribution demonstrates capabilities to reduce critical velocities by well-tuned powder sizes and particle impact temperatures. A newly designed temperature control unit was implemented to a conventional cold spray system and various spray experiments with different powder size cuts were performed to verify results from calculations. Microstructures and mechanical strength of coatings demonstrate that the coating quality can be significantly improved by using well-tuned powder sizes and higher process gas temperatures. The presented optimization strategy, using copper as an example, can be transferred to a variety of spray materials and thus, should boost the development of the cold spray technology with respect to the coating quality. 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.     

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.     

The characteristics of a low-power-consumption plasma jet and ceramic coatings

The effects of the composition of plasma gases (Ar-N₂, Ar-H₂), arc current, and voltage on the temperature and velocity of a low-power (5 kW) plasma torch in the arc field free region has been investigated using an enthalpy probe. Coatings of Al₂O₃-13TiO₂ were deposited under different conditions. The results show that in the Ar-N₂ plasma, the enthalpy, temperature, and velocity change little with arc current and voltage when regulating the nitrogen proportion in the plasma gas. The hardness of the resulting coatings is 800 to 900 kg/mm² HV.300. For Ar-H₂ plasma, however, increases in the H₂ content in the mixture of the gases remarkably enhanced the velocity and heat transfer ability of the plasma jet, with the result that the coatings showed high hardness up to 1200 HV.     

Effect of particle morphology on flow characteristics of a composite plasma spray powder

The effects of BaF₂-CaF₂ particle morphology on National Aeronautics and Space Administration (NASA) PS304 feedstock powder flowability were investigated, BaF₂-CaF₂ eutectic powders were fabricated by comminution (producing an angular morphology) and by gas atomization (producing a spherical morphology). The fluoride powders were added incrementally to the other powder constituents of the NASA PS304 feedstock, (Ni-Cr, Cr₂O₃, and Ag powders). A linear relationship between flow time and concentration of the BaF₂-CaF₂ powder was found. The flow of the powder blend with spherical BaF₂-CaF₂ was better than that with angular BaF₂-CaF₂. The flowability of the powder blend with angular fluorides decreased linearly with increasing fluoride concentration. However, the flow of the powder blend with spherical fluorides was independent of fluoride concentration. The results suggest that for this material blend, particle morphology plays a significant role in flow behavior, offering potential methods to improve powder flowability and enhance the commercial potential. These findings may be applicable to other difficult-to-flow powders such as cohesive ceramics.     

Calibration of a two-color imaging pyrometer and its use for particle measurements in controlled air plasma spray experiments

Advances in digital imaging technology have enabled the development of sensors that can measure the temperature and velocity of individual thermal spray particles over a large volume of the spray plume simultaneously using imaging pyrometry (IP) and particle streak velocimetry (PSV). This paper describes calibration, uncertainty analysis, and particle measurements with a commercial IP-PSV particle sensor designed for measuring particles in an air plasma spray (APS) process. Yttria-stabilized zirconia (YSZ) and molybdenum powders were sprayed in the experiments. An energy balance model of the spray torch was used to manipulate the average particle velocity and temperature in desired ways to test the response of the sensor to changes in the spray characteristics. Time-resolved particle data were obtained by averaging particle streaks in each successive image acquired by the sensor. Frame average particle velocity and temperature were found to fluctuate by 10% during 6 s acquisition periods. These fluctuations, caused by some combination of arc instability, turbulence, and unsteady powder feeding, contribute substantially to the overall particle variability in the spray plume.     

喷涂工艺参数对硅灰石涂层结构的影响

采用等离子喷涂方法,在不同喷涂距离、主气流量和喷涂功率下制备硅灰石涂层.使用扫描电镜观察了涂层的微观形貌,研究了喷涂工艺参数对涂层结构的影响.结果表明,在较大主气流量下,随着喷涂距离增加,涂层粒子扁平化程度降低,涂层内孔隙逐渐增多;在较小主气流量下,涂层粒子扁平化程度随喷涂距离增加呈现先增加后减小的趋势.主气流量增加,涂层致密,粒子扁平充分.喷涂功率增加,粒子熔化好,涂层致密;但随喷涂功率进一步增加,涂层中出现较多的圆形孔隙.喷涂工艺参数对涂层结构的影响主要通过影响熔融粒子的温度和速度所致.     

Computational study and experimental comparison of the in-flight particle behavior for an external injection plasma spray process

A three-dimensional computational fluid dynamic (CFD) analysis using Fluent V5.4 was conducted on the in-flight particle behavior during the plasma spraying process with external injection. The spray process was modeled as a steady jet issuing from the torch nozzle via the heating of the are gas by an electric are within the nozzle. The stochastic discrete model was used for the particle distribution. The particle temperature, velocity, and size inside the plasma plume at a specified standoff distance have been investigated. The results show that carrier gas flow rate variation from 2 standard liters per minute (slm) to 4.0 slm can increase the centerline particle mean temperature and mean velocity by 10% and 16%, respectively, at the specified standoff distance. A further increase of the carrier gas flow rate to 6 slm did not change the particle temperature, but the particle velocity was decreased by 20%. It was also found that an increase in the total arc gas flow rate from 52 slm to 61 slm, with all other process parameters unchanged, resulted in a 17% higher particle velocity, but 6% lower particle temperature. Some of these computational findings were experimentally confirmed by Kucuk et al. For a given process parameter setting, the kinetic and thermal energy extracted by the particles reached a maximum for carrier gas flow rate of about 3.5–4.0 slm.     

等离子喷涂过程中粒子的氧化及其对涂层性能的影响

利用粒子收集装置和附加氩气保护罩,研究了铁粒子和NiCoCrAlY粒子在等离子喷涂过程中的氧化行为及其对涂层性能的影响.结果表明,粒子在飞行过程中存在对流氧化和扩散氧化两种氧化机制,粒子的氧化方式取决于离开喷嘴的距离;离开喷嘴距离越长,粒子氧化越严重;采用附加氩气保护罩能明显减少喷涂过程中外界空气对粒子的氧化,降低涂层孔隙率,提高NiCoCrAlY涂层的抗高温氧化性能.

Abstract：

The oxidation mechanisms of iron particles and NiCoCrAlY particles during plasma spraying process and its effect on the sprayed coatings were investigated by the in-flight particles collection setup and the gas shrouding. The results show that there are two oxidation mechanisms during in-flight oxidation: one is the diffusion oxidation; the other is the convective oxidation, which are decided by the distance from the spraying particles to the nozzle. The oxidation content increases with the increasing of the standoff distance. The shrouded gas can decrease the oxidation content of inflight particles and increase the oxidation resistance of NiCoCrAIY coatings.