热喷涂过程中压强对粒子扁平化的影响

为了了解热喷涂过程中压强对粒子扁平固化过程的作用,利用减压等离子喷涂装置.在不锈钢SUS304基材表面喷涂了Ni、Cu以及Al粉末,用光学显微镜和扫猫电镜对沉积物的正面、底面以及断面形态进行了观察.结果显示,压强影响等离子焰的长度,从而影响到粒子的熔化状态,同时还影响到基材表面吸附物质的吸附量:熔点低的粒子在与基材碰撞后能较长时间维持在液态,易于在基材表面铺展,因而低压条件下更易于形成盘状沉积.     

热喷涂NiCoCrAlYTa+7YSZ热障涂层颗粒沉积行为

分别采用低压等离子喷涂和大气等离子喷涂在K4169基体上收集了NiCoCrAlYTa颗粒沉积物及涂层,并对颗粒沉积物的形貌及涂层性能进行了观察分析。结果表明:低压等离子喷涂收集到的单个NiCoCrAlYTa扁平颗粒主要呈圆盘状,涂层致密且氧含量低。而大气等离子喷涂收集到的扁平颗粒主要呈溅射状,涂层孔隙率和氧含量均较高。又在经镜面抛光的NiCoCrAlYTa涂层和K4169基体上分别收集了7YSZ颗粒沉积物,并对其沉积形貌进行了观察分析,结果表明:在K4169基体上收集到的7YSZ颗粒沉积物主要呈圆盘状,表面存在大量的网状微裂纹及宏观环状贯通裂纹。在镜面抛光的NiCoCrAlYTa涂层表面收集的7YSZ颗粒沉积物,周围有少量的指状溅射物,中心部存在一定数量的网状微裂纹,但宏观环状裂纹消失。     

热喷涂镍粉在SUS304及A6063基体上的沉积行为

为阐明基体材料对单个颗粒沉积行为的影响,采用大气等离子喷涂技术将镍粉喷涂到镜面研磨后的不锈钢SUS304及铝合金A6063基体上,并通过扫描电子显微镜及聚焦离子束等技术观察在基体上收集的沉积物正面及截面形貌。结果表明:Ni在SUS304基体上呈明显的溅射沉积,单个沉积物的中心部位与周围溅射物相分离,沉积物底部及内部均可见明显气孔,溅射可能是由基体表面的吸附质在熔滴在基体表面铺展过程中脱附所导致。同时,Ni粉在A6063基体上呈现花朵状溅射,中心部位有明显的分层现象,这可能与基体材料的热导率、熔点以及基体表面吸附质的脱附等因素密切相关。     

Study of Substrate Preheating on Flattening Behavior of Thermal-Sprayed Copper Particles

In this study, the effect of substrate preheating on flattening behavior of thermal-sprayed particles was systematically investigated. A part of mirror-polished AISI304 substrates were preheated to 573 and 773 K for 10 min, and then exposed to an air atmosphere for different durations of up to 48 h, respectively. Contact angle of water droplet was measured on the substrate under designated conditions. It was found that the contact angle increased gradually with the increase of substrate duration after preheating. Moreover, smaller contact angle was maintained on the substrate with higher preheating temperature. Commercially available Cu powders were thermally sprayed onto the substrates with the same thermal treatment history as contact angle measurement using atmospheric plasma-spray technique. The splat shape had a transitional changing tendency from a splash splat to a disk one on the substrate with a short duration after preheating, while reappearance of splash splat with the increase of duration was confirmed. In general, wetting of substrate surface by molten particles may dominate the flattening behavior of thermal-sprayed particles. The occurrence of desorption of adsorbed gas/condensation caused by substrate preheating likely provides good wetting. On the other hand, the poor wetting may be attributed to the re-adsorption of gas/condensation on the substrate surface with the increase of duration. In addition, the shear adhesion strength of coating fabricated on blasted AISI304 substrate was enhanced on the once-heated substrate, but weakened with the increase of duration. The changing tendency of the coating adhesion strength and the wetting of substrate by droplet corresponded quite well with each other.     

7075铝合金表面HVOF喷涂WC-12Co颗粒的沉积行为（英文）

在抛光的7075铝基体上采用HVOF（超音速火焰喷涂）沉积了WC-12Co颗粒,用SEM、EDS和纳米压痕硬度仪对沉积物的显微组织、成分和硬度进行了分析。研究了未融颗粒、未完全熔融颗粒和熔融颗粒这3种不同熔融状态下6种颗粒的沉积行为,发现不同类型的颗粒均对基体有冲击,使其发生变形或有一定的撕裂。未熔融颗粒沉积时,高速冲击铝基体使其发生挤压变形,颗粒反弹后,基体遗留挤压坑。除了反弹的未熔融颗粒,未完全熔融颗粒和熔融颗粒的沉积物与原始粉末相比,沉积物的表面形貌和横截面形貌与原始粉末不同,沉积物表面有一定的熔化特征,这是颗粒在HVOF焰流中受热温度较高使其有一定的熔融;高温高速的颗粒冲撞基体后,沉积物横截面更为致密,它们与基体之间存在冶金结合,形成了一个互熔区,表明沉积物撞击基体时温度高于铝的熔点,将铝融化并挤压进颗粒中。颗粒沉积后,在基体表面上形成一层厚度约为5μm的硬化层,该层的硬度呈梯度变化,近表面处硬度为3420 MPa,是基体（2200 MPa）硬度的1.56倍。硬度的增加源于两个因素：高温高速颗粒的喷丸作用,及颗粒挤压基体塑形变形的加工硬化。     

Effect of Oxidation Behavior on the Mechanical and Thermal Properties of Plasma Sprayed Tungsten Coatings

Tungsten (W) coatings have been prepared via air (APS) and vacuum plasma spraying (VPS) technologies, respectively. The microstructures and chemical compositions of the coatings were comparatively studied; meanwhile, the mechanical and thermal properties were evaluated. The results obtained showed that oxide content in the VPS-W coating was apparently lower than that of the APS-W coating because of the different surrounding atmosphere, which influenced the mechanical and thermal properties of the coatings directly. Similar microstructures were observed for the VPS-W and the APS-W coating, but the VPS-W coating was much denser. The bonding strength of the VPS-W coating was much higher than that of the APS-W coating. Thermal conductivity of the VPS-W coating was 59.3 W/m · K at room temperature while the APS-W coating was 32.2 W/m  K. Thermal loading experiments of electron beam showed that the VPS-W coating could withstand the heat load of 10.75 MW/m², while the APS-W coating formed serious cracks on its surface at the load of 7.5 MW/m².     

基于SPH的超音速火焰喷涂WC-12Co粒子速度对其沉积行为的影响

目的 以超音速火焰喷涂过程为基础,探究粒子撞击速度对粒子在基体上沉积行为的影响。方法 应用SPH方法,模拟分析WC-12Co粒子速度在400～800 m/s内,单个粒子在相同基体上的沉积行为。结果 粒子撞击速度与粒子扁平率、粒子基体结合面积、结合方式等有密切关系。随着粒子撞击速度的增加,基坑深度持续增大至最小深度的4.6倍,金属射流对提高粒子扁平化程度及粒子与基体的有效结合面积起到促进作用,总接触面积最大可达到原有效接触面积的2.7倍。撞击速度的提升使得有效塑性应变及应变区域增加,形变区域增大。同时,结合面温升总体增加,增强了粒子与基体的结合条件。沉积过程存在能量耗散,初始能量的提高有利于粒子与基体总能量的增加,强化了压实效应,进一步促进粒子与基体的结合。结论 在数值模拟选取的范围内,超音速火焰喷涂WC-12Co粒子的撞击速度越高,粒子与基体的结合状态越好。     

冷喷涂粒子碰撞行为三维有限元热力耦合分析

冷喷涂粒子的碰撞变形行为对粒子的沉积起着重要的作用.采用ABAQUS/Explicit显式有限元分析软件对冷喷涂过程中粒子碰撞行为进行了三维数值模拟.通过引入材料的失效模型,获得了与文献报道试验结果相吻合的计算结果.计算结果表明,随着粒子速度增加,粒子变形程度增加,基体坑深增加.粒子大小对其碰撞变形形貌影响不大,不同尺寸粒子的变形具有相似性.     

HVOF喷涂WC-12Co粒子在不同基体上的沉积行为

采用超音速火焰喷涂方法(HVOF)在铝合金、紫铜和不锈钢基体上制备WC-12Co扁平粒子,利用扫描电子显微镜(SEM)对半熔化两相粒子的扁平行为及与基体结合状况进行观察分析,并将半熔化WC-Co粒子与基体碰撞模型简化为液相的Co粒子和固相的WC颗粒分别与基体相互作用的过程,通过改进后的数学模型计算基体与粒子的相对形变比λ。结果表明:HVOF喷涂WC-12Co扁平粒子在铝、铜和不锈钢基体上分别呈现半球状、薄饼状和溅射状形貌,不同形貌的扁平粒子形变比λ不同。与半球状(λ1)和溅射状(λ1)扁平形式相比,形成薄饼状(λ≈1)的扁平粒子时粒子与基体均发生适度的变形,有助于增加粒子与基体的有效结合面积,提高结合强度。     

热处理对微束等离子喷涂羟基磷灰石涂层的影响

羟基磷灰石由于其良好的生物活性,被广泛的用作医用植入体的表面涂层材料.采用微束等离子喷涂(Microplasma Spraying,MPS)I艺在Ti-6Al-4V基体上制备羟基磷灰石涂层,通过扫描电镜(SEM)、X射线衍射(XRD)和傅里叶红外光谱(FTIR)分析了热处理对涂层相组成和表面形貌的影响规律.研究表明:微束等离子喷涂制备的羟基磷灰石涂层在经过热处理后结晶度提高,并且非晶相和杂质相转化成为HA结晶相.同时,羟基和磷酸根的完整性得到了恢复.过高的热处理温度易引起涂层裂纹等缺陷的增加,也容易造成羟基脱离造成HA分解.合理的热处理温度范围为600～700℃,保温时间为3 h.     

冷喷涂金属颗粒变形行为数值模拟研究进展

理解冷喷涂中的颗粒变形和沉积行为一直是科学工作的焦点。由于颗粒撞击基底后的瞬时变形行为难以通过实验观测,因此多数研究工作聚焦于数值模拟。总结了一些颗粒撞击基底的建模方法,在前人研究的基础上,针对每个模型的原理及优缺点,分析了每个方法的适用场景,给出了改善模型的方法。综述了颗粒特性、入射角度、气体预热温度等对颗粒变形行为的影响,其中粒径大小、颗粒形状等是影响颗粒变形行为的主导因素,因此重点探讨了颗粒特性的影响。颗粒的撞击变形是影响冷喷涂涂层残余应力分布的重要因素,对涂层残余应力的相关数值模拟研究进行了综述,分析了颗粒变形与颗粒残余应力的关系。最后就目前冷喷涂残余应力建模较单一的形势,探讨了如何建立一种新模型以分析涂层残余应力。     

Effect of Thermally Softened Bronze Matrix on the Fracturing Behavior of Diamond Particles in Hybrid Sprayed Bronze/Diamond Composite

In our previous study (Na et al., Compos Sci Technol 69:463-468, 2009), optimized thickness of protective nickel film was proposed for smaller diamond feedstock to obtain reduced impact stress and uniform flight behavior of particles during kinetic (or cold) spraying. However, in this study, nickel-coated diamond particles were severely fractured with increasing particle size due to high kinetic energy. Hence, an innovative hybrid spraying technique (a combination of kinetic and thermal spraying) was introduced to embed relatively large diamond particles into the bronze matrix. Size distributions of the diamond particles in the composite coatings were analyzed by scanning electron microscopy, an electron probe micro analyzer, and image analysis methods. In addition, impact behaviors of diamond particles in kinetic and hybrid gas flows were simulated through finite element analysis (ABAQUS/Explicit 6.7-2). Diamond fracturing was significantly minimized by the reduced impact energy afforded by the thermally softened bronze matrix through hybrid spraying.     

Effect of the Shape Factor on the Cold-Spraying Dynamic Characteristics of Sprayed Particles

Silicon powder was chosen to be deposited by cold spraying for the consideration of possible applications in lithium ion batteries. The influence of the silicon particle shapes other than spherical on the impact velocity and temperature for different working parameters of the gas streams have been numerically investigated by using computational fluid dynamics modeling. The results show that, for same equivalent diameter, the particle impact velocities increase to a maximum velocity when the shape factor increases to a certain value and then decreases to the impact velocity of spherical particles. In the cold-spraying process, the particle velocity profile for smaller shape factors is much closer to that of the gas stream due to the larger particle surface area. Furthermore, the particle impact velocity increment for smaller shape factors is much more remarkable with a higher main propulsion gas temperature and higher carrier gas pressure. The effect of raising the main propulsion gas pressure on the impact velocity of the particles with very smaller shape factors is negligible. The particle impact velocity and temperature can be altered by not only the change of the working parameters of the gas steams but also the change of the sizes and shapes of the sprayed particles.     

激光合金化掺杂TiC对等离子喷涂8YSZ热障涂层热腐蚀行为的影响*

传统的等离子喷涂热障涂层在高温环境下服役易受熔融腐蚀盐渗透而过早剥落失效,研究激光合金化掺杂自愈合材料 TiC 对热障涂层热腐蚀行为的影响具有重要意义。采用大气等离子喷涂技术（Atmospheric plasma spray,APS）在 Inconel 718 镍基高温合金表面制备 NiCrAlY 粘结层,采用大气等离子喷涂技术在 NiCrAlY 粘结层上制备 8 wt.%氧化钇部分稳定的氧化锆（8 wt.% yttria partially stabilized zirconia,8YSZ）陶瓷层,构建典型双层结构热障涂层体系。采用 1 kW 光纤耦合激光器将自愈合材料 TiC 熔于 8YSZ 热障涂表层,并考察其在 900 ℃下 25%NaCl+75%Na₂SO₄混合熔盐中保温 4 h 的热腐蚀行为。结果表明,与等离子喷涂涂层相比,激光合金化改性热障涂层表面更加光滑,分布有网状裂纹,且结构致密。等离子喷涂涂层的热腐蚀产物主要是针状颗粒 Y₂(SO₄)₃ 和 m-ZrO₂,但仅有较少的热腐蚀盐渗透至激光合金化改性热障涂层内部,其热腐蚀产物为 Y₂(SO₄)₃ 和少量的 TiO₂。激光合金化改性热障涂层的抗热腐蚀性能较等离子喷涂态热障涂层提升 55.5%,一方面激光合金化改性层组织致密,可阻止热腐蚀盐渗透至涂层内部,另一方面,激光合金化改性热障涂层表面粗糙度更低,能减少与热腐蚀盐的接触面积。此外,自愈合材料 TiC 在高温下发生氧化反应引起体积膨胀,实现裂纹的部分自愈合效应,进一步阻止了热腐蚀反应的发生。采用激光表面改性技术将自愈合材料 TiC 引入热障涂层,激光合金化改性热障涂层不仅具有光滑的表面形貌,还具有致密的微观组织结构;同时自愈合材料 TiC 在高温环境下的裂纹自愈合效应有助于抑制热腐蚀盐的渗透, 最终提高热障涂层的抗热腐蚀性能。     

等离子喷涂热障涂层高温风洞热震行为

采用等离子喷涂工艺制备ZrO2-8%Y2O3(质量分数,下同)陶瓷层,冷喷涂制备CoNiCrAlY粘结层,在高温燃气风洞条件下测试热障涂层的热震性能,并研究了高温氧化处理对试样热震性能的影响.结果表明,等离子喷涂热障涂层具有较好的抗热震性能,经过100次热震循环后,涂层与基体结合良好,涂层较为完整,未出现大面积的剥落;经过氧化处理后的试样抗热震性较差.     

Non-Linear Mechanical Behavior of Plasma Sprayed Alumina Under Mechanical and Thermal Loading

Mechanical response of plasma sprayed ceramic coatings to mechanical and thermal loading of various extents was studied. Coated samples were subjected to four-point bending (4PB), with coatings loaded in tension and compression, respectively. Thermal loading was provided by heating the samples, while stresses were generated by thermal mismatch between the coatings and substrates. In both cases, cyclic loading was applied. Non-linear behavior and significant hysteresis were observed, indicating inelastic phenomena taking place. The tests were complemented by structural observations in SEM and indentation tests. Relevant structural features and possible mechanisms underlying this behavior are discussed.     

送粉位置对等离子喷涂YSZ粒子熔化状态的影响

研究了等离子喷枪采用3个送粉位置时距离喷嘴90mm处YSZ粒子的熔化状态(包括粒子温度及速度、粒子粒度分布、粒子撞击基体后的扁平形貌),其中送粉位置1和2为枪外送粉,送粉孔轴线距离喷嘴端面分别为9mm和3.5mm,送粉位置3为枪内送粉,送粉孔轴线距离喷嘴端面5mm。结果表明,送粉位置沿等离子射流逆流方向移动时(分别对应送粉位置1、2和3),粒子熔化效果明显增强,粒子扁平化程度提高;涂层中未熔颗粒和孔隙百分比由33.25%减小至10.13%,涂层结合强度由16.25MPa增加至37.25MPa,涂层表面剥落20%时经历的热震次数由35次增加至130次;采用送粉位置3时,喷涂功率33.60kW,低于其他送粉位置的电弧功率(46.75kW),实现了低功率制备高性能YSZ涂层。     

超音速火焰喷涂CoCrW涂层热震过程中的裂纹扩展行为

为研究CoCrW涂层的抗冷热冲击性能,采用JP5000型超音速火焰喷涂设备在高温合金表面制备了该涂层,分析了裂纹在热震过程中的扩展行为。结果表明,在800 ℃保温,25 ℃水淬的热循环条件下,经过40次热震后,涂层表面均匀地分布着网状裂纹,截面上存在垂直裂纹,但未出现涂层脱落现象;在裂纹与基体、涂层界面交汇处生成了弥散分布的以Al2O3为主要成分的氧化物。分析认为,热应力和组织应力是裂纹产生和扩展的主要驱动力,但裂纹吸收了热震过程中产生的能量,避免了应力集中,有利于提高涂层的抗热震性能。界面处弥散分布的氧化物降低了涂层与基体的结合强度,热震试验最终的失效形式可能是界面处涂层的剥离。     

碰撞对喷涂陶瓷涂层粒子的影响

通过Ti-B4C-C喷涂体系的自蔓延反应火焰喷涂TiC-TiB2复相陶瓷涂层试验,研究了喷涂过程中处于自蔓延反应状态的飞行粒子与基体的碰撞行为,分析了飞行粒子的反应中间状态及其与基体碰撞变形形态,揭示了碰撞造成粒子自蔓延反应终止的本质原因.结果表明,飞行粒子的自蔓延反应是由表向内进行的,碰撞极大地影响飞行粒子的自蔓延反应进程,由于碰撞压缩弹性波作用、接触物理介质突变和热传导快速凝固等三方面作用导致飞行粒子的自蔓延反应终止.     

粒子扁平现象研究现状及发展

热喷涂过程中熔滴在与基材撞击后的扁平及固化行为是形成涂层过程中的一个基本现象,因此,关于单个粒子扁平化行为的研究不可或缺.从等离子喷涂过程中基材预热温度、喷涂压强环境、材料润湿能力、基材的表面粗糙度、固化能力、脱附吸附能力等因素对粒子扁平化转变的影响,以及研究过程中自由下落试验和数值模拟方法的应用,概述了关于粒子扁平现象的研究现状.指出了未来关于粒子扁平化研究的发展趋势在于结合数值模拟和喷涂试验,以期找出粒子扁平化的控制因素.并解释了基材在较高的预热温度和低压条件下,盘状沉积为何更容易出现.