HVOF喷涂WC-12Co粒子沉积行为分析

目的 研究不同超音速火焰喷涂条件下WC-12Co粒子在45^#碳钢基体上的沉积变形行为。方法 基于Johnson-Cook塑性材料模型与Thermal-Isotropy-Phase-Change热材料模型，采用LS-DYNA进行建模分析。结果 不同喷涂参数下，WC-12Co粒子在45^#碳钢基体上的沉积行为存在明显差异。沉积过程中，粒子等效塑性应变幅度高于基体;粒子边缘位置等效塑性应变幅度高于粒子中心轴线位置;粒子初始速度与初始温度的增加有助于提升结合界面温度与粒子扁平化程度;粒子初始温度与粒子初始速度对接触界面能量变化影响程度基本一致，单位粒子初始速度与温度提升的能量贡献比 分别为0.78以及0.76，二者的能量贡献比近似相同;适度的基体预热( =500 K)可以促进粒子变形，加深沉积坑深度，增大粒子与基体的结合面积，有助于提升粒子与基体之间的结合强度。基体过冷( =300 K)将导致粒子“翘曲”，降低粒子与基体之间的结合面积，基体过热( =600 K)将导致二者结合处于不稳定状态，易引起粒子剥落，二者均不利于粒子与基体的有效结合。结论 一定范围内提升粒子初始速度、温度与基体初始温度，可以提高粒子扁平化程度，增大粒子与基体结合面积，提升粒子与基体的结合性能，进一步提高涂层质量。     

基体表面粗糙度对冷喷涂Ti6Al4V界面结合的数值模拟∗

在冷喷涂过程中,基体的表面粗糙度会影响涂层和基体之间的结合,目前对该问题关注还不够,且存在一定争议。以冷喷涂修复 Ti6Al4V 钛合金(TC4)过程为研究对象,利用有限元模拟手段,建立二维和三维单粒子在不同表面粗糙度基体上的撞击模型。通过分析粒子在撞击到光滑表面、研磨表面和喷砂表面三种情况下界面的温度、等效塑性应变及系统能量的变化,得出以下结论：随着基体表面粗糙度的增加,粒子的等效塑性应变和扁平率逐渐减小。界面温度和等效塑性应变在基体“波峰”处较高,在“波谷”处较低,在高的表面粗糙度下,粒子的塑性变形减弱,反弹趋势增强。研究结果表明,对冷喷涂 TC4 修复过程而言,基体的粗糙化不利于涂层与基体的结合。研究结果可为冷喷涂修复钛合金过程中基体预处理方式的选择提供理论指导。     

Fe粒子参数对低温超音速火焰喷涂层构建的影响

应用LS-DYNA大应变有限元耦合算法,研究了低温超音速火焰喷涂Fe粒子参数对喷涂层构建的影响.结果表明,随着粒子温度或者速度的升高,粒子所含内能的增加,使得涂层界面温度不断升高,粒子的沉积塑性应变发生变化.粒子在不同基体上的沉积特征表明基体硬度将影响沉积粒子与基体界面的结合状态.随着涂层的构成,后续粒子对已沉积粒子的高速撞击使得先沉积的粒子产生二次塑性变形,并引发温变.先沉积的粒子塑性变形引起的粗化作用将降低后续粒子沉积的临界速度.这些将导致涂层在拉应力作用下发生脆性断裂.     

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。     

基于稳定最大应变的冷喷涂粒子临界速度预测

利用ABAQUS显式有限元分析软件,对冷喷涂铜粒子与铜基体的碰撞过程进行了欧拉法数值分析.结果表明,欧拉模型可有效模拟冷喷涂粒子碰撞变形行为,粒子撞击基体形貌的模拟结果与试验观察吻合较好.在不同碰撞速度下,最大等效塑性应变均会快速上升并达到各自稳定值,并且在290～400 m/s内稳定等效应变最大值基本不变,但随着粒子速度增加,粒子扁平化程度、与基体结合面积与金属射流量均明显增加.最后,结合金属射流形貌与等效塑性应变稳定最大值的变化规律,提出了一种冷喷涂粒子临界速度预测的新方法,计算获得了20 μm铜粒子冷喷涂临界速度约为290m/s.     

基体表面粗糙度对冷喷涂粒子沉积过程影响的物质点法数值分析

目的 解决有限元法模拟冷喷涂粒子沉积过程时存在的网格畸变等问题,并探讨粒子和粗糙基板的结合方式。方法 基于物质点法建立冷喷涂粒子沉积的仿真模型。利用FORTRAN语言自编程序对铜粒子冷喷涂铜基板的过程进行仿真分析,并与其他研究中的试验结果进行对照,结果吻合较好,表明物质点法模拟冷喷涂粒子沉积问题是可行且有效的。此外,分析基体表面粗糙度对粒子沉积过程的影响规律,并探讨粒子在不同位置沉积的结合机理。结果 随着表面粗糙度的增大,粒子扁平化趋势增大,回弹动能减小。表面粗糙度足够大时,粒子射流可能和基板形成机械咬合结构;粒子在波谷处沉积时受两侧波峰作用难以扁平化,但是凹坑深度增大,回弹动能减小,粒子基板结合强度增大;粒子在左侧半腰处沉积时,其在切向速度分量作用下与右侧波峰形成二次接触,形成了较长的射流。结论 粒子与基板的结合强度随着表面粗糙度的增大而增大。粒子在波峰处可以形成机械咬合结构;在波谷处凹坑深度增大、回弹动能减小,起填充作用;在半腰处能够与右侧波峰产生二次接触,增大结合强度。研究结果可为冷喷涂工艺生产提供一定指导。     

低温超音速喷涂团聚铁粒子沉积的SPH模拟

为了研究纳米团聚粒子形态对涂层特性的影响,应用SPH方法研究了低温超音速火焰喷涂金属团聚粒子的沉积行为.结果表明,纳米粒子团聚为微米级粒子后,基体碰撞出现了飞溅现象,应变变化明显.团聚粒子的等效塑性应变小于普通微米粒子,但团聚粒子的面积扩大比大于普通微米粒子.沉积过程中,当超过临界沉积速度后,金属团聚粒子与基体之间存在过渡区域,过渡区域随粒子速度的增加而扩大.     

高速旋转丝变形表面纳米化

采用高速旋转丝变形工艺对低碳钢表面进行塑性变形,以实现材料的表面纳米化.用光学显微镜、x射线衍射、扫描电子显微镜、透射电子显微镜、显微硬度计和表面粗糙度测量仪等研究塑性变形处理后样品的显微组织及表面性能变化.结果表明:低碳钢经过高速旋转塑性变形处理后,在表面形成厚度为40μm的塑性变形层,最表面层的晶粒尺寸约为16nm,晶粒尺寸沿深度方向不断增大;表层显微硬度比心部基体硬度提高3倍;但表面粗糙度 Ra 增加到10μm.     

粉末结构对冷喷涂纳米结构WC-Co沉积行为的影响

纳米结构WC-Co具有比常规WC-Co更高的硬度,因此受到了广泛关注.冷喷涂制备纳米结构WC-Co涂层过程中,因粒子温度低于熔点,沉积过程需要依靠WC-Co粒子的塑性变形,然而WC-Co粒子变形能力有限,使得WC-Co涂层难以实现有效沉积.文中从粉末结构角度出发,选用3种不同孔隙结构的WC-12Co粉末,运用扫描电镜研究不同结构WC-12Co单个粒子在基体上的沉积行为,分析了3种粉末在相同喷涂工艺参数下沉积的涂层的组织结构.研究发现,定点喷涂容易实现,沉积的WC-12Co沉积层组织结构致密,硬度接近块材,为粉末的连续沉积制备涂层提供了可能.涂层的连续沉积需要粉末和基体材料均产生一定的变形,具有一定孔隙结构的纳米结构WC-Co粉末,因其多孔结构促进了粉末拟变形的发生,适合于冷喷涂制备纳米结构WC-Co涂层.     

低表面粗糙度金刚石涂层刀具的制备

降低表面粗糙度是改善金刚石涂层刀具使用性能的有效手段.采用微波等离子体化学气相沉积(MPCVD)金刚石膜,通过在沉积过程中调整工艺参数,先后在硬质合金基体上沉积了2层不同的金刚石薄膜.研究了基体位置、甲烷浓度等对薄膜表面形貌的影响.用扫描电子显微镜(SEM)、原子力显微镜(AFM)和压痕法对样品进行了分析测试,结果表明,该方法在保证金刚石涂层质量的同时有效降低了薄膜表面的粗糙度,表面粗糙度值Ra＜0.2 μm.     

纳米材料的颗粒尺寸分析方法

介绍了纳米材料颗粒尺寸的定义，对测量纳米颗粒尺寸的常规方法及其特点进行了评述，同时介绍了测量纳米颗粒尺寸的一些新方法。     

Photoluminescence properties and energy-transfer of thermal-stable Ce, Mn-codoped barium strontium lithium silicate red phosphors

A series of thermal-stable Ce³⁺, Mn²⁺-codoped barium strontium lithium silicate (BSLS) phosphors was synthesized by a high-temperature solid-state reaction. The XRD patterns of this phosphor seem to be a new phase that has not been reported before. BSLS:Ce³⁺, Mn²⁺ showed two emission bands under 365 nm excitation: one observed at 421 nm was attributed to Ce³⁺ emission, and the other found in red region was assigned to Mn²⁺ emission through Ce³⁺-Mn²⁺ efficient energy transfer. The Mn²⁺ emission shifted red along with the replacement of barium by strontium, which was due to the change of crystal field. A composition-optimized phosphor, BSLS:0.10Ce³⁺, 0.05Mn²⁺ (Ba = 65), exhibited strong and broad red-emitting and supreme thermal stability. The results suggest that this phosphor is suitable as a red component for NUV LED or high pressure Hg vapor (HPMV) lamp.     

粉末粒度测试方法述评

综述了目前常用的粉末粒度与粒度分布测定方法的原理、特点及适用范围 ,并对粒度测试技术的发展作了展望     

FRACTAL DIMENSION AS MORPHOLOGY AND SIZE PARAMETERS OF FRACTURED PARTICLES OF ROCK

Semi-automatic image analysis system was used for the surface fractal dimension measurement of 15 kinds of rock-fractured particles. The results indicate that the surfaces of the particles that have a size of about 200 mesh are fractal, and that the fractal dimension is in the range of 2.07～2.11. Therefore, some definitions of particle size such as surface diameter, equivalent volumetricly surface diameter are equivocal without giving the step length and the drag diameter, free-fall diameter, and stokes'diameter may be modified by the fractal dimension.     

Effect of plasma fluctuations on in-flight particle parameters

The influence of arc root fluctuations in direct current (DC) plasma spraying on the physical state of the particle jet is investigated by correlating individual in-flight particle temperature and velocity measurements with the instantaneous voltage difference between the electrodes. In-flight diagnostics with the DPV-2000 sensing device involve two-color pyrometry and time-of-flight technique for the determination of temperature and velocity. Synchronization of particle diagnostics with the torch voltage fluctuations are performed using an electronic circuit that generates a pulse when the voltage reaches some specific level; this pulse, which can be shifted by an arbitrary period of time, is used to trigger the acquisition of the pyrometric signals. Contrary to predictions obtained by numerical modeling, time-dependent variations in particle temperature and velocity due to power fluctuations induced by the arc movement can be very large. Periodic variations of the mean particle temperature and velocity, up to ΔT=600 °C and Δv=200 m/s, are recorded in the middle of the particle jet during a voltage cycle. To our knowledge, this is the first time that large time-dependent effects of the arc root fluctuations on the particle state (temperature and velocity) are experimentally demonstrated. Moreover, large fluctuations in the number of detected particles are observed throughout a voltage cycle; very few particles are detected during parts of the cycle. The existence of quiet periods suggests that particles injected at some specific moments in the plasma are not heated sufficiently to be detected.     

Nanocrystallization and photoluminescence of Ce/Dy/Eu-doped fluorosilicate glass ceramics

Ce³⁺-Eu²⁺-Dy³⁺-Eu³⁺-doped fluorosilicate glass ceramics containing orthorhombic CaCeOF₃ nanocrystals were prepared by annealing the precursor glass above 640 °C, along with the reduction of Eu³⁺ → Eu²⁺. Under near ultraviolet excitation, the emission bands of Eu²⁺ or Dy³⁺ were enhanced by several ten or hundred times, owing to energy transfers from Ce³⁺ to Eu²⁺ or Dy³⁺. The glass and glass ceramics emitted warm white light deriving from the blue, yellow and red emission from Eu²⁺, Dy³⁺ and Eu³⁺. Tuning the annealing temperature, the Eu²⁺/Eu³⁺ ratio and the warm white Commission Internationale de I’Eclairage (CIE) coordinates can be adjusted. Thus, the present materials can be applied on warm white high power light-emitting-diodes for indoor illumination application.     

Upconversion luminescence of Yb/Tb/Er-doped fluorosilicate glass ceramics containing SrF2 nanocrystals

Yb³⁺/Tb³⁺/Er³⁺-doped transparent alkaline earth fluorosilicate glass ceramics containing SrF₂ nanocrystals were prepared and their microstructures and spectroscopic properties were investigated. The formation of SrF₂ nanocrystals enriched with Yb³⁺/Tb³⁺/Er³⁺ in the glass ceramics was confirmed by XRD, HRTEM and SAED. The glass ceramics exhibited intense upconversion luminescence behaviors, owing to efficient energy transfers from Yb³⁺ to Er³⁺ and Tb³⁺ and low phonon assistant non-radiative transition probabilities of excited Er³⁺ and Tb³⁺. The upconversion could be enhanced significantly by increasing the annealing temperature and the luminescence color could be adjusted by varying the Yb³⁺/Tb³⁺/Er³⁺ ratio. Upconversion of Er³⁺ could be described as sequential energy transfer from single Yb³⁺ to single Er³⁺, while upconversion of Tb³⁺ described as cooperative energy transfer from double Yb³⁺ to single Tb³⁺.     

多功能超音速火焰喷涂喷枪拉伐尔喷嘴的设计

粒子的速度和温度对多功能超音速火焰喷涂层的性能有决定性作用,它取决于经拉伐尔喷嘴加速后的焰流速度和温度。文中计算了拉伐尔喷嘴入口、喉部与出口三个特征截面的燃气速度和温度,并对喷嘴特征尺寸和型面进行了优化设计。保证在氧气和空气助燃状态下都能达到超音速,实现了焰流速度与温度在大范围内的连续可调。并在喷嘴的出口形成负压以实现送粉的通畅,焰流速度调节范围约为1400～2150m／s．温度调节范围约为1400～2600℃,可满足金属、合金和陶瓷材料的喷涂要求。     

SiCp增强金属基复合材料的研究进展

综述了SiCp增强金属基复合材料的国内外研究现状，着重介绍了SiCp增强金属基复合材料的制备、性能与应用前景。     

Substrate Effect on the High-Temperature Oxidation Behavior of a Pt-Modified Aluminide Coating. Part I: Influence of the Initial Chemical Composition of the Coating Surface

The effect of substrate composition on the oxidation behavior of the industrial NiPtAl coating RT22 ^TM was investigated by studying the isothermal and cyclic-oxidation behavior of this coating deposited on three different Ni-base superalloys (CMSX-4 ^TM , SCB ^TM and IN792 ^TM ). Isothermal tests were performed at 900, 1050 and 1150°C for 100 h. Cyclic oxidation was studied at 900°C with a holding time of 300 h for up to 52 cycles (i.e, 15,600 h at 900°C). Thermogravimetric analysis (TGA), X-ray diffraction (XRD), microstructural and analytical investigations using scanning-electron microscopy (SEM) and transmission-electron microscopy (TEM), both equipped with energy-dispersive X-ray spectroscopy (EDS) were performed to characterize the oxidation behavior of the systems studied. An effect of the superalloy substrate was observed and related to the initial chemical composition of the coating surface which depends on the superalloy and the associated heat treatments. The effect of the substrate’s alloying elements is discussed. Particularly the influence of Ti and Ta that formed rutile-type oxides inducing oxide-scale cracking and spallation. The excellent resistance to cyclic oxidation of the coating systems studied at 900°C was also demonstrated from very long duration tests of 15,600 h.