Particle Behavior During the Arc Spraying Process with Cored Wires

To use the manifold possibilities that arc spraying offers to deposit wear resistance layers, knowledge of the particle formation and their behavior is necessary. This work is focused on studying the particle properties during arc spraying with cored wires. Different cored wires under various spraying parameters are investigated by means of a high speed camera. Particle properties in-flight, such as velocity and temperature, are determined. Correlation between particle behavior and particle characteristics at different spraying conditions is established. At the same time, the particle-laden gas flow is simulated numerically and the computed solutions are used to illustrate the utility of the proposed CFD model and compared with experimental results. The employed mathematical model represents a system of macroscopic conservation laws for the continuous gas phase and for the gas-solid mixture. This approach formulation makes it possible to circumvent the numerical difficulties associated with the implementation of a (potentially ill-posed) two-fluid model. The discretization in space is performed using a high-resolution finite element scheme based on algebraic flux correction in terms of local characteristic variables. The artificial diffusion operator is constructed on the discrete level and fitted to the local solution behavior using a multidimensional flux limiter of TVD type.     

Comparison of In-Flight Particle Properties, Splat Formation, and Coating Microstructure for Regular and Nano-YSZ Powders

The relationship between atmospheric pressure plasma spray parameters and in-flight particle characteristics was determined. The morphologies of individual splats and the coating microstructure were studied for different stand-off distances and arc currents. Coating cross-sectional analysis showed that the total porosity of the coating increased with decreasing arc current, and increasing stand-off distance. Two different materials were used: the regular (r-YSZ) feed stock and the nano size (n-YSZ) agglomerated powder. The results illustrate that the r-YSZ coating has higher total porosity at higher arc currents than n-YSZ coating. The splat flattening degree and circularity was examined at different substrate temperatures for both powders. The results indicate that the flattening degree increased at high temperatures for the two materials, but the values for n-YSZ were higher than those for the r-YSZ. This study showed the operating regimes in which the use of n-YSZ yields improved coating properties.     

AIMg/AI2O3粉芯丝材电弧喷涂的粒子和涂层特征

目的 研究AlMg/Al2O3粉芯丝材电弧喷涂的飞行粒子、扁平粒子、涂层结构及涂层抗冲击性能.方法 研制了2种含微米级Al2O3粉料的铝基粉芯丝材,利用扫描电镜对收集到的电弧喷涂过程中形成的飞行粒子、扁平粒子以及喷涂层的微观结构进行表征.采用自制的循环冲击设备测试了涂层的抗冲击性能.结果 AlMg/Al2O3粉芯丝材电弧喷涂过程中形成了含有铝镁、铝镁包覆氧化铝、氧化铝3种不同类型的飞行粒子,添加的Al2O3粒径越小,铝镁包覆氧化铝飞行粒子中的铝镁膜增厚,所包覆的Al2O3颗粒越多.喷涂形成的扁平粒子形状复杂多样,表面不平坦,有溅射现象.制备的涂层结构致密、缺陷少,Al2O3粉料粒径范围为400～500μm和30～50μm制备的AlMg/Al2O3涂层表面的Al2O3颗粒平均面积含量分别为5.52％、13.54％,说明添加小粒径Al2O3颗粒的涂层中残留的Al2O3颗粒增多.在500次循环冲击试验下,AlMg涂层和AlMg/Al2O3涂层没有明显的径向、环形裂纹和大面积剥落现象,但存在明显的塑性变形.结论 随着添加的微米级Al2O3颗粒粒径的减小,涂层中Al2O3颗粒的含量增加.制备的AlMg/Al2O3涂层以塑性变形吸收了大部分冲击功,降低了冲击疲劳裂纹产生的可能性,涂层与基体保持良好的结合状态.     

铑粉粒度对其溶解的影响

铑是最难溶解的铂族金属之一,但在铑的提取和应用中铑的溶解又是必不可少的关键环节,研究发现铑粉粒度对铑的溶解有着直接的影响。考察了铑粉粒度和铑粉表面状态对铑溶解的影响。实验结果表明,铑的溶解率与其粒度呈现负相关的关系,粒度≥100μm的铑粉基本不溶解,粒度≤10μm级的铑粉有着很高溶解率。对王水溶解后的铑粉表面通过微区能谱分析表明,铑粉表面并没有氧化物形成,铑粉溶解过程中的微溶现象,是由于溶解时铑粉中的小颗粒铑粉首先溶解,当小颗粒铑粉溶解完,大颗粒铑粉不溶解所致。     

仲钨酸铵的粒度与形貌对掺杂钨丝性能的影响

将颗粒形貌及粒度不同的２种仲钨酸铵（ＡＰＴ），按工业生产条件，进行掺杂钨丝生产的对比试验。结果发现：当ＡＰＴ的平均粒度为４０～４５μｍ，且具有多个晶块嵌镶成类球状的形貌特征时，可以进一步改善掺杂钨丝的综合性能。     

粉末粒度对一种新型镍基粉末高温合金热变形行为的影响

利用EBSD、SEM、OM、热模拟试验机等对比研究了不同粉末粒度制备的一种新型镍基粉末高温合金(WZA3)在不同热压缩变形条件下的变形行为和组织差异性。结果表明：相比细粉制备的HIP-01样品而言,粗粉枝晶组织明显,成分偏析严重,其制备的HIP-02样品中残余粗大γ′较多。低温(1050、1080℃)高应变速率(1、0.1s-1)时,HIP-01样品峰值应力值高于HIP-02。热压缩后HIP-01样品边缘开裂情况较HIP-02严重,HIP-01样品保留了大部分原始热等静压组织,裂纹优先在粉末原始颗粒边界(priorparticleboundary,PPB)处产生,HIP-02样品边缘出现了部分再结晶组织。在1080℃/0.001 s^-1时,HIP-02样品峰值应力较HIP-01低约30 MPa,HIP-02样品热压缩过程再结晶现象明显,再结晶晶粒均匀,HIP-01样品出现项链晶组织,再结晶不充分。粗大γ′有利于促进1050和1080℃时HIP-02样品的再结晶。高温(1150℃)、低应变速率(0.001、0.01s^-1)时,γ′全部溶解进基体...     

添加剂对金属银粉形貌和粒径的影响

选择结构和性质各异的添加剂制备金属银粉,在其他实验条件相同的情况下对比分析了不同添加剂对银粉形貌和粒径的影响机理。结果表明,选择无支链或少支链的长链状高分子化合物作为添加剂,更有利于制备出表面光滑、近球形的金属银粉。以PVP K.30为添加剂,通过调整和优化实验参数,成功制备出分散性优异、近球形、结晶性好的金属银粉,粒径为2.5~3μm,振实密度4.2 g/cm~3,符合太阳能电池电子浆料用金属银粉的指标要求。     

HA粉末粒径对微束等离子喷涂扁平粒子形貌及涂层微结构的影响

目的研究粉末粒径对微束等离子喷涂羟基磷灰石(HA)扁平粒子形貌和涂层的微观组织结构的影响。方法选取三组不同粒径范围(25～38μm、38～45μm、45～63μm)HA球形粉末,采用微束等离子喷涂方法在经镜面抛光的Ti-6Al-4V基体上收集扁平粒子,在经过喷砂处理的Ti-6Al-4V基体上沉积HA涂层。利用冷场发射扫描电子显微镜和X射线衍射仪,对扁平粒子形貌,以及涂层的形貌、相组成和择优取向进行分析。通过激光共聚焦显微镜(LSCM)观察扁平粒子的三维相貌,并对比分析扁平粒子的差异。结果微束等离子喷涂过程中,可形成几种典型形貌特征的扁平粒子,一是中间区域较厚,边缘位置较薄的扁球形;二是中间区域较薄,边缘位置较厚的圆盘状,该种扁平粒子相比于扁球形,其厚度较薄,直径较大;三是边缘位置存在"指状"溅射的圆盘状,其厚度与圆盘状扁平粒子厚度相当,但其直径范围较大。HA涂层的结晶度随着粉末粒径的减小而减小,HA的分解和非晶化逐渐增强,涂层的择优取向强度减弱,涂层中柱状晶比例减少。结论微束等离子喷涂过程中,粉末粒径对扁平粒子形貌和涂层相结构有显著影响。随着粒径的增加,扁平粒子由扁球形转变为边缘有少量"指状"溅射的圆盘状。粒径较小的HA粉末在等离子焰流中的熔化程度较高,导致涂层中分解相和非晶相含量增多,择优取向程度减小。     

WC-Co复合粉形貌遗传特性及粒度分布研究

以偏钨酸铵、可溶钴盐、有机碳为原料,经喷雾转化、煅烧、低温还原碳化制备WC-Co复合粉。对前驱体、复合粉物相组成、WC晶粒度、微观形貌、平均粒度及分布进行研究。结果表明:复合粉由WC和Co两相组成,WC晶粒度约为60 nm;前驱体粉末呈空壳球形结构,部分颗粒破裂;经煅烧后,形貌未发生明显变化;再经还原碳化处理,颗粒表面产生大量孔隙,形貌与前驱体相似,具有很好的形貌结构遗传特性;复合粉平均粒度比前驱体略有减小且粒度分布更窄;溶液浓度、给料速度越大,离心转速越小,则平均粒度越大;进气温度对粒度影响很小。     

粗晶碳化钨粒度对WC-Co合金晶粒度的影响

选用供应态分别为30μm和12μm的二种粗颗粒WC粉末,研究不同方法表征的粉末粒度与合金晶粒度的关系。结果表明:三种粉末粒度测定方法给出的结果都呈现粒度越粗合金的晶粒度也越粗的规律。粗颗粒WC的研磨态粒度与合金的晶粒度相当接近,金相法测得的12μmWC的晶粒分布与所制备的合金的晶粒度的一致性比30μmWC制备的合金要好。粗晶WC研磨态的Fsss粒度可以用于评价粗晶WC晶粒度,也可以预测WC-Co合金的晶粒度。     

硬质合金混合料粒度分布对成型尺寸精度的影响

针对影响硬质合金产品成型尺寸精度的混合料压制性能参数进行分析,确认混合料粒度分布组成是关键影响因素之一。混合料粉末各级粒度分布相对均匀,能够有效提高压制过程中粉末填充的均匀性,保证压坯密度相对均匀,减小烧结后发生变形,有利于产品成型尺寸的控制。而利用双螺旋混合机采用混合料干混合合批工艺,能够有效提高混合料批次内粉末各级粒度的均匀性,缩小各级粉末质量分数极差,达到提升数控刀片成型尺寸精度的目的。     

Influence of Powder Particle Size on the Oxidation Behavior of a PM Ni3Al Alloy

The influence of particle size on the oxidationbehavior of Ni₃Al prepared by powdermetallurgy (PM) was investigated in the temperaturerange of 535 to 1020°C for exposures up to 200 hr.Four alloys were obtained, each one processed with a differentpowder particle size fraction (<25, 25-50, 50-100,and 100-200 m). For temperatures below 730°C,the scale consists of an outer NiO layer, a thindiscontinuous intermediate nickel layer, and an internaloxidation zone. The lowest oxidation rate corresponds tothe material with the smallest particle size. Thisresults from its higher grain-boundary density; the boundaries act as easy-diffusion paths foraluminum leading to the rapid formation of a continuousinner alumina layer. At temperatures above 730°C, athree layered scale is observed consisting of an outer NiO layer, an intermediate layer that,depending on temperature, consisted of a mixture ofnickel and aluminum oxides orNiAl₂O₄, and an inner layer ofAl₂O₃, which accounts for thehigher oxidation resistance. The oxidation attack is characterized byintrusions of the scale into the alloy, the intrusionnumber increasing as the particle size decreases. It isassumed that oxide particles and impurities present at the original particle boundaries facilitatealumina growth along these regions. Thus, the lowestoxidation rate for the highest temperature rangecorresponds to the largest particle-sizematerial.     

Numerical Study to Examine the Effect of Porosity on In-Flight Particle Dynamics

High velocity oxygen fuel (HVOF) thermal spray has been widely used to deposit hard composite materials such as WC-Co powders for wear-resistant applications. Powder morphology varies according to production methods while new powder manufacturing techniques produce porous powders containing air voids which are not interconnected. The porous microstructure within the powder will influence in-flight thermal and aerodynamic behavior of particles which is expected to be different from fully solid powder. This article is devoted to study the heat and momentum transfer in a HVOF sprayed WC-Co particles with different sizes and porosity levels. The results highlight the importance of thermal gradients inside the particles as a result of microporosity and how HVOF operating parameters need to be modified considering such temperature gradient.     

Effect of Particle Morphology and Size Distribution on Cold-Sprayed Pure Titanium Coatings

The effects of commercially pure titanium particle morphology (spherical, sponge, and irregular) and size distributions (mean particle sizes of 20-49 μm) on the cold spray process and resulting coating properties were investigated. Numerous powder and coating characterizations were performed including: powder oxygen and nitrogen contents, powder flowability, powder compressibility, coating microhardness, coating porosity, LOM/SEM analyses, and XRD. Compared to spherical powders, the sponge and irregular CP-Ti powders had higher oxygen content, poorer powder flowability, higher compression ratio, lower powder packing factor, and higher average particle impact velocities. XRD results showed no new phases present when comparing the various feedstock powders to corresponding coatings. A higher particle temperature was also obtained with larger particle size for all feedstock powder morphologies processed with the same set of spray parameters. A spherical powder with 29 μm mean particle size was found to have the lowest porosity coating and best cold sprayability. The relationships of several as-cold sprayed coating characteristics to the ratio of particle impact and critical velocities were also discussed.     

碳化钨颗粒尺寸对超音速火焰喷涂WC-Co涂层形成的影响

通过探讨WC颗粒对扁平粒子厚度及喷涂后WC颗粒尺寸变化的影响，研究了超音速火焰喷涂过程中WC－Co深层的沉积过程。使用具有不同WC尺寸的四种WC-Co粉末，采用JET－KOTE喷枪系统喷制了WC－Co涂层。结果发现涂层中WC颗粒的大小主要取决于原始粉末中WC的尺寸．在粉末穿越火焰的过程中，大多数WC处于固态；WC-Co涂层的沉积涉及固液两相离子的扁平化，而不是象在优化条件下金属或陶瓷材料喷涂过程中仅存在单一液相的情况。很明显WC-Co粉末中的WC的大小对涂层的形成影响很大、在超音速火焰喷涂条件下当液固粒子碰撞到已形成的涂层表面上时，其中的大颗粒WC粒子容易被反弹脱落。基于实验结果，提出了计算由液相聚积固相形成的波固两相颗粒碰撞到表面时形成扁平粒子的厚度的模型。     

磁粉粒度分布和抗氧化剂对注射成型NdFeB粘结磁体性能的影响

本文研究了磁粉的粒度分布以及不同抗氧化剂的加入对注射成型NdFeB粘结磁体密度和磁性能的影响。结果表明,磁粉的粒度分布影响熔体的粘度,适当的粒度分布可以提高磁粉的松装密度和磁体的密度,获得高性能的粘结磁体;抗氧化剂的加入,很好地解决了NdFeB粘结磁体在湿热环境下易氧化生锈的问题,大大提高了磁体的抗氧化性能。     

蓝钨循环氧化还原对钨粉末粒度分布的影响

以特纯仲钨酸铵为原料,通过特纯仲钨酸铵在氩气中煅烧获得蓝钨,此蓝钨在纯度为99.99%、露点小于-40℃的氢气中进行还原,蓝钨还原的钨粉在空气中被氧化为三氧化钨,对此三氧化钨再在氢气中还原,然后利用扫描电子显微镜和激光粒度分析仪对试样进行分析,结果表明:经过循环一次氧化和两次还原,制备出了粒径分布在3～10μm之间占83.86%、比表面积为0.180m2/g的中颗粒钨粉。     

Effect of Powder Particle Size on the Properties and Microstructure of Ti(C,N)-Based Cermet

1 IntroductionTo improve the durability of Ti(C, N)-basedcermet, many scholars have gained some measures, for example, using advanced sintering methods, Processing HIP blot isostatic pressing)trCdrieflt. Later in 1990's, there are a few reports on submicron cermets [1, 2].In this Study, we have characterized themicroS~ture of tWo cermets and interpretedthe difference between them. Moreover the effect of temper~ on phase transition and lattice-consuls of main Phases and the gradingsof main…