射频等离子体球化SiO2粉体的研究

采用射频等离子体球化颗粒形状不规则的二氧化硅粉体,研究了加料速率、颗粒大小等因素对球化率的影响.用光学显微镜观察球化前后颗粒的形貌;用流动仪测定球化后粉体的松装密度.结果显示,球化后的二氧化硅颗粒球形度高,细颗粒长大,并且随着球化率的增大粉体松装密度增加.初步查明加料速率、原料粒度等参数对球化率的影响.在适当的条件下可以得到球化率高、球形度好的粉体.     

选区激光熔化用高强合金钢粉末制备及其成形性研究

目的 研究真空感应熔炼气雾化法(VIGA)制备球形24CrNiMoY高强钢粉末并验证其激光3D打印性能。方法 阐明不同雾化气压对粉末形貌、流动性等粉体特征的影响,分析选区激光熔化技术快速成形合金钢样品的微观组织和力学性能。结果 在9.0 MPa雾化气压下制备的粉末球形度最佳,粉末松装密度达到4.89 g/cm³,流动性能为21.4 s/(50 g),粉末含氧量0.023%,空心球率＜3%,粉末的微观组织主要是马氏体。经过激光工艺参数调控,SLM成形合金钢试样的激光熔池内存在两个明显不同的微区:激光熔化区(LMZ)和热影响区(HAZ)。LMZ主要是马氏体组织,HAZ主要为下贝氏体组织。合金钢试样的平均显微硬度为(402±5.7)HV0.2,其抗拉强度达到(1 246±12) MPa,断后伸长率为(11.6±0.5)%。结论 VIGA方法制备的 24CrNiMoY高强钢粉末满足SLM技术使用要求,具有良好的激光3D打印成形性。     

热等离子法制备高致密球形钼粉颗粒

采用自行研制的等离子设备实现钼粉颗粒的球形化,研究工艺参数对钼粉颗粒球形化的影响,采用电子扫描显微镜、霍耳流速仪和斯科特容量计观测球形钼粉的微观形貌,检测其流速和松装密度。结果表明,等离子体处理后钼粉颗粒的形状由不规则变为球形,钼粉流动性显著提高,松装密度增大;当输入功率为25 kW,送粉量为50 g/min时,钼粉颗粒的球形化最理想。     

反应等离子喷涂TiC/ Fe-Ni复合涂层及其耐冲蚀性能

以TiFe粉、Ni粉和蔗糖(碳的前驱体)为原料,通过蔗糖的热分解碳化制备Ti-Fe-Ni-C系反应热喷涂复合粉末,并利用等离子喷涂制备了TiC/Fe-Ni复合涂层。复合涂层主要由TiC颗粒均匀分布于(Fe、Ni)固溶体中形成的复合强化片层构成,片层中TiC颗粒呈球形或近球形,粒度为亚微米级和纳米级。TiC/Fe-Ni复合涂层的耐冲蚀磨损性能研究表明：涂层冲蚀失重率随攻角的增大而增加,表现出脆性材料冲蚀特性,但冲蚀失重率对攻角不敏感,涂层具有较好的塑性与硬度的配合;复合涂层的耐冲蚀磨损性能优于相同工艺条件下制备的C_r2C₃/Ni-Cr复合涂层,约为20G钢的2倍以上。     

二氧化硅喷雾造粒粉体的热处理工艺研究

研制了一种以SiO2为基体的高温可磨耗封严涂层,为了改善二氧化硅喷雾造粒粉体的性能,研究了热处理工艺对粉体松装密度、流动速度及粒度分布的影响。结果表明,热处理过程中伴随着SiO2颗粒的烧结,热处理温度对粉体性能的影响较热处理时间更为显著,随着温度的升高,喷雾造粒SiO2球逐渐烧结,粉体粒度减小,松装密度增加,流动性提高,采用1000～1050℃、30～60min的工艺对粉体进行热处理能够获得最优的粉体性能。     

回转体表面喷射电沉积Ni-P-ZrO2复合镀层耐腐蚀性能研究

为延长回转体零件的使用寿命,提高其耐腐蚀性能,本文利用喷射电沉积技术在45钢外圆表面制备Ni-P合金镀层和Ni-P-ZrO₂复合镀层,采用扫描电镜、腐蚀失重法和电化学测试分析等测试手段对Ni-P-ZrO₂复合镀层、Ni-P合金镀层和45钢基体在50 g/L NaCl溶液中的表面形貌和耐腐蚀性能进行研究,并探究腐蚀机理。研究表明:Ni-P-ZrO₂镀层相对Ni-P镀层表面致密度更高,缺陷较少;浸泡相同时间, Ni-P-ZrO₂镀层的失重量最小,腐蚀速率最小;电化学测试实验中,Ni-P-ZrO₂复合镀层的腐蚀电流最低(43.2×10^-5 A/cm²),共沉积ZrO₂颗粒后,Ni-P-ZrO₂复合镀层容抗弧半径更大,极化电阻值R_p增大为Ni-P合金的3倍,双层电容值C_d由4.743 8 μF/cm²降低为3.887 2 μF/cm²。在相同条件下腐蚀后,Ni-P-ZrO₂复合镀层的表面较为完好,腐蚀产物较少;Ni-P合金次之,有较多黑色腐蚀产物;45钢表面形貌最差。综上,采用喷射电沉积在回转体表面制备的Ni-P-ZrO₂复合镀层相对Ni-P合金镀层和45钢基体表现出更优良的耐腐蚀性能。     

碳化钨粉末对聚晶金刚石复合片钻头胎体组织与力学性能的影响

以铸造碳化钨粉末混合镍粉作为骨架粉末,采用无压浸渍工艺制备了聚晶金刚石复合片（PDC）钻头胎体材料。研究了碳化钨的粉末粒形、粒度及质量分数对PDC钻头胎体的微观组织和力学性能的影响。结果表明,碳化钨的粉末粒形、粒度及质量分数是影响胎体微观组织和力学性能的重要因素。与破碎碳化钨相比,粉末粒度适中的球形碳化钨作为骨架制备的胎体组织更均匀、更致密,胎体的力学性能明显提高。采用150~180 μm的球形碳化钨混合13wt%的镍粉作为骨架粉末制备的胎体力学性能优于石油天然气行业标准SY/T 5217—2000,其硬度、冲击韧性和抗弯强度分别为HRC 34、6.7 J/cm2和820 MPa。      

磁场辅助下ZrO2纳米颗粒质量浓度对镀层耐磨性能的影响研究

为了进一步延长45钢工件的耐磨性能,减少企业维修和更换45钢类零件的成本,在传统材料45钢表面,开展了稳恒磁场辅助的电喷镀试验研究,通过配制不同ZrO₂纳米颗粒质量浓度的镀液,制备了Ni-P-ZrO₂镀层,利用扫描电子显微镜(SEM)、能谱分析仪(EDS)、显微硬度检测仪和共聚焦显微镜等仪器对镀层表面形貌、Zr元素含量、显微硬度以及耐磨性能进行了分析。研究发现:ZrO₂纳米颗粒和稳恒磁场的加入改善了镀层表面形貌,提高了显微硬度和耐磨性能；当ZrO₂纳米颗粒质量浓度达到15 g/L时,ZrO₂纳米颗粒易出现团聚现象,不利于镀层表面性能的进一步提升。磁场辅助下,镀液中ZrO₂纳米颗粒质量浓度为10 g/L时,得到的镀层表面更加平整、显微硬度最高达到了739.30HV,且磨痕宽度、深度以及截面面积达到最小值,分别为367.617、5.673 μm和1 288.155 μm²,镀层耐磨性能最佳。     

喷雾干燥YPSZ纳米结构热喷涂粉末材料制备及表征

YPSZ纳米结构粉末材料的研究是热喷涂制备YPSZ纳米结构涂层必须首先进行研究的问题。本文采用喷雾干燥方法制备适合于热等离子体喷涂的YPSZ纳米结构粉末原料,同时采用等离子体喷涂制备涂层。利用扫描电子显微镜分析晶粒大小、颗粒形貌,X射线衍射分析相组成,对喷雾干燥后粉末进行热重-差热分析,测定粉末的松装密度、振实密度及流动性。结果表明制备的YPSZ粉末材料具有实心、流动性好、松装密度高、振实密度高、球形度高、单斜相少等优点,采用热等离子体喷涂沉积制备YPSZ纳米结构涂层。     

棒磨法制备鳞片状锌铝合金的工艺研究

为了提高片状锌铝粉的生产水平,本文以球形锌铝合金粉体为原料,采用湿法棒磨的方式制备鳞片状锌铝合金,用激光粒度分析仪、扫描电镜、比表面仪以及遮盖率仪对制备的鳞片状锌铝合金的粒径分布、微观形貌、比表面积以及水面遮盖率进行了表征,研究了磨棒级配、棒磨时间、棒磨机转速、棒磨助剂种类等工艺参数对产品的影响.结果表明,以硬脂酸为棒磨助剂时,棒磨级配中适当增加直径较大的磨棒比例,选择相对较快的棒磨转速(150~200 r/min)和适中的棒磨时间(12~20 h)可获得较好的棒磨效果;由正交实验可知,各因素对产品水面遮盖率的影响顺序为：棒磨时间＞棒磨机转速＞棒磨级配＞棒磨助剂种类;最优水平组合为高分子F作为棒磨助剂,棒磨级配为B组合,棒磨转速150 r/min,棒磨时间16 h。最优水平组合条件下得到的产品片状化程度高且颜色光亮,平均粒径为12.83 μm,比表面积为2 402.3 cm²/g,水面遮盖率达到3 856 cm²/g.     

Study on the flow properties of Ti-6Al-4V powders prepared by radio-frequency plasma spheroidization

Spherical Ti-6Al-4V powders were prepared using radio-frequency plasma spheroidization. A laser particle size analyser, a scanning electron microscope, an X-ray diffractometer and a Freeman FT4 powder rheometer were used to analyse the granulometric parameters, micro-morphologies, phase constitutions and flow properties of the raw and the spheroidized powders, respectively. The spheroidized powders exhibited an almost 100% degree of sphericity, smooth surfaces, favourable dispersion and narrow particle size distribution under appropriate plasma technological parameters. The average particle size of the spheroidized powders increased slightly as compared with that of the raw powders. In addition, the spheroidized powders exhibited higher conditioned bulk density and improved flow properties (including the dynamic flow properties, aeration, compressibility, permeability and shear properties) as compared with those of the raw powders.     

Plasma spheroidization of iron powders in a non-transferred DC thermal plasma jet

In this paper, the results of plasma spheroidization of iron powders using a DC non-transferred plasma spray torch are presented. The morphology of the processed powders was characterized through scanning electron microscopy (SEM) and optical microscopy (OM). The percentages of spheroidized powders were calculated by the shape factors such as the Irregularity Parameter (IP) and Roundness (RN). A maximum of 83% of spheroidization can be achieved. The spheroidization results are compared with the theoretical estimation and they are found to be in good agreement. The phase composition of the spheroidized powder was analyzed by XRD. The effect of plasma jet temperature and plasma gas flow rate on spheroidization is discussed. At low plasma gas flow rates and at high plasma jet temperatures, the percentage of spheroidization is high.     

Characterization of Virgin,Re-used,and Oxygen-reduced Copper Powders processed by the Plasma Spheroidization Process

Fabrication of parts with high mechanical properties heavily depend on the quality of powder deployed in the fabrication process. Copper powder in three different powder types were spheroidized using radio-frequency inductively coupled plasma (ICP) spheroidization process (TekSphero-15 system). The characterized powders include virgin powder as purchased from the powder manufacturer, powder used in electron beam powder bed fusion (EB-PBF) process, and reconditioned powder, which was used powder that underwent an oxygen-reduction treatment. The goal of spheroidizing these powder types was to evaluate the change in powder morphology, the possibility of enhancing the powder properties back to their as-received conditions, and assess oxygen reduction of the powder lots given their initial oxygen contents. Also, to investigate the impact of re-spheroidization on powder properties, the second round of spheroidization was performed on the already used-spheroidized powder. The impact of powder type on powder sphericity and particle size distribution was evaluated using the image analysis of scanning electron microscope (SEM) micrographs and laser diffraction, respectively. The spheroidized powder showed higher sphericity and more uniform particle size distribution overall. Depending on the powder collection bin, second round of spheroidization affected the powder sphericity differently. The possibility of deploying the plasma spheroidization process as an alternative oxygen-reduction technique was also investigated through tracking the powders’ oxygen content using inert gas fusion method before and after the spheroidization. The plasma spheroidized powder showed less oxygen content than the hydrogen-treated powder. The second round of spheroidization caused no change in oxygen content. The correlation between oxygen-reduction and created cracks was discussed and compared between plasma spheroidization and hydrogen-treatment. The plasma spheroidization process created a powder with higher sphericity, uniform particle size, and less oxygen content.     

Spheroidization of tantalum powder by radio frequency inductively coupled plasma processing

In this work, we used radio frequency (RF) plasma spheroidization to transform irregularly shaped tantalum powders to spherical ones. After RF plasma treatment, the majority of particles were spheroidized with the presence of a small number of irregular particles. The mean particle size becomes finer and the particle size distribution narrower, as compared with the starting powder. A few non-spherical or even irregular tantalum powders still existed. Although argon gas was used in the plasma chamber, oxygen contamination still occurred. A thin layer of oxide film was found on the surface of particles, while the particle interiors were inferred free of oxygen. The powder characteristics had been significantly improved. After spheroidization treatment, the apparent density, tap density and powder flowability significantly increased from 7.03 g/cm³ to 8.9 g/cm³, 8.6 g/cm³ to 10.05 g/cm³, and 12.41 s/(50 g) to 7.96 s/(50 g), respectively, in comparison with that of raw powders. This study presents a feasible method for fabricating spherical tantalum powders, which may potentially broaden the application for metal additive manufacturing.     

Characterization and comparison between APS coatings prepared from ball milled and plasma processed nickel–aluminium powders

Plasma spraying has wide range of applications which include corrosion, thermal and abrasion resistance coatings. In the present work, nickel and aluminium powders were ball milled and the same were thermal plasma processed to produce spherical nickel alumindes particles. Both ball milled and plasma processed powders were spray deposited on stainless steel (SS 304) substrate using atmospheric plasma spray technique (APS). The experiments were carried out for different plasma input power levels, torch to base distances and coating thicknesses. Microstructure, micro hardness, adhesive strength, and porosity of the coatings are reported and discussed. Effect of plasma processing parameters and plasma spheroidization of powders on coating properties has been evaluated and reported. High plasma power, low torch to base distance lead to high temperature supplied to in-flight particles which correspond to high hardness, low porosity and high adhesion. Spherical morphology and formation of nickel aluminide intermetallic were achieved by plasma spheroidization. Coatings prepared from plasma processed powders enhance the coating properties positively.     

Laser cladding nickel-titanium carbide composite coating on a 45 carbon steel: Preparation,microstructure and wear behavior

Almost fully dense nickel-titanium carbide composite coatings with varied titanium carbide content were deposited on 45 carbon steel by laser cladding. High content of titanium carbide particles up to 50 wt.% with bimodal microstructure could be homogeneously distributed in the nickel based matrix. Due to the presence of the harder nickel-titanium carbide composite coating on the 45 carbon steel, the surface hardness and wear properties were significantly improved. The Vickers hardness (HV 3) increased from about 260 HV 3 for the 45 carbon steel to 300 HV 3 – 360 HV 3 for nickel based composite coating containing 30 wt.% titanium carbide and 550 HV 3 – 680 HV 3 for nickel based composite coating containing 50 wt.% titanium carbide composite coating, respectively. The coefficient of friction and volume wear rate was reduced down to 0.41×10⁻⁶ mm³ N⁻¹ m⁻¹ and 9.3×10⁻⁶ mm³ N⁻¹ ⋅ m⁻¹ when a nickel based composite coating containing 50 wt.% titanium carbide was coated on the 45 carbon steel, respectively. The enhanced wear performance of the composite coating was due to presence of harder nickel-titanium carbide composite coating and formation of varied soft and lubricant metal oxides consisting of mainly titanium oxides and minor iron and nickel oxides.     

Microstructure of alumina reinforced with tungsten carbide

Carbides and nitrides reinforced alumina based ceramic composites are generally accepted as a competitive technological alternative to cemented carbide (WC-Co). The aim of this work was to investigate the effect of dispersed tungsten carbide (WC) on the microstructure and mechanical properties of alumina (Al₂O₃). Micron size alumina and tungsten carbide powders were mixed in a ball mill and uniaxially pressed at 1600°C under 20 MPa in an inert atmosphere. The hardness of WC reinforced alumina was 19 GPa and fracture toughness attained up to 7 MPa m^1/2. It was demonstrated by TEM analysis that coarse, micrometersized tungsten carbide grains were located at grain boundaries of the alumina matrix grains. Additionally, sub-micrometer tungsten carbide spheres were found inside the alumina particles. Crack deflection triggered by the tungsten carbide at the grain boundaries of the alumina matrix is supposed to increase fracture toughness whereas the presence of intergranular and intragranular hard tungsten carbide particles are responsible for the increase of the hardness values of the investigated composite materials.     

Electron beam synthesised hard layers on mild steel

Abstract

Hard surfaces have been synthesised on mild steel. The technique involves surface coating followed by electron beam mixing by melting. The coating comprised metallic or metalloid powders, graphite powder, and a water soluble binder. Modified surface layers of various dimensions were prepared by controlling electron beam processing parameters. Many carbide forming elements were investigated and boron and tungsten were found to be the most promising. The hardnes of the modified layers depended on the concentration of the alloying elements and varied between ~600 and 1000 HV(500 g). The technique is advantageous mainly because hard coatings can befabricated on almost any substrate that melts under an electron beam. Modified surfaces produced on mild steel are described in the present paper.

MST/2025