Preparation of high-purity and ultrafine WC-Co composite powder by a simple two-step process

In this study, high-purity and ultrafine WC-6%Co composite crystallites was synthesized by a simple two-step process consisting of the precursor-formation of the mixture of blue tungsten oxide (WO_2.9) and cobaltic oxide (Co₂O₃) and the following deep reduction and carburization with CH₄-H₂ mixed gases. The experimental results revealed that after the first carbothermic reduction stage at 1050 or 1150 °C, a mixture of W, WO₂ and Co₇W₆ was obtained, which was further carburized to the WC and Co phases by CH₄-H₂ mixed gases at 900 °C. With the increase of C/WO_2.9 molar ratio, the particle sizes of first-stage precursor and carbonized product were both decreased. The particle sizes of final products are mainly determined by C/WO_2.9 ratio and reaction temperature at the first stage. When the C/WO_2.9 ratio was in the range of 2.3–2.7, the high-purity WC-6%Co composite powder with the average particle sizes of 160–410 nm could be obtained.     

WC-Co涂层的发展现状与展望

WC-Co涂层因具有优良的耐磨抗腐蚀性能而被广泛应用于工业的各个领城,并且WC-Co 涂层的制备技术及其性能的研究也已成为热点课题.介绍了近些年来WC-Co涂层的最新研究进展、以及WC-Co涂层目前存在的问题与缺陷.通过对纳来WC-Co涂层和普通WC-Co涂层性能的研究比较,对WC-Co涂层的发展方向进行了展望.     

粉末结构对HVOF喷涂WC-Co涂层组织性能的影响

选用4种不同WC尺度的WC-12Co粉末作为初始喂料,通过超音速火焰喷涂系统(HVOF)制备了涂层。考察了不同粉末结构对涂层沉积过程的脱碳行为和涂层组织性能的影响。结果表明:WC颗粒尺寸减小加剧了涂层脱碳行为,涂层中W2C含量增加,粘结相非晶化现象明显,涂层硬度增加,但是当WC颗粒尺寸减小到纳米尺度时,韧性下降。双峰结构涂层表现出最好的韧性同时兼备较高的硬度。     

CoWO4-WO3纳米复合粉体的合成及其研究

采用共沉淀法制得了超细粒碳化钨钴金属陶瓷前驱体原料CoWO4－WO3纳米复合粉体,其粒径约10nm,结构特征为非晶态。探讨了合成条件对产物性能的影响,并采用TG-DTA,XRD,TEM等测试方法对粉体的特性以及反应机理进行了研究。     

超音速火焰喷涂WC-Co与NiCr-Cr2C3涂层磨损性能研究

采用超音速火焰喷涂(HVOF)工艺制备了WC-Co和NiCr-Cr2C3涂层,测定了涂层孔隙率、显微硬度及油润滑下摩擦磨损过程中涂层材料失重,得出涂层摩擦系数随时间的变化关系,分析了涂层摩擦磨损机理.结果表明,WC-Co和NiCr-Cr2C3涂层致密,孔隙率分别为1.29%和1.08%,显微硬度分别为1140HV0.3和950HV0.3.两种涂层均在摩擦时间25min时进入稳定磨损阶段,稳定摩擦系数均为0.1,涂层摩擦失重极小.油润滑下WC-Co涂层的摩擦磨损方式主要以为接触疲劳为主,伴随轻微的粘着磨损和磨粒磨损;NiCr-Cr2C3涂层碳化物的剥落和表面划痕较为明显,表面裂纹明显增多.     

超音速火焰喷涂WC-17Co涂层微观结构与性能研究

采用超音速火焰喷涂技术喷涂了两种不同WC颗粒尺寸的WC-17Co粉末.对制备的两种涂层的硬度、孔隙率、断裂韧性、结合强度和电化学腐蚀行为进行了测试.结果表明:具有亚微米结构WC颗粒的粉末制备的涂层,在硬度、孔隙率、断裂韧性方面具有一定优势,而含有大颗粒WC相的粉末制备的涂层在结合强度、腐蚀行为方面优势明显,这说明WC颗...     

爆炸喷涂WC-Co/MoS_2-Ni多层复合自润滑涂层的摩擦学行为

采用爆炸喷涂技术研制WC-Co/MoS_2-Ni多层复合自润滑涂层,系统研究涂层的微观结构、元素分布、结合强度和摩擦磨损性能。结果表明:在高温爆炸喷涂过程中,少量MoS_2发生氧化分解,生成SO_2气体,残留在涂层内的SO_2气体可使局部形成微小孔洞。在摩擦测试中,WC-Co涂层在预磨阶段摩擦因数迅速上升,进入稳定阶段后,摩擦因数缓慢增加;而多层复合涂层的摩擦因数在经历预磨阶段迅速上升后,很快进入稳定阶段,直至表层WC-Co涂层被磨穿后,摩擦因数开始逐渐下降。添加自润滑涂层MoS_2-Ni后,WC-Co涂层的内聚结合强度略有下降,但减摩效果显著,摩擦因数下降了约40%,耐磨性能略有提升。     

Preparation of spherical WC-Co powder by spray granulation combined with radio frequency induction plasma spheroidization

In this paper, spray granulation and radio frequency plasma spheroidization were used to obtain spherical WC-Co powder for laser powder bed fusion from mixed WC and Co powder. The effects of solid content and polyvinyl alcohol content of the slurry on granulated powder were studied. Then the spheroidization effects of different granulated WC-Co powders were investigated and compared. Results show that the granulated powder obtained from the slurry with solid content of 65 wt% and polyvinyl alcohol content of 2.5 wt% has the best performance after plasma spheroidization, whose flowability and apparent density are 10.20 s/50g and 6.76 g/cm³, respectively. Moreover, W and C distribute uniformly in the spheroidized WC-Co powder while the Co element is mainly distributed in the gaps of tungsten carbide. It is also noted that W₂C, free carbon and Co₃W₃C appear in the spheroidized WC-Co powders due to the decomposition of WC during the plasma spheroidization process. Furthermore, the decomposition of WC-Co powder particles with smaller size is more serious, which leads to the presence of black and white particles with significantly different carbon content distribution in the spheroidized powder.     

S-doped crosslinked porous Si/SiO2 anode materials with excellent lithium storage performance synthesized via disproportionation

The volume expansion during cycling and low electrical conductivity of a Si anode limit its commercial development. Nanostructure can effectively alleviate the volume expansion and doping can increase the electrical conductivity of silicon. Hence, in this paper, uniformly S-doped crosslinked porous Si/SiO₂ (S-doped pSi/SiO₂) were prepared by the disproportionation reaction of SiO at a high temperature. As a bifunctional additive, sulphur can be used to prepare crosslinked porous silicon by a silicon-sulphur reaction. Furthermore, sulphur can improve the conductive properties of the bulk Si via doping. At the same time, residual SiO₂ can also be used as a buffer material. This strategy not only provides space for the volume expansion of silicon, but also enhances its electrical conductivity and improves charge transfer. Consequently, the S-doped pSi/SiO₂ anode exhibits superior cycling capacity and rate performance (1035 mAh·g^?1 at 1 A g^?1 after 300 cycles and an exceptional rate performance of 1233 mAh·g^?1 at 2 A g^?1). Moreover, the electrochemical performance of the S-doped pSi/SiO₂//LiFePO₄ full cell was also evaluated, which exhibits favourable lithium storage performance.     

电火花表面强化过程中的"阳极粘连"现象

通过对TC1合金表面强化WC—Co过程中的“阳极粘连”现象研究,揭示出电极旋转式电火花表面强化过程的实质是一种混合冶金过程。由于存在“阳极粘连”现象,电火花强化过程中两极间的放电过程具有不规律交变放电的特征。上述结论为解释TC1合金表面WC—Co电火花强化层中存在TiC等新相提供了理论依据。