含WB烧结硬质合金的组织结构和性能研究

将不同含量的WB粉末添加到传统成分的WC-Co粉末中,利用低压烧结技术制备了系列含WB的WC-Co型硬质合金,并对其物相组成、组织结构和力学性能进行了系统表征分析。研究发现,在低压烧结过程中WB与Co发生反应,生成了具有超高硬度的WCoB相,由此降低了粘结相Co对WC晶粒的隔离,增加了WC晶粒间的接触度,引起合金韧性下降。添加WB制备的硬质合金材料其摩擦系数更低,随WB添加量的增加,硬度和耐磨性明显提高,当WB添加量为30%(质量分数)时,制备的硬质合金材料的硬度达到19 000 MPa,其磨损速率仅为传统WC-Co硬质合金1/10。然而,添加WB的WC-Co合金的断裂韧性约为传统WC-Co硬质合金的83%~91%。     

High-temperature oxidation and wear resistance of WC-Co based coatings with WB addition

A new type of WC-based coating with high oxidation- and wear-resistance at elevated temperature was fabricated by thermal spraying the pre-treated WC-Co powder doped with WB. Addition of WB led to in situ formation of WCoB, which acted as a substitute for Co in the powders and the resultant coatings. It was shown by thermal analysis that WCoB has obviously higher oxidation resistance at high temperatures than that of WC and Co. Thus, the oxidation of the WC-WCoB coating was mainly initiated from WC, rather than from Co in the conventional WC-Co coatings. Most of WCoB was preserved in the coating after high-temperature wear tests. Particularly, with an addition of 40 wt.% WB, the wear rates of the WC-Co coating were dramatically decreased by 90% and 77% at the room and elevated temperatures, respectively.     

First-principles calculation of mechanical properties and electronic structures of W4Co4−nXnB4 (X = V,Mn, Fe,Ni; n = 0,1)

The first-principles calculation is performed to explore the mechanical properties and electronic structures of transition elements X (X = V, Mn, Fe, Ni) doped WCoB (tungsten cobalt boron), which has shown high oxidation resistance and melting point under high pressure. The energy analysis indicates that the high pressure leads to the lower lattice constants and less stable structures. The deviation of cohesive energy and formation enthalpy between doped and undoped structures indicates that W₄Co₃FeB₄ and W₄Co₃NiB₄ have similar stability. The high pressure contributes to the increasing of elastic, shear, and bulk moduli, which indicates the increase of covalence. The increase of Poisson's ratio, B/G ratio, and anisotropy index A^U indicates the higher ductility and higher anisotropy under high pressure. Based on bulk modulus and shear modulus, the hardness of W₄Co₄B₄, W₄Co₃FeB₄, and W₄Co₃NiB₄ increases under high pressure, which consists of the variation of electronic structures. The density of states (DOS) and partial DOS analysis indicate that the high pressure leads to lower density around Fermi level and higher hybridization. W₄Co₄B₄, W₄Co₃FeB₄, and W₄Co₃NiB₄ show similar variation of mechanical properties, which is determined by the similar atom properties of Co, Fe, and Ni. Similarly, W₄Co₃VB₄ and W₄Co₃MnB₄ also imply similar variation of mechanical properties and electronic structures.     

WCoB金属陶瓷的制备及其性能研究

以WC、TiB2、Co粉末为原料,采用真空液相反应烧结技术制备WCoB金属陶瓷,并利用XRD、SEM和EDS对其微观形貌及相组成进行了表征。结果表明,WCoB金属陶瓷由WCoB、W2CoB2、TiC、Co2B和TiB2等相组成,其硬度为HRA84.4～92.2,合金密度为9.3～10.2g/cm3。随着钴含量的增加,烧结后WCoB金属陶瓷的合金密度和硬度值均有所下降,较高的烧结温度有利于晶粒细化。磨损试验发现WCoB金属陶瓷的耐磨性优于YG8硬质合金。     

Synthesis and microstructure evolution of WCoB based cermets during spark plasma sintering

WCoB based cermets were prepared by spark plasma sintering at sintering temperature among 600°C-1200 °C. The phase evolution was investigated by detecting density behavior, phase composition, microstructure and mechanical properties during sintering process. The sintering process can be divided into three stages: powder densification, solid phase reaction and liquid phase sintering. WCoB hard phase forms at 1000 °C during solid phase sintering, showing better mechanical properties than Co₂B, especially on Vicker's hardness. WCoB hard phase forms on the basis of Co₂B binary boride and its content increases in liquid phase sintering stage with high density. The Vicker's hardness and transverse rupture strength (TRS) reach the maximum value of 1262 Hv and 1212 MPa at 1200 °C and 1170 °C, respectively. The fracture toughness reaches the maximum value of 21.8 MPa m^1/2 at 1050 °C, and the inter-granular fracture is the main fracture mechanism.