WC-TiC-TaC无金属粘结相硬质合金的热压致密化与晶粒生长行为

采用Cr、V掺杂超细WC与TaTiC2型单一相成分WC-36.5TiC-24.5TaC复式碳化物粉末为原料,通过1 700℃、20 MPa热压工艺,制备WC-3.65TiC-2.45TaC-0.47Cr3C2-0.28VC无金属粘结相硬质合金。采用X射线衍射分析技术研究烧结过程中的物相转变,采用扫描电镜与能谱仪对合金微观组织结构特征进行观察与分析。结果表明,在高温、高压固相烧结过程中,发生了W原子向复式碳化物中的大量固溶、TaTiC2型固溶体向TiWC2型固溶体的物相转变以及固溶体中Ta、Ti原子向WC中的反向固溶。合金固相烧结致密化主要机制为W原子与Ta、Ti原子之间的非平衡体扩散机制以及高温、高压下物质的粘性/塑性流动机制。W原子在固溶体型复式碳化物粘结相中的各向异性溶解-析出会显著削弱晶粒生长抑制剂的功能,导致板状WC晶粒的形成。

Hot pressing densification and grain growth behavior of WC-TiC-TaC binderless carbide

WC-3.65TiC-2.45TaC-0.47Cr3C2-0.28VC binderless carbide was prepared by hot pressing at the temperature of 1 700 ℃ and pressure of 20 MPa.Ultrafine tungsten carbide doped with V and Cr and WC-36.5TiC-24.5TaC mixed carbide with TaTiC2 type phase composition were used as the raw materials.X-ray diffraction technology was used to study the phase transformation during the sintering process.Scanning electron microscopy and energy dispersive X-ray spectroscopy were used to characterize the microstructure.The results show that during the sintering process W atoms dissolve on a mass scale into the crystal lattices of the mixed carbide,which results in the phase transformation of the solid solution from TaTiC2 type to TiWC2 type.Meanwhile,the reverse dissolution of Ta and Ti atoms into the WC crystal lattices takes place.The mechanism for the densification through solid phase sintering is dominated by the bulk diffusion among W,Ta and Ti atoms in a nonequilibrium manner and a viscosity/plastic flow of material caused by the high temperature and high pressure.The anisotropic dissolution and precipitation of W atoms in the mixed carbide binder phase can substantially weaken the function of the grain growth inhibition and result in the formation of platelet WC grains.