Ni_3Al含量对WC基钢结硬质合金组织与性能的影响

Effects of Ni_3Al content on microstructure and properties of WC based steel bonded carbide

为了改善WC基钢结硬质合金性能,以热力学计算为基础,探索Ni_3Al添加量对WC-Fe(Cr,Mo)钢结硬质合金组织与性能的影响。采用粉末冶金方法,以添加Ni_3Al预合金粉的方式添加Al,通过液相烧结制得不同Ni_3Al含量(0,0.5%,1.0%,1.4%,质量分数)的WC-50%(Fe-Ni-Al-Cr-Mo)合金样品。采用差示扫描量热分析(DSC)、X射线衍射仪(XRD)、扫描电子显微镜(SEM)和金相显微镜分别对合金的液相温度点、相组成和显微组织进行了检测分析,并讨论了合金物理力学性能和磁性能的变化规律。结果表明:粘结相主要由γ-α+β′三相构成,且随着Ni_3Al含量的增加,Ni元素可以稳定奥氏体,粘结相中γ-Fe含量增加,1250℃时,Fe-Ni-Al粘结相从液相中析出γ-Fe相的形核驱动力增大,使得粘结相的晶粒细化,粘结相中析出的Ni Al相增多;合金硬质相主要为WC和Fe_3W_3C,WC沿晶界偏聚;γ-Fe含量增多,固溶了更多C元素,使Fe_3W_3C的含量随Ni_3Al含量增加而减少;WC晶粒细化,分布更为弥散。在上述因素共同影响下,合金密度略有降低,粘结相的磁饱和强度下降,矫顽磁力上升;硬度上升,抗弯强度先下降后上升,并在添加Ni_3Al含量为1.4%时,硬度和抗弯强度达到最大值。

In order to improve the performance of WC based steel bonded carbide, the effects of Ni3Al content on microstructure and properties of WC-Fe（Cr, Mo） steel bonded carbide were explored based on thermodynamic calculation. The alloys with different Ni3Al contents （0, 0.5%, 1.0%, 1.4%, mass fraction） were prepared by liquid phase sintering method through adding Al with the form of Ni3Al prealloyed powders. The liquidus temperature, phase composition and microstructure of alloys were analyzed by the differential scanning calorimetry （DSC）, X-ray diffractometer （XRD）, scanning electron microscope （SEM） and metalloscope, respectively. The effects of Ni3Al content on the mechanical and magnetic properties of alloys were investigated. The results show that, with the increase of Ni3Al content, γ-Fe content increase, due to the improved stabilities of austenite through the solution of Ni element. The driving force for the nucleation of the γ-binder precipitating from liquid phase at 1250 ℃ increases, which refines the grains, NiAl precipitation in the binder phase increases. The hard phases are mainly WC and Fe3W3C, with the increase of Ni3Al content, more C element dissolves in γ-Fe binder phase, which leads to a less precipitation of Fe3W3C, refined WC grains are distributed more dispersedly. Above all, with the increase of Ni3Al content, the density of alloys decreases slightly. The magnetic saturation of binder phase decreases while coercive force increases. The hardness of alloys raises while the transverse rupture strength of alloys first decreases, then increases. Both the hardness and transverse rupture strength reach maximum value when the Ni3Al content is 1.4%.