富Co-layers硬质合金表面渗氮处理微观结构和性能研究

Study on Microstructure and Properties for Co-rich Layers Cemented Carbides by Surface Nitriding Treatment

采用两步法烧结工艺制备了表面富Co-layers硬质合金和表面富Ti基硬质相层硬质合金,对比研究了氮化处理前后硬质合金表面微观形貌、生成相和力学性能的差异。研究表明:真空条件下烧结可在试样表层生成约20μm厚的Co-layers,该层中不含立方碳化物相,微观结构分析发现试样表面呈现山丘形貌且具有金属亮银色光泽,可用于修复试样表面缺陷,如微观裂纹、孔洞等,并且改善硬质合金表面韧性和提高涂层与基体之间的界面结合强度。氮化处理可在合金表面原位生成富含细晶粒的TiN相层,层厚约1μm,微观结构分析发现该层呈金色或棕色,表面较为平整。通过性能对比分析发现渗氮虽然导致试样密度小幅降低,但是可显著改善晶粒尺寸分布不均和增加表层硬质相中的微应变,能够在提高表面硬度的同时依然保持较高韧性,同时可有效改善硬质合金的刀具耐磨性和使用寿命。

The Co-rich layers and Ti-rich hard phase-layers, on cemented carbides were prepared by.a two-step sintering tech- nology, respectively. The microstructure, sintering phases and mechanical properties of cemented carbides before and after nitriding treatment were studied. The ～20/μm-thick Co-rich layers were obtained on the surface of specimen under vacuum sintering condi- tion, and no cubic carbide phase was contained in the Co-rich layers. The surfaces of specimen appear a kind of hill topography and own bright silver metal luster which were confirmed by mierostructure morphology analysis. It can be used to repair the micro-de- fects, e.g. micro-cracks or micro-holes, on the surface of specimens, improve the toughness of cemented carbides surface, and en- hance the interracial bonding strength between the coating and the substrate. The fine grain ～1 μm-thick Ti-rich hard phase layers could be prepared in situ on the specimen surface by nitridation. The Ti-rich hard phase layers appear gold or brown color and a rela- tively smooth surface by microstructure analysis. Through comparison and analysis, it could be concluded that though the densities of specimens are decreased as a result of nitridation treatment, but simultaneously some properties can be significantly improved, such as fine grain size distribution and favorable surface micro-strain in the Ti-rich hard phase, which can promote surface hardness with remote toughness loss, and also effectively improve wear resistance and lifetime of cemented carbide tools.