中粗WC含量对Ni-Co粗晶硬质合金微观组织及性能的影响

研究了中粗WC含量对Ni-Co粗晶硬质合金微观组织与晶粒分布的影响,进而讨论了晶粒分布对硬质合金力学性能的影响。通过金相分析了中粗WC含量对硬质合金晶粒度与邻接度的影响,并利用截线法研究了微观组织的晶粒的分布规律;研究了晶粒度与晶粒分布对磁力、密度及其它力学性能的影响。结果显示,中粗WC晶粒可均匀分布在粗晶WC周围阻碍粗晶与粘结相接触,抑制了粗晶粒的快速粗化,降低了合金平均晶粒度与平均自由程,使晶粒分布逐渐转变为双峰分布;在压力烧结下所有合金的相对密度均在99.5%以上,通过对矫顽磁力的测试分析,验证了微观组织中晶粒双峰分布的准确性;平均晶粒度的降低使合金硬度逐渐增加、断裂韧性逐渐降低;微观组织中超粗晶粒逐渐减少,有利于硬质合金抗弯强度与耐磨性的提高。在Ni-Co粗晶硬质合金中加入部分中粗WC颗粒有利于减少晶粒粗化进而提高耐磨性,加入30%中粗WC颗粒时综合性能最好。     

Influence of the cemented carbide specification on the process force and the process temperature in grinding

Cemented carbides are hard and brittle materials. Their material properties are adjusted by their chemical composition, in particular their average hard phase grain size and their binder fraction. The research paper focusses on grinding of cemented carbides with cobalt (Co) as binder and tungsten carbide (WC) as hard phase material. Within the research paper, it is discussed if and to what extent the cemented carbide composition affects the occurring thermo-mechanical load collective in the grinding process. In particular, the influence of the average WC grain size and the cobalt fraction on the thermo-mechanical load collective is investigated and explained by the cemented carbide material properties. The results of the publication contribute to a knowledge-based design of cemented carbide grinding processes.     

A study of grain boundaries in a binderless cemented carbide

The microstructure of a binderless cemented carbide with < 0.5 wt% Co has been analysed using transmission electron microscopy (TEM) in combination with an electron energy loss spectroscopy (EELS) detector and an imaging filter. In particular, microstructural properties of the grain boundaries were studied. The analysis identified different kinds of grain boundaries in the material: boundaries between WC grains containing nanometre-thick layers of Co; WC-WC grain boundaries with perfect lattice matching and no or very small amounts of Co; and boundaries between WC and TiC grains containing high amounts of C, but no Co. The influence of the grain boundaries on the mechanical properties is discussed.     

Ni3Al添加量对WC-Co硬质合金中WC晶粒形状的影响

采用粉末冶金制备技术,以粗WC粉末、Co粉和WC＋Ni3Al预合金粉末为原料制备出WC-40vol％（Co—Ni,Al）硬质合金。利用扫描电镜和透射电镜研究了不同NbAl含量对WC-40vol％（Co—Ni3Al）硬质合金中WC晶粒形状的影响规律。结果表明：W在Co粘结相中的固溶度接近25．4wt％,而W在Ni,Al粘结相中的固溶度接近9．5wt％,随着NbAl含量的增加,粘结相对W的固溶度减小,合金中的WC晶粒圆钝和细小;WC晶粒表面上出现明显的台阶。相应的,延长烧结时间,WC—Co—Ni3Al硬质合金具有与WC—Co硬质合金相同的WC生长行为,WC-40vol％（Co—Ni3Al）硬质合金中的WC晶粒表面上的台阶处出现明显的刻面。     

超细硬质合金晶粒生长抑制剂VC、Cr_3C_2作用机理的研究

本文以液相复合-连续还原碳化方法制备的掺杂有VC和Cr3C2抑制剂的纳米复合WC-10Co粉末为原料,采用真空烧结+低压处理的工艺制备超细WC-10Co硬质合金,运用原子力显微镜(AFM)和场发射扫描电镜(FESEM)确定VC和Cr3C2抑制剂在硬质合金中的分布,讨论其抑制晶粒生长的机理。一部分VC、Cr3C2抑制剂吸附在WC晶粒表面形成30nm～50nm的沉淀物,降低WC晶粒的表面能;一部分VC、Cr3C2溶解在Co相中,降低WC在液相中的溶解度;其余VC、Cr3C2沉积在WC晶界,从而有效地抑制WC晶粒的长大。     

工程陶瓷超精密磨削表面质量的研究

本文从几何和物理特性两方面研究了ZrO2和Sialon陶瓷超精磨制削的表面质量。实验结果表明：金刚石砂轮磨粒尺寸和磨削深度对磨削表面的微观形貌如几何形态和表面纹理具有重要影响。超精密磨削的表面存在着残余应力，但其数值较小，残余应力从表面向材料内部迅速减小，砂轮磨粒尺寸和磨削深度是残余应力的主要影响因素。在ZrO2和Sialon陶瓷超精密加工的表面上亦存在着相变，ZrO2陶瓷的相变将引起表面残余压应力的增加，Sialon陶瓷的相变对表面残余应力的影响很小，采用TEM和XRD对超精密磨削表层结构的研究表明，在加工表层存在着很深的变质层，它由表面的非晶层和相邻的塑性变形层组成，然后逐步过渡到基体组织。     

Influence of surface topography evolution of grinding wheel on the optimal material removal rate in grinding process of cemented carbide

Most of the reported studies on the optimization of grinding parameters do not consider the evolution of the surface topography of grinding wheels, and the established empirical models will no longer apply when the surface conditions of the grinding wheel changes. In this paper, an integrated model based on the surface topography of grinding wheel is established. The grinding process of cemented carbide is simulated using the established model, and the simulation results are analyzed to obtain the surface roughness model and the specific grinding energy model based on the undeformed chip thickness distribution. Subsequently, the grinding constraint models are defined according to the two grinding constraints—surface roughness and specific grinding energy. Through inversion analysis, the maximum material removal rate of the given grinding wheel surface conditions satisfying the defined grinding constraints are obtained, and the influence rules of the grinding wheel surface conditions on the maximum material removal rate are analyzed. Then the grinding wheel surface conditions are adjusted by changing the radial dressed height of the grinding wheel and the arrangement distance of the grains in wheel circumferential direction to improve the maximum material removal rate of the grinding wheel. Finally, the optimization results are verified through grinding tests of cemented carbide.     

WC粒度分布对WC-Co硬质合金力学性能影响的模拟分析

本文旨在建立基于WC-Co硬质合金真实微观组织的力学性能预测有限元分析方法,进而分析WC颗粒粒度分布对微区变形和力学行为的影响。实验设计和制备了具有Co含量相同,WC晶粒分布均匀和非均匀的两种WC-Co硬质合金,并进行维氏硬度测试和用SEM进行组织观测。通过对合金组织的SEM形貌照片进行WC颗粒边界的重构,建立WC和Co两相真实组织的二维有限元模型。通过有限元模拟对两种合金的弹性模量、泊松比和强度等力学性能进行预测和微观变形机理分析。有限元模拟结果表明均匀合金强度高于非均匀合金,与实验测试的硬度所揭示的规律相吻合。对微观变形机理分析揭示了均匀合金应力分布更均匀是强度较高的主要内在机理,而WC/WC邻接界面的应力集中是弱化力学性能的主要机制。     

Cr_3C_2对WC-6.5％Co硬质合金组织和性能的影响

通过向WC-6.5%Co硬质合金中添加0%～2.0%的晶粒长大抑制剂Cr_3C_2,研究了其对硬质合金组织和力学性能的影响。研究结果表明,Cr_3C_2的添加细化了WC晶粒,但不能完全抑制WC晶粒的异常长大。Cr_3C_2使合金的硬度提高,但是却降低了合金的致密度和抗弯强度。Cr_3C_2添加量为0.5%时,合金的综合性能最好。     

深冷处理对硬质合金的影响

综述了国内外硬质合金深冷处理的工艺过程及其深冷处理对硬质合金微观组织、相结构、残余应力状况、机械性能与切削性能的影响。深冷处理工艺包括降温和保温两个基本阶段,部分研究增加回火处理;深冷处理后硬质合金中η相含量增多且尺寸减小,Co对WC的粘结更紧密,但也有认为微观组织形貌变化不大的观点;Co相由面心立方向密排六方转变,而WC相变化不大;深冷处理可提高硬质合金耐磨性和延长使用寿命已得到共识,但对表面残余应力状况及硬度等影响尚存在不同观点。探索深冷处理对硬质合金的作用机理,并进行工艺参数的优化是目前研究工作的方向。     

基于ELID磨削WC-Co硬质合金表面机械研抛研究

本文采用ELID磨削和机械研磨抛光复合技术,对WC-Co硬质合金表面进行了超精密加工实验研究。首先采用ELID磨削对WC-Co硬质合金表面进行预加工,获得表面粗糙度Ra18 nm的精密加工表面。在此基础上对其进行机械研磨抛光加工,研抛盘转速设定为150～200 r/min,研抛压力控制在0.2～0.5 N/cm2范围;机械研抛时,首先采用含W1金刚石磨粒的研抛液,对ELID磨削后的表面进行加工100min左右,以达到快速去除的目的。再用含W0.5金刚石磨粒的研抛液,进行机械研抛约100 min,最后获得Ra4 nm的超精密表面。同时,针对机械研磨抛光过程,本文深入研究了磨料种类、粒度、抛光液溶剂、研抛压力、研抛加工时间等因素对加工表面粗糙度的影响。     

WC-base cemented carbides with partial and total substitution of Co as binder: Evaluation of mechanical response by means of uniaxial compression of micropillars

The influence of the chemical nature of the metallic binder on the plastic deformation of cemented carbides was studied. Three different cemented carbide grades - WC-Co, WC-CoNi and WC-NiMo - with similar microstructural characteristics (binder content and carbide grain size) were investigated. Mechanical response was evaluated by means of uniaxial compression of micropillars, and tests were carried out in-situ in a FESEM with a nanoindenter equipped with a flat-diamond punch. After uniaxial compression, inspection of deformation phenomena was done at both surface and bulk of micropillars through scanning and transmission electron microscopy, respectively. It is found that yielding phenomena and strain hardening increase as Co is totally substituted by a NiMo alloy, while contrary effect results from partial replacement of Co with Ni. Relative differences are directly linked to intrinsic ductility of the metallic phase and operative plastic deformation mechanisms. Moreover, for the three materials studied, stress-strain responses show pronounced yielding events related to glide at WC/WC interfaces. Although they are discerned at different stress levels, estimated values of sliding resistance of WC/WC boundaries are found to be alike for the three grades studied.     

树脂金刚石砂轮加工氧化铝陶瓷的磨削工艺试验研究

为改善氧化铝陶瓷的磨削效果,分别使用粒度尺寸125~150 μm和38~45 μm的金刚石制备树脂结合剂砂轮,并进行磨削实验,研究表面粗糙度、材料去除方式和材料去除比例随磨削参数的变化规律,观察并分析氧化铝陶瓷磨削后的表面微观形貌。结果表明:氧化铝陶瓷的表面粗糙度可以达到R_a 0.418 μm,材料去除比例可达到95%;用粒度尺寸38~45 μm的金刚石制备的树脂结合剂砂轮在切深≤ 2 μm,工件移动速度为0.15 m/min加工时,材料由延性域的塑性去除转变为脆性去除。优化后的加工工艺为先以磨料粒度尺寸125~150 μm的树脂金刚石砂轮在切深为4 μm时进行初步加工,再用磨料粒度尺寸38~45 μm的树脂金刚石砂轮进行光磨,可以兼顾高效与精密两方面的要求。      

Effect of VC and NbC additions on microstructure and properties of ultrafine WC-10Co cemented carbides

The nanocomposite WC-Co powders were prepared through planetary ball milling method. Effects of grain growth inhibitor addition and the vacuum sintering parameters on the microstructure and properties of ultrafine WC-10Co cemented carbides were investigated using X-ray diffractometer, scanning electron microscope and mechanical property tester. The results show that VC and NbC additions can refine the WC grains, decrease the volume fraction of Co₃W₃C phase in ultrafine WC-10Co cemented carbides, and increase the hardness and fracture toughness of the base alloys. After sintering for 60 min at 1400 °C, the average grain size and hardness of ultrafine-grained WC-10Co-1VC cemented carbide are 470 nm and HRA 91.5, respectively. The fracture toughness of cemented carbide WC-10Co-1NbC alloy is over 7 MN·m^?3/2.     

Microstructure and properties of CVD coated on gradient cemented carbide with different WC grain size

In this paper, cemented carbides with gradient surface enriched in Co phase and depleted of cubic phases were prepared by one-step vacuum sintering. The gradient cemented carbides of different WC grain size were used as the substrates of CVD coatings. The effects of WC particle size on the formation of gradient layer, microstructure and properties of the gradient cemented carbides were investigated. Besides, the influence of WC grain size and gradient layer on microstructure, growth and adhesion strength of the coatings were studied. The results showed that the thickness of surface gradient layer decreased with increasing WC particle size, which was attributed to the decreased diffusion paths and the increased diffusion distance. The interface between the surface gradient layer and the bulk was disordered due to abnormal grain growth of WC in ultrafine cemented carbide. The microhardness across the direction of the fcc-free (Face Center Cubic Free) surface layer to the bulk were similar in the three gradient cemented carbides, and could be expressed as: from the surface to the inner, the microhardness decreased firstly, then increased sharply around the interface, and subsequently dropped to the bulk level. The coating on the fcc-free surface layer was thicker than that on bulk, and the coating on the substrate with fine-sized WC grains is the thickest. The increase of the WC grain size in the substrate could improve the bonding strength of the coating. Furthermore, the presence of Co-rich layer could improve the bonding strength. However, bonding strength was poor for the grain size of ultrafine.     

Synthesis of Cr-doped APT in the evaporation and crystallization process and its effect on properties of WC-Co cemented carbide alloy

WC grain size has significant effect on WC-Co cemented carbide alloy properties. In order to inhibit WC grain growth during sintering process, grain growth-inhibitor Cr₃C₂ is usually added to tungsten carbide powder in advance through mechanical milling. While, homogeneous distribution of Cr₃C₂ in the tungsten carbide powder is difficult to achieve and result in abnormal growth of WC grains. For this purpose of growth-inhibitor uniform distribution, (CH₃COO)₃Cr is added into ammonium tungstate solution during evaporation and crystallization process to prepare Cr-doped APT powder, which can be used as precursor for ultrafine-grained WC-Co cemented carbide alloy preparation. Compared with conventional APT powder, the Cr-doped APT has smaller particle size and bulk density, moreover, chromium is evenly distributed within it. The Cr-doped APT is then used to produce Cr-doped tungsten powder, which also has smaller particle size than that of conventional tungsten powder. Cr-doped tungsten powder is subsequently prepared into tungsten carbide powder and WC-Co cemented carbide alloy through carbonization and sintering process, respectively. Compared with conventional WC-Co cemented carbide alloy, the obtained WC-Co cemented carbide alloy has smaller mean WC grain size (0.36 μm), and more uniform microstructure. Furthermore, the phenomenon of WC grain abnormal growth during sintering process is not observed, because the grain growth-inhibitor Cr₃C₂ is well dispersed in tungsten carbide and cobalt composite powder. Results show that the obtained WC-Co cemented carbide alloy presents better mechanical properties (HRA, bending strength, coercive force) than those of conventional WC-Co cemented carbide alloy. Accordingly, the novel addition of (CH₃COO)₃Cr during the evaporation and crystallization process is the key factor of ultrafine-grained WC-Co cemented carbide alloy production.     

硬质合金中异常长大晶粒生长方向的EBSD研究

在硬质合金烧结过程中的晶粒异常长大是影响硬质合金产品质量的重要问题,本文采用EBSD分析硬质合金中异常长大晶粒的取向,结果表明:由于硬度大,样品进行金相抛光后可直接进行EBSD分析;粗晶晶粒生长完整,没有亚晶界;在烧结过程中,WC晶粒沿晶向{1120}﹤110﹥择优生长。     

Influence of the type and grain size of the electro-conductive phase on the Wire-EDM performance of ZrO2 ceramic composites

This paper investigates the Wire-EDM behaviour of various newly developed electro-conductive ZrO₂ ceramic matrix composites. The influence of the type and grain size of the second phase (WC, TiC and TiCN, from micro sized to nano sized grains) on the EDM material removal rate and obtained surface roughness is experimentally studied. This investigation is based on a design of experiments supported by a fundamental study of the material removal mechanisms. It is shown that a variation in grain size of the second phase material significantly influences the EDM performance, which can be largely related to the microstructure and the properties of the developed material.     

过渡族金属碳化物在WC-Co硬质合金中的界面偏析与固溶行为

过渡族金属碳化物是最常见的硬质合金微观组织结构与性能调控添加剂,添加剂在硬质合金中赋存状态的研究是WC晶粒生长抑制机理研究的基础,也是硬质合金材料与工艺设计的基础。从基于第一性原理计算的理论研究、基于高分辨透射电镜和原子探针层析法的实验观察分析等2个方面,综述了过渡族金属碳化物在WC/β(钴基固溶体粘结相)相界偏析行为的研究现状。基于过渡族金属碳化物在硬质合金中晶界与相界的偏析行为、在硬质相与粘结相中的固溶行为,讨论了硬质合金中WC晶粒生长机理与晶粒生长抑制机理以及过渡族金属碳化物对硬质合金性能的影响机理,提出了硬质合金材料与工艺设计的建议。