粘结剂对WC硬质合金模具力学性能的影响

通过烧结工艺制备了不同粘结剂含量的WC基硬质合金,研究了Co、Ni粘结剂对合金力学性能的影响。结果表明,随着粘结剂含量的增加,WC硬质合金制品的密度、洛氏硬度、抗弯强度和抗压强度都逐渐降低,而冲击韧度逐渐升高,耐磨性先增大后减小。当添加13%Co+6.5%Ni时,合金晶粒尺寸细小,完全包覆了WC粒子,大大提高了耐磨性。     

粘结剂对WC硬质合金模具力学性能的影响

通过烧结工艺制备了不同粘结剂含量的WC基硬质合金,研究了Co、Ni粘结剂对合金力学性能的影响。结果表明,随着粘结剂含量的增加,WC硬质合金制品的密度、洛氏硬度、抗弯强度和抗压强度都逐渐降低,而冲击韧度逐渐升高,耐磨性先增大后减小。当添加13%Co+6.5%Ni时,合金晶粒尺寸细小,完全包覆了WC粒子,大大提高了耐磨性。     

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。     

Ni含量对粗晶WC-Co-Ni硬质合金组织和性能的影响

以WC-10%(Co+Ni)硬质合金为研究对象,在相同含量的Co+Ni粘结相中采用不同的钴镍比来研究Ni含量对WC-Co-Ni硬质合金组织和性能的影响。结果表明随Co+Ni粘结相中的镍含量的增加,合金中显微组织结构中的粘结相的分布均匀性变差;WC晶粒的尺寸和圆度增大。合金的强度性能结果表明WC-(Co+Ni)硬质合金在粘结相质量分数为60%Co-40%Ni时抗弯强度出现最大值;随Ni含量的增加,WC-(Co+Ni)硬质合金的硬度值相差不大,但呈下降趋势;合金的密度几乎没有变化;合金的钴磁降低,磁力呈现先增后降。     

WC对碳化钛基高锰钢钢结硬质合金组织与性能的影响

以Fe-Mo、Fe-Mo-Cr预合金粉为粘结剂,加入WC以及Ni、Mn、C等合金元素,采用粉末冶金工艺制备了TiC基高锰钢钢结硬质合金,研究了WC对TiC基高锰钢钢结硬质合金组织与性能的影响。采用扫描电子显微镜对实验合金的组织进行了观察和分析,并对合金的物理力学性能进行了检验。结果表明,未加WC的合金中出现了黑芯-灰环和灰色粘结剂两种结构;添加WC的合金中观察到了黑芯-灰环、灰色粘结剂和其他多种复杂的结构。并且,随着WC含量的增加,合金组织的硬质相晶粒尺寸明显细化。结果还表明,随着WC含量的增加,合金的相对致密度、硬度一直增大,但抗弯强度和冲击韧性先增大后减小。当WC质量分数为15%时,合金的冲击韧性达到最大值12.2 J/cm2,相对致密度、硬度和抗弯强度分别达到98.5%、88.2 HRA、1 852 MPa。因此,这种合金(WC质量分数15%)可以用于代替硬质合金制造挖掘机装载机斗齿的镶嵌件以及采煤机截齿等在冲击条件下使用的耐磨零件。     

WC粒度、配碳量对WC-9%Ni硬质合金组织与性能的影响

采用Ni作为黏结相，通过粉末冶金工艺制备WC-9%Ni(质量分数)硬质合金，通过光学显微镜、硬度仪、X衍射分析仪等仪器，研究WC粒度、配碳量对WC-9%Ni硬质合金组织与性能的影响。结果表明：合金晶粒度受配碳量的影响较小，随WC粒度增大而增大；合金硬度随配碳量增加而降低，随WC粒度增大而降低。费氏粒度1.78μm的WC与费氏粒度2.4μm的WC制备的合金洛氏硬度最高分别为88.6HRA、87.5HRA，维氏硬度HV₃₀最高分别为11.9、11.0 GPa。合金矫顽磁力与比饱和磁化强度极低，合金断裂韧性随配碳量的增加而降低，随WC粒度增加而增加，抗弯强度受配碳量影响较小，随WC粒度增加而降低。     

球磨时间对WC-6％Ni硬质合金微观结构及性能的影响

以WC-6％Ni硬质合金为研究对象,采用不同球磨时间制备了5组合金试样,通过对烧结后合金磁、力学性能的检测及显微结构观察,分析研究了球磨时间对WC-6％Ni硬质合金的微观结构及其性能的影响.结果表明:球磨时间对WC-6％Ni硬质合金的微观结构和性能影响明显,过短的球磨时间导致合金中存在粗大WC晶粒,适当延长球磨时间可使WC晶粒得到细化并获得微观结构均匀的合金,但过长的球磨时间则会导致合金中粗WC晶粒的再次出现.随着球磨时间的增加,抗弯强度、硬度、矫顽磁力均随之经历先上升到峰值后下降的过程;而球磨时间对WC-6％Ni合金的密度影响很小.当球磨时间为36 h时,WC-6％Ni硬质合金具有最小的WC平均晶粒度和相对均匀的微观结构,合金抗弯强度、硬度及矫顽磁力出现峰值,分别为2 250 MPa、89.4 HRA、4.9 kA/m.     

WC-Ni-Fe-Mo硬质合金的微观结构与性能研究

本文采用低压烧结的方式制备了性能良好的 WC–Ni–Fe–Mo 硬质合金,研究分析了不同 Mo 添加量对 WC–Ni–Fe硬质合金组织性能的影响。结果表明：不同 Mo 添加量对 WC–Ni–Fe 硬质合金的微观结构与性能有着显著地影响。添加微量的 Mo 可以抑制 WC-Ni-Fe 硬质合金中 WC 晶粒的溶解再析出长大,一定程度上可以细化 WC 晶粒。随着 Mo 在 WC–Ni–Fe 合金中的含量增加,合金孔隙率逐渐下降。密度先下降后升高,而抗弯强度的变化趋势则相反。当 Mo 添加量较少时,合金的硬度较为稳定,抗弯强度明显提升,而断裂韧性逐渐降低;当 Mo 添加量较大时,合金的硬度、抗弯强度降低,而断裂韧性上升。当 Mo 的添加量为0.5 wt %时,合金具有最佳的力学性能,可与同比例 Co 含量的 WC–Co 硬质合金相媲美,其维氏硬度为 HV 1460、抗弯强度为 4245 MPa、断裂韧性为 17.01 MPa·m1/2。     

贫碳WC-12%(Co+Ni)硬质合金微观组织与性能

硬质合金的组织和性能对C含量具有很高的敏感性，但对WC硬质合金两相区下限碳含量的综合性能研究甚少。本文分析了两相区下限附近碳含量（5.06%～5.21%）对烧结制备WC-12%(Co+Ni)硬质合金微观组织和性能的影响。研究发现：在两相区内较高C量会抑制Ostwald机制(较小颗粒溶解而较大颗粒继续长大的机制)中WC的溶解过程；在两相区以下较低C量，脱碳相的存在会抑制Ostwald机制中WC的沉积过程。随着碳含量的增加，WC平均晶粒度呈先增大后减小的趋势，在C含量为5.11%时达到最大值。碳含量的增加会影响W的溶解度，W在缺碳区形成η相和在两相区沉淀形成WC都会造成黏结相W溶解度的降低。能谱(EDS)显示碳含量为5.21%时合金黏结相溶解的W约19.41%，较5.11%碳含量的合金下降了19.45%。碳含量和微观组织对硬质合金的性能具有敏感性：密度随碳含量的增加略有下降，而钴磁上升却很明显；合金的洛氏硬度HRC和抗弯强度随着碳含量成抛物线变化趋势，在5.16%达到极大值，分别为83和2070 MPa。     

多物理场耦合烧结制备超细WC-Ni硬质合金致密化机理

为了研究Ni含量对WC-Ni硬质合金性能的影响,利用多物理场耦合烧结方法制备不同Ni含量的超细WC-Ni硬质合金,结果显示:多物理场耦合烧结方法可以成功制备WC-Ni硬质合金,随着Ni含量增加,WC-Ni硬质合金的组织更加致密,试样的相对致密度逐渐增加,但WC颗粒发生了轻微的长大现象;同时,显微硬度先增后减,在Ni质量分数为8%时达到最大值,断裂韧性K_(IC)则随Ni含量的增加迅速增加到8.5 MPa·m~(1/2)。     

Effects of Ni addition and cyclic sintering on microstructure and mechanical properties of coarse grained WC–10Co cemented carbides

Coarse grained WC–10(Co, Ni) cemented carbides with different Ni contents were fabricated by sintering-HIP and cyclic sintering at 1450 °C. The effects of Ni addition and cyclic sintering on the microstructures, magnetic behavior and mechanical properties of coarse grained WC–10(Co, Ni) cemented carbides have been investigated using scanning electron microscope (SEM), magnetic performances tests and mechanical properties tests, respectively. The results showed that the mean grain size of hardmetals increases from 3.8 μm to 5.78 μm, and the shape factor Pwc decreases from 0.72 to 0.54, with the Ni content increases from 0 to 6 wt.%. Moreover, the W solubility reaches the highest value of 10.33 wt.% when the Ni content is 2 wt.%. The hardness and transverse rupture strength of WC–8Co–2Ni are 1105 HV₃₀ and 2778 MPa, respectively. The cyclic sintering is conducive to increase the WC grain size of WC–10(Co, Ni) and improves the transverse rupture strength of WC–10Co without compromising the hardness of alloys.     

Wear resistance of nanostructured Cr-based WC hardmetals sintered by spark plasma sintering

Nanostructured Cr-based WC hardmetals are successfully sintered by spark plasma sintering. The wear behaviour of these Cr-based WC hardmetals with different C contents ranging from 5.57 wt% to 6.91 wt%, is evaluated performing sliding wear tests under two different wear conditions. This work analyses the influence of the C content on the wear performance through the study of the phase formation and WC grain size. The Cr-based hardmetal with 5.57 wt% C content exhibits a lower wear rate than Co-based WC hardmetals tested under similar dry ball-on-plate wear conditions, even considering that these Co-based WC hardmetals have higher WC content (90 wt%) than Cr-based WC hardmetals (83.2 wt%). The combination of a nanosized WC grain and the avoidance of brittle (Cr,Fe)₇C₃ or soft graphite phases leads to a superior wear performance. Thus, the use of Cr-based binders in the hardmetal industry, alternatively to Co-based binders, is promising in applications in which high wear resistance is needed.     

纳米材料在硬质合金中的应用

WC晶粒不断细化是硬质合金发展的一个重要特征。从硬质合金的纳米原料、纳米硬质合金、纳米材料助长或增强超粗晶硬质合金以及硬质合金的纳米涂层材料等4个方面论述了纳米材料在硬质合金中的应用,着重报道了中国在这些方面的优势。纳米粒径原料的制备是首要难题,1997年发明的“紫钨原位还原”技术利用传统工艺制备纳米、超细碳化钨粉末,碳化钨粉的粒径可小于20 nm。纳米硬质合金技术利用低压热等静压或热等静压,克服了烧结过程中 WC异常长大的难题,制备100～200 nm纳米硬质合金,抗弯强度在5000 MPa以上,使用性能优于亚微或超细晶硬质合金,已用于生产。利用“纳米颗粒溶解法”制备的超粗晶硬质合金晶粒度可达12μm;而含有纳米Co2 W4 C增强相的超粗晶硬质合金产品,使用寿命比普通合金产品提高了2～3倍。涂层材料纳米化,是硬质合金工具的一个发展方向,在耐磨性、硬度和抗裂纹扩展方面有明显优势,加工工件表面质量更好,工具使用寿命更长。     

Implementation of an effective time-saving two-stage methodology for microstructural characterization of cemented carbides

Linear intercept on scanning electron microscopy micrographs is the most commonly used measurement method to determine carbide grain size and contiguity in WC–Co cemented carbides (hardmetals). However, it involves manual time-consuming measurements and is critically dependent on the quality of the micrographs as well as on the identification and definition of grain boundaries. In this study a two-stage methodology for microstructural characterization of hardmetals is presented. First, a digital semi-automatic image analysis procedure for grain size determination of the carbide phase is presented. It involves an experimental assessment of grain size on processed images corresponding to a series of WC–Co and WC–Ni cemented carbide grades with different microstructural characteristics. Obtained results are then compared to the values obtained by means of the linear intercept technique. A good correlation between the mean grain sizes determined following both measurement techniques was attained. Based on experimental findings, a series of empirical relations were found to correlate grain size distributions obtained following both methods. Second, an empirical relation for estimating carbide contiguity in WC–Co cemented carbides is proposed. This relation considers simultaneously the influence of the binder content and the experimentally determined mean grain size on contiguity. The proposed equation for contiguity estimation is based on extensive data collection from open literature. An excellent agreement was attained between contiguity values estimated from such equation and those obtained using the linear intercept technique. This validates the two-stage procedure as an effective time-saving methodology for microstructural characterization of WC–Co cemented carbides.     

Carbon content dependence of grain growth mode in VC-doped WC–Co hardmetals

Carbon content dependency of grain growth mechanism and grain growth inhibition mechanism in VC-doped WC–Co hardmetals is investigated. VC-doped WC–Co hardmetals with three different carbon contents were sintered with liquid phase and then rapidly quenched to freeze up the structure at the sintering temperature. In these samples, spatial distributions and atomic scale structures of V-rich phases are investigated using transmission electron microscopy (TEM) and related techniques. In these measurements, doped V is found in liquid phase as solute, in large (W,V)C_x precipitates and in interface segregations. Further detailed observations and discussions are carried out for the (W,V)C_x segregated at the WC grain/Co phase interfaces. These (W,V)C_x phases change their form from planar films to small islands depending on the carbon content. The WC grain/Co phase interfaces are fully covered by planar (W,V)C_x in the sample of low carbon content. On the other hand, the WC grain/Co phase interfaces are partially covered by (W,V)C_x islands in the material of high carbon content. During sintering, the WC grains in this sample grew much faster than those in the sample of low carbon content. These structural differences are discussed in terms of WC grain/(W,V)C_x interface energy.     

Microstructure and mechanical properties of ultrafine-grained hardmetals

The interest in ultrafine-grained hardmetals as woodcutting tool materials derives from their excellent mechanical properties compared with those of conventional hardmetals. The aim of this work was to determine the mechanical properties of ultrafine-grained hardmetals and to correlate the measured effects with microstructural parameters. The ultrafine-grained hardmetals (WC grain size 0.3 μm) investigated consisted of different WC powders and different binder systems: Co and complex binder systems. The mechanical properties of ultrafine-grained hardmetals were tested under two different loading conditions: monotonically increasing and cyclic alternating bending loads. It could be shown that the binder systems of different compositions show different behaviours under cyclic loads. Ultrafine-grained hardmetals with Co binder exhibit high bending strength values, but high fatigue sensitivity. Ultrafine-grained hardmetals with complex binders show lower bending strength values but their sensitivity to fatigue is lower. This implies that different damaging mechanisms exist for ultrafine-grained hardmetals with Co and complex binders.     

Defect Control of the WC Hardmetal by Mixing Recycled WC Nano Powder and Tungsten Powder

Tungsten metal powder was added to recycled WC nano powder to control the macro and micro defects of WC hardmetal. The macro and micro defects caused by the excess carbon in the recycled WC powder were markedly removed after the addition of tungsten metal powder ranging from 2 to 6 wt%. The density and hardness of the WC hardmetals also increased due to the removal of defects after adding the tungsten metal powder. The density and hardness of WC hardmetals with the addition of W metal powder ranged from 8 to 12 wt% increased linearly as the W metal powder content increased due to the formation of a new (Co- and W-rich WC) composition. The surface morphology of the WC hardmetals was observed via field emission scanning electron microscopy, and a quantitative elemental analysis was conducted via X-ray fluorescence spectrometry and energy dispersive X-ray analysis. The density and hardness of the WC hardmetals were respectively measured using an analytical balance and a Vikers hardness tester. The effect on the defects in the recycled WC hardmetals through the addition of the tungsten metal powder was discussed in detail.     

Properties of WC–8Co hardmetals with plate-like WC grains prepared by plasma-assisted milling

WC-8C0 hardmetals with different proportions of prismatic WC grains and plate-like WC grains were directly produced through sintering the W-C-8C0 elemental powder mixture which was fabricated by dielectric barrier discharge plasma(DBDP)-assisted milling.The morphology of prepared WC-8C0 hardmetals,geometry and the preferential orientation of plate-like WC were investigated by X-ray diffraction(XRD) and scanning electron microscopy(SEM) analysis.The results demonstrate that the microstructure and mechanical properties of the sintered hardmetals are related to the morphology of W grain which is dependent on DBDP-milling time.The DBDP for 1 h(DBDP-1 h)-milled W-C-Co powder contains granular W particles that tend to form prismatic WC grains,while the DBDP for 3 h(DBDP-3 h)-milled powder contains lamellar W particles that generate plate-like WC grains.By adjusting the weight ratio of DBDP-1 h powder and DBDP-3 h powder in W-C-8C0 mixture,the proportion of plate-like WC in the hardmetals can be controlled,and relatively high transverse rupture strength(TRS) is obtained as the proportion of plate-like WC grain in the hardmetals is about 35%in present experimental condition.     

A new approach to fabrication of gradient WC–Co hardmetals

WC–Co hardmetals with gradient structure comprising neither η-phase nor grain growth inhibitors were produced for the first time by regulating the WC re-crystallisation and carbon content in their near-surface layer and core. Hardmetals with low Co contents in the surface region were obtained by selective carburisation of the near-surface zone of green articles with the original low carbon content and their consequent liquid-phase sintering. The surface region of such gradient hardmetals has a hardness of up 150 Vickers units higher and fracture toughness significantly superior than those of the core. Gradient hardmetals with high Co contents in the surface region were obtained by selective decarburisation of the near-surface zone of green articles with the original high carbon content and their consequent liquid-phase sintering. The new approach for fabrication of gradient WC–Co materials appears to be a unique tool for increasing both the hardmetal hardness and fracture toughness.     

Influence of microstructure on hardness and thermal conductivity of hardmetals

Hardmetals or cemented carbides are used in a wide range of applications due to their excellent mechanical properties. WC-Co hardmetals with the same room temperature hardness can be obtained by different combinations of the WC grain size and cobalt content. However, the thermal conductivity of such hardmetal grades is not equal. Applications such as cutting may require a certain combination of hardness and thermal conductivity, which means that a targeted adjustment is desirable. In this study a wide range of hardmetal grades was studied in respect of microstructure, hardness and thermal conductivity in the temperature range between 20 °C and 1000 °C. Results show that thermal conductivity is considerably influenced by Co content, WC grain size and Cr₃C₂ content. Furthermore, hardmetal grades with the same hardness at room temperature retain hardness very differently at elevated temperatures. For the selection of hardmetal grades for high temperature applications these findings help to choose the right composition in regard to Co content and WC grain size.