Fabrication of WC-Co/(Ti,W)C graded cemented carbide by spark plasma sintering

The WC-Co/(Ti, W)C graded cemented carbide was prepared by spark plasma sintering. The substrate is WC-8Co, and the hard layer is (Ti, W)C solid-solution. The effects of sintering temperature and holding time on the microstructure and properties of graded cemented carbide were analyzed. The hard layer is mainly formed by dissolving WC in the Co-phase and then by solid-solution reaction with TiC. As the sintering temperature increases, the migration rate of WC increases. When the holding time is 5 min, the thickness and the W content of the (Ti, W)C solid-solution hard layer increases with the increasing of sintering temperature. The thickness of the (Ti, W)C solid-solution can reach 51 ± 2 μm at the sintering temperature of 1700 °C for the holding time of 5 min. The hardness of hard layer surface increases first and then decreases with the increasing of sintering temperature. The Vickers hardness is the highest at 1600 °C, which can reach HV_0.221.53GPa. As the holding time increases, the thickness of the solid-solution hard layer increases, but the rate of growth decreases. As the thickness increases, the difference in the W element concentration between the solid-solutions of the same pitch decreases along the layer depth direction, and W element concentration in the entire hard layer increases. The oxidation behavior of graded cemented carbide at 400 °C and 600 °C was investigated. The (Ti, W)C hard layer has superior oxidation resistance relative to the WC-Co substrate.     

烧结工艺对梯度结构硬质合金梯度层组织和厚度的影响

本文用两步烧结方法制备了梯度结构硬质合金,用扫描电子显微镜(SEM)和能谱分析研究了不同的烧结工艺和基体中Co含量对梯度层元素浓度分布、梯度层厚度及显微组织的影响。实验结果表明,烧结温度和保温时间对脱β层厚度有很大影响,基体中高的Co含量有利于梯度层厚度的增加。     

烧结制备含Ti功能梯度硬质合金的研究进展

随着科学技术的发展,对硬质合金的性能提出了越来越高的要求。功能梯度硬质合金通过赋予材料不同部位以不同的性能,成功应用于现代工业技术领域。本文综述了气氛烧结制备含Ti功能梯度硬质合金的研究进展,分析了国内外对表面梯度层的形成机理、制备工艺、梯度结构特征及切削性能的研究成果,指出加强相关机理研究和实验工艺优化是今后研究工作的重点。     

Liquid phase sintering of functionally graded WC–Co composites

Functionally graded cemented tungsten carbide (WC–Co) is an example of functionally graded materials (FGM) in which mechanical properties are optimized by the presence of microstructural gradients such as cobalt gradient and grain size differences within the microstructure. In particular, a cobalt gradient is preferred. However, the manufacture of FGM WC–Co with a cobalt gradient is difficult because the flow of the liquid phase during liquid phase sintering (LPS) would eliminate any initial cobalt gradient built into the powder compacts. In this paper, different factors, which can be used to influence the migration of liquid during sintering, are investigated. These factors include gradients in grain size, carbon and cobalt content, and sintering time. It is shown that a difference in particle size may induce a step-wise profile of cobalt concentration. Initial carbon content differences, however, can be used to obtain a gradient of cobalt during sintering. The effects of these factors are explained based on the roles of capillary force and phase reactions.     

烧结工艺对脱β层厚度及性能的影响

改变硬质合金烧结工艺控制的几个关键因素,通过测量合金的理化性能,利用扫描电镜分析合金的内部结构,研究了烧结气氛(真空,N_2)、烧结温度、烧结压力对硬质合金梯度结构和机械性能的影响。结果表明,对于含氮硬质合金的梯度烧结,适时引入一定量的氮气可抑制合金中含氮物质的早期分解,可用氮压来控制梯度增长速率,烧结气氛中氮气压力适宜控制在100～200 mbar;随着烧结温度的提高,合金的致密度和脱β层梯度厚度增加明显,合金抗弯强度增加;随着烧结压力的增大,合金脱β层梯度厚度变薄。     

Relation Between the Microstructure and Properties of Commercial Titanium Alloys and the Parameters of Gas Nitriding

Titanium alloys are unique materials with an excellent combination of properties. However, their applications are limited due to low surface hardness. In the present work gas nitriding is performed with the aim of improving the surface properties of commercial titanium alloys. Four widely used titanium alloys, namely, Ti – 6% Al – 4% V, Ti – 6% Al – 2% Sn – 4% Zr – 2% Mo, Ti – 8% Al – 1% Mo – 1% V, and Ti – 10% V – 3% Fe – 3% Al, are studied. The process is performed in a nitrogen atmosphere at 950 and 1050°C for 1, 3, and 5 h. The resulting surface hardness exceeds the normal value for titanium alloys by a factor of 3 – 5 due to the change in the phase composition of the surface layer, yielding a solid solution of nitrogen in an α-Ti phase, a TiN nitride, and TiO₂ dioxide. The influence of the parameters of the treatment process and the chemical composition of the alloys on the phase composition, microstructure, microhardness, and thickness of the surface layer is analyzed. It is shown that nitriding of alloys with α- and (α + β)-structures at 1050°C yields surface layers with inhomogeneous composition and irregular thickness, whereas after nitriding at 950°C the surface layers are homogeneous and have high properties. Practical recommendations are given for choosing nitriding parameters for different alloys and variants of application are discussed.     

脱β层厚度对CVD涂层硬质合金性能的影响

通过对WC-TiC-(Ta,Nb)C-Co硬质合金在1 300～1 380℃的渗氮气氛处理和随后的脱N烧结制得了不同脱β层厚度的合金基体,通过化学气相沉积(CVD)工艺制成从内到外依次为TiN/MT-TiCN/Al2O3/TiN的涂层硬质合金。采用光学显微镜、扫描电镜和能谱仪、抗弯(TRS)和切削试验对合金基体涂层前后的组织特征与性能进行了研究。结果表明,随着脱β层厚度的增加,试样涂层前后的抗弯强度均增加,在厚度达到20μm以上时,增加不明显。CVD涂层硬质合金可转位刀片的抗冲击性能也有相应的规律,而耐磨性则基本上保持一致。     

渗氮温度对42CrMo钢零件表面后氧化渗层的影响

采用硬度测试、显微组织观察、脆性等级和疏松等级评价等方法研究了渗氮温度对42CrMo钢零件渗氮后氧化渗层性能的影响.结果表明:在渗氮后氧化处理过程中,渗层的表面硬度随着渗氮温度的升高出现先增后降的趋势;渗层深度和疏松等级随渗氮温度的升高而增加,但脆性等级变化不大.当渗氮温度为560℃时,42CrMo钢零件可获得表面硬度...     

Ti(C,N)基金属陶瓷材料显微结构与性能研究进展

对国内外近年来有关Ti(C,N)基金属陶瓷材料的显微结构与性能的研究成果进行了总结。首先,介绍了Ti(C,N)基金属陶瓷材料的发展史;Ti(C,N)基金属陶瓷的显微结构、力学性能,以及显微结构与其性能的关系等。其次,列举并比较了不同的烧结方法所制备的Ti(C,N)基金属陶瓷材料的力学性能;结果表明:微波烧结和放电等离子烧结技术在较低的温度就可以成功烧结高硬度、高抗弯强度与断裂韧性高的产品,但实际生产中,这类技术还没有广泛被应用,应用最广的是真空烧结方法。最后介绍了Ti(C,N)基金属陶瓷材料的今后的研究趋势。     

Ti(C,N)的碳氮比及粒度对脱β层梯度硬质合金的影响

研究了Ti(C,N)的粒度和组成对脱β层梯度硬质合金性能和组织结构的影响。结果表明,Ti(C,N)粒度范围位于1.5μm～3.0μm之间和碳氮质量比控制为1∶1最有利于梯度硬质合金脱β层的形成。     

A research on WC–8Co preparation by microwave sintering

The microwave sintering technique has been used in WC–Co alloy preparation for many years. The properties of the alloy can be improved using the microwave method even in a very short processing cycle. In this work, the influencing factors of the heating rate on WC–8Co hard metal during the microwave processing were discussed by using a multi-mode high temperature furnace. The experimental results demonstrate that the assisted materials principally contribute to heat insulation, rather than heating. Our results show that, when the temperature exceeds 1100 °C, the heating rate of Co compact slows down and displays slight fluctuations. Porosity of the compacts is shown to have little effect on the heating rate. Further, the special microstructure (overall even and local uneven) of the microwave-prepared WC–8Co alloy is discussed. Besides, the relationships between the microstructure and the mechanical properties of microwave-prepared WC–8Co are explored.     

烧结温度对WC-Co-Ti3SiC2硬质合金微观组织与力学性能的影响

以掺杂3.0%Ti₃SiC₂(质量分数)的WC-Co-Ti₃SiC₂硬质合金为对象,研究了烧结温度(1350～1470℃)对WC-Co-Ti₃SiC₂硬质合金中的Ti₃SiC₂分解产物和比例、微观组织及力学性能的影响规律与机制。结果表明：烧结温度的升高促进了WC-Co-Ti₃Si C₂硬质合金中Ti₃Si C₂的分解以及(W,Ti)C和WSi₂相的生成,同时导致WC晶粒尺寸逐渐增大。硬质合金的硬度随烧结温度的升高呈现出先增大后降低的趋势,而断裂韧性则逐渐下降。当烧结温度为1410℃时,WC-Co-Ti₃Si C₂硬质合金的致密性最佳(孔隙率仅为0.47%),其力学性能也较为优异,硬度与断裂韧性分别为20 348.328 MPa和10.15 MPa·m^1...     

陶瓷材料微波烧结研究进展与工业应用现状

本文主要介绍了微波烧结原理、烧结设备和微波技术在陶瓷粉末合成、硬质合金、金属陶瓷、功能陶瓷材料烧结及涂层制备方面的应用;微波烧结新技术在溶胶凝胶、自蔓延高温合成、水热法、电热法、涂层溶解、陶瓷材料干燥、连接等领域的最新发展。微波烧结具有加热速度快、烧结坯体温度分布均匀;活化烧结、烧结时间短、抑制晶粒长大、组织结构可控、高效节能等优点。探讨微波烧结产业化的现状和存在的问题,烧结材料介质特性数据缺乏和设备的缺乏、昂贵,是阻碍微波烧结技术发展产业化最主要的两大障碍。对解决微波烧结工业化的难题阐述了观点,微波场的优化设计、陶瓷材料的介电性能的数据库建设及理论发展、微波设备和烧结工艺的联合开发等是目前微波技术研究主要的努力方向。     

钢的渗氮低温淬火

提出一种能增加硬化层厚度的渗氮钢低温淬火技术,研究了硬化层的组织、涌氮温度和加热时间对２０ＣｒＭｎＴｉ钢的硬化层厚度的影响。实验结果表明,硬化层是由化合物层和马氏体层组成、适当的控制工艺参数,表面硬度能达到７００ＨＶ左右,硬化层厚度可达０．２０￣０．３０ｍｍ。     

Effect of powder particle size on gradient formation and grain growth in ultrafine crystalline gradient cemented carbide

Sinter-HIP combining vacuum and pressure in one-step sintering process has been applied to prepare ultrafine crystalline cemented carbide with a surface gradient layer enriched in binder. The effect of powder particle size on gradient formation and grain growth has been examined. The results show that the gradient layer thickness increases with decreasing WC and Ti(C,N) powder particle size. The number of abnormal WC grains increases with decreasing WC powder particle size. The formational mechanism of the gradient cemented carbide with ultrafine grains is discussed through analyzing the decomposability of nanoscale Ti(C,N), atomic diffusion and grain growth during one-step Sinter-HIP process.     

稀土含量对Ti6Al4V钛合金等离子渗氮层组织和摩擦学性能的影响

目的研究稀土含量对Ti6Al4V钛合金表面等离子体渗氮层结构和性能的影响。方法运用等离子表面改性技术对Ti6Al4V(TC4)钛合金进行等离子渗氮处理,渗氮过程中通入不同含量的稀土作为催渗剂,以获得钛合金表面强化层。利用金相显微镜和扫描电子显微镜(SEM)观察渗氮层组织,用X射线衍射仪(XRD)分析渗层相组成,用能谱仪(EDS)检测渗层的化学成分,用维氏显微硬度计测量渗层的显微硬度,用球-盘式摩擦磨损试验机和三维轮廓仪检测渗层的摩擦磨损性能。结果TC4钛合金表面等离子渗氮层结构包括表面化合物层(主要成分为δ-TiN)和扩散层(主要为N原子扩散形成的N-Ti固溶体),加入稀土可以促进N原子向基体的扩散,提高渗氮速度。渗层厚度增加,硬度和耐磨性能提高,扩散层使钛合金基体与化合物层之间的硬度梯度更加平缓。当稀土通入速率为60 mL/min时,渗层厚度可达155μm,表面硬度为1275HV0.05,摩擦系数降到0.27,磨损率明显降低。结论钛合金等离子渗氮过程中加入稀土可以有效提高渗速,改善渗氮层硬度,提高材料表面的耐磨性能。     

不同压力对 TC4 钛合金真空脉冲渗氮的影响

目的采用不同压力对TC4钛合金进行真空脉冲渗氮处理,提高其表面硬度及耐磨性。方法通过金相显微镜、X射线衍射仪、显微硬度计及耐磨试验机分析渗氮硬化层的组织与性能。结果 TC4钛合金经过真空气体渗氮处理后,形成了由Ti N,Ti2Al N和钛铝金属间化合物Ti3Al组成的复合改性层。渗氮压力太低,表面氮化物数量较少,氮化物层较薄;随渗氮压力的增大,表面氮化物数量增多,表面硬度及耐磨性增加。压力为0.015 MPa时,氮化物层表面硬度最大,表面硬度为1100~1200HV,有效硬化层深度为50~60μm。渗氮压力继续增加,表层组织变得疏松,表面硬度及耐磨性开始降低。结论选择合适的渗氮压力和表面氮浓度进行真空脉冲渗氮,可以提高钛合金表面硬度,改善耐磨性。     

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.     

初始成分对梯度硬质合金微观组织及脱β层厚度的影响

采用普通市售中颗粒Ti(C,N)粉末,以一步烧结法制备脱β层梯度硬质合金;利用显微组织分析和图像分析等手段,研究合金初始成分对其微观组织及脱β层厚度的影响规律。结果表明:当Ti(C,N)含量低于1.6%(质量分数)时,随着Ti(C,N)含量的增加,脱β层厚度明显增大,而当Ti(C,N)含量超过1.6%时,脱β层厚度呈缓慢缩小的趋势;随着钴含量的增加,脱β层的厚度迅速增大,但当钴含量达到10%(质量分数)左右时,在脱β层与芯部的界面处钴相聚集现象严重;总碳含量为6.51%(质量分数)的合金中WC晶粒度较大且呈规则的多边形,在1 450℃、2 h梯度烧结工艺下制备的脱β层厚度可达38μm左右,而总碳含量为6.23%的合金中WC晶粒度较小且呈等轴化趋势,同时脱β层的厚度仅为17μm左右。