Research on Ultrafine WC-10Co Cemented Carbide with High Propertie

1 IntroductionMaterials scientists overthe world have been workingto seek for materials with both high hardness and hightoughness. The ultrafine grained WC-Co (cobalt-bondedtungsten carbide) is one of ideal materialstill now.Nano-crystalline WC-Co cemented carbides have both highhardness and hightoughness[1-8].Submicron hardmetals are used as wear parts ,circu-lar shearing and cutting blades , magnetic video tapes ,chipless formingtools ,dental tools and others .The per-formances of these t…     

Powder Extrusion Molding of Nanocrystalline WC-10Co Composite Cemented Carbide

The rods that were shaped from nanocrystalline WC- 10.21 Co-0.42 VC/ Cr3 C2 （ wt% ） composite powders by using powder extrusion molding （PEM） were investigated. The nanocrystalline WC- 10.21 Co- 0. 42 VC/ Cr3 C2 （ wt% ） composite powders were prepared by the spray thermal decomposition-continuous reduction and carburization technology. In order to improve the properties of rods shaped by using powder extrusion molding, the cold isostatic pressing （CIP） technology was used before or after debinding. Specimens were siutered by vacuum siutering and hot isostatic pressing （HIP）. The density, Rockwell A hardness, magnetic coercivity , and magnetic saturation induction of siutered specimen were measured. The microstructure of the green bodies and the siutered specimens was studied by scanning electron microscopy （SEM）. Results show that the rod formed by using powder extrusion molding after debinding and followed by cold isostatic pressing can be siutered to 99.5% density of composite cemented carbide rods with an average grain size of about 200- 300 nm, magnetic coercivity of 30.4 KA / m, Rockwell A hardness of 92.6 and magnetic saturation induction of 85% . Superfine WC- 10 Co cemented carbide rods with excellent properties were obtained.     

Influences of Carbon Content on the Properties and Microstructure of Ultrafine WC-10Co Cemented Carbide

WC-10Co nanocrystalline composite powders prepared by spray pyrogenation-continuous reduction and carburization technology were consolidated by vacuum sintering plus hot isostatic pressing (HIP). Influences of carbon content on properties and microstructure of ultrafine WC-10Co cemented carbide were investigated. The results show that the relative density of the ultrafine WC-10Co cemented carbides can reach 99.72%, and the transverse rupture strength (TRS) was higher than 3 890 MPa, Rockwell A hardness (HRA) was higher than 92.5, the average grain size was less than 460 nm, when carbon content in nanocrystalline composite powder was 5.54wt% and the ball-milled time was 48 hours, ultrafine WC-10Co cemented carbide with excellent properties and homogeneous microstructure was obtained. Funded by the National Natural Science Foundation of China (No.50502026), the Youth Science Plan for Light of the Morning Sun of Wuhan City(No.200750731270), and Key Project for the Science & Technology Research Department, Chinese Ministry of Education (No.105123)     

Manufacture of the Ultrafine Grain WC/Co Cemented Carbides by Combined Sintering Processing

A new kind of sintering process, combined sintering process. i.e. vacuum sintering plus hot isolate pressure sintering (HIP), was introduced for producing ultrafine WC-10% Co (mass fraction. so as the follows) cemented carbides. The effects of some processing parameters on the microstructure and mechanical properties of the obtained cemented carbides were studied. The results show that the rapid shrinkage and the pronounced densification of tile cemented carbides took place during the vacuum sintering stage, which is intinaately correlated with the local liquid sintering occurred during this earl} sintering stage for the high surface activity of ultrafine WC-Co powder. The way of high pressure imposing. isothermal treatment cycle during ac.acuum sintering and HIP sintering stage directly influence the densitication of compacts and the mechanical properties of the produced WC-10%Co cemented carbides.     

Preparation of Superfine-Cemented Carbide by Spark Plasma Sintering

92WC-8Co puwder mixture with superfine-tungsten carbide was respectively sintered by spark plasma sintering（ SPS ） and sintering isostutic pressure （SIP）. Complete dense samples with 200 nm WC grains and 94.2HRA hardness were prepared by spark plasma sintering at 1 150 ℃ and under 4.5 kN for 5 minutes. SIP was carried out at 1 400 ℃ for 30 minutes with a result of 300-400 nm WC grains and 93 HRA hardness. The results show that sintering temperature is greatly decreased by SPS, sintering time is largely shortened and WC grain growth is effectively retarded. Micropores and drawb（wks in superfine-cemented carbide made by SPS are greatly declined, which is very useful to improving nwehanical properties.     

Microstructures and properties of WC-20Co-1Y_2O_3 cemented carbide by hot-press and liquid phase sintering

1　INTRODUCTIONInRef .[1],averyinterestingandinexplicablefindingwasreportedthataspecialwhisker likeWCgrainstructure ,mostintherangeof 10 0 2 0 0nmindiameterand 1 2mminlength ,wasformedinWC 2 0Co 1Y2 O3cementedcarbidepreparedbyhot pressbelowtheeutectictemperature .ItwasmentionedinthepaperthatWCpowderwithFisherSubsiereSizer(FSSS)of 1μm ,ultrafineCopowder ,andY2 O3powderof 1μmwereusedastherawmaterialsofWC 8Cocementedcarbide .However ,whetherthesamerawmaterialswereusedinWC 2 0Co …     

Microstructures and properties of WC-2OCo-1Y2O3 cemented carbide by hot-press and liquid phase sintering

Ultrafine tungsten carbide and fine cobalt as well as nano yttrium oxide powders were used as the raw materials. The effects of hot-press below the eutectic temperature and conventional liquid phase sintering on the structures and properties of WC-20Co-1Y2O3 cemented carbide were studied. It is shown that hot-pressed alloy has the character of isotropic properties and microstructure with homogeneous and ultrafine WC grains. However, the ultrafine and fully-densified structure is developed at the cost of the presence of large amount of cobalt-lake (uneven-ly distributed binder phase), and thus lower strength. Yttrium oxide in the alloy cannot play the role of grain growth inhibitor fully when cemented carbide with high content of cobalt and ultrafine raw materials is sintered at high liquid phase sintering temperature. Peculiar platelet-enhanced bi-model structure is formed in WC-20Co-1Y2 O3 cemented carbide by conventional liquid phase sintering, which points out that yttrium oxide in the alloy facilitates the formation of plate-like WC grain.     

微波单模腔烧结WC-10Co硬质合金的研究

利用微波烧结技术，将WC-10Co硬质合金分别置于TE103单模谐振腔中纯电场、纯磁场以及电场和磁场的混合场中进行烧结，研究了这些区域下WC-10Co硬质合金的烧结行为以及对其性能的影响。     

Effects of Phosphorus Additions on Microwave Sintering Properties of UltrafineWC-lOCo Cemented Carbides

Using the microwave sintering technology, the effects of phosphorus （P） additions on the microstructure and properties of the ultrafine WC-10Co alloys were investigated. The experimental results show that with only 0.3wt% P additions, full density WC-10Co cermets were obtained at temperature of 1250℃, which is 70 ℃ lower than that of the undoped counterparts. Lower sintering temperature can result in finer WC grain growth; therefore, the P-doped WC-10Co alloys exhibited higher hardness than the undoped ones. But at the same time, P doping could lead to sacrifice of fracture toughness ofWC-10Co cemented carbides.     

球磨WC-8Co粉末的放电等离子烧结

对WC-8Co粉末不同球磨时间后进行放电等离子烧结,研究了球磨时间及烧结温度对WC-8Co硬质合金微观结构及性能的影响。结果表明:球磨时间延长,粉末颗粒变细,晶格畸变增加,衍射峰强度降低,并随时间延长,团聚现象严重;采用放电等离子烧结,在1 200℃时,可以得到接近全致密的烧结样品,烧结温度低于传统方法的烧结温度;球磨时间在2 h以下时,样品的致密度、硬度和断裂韧性达到最佳,晶粒较小且分布均匀;延长球磨时间,性能显著下降且出现较多粗晶、空洞、Co池等缺陷。     

Corrosion behaviors of NdFeB magnets prepared by spark plasma sintering

The spark plasma sintering (SPS) technique was introduced into the field of NdFeB preparation due to its own advantages. High property NdFeB magnets with fine grains were prepared by SPS method. The corrosion behaviors of SPS NdFeB were studied by electrochemical measurements and 92% RH hyther tests at 353 K. The results were compared with those of the traditional sintered NdFeB magnets. It shows that both the SPS NdFeB and the traditional sintered NdFeB have good corrosion resistance in alkaline environment due to surface passivation; while, the fine grain microstructure of SPS NdFeB results in a more homogeneous phase com-position distribution and thus reduces the electrochemical inhomogenity between the ferromagnetic phase and the Nd-rich inter-granular phase in the magnet. Therefore, the SPS NdFeB exhibits better corrosion resistance than the traditional sintered NdFeB in neutral and weak acidic environment.     

Rare earth doped new cemented carbide with Ni-Co binder for mining

ＴｈｅｗｅａｒｒｅｓｉｓｔａｎｃｅｏｆｔｈｅｔｒａｄｉｔｉｏｎａｌＷＣ Ｃｏｃｅ ｍｅｎｔｅｄｃａｒｂｉｄｅｆｏｒｍｉｎｉｎｇ ,ｗｉｔｈｔｈｅａｄｄｉｔｉｏｎｏｆｒａｒｅｅａｒｔｈ ,ｃａｎｂｅｉｍｐｒｏｖｅｄｏｂｖｉｏｕｓｌｙ[1] .Ｂａｓｅｄｏｎｔｈｅｉｎ ｈｅｒｅｎｔｓｉｍｉｌａｒｉｔｙｂｅｔｗｅｅｎＷＣ ＣｏａｎｄＷＣ Ｃｏ Ｎｉｃｅｍｅｎ ｔｅｄｃａｒｂｉｄｅｓｉｎｔｅｒｍｓｏｆｍｉｃｒｏｓｔｒｕｃｔｕｒｅ ,ｗｅｃａｒｒｉｅｄｏｕｔｔｈｅｓｔｕｄｙｏｆＷＣ Ｃｏ Ｎｉｃｅｍｅｎｔｅｄｃａｒｂｉｄｅｗ…     

Comparative study of β-Si3N4 powders prepared by SHS sintered by spark plasma sintering and hot pressing

β-Si3N4 powders prepared by self-propagating high-temperature synthesis (SHS) with additions of Y2O3 and Al2O3 were sintered by spark plasma sintering (SPS). The densification, microstructure, and mechanical properties of Si3N4 ceramics prepared using this method were compared with those obtained by hot pressing process. Well densified Si3N4 ceramics with finer and homogeneous microstructure and better mechanical properties were obtained in the case of the SPS technique at 200℃ lower than that of hot pressing. The microhardness is 15.72 GPa, the bending strength is 716.46 MPa, and the fracture toughness is 7.03 MPa.m1/2.     

放电等离子烧结具有优异综合性能的新型NdFeB永磁材料

采用放电等离子烧结技术和传统烧结技术制备了烧结NdFeB永磁体,并研究了2种磁体的磁性能、力学性能和化学稳定性.与传统烧结磁体相比,放电等离子烧结磁体具有与其相当的磁性能及更好的耐腐蚀和力学性能.显微组织结果表明,放电等离子烧结磁体主相Nd_2Fe_(14)B的晶粒细小、均匀.边界富钕相仅有少量位于主相Nd_2Fe_(14)B颗粒周围,大部分以颗粒形式分布在主相三角晶界处.这种独特的显微组织特征对于晶间腐蚀过程及脆性沿晶断裂过程具有明显的抑制作用.因此,放电等离子烧结磁体表现出优异的综合性能.     

Research of Ultrafine Cemented Carbides for PCB Microdrills

The nanocrystalline WC-10Co composite powders were produced with the processing method of spray thermal decomposition-continuous reduction carburization.The grain growth inhibitors of 0.4wt% Cr_3C_2 and 0.4wt% VC were added into the composite powders to obtain advanced ultrafine hardmetals with minimal porosity,defects and discontinuous.The rod samples were formed by extrusion.They were sintered in cacuum with SIP treatment.The sintered rods were made into PCB microdrill samples after polishing.Mechanical properties(such as density,hardness,transverse rupture strenth(TRS),magnetic saturation induction and magnetic coercivity) of the sintered ultrafine cemented carbides were measured.The microstructures of them were investigated by scanning electron microscopy(SEM) and?transmission electron microscopy(TEM).The experimental results show that the transverse rupture strength of the samples sintered in vacuum with sinterhip(SIP) treatment is more excellent.The grain size could be controlled in a range of 200-400 nm with the help of grain growth inhibitors.And the superfine grained materials have superior strength(3900 MPa) and high hardness(HRA=93.3).These features are ideal for PCB microdrills.     

VC/Cr3C2对微波烧结超细WC-10Co性能的影响

利用微波烧结技术，研究了添加VC／CBQ晶粒生长抑制剂对WC-10Co超细硬质合金微观结构及性能的影响。结果表明，添加总量质量分数为0．6％的抑制剂的合金的综合性能最好，过量的抑制剂反而会降低合金性能；并且微波烧结合金不论是否有晶粒长大抑制剂，均能得到均匀的细晶结构。     

Effect of sintering atmosphere on microstructure and properties of TiC based cermets

The effect of the sintering atmospheres （vacuum, N2, Ar） on the microstructures and properties of the TiC based cermets was studied using XRD, SEM/BSE and energy dispersive spectrometer. Compared with the alloy sintered in vacuum, the carbon content of the specimen sintered in N2 and Ar is lower by 0.5%; and the nitrogen content is higher by 0.3% when sintered in nitrogen. The central part of the ring structure may be carbide with either a high W or Ti content. The ring structures are （Ti, W, Ta, Mo, Co, Ni）C solid solutions with different metallic elements and distributions. The composition of the binder phase is （Co, Ni） solid solution with different Ti, W, Ta, Mo, C contents. The structures are uniform for the cermets sintered in vacuum and the properties are the best. When sintered in Ar or N2, the O2 and N2 in the atmosphere take part in the sintering reaction to break the carbon balance in the cermets to form a shell structure and defects, which results in poor density, microhardness （HV） and transverse rupture strength （TRS）.     

Fabrication of Ti_2AlC by Spark Plasma Sintering from Elemental Powders and Thermodynamics Analysis of Ti-Al-C System

A ternary-layered carbide Ti 2 AlC material could be synthesized by spark plasma sintering(SPS)technology using elemental powder mixture of Ti,Al and active carbon.By means of XRD and SEM,phases were identified and microscopically evaluated.The experimental results show that the main phase in the product was fully crystallized Ti 2 AlC with small particle size when sintered at 1200 C.The syn-thesis temperature of SPS was 200-400 C lower than that of hot pressing(HP)or hot isostatic pressing(HIP). Through thermodynamics calculations,the mechanism of Ti 2 AlC was studied by calculating changes of Gibbs free energy of reactions.     

WCoB金属陶瓷的制备及其性能研究

以WC、TiB2、Co粉末为原料,采用真空液相反应烧结技术制备WCoB金属陶瓷,并利用XRD、SEM和EDS对其微观形貌及相组成进行了表征。结果表明,WCoB金属陶瓷由WCoB、W2CoB2、TiC、Co2B和TiB2等相组成,其硬度为HRA84.4～92.2,合金密度为9.3～10.2g/cm3。随着钴含量的增加,烧结后WCoB金属陶瓷的合金密度和硬度值均有所下降,较高的烧结温度有利于晶粒细化。磨损试验发现WCoB金属陶瓷的耐磨性优于YG8硬质合金。     

Microstructure and properties of W-15Cu alloys prepared by mechanical alloying and spark plasma sintering process

W-15Cu composite powders prepared by mechanical alloying （MA） of raw powders were consolidated by spark plasma sintering （SPS） process at temperature ranged 1 230-1 300 ℃ for 10 min and under a pressure of 30 MPa. By using high energy milling, particles containing very fine tungsten grains embedded in copper, called composite particles, could be produced. The W grains were homogeneously dispersed in copper phase, which was very important to obtain W-Cu alloy with high mechanical properties, fine and homogeneous microstructure. The microstructure and properties of W-15Cu alloys prepared by SPS processes at different temperature were researched. The results show that W-15Cu alloys consolidated by SPS can reach 99.6 % relative density, and transverse rupture strength （TRS） is 1 400.9 MPa, Rockwell C hardness （HRC） is 45.2, the thermal conductivity is 196 W/m-K at room temperature, the average grain size is less than 2 μm, and W-15Cu alloy with excellent properties, homogeneous and fine microstructure is obtained.