Influence of Fe-Ni-Co binder composition on nitridation of cemented carbides

Nitridation of cemented carbides leads to the formation of wear resistant Ti(C,N)-enriched outer-surfaces (fcc-rich outer-surfaces). In this work the influence of the binder phase composition on the kinetics of formation of fcc-rich outer-surfaces was investigated. Sintered cemented carbides were nitrided at 1200 °C in a 5 bar N₂ atm for 2 and 4 h. The thickness of the nitrided fcc-rich outer-surfaces increases with the addition of Fe to the Co and Ni binders. Correlations between nitrogen diffusion coefficients and nitrogen solubility levels in Fe-Ni-Co systems are investigated to understand the mechanisms governing the formation of graded layers on nitrided cemented carbides with Fe-Ni-Co binders.     

Effect of Mo and Co additions on the microstructure and properties of WC-TiC-Ni cemented carbides

In this work, the effects of 1.0 wt.% additions of Mo and Co on the microstructure and properties of WC-TiC-Ni cemented carbides were investigated using scanning electron microscope, mechanical properties tests, corrosion resistance and abrasion resistance tests. The results show that 1.0 wt.% Mo addition can refine the WC grains and increase the hardness. Moreover, with the addition of minor Mo, the corrosion resistance and abrasion resistance of alloys improved significantly. The addition of 1.0 wt.% Co can inhibit the growth of WC grains, improve the density and hardness slightly, and enhance the abrasion resistance of cemented carbides. However, the minor Co has negative effect for the corrosion resistance.     

Application of a wax-based binder in PIM of WC–TiC–Co cemented carbides

A wax-based binder was developed for powder injection molding of WC–TiC–Co cemented carbides. The critical powder loading and the rheologic behavior of the feedstock were determined. It was found that the critical powder loading could achieve up to 62.5 vol% and the feedstock exhibited a pseudo-plastic flow behavior. The injection molding, debinding and sintering processes were studied. The dimensional deviation of the sintered samples could be controlled in the range of ±0.2% with the optimized processing parameters. The mechanical properties were better than or equivalent to those of the same alloy made by the conventional press-sintering process.     

Influence of microstructure on ultraprecision grinding of cemented carbides

The influence of microstructure on the ultraprecision grinding response of a series of cemented carbides for spherical mirrors was characterized by means of optical and laser interferometry, atomic force microscopy, scanning electron microscopy and X-ray diffraction. Surface roughness, form accuracy, grinding-induced residual stress and material removal behaviors were studied as a function of tungsten carbide (WC) grain size. In connection with the removal mechanisms in ultraprecision grinding, microindentations performed on each material showed similar deformation patterns, all in the plastic regime. The microstructure of WC-Co materials was found to have little influence on the nanometre surface roughness and submicron form accuracy. However, the X-ray stress measurements indicated that the microstructure of carbide materials had a significant influence on the grinding-induced residual stresses; i.e. an increase in grinding-induced residual compressive stress with an decrease in WC grain size. No grinding-induced cracks were observed in the ground cemented carbide surfaces. The material removal in ultraprecision grinding was considered to occur within the ductile regime. The formation of microgrooves and plastic flow regions via slip bands of WC grains along the cobalt binder without visible resultant microfracturing of WC grains were the dominant removal mechanisms.     

Investigations on kinetics of formation of fcc-free surface layers on cemented carbides with Fe-Ni-Co binders

The formation of surface layers free of face centered cubic (Ti,Ta,Nb,W)(C,N) carbonitrides and enriched in ductile binder phase (fcc-free surface layers) was investigated on cemented carbides containing Fe-Ni-Co binders. Cemented carbide alloys with varying Fe-Ni-Co binders were sintered in vacuum atmospheres at 1450 °C for 2, 3 and 5 h. Independent of the binder composition the growth of fcc-free surface layers obeys a parabolic law. For same sintering conditions, fcc-free layer growth kinetics is enhanced by the addition of Fe to Co and Ni binders. Thermodynamic calculations showed that adding Fe to Co and Ni binders increases the solubility of the element nitrogen in the liquid binder phase. The higher solubility of N in Fe-containing binder phases promotes the formation of larger fcc-free surface layers, so that the width of fcc-free surface layers can be modified by controlling the Fe content in the binder phase.     

Effect of WC particle size on the microstructure, mechanical properties and fracture behavior of WC–(W, Ti, Ta) C–6 wt% Co cemented carbides

This study deals with the microstructure and mechanical properties of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides fabricated by conventional sintering. The conventional WC particles of 4 μm size and ultrafine particles of 0.2 μm were introduced in the system with varying ratio. The ratios of conventional WC particles to ultrafine WC particles were 2:1, 1:1, and 1:2. The microstructures of sintered WC–(W, Ti, Ta) C–9 vol.% Co cemented carbides were sensitively dependent on the ratio of conventional WC particles to ultrafine WC particles. The rim phase increased with the increase in the amount of ultrafine particles. Hardness of WC–(W, Ti, Ta) C–9 vol.% Co cemented carbide increased with increase in the amount of rim phase and decrease in the average grain size of WC particles. The bending strength showed the similar trend of the hardness. The fracture morphologies are reported. The fracture behavior changed from mixed mode to transgranular fracture mode, when the ratio of conventional WC particles to ultrafine WC particles was changed from 2:1 to 1:2.     

Mechanical properties of WC–10Co cemented carbides sintered from nanocrystalline spray conversion processed powders

Mechanical properties and microstructures of nanocrystalline WC–10Co cemented carbides were investigated. The nanocrystalline WC–10Co cemented carbide powders were manufactured by reduction and carbonization of the nanocrystalline precursor powders which were prepared by spray drying process of solution containing ammonia meta-tungstate (AMT) and cobalt nitrate. The WC powders were about 100 nm in diameter mixed homogeneously with Co binder phase and were sintered at 1375 °C under a pressure of 1 mTorr. In order to compare the microstructures and mechanical properties with those of nanocrystalline WC–10Co, commercial WC powders in a diameter range of 0.57–4 μm were mixed with Co powders, and were sintered at the same conditions as those of nanocrystalline powders. TaC, Cr₃C₂ and VC of varying amount were added into nanocrystalline WC–10Co cemented carbides as grain growth inhibitors. To investigate the microstructure of Co binder phase in the WC–10Co cemented carbides, Co–W–C alloy was fabricated at the temperature of sintering process for the WC–10Co cemented carbides. The hardness of WC–10Co cemented carbides increased with decreasing WC grain size following a Hall–Petch-type relationship. The fracture toughness of WC–10Co cemented carbides increases with increasing HCP/FCC ratio of Co binder phase by HCP/FCC phase transformation.     

WC-Co梯度硬质合金的制备及渗碳对其组织的影响

采用光学金相检测、扫描电镜分析、能谱分析等方法对WC-6Co硬质合金渗碳处理后的成分和梯度组织结构进行分析.结果表明:对硬质合金渗碳处理后可形成显微组织和钨、钴含量的梯度分布,其特征是合金表层和次表层的η相已经完全消失,属正常的WC γ两相组织,合金的芯部依然是含η相的三相组织,中间形成了一个富钴层;碳原子的扩散和液相钴的流动是形成梯度的原因;在各渗碳温度下,合金的梯度结构厚度均随渗碳时间的增加而增加;在渗碳时间和渗碳温度相同的情况下,合金的梯度层厚度均随合金初始总碳含量的增加而增厚.渗碳处理后外表面的WC晶粒可能会产生一定的粗化现象.     

Kinetics of formation of graded layers on cemented carbides: Experimental investigations and DICTRA simulations

Kinetics of formation of fcc-free layers on Co-W-Ti-Ta-Nb-C-N cemented carbides was investigated by experimental methods and DICTRA simulations. The layer formation obeys a parabolic law, indicating a diffusion-controlled process. For DICTRA simulations, the influence of the mobilities for all diffusing elements in the liquid binder phase at the sintering temperature was investigated. The best agreement between experimental and simulations was obtained considering that the mobility of all metallic elements is two times slower compared with the mobility of the non-metallic elements.     

TiC含量对微波烧结钢结硬质合金组织及性能影响

以铁粉为基体,TiC颗粒为增强相,通过球磨、压制成型,微波烧结制备出TiC钢结硬质合金。结果表明,在1400℃微波烧结时,TiC颗粒与Fe具有良好的润湿性和流动性。随TiC含量升高,合金的晶粒逐渐变得均匀细小,合金的相对密度、显微硬度和抗弯强度均先升高后下降,相对密度和抗弯强度在TiC含量5%时达到最高值,分别为94.61%和1327.20 MPa,显微硬度在TiC含量10%时达到最高值,为760 HV。随TiC含量增加,钢结硬质合金的断裂方式由韧性断裂向脆性断裂过渡。     

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.     

Properties and microstructure of VC/Cr3C2-doped WC/Co cemented carbides

This paper deals with the effects of codoped VC/Cr3C2 and sintering temperature on the magnetic and mechanical properties of ultra-fine grained WC-12%Co alloys. Results show that the synergistic action of doped VC/Cr3C2 in optimal proportion enhances both the hardness and transverse rupture strength (TRS) of the alloys, with more homogeneous microstructure. When the alloy is sintered at 1430℃ and with 0.5% Cr3C2/0.2% VC, the TRS reaches 3786 MPa, the hardness is 91.7 HRA and the grain size srnaller than 0.6 μm. The numerical analyses on grain growth during the sintering process show that both VC precipitating on the WC grain boundary and Cr3C2 dissolving in the Co phase decrease the solid/liquid interfacial energy γ, the process of dissolution and reprecipitation is greatly retarded and the coarsening of WC grains is inhibited.     

WC－20Co硬质合金钎焊的热处理机理

研究了高频钎焊同时淬火处理对ＷＣ－２０Ｃｏ硬质合金刀片显微结构和性能的影响。结果表明，在１０００～１２００℃温度范围内处理将导致ＷＣ－２０Ｃｏ合金刀片中ＷＣ相邻接度∑ＷＣ－ＷＣ下降、ｒ相平均自由程Ｌ＿ｒ增加、韧性改善和硬度提高等一系列淬火效果。断口形貌微观特征也表明了合金韧性的提高。当处理温度超过１２００℃后，ＷＣ－２０Ｃｏ合金的显微结构和性能将恶化。     

Effects of carbide size and Co content on the microstructure and mechanical properties of HVOF-sprayed WC-Co coatings

Twelve commercially available WC-Co powders with different average WC grain sizes (0.2, 2, and 6 μm) and cobalt contents (8, 12, 17 and 25 wt.%) were sprayed on carbon steel substrates using High Velocity Oxy-Fuel (HVOF) spraying process. Hardness, Young's modulus, and fracture toughness of the coatings were measured. While the hardness and Young's modulus decreased with increasing cobalt content from 1600 to 1100 Hv and from 400 to 300 GPa respectively, the fracture toughness remained in the range from 4 to 6 MPam^1/2. The coatings with 2 μm carbide showed lower hardness than those deposited from 0.2 and 6 μm carbide. These measured mechanical properties were discussed with the help of microstructures of the coatings investigated by scanning electron microscopy, X-ray diffraction and chemical analysis. Finally, the hardness of the binder phase in these coatings was estimated to range from 1000 to 1300 Hv by applying the mixture rule for composites to the experimental data, demonstrating that such hardening of the binder phase is a key factor affecting the mechanical properties of the coatings.     

Characterization and properties of MTCVD Ti(C,N) coated cemented carbide substrates with Fe/Ni binder

Two developments, including the deposition of hard chemical vapour deposition (CVD) coatings on cemented carbides and the use of innovative binders instead of Co for cemented carbides, have attracted worldwide interest. In this paper, ISO grade P30 cemented carbides with Fe/Ni and Co binders are prepared as the substrates, and adherent Ti(C,N) coatings are deposited on them by moderate temperature chemical vapour deposition (MTCVD) technique. The microstructure and properties of both the substrates and coated cemented carbides are studied.     

Influence of magnetic field on microstructure and properties of Ni60 plasma surfacing layer

0IntroductionWear is a main failure mode for many engineeringcomponents.Many surface treating technologies have beendeveloped in order to enhance wear resistance of materi-als[1].Plasma surfacing technology is of the greatest appli-cation potential due to…     

Influence of heat treatment on microstructure and mechanical properties of Al/Al-Cu graded materials

Five-layered Al/Al-Cu functionally graded material (FGM) was prepared by powder metallurgy technology, and the subsequent heat treatment was carried out for the graded material. The microstructures and distribution of Cu element under pressure sintering (F), solution treatment (T4) and artificial aging treatment (T6) were investigated, and the Vickers hardness and flexural properties of different states were tested. The results showed that sintered compact with dense structure and compositional continuous c...     

直接双相区热处理工艺参数对9Ni钢组织性能的影响

研究了直接双相区热处理工艺的保温时间和回火时间对9Ni钢组织性能的影响。结果表明:在相同回火条件下,保温时间为40 min时低温韧性最好,少于Quenching+Lamellarizing+Tempering(QLT)工艺中双相区保温所需时间;保温时间为20 min时,强度增加但低温韧性降低;保温时间过长(60 min)会导致组织粗化、低温韧性差,延长回火时间低温冲击功也基本不变。保温时间为40 min时,随着回火时间的增加,回转奥氏体增加,抗裂纹扩展能力增强,低温冲击功增加,但强度降低,这主要归因于回转奥氏体在板条束间的析出和对马氏体中C及其它有害元素的净化作用。     

Influence of deposited particles of Ni and Co on the passivity of aluminium

The cathodic deposition of transition metals allows obtaining surface conditions similar to those found in alloys and to study the anodic processes occurring on them. In this work, some aspects dealing with the influence of the presence of electro-deposited particles on the growth of anodic oxide films at potentials lower than 10 V in neutral acetate buffer solution were analysed by conventional electrochemical techniques supported by SEM and TEM. At the first stages of anodization, the particles lose progressively their contact with the substrate due to the growth of the aluminium oxide film leaving a defective structure. Thus, at potentials higher than 0.9 V SSE, the electrical contact of particles is established by tunnelling through localized states generated by defects in the band-gap. This, in turn, leads to the formation of preferential conductive paths. Thus, the dissolution/passivation of particles and the evolution of oxygen on them at higher anodic potentials could be observed. At potentials higher than 4 V, defects are released towards the oxide/electrolyte interface and the behaviour of pure aluminium oxide is observed again.     

不同退火工艺对H13钢组织和力学性能的影响

用OM、SEM研究了亚温退火、等温退火、缓慢冷却退火3种工艺对H13钢组织和力学性能的影响。结果表明,亚温退火后碳化物粒度最小,缓慢冷却退火后碳化物粒度较大,退火硬度较低;等温退火及缓慢冷却退火对提高碳化物尺寸、分布均匀性有一定作用,同时碳化物均匀性的提高对提升H13钢退火态及淬、回火态冲击韧性有一定作用,但组织中夹杂物、一次碳化物制约着H13钢韧性的提高。