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.     

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.     

Effects of fine WC particle size on the microstructure and mechanical properties of WC-8Co cemented carbides with dual-scale and dual-morphology WC grains

Dual-scale and dual-morphology WC grained WC-8Co cemented carbides comprising triangular or hexagonal fine WC grains and plate-like coarse WC grains were synthesized by vacuum sintering using Co, flaky graphite, WC, and coarse W as the starting materials. The effects of fine WC particle sizes on microstructure, relative densities, and mechanical properties of the dual-scale and dual-morphology WC grained cemented carbides were investigated. The results revealed that the growth of plate-like coarse WC grains was further promoted with the decrease in the particle size of the added fine WC; hence, their aspect ratio increased. In addition, added fine WC led to the separation of plate-like coarse WC grains so as to break their oriented arrangement and prevent their face contact; hence, plate-like coarse WC grains were completely covered by the Co binder phase. Moreover, the addition of smaller particle size of fine WC contributed to more uniform Co binder phase. When 0.4-μm WC powders was added, the aspect ratio of plate-like coarse WC grains was greater than that of plate-like WC grained cemented carbides without the addition of fine WC. The dual-scale and dual-morphology WC grained cemented carbides by adding 0.4-μm fine WC exhibited good comprehensive mechanical properties, with a transverse rupture strength of 3645 MPa, a Rockwell hardness of 91.5 HRA, and a fracture toughness of 12.3 MPa∙m^1/2.     

Effects of submicron WC addition on structures,kinetics and mechanical properties of functionally graded cemented carbides with coarse grains

Functionally graded cemented carbides (FGCCs) were prepared by pre-sintering and carburizing of carbon-deficient WC–Co cemented carbides. Submicron WC powder with different contents was added in FGCCs with coarse grains to study the influences of microstructures, kinetics and mechanical properties. The results show that the addition of submicron WC can increase the thickness of the gradient layer, and improve the carburizing rate in FGCCs. The average grain size becomes finer with the content of submicron WC increasing. The FGCCs with the addition of submicron WC has a higher grain growth rate, and the grain growth kinetics is proposed to be diffusion-controlled. Meanwhile, a simplified equation for estimating the final average grain size of FGCCs is provided. The hardness and the transverse rupture strength of FGCCs can be efficiently improved by the addition of submicron WC due to the fine microstructures and thick gradient layer.     

WO3添加量对超粗硬质合金微观结构及性能影响*

本文以WC、WO₃、Co、C为原料,通过原位细晶溶解-析出长大法制备了超粗硬质合金,并分析了不同WO₃添加量对合金微观结构及性能影响规律。结果表明：初始粉末中加入的WO₃和C在烧结过程中将发生原位一步还原碳化反应转化为高活性的细WC,促进溶解-析出长大现象,使超粗硬质合金WC平均晶粒度随着WO₃含量增加而增大。同时,WO₃添加能够减少粗WC晶粒微观缺陷和曲边的阶梯状表面,平直化晶粒边界,使其形貌趋于形成完整的三角棱柱体,其(0 0 0 1)晶面占比高,能够有效提高合金硬度,阻碍裂纹扩展,增加钴相韧性断裂比例。当WO₃添加量为4.20wt.%时,制备的超粗硬质合金具有最大的硬度(1085kgf/mm₂⁾和抗弯强度(2692MPa)。     

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.     

微波烧结超细WC-8Co硬质合金中的脱碳及其改进(英文)

通过微波烧结技术制备超细WC-Co硬质合金。烧结过程中在试样的表层形成脱碳相W3Co3C。在混料过程中添加炭黑,研究碳含量与合金力学性能之间的关系。结果表明:当碳含量为0.45%时,合金的硬度和断裂强度达到最大值,分别为HRA93.2和3396MPa。SEM观察发现在微波烧结超细硬质合金过程中,WC晶粒的长大主要为初期的合并长大。     

Al、Mn 等合金元素在烧结过程中对多孔砂轮铜基胎体的作用研究

本文通过正交试验设计和方差分析,研究添加不同含量的Cr、Co、Ni、Mn、Al等合金元素对多孔砂轮铜基胎体力学性能和显微组织的影响。试验结果表明：添加Co和Mn能同时提高胎体的抗弯强度和硬度;添加Al会降低胎体的抗弯强度但却使胎体的硬度增加;添加Cr使胎体的抗弯强度和硬度均降低;添加Ni对胎体的硬度影响很小,但却使胎体的抗弯强度明显降低。     

Effect of Mo2C additions on the properties of SPS manufactured WC–TiC–Ni cemented carbides

The effect of spark plasma sintering (SPS) on the microstructure and mechanical properties of WC–Co and WC–Ni cemented carbides was studied, and compared to WC–Co produced by liquid phase sintering (LPS). There were finer WC grains with larger Co pools in the spark plasma sintered WC–Co, resulting in higher hardness and slightly lower fracture toughness than the liquid phase sintered WC–Co. The influence of the addition of 0.5–5 wt.%Mo₂C to WC-based cemented carbide containing 6.25 wt.%TiC and 9.3 wt.%Ni prepared by SPS was also studied. This addition improved the wettability between WC and Ni and lead to the improvements of microstructures, resulting in good combinations of hardness, fracture toughness and modulus of elasticity that were comparable to WC–Co based cemented carbides.     

WC—8（Fe／Ni／Co）R硬质合金的研究

用Ｆｅ、Ｎｉ部分取代ＷＣ－８Ｃｏ合金（牌号ＹＧ８）中的粘结剂Ｃｏ,再添加微量稀土Ｒ制得ＷＣ－８（Ｆｅ／Ｎｉ／Ｃｏ）Ｒ硬质合金,测试了其物理机械性能,研究了粘结剂各种成份比例及烧结温度对硬质合金的影响。结果表明：ＷＣ－８（Ｆｅ／Ｎｉ／Ｃｏ）Ｒ硬质合金的性能可以达到ＹＧ８的性能标准。利用扫描电镜（ＳＥＭ）及Ｘ射线衍射（ＸＲＤ）对其作了显微结构分析,同时探讨了影响ＷＣ－８（Ｆｅ／Ｎｉ／Ｃｏ）Ｒ合金性能的     

Effects of graphite on the microstructure and properties of ultrafine WC-11Co composites by spark plasma sintering

Ultrafine WC-11Co hard metals added with different proportions of graphite were prepared by spark plasma sintering at 40 MPa/1200°C for 5 min,and the influence of graphite as free carbon on the microstructure and mechanical properties were investigated.The XRD analysis showed that decarbonization could be prevented by adding graphite.Compact hard metals composed of finer and more homogeneous WC grains with little flaws can be achieved after 0 wt.% to 1.5 wt.% graphite was added.The hardness and fracture toughness increase initially with increasing graphite content,and with over 1.5 wt.% they descend due to coarse grains and more defects.Therefore,1.5 wt.% graphite is the optimal addition content in view of the hardness and transverse rupture toughness.Furthermore,the coercive force decreases while the saturated magnetic intensity increases with the increase of graphite content.     

Microstructure and properties of ultrafine WC-10Co composites with chemically doped VC

Vanadium carbide is the most effective grain growth inhibitor for ultrafine WC-Co composites due to its high solubility and mobility in the cobalt phase at relatively low temperatures;however,there are still some debates over the best way to introduce it into the WC-Co formulation.In this paper,the differences between admixed and chemically doped grain growth inhibitors on the microstructural development and properties of an ultrafine WC-10Co composite are discussed.The densification rate of chemically doped samples is slower in the early stage of sintering and the WC grain sizes of the sintered alloys are finer than those of admixed samples,leading to the increase of hardness and transverse rupture strength of the sintered alloys.The effectiveness of the chemically doped inhibitor is attributed to the formation of vanadium rich layers on the surfaces of tungsten carbide powders during reduction and carbonization,which alters the surface and interface energies of WC grains,impedes the contact with each other of WC grains and contributes to the resistance to W diffusion across the layer during sintering,resulting in the inhibition of nanosized particle coalescence.     

含板状WC晶粒硬质合金的强韧化机制研究

通过加入2.5%板状WC晶种,制备含板状WC晶粒硬质合金,研究其强韧化机制。结果表明:WC晶粒的各向异性和形状改变诱导的Hall-Petch硬化是硬质合金硬度增加的主要原因。加入板状晶种后,裂纹在扩展过程中出现了明显的穿晶断裂和Co相桥接,增加了裂纹偏转,硬质合金的抗弯强度大大提高。不同Co含量和初始WC粉体粒度制备的含板状WC晶粒硬质合金,穿晶断裂、Co相桥接和裂纹偏转对抗弯强度增加的贡献不同。     

板状WC晶种加入对硬质合金性能的影响

通过加入板状WC晶种制备含板状WC晶粒的WC-10%Co和WC-20%Co硬质合金,研究了加入板状WC晶种对两种硬质合金显微组织和性能的影响。结果表明,加入板状WC晶种后硬质合金中的WC晶粒具有明显的板状特征,WC-20%Co中的板状WC晶粒比WC-10%Co多且尺寸大。少量晶种的加入对WC-10%Co和WC-20%Co硬质合金密度基本无影响,但两者的硬度和抗弯强度都有所增加,特别是抗弯强度分别提高了12%和11%。     

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。     

Influence of Mo on the microstructure and mechanical properties of TiC-based cermets

The microstructures and mechanics properties of TiC-based cermets composed of TiC, WC, Ni, Co, Mo, and Cr₃C₂ were investigated. The results show that Mo has a great effect on the sintering densification, microstructures, and mechanical properties. The microstructures and distribution of Mo and Ti in the TiC-based cermets were analyzed. It was indicated that a new phase with Ti, Mo, W, and C was formed on the rim of (Ti,W)C grains by means of an addition of Mo into the TiC-based cermets. The new phase with a surrounding structure was of great aid to improve the wettability of the liquid phase on the solid phase surface of TiC, decrease the porosity and refine the grains of the hard phase, which gave rise to the increase in strength and hardness. The properties of the TiC-based cermets could be further improved to some extent by adding WC, Cr₂C₃, and Co.     

烧结温度对含钽双晶硬质合金组织和性能的影响

同时采用不同粒度WC原料制备WC-TaC-Co硬质合金,并在不同的温度下进行烧结。研究表明:合金主要由两相组成,晶粒大小相间。所测硬度、密度和矫顽磁力随温度升高先升后降,抗弯强度随烧结温度升高而略有升高,但变化不明显。烧结温度为1450℃保温1.5h时,合金的综合性能达到最优,维氏硬度(HV30)为1668.8,抗弯强度为988MPa,密度为14.87g/cm3,矫顽磁力为15.2kA/m,此时Ta元素对WC晶粒的抑制效果最佳,晶粒尺寸达到0.75μm±0.33μm。     

Y2O3- and NbC-doped ultrafine WC–10Co alloys by low pressure sintering

The nanocomposite WC–10Co powders were prepared through planetary ball milling method. The effects of minor Y₂O₃ and NbC additions on structure, hardness and fracture toughness of ultrafine WC–10Co alloys were investigated using X-ray diffraction, optical microscope, scanning electron microscope and mechanical properties tests. The results show that minor NbC additions refine the WC grains and increase the hardness of the base alloys. The additions of Y₂O₃ decrease the volume fraction of Co₃W₃C phase in ultrafine WC–10Co alloys after low pressure sintering, and thus increase the fracture toughness of the base alloys from 6.2 MN m^−3/2 to 9.8 MN m^−3/2.     

细WC配比对非均匀YG20C合金性能的影响

研究了碳化钨粗颗细粒搭配对YG20C合金的力学性能与组织结构的影响,即在WC颗粒平均粒径为25μm的合金中,加入不同比例的平均粒径为2.0μm的WC颗粒,构成非均匀晶粒硬质合金。结果表明,非均匀YG20C合金的硬度和抗弯强度随着细晶粒碳化钨含量的增加都是先升高再降低。当细颗粒碳化钨比例为20%(文中含量均为质量分数)时,YG20C合金的综合力学性能最好,硬度和抗弯强度都达到"双高",其值分别为HRA83.5和2 800 MPa,比均匀YG20C合金的硬度和抗弯强度分别提高HRA1.2和400 MPa。并且非均匀YG20C合金的冲压使用效果最佳。     

Influences of sub-micrometer Ta and Co dopants on microstructure and properties of tungsten heavy alloys

Tungsten heavy alloys are aggregates of particles of tungsten bonded with Ni/Fe or Ni/Cu via liquidphase sintering. The sub-micrometer Ta Co powder was added to this aggregate to strengthen the bonding phase. It is found that the main fracture pattern of the alloys is cleavage of tungsten grains and ductile rupture of bond phase,leading to improved tensile strength and elongation. Dopant Ta can act as grain size inhibitor in tungsten heavy alloys.