热处理对复合电冶熔铸WC颗粒增强钢基复合材料力学性能的影响

采用复合电冶熔铸工艺制备了以5CrNiMo钢为基体、WC颗粒为增强相的颗粒增强钢基复合材料,通过宏微观硬度试验、三点弯曲试验和冲击韧性试验对比分析并综合评定复合材料和5CrNiMo钢的各项力学性能,同时采用扫描电子显微镜观察断口形貌并判定断裂机理。结果表明：大量WC颗粒增强体分布在较软的钢基体上,提高了复合材料的整体硬度,淬透性和淬硬性也较好,但塑性比5CrNiMo钢稍差。在950 ℃到1050 ℃淬火时,复合材料的洛氏硬度达到60~66 HRC,抗弯强度达到1600~1650 MPa,均呈现先上升后下降的波动趋势,而冲击韧度变化不明显。对比基体和中小块WC颗粒聚集区,大块硬质相的显微硬度值变化幅度较小。在锻造退火状态下,复合材料为准解理+韧窝的复合断裂机理,而在淬火回火态时,则转变为解理断裂机制。     

WC粒度对梯度硬质合金组织和性能的影响

由于不同材料的热膨胀系数不同,涂层在冷却过程中可能因为热应力不同而产生裂纹,表面富粘结相的梯度硬质合金基体因粘结相含量高,韧性好,能有效吸收裂纹扩展时的能量,延长涂层刀具的使用寿命。为了研究WC晶粒度对梯度硬质合金的组织及性能的影响,制备了三种WC粒度的硬质合金。采用XRD和SEM对梯度硬质合金的相成分、微观组织进行了分析。实验结果表明,三种WC晶粒度的硬质合金表面均形成了梯度层。随着WC晶粒度的增大,梯度层厚度减小,抗弯强度和断裂韧性增大。三种梯度硬质合金表层显微硬度分布趋势相似。当WC晶粒度较小时,梯度硬质合金无梯度的合金芯部断裂形式均以沿晶断裂方式为主,随着WC晶粒度的增加,穿晶断裂方式增多;梯度表层出现了Co相变形和撕裂形貌,存在蜂窝状的韧性花样。     

TiC硬质合金颗粒复合耐磨材料的研究

用钨极氩孤堆焊获得含有TiC硬质合金颗粒及金属基体成分不同的两种复合耐磨材料。研究了两种材料的显微组织、相组成并测定了材料的宏观及显微硬度，用三种硬度不同的磨料测定了两种材料的磨料磨损耐磨性并分析了其磨损特点。结果表明，材料的耐磨性明显地受到其中TiC硬质合金颗粒的含量、金属基体的成分组织和硬度以及磨料的硬度的影响。当磨料一定时，随着TiC颗粒含量及金属基体硬度的提高，材料的耐磨性明显地提高，当磨料硬度提高时，材料的耐磨性则明显下降。金属基体的磨损主要是显微切削及显微犁沟，而TiC颗粒则是以显微脆断方式产生磨损。     

高Ni钎料-WC硬质合金颗粒复合堆焊焊条的探讨

以SiC材质成型舟皿作为模具，尺寸为2~5 mm的YG8型WC硬质合金颗粒为耐磨相，CuZnNi合金为胎体金属，加入NiCrBSi合金粉末以提高胎体金属的Ni含量与Cr含量，采用钼丝氢气炉烧结制备高Ni钎料 WC硬质合金颗粒复合堆焊焊条，并对成型后焊条的断面形貌及胎体金属成分进行分析。结果表明，硬质合金颗粒在焊条内呈相对均匀的分布，胎体金属中Ni的质量分数高达32.39%，适量的Cr元素能够增强胎体金属的强度，同时提高胎体金属的耐腐蚀性能与高温抗氧化性能，用氧乙炔火焰堆焊时，胎体金属流动性好，与基体润湿性好，焊层内胎体金属硬度大于60HRA，可在石油、矿山等耐磨领域推广应用。     

电冶熔铸WCp/钢基复合材料的组织及断口研究

用电冶熔铸法制备了20wt％WC颗粒增强钢基复合材料，进行三点弯曲法破断试验，并观测材料的显微组织及断口形貌，分析热处理工艺对显微组织和断口形貌的影响。结果表明：WC颗粒相基本溶解于钢基体相中，并沿品界生成Fe，W3C复式碳化物，同时两相实现了冶金结合；断口分析证实此类断口为韧——脆复合断口，其中，部分硬质相颗粒表面出现解理断口。热处理工艺和颗粒本身特征均可影响基体断口形貌和断裂机制。淬火态断口基本为沿晶断裂；低温回火态断口以细韧窝及部分沿晶断口为主要断裂机制；退火态断口为准解理及韧窝复合断口。     

电冶熔铸WC/钢复合材料中WC的溶解行为

用电冶熔铸工艺制备不同WC含量的WC/钢复合材料,研究了WC颗粒在复合材料钢基体中的溶解行为和影响因素.结果表明:随着WC含量的增加,碳化物从钢基体晶界处分布逐渐转向晶内分布;随着WC颗粒尺寸的增大,在WC颗粒与钢基体界面处形成一层反应物,它阻止了WC颗粒在钢基体中的进一步溶解,同时也提高了两相界面的结合强度.通过调整电冶熔铸工艺参数和WC颗粒的尺寸及含量,可以控制WC颗粒在复合材料中的溶解行为.     

电冶熔铸WC/钢复合材料的显微缺陷

采用电冶熔铸工艺将废弃的WC钢结硬质合金制备成WC/钢复合材料, 研究了复合材料中显微缺陷的形貌及形成机理.结果表明: 电冶熔铸WC/钢复合材料的气孔及夹杂含量少, 可有效解决WC颗粒的偏析.X射线衍射、扫描电镜和透射电镜分析显示, WC颗粒和钢基体界面上发生了界面反应, 生成了高稳定性的Fe3W3C界面层.     

激光熔覆微纳米WC颗粒增强镍基金属陶瓷涂层的裂纹研究

采用激光熔覆技术在45钢表面制备了微纳米WC颗粒增强镍基金属陶瓷涂层,研究了不同含量WC颗粒涂层的开裂行为。结果表明:当涂层中加入的WC含量分数不超过20%时,涂层具有较好的韧性,采用合适的激光熔覆工艺可以制备出无裂纹的Ni基金属陶瓷涂层。当涂层中WC质量超过30%时,涂层脆性增加,且其开裂敏感性随WC含量的增加而增加。涂层内的裂纹主要有萌生于涂层表层的粗大裂纹及萌生于气孔的内部微裂纹等。涂层中的微裂纹扩展机制主要为颗粒与基体间的界面脱粘以及基体金属的韧性开裂。涂层中未出现微米级颗粒增强金属陶瓷常见的颗粒开裂现象。     

高Ni钎料-WC硬质合金颗粒复合堆焊焊条的探讨

以SiC材质成型舟皿作为模具,尺寸为2～5 mm的YG8型WC硬质合金颗粒为耐磨相,CuZnNi合金为胎体金属,加入NiCrBSi合金粉末以提高胎体金属的Ni含量与Cr含量,采用钼丝氢气炉烧结制备高Ni钎料-WC硬质合金颗粒复合堆焊焊条,并对成型后焊条的断面形貌及胎体金属成分进行分析.结果 表明,硬质合金颗粒在焊条内呈...     

新型铸造WC颗粒复合耐磨材料的研究

新型铸造WC颗粒复合耐磨材料中的金属基体采用多元合金化,用氧-乙炔焰进行堆焊。研究了该材料的显微组织和相组成并测定了材料的宏观硬度和显微硬度。在两种不同的磨损条件下,测定材料的磨料磨损耐磨性,并分析了其磨损机制,研究结果表明,新型铸造WC颗粒复合材料的金属基体组织细化了,其中含有一定量M7C3型碳化物,使金属基体具有较高硬度。在两种磨损条件下,新型复合材料的耐磨性均明显高于常用的D35－4及YZ－4材料的耐磨性,在两体磨料损磨时,金属基体的磨损方式主要是显微切削,铸造WC颗粒的磨损则是脆性显微剥落。     

Mechanical properties of a hybrid cemented carbide composite

Microstructural effects on the mechanical properties of a hybrid metal matrix composite, double cemented (DC) carbide, have been investigated. DC carbide contains granules of WC/Co cemented carbide in a matrix of cobalt. Overall composite hardness increases with decreased granule cobalt content as well as with decreased intergranular matrix fraction of cobalt. High-stress abrasive wear resistance also increases with decreased granule cobalt content and matrix fraction. Fracture toughness of the composite increases with increased cobalt matrix fraction and to a lesser extent with increased granule cobalt content. Increased granule size increases both fracture toughness and wear resistance. DC carbide exhibits a superior combination of fracture toughness and high-stress wear resistance than conventional cemented carbide. The combination of toughness and wear resistance in the composite improves with increased granule hardness.     

Effect of interfacial characteristics on toughness of nanocrystalline cemented carbides

Dense nanocrystalline cemented carbide bulks were prepared using a unique in situ synthesized WC–Co composite powder with a super-ultrafine nanostructure. Remarkable enhancement in the fracture toughness (with high hardness being maintained) was obtained in the nanocrystalline cemented carbides. Based on detailed studies on the combination of WC and Co phases, the WC/Co orientation relationship and the atomic correspondence at interfaces, the mechanisms for high toughness in the present nanocrystalline cemented carbides were demonstrated. The study proposed that interfacial characteristics play a significant role in the toughness of the nanocrystalline cemented carbides, and provided an effective approach to achieve superior combination properties of hardness and toughness in cermet materials.     

矿用纳米稀土硬质合金的磨损性能研究

以石英砂为磨料,研究了YG12硬质合金的冲击磨料磨损性能与其纳米稀土添加量、硬度及断裂韧度之间的关系。结果表明,随着纳米稀土含量的增加,该硬质合金的磨损体积先减小再增大,加入1wt%纳米稀土时,其磨损量最小;随着硬度、断裂韧度的增加,合金的抗磨损性能提高。岩石颗粒的混合、粘结相的脆变和WC晶粒的破碎是矿用纳米稀土硬质合金的主要磨损机制。     

Consolidation and properties of ultrafine binderless cemented carbide by spark plasma sintering

Owing to the absence of metal binder, binderless cemented carbides have higher wear, corrosion, and oxidation resistance. WC-0.3VC-0.5Cr3C2 powders with an average particle size of 200nm and a little amount of active element were consolidated by spark plasma sintering. The sintered microstructure revealed that the average WC grain size was 0.24μm, which was almost consistent with the initial fine powder. The results of XRD showed that W2C phase was formed. Nearly complete densification of ultrafine binderless cemented carbide was achieved by sintering at 1400℃ for 120s under 50MPa. The resulting hardness and the fracture toughness were 28.18 GPa and 6.05MPa·m1/2, respectively.     

Additive manufacturing of WC-13%Co by selective electron beam melting: Achievements and challenges

Additive manufacturing is a powerful tool for rapid prototyping and fabricating metal articles having a complicated geometry. This method is known to be used almost solely for the manufacture of articles consisting of pure metals and alloys. In the present work the possibility of obtaining dense carbide articles by a single-step process of additive manufacturing based on selective electron beam melting was evaluated. A new technology for fabricating cemented carbide granules suitable for selective electron beam melting was developed. It includes conventional granulating WC-Co powders followed by solid-state pre-sintering and preliminary screening of the granules. After that their liquid-phase sintering and final screening are carried out to obtain a desired fraction needed for the additive manufacturing process. Results of experiments on selective electron beam melting at different scan rates and current values indicated that it was possible to obtain non-porous carbide articles of complex geometry from WC-Co granules initially containing 13 wt% Co. The selective electron beam melting process led to the evaporation of some liquid Co and very intense local WC grain growth resulting in peculiar microstructures of the cemented carbide articles comprising layers with medium-coarse and abnormally large WC grains. A near-surface layer of the cemented carbide articles obtained by additive manufacturing is characterized by a high roughness comparable with the mean size of the original WC-Co granules.     

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.     

Synthesis of WC-Co composite powders with two-step carbonization and sintering performance study

In this study, WC-Co composite powder was synthesized by two-step carbonization method using W, Co and C as raw materials. X-ray diffraction (XRD) showed that the η phase (Co₆W₆C) was kept at 1100 °C for 1 h under vacuum, and it could be completely carbonized into WC-Co composite powders. The surface morphology of WC-Co composite powders was analyzed by scanning electron microscope (SEM). The effects of η phase and second phase (W phase) on WC morphology and Co phase distribution were investigated. Electron backscattered diffraction (EBSD) was used to analyze WC-10 wt% Co cemented carbide particle distribution. Comparison of transverse rupture strength, hardness and fracture toughness of two kinds of WC-10 wt% Co cemented carbides synthesized by WC-Co composite powders + WC and WC + Co respectively, the cemented carbide of composite powders + WC increases the fracture toughness from 11.4 ± 0.3 MPa·m^1/2 to 12.4 ± 0.3 MPa·m^1/2.     

Effects of nano-alumina on mechanical properties and wear resistance of WC-8Co cemented carbide by spark plasma sintering

The effects of adding different nano-alumina on the structure, mechanical properties and wear resistance of WC-8Co cemented carbide during spark plasma sintering (SPS sintering) were investigated. The results show that the nano-alumina is dissolved in the Co phase, which results in a larger proportion of FCC-Co in the γ phase on the surface of the WC-Co cemented carbide. Under the scanning electron microscope, it is observed that the grains of cemented carbide are refined, and when the addition amount is 0.5 wt%, the effect of WC grain refinement is the most significan. The hardness, flexural strength and fracture toughness showed a trend of increasing first and then decreasingwith nano-alumina added. The peak value is reached when the nano-alumina content is 0.5 wt%, Which means that the alloy has the best combination of mechanical properties, that is, hardness reaches 1716 HV₃₀, bending strength reaches 2728 MPa, and fracture toughness is 12.95 MPa·m^1/2. Adding nano-alumina is beneficial to improve the wear resistance of cemented carbide. As a matter of course, when the content of nano-alumina is 0.5 wt%, the friction coefficient is the lowest, the wear rate is the smallest, and the wear resistance is the best.     

Effect of stress ratio on fatigue lifetime and crack growth behavior of WC–Co cemented carbide

Two types of fatigue tests, a rotating bending fatigue test and a three- or four-point bending fatigue test, were carried out on a fine grained WC–Co cemented carbide to evaluate its fatigue crack growth behavior and fatigue lifetime. From successive observations of the specimen surface during the fatigue process, it was revealed that most of the fatigue lifetime of the tested WC–Co cemented carbide was occupied with crack growth cycles. Using the basic equation of fracture mechanics, the relationship between the fatigue crack growth rate (da/dN) and the maximum stress intensity factor (K_max) was derived. From this relation, both the values of the threshold intensity factor (K_th) and the fatigue fracture toughness (K_fc) of the material were determined. The fatigue lifetime of the WC–Co cemented carbide was estimated by analysis based on the modified linear elastic fracture mechanics approach. Good agreement between the estimated and experimental fatigue lifetimes was confirmed.