Ru添加对WC-Co硬质合金结构与性能的影响

粘结相是硬质合金重要的组成部分,随着硬质合金材料技术的发展,目前,越来越多的研究者希望能够通过粘结相的掺杂技术来提升合金的综合性能。本文通过对比分析WC-Co和WC-Co-Ru硬质合金,发现Ru的添加能够抑制WC晶粒的长大,有效抑制WC晶粒的异常长大,可以提高合金中粘结相Co的显微硬度和合金的整体硬度,能够显著提升硬质合金的高温抗氧化性,在粘结相结构方面,Ru元素会促进钴的亚稳态α-Co相向室温稳定态ε-Co相的转变。经过镍基高温合金车削和钛合金铣削对比实验,Ru添加硬质合金表现出更好的耐磨性、抗冲击韧性以及高温抗氧化性。     

淬火温度对ZL40.5硬质合金微观组织结构的影响

传统硬质合金中硬度和韧性是难以兼得的一对矛盾体,而通过热处理改善WC-Co硬质合金结构与性能则可获得具有优异综合性能的硬质合金。本文以压制烧结制成的ZL40.5硬质合金为研究对象,在1 050～1 300℃范围内进行油性介质淬火,采用扫描电镜(SEM)及X射线衍射(XRD)等检测方法研究了淬火温度对ZL40.5硬质合金微观组织结构的影响。结果表明:淬火过程中WC晶粒尖角溶解,形貌变得圆钝;随淬火温度升高,Co相体积分数升高,WC晶粒尺寸、邻接度略有降低;W、C原子在Co中的固溶度随淬火温度增加而增加,进而使室温下保留的α-Co含量随之增加,淬火温度在1 250℃时具有最佳结构参数。     

淬火回火热处理对WC-25%Co硬质合金组织与性能的影响

本文选用钴含量25%的WC-Co硬质合金,在1 250℃,真空条件下,对合金进行淬火,并于500℃回火,研究了淬火回火热处理对WC-25%Co硬质合金组织与性能的影响。研究结果表明,经1 250℃真空淬火并于500℃回火后,合金粘结相Co中面心立方结构α-Co的含量趋近于100%,WC平均晶粒尺寸保持不变,而WC晶粒邻接度明显减小,粘结相Co中固溶的W原子数量显著提高,裂纹的萌生和扩展受到抑制,合金的韧性获得改善。热处理后合金的矫顽磁力值和钴磁降低,合金中出现了明显的细小孔洞,其密度和硬度略微降低,但是合金抗弯强度由3 300 MPa提高至3 500 MPa。     

热处理对高钴ZL40.5硬质合金组织与性能的影响

以冲模用高钴ZL40.5硬质合金作为研究对象,采用扫描电镜(SEM)、X射线衍射(XRD)等方法对系列热处理试样进行分析,基于晶体学理论并结合Image J、Jade软件研究ZL40.5硬质合金微观组织结构参数(粘结相体积分数、晶粒度、邻接度、残余应力及晶格常数)、断口形貌及其性能。结果表明:淬火处理使WC晶粒形貌变圆润,降低应力集中的发生,减少断裂源;淬火回火处理后,粘结相中α-Co含量大幅提升,WC邻接度降低,合金在保证硬度的同时强度和韧性得到提升;热处理后合金断裂以沿晶和韧性复合形式为主,淬火回火后表面压应力提升最高。     

粘结相Co的切变机制及微观结构的研究

本文以工业纯钻粉、钴基合金、硬质合金作为研究对象,分别运用X射线衍射、金相、扫面电镜能谱、EBSD等分析技术,并结合晶体学的相关知识研究了钴的基本特性、微观结构及其切变机制。通过研磨工业纯钴粉,比较分析研磨前后X射线衍射分析结果,定性描述了钻粉的α-Co向ε-Co的转变过程;实验制备了不同固溶W含量的Co基合金,并对合金金相组织及相结构进行了分析;对淬火后的WC-10％Co硬质合金,研究了在不同回火温度、时间工艺参数条件下合金粘结相Co的微观组织结构变化规律及其主要影响因素;通过离子束抛光制样,运用背散射电子衍射（EBSD）技术研究了WC-20％Co硬质合金中的α-Co与ε-Co形貌特征及其分布状态。实验结果表明：α-Co结构的稳定性较差,α-Co向ε-Co的转变的相变驱动力仅几J/mol;固溶W含量对钴基合金中晶粒的孪晶组织有重要的影响,Co基合金中固溶的W含量越多其孪晶组织越少,且α-Co含量越多;硬质合金淬火后回火实验说明硬质合金粘结相Co的8马氏体相变过程既可在较高温度、短时间内形成变温马氏体ε-Co,也可在较低温度、长时间下形成恒温马氏体ε-Co,合金内部组织内应力的释放会引起α-Co向ε-Co的转变;EBSD分析发现硬质合金中粘结相大部分是以α-Co结构存在,ε-Co呈条带状,厚度在2μm以下,长度在6μm左右,主要分布在粘结相与WC相的界面处或较厚钴层的中间部位。文中重点论述了硬质合金ε-Co马氏体的基本特征及其切变机制。     

淬火与深冷处理对YG6硬质合金微观结构与性能的影响

本文以压制烧结合成的YG6硬质合金为研究对象,采用扫描电镜(SEM)、电子探针(EMPA)及X射线衍射(XRD)检测方法研究了淬火及深冷处理对YG6硬质合金微观结构的影响,并且测量了合金的相关性能,如硬度、抗弯强度及表面残余应力等。结果表明:淬火处理合金中的面心立方α-Co含量提高,W在Co相中的固溶度增加。深冷过程中由于发生Co相马氏体相变使密排六方ε-Co的含量提高,W在Co相中的固溶度降低。YG6硬质合金的硬度、钴磁等性能受到了影响,合金的抗弯强度以及表面宏观残余应力都呈增加趋势。     

深冷处理对不同碳含量WC-11Co硬质合金显微组织及性能的影响（英文）

研究深冷处理对不同碳含量WC-11Co硬质合金显微组织和性能的影响。结果表明:经深冷处理后WC晶粒的形状通过球化方式变成具有圆滑过度角的三角菱柱状,但其尺寸无明显变化。在经深冷处理后的合金中,W在Co中的固溶度减小,且Co相发生了从面心立方α-Co到密排六方ε-Co的转变。此外,深冷处理提高了合金的硬度与抗弯强度,但是对于合金的密度与钴磁性能影响不大。     

热处理对超细晶WC-15Co-0.2VC-0.4Cr_3C_2组织和性能的影响

分析了淬火和回火对WC-15Co-0.2VC-0.4Cr3C2超细晶硬质合金力学性能、微观组织及相结构的影响。研究发现,1 050℃淬火后横向断裂强度(TRS)由烧结态的4 020 MPa提高到4 590 MPa。TEM观察发现WC晶变得圆整,XRD分析显示高温淬火后的试样中塑性粘接相α-Co的含量明显高于烧结态,这使得合金的横向断裂强度显著提高。淬火后低温回火时消除淬火残余应力,TRS进一步提高,但回火温度高于300℃后TRS值下降,原因是高温回火时塑性粘结相α-Co转变成为ε-Co。     

淬火与回火工艺对WC-20%Co硬质合金微观结构和性能的影响

WC-Co硬质合金在刀具材料中被广泛应用,热处理可以有效地改善WC-Co硬质合金的综合性能。本文采用扫描电镜(SEM)、X射线衍射(XRD)和电子探针(EMPA)等分析手段,研究了淬火和回火处理对WC-20%Co硬质合金的微观结构与力学性能的影响。结果表明:随着淬火温度升高,WC晶粒尺寸呈现先增大后减小的变化趋势。在一定温度范围内,淬火温度越高,材料的硬度和抗弯强度也越高;抗弯强度在1 250℃淬火时达到最大值3 090 MPa,相对于未处理样品增加了13.2%。但当淬火温度达到1 350℃时,其硬度和抗弯强度开始下降,分别为985.0 HV和2 810 MPa。在淬火温度一定的条件下,回火温度越高,钴相中保留的高温相α-Co分数和固溶的W含量越低,材料的力学性能也随之降低。对比不同淬火介质后发现,相比于油淬,水淬处理更有助于提高材料的综合性能。     

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。     

基体碳含量对梯度结构硬质合金微观结构与性能的影响

Co相梯度结构硬质合金与传统硬质合金(WC-Co)相比具有良好的硬度和韧性组合。本文通过固体渗碳烧结处理制备出了Co相梯度结构硬质合金,研究了贫碳量对固体渗碳后硬质合金中Co相梯度结构、力学性能的影响,探索了Co相梯度结构的形成机制。结果表明,贫碳合金碳含量越低,η相体积分数越大,渗碳时需要消耗更多的活性碳原子,渗碳烧结后,Co相梯度结构厚度减小,富钴层厚度增加。Co相梯度结构硬质合金中,由于存在Co相梯度结构,硬质合金内部硬度呈现由高(1 600 HV5)到低(1 300 HV5)再到高(1 600 HV5)的变化,合金抗弯强度较传统硬质合金有所提升,碳含量为5.26%的贫碳合金在渗碳烧结后抗弯强度为2 860.1 MPa。     

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.     

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.     

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.     

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.     

含WB烧结硬质合金的组织结构和性能研究

将不同含量的WB粉末添加到传统成分的WC-Co粉末中,利用低压烧结技术制备了系列含WB的WC-Co型硬质合金,并对其物相组成、组织结构和力学性能进行了系统表征分析。研究发现,在低压烧结过程中WB与Co发生反应,生成了具有超高硬度的WCoB相,由此降低了粘结相Co对WC晶粒的隔离,增加了WC晶粒间的接触度,引起合金韧性下降。添加WB制备的硬质合金材料其摩擦系数更低,随WB添加量的增加,硬度和耐磨性明显提高,当WB添加量为30%(质量分数)时,制备的硬质合金材料的硬度达到19 000 MPa,其磨损速率仅为传统WC-Co硬质合金1/10。然而,添加WB的WC-Co合金的断裂韧性约为传统WC-Co硬质合金的83%~91%。     

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.     

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.