镍、铬对硬质合金酸性盐雾腐蚀性能的影响

本文采用传统粉末冶金工艺制备了WC-8%Co、WC-6%Co-2%Ni-0.4%Cr3C2、WC-8%Ni-0.4%Cr3C2硬质合金样品,利用酸性盐雾试验、极化曲线测试、扫描电镜观察和能谱分析等手段,研究了添加Ni、Cr等元素对硬质合金酸性盐雾环境中腐蚀行为的影响。试验结果表明:WC-Co硬质合金在酸性盐雾环境下由于粘结相标准还原电极电位低,更容易发生电化学腐蚀,造成粘结相流失;添加Ni和Cr,可以提高WC-Co硬质合金的电极电位,降低极化电流密度,提高其在酸性盐雾溶液中的抗腐蚀能力;扫描电镜和能谱分析结果表明添加Ni和Cr,可以降低硬质合金在酸性盐雾溶液中粘结相的流失。     

烧结态硬质合金的腐蚀行为

研究人员运用不同溶液浸入试验和电极化试验等电化学方法并通过分析其腐蚀行为研究了WC—Ni—Cr硬质合金和TiC—Ti—Mo烧结硬质合金的腐蚀机理。WC—Ni—Cr硬质合金的腐蚀主要是由粘结剂Ni相在中性和酸性溶液中的溶解作用以及WC相中W和粘结剂Ni相在碱性溶液的溶解作用所致。     

深冷处理对不同w(Co)/w(Ni)粘结相的Ti(C,N)基金属陶瓷硬度及耐腐蚀性的影响

本文采用传统粉末冶金技术制备了不同粘结相成分的Ti(C,N)基金属陶瓷,并研究了深冷处理对其硬度、耐腐蚀性和电化学腐蚀性能的影响。研究结果显示,深冷处理能够提高材料的耐腐蚀性,其中对以Co或Co-Ni为粘结相的材料的提高最为显著;同时,深冷处理能促使材料腐蚀电位的正移和腐蚀电流密度的下降,降低其在酸性溶液中的电化学腐蚀倾向和腐蚀速率;此外,深冷处理会导致以纯Ni为粘结相的金属陶瓷材料的硬度下降,而对含Co金属陶瓷材料的硬度不产生影响。     

WC基硬质合金在碱性溶液中腐蚀行为的研究

本文以WC-Co、WC-Co-Ni-Cr硬质合金为研究对象,采用电化学极化曲线测试以及扫面电镜观察等试验手段,研究了两种合金在不同pH值的碱性溶液中的腐蚀行为。结果表明:在pH=13的NaOH溶液中,WC-Co和WC-Co-Ni-Cr合金腐蚀行为一致,都以WC的溶解析出为主,而在pH=10～11的Ca(OH)_2溶液中,两种合金各相的析出略有差别,WC-Co合金中粘结相Co析出略大于WC,而WC-Co-Ni-Cr合金相反。在pH=9～10的磨削液中,WC-Co和WC-Co-Ni-Cr合金的腐蚀行为完全不同,前者粘结相Co的溶解析出量远大于WC,后者粘结相析出量略小于WC。在pH=7～8的冷却水中,WC-Co合金中粘结相Co的溶解析出量略大于WC,而WC-Co-Ni-Cr合金中粘结相和WC的溶解量接近。在不同pH值的碱性溶液中,WC-Co-Ni-Cr合金的自腐蚀电位与溶液的pH值有关,pH值越高,自腐蚀电位越负;WC-Co合金的自腐蚀电位与pH值并不是简单的线性关系,与溶液的成分密切相关。     

WC-Co-(Ni)-(Cr)硬质合金在中性溶液中的腐蚀行为

以WC粉、Co粉、Ni粉及Cr3C2粉为原料,采用粉末冶金方法制备了3组不同粘结相成分的WC-Co-(Ni)-(Cr)硬质合金,通过极化曲线测试和浸泡实验研究了3组合金在中性溶液中的腐蚀行为,并采用扫描电镜、能谱分析、X射线光电子能谱(XPS)和EBSD等手段对其腐蚀机理进行了探讨。结果表明,WC-Co和WC-Co-Cr硬质合金在中性溶液中主要发生粘结相Co的腐蚀,浸泡产生的腐蚀产物主要是Co(OH)2;添加Cr将提高WC-Co硬质合金在中性溶液中的耐腐蚀性能,这可能与Cr的添加明显降低了粘结相中密排六方Co的含量有关;同时添加Ni和Cr可进一步提高WC-Co合金在中性溶液中的耐腐蚀性能,在pH=7的Na2SO4溶液中浸泡480 h后,WC-Co-Ni-Cr合金发生很少量的腐蚀。     

硬质合金冲击疲劳行为的研究

本文综述了国内外有关硬质合金冲击疲劳行为的研究进展,旨在认识和揭示硬质合金在反复冲击载荷作用下的失效和断裂机理。重点总结了实验室中常用的硬质合金冲击疲劳性能评价方法,包括应力法和能量法;从WC平均晶粒尺寸、粘结相种类及含量、C含量、合金元素(Cr、V、Ta等)、腐蚀介质等方面分析了微观结构和服役环境对硬质合金冲击疲劳性能的影响;从裂纹的萌生、扩展及断裂方面阐述了硬质合金的冲击疲劳断裂机理。服役条件下的硬质合金往往不是受到单一的冲击作用,而是多种因素(载荷、温度、腐蚀介质等)的联合作用,今后有必要开展这方面的研究;另外硬质合金在冲击过程中的组织演变机理还不清楚,研究者可借助更为先进的手段(例如透射电镜原位观察等)对硬质合金的微区进行研究;此外研究者可以在总结试验数据和规律的基础上构建理论及数学模型并借助计算机软件对硬质合金的冲击过程进行动态模拟。     

Ti(C,N)基金属陶瓷的耐腐蚀性

研究了Ti（C,N）基金属陶瓷在5％HNO3、50％NaOH溶液中的耐腐蚀性能,对比了金属陶瓷与YG8硬质合金在同种腐蚀介质中的耐蚀性优劣,并对金属陶瓷在5％HNO3溶液中的腐蚀形貌进行观察。试验结果表明：金属陶瓷有良好的耐酸碱腐蚀性能,其耐蚀性与粘结相的含量密切相关,粘结相的含量愈低,耐蚀性愈好;金属陶瓷的耐蚀性明显优于YG8硬质合金;金属陶瓷的腐蚀机理为钝化膜保护的电化学腐蚀。     

氯离子对9Cr马氏体钢静态腐蚀和应力腐蚀行为的影响

目的研究9Cr马氏体钢在非服役条件下的腐蚀行为。方法运用传统电化学测试和微区扫描振动电极(SVET)技术研究材料的静态腐蚀行为,采用慢应变速率动态拉伸腐蚀试验与传统电化学测试技术相结合的方法研究材料的应力腐蚀行为。结果获得常温下氯离子对马氏体钢静态腐蚀行为的影响规律,以及慢拉伸过程中材料表面钝化膜生成和破裂过程。结论马氏体钢在氯化钠溶液中的腐蚀为阳极溶解型,且随着氯离子浓度的上升,局部腐蚀电流密度增大。常温下材料在含氯离子环境中发生弹性变形时,表面生成的钝化膜使材料的抗腐蚀性能升高。当材料进入塑性变形阶段后,由于金属表面缺陷的增多、颈缩区体积的收缩,以及钝化膜与基体金属塑性变形能力的差异,钝化膜逐渐溶解并发生破裂。     

pH和Cl~-对Cu-Cr-Zr合金电化学腐蚀的影响

采用电化学方法研究了Cu-Cr-Zr合金在不同pH条件下含0.6mol/L的NaCl和纯水溶液中的耐蚀性,采用扫描电子显微镜(SEM)、能谱(EDS)表征了浸泡试验72h后试样的表面形貌。将其在不同腐蚀介质中的耐电化学腐蚀性作对比,结果表明,Cl-的加入使合金在同等pH条件下的耐蚀性下降;碱性环境降低了Cl-对合金的腐蚀;在强酸溶液中合金会发生全面均匀的腐蚀,在强碱溶液中合金发生局部腐蚀。     

Cu-Cr合金在3.5%NaCl+NH3溶液中的腐蚀行为

通过金相、X射线衍射及扫描电镜(SEM／EDX)，结合电化学测试手段，研究了Cu-Cr合金在3．5％NaCl NH3溶液中的腐蚀行为，并探讨了NH3浓度对其腐蚀性能的影响。结果表明：Cu-Cr合金中铜相较铬相易腐蚀，其腐蚀速率随NH3浓度的增加而增大。     

Mo_2C对Ti(C,N)基金属陶瓷腐蚀性能的影响

通过静态浸泡腐蚀和动电位极化两种方法,研究了Mo2C对Ti(C,N)基金属陶瓷在NaOH溶液中腐蚀性能的影响。实验结果表明:Ti(C,N)基金属陶瓷的耐蚀性明显优于WC-Co硬质合金;添加Mo2C可以大幅度提高Ti(C,N)基金属陶瓷的机械性能,硬度从91.2到94.0 HRA和抗弯强度从930到1 350 MPa,但会降低金属陶瓷的耐蚀性能;由于Mo2C的加入,会使金属陶瓷的动电位极化曲线出现两个钝化区,但是两个钝化区域的电流均未达到真正的钝化电流(10-5A/cm2),因而这些钝化现象均为伪钝化;在经动电位极化后的试样表面,粘结相Ni和白色的内环相均会被腐蚀,其中内环相为富Mo的(Mo,Ti)(C,N)固溶体,其耐腐蚀性较未溶的Ti(C,N)芯更差。随着Mo2C添加量的提高,内环形相的厚度随之会增加,从而降低了Ti(C,N)基金属陶瓷的耐蚀性能。     

Corrosion properties of Co-based cemented carbides in acidic solutions

The corrosion properties of cemented carbides with cobalt binder phase have been examined in HCl and H₂SO₄ solution at room temperature. Potentiodynamic polarization technique with saturated calomel reference electrode was employed in this study. Air and inert argon were used as a circulating media. The effect of magnetic saturation property of cemented carbide on corrosion behavior is described. Specimens were prepared in industrial sinter furnaces under various conditions to obtain different magnetic saturation at various binder contents. According to aerated experiment, there was a difference of anodic behavior of cemented carbides between HCl and H₂SO₄ solution. The specimen in H₂SO₄ solution shows lower current density than in HCl by up to two orders of magnitude. This can be explained by the effect of anion on corrosion behavior of cemented carbides. A large difference between aerated and deaerated acidic solution was not observed. There was a small change of polarization curve in cathodic regime due to different extent of cathodic reaction. In addition, free corrosion potential was slightly shifted to more noble values in aerated solution. In anodic polarization, both curves were almost identical. This shows that dissolved oxygen has small influence on anodic behavior of cemented carbides. Chronoamperometric measurement as well as electrochemical investigations showed that pseudopassivity is caused by a diffusion controlled process, which is in contradiction to literature where coverage of surface is claimed. Unstable precipitates are formed in cemented carbides with high tungsten containing binder during anodic dissolution.     

含有金属黏结相的热喷涂WC涂层在盐雾中的腐蚀行为

研究黏结相化学成分对涂层材料的耐盐雾腐蚀性能的影响,对采用超音速火焰喷涂制得的WC?17Co和WC?10Co?4Cr涂层进行电化学试验和长时间的盐雾腐蚀实验(浓度为5%的NaCl溶液,温度35°C)。结果表明：WC?10Co?4Cr涂层的耐盐雾腐蚀性能优于WC?17Co涂层。对于WC?17Co涂层,主要腐蚀行为除了粘结金属的腐蚀外还包括WC颗粒与粘结相金属之间发生的微点偶腐蚀;对于WC?10Co?4Cr涂层,形成的氧化物有利于抑制金属相与粘结相的腐蚀。说明金属材料成分是影响超音速火焰喷涂WC基涂层耐盐雾腐蚀性能的重要因素之一。     

WC-6%Co硬质合金的冲击磨粒磨损性能研究

用MLD-10型动载磨粒磨损试验机研究了不同晶粒度YG6硬质合金的冲击磨粒磨损性能。对试样进行了失重测量,并用FESEM分析磨损试样表面形貌。结果表明,硬质合金的耐磨性能与粘结相自由程、WC晶粒度有关;在本实验条件下,随着WC晶粒度或粘结相自由程增加,合金耐磨性先增加后减小,特定WC晶粒度配比的混晶WC-6%Co合金的抗冲击耐磨性能最好。合金的磨损失效机制也发生了转变:细晶合金主要表现为WC颗粒的剥落;随WC晶粒度增加,合金主要表现为大颗粒WC破碎后脱落。在以SiC为磨料的冲击磨粒磨损试验中,WC-6%Co合金的磨损是以WC颗粒的破碎和碎片脱落为主要的失效机制。     

Corrosion of cemented carbide grades in petrochemical slurries. Part I - Electrochemical adsorption of CN¯, SCN¯ and MBT: A study based on in situ SFG

Owing to their unique combination of wear resistance and toughness, cemented carbides are developing relevance in a systematically increasing number of applications, many of which involve notably corrosive environments. Petrochemical offshore extraction is one of the most appealing prospective fields of use of cemented carbides for critical general-purpose components (e.g. pumps and valves), as well as specialised devices, such as drilling mud circulation systems, as they undergo extremely severe erosion-corrosion related to the handling of tetraphasic flows comprising condensed and gas-phase hydrocarbons in addition to sand or other solid components of slurries. Moreover, oilfields of current interest bear high concentrations of strongly corrosive impurities. The present study is aimed at contributing to the knowledge of the corrosion and corrosion inhibition processes of a range of alloyed Co- and Ni-based cemented carbide grades in solutions containing cyanide (CN¯) and thiocyanate (SCN¯) - typical corrosive contaminants found in crude oil - and 2-mercaptobenzothiazole (MBT), a prospective corrosion inhibitor in the petrochemical field. To this aim, we employed: (i) linear sweep voltammetry (LSV) to assess the cathodic and anodic activity of the hardmetal grades; (ii) in situ Sum-Frequency Generation (SFG) spectroscopy as a sensitive probe of the potential-dependent interfacial chemistry and corrosion behaviour in terms of both adsorption and interaction of adsorbates with the electronic structure of the substrate; (iii) ex situ spectro-ellipsometry to characterise the films formed on the different grades in the investigated environments. We have found that: (i) the grade with Co‐Ru binder exhibits a generally better corrosion resistance in all investigated ambients; (ii) Ni affords protective action provided the oxidising power is below a given threshold and CN¯ is absent, and (iii) MBT improves the pseudopassivation of all the investigated cemented carbides. Typical potential-dependent SFG spectral scenarios have been pinpointed for the different electrode/electrolyte combinations, accurately matching the electrochemical behaviour assessed by LSV and the optical properties of the corroded surfaces investigated by spectro-ellipsometry. This multi-method study offers a comprehensive and insightful understanding of the corrosion of cemented carbides in contact with additive-containing solutions.     

Influence of the cemented carbide specification on the process force and the process temperature in grinding

Cemented carbides are hard and brittle materials. Their material properties are adjusted by their chemical composition, in particular their average hard phase grain size and their binder fraction. The research paper focusses on grinding of cemented carbides with cobalt (Co) as binder and tungsten carbide (WC) as hard phase material. Within the research paper, it is discussed if and to what extent the cemented carbide composition affects the occurring thermo-mechanical load collective in the grinding process. In particular, the influence of the average WC grain size and the cobalt fraction on the thermo-mechanical load collective is investigated and explained by the cemented carbide material properties. The results of the publication contribute to a knowledge-based design of cemented carbide grinding processes.     

过渡族金属碳化物在WC-Co硬质合金中的界面偏析与固溶行为

过渡族金属碳化物是最常见的硬质合金微观组织结构与性能调控添加剂,添加剂在硬质合金中赋存状态的研究是WC晶粒生长抑制机理研究的基础,也是硬质合金材料与工艺设计的基础。从基于第一性原理计算的理论研究、基于高分辨透射电镜和原子探针层析法的实验观察分析等2个方面,综述了过渡族金属碳化物在WC/β(钴基固溶体粘结相)相界偏析行为的研究现状。基于过渡族金属碳化物在硬质合金中晶界与相界的偏析行为、在硬质相与粘结相中的固溶行为,讨论了硬质合金中WC晶粒生长机理与晶粒生长抑制机理以及过渡族金属碳化物对硬质合金性能的影响机理,提出了硬质合金材料与工艺设计的建议。     

Cyclic contact fatigue of cemented carbides under dry and wet conditions: Correlation between microstructure,damage and electrochemical behavior

The correlation between the damage induced under cyclic contact fatigue and their electrochemical behavior (anodic polarization curves) for different WC-Co-based cemented carbides grades was investigated at the macrometric and micrometric length scale. Under both, dry (i.e. air atmosphere) and wet (cutting lubricant fluid) conditions, the crack path propagates near the carbide/metallic binder interface, resulting in tortuous cracks of several micrometers. Despite the alkaline conditions imposed by the cutting fluid (pH 9.2), the cobalt binder is preferentially dissolved, and the carbide-skeleton keeps stable. The presence of cutting fluid in the contact fatigue zone changes the morphology of the cracks due to the partial dissolution of the binder phase. The addition of chromium to the WC-Co composition enhances corrosion resistance of the metallic binder phase resulting in reduced damage of the cemented carbides in environmental assisted cyclic contact fatigue conditions.