涂层强度冲砂测试法

综述了涂层强度的常用测试方法，比较了这些方法的优缺点，指出了应用时应注意的问题。研究了涂层强度冲砂测试法的特点，提出了改进措施，以冲击用砂量与涂层被冲掉的质量之比表征涂强度，提高了测试结果的合理性和可比性。给出了详细测试方法。     

纳米结构WC-Co涂层的研究现状

纳米结构的WC-Co硬质合金由于具有高硬度、高强度和非常好的耐磨性而倍受研究者关注,并应用于各种切削工具、钻井钻头、采矿工具及其它各种耐磨零件的制备中.纳米结构的WC-Co涂层具有很多优点,主要表现在其硬度、结合强度和断裂韧性均高于传统涂层.然而,由于WC的热稳定性比较差,致使制备的涂层的性能下降.本文对纳米结构的WC-Co涂层所存在的问题进行了总结,并对其改性的研究现状进行了概述.     

An Effective Electrical Resonance-Based Method to Detect Delamination in Thermal Barrier Coating

This research proposes a simple yet highly sensitive method based on electrical resonance of an eddy-current probe to detect delamination of thermal barrier coating (TBC). This method can directly measure the mechanical characteristics of TBC compared to conventional ultrasonic testing and infrared thermography methods. The electrical resonance-based method can detect the delamination of TBC from the metallic bond coat by shifting the electrical impedance of eddy current testing (ECT) probe coupling with degraded TBC, and, due to this shift, the resonant frequencies near the peak impedance of ECT probe revealed high sensitivity to the delamination. In order to verify the performance of the proposed method, a simple experiment is performed with degraded TBC specimens by thermal cyclic exposure. Consequently, the delamination with growth of thermally grown oxide in a TBC system is experimentally identified. Additionally, the results are in good agreement with the results obtained from ultrasonic C-scanning.     

纯铜表面激光熔覆WC-Co涂层研究

利用超音速火焰喷涂和激光重熔技术在纯铜基体上制备WC-Co涂层.利用维氏硬度计测试了其显微硬度,用扫描电镜分析了激光熔覆层的微观形貌.结果表明:所制得熔覆层组织致密、无裂纹,与基体形成了良好的冶金结合.熔覆区表层的WC颗粒均匀分布,颗粒较小,形成了一层硬度很高的耐磨层,在熔化区中下部,组织为基体Cu和Co、W等组成的固溶体以及呈散落状分布着一些未熔化的大小不一的WC颗粒.激光熔覆区的显微硬度约为基体的10倍.     

金属材料表面爆炸喷涂WC-Co涂层的均匀性性能分析及数学描述

利用扫描电子显微镜和X射线衍射分析仪研究喷涂距离和氧燃率对爆炸喷涂WC-Co涂层性能的影响。结果表明,WC-Co涂层的最佳爆炸喷涂距离为110 mm,氧燃率为1.06。WC-Co涂层结构致密、耐磨性好,拥有近似各向同性的特征。     

Fe/Al金属间化合物光束合金化涂层的组织分层现象

在45钢表面预涂纯Al粉,用光束合金化的方法合成了Fe／Al化合物涂层。使用SEM、EDS、X-ray衍射研究了涂层的组织特点及物相组成。研究结果表明,Fe／Al化合物涂层发生了组织分层现象,表层为FeAl Fe3AlC0.5层,第二层为Fe3Al Fe3AlC0.5层。发生组织分层现象是由合金化过程熔池中Al的含量由表层到底部逐渐减小所引起的。其原因可能与Al的密度较低和熔池搅拌不充分有关。     

WC-Co硬质合金热喷涂层中温处理后的摩擦磨损特性研究

在室温干摩擦条件下，对WC-Co热喷涂中温处理涂层／GCr15摩擦副在摩擦系数和耐磨性方面与45钢／GCr15作了滑动摩擦对比试验，观察分析了磨痕形貌，并对WC-Co热喷涂中温处理涂层的磨损机理进行了分析。结果表明：在干摩擦情况下，WC-Co热喷涂中温处理涂层的摩擦系数比45钢的高，耐磨性比45钢提高约100倍。WC-Co热喷涂中温处理涂层的磨损机理为脆性微剥落和磨粒磨损。     

WC-Co硬质合金热喷涂层中温处理后的摩擦磨损特性研究

在室温干摩擦条件下,对WC-Co热喷涂中温处理涂层／GCr15摩擦副在摩擦系数和耐磨性方面与45 钢／GCr15作了滑动摩擦对比试验,观察分析了磨痕形貌,并对WC-Co热喷涂中温处理涂层的磨损机理进行了分析。结果表明:在干摩擦情况下,WC-Co热喷涂中温处理涂层的摩擦系数比45钢的高,耐磨性比45钢提高约100 倍。WC-Co热喷涂中温处理涂层的磨损机理为脆性微剥落和磨粒磨损。     

NiCoCrAlYTa/WC-Co复合涂层的制备及摩擦学性能研究

目的 为了改善MCrAlY涂层的耐磨损性能,通过在NiCoCrAlYTa粉末中添加不同比例的硬质相WC-Co粉末（质量分数为25%、50%、75%）,将2种粉末充分地机械混合、振荡均匀后,采用超音速火焰喷涂（HVOF）技术,制备不同配比的NiCoCrAlYTa/WC-Co复合涂层。方法 利用SEM、XRD、EDS等分析了复合涂层的微观形貌、物相组成和元素分布规律等;研究该复合涂层的力学性能、摩擦学性能以及摩擦磨损机理等。结果 采用HVOF技术制备的Ni CoCrAlYTa/WC-Co复合涂层结构致密,各元素及物相分布均匀;硬质相WC-Co的添加提高了涂层的显微硬度,同时也可显著改善复合涂层的耐磨损性能;复合涂层的摩擦因数随着WC-Co含量的增加逐渐增大,而磨损率逐渐减小。当WC-Co的添加量为75%时,复合涂层的摩擦因数最大,约为0.84;磨损率最小,约为9.28×10^-6 mm³/（N·m）。结论 在金属基涂层中引入硬质相WC-Co可有效提高涂层的硬度,并且提升该涂层的耐磨损性能,为金属基涂层发挥优异的摩擦学性能提供理论基础。     

Effect of Residual Stresses and Prediction of Possible Failure Mechanisms on Thermal Barrier Coating System by Finite Element Method

This work is focused on the effect of the residual stresses resulting from the coating process and thermal cycling on the failure mechanisms within the thermal barrier coating (TBC) system. To reach this objective, we studied the effect of the substrate preheating and cooling rate on the coating process conditions. A new thermomechanical finite element model (FEM) considering a nonhomogeneous temperature distribution has been developed. In the results, we observed a critical stress corresponding to a low substrate temperature and high cooling rate during spraying of the top-coat material. Moreover, the analysis of the stress distribution after service shows that more critical stresses are obtained in the case where residual stresses are taken into account.     

电沉积Ni/WC-Co纳米复合镀层制备及腐蚀性能研究

利用直流电沉积方法将WC-Co双纳米颗粒和Ni复合镀于黄铜基体,采用XRD和SEM表征复合镀层相组成和表面形貌,用显微硬度计测定其硬度并用电化学方法评估镀层的耐蚀性.结果表明,与纯Ni镀层相比,纳米复合镀层中Ni平均晶粒尺寸略有降低,约为18 nm;显微硬度提高58%,约为HV 500.在3.5%NaCl溶液中纯Ni镀层自腐蚀电流密度和自腐蚀电位分别为1.467μA/cm2和-0.179 V,纳米复合镀层则分别为8.369μA/cm2和-0.265 V.Ni/WC-Co纳米复合镀层的硬度显著提高,但其耐蚀性降低.     

WC-Co复合粉末的原位合成及于硬质合金涂层制备中的应用

目的为解决超细/纳米WC-Co热喷涂时易于脱碳等瓶颈问题,制备具有高的硬度、断裂韧性、耐磨性和表面质量等优异综合性能的超细及纳米结构硬质合金涂层,并推广其在工业领域中的应用。方法以原位合成技术批量制备的超细/纳米WC-Co复合粉末为原料,利用团聚造粒技术制备得到具有高球形度和致密性,并保持原有超细/纳米结构的喷涂喂料粉末,利用超音速火焰喷涂工艺制备低脱碳、高致密的超细结构WC基涂层。结果降低喂料粉末孔隙度可有效减少涂层中W2C等脱碳相的含量,在优化工艺下制备的超细结构WC基涂层的硬度达到1450HV0.3以上,韧性相对于常规微米结构涂层提高40%以上,在两种载荷和磨料条件下均表现出更高的耐磨性。结论利用原位反应技术批量合成的超细/纳米WC-Co复合粉制备的硬质合金涂层具有优良的综合性能,可应用于对涂层的硬度、耐磨性、强韧性配合和表面质量有较高要求的工况。     

宽带激光重熔WC-Co陶瓷涂层组织与摩擦磨损性能

对热喷涂WC-Co陶瓷涂层材料进行了宽带激光重熔试验,分析了熔覆层组织和物相组成,测试了熔覆层的硬度分布和摩擦磨损性能,分析了工艺参数对涂层物相,硬度的影响.结果表明,重熔后的熔覆层主要由WC、C、Cw,、Co6W6C、CCo2W4等构成.在重熔的过程中,WC有不同程度的分解,功率越大,WC分解越严重.适当控制激光功率至关重要.较大的扫描速度对提高熔覆层的硬度有一定的作用.热喷涂的WC-Co陶瓷涂层材料经宽带激光重熔能够得到结合良好的激光重熔层,基体与结合强度增强,孔隙率明显减少,涂层的致密程度和硬度提高,同时,耐磨性能也得到增强.磨损试验表明在干滑动摩擦下,WC-Co涂层的主要磨损机制为WC颗粒的磨粒磨损.     

热障涂层脱粘裂纹缺陷的高温表征方法与演变规律EI北大核心CSCD

热障涂层在服役过程中相邻区域脱粘裂纹的扩展合并是造成陶瓷层最终剥落的重要原因,然而缺乏简单有效的无损测试方法。提出利用空腔高热阻在陶瓷层表面局部热积累,形成表面亮斑的特点,通过亮斑反向跟踪脱粘缺陷的新方法。结果表明,在界面处制备水溶性盐斑,继续喷涂陶瓷层后用水浴溶解的方式可在YSZ与金属粘结层界面有效预制特定外形与尺寸的人造脱粘裂纹缺陷;预制脱粘裂纹与表面高温亮斑尺寸呈正相关,且近似呈现为比例系数为1.031的线性关系,当预制裂纹直径大于0.4 mm时,可在涂层表面观测到亮斑,当预制裂纹直径大于0.7 mm时,用亮斑尺寸预测裂纹尺寸的相对误差低于15%;在梯度热冲击循环下,热障涂层随热冲击次数的增加,表面首先出现亮斑,随后亮斑长大、合并,在2500次左右热循环时合并速度加快,最终陶瓷层在亮斑处局部剥落。基于脱粘裂纹对于纵向热流的阻碍作用,提出一种人造脱粘裂纹缺陷的预制方法,并确立一种通过测量表面亮斑尺寸估计内部裂纹尺寸的热障涂层无损测量方法。解决了热障涂层高温缺陷难以实时观测的问题,并进一步研究了其高温演变规律,可为热障涂层的寿命预测提供数据支持。     

喷涂工艺对低能等离子喷涂WC-Co的涂层硬度与微观结构的影响

采用低能等离子喷涂技术，在不锈钢基体上制备WC-12％Co涂层。粉末被气体送到喷嘴内、阴极与阳极之间的区域，喷涂功率为3．9～9．1kW。利用XRD和SEM分析技术，对涂层的微观结构和相组成进行分析，研究喷涂功率对涂层硬度的影响。结果表明：在功率3．9kW时制备的涂层主要由WC相组成；喷涂功率在5-9kW时，涂层中开始出现W2C；在功率6．5kW时，涂层硬度最高为1500HV，喷涂功率超过6．5kW时，由于涂层中出现α-W2C，涂层的硬度降低。这表明低能等离子炬可以制备高性能的WC-Co涂层。     

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 在测定热喷涂抗拉结合强度时，喷涂试样的制备很重要，关系到涂层抗拉结合强度测定的准确性。文章介绍一种用于测定热喷涂涂层抗拉结合强度的制样方法及装置，这对准确测定涂层抗拉结合强度会有帮助。     

Effects of Particle Strength of Feedstock Powders on Properties of Warm-Sprayed WC-Co Coatings

Warm spray (WS) process, which can control the temperature of a combustion gas jet used to propel powder, has been successfully applied to deposit WC-Co coatings. Detrimental reactions resulting from dissolution of WC into Co binder and decarburization were suppressed effectively by keeping the WC-Co particles’ temperature below the m.p. of the binder phase. In this study, three nano-structured WC-12Co powders with different particle strengths were prepared by changing the sintering conditions of spray-dried powder and were deposited by WS. The deposition efficiency and porosity of the coatings decreased with increasing the particle strength. The coating deposited from the powder with very low particle strength showed significant phase changes, while those deposited from the higher particle strengths showed almost no change. Particle Image Velocimetry revealed significant disintegration of the weakest powder, which explains the changes observed. The hardness and wear properties of the former coating, therefore, were inferior to the other two.     

Strength of WC-Co hard metals as a function of the effectively loaded volume

WC-Co hard metals show defect-controlled fracture behaviour. This means that the fracture stress under tensile loading conditions is directly related to the size of the largest defect within the loaded volume. The size distribution of these defects relevant to failure under static and cyclic loading conditions can be quantitatively described by Weibull statistics.Prior studies on the fracture behaviour of hard metals and the nature and size of material inhomogeneities, i.e. defects, do not attain their data from one single batch of material. To avoid uncertainties from possible variations in material composition the current work studies the fracture behaviour of a single material batch as a function of the effectively loaded volume V_eff. A variety of specimen geometries and loading arrangements was applied in order to vary V_eff over five orders of magnitude. Fracture stress values are found to increase from about 1500 MPa to 4200 MPa while decreasing the effectively loaded volume from about 100 mm³ down to about 0.01 mm³. The observed volume effect of strength shows the expected qualitative trends with quantitative deviations from Weibull-like strength behaviour. The presence of two different kinds of defects in the form of pores and single enlarged WC grains on the attained fracture surfaces, as found by a fractographic analysis in the SEM, is a possible explanation for this observation. Information provided by the current study is the basis for the judgment of the relevance of volume defects regarding the failure of tools or structural components made of WC-Co hard metals under certain loading conditions.     

电场作用下预设烧结温度对WC-Co体系烧结的影响

采用G1eeble热模拟机,在电场作用下制备了WC/Co系硬质合金,针对预设烧结温度对该体系烧结产物的影响进行了探讨,并对该体系烧结过程的温度场和合成产物进行了分析。结果表明,电场作用可降低体系的液相形成温度(750℃),这远低于传统烧结时液相的形成温度(1350℃)。由于电场烧结的时间短,有效地抑制了WC晶粒的聚集长大。在烧结过程中出现了Co3W3C和Co6W6C中间相。随着烧结温度的升高,烧结产物颗粒呈现长大的趋势,当烧结温度达到1000℃时,WC的平均颗粒尺寸约为1.5μm,但仍远小于传统烧结的颗粒尺寸。