滚动接触疲劳法评定硬质薄膜的结合强度

工件大多在交变应力下服役,薄膜的剥落是一个长时间高周次过程,其失败过程属疲劳失效。采用高周次界面疲劳强度作为膜基结合强度的判据,以膜基界面处的切应力△τ表征膜基界面疲劳强度。采用该方法对气相沉积硬质薄膜的结合强度进行了评定,并与划痕法比较。结果表明,薄膜在膜基界面处剥落,该方法对同因素十分敏感,而对非界面因素不敏感,因而是一个有效的测量膜基界面结合强度的方法。可用来比较不同方法制备的不同成分和硬度     

涂、镀层的结合强度评定

涂、镀层与基体的结合强度是评价其质量的重要性能指标．常用的结合强度评定方法：厚涂层采用粘结拉伸法;薄膜镀层用划痕法。本文指出了这两种方法存在的问题。我们自行设计制造的涂层压入仪．采用楔压法测得热喷涂层的结合强度．当结合强度高于粘胶强度时仍有效。采用正压法测定气相沉积薄膜的结合强度并与划痕法作了比较。我们提出用接触疲劳试验测定硬质薄膜的界面疲劳强度评定结合力。这种方法接近于工具服役状况,其破坏形式是界面剥落．只对界面状态敏感。不受非界面因素影响,因而可作为动态结合强度的判据。     

铜基体上类石墨膜结合强度评价及其与干摩擦性能关系

用非平衡磁控溅射离子镀技术在铜合金上制备了不同Ti含量的类石墨碳膜,用维氏压入、洛氏压入、划痕等方法测试薄膜的附着性能,用高速线性往复磨损实验机检测薄膜的干磨性能,并用光学显微镜、白光干涉仪观察磨痕。结果表明:压痕法更适合评价软基体上硬膜的结合强度,且维氏压入法因加载载荷较小,基体塑性变形小,评定的结合强度与干摩擦磨损时膜基体系的耐磨性具有对应关系。当靶电流为0.2 A时,铜合金上的类石墨膜与对磨球的摩擦系数和磨损率达最小值,分别为0.14和2.89×10~(-16)m~3/(N·m)。划痕法不适合用来快速评定和预测软基硬膜体系的结合强度。载荷较小的维氏压入法具有更好的结合强度鉴别区分度。     

溶胶-凝胶法45钢表面制备Al2O3陶瓷涂层及性能

采用溶胶-凝胶法在45钢表面制备了Al2O3陶瓷涂层,研究了通过化学镀Ni-P层为中间过渡层对45钢表面Al2O3陶瓷涂层性能的影响.通过压入法和划痕法研究了膜基结合强度,观察了复合涂层压痕和划痕形貌,通过扫描电子显微镜(SEM)对复合涂层表面形貌进行了分析.结果表明,中间层与基体材料、Al2O3层与中间层结合良好,涂层均匀致密,表面显微硬度最大值为1030HV,压入法结果表明膜与45钢基体结合较好.     

用球滚接触疲劳法评定硬质薄膜的结合强度

采用滚动接触疲劳法对气相沉积硬质薄膜的结合强度进行了研究。结果表明,反映膜基结合强度的力学参量为界面最大剪应力幅。采用数值计算的方法,可以定量得到膜基界面处的应力分布。     

金刚石薄膜膜基界面结合强度测量技术的研究进展

膜基界面结合强度的测量与评价是金刚石薄膜制备与应用关键问题，本文介绍了国内外金刚石薄膜膜基界面结合强度的几种典型的测量方法，着重探讨了膜基界面结合强度的精确定量测量技术的研究现状以及发展趋势，提出了用一种新的内涨鼓泡测量法，对复杂形状基体上金刚石薄膜膜基界面结合强度进行精确定量检测，为金刚薄膜的制备工艺优化及其质量的评估提供可靠的依据和标准。     

用单摆冲击划痕法测定膜基界面结合强度

膜和基体之间界面结合强度是评价膜层质量很重要的性能指标.采用单摆冲击划痕法对膜基界面结合强度进行了定量研究.单摆冲击划痕法具有动态加载的特性,可从力和能量两个方面获得膜基破坏过程信息,用其测定的膜基界面单位面积所消耗的能量ε可用来定量表征膜基界面结合强度.研究结果表明,提高镀层磷含量、选择合适的基材表面粗糙度(Ra≈0.4μm)和合适的热处理温度(400℃)有利于提高Ni-P化学镀层的界面结合强度和临界法向载荷.     

高速钢W18Cr4V离子渗氮层组织对TiN膜与基体结合强度的影响

采用Ｗ１８Ｃｒ４Ｖ高速钢进行离子渗氮－ＰＥＣＶＤ ＴｉＮ复合处理,运用透射电子显微镜、Ｘ射线衍射仪和光学显微镜研究试样的表层组织结构。采用连续压入法研究ＴｉＮ膜与基体的结合强度,结果表明,离子渗氮能够提高膜基结合强度,通过分析渗氮层与膜－基界面的组织特点,认为ＴｉＮ膜在渗氮层上一些与其具有相同或相似晶体结构的氮化物上外延生长,以及强度较高的渗氮层对膜的支撑是基体渗氮提高膜－基结合强度的两大因素。     

表面纳米化对304不锈钢/CrN薄膜力学性能的影响

表面纳米化可以显著改善金属材料的表面力学性能,并促进氮、铬等原子的热扩散,文中尝试采用表面纳米化技术改善金属基体/硬质薄膜的力学性能.对304不锈钢采用表面机械研磨处理获得纳米晶粒表层,采用多弧离子镀镀方法在表面纳米化和粗晶粒的304不锈钢基体上沉积CrN薄膜.对两种膜基体系采用X射线衍射、显微硬度测试、压入法和划痕法膜基结合性能评价.结果表明,表面纳米化影响了CrN膜层的组织结构,明显提高了膜基体系的硬度和承载能力,还改善了膜层的韧性,膜基结合性能也得到提高.     

鼓泡法定量测量金刚石薄膜膜基界面结合强度的实验研究

金刚石薄膜膜基结合强度的测量与评价是其制备与应用的关键。本文根据内涨作用下薄膜发生鼓泡变形的原理，开发了一种新的适用于金刚石薄膜膜基结合强度定量检测的测试系统，并采用光刻法和湿式各向异性刻蚀技术制备得到金刚石薄膜自支撑窗口试样。采用OFV-3000光纤激光振动仪测量薄膜鼓泡时的垂直位移，测量精度可以达到0．3164μm。通过实验实现了对硅基底金刚石薄膜结合强度的定量检测，实验得到的薄膜结合强度为4．28726J/m^2。这种鼓泡测量法不仅适用于硅平面基底电子元器件的膜基界面结合强度的测量，而且还可以推广应用到硬质合金复杂形状基底的膜基界面结合强度的测量中，从而为金刚石薄膜在电子元器件行业以及工具行业中的应用提供了可靠的依据。     

Development of a novel lateral force-sensing microindentation technique for determination of interfacial bond strength

The interfacial bond strength is a crucial factor determining ultimate mechanical properties and performances of composites, thin films and coatings. Great efforts have been made to develop effective techniques for determination of interfacial bond strength. However, none of existing methods is “ideal” and results obtained using these techniques are generally qualitative. In this paper, a new technique is proposed to determine the interfacial bond strength for composites and coatings. During the test, microindentation was performed near an interface with in situ monitoring changes in lateral force. It was demonstrated that the lateral force (Fx) was very sensitive to interfacial debond. The critical indentation load that corresponds to interfacial debond can be used to quantitatively determine the interfacial bond strength. The method was justified using experimental and computational approaches. As an example, an Al₂O₃/Al alloy interfacial bond was analyzed.     

Determination of interfacial properties of thermal barrier coatings by shear test and inverse finite element method

Determination of interfacial properties of thermal barrier coatings (TBCs) is very important for designing and evaluating the durability of TBCs. A new method combining a simple shear test and an inverse finite element analysis was developed and applied to measure the interfacial properties of two flame-sprayed yttria-stabilized zirconia TBCs. Nanoindentation testing was performed to determine the mechanical properties of different materials of the TBC systems. Variation of the lateral force during the shear test was recorded and analyzed to obtain the nominal ultimate shear strength of TBCs. The interfacial properties, namely fracture energy and stress intensity factor (mode II), of different TBC systems under both as-deposited and heat-treated conditions were determined through inverse finite element analysis.     

The mechanisms of interfacial failure for lateral force-sensing microindentation test: finite element analysis

The interfacial bond strength for coatings and composites can be quantitatively determined using a newly developed lateral force-sensing microindentation method. In this study, a finite element analysis was made to investigate the interfacial failure mechanisms for Cu–ceramic and Al alloy–ceramic interfaces. The model is validated by comparing obtained results of the finite element analysis with analytical solutions. Two different interfacial failure mechanisms, depending on material properties and microindentation positions, are proposed. As demonstrated, interfacial debonding may result from shear stress or a coupling of tensile stress and shear stress at the interface, corresponding to material “pile-up” deformation or “sink-in” deformation. In addition, the high sensitivity of the lateral force response to interfacial debonding, associated with two different interfacial failure mechanisms, is also examined.     

Study of Interfacial Stress Distribution in SiC Fiber Reinforced Titanium Matrix Composites on Transverse Tensile Tests

A combination of the transverse tensile test and the unilaterally coupled finite element method was used to evaluate the interfacial normal bond strength and stress distribution of titanium matrix composites (TMCs). In addition, in order to identify the interface shear failure mode of TMCs under transverse loading, both the push-out test and the finite element method have been developed to characterize the interfacial shear strength of TMCs, which is the interfacial shear failure criterion. This article studies the results of the experiments, which suggested that the interfacial normal bond and shear strength of SiC_f/Ti-6Al-4V were 300 and 350 MPa, respectively, and the interface failure mode of TMCs under the transverse tensile test was radial failure rather than shear failure. Moreover, the effect of residual stress on the radial stress is also discussed in detail in this article.     

Determination of Interfacial Fracture Toughness of Thermal Spray Coatings by Indentation

Adhesion is an important and basic property for thermal spray coatings. The standard tensile test method “ISO 14916” is usually used to evaluate the adhesive strength of coatings. On the other hand, the indentation test method has some advantages to evaluate the interfacial fracture toughness as the adhesive strength, arising from the following reasons: the test procedure and the specimen preparation are easy in comparison with the typical testing method. Collaborative research has been conducted by “Committee on Standard Development” in the Japan Thermal Spray Society to establish a standard test method for evaluating interfacial fracture toughness of thermal spray coatings using a conventional Vickers indenter. This article reports the differences among collaborators in round-robin tests performed in this committee and discusses the validity of the test method and test conditions with respect to the test results and finite element analyses. Comparison among collaborators reveals that interfacial fracture toughness can be obtained with a small scattering from the indentation test under constraints found on the basis of the results.     

Micromechanisms of damage nucleation during contact deformation of columnar multilayer nitride coatings

In order to resolve some missing micromechanistic details regarding contact deformation in nitride multilayer coatings we report here observations from cross-sectional transmission electron microscopy and focused ion beam studies of the Vickers indentations on TiN/TiAlN multilayer films of various total thicknesses as well as bilayer periods. The study of damage induced by contact deformation in a nitride multilayer coating is complemented by stress calculated using an analytical model. Kinked boundaries of sliding columns give rise to cracks which propagate at an angle to the indentation axis under a combination of compressive and shear stresses. It is seen that multilayers provide more distributed columnar sliding, thereby reducing the stress intensity factor for shear cracking, while interfacial dislocations provide a stress relief mechanism by enabling lateral movement of material.     

评价强界面涂层界面结合能力的横截面压入法

为了解强界面脆性涂层/硬性金属基体涂层结构横截面压入时的涂层剥落特点,以电镀铬层/硬性金属基体为研究模型,在原位观察系统下进行横截面压入试验,其结果表明:铬层断裂和剥落与载荷-位移曲线上出现的3个载荷下降点相对应,首先是在铬层横截面上形成一条与压头轴线平行的中间裂纹;随后又出现了以第1条裂纹为对称轴的2条斜裂纹;随着3条裂纹的稳态扩展和汇合,形成了与周围铬层相隔离、仅靠基体支撑的2块1/4圆形局部"孤岛"铬层;最后"孤岛"铬层沿界面剥落.以此"孤岛" 剥落为力学计算模型,提出定量评价强界面脆性涂层/硬性金属基体的界面结合能力的横截面压入法,该方法利用载荷-位移曲线计算"孤岛"剥落所需要的总能量,测量界面剥落面积,并计算两者的比值,给出临界界面能量释放率,以此数据作为评价界面结合能力的指标,并给出了应用举例.     

Delamination Strength of WC-Co Thermal-Sprayed Coating Under Combined Stresses by Torsion-Tension Pin-Test Method

In this report, the delamination strength of WC-Co thermal-sprayed coatings under combined torsion and tension is evaluated using a newly developed method, which is called the torsion-tension pin-test. First, the effects of both the pin diameter and the coating thickness on the apparent delamination strength were investigated experimentally. Second, the stress distributions around the interface edge between the pin and the coating were numerically obtained by using the finite element analysis program “MARC.” It was confirmed that the fractured plane of the torsion pin coincides with the interfacial plane between the coating and the pin. The apparent delamination strength obtained experimentally decreased linearly with increasing pin diameter and increased with increasing coating thickness t, but it was stable at t of 400 μm or more. The shear delamination strength decreased with increasing tensile stress. Similar stress distributions were observed at the interface when delaminations occurred for rather thick coatings, independent of the pin diameter. The critical combination of the strength of shear stress fields (Ks) with that of tensile stress fields (Ka), i.e., the delamination criteria of the coating under combined shear and tensile loadings, was obtained for a WC-12Co thermal-sprayed coating. These combinations were found to be independent of pin diameter and coating thickness.     

Extremely hard,damage-tolerant ceramic coatings with functionally graded,periodically varying architecture

Functionally graded, multilayer coatings consisting of alternating TiN/TiSiN layers were synthesized in an attempt to overcome the innate brittleness of TiSiN nanocomposite coatings, whilst maintaining high hardness. These coatings exhibited key structural characteristics that are known to render many naturally occurring materials extremely hard and robust. Transmission electron microscopy revealed that shear sliding of columnar TiN grains played a vital role in controlling the inelastic deformation of these coatings, conferring a greater resistance to contact damage. Moreover, nanoindentation experiments showed that the multilayer coatings exhibited high hardness, attributed to the strong shear resistance offered by the hard TiSiN layers. A dependence of coating hardness upon indentation penetration depth (h_t) was found to be proportional to 1/√h_t, according to a mechanistically based model, from which the shear stress was determined. The energy dissipation during indentation was also quantified to show the critical role of the shear stress, regulated by the thickness of TiSiN layers, in resisting contact damage in the coatings. Finite-element models were constructed and the presence of transgranular cracks in the monolithic TiSiN coating was clarified based upon experimental observations. Furthermore, the simulations revealed that the transition of the dominant deformation mechanism from brittle transgranular cracking to intergranular shear sliding was controlled by the microstructural characteristics of the coatings. Enabled by the shear sliding, as well as periodic changes in elastic modulus, such a functionally graded multilayer structure was effective in lowering the magnitude and extent of stress concentrations, thereby extending the damage tolerance accessible to a ceramic coating.