热浸铝钢等离子体电解氧化陶瓷层的微观力学特性

采用纳米压入方法表征了热浸镀铝钢表面由Al_2O_3层、Al层和FeAl层组成的复合涂层的纳米硬度、弹性模量及断裂韧性等微观力学性能,采用扫描电镜(SEM)观察了纳米压痕形貌,并分析了孔洞对陶瓷层的纳米压入行为和压痕裂纹扩展的影响.结果表明:等离子体电解氧化(PEO)陶瓷层中包含许多微米和亚微米尺度的细小孔洞,陶瓷层弹性模量约为226.4 GPa,纳米硬度约为19.6 GPa.当纳米压入深度为250 nm时,所测得陶瓷层的力学参数分散性较大.与FeAl层比较,PEO陶瓷层具有较高的裂纹扩展阻力.FeAl层纳米压痕顶端产生了沿直线扩展的径向裂纹;而陶瓷层纳米压痕中除径向裂纹外出现了侧边裂纹.

Structure and mechanical properties of ceramic coatings fabricated by plasma electrolytic oxidation on aluminized steel

Ceramic coatings were formed by plasma electrolytic oxidation (PEO) on aluminized steel. Characteristics of the average anodic voltages versus treatment time were observed during the PEO process. The micrographs, compositions and mechanical properties of ceramic coatings were investigated. The results show that the anodic voltage profile for processing of aluminized steel is similar to that for processing bulk Al alloy during early PEO stages and that the thickness of ceramic coating increases approximately linearly with the Al layer consumption. Once the Al layer is completely transformed, the FeAl intermetallic layer begins to participate in the PEO process. At this point, the anodic voltage of aluminized steel descends, and the thickness of ceramic coating grows more slowly. At the same time, some micro-cracks are observed at the Al2O3/FeAl interface. The final ceramic coating mainly consists of gamma-Al2O3, mullite, and alpha-Al2O3 phases. PEO ceramic coatings have excellent elastic recovery and high load supporting performance. Nanohardness of ceramic coating reaches about 19.6 GPa. (c) 2007 Elsevier B. V. All rights reserved.

Small scale, grain size and substrate effects in nano-indentation experiment of film-substrate systems

The mechanical properties of film-substrate systems have been investigated through nano-indentation experiments in our former paper (Chen, S.H., Liu, L., Wang, T.C., 2005. Investigation of the mechanical properties of thin films by nano-indentation, considering the effects of thickness and different coating-substrate combinations. Surf. Coat. Technol., 191, 25-32), in which Al-Glass with three different film thicknesses are adopted and it is found that the relation between the hardness H and normalized indentation depth h/t, where t denotes the film thickness, exhibits three different regimes: (i) the hardness decreases obviously with increasing indentation depth; (ii) then, the hardness keeps an almost constant value in the range of 0.1-0.7 of the normalized indentation depth h/t; (iii) after that, the hardness increases with increasing indentation depth. In this paper, the indentation image is further investigated and finite element method is used to analyze the nano-indentation phenomena with both classical plasticity and strain gradient plasticity theories. Not only the case with an ideal sharp indenter tip but also that with a round one is considered in both theories. Finally, we find that the classical plasticity theory can not predict the experimental results, even considering the indenter tip curvature. However, the strain gradient plasticity theory can describe the experimental data very well not only at a shallow indentation depth but also at a deep depth. Strain gradient and substrate effects are proved to coexist in film-substrate nano-indentation experiments. (c) 2006 Elsevier Ltd. All rights reserved.

测量镀铬层界面韧性的激光屈曲法

为了测量强界面电镀铬层的界面韧性，利用连续CO_2激光器对钢基体上的电镀铬层表面进行循环扫描实验。结果表明：该种加热方式能够诱发铬层沿激光扫描方向呈周期性分布的屈曲变形。在此基础上，结合涂层屈曲变形理论，提出测量镀铬层界面韧性的激光屈曲法。该方法只需对一个屈曲单元的最大屈曲高度和屈曲半长进行测量，就可给出界面韧性。作为应用举例，利用该方法对上述镀铬层／钢基体结构界面韧性进行了测量。

脆性涂层/韧性基体材料在拉伸应变作用下的开裂行为

提出一种在脆性涂层/韧性基体材料中含弹塑性界面层的剪滞模型.研究脆性涂层/韧性基体材料在拉伸应变作用下,其表面脆性涂层的开裂行为特征,探讨涂层内正应力、界面切应力、涂层的裂纹密度与涂层几何、力学等参数之间的内在联系,获得了涂层内正应力、界面切应力和(饱和)裂纹密度的解析表达式.最后利用这些参量及其间的内在联系,以工程实际中的脆性Cr涂层/韧性钢基体材料为研究对象,研究该种材料在拉伸过程中出现的断裂行为特征.研究结果表明,该材料在拉伸应变作用下出现的饱和裂纹密度与理论结果预测值符合较好.

钢基铝镀层转化为陶瓷层的演变规律研究

热浸镀铝钢经等离子体电解氧化（Plasma Electrolytic Oxidation,PEO）处理后,表面铝镀层转化为陶瓷层.实验对阳极电压变化、陶瓷层生长规律、涂层截面形貌和成分等进行了研究.结果表明：在PEO初期,热浸铝试件的阳极电压变化趋势与纯铝试件相同,在PEO后期电压有下降趋势.铝镀层消耗和陶瓷层厚度增长近似为线性变化.当铝镀层完全陶瓷化后,FeAl层参与PEO反应,但陶瓷层生长速率变慢,在界面处出现大量裂纹;陶瓷层主要成分为Al、Si、O元素,相结构主要为γ-Al_2O_3与莫来石相,在PEO后期出现α-Al_2O_3相.复合陶瓷层硬度呈区域性分布,陶瓷层最高硬度可达HV1800.

铝合金表面等离子体电解氧化陶瓷涂层在NaCl溶液中的电化学阻抗谱研究

通过调整电解液中硅酸钠的浓度，利用等离子体电解氧化（PEO）技术在铝合金LY12表面制备了各种陶瓷涂层，利用光学显微镜、XRD、电化学阻抗谱（EIS）对涂层的形貌、成分和涂层在NaCl溶液中耐腐蚀性能进行了研究．结果表明：提高电解液中硅酸钠的浓度可以使得涂层的总厚度增加，但过高或过低的浓度都会导致致密层厚度的减薄．当浓度为20g／L时，所制备的涂层的成分以氧化铝为主；当浓度为40g／L时，涂层的成分主要是莫来石和氧化铝；当浓度超过60g／L时，涂层的成分主要为非晶相．EIS的研究表明，涂层耐腐蚀性取决于涂层中的致密层，增加致密层的厚度可以提高PEO涂层的耐腐蚀性，在中性、酸性、碱性腐蚀介质中，PEO涂层都显示出对基体良好的保护作用．

热浸铝钢等离子体电解氧化陶瓷层的微观力学特性

采用纳米压入方法表征了热浸镀铝钢表面由Al2O3层、Al层和FeAl层组成的复合涂层的纳米硬度、弹性模量及断裂韧性等微观力学性能，采用扫描电镜（SEM）观察了纳米压痕形貌，并分析了孔洞对陶瓷层的纳米压入行为和压痕裂纹扩展的影响．结果表明：等离子体电解氧化（PEO）陶瓷层中包含许多微米和亚微米尺度的细小孔洞，陶瓷层弹性模量约为226．4 GPa，纳米硬度约为19．6 GPa．当纳米压入深度为250nm时，所测得陶瓷层的力学参数分散性较大．与FeAl层比较，PEO陶瓷层具有较高的裂纹扩展阻力．FeAl层纳米压痕顶端产生了沿直线扩展的径向裂纹；而陶瓷层纳米压痕中除径向裂纹外出现了侧边裂纹．

热喷涂构件中残余应力的理论分析

本文发展一种新的分析涂层结构（平板、梁）热残余应力的模型，可以研究骤冷过程（Quenching）和冷却过程（Cooling）在涂层结构内引发的残余应力分布。与以往模型相比，其优势在于：它可以考虑源于喷涂过程的涂层孔隙率、温度梯度等因素对于涂层和基底内残余应力的影响。其中孔隙率和温度分布由计算机模拟涂层沉积过程得到。另外，当基底的材料和几何参数被固定时，我们分析了诸如涂层的理想模量、厚度、热膨胀系数等参数，对于涂层结构中最终残余应力分布的改变机理。

涂层断裂韧性的声发射辅助拉伸测量方法

涂层的断裂韧性与界面结合强度是表征涂层/基体材料体系力学性能的重要指标.但如何准确地测量涂层的断裂韧性和强界面结合的涂层/基体材料体系的界面结合强度至今仍存在困难.以铬涂层/钢基体材料为对象,采用声发射和显微镜实时动态检测技术与拉伸实验相结合的方法,探索了铬涂层的断裂韧性以及铬涂层/钢基体的界面剪切强度.根据相关力学模型和实验测量结果,得到铬涂层在室温下的断裂韧性为27.41J/m~2. 同时,发现在铬涂层裂纹饱和后界面开裂都未发生,获得了该种材料体系界面剪切强度的一个下限值.

激光辐照热障涂层中平面应变问题的热弹性变分分析

针对激光辐照热障涂层材料的平面应变问题,提出热障涂层热弹性分析的基本方程,对定常温度场给出级数形式解析解,并用最小余能原理和变分法分析了结构的热弹性应力场,研究了最大应力和界面应力的分布特征,并就一些物理参数的影响进行了讨论.结果表明,热障涂层的主要破坏因素为表面拉伸应力,界面应力相对较小,但在自由边界有集中现象,剥落应力大于剪切应力,是导致涂层破坏的重要原因.涂层厚度增加会改变厚度方向上的应力分布,界面应力向中心集中.

激光熔覆MoSi_2涂层的研究

本文用高能激光束熔覆MoSi_2粉末在45钢基体上制备了耐高温结构用涂层，用XRD、SEM、EDAX和显微硬度仪分别对熔覆层的组织结构和硬度进行了研究。试验结果表明，由于基体的稀释作用，涂层的相组成为FeMoSi、Fe_2Si和少量的Mo_5Si_3。涂层组织呈现典型的细小枝晶组织特征，枝晶为FeMoSi领先相，枝晶间为FeMoSi和Fe_2Si两相共晶，组织中无孔隙和裂纹等缺陷存在。Mo，Si，Fe线扫描成分布在涂层-基体界面处均缓慢过渡，基体与涂层发生互扩散，为冶金结合。涂层硬度可达HV_(0.5)845，基体硬度为180，涂层硬度比基体提高3.7倍。

四氧化二氮对卫星漫反射试片氟化镁涂层的污染和侵蚀

利用漫反射率、X射线光电能谱和质谱等测量方法,研究了固态和气态四氧化二氮(N2O4)对漫反射试片氟化镁(MgF2)涂层表面的污染情况.实验表明,固态N2O4对MgF2涂层有严重侵蚀作用,N2O4固粒污染后的涂层表面漫反射率下降了20%～30%.在一定的时间内,气态N2O4对涂层表面的影响显著地依赖它的压力.试片在压力为6.9×104 Pa和200Pa的N2O4蒸气中分别放置10 min,前者厚度为40μm的MgF2涂层基本消失,表面漫反射率下降约20%;后者涂层表面的原子组成和漫反射率变化很小.还给出了MgF2涂层表面N2O4分子吸附摩尔密度,以及与涂层表面碰撞的N2O4分子通过化学吸附过程提取MgF2的几率.

What Do We Know about Long Laminar Plasma Jets?

Silent and stable long laminar plasma jets can be generated in a rather wide range of working parameters. The laminar flow state can be maintained even if considerable parameter fluctuations exist in the laminar plasma jet or if there is an impact of laterally injected particulate matter and its carrier gas. The attractive special features of laminar plasma jets include extremely low noise level, less entrainment of ambient air, much longer and adjustable high-temperature region length, and smaller axial gradient of plasma parameters. Modeling results show that the laminar plasma jet length increases with increasing jet inlet velocity or temperature and the effect of natural convection on laminar plasma jet characteristics can be ignored, consistent with experimental observations. The large difference between laminar and turbulent plasma jet characteristics is revealed to be due to their different laws of surrounding gas entrainment. Besides the promising applications of the laminar plasma jet to remelting and cladding strengthening of the metallic surface and to thermal barrier coating preparation, it is expected that the laminar plasma jet can become a rather ideal object for the basic studies of thermal plasma science owing to the nonexistence of the complexity caused by turbulence.

A neural extracellular matrix-based method for in vitro hippocampal neuron culture and dopaminergic differentiation of neural stem cells

Background: The ability to recreate an optimal cellular microenvironment is critical to understand neuronal behavior and functionality in vitro. An organized neural extracellular matrix (nECM) promotes neural cell adhesion, proliferation and differentiation. Here, we expanded previous observations on the ability of nECM to support in vitro neuronal differentiation, with the following goals: (i) to recreate complex neuronal networks of embryonic rat hippocampal cells, and (ii) to achieve improved levels of dopaminergic differentiation of subventricular zone (SVZ) neural progenitor cells. Methods: Hippocampal cells from E18 rat embryos were seeded on PLL- and nECM-coated substrates. Neurosphere cultures were prepared from the SVZ of P4-P7 rat pups, and differentiation of neurospheres assayed on PLL- and nECM-coated substrates. Results: When seeded on nECM-coated substrates, both hippocampal cells and SVZ progenitor cells showed neural expression patterns that were similar to their poly-L-lysine-seeded counterparts. However, nECM-based cultures of both hippocampal neurons and SVZ progenitor cells could be maintained for longer times as compared to poly-L-lysine-based cultures. As a result, nECM-based cultures gave rise to a more branched neurite arborization of hippocampal neurons. Interestingly, the prolonged differentiation time of SVZ progenitor cells in nECM allowed us to obtain a purer population of dopaminergic neurons. Conclusions: We conclude that nECM-based coating is an efficient substrate to culture neural cells at different stages of differentiation. In addition, neural ECM-coated substrates increased neuronal survival and neuronal differentiation efficiency as compared to cationic polymers such as poly-L-lysine.