The delamination of polymeric coatings from steel. Part 1: Calibration of the Kelvinprobe and basic delamination mechanism

In the first part of this study are presented the theory and the experimental techniques which are necessary to investigate the delamination of model coatings on steel. It is shown that the electrochemical reactions taking place at the substrate/electrolyte and substrate/polymer interfaces are responsible for delamination. Due to the fact that the electrochemical reactions are accompanied by changes in the corrosion potential, it is possible to identify and follow the delamination by measuring the corrosion potential as a function of time and local position. Furthermore, it is demonstrated that the Volta-potential difference between a reference metal and the model polymer surface is determined by the corrosion potential, whereas the influence of the Donnan-potential is small and constant. By combining several experimental techniques, like the Scanning Kelvinprobe, Auger electron spectroscopy and mechanical de-adhesion tests, the delamination process is studied in detail and a model is presented, which is based on the existence of a galvanic element at the substrate/polymer interface. The uncoated iron is the local anode, where the iron dissolution predominates, whereas the delaminated part represents the local cathode and, within this area, only the oxygen reduction takes place. The second and third part of this paper deal with an experimental verification of this model.     

界面非平衡氧传递过程动力学的解析

将氧通过界面反应在两相间的传递过程简化为界面化学反应和扩散传质两个步骤,对此过程的动力学进行了数学解析,得到了一个新的动力学模型.同时显示,反应过程中界面氧浓度随反应过程的进行不断发生变化,这表明该界面反应是一个非平衡过程.应用得到的动力学模型对几个体系的动力学实验数据进行了拟合,符合很好,根据拟合的参数可以很好地解释实验现象.初步讨论了模型参数的意义和对动力学过程的影响.     

Development of a virtual machining system, part 1: approximation of the size effect for cutting force prediction

In this three-part paper, components of a virtual machining system for evaluating and optimizing cutting performance in -axis NC machining are presented. Part 1 describes a new method of calculating cutting-condition-independent coefficient and its application to the prediction of cutting forces over a wide range of cutting conditions. The prediction of the surface form error and transient cutting simulations, described in Parts 2 and 3, respectively, can be effectively performed based on the cutting force model with the improved size effect model that is presented in Part 1.

The relationship between the instantaneous uncut chip thickness and the cutting coefficients is calculated by following the movement of the center position of the cutter, which varies with nominal feed, cutter deflection and runout. The salient feature of the presented method is that it determines the cutting-condition-independent coefficients using experimental data processed for one cutting condition. The direct application of instantaneous cutting coefficient with size effects provides more accurate predictions of the cutting forces. A systematic comparison of the predicted and measured cutting forces over a wide range of cutting conditions confirms the validity of the proposed mechanistic cutting force and size effect models.     

基于金属液滴水平重叠沉积工艺对表面形貌和内部质量优化研究

在铝熔滴在铝基板上沉积、凝固过程中,研究了不同工艺参数下的对成形表面形貌和内部质量的影响规律。通过对单一金属液滴沉积行为研究,建立了横向搭接沉积数值模型,并对两个,三个,四个熔融液滴重叠形态的进化和温度变化过程进行分析和实验验证。实验表明：数值模拟与实验结果有良好的一致性,从而得到了最优参数。该研究对实现金属微液滴重叠沉积生产的有效过程控制至关重要,为液滴水平重叠沉积复杂金属提供了技术支持和参考。     

金属液滴垂直搭接成形工艺研究

通过研究铝合金熔滴的垂直搭接过程中不同工艺参数下的对成形表面形貌和内部质量的影响规律。通过对单一金属液滴沉积行为研究,建立了垂直搭接沉积数值模型,并对多个熔融液滴垂直重叠形态的进化和温度变化过程进行分析和实验验证。实验表明：数值模拟与实验结果有良好的一致性,从而得到了最优参数。该研究对实现金属微液滴垂直搭接生产的有效过程控制至关重要,为制造复杂金属提供了技术支持和参考。     

Modelling the shape and thermal dynamics of Ni superalloy rings during spray forming. Part 2: Thermal modelling – Heat flow and solidification

In Part 1 of this paper, a model was described to simulate the dynamic shape evolution of Ni superalloy rings during spray forming, concentrating on the effects of droplet splashing and redeposition. In this part, a companion model is presented that simulates the heat flow and solidification of the Ni superalloy rings during spray forming. In this model, generic algorithms of (1) coupling of droplet mass and enthalpy at a deposition surface, and (2) data mapping between time-evolving computational domains were developed and implemented. The effects of (1) droplet redeposition, and (2) changes in the convective heat transfer coefficients and their distributions on the resulting ring preform heat flow and solidification were studied; and simulations were again compared with experiments. The model was applied to investigate the effects of key processing parameters on the internal heat flow and solidification of large diameter IN718 alloy rings.     

Measurements of cold spray deposition efficiency

An analytical model of the kinetics of coating formation during cold spray is presented. The model is used to correct experimental data on deposition efficiency. The experimentally observed values are shown to be affected by experimental conditions, such as the velocity of substrate motion, the number of passes, the mass of a single portion of powder, and the exposure time of a given surface section. It is noted that experimental conditions can exert a significant effect on the consequences of the high-speed interaction of particles with a substrate. Relations are suggested that allow one to correct the results of deposition efficiency determined experimentally and to avoid mistakes in interpreting the data obtained.     

Generalized modeling of drilling vibrations. Part II: Chatter stability in frequency domain

A time domain model of the drilling process and hole formation mechanism is presented in Part I, and the general solution of drilling chatter stability in frequency domain is presented in this paper. The drill's flexibility in torsional, axial and lateral directions are considered in determining the regenerative chip thickness. Stability is modelled as a fourth order eigenvalue problem with a regenerative delay term. The critical radial depth of cut and spindle speed are analytically determined from the eigenvalues of the characteristics equation of the dynamic drilling process in frequency domain. The method is compared against the extensive numerical solutions in time domain which were presented in Part I, cutting experiments and previously published partial stability laws. The time domain model presented in Part I of the paper considers tool geometry dependent mechanics, all vibration directions and the true kinematics of drilling, while allowing for nonlinearities such as tool jumping out of cut and nonlinear cutting force models. It is shown that accurate prediction of drilling stability requires modeling of drill/hole surface contact stiffness and damping which is still a research challenge.     

Mechanics of boring processes—Part II—multi-insert boring heads

Mechanics of boring operations are presented in the paper. The distribution of chip thickness along the cutting edge is modeled as a function of tool inclination angle, nose radius, depth of cut and feed rate. The cutting mechanics of the process is modeled using both mechanistic and orthogonal to oblique cutting transformation approaches. The forces are separated into tangential and friction directions. The friction force is further projected into the radial and feed directions. The cutting forces are correlated to chip area using mechanistic cutting force coefficients which are expressed as a function of chip-tool edge contact length, chip area and cutting speed. For tools which have uniform rake face, the cutting coefficients are predicted using shear stress, shear angle and friction coefficient of the material. Both approaches are experimentally verified and the cutting forces in three Cartesian directions are predicted satisfactorily. The mechanics model presented in this paper is used in predicting the cutting forces generated by inserted boring heads with runouts and presented in Part II of the article [1].     

表面活性剂对铝合金表面电化学沉积硅烷膜层的影响

采用交流阻抗技术研究了表面活性剂对不同条件下双-1,2-[3(三乙氧基)硅丙基]四硫化物硅烷在铝合金表面阴极电化学辅助沉积成膜的影响.研究表明:在硅烷溶液中加入表面活性剂进行改性,可降低硅烷在铝合金表面电化学沉积的阴极沉积电位,抑制硅烷沉积过程中的析H2作用,改善电极界面区域硅烷成膜环境.试验证明:硅烷溶液中表面活性剂的最佳改性浓度为0.03%,在此浓度下,铝合金表面硅烷阴极电沉积的最佳沉积电位为-1.6V.     

Mechanics of boring processes—Part I

Mechanics of boring operations are presented in the paper. The distribution of chip thickness along the cutting edge is modeled as a function of tool inclination angle, nose radius, depth of cut and feed rate. The cutting mechanics of the process is modeled using both mechanistic and orthogonal to oblique cutting transformation approaches. The forces are separated into tangential and friction directions. The friction force is further projected into the radial and feed directions. The cutting forces are correlated to chip area using mechanistic cutting force coefficients which are expressed as a function of chip-tool edge contact length, chip area and cutting speed. For tools which have uniform rake face, the cutting coefficients are predicted using shear stress, shear angle and friction coefficient of the material. Both approaches are experimentally verified and the cutting forces in three Cartesian directions are predicted satisfactorily. The mechanics model presented in this paper is used in predicting the cutting forces generated by inserted boring heads with runouts and presented in Part II of the article [1].     

Influence of contact loss between workpiece and grinding wheel on the roundness errors in centreless grinding

The objective of this paper is the study of certain non-linear phenomena in the centreless grinding process and their effect on roundness quality. These phenomena arise as a consequence of contact loss between workpiece and grinding wheel. A simplified analysis of the problem is carried out to determine the main parameters involved. A qualitative assessment of the effect of these parameters is undertaken by means of a time simulation based on a non-linear bi-dimensional model of the centreless grinding process. Two situations are analysed: the steady process, and the transient spark-out process. The results, which are generalised in graphics form provide an estimation of roundness errors resulting from working under linearly unstable conditions. Finally, a correlation between theoretical and experimental results is presented.     

High speed CNC system design. Part II: modeling and identification of feed drives

Accurate modeling and identification of the feed drives' dynamics is an important step in designing a high performance CNC. This paper presents a method for identifying the dynamic parameters, as well as the friction characteristics of machine tool drives. The inertia and viscous friction are estimated through an unbiased least squares scheme. The friction model is developed by observing the disturbance torque through a Kalman filter, while jogging the axes under closed loop control at various speeds. The overall axis model is used in designing a high speed feed drive control system, which has been presented in Part III of this paper. As verification of the identified friction model, contouring test results without and with friction compensation are also presented.     

Effects of Powder Geometry and Composition in Coaxial Laser Deposition of 316L Steel for Rapid Prototyping

Multiple layer laser powder deposition has recently been applied to producing fully dense 3-D metallic engineering parts for rapid prototyping and tooling. To date, however, the process has been limited to using only gas-atomised, spherical powders. In this paper, the feasibility of using water-atomised powders is investigated, based on an experimental comparison of gas- and water- atomised powders in multiple layer, laser fused deposition of 316L stainless steel. The work shows that, despite much lower cost (approximately 25% of the pries of gas-atomised powders), the water-atomised, irregular powders have superior deposition quality in terms of surface finish, deposition uniformity, microstructures and bonding between layers, compared to the gas-atomised powders under the same processing conditions, although deposition rate is lower. Powder geometry and oxygen content differences of the two powders have been found to be the principal reasons for the observed effects. Theoretical analyses of the beam-material interaction processes and malt pool behaviour are presented to explain the observed phenomena. The results indicate that there are both functional and economic reasons for using water-atomised powders for this additive manufacturing application.     

About the Role of Chromium and Oxygen Ion Diffusion on the Growth Mechanism of Oxidation Films of the AISI 304 Austenitic Stainless Steel

To study the role of ion diffusion on the oxidation process of the AISI 304 austenitic stainless steel, chromium diffusion coefficients were determined in oxide films grown on this steel at 750, 800 and 850?°C, in air. The isotope ⁵⁴Cr was used as a chromium tracer and the diffusion profiles were established by SIMS. The bulk diffusion coefficients are five orders of magnitude smaller than the grain boundary diffusion coefficients. It was found that the values of the chromium diffusivities are lower than the corresponding oxygen diffusivities obtained in previous work. Parabolic oxidation constants calculated as a function of the chrome and oxygen diffusivities, using Wagner′s theory, are close to those determined experimentally, which shows that the growth rate of chromia is controlled by ion diffusion, but inward oxygen diffusion plays the main role on the growth kinetics of chromia formed by the oxidation of the AISI 304 steel.     

Orientation stability in equal channel angular extrusion. Part I: Face-centered cubic and body-centered cubic materials

Stability of crystallographic orientations is a key aspect in the characterization and understanding of texture evolution during plastic deformation. In this study, a rate-dependent crystal plasticity model was applied to investigate orientation stability during equal channel angular extrusion (ECAE) of face-centered cubic (fcc) and body-centered cubic (bcc) crystals. The stability of experimentally observed ideal orientations was examined according to lattice rotation fields computed at and around the orientations. It is shown that these ideal orientations are meta-stable under rate-sensitive conditions, and their stability generally increases with the decrease of strain rate sensitivity. The results also reveal a well-preserved duality in the lattice rotation and orientation stability between the two types of crystal structure. The stability results simulated at low strain rate sensitivities agree well with the experimental observations in one-pass ECAE of Al and Cu single crystals. In Part II of the paper, this analysis is extended to hexagonal materials.     

Fuzzy Logic Analysis of Alumina-Titania Deposition Yield During APS Process

The behavior modeling of Atmospheric Plasma Spray (APS) process requires a global approach which considers interrelated non-linear relationships between coating characteristics/properties in-service and process parameters (power, feedstock injection, kinematics, etc.). Such an approach would permit to reduce the development costs. To reach this objective, the knowledge of the interactions between process parameters plays a relevant role in the optimization. This work intends to develop a behavior model based on fuzzy logic concepts. Here, the model considers the deposition yield as the result of the process and it establishes relationships with power process parameter (arc current intensity, plasma gas total flow rate, hydrogen content) on the basis of fuzzy rules. The model hence permits to discriminate the role and the effects of each power process parameters. The modeling results are compared to experimental data. The specific case of the deposition of alumina-titania (Al₂O₃-TiO₂, 13% by weight) by Atmospheric Plasma Spraying (APS) is considered. This article is an invited paper selected from presentations at the 2007 International Thermal Spray Conference and has been expanded from the original presentation. It is simultaneously published in Global Coating Solutions, Proceedings of the 2007 International Thermal Spray Conference, Beijing, China, May 14-16, 2007, Basil R. Marple, Margaret M. Hyland, Yuk-Chiu Lau, Chang-Jiu Li, Rogerio S. Lima, and Ghislain Montavon, Ed., ASM International, Materials Park, OH, 2007.     

Polarisation behaviour of steel bar samples in concrete in seawater. Part 2: A polarisation model for corrosion evaluation of steel in concrete

In the companion paper [Z.T. Chang, B. Cherry, M. Marosszeky, Polarisation behaviour of steel bar samples in concrete in seawater, Part 1: Experimental measurement of polarisation curves of steel in concrete, Corrosion Science 50(2) (2008) 357-364], influences of the experimental procedure on measured polarisation curves of steel in concrete in seawater were investigated. It was found that an undistorted full polarisation curve of a steel sample in concrete can be obtained by the two-test procedure to conduct separate anodic and cathodic polarisation tests and combine the two partial curves into one curve. However, polarisation curves of steel samples in concrete in seawater were found not to fit with the theoretical curves based on the kinetics of charge transfer reactions. This was considered to be due in the main to the influence of a passive film on the steel surface in concrete. This paper proposes an empirical model for the polarisation behaviour of steel in concrete based on the assumption of two major electrochemical processes taking place at the interfaces of steel/passive-film/concrete: one is the active corrosion process and the other is the passive film growth or dissolution process. Typical curve-fit results are presented using the proposed model to simulate the polarisation behaviour and to evaluate the corrosion rate and Tafel parameters of three types of steel corrosion in seawater: steel bars in concrete, new steel bars and corroded steel bars.     

Identification and modeling of process damping in turning and milling using a new approach

Process damping can be a significant source of increased stability in machining particularly at low cutting speeds. However, it is usually ignored in chatter analysis as there is no model available to estimate process damping coefficients. In this study, a practical identification and modeling method is presented where process damping coefficients are obtained from chatter tests. The method is generalized by determining the indentation force coefficient responsible for the process damping through energy analysis. This coefficient is then used for process damping and the stability limit prediction in different cases, and predictions are verified by time domain simulations and experimental results.     

Use of a theoretical model to investigate RF and DC reactive sputtering of titanium and chromium oxide coatings

An analysis of RF and DC reactive sputtering techniques is presented. The transition between a metal sputtering mode and a compound sputtering mode is usually noticed with a metallic target and an argon+oxygen gas mixture. The so-called hysteresis effect often observed for small amounts of reactive gas is explained in recent models. By considering gas kinetics parameters, it is possible to evaluate quite simple relationships between the main processing parameters. These theoretical calculations enable the prediction and aid the understanding of instability phenomena observed in reactive sputtering. In this paper, the effects of some parameters on the position and size of instability regions are discussed, and the difference between DC and RF reactive deposition is investigated. Simulations and experimental results are compared for the case of titanium and chromium oxide thin films prepared by DC and RF reactive sputtering. The influence of sputtering power on the position of the hysteresis loop is analysed theoretically and experimentally, and the changes observed between the reactive sputtering of titanium and chromium oxide materials are also discussed.