International Journal of Surface Science and Engineering (15 papers in press)
An assessment of erosive wear of hydro-turbine steel using statistical modeling and optimization
by Ishfaq Amin Maekai, G.A. Harmain
Abstract: The current study pertains to the influence of chosen process parameters on erosive wear of F6NM stainless steel. The sand used in the experimentation has been obtained from Dul-Hasti power plant dam site located in northern Himalayan rugged terrain of Jammu and Kashmir, India. Response surface methodology (RSM) was used to plan experiments. The wear experiments were conducted using slurry erosive wear tester (TR-40). Response surface method with face-centred composite design has been adopted to develop a regression model. Development of erosive wear model was based on five factors, which included sediment concentration (A), particle size (B), angle of impact (C), test duration (D) and rotational speed of slurry (E). Three levels were chosen for each factor considered in the study. A mathematical model was developed to predict the deterioration through wear on F6NM stainless steel and the appropriateness of the model was certified using analysis of variance. The developed regression model provides valuable information to control the damage (wear) and revealed that the rotational speed of slurry, particle size and sediment concentration were the three main contributing parameters for erosive wear of F6NM stainless steel. Rotational speed-sediment concentration was the main significant interactive pair. Subsequently, the damage model was developed based on the main contributory factors responsible for wear and significant interactions. The contribution of a rotational speed of slurry, particle size and sediment concentration was 30.58%, 18.82% and 17.64% respectively for an overall erosion wear process. A robust correlation is attained between the model predicted and experimentally obtained values for weight loss (response) and the percentage of error is 12%. On the basis of the mathematical model, single-objective optimization of operating parameters has been performed with genetic algorithm (GA) technique and this optimization method yields a reduction of 34.78% for material wear.
Keywords: Erosive Wear; Genetic Algorithm; Modeling; Optimization; Analysis of variance.
Root Cause Analysis of Pitting Corrosion of AA2024 and AA7075 after Exposure in Salt Fog Environment
by Pitichon Klomjit, Piya Khamsuk, Ekkarut Viyanit
Abstract: Two grades of anodized aerospace aluminum alloys, AA2024 and AA7075, were analyzed to determine root causes of pitting corrosion after the samples were exposed to a salt spray test according to ASTM B177. Methods to investigate pitting corrosion behavior of the aluminum alloys were divided into two steps: 1) characterization of pre-exposed (intact) anodized film and stimulated pitting corrosion by polarization and 2) comparison of samples that passed and failed the salt spray test. The surface properties were characterized by roughness measurements, scanning electron microscopy (SEM), energy dispersion X-ray spectroscopy (EDS). Pitting corrosion was stimulated by potentiodynamic polarization prior to characterization of pitting by SEM and EDS to determine pitting initiation point. The results reveal that thickness of the film does not prevent localized corrosion. Cu-bearing intermetallic particles are detrimental to anodic film formation and cause pitting in the film. Potentiodynamic polarization tests alone cannot determine whether the film will pass or fail the salt spray test for 96 hours.
Keywords: anodized film; pitting corrosion; aluminum alloys; salt spary exposure; localized corrosion; intermetallic particles.
Surface modification of carbonised waste rice husks by mild hydrothermal treatment
by Wong Min Jin Karen, J.X. Ooi, Zhipeng Wang, Nancy J. Siambun, Willey Y.H. Liew, W.K. Muzammil, K. Sopian, G.J.H. Melvin
Abstract: Carbonisation process is a way in exploiting rice husk to produce alternative carbon material. In this study, rice husk was carbonised at 500°C, 2h in inert environment. Mild hydrothermal treatment of carbonised rice husk was conducted by using potassium hydroxide (KOH) and potassium persulfate (KPS) as reactants in different parameters: (i) the reactants molar ratio and, (ii) reaction time. The treated carbonised rice husks were tested for its dispersion, morphology observation, elements, and functional groups determination. From the results, the modified carbonised rice husks showed improvement in its dispersion with polar solvent while no defects in the structures was observed from the SEM images. High oxygen content was found in EDX analysis for modified carbonised rice husks treated in KOH:KPS with molar ratio of 3:1. The presence of hydroxyl and carboxyl groups from the FTIR spectra shows that the treatment successfully introduced functional group to the carbonised rice husk surface.
Keywords: Rice husk; Carbonisation; Mild hydrothermal; Surface modification.
Laser surface texturing and tribological behaviour under solid lubrication on titanium and titanium alloy surfaces
by Wenhui Cao, Tianchang Hu, Hengzhong Fan, Litian Hu
Abstract: Surface textures with dimple and groove were fabricated on titanium and its alloy surfaces by a Nd:YAG pulsed laser. The effect of laser parameters on the two types of texture morphologies was investigated. The unidirectional sliding tests were carried out for the Ti6Al4V surface under solid lubrication conditions and the effect of dimple density from 5% to 30% was examined. The results show that laser parameters have a significant effect on the size and depth of texture for titanium and its alloy surfaces. Comparing with the untextured surface, the longevity of solid lubricant film on the textured surface is prolonged by 90% at least. The beneficial effect of dimples is to act as solid lubricant reservoirs under solid lubrication.
Keywords: titanium; titanium alloy; laser parameters; surface texture; friction; solid lubrication; wear.
Experimental Investigation on Abrasive Water Jet Polishing of Stainless steel: A Preliminary Study
by Yuvaraj Natarajan
Abstract: Abrasive water jet (AWJ) is a versatile machining technique for the production of components in various applications. In this paper, AWJ machining technique is extended to polishing operations on Stainless Steel 304. The production of polished surface through AWJ process is a breakthrough technique in the manufacturing process. The polishing operations were carried out in the OMAX-AWJ machining centre by controlling the process parameters, namely, the traverse rate and the abrasive mesh size. The single and double pass roster method was considered for the production of polished surface by AWJ. Experiments in a limited combination were carried out in the present study for identifying process feasibility for the production of the beneficial surface texture meant for various applications. In this study, in-depth analysis of 3D surface topography and surface morphology have been done on various polished surfaces. The experimental results indicated the yield of a surface texture with beneficial roughness features for the double pass jet operation through the employment of an abrasive mesh size of #300 and a traverse rate of 39.96 mm/min. Most of the polished surfaces have a rough texture with wear tracks and contamination. In future, a favourable surface texture should be generated on the target material by increasing the AWJ passes along with use of other significant parameters for the production of precise components with micro/nano level roughness features.
Keywords: AWJ; Polishing; SS 304; Surface texture; Jet pass; Traverse rate; Abrasive mesh size.
A Study of Recognizing the Friction State of Revolute Pairs Based on the Motor Current Signature Analysis
by Naiming JIANG, Guofu Li
Abstract: The recognition of the friction state of revolute pairs can help with the monitoring of their operating conditions to avoid equipment fault and other problems due to their failure. A new method for recognizing the friction state of revolute pairs based on motor current signature analysis was proposed in this paper to solve the problems of current common means for monitoring friction state, such as involving too many devices, high costs, difficult field application and low accuracy. Current signals were decomposed and multidimensional features were extracted by variational mode decomposition, and a method for searching the extreme point was proposed according to fast Fourier transform to determine the adaptive parameter selection strategy for variational mode decomposition parameters and extract the friction features of time-frequency domain. Meanwhile, the enhanced recognition of features of time domain and frequency domain was extracted, feature redundancy was reduced by principal component analysis, and the dimension reduction sample intervals were categorized according to the variation tendency of first principal component features after dimension reduction as the training sample for the support vector machine classifier. The support vector machine was trained by ensemble learning, a combined classifier was built and the penalty factors and kernel parameters of the support vector machine were optimized by quantum particle swarm optimization algorithm to further improve recognition accuracy and thus evaluate the time period of the friction state of revolute pairs a certain point of time. The friction state of revolute pairs at this moment could be evaluated precisely after their friction feature signal was recognized by multiple types of classifiers with different classification intervals, and the time before dry friction could be preliminarily estimated. The results indicate that, the friction fluctuation during movement of revolute pairs could lead to amplitude and phase modulation of the motors stator current signal, and the modulated signal was more obvious near the baseband signal while the first principal component of multi-domain and multi-dimensional features decreased before increasing after dimension reduction, reflecting the variation of the friction state of revolute pairs. The change of the friction state of revolute pairs could be represented completely by analyzing the stator current features of the motor driving the revolute pairs and extracting the multi-domain and multi-dimensional friction features. A new idea was provided for monitoring the operating conditions of revolute pairs and related mechanisms by machine learning and recognition of the friction state of revolute pairs by multiple classifiers and classification intervals.
Keywords: revolute pairs;motor current signal;friction feature;variational mode decomposition;support vector machine.
An indentation hardness-testing temperature model for ceramics and tungsten carbides
by Jeongki Jang, Kyungmok Kim
Abstract: This article describes an indentation hardness-temperature model based on a Kachanov-type damage law. The indentation hardness of materials varies with testing temperature. It is found that the surface area of the indentation increases exponentially with the testing temperature during hardness measurements. The change rate of the total contact area of the resulting indentation can be described as a function of the indentation area itself. Two parameters, a softening coefficient and an exponent, are able to determine the change rate of the indentation area with the testing temperature. In particular, the softening coefficient is found to increase as the film thickness increases. This proposed model will enable tribologists to predict the indentation hardness of materials and quantify the influence of various factors affecting indentation hardness.
Keywords: Indentation hardness; Vickers; Temperature; Kachanov damage; Film.
Effects and characterizations of pulse electrodeposition parameters of silver in terms of scattering parameter and surface roughness for waveguides operating at high frequencies
by Caner Basaran, Ishak Karakaya
Abstract: The signal quality of antennas and waveguides in the transmission of electromagnetic waves are very much dependent on the surface finish of these devices. The use of pulse current produces homogenous deposits of better surface finish than direct current. Effects of pulse parameters on the surface properties of silver coatings of the copper substrates have been analyzed in terms of surface roughness and S-parameter (scattering parameter). Grain size and morphology of silver coatings were characterized by SEM and XRD. The duty cycle, frequency and average current density were used as three pulse parameters. Three levels were selected for each parameter in the experimental design. The surface finish was found to be directly proportional to duty cycle and average current density but inversely proportional to frequency. The S11 scattering parameter observations were made relative to a gold-plated reference coupon. It was analyzed that the smoother surface had more reflection power in terms of S11 parameter thus decreasing the loss of radiation. Scanning Electron Microscope (SEM) was used to characterize the microstructure of silver plating. As a result of SEM analysis, pyramidal growth was obtained with pulse electrodeposition. Smaller grains and fewer valleys in the grain morphology were detected with the increasing average current density at high frequencies and high duty cycles. Irregularity was observed in the grain structure with decreasing average current density. According to X-Ray diffraction (XRD) analysis, smaller silver grains were observed at high duty cycle, high frequency and high average current density. Effects of pulse parameters on the diffusion of silver into the copper base material were analyzed by Energy-dispersive spectrometer (EDS) line analysis.
Keywords: Silver plating; pulse electrodeposition; morphology; grain size; scattering parameter; return loss.
An Experimental Study on the Surface Roughness of Galvannealed Low Carbon Al-killed and Ti-Nb Stabilized Interstitial Free Steels
by Candan Sen Elkoca, Bulent Ekmekci, Oktay Elkoca
Abstract: This study elucidates the surface microstructures forming surface roughness during the galvannealing process and establish relations between surface roughness, galvannealing process parameters, and coating iron content. Galvannealed low carbon Al-killed (AK) and Ti-Nb stabilized interstitial free (IF) steels were used to simulate the industrial galvannealing process using different annealing temperatures and times.
The craters were observed on the galvannealed coatings, resulting in high surface roughness. An exponential behaviour of the surface roughness was displayed with increasing annealing time at each annealing temperature in both steel coatings, which was in an increasing order in the AK steel coating, whereas in a reverse order in IF one. The increasing iron content in the coatings indicates a decrease in surface roughness with the cubic ?1k phase, favourable for the subsequent forming process.
Keywords: galvannealing; hot-dip galvanizing; Fe-Zn phases; surface roughness; surface morphology.
Electric Discharge Coating process variation and its wear Properties
by Ilangovan Arun, Yuvaraj C, Chandra Sekhar Reddy G
Abstract: In the present study elaborates about process variation of Electrical Discharge coating process through powder mixed and powder metallurgy (semi-sintered) electrode that influences mechanical and metallurgical properties of over duplex stainless are compared. Occurrences of surface roughness, poke, splatters and carters are minimal in deposition of pyrolysis carbon while using the powder metallurgical electrode process of deposition than powder mixed. Coating layer thickness and porosity are greater in powder mixed having similar decarburizing depth that deserves hardness values with an average of 1001HV to 1010HV across its section. Pyrolysis carbon restricts alloying element deposition that reduced frictional coefficient with greater wear rate compared with powder metallurgical process. The metallurgical characterization are performed through scanning electron microscope (SEM), Energy Dispersive X-Ray Spectroscopy (EDS), Phase identification through X-ray powder diffraction (XRD), Optical Microscope (OM), mechanical testing through Vickers Microhardness, and wear testing by Pin-On-Disc (POD) tribometer.
Keywords: Electrical Discharge Coating; Porosity; decarburizing depth; phase transformation carbon flakes; hardness; wear.
Comparative EIS study of Titanium based materials in high corrosive environments
by Pedro P. Socorro Perdomo, Nestor R. Florido Suárez, Amparo Verdú-Vazquez, Julia C. MIrza Rosca
Abstract: Electrochemical Impedance Spectroscopy (EIS) is a technique relatively complex and modern that owes its existence to the emergence of electronic circuits. In this work, the behavior in HCl 20% of three materials, Ti, Ti-15 Mo and Ti-15Mo-5Al fabricated by laser beam melting, was analyzed using EIS. Impedance spectra have been obtained at various potentials, from open circuit potential to +2.0 V vs. Ref. Once the profiles of the impedance spectra were analyzed, the experimental data were adjusted to an equivalent electrical model. Two models of equivalent circuits were presented: at Ecorr simple circuit is used while in the passive potential range an equivalent circuit with 2 time constants was used for fit the experimental data. It was concluded that titanium and studied titanium alloys undergo spontaneous passivation due to the oxide film formed on their surface in the reducing acid solution
Keywords: Titanium; Titanium alloys; equivalent circuit; EIS; HCl; corrosión.
Fretting behavior of textured Ti-6Al-4V alloy under oil lubrication
by Wenhui Cao, Tianchang Hu, Hengzhong Fan, Qi Ding, Litian Hu
Abstract: The micro-textures with different dimples densities and diameters are prepared on the Ti-6Al-4V surfaces. The influences of surface texture parameters on the fretting wear behaviors of TC4 self-matching pair have been investigated by using a pin-on-disk machine in a reciprocating sliding mode under different applied loads and fretting frequencies at oil lubrication. Results indicated that the proper texture on titanium alloy can greatly improve the fretting tribological properties under different loads. The 10% texture density surface showed the minimum wear volume at a low fretting frequency, whereas the 20% texture density surface had the lowest wear volume at a high fretting frequency. Under the tested condition, the surface with dimple diameter of 50 ?m had the best anti-fretting wear performance under the applied fretting frequencies. In addition, the mechanisms for friction-reducing and anti-wear were discussed. The existence of surface texture promoted the transition from dry friction to boundary lubrication state under high fretting frequency, and the dimples can effectively capture wear debris to alleviate the abrasive wear of the material.
Keywords: Metal wear; Fretting; Surface texture; Oil lubrication.
System kinetics characteristics of multi-parameter coupling of rolling mill based on mixed lubrication process of rolling interface
by Qiaoyi Wang, Pengcheng Yu, Han Wang, Xin Jiang, Huijun Zhao
Abstract: Based on the theories of rolling, hydromechanics and vibration, a multi-parameter coupling kinetic model was established, in which the interface friction, geometric constraint and stress distribution were modeled for dynamic roll gap. A quantitative analysis was performed on the key parameters affecting the amplitude and critical speed of vertical vibration of the rolling mill. The variation of friction stress and compressive stress in the work zone with time was analyzed systematically when the rolling mill was in the mixed lubrication state with a constant reduction rate and surface roughness. The results reveal that the critical vibration speed is directly proportional to the thickness of the workpiece in the outlet zone, the surface roughness of the roll and workpiece, and the roll radius, but inversely to the lubricant viscosity and the thickness of the workpiece in the inlet zone. The amplitude is proportional to the rolling speed, and the compressive and frictional stresses are inversely proportional to the post-tensile stress.
Keywords: rolling interface; mixed lubrication; multi-parameter coupling; kinetics characteristics; reduction rate.
Enhanced hardness and friction behavior of 40Cr steel by Laser Surface Texturing after Ultrasonic Surface Rolling
by Yang Zhou, Genshang Wu, Jinggan Shao
Abstract: This paper construct a new type of wear-resistant layer on material surface by laser surface texturing and ultrasonic surface rolling. Different from the traditional anti-wear layer, there is no obvious mechanical property difference between the anti-wear layer and material matrix, which can effectively prevent the anti-wear layer falling off and improve fatigue life of material. Meanwhile, the anti-wear layer can also collect wear debris. A hardening layer is formed on the material surface by ultrasonic rolling, and then the surface texturing is machined on the hardening layer by laser. The friction behavior of anti-wear layer is studied by friction and wear experiment. The experimental results show that the new anti-wear layer has low friction coefficient and surface roughness. The specimen with Laser Surface Texturing(LST) and Ultrasonic Surface Treatment(USR) has more smaller wear depth under the same conditions.
Keywords: Laser Surface Texturing; Ultrasonic Surface Rolling; anti-wear layer; friction coefficient; wear depth.
Coatings with embedded particles to increase interfacial anchorage of steel and GFRP rebars in concrete
by Jose De Jesus Perez Bueno, Jorge Luis Soto Corral, José Luis Reyes Araiza, Maria Luisa Mendoza López, Alejandro Manzano-Ramírez
Abstract: The conventional structures of concrete are reinforced and pre-strengthened with rebars and steel wires. Initially, the steel is protected against corrosion by forming a passive layer due to the alkalinity of the concrete. Nevertheless, once it was lost, either by carbonation or another factor, the corrosion is reactivated, propitiating the flaw of the reinforcement element. This can cause concrete breakage due to increased volume for transforming the metallic iron into iron oxides. In this research, three different types of coatings were studied: sol-gel silica, an organic polymer (bisphenol A-fumarate), and an organic-inorganic hybrid nanometric compound. This work proposes the addition of particles of about 5 mm in size, heterogeneously distributed, such as recycled glass on the coatings or sand to gain mechanical anchorage between the coated steel rebars and the concrete. This surface change was tested in rebars of fiber-reinforced polymer (GFRP) with fiberglass. The result was that this factor increased the force required for the extraction of the rebars. The low thickness of sol-gel SiO2 coatings made with TEOS did not turn out to be suitable for this application. The coatings with polymeric resin were suitable, offering protection against corrosion in an economical and straightforward form. The organic-inorganic hybrid coatings, possessing properties of organic and inorganic constituents, and using silane coupling agents, provide coatings with adequate protection but depending on the preparation process and a cost increase regarding the polymeric resin.
Keywords: Hybrid coatings; Concrete; Sol-gel; Corrosion; Fly ash.