Service Life Of Engineering Components Research Articles

Notch effect in very high-cycle fatigue behaviour of a structural steel

The presence of a notch or a detail which leads to stress concentration due to complex geometries has a considerable impact on the fatigue life of engineering structures. Therefore, on the one hand, the notch effect must be investigated and considered in the fatigue assessment of these structures. On the other hand, in the last decades, an interest in studying the very high-cycle fatigue regime (VHCF) has been perceived, due to the extension of the service life of engineering components beyond the 10 million cycles. Thus, the notch effect in the VHCF regime was analysed for the S690 structural steel. Therefore, an analytical approach to design notch specimens was developed and a numerical simulation was performed to assess it. Then, an experimental campaign with smooth and notched specimens with two different stress concentration factors was performed in an ultrasonic fatigue machine to assess the VHCF behaviour. The mechanisms of failure and fracture surfaces were also investigated. It was observed a fully notch sensitivity as well as the dominance of surface crack initiation for the S690 steel in the VHCF regime.

Neural Network Prediction of Surface Roughness with Bearing Clearance Effect

In manufacturing industry, the quality of manufactured machine components, is determined by how well they follow a defined product's criteria for dimensional accuracy, tool wear, and surface finish quality. For this reason, manufacturers must be able to regulate machining processes to ensure improved performance and service life of engineering components. This research work presents a study on the optimization of machining parameters for mild steel using artificial neural networks (ANNs). The focus is on developing an effective and efficient machining technique for mild steel by leveraging the capabilities of ANNs to predict optimal machining parameters. To bridge the gap between laboratory figures, model-simulated values, and real-world application, experiments were conducted to obtain data used in the research analysis. Levenberg-Marquardt method were utilized to train the ANNs, with input factors like depth of cut, bearing clearance, cutting speed, and feed rate considered, while the surface roughness of the cut, normalized within 0 to 1 range. A statistical measure of the surface roughness predicted using indicated MAPE value of 0.002% while the correlation coefficient (R) was 0.99995. The results showed that ANNs are a viable machining parameter optimization method and can improve product quality, while providing significant economic and production benefits.

The impact of surface scratches on the corrosion behavior of nanocrystalline high entropy alloy coatings: Electrochemical experiments and first-principles study

To prolong the service life of engineering components used in aggressive environments, a TiZrHfMoW refractory high entropy alloy (RHEA) coating was prepared onto a titanium alloy substrate. Various electrochemical analytical techniques were used to evaluate the corrosion resistance of the scratched RHEA coating in a 3.5 wt.% NaCl solution. The electrochemical corrosion tests indicate that the scratched RHEA coating exhibits a higher electrochemical stability and a lower corrosion rate than the bare titanium alloy. The effects of the localized plastic deformation on the corrosion behavior for the RHEA coating was investigated. A slab model for the RHEA surface was proposed for the first-principles calculation to explored the change of the electron work function (EWF) as a function of external stress. The influence of the constituent elements in the RHEA on the mechanical properties and the electron work function was study to uncover the mechanism underlying the high scratch corrosion resistance of the RHEA coating and provide guidance for the composition design of refractory high entropy alloy.

On the enhanced wear resistance of laser-clad CoCrCuFeNiTix high-entropy alloy coatings at elevated temperature

One major hindrance that high-temperature working components face nowadays is wear. The CoCrCuFeNiTix (x = 0, 0.5, 1.0 and 1.5) high-entropy alloy coatings were synthesized on 45 steel substrates via laser cladding to prolong the service life of engineering components under high-temperature working conditions. The microstructure and 600 °C tribological properties of the coatings were systematically investigated. Ti addition facilitated the precipitation of hard phases (i.e., Laves phase and Ti-rich phase) and refined the grains. The formation of a protective TiO2 layer on the worn surface of CoCrCuFeNiTi1.5 coating inhibited abrasion and oxidative wear, contributing to the lowest wear rate. The enhanced wear resistance of CoCrCuFeNiTi1.5 coating at elevated temperature benefited from the synergistic effect of improved microhardness and oxidation resistance.

Wear-resistant Fe68Cr8Mo4Nb4B16 glass former coatings – From powder production by gas atomization to coating build-up by Laser Powder Bed Fusion

Fe-based glassy/crystalline alloys are promising cost-effective protective coatings to increase the service life of engineering components operating in a wide array of aggressive environments. In this work, gas-atomized 53–106 μm Fe68Cr8Mo4Nb4B16 (at.%) powders, produced from commercial-grade precursors, were deposited onto an AISI 1020 steel substrate by Laser Powder Bed Fusion (L-PBF). The coatings were thick (500–700 μm), dense (2–3%vol. porosity), hard (> 1000 HV0.5), metallurgically bonded to the substrate with reduced dilution, and their microstructures were composed of M2B-tetragonal and ferrite within the remaining glassy phase. Nevertheless, some cracks were observed. Good wear resistance characterizes the L-PBF coatings, with a specific wear rate of ~8.40 × 10−5 mm3/N·m, much lower than the value obtained from the soft (~114 HV0.5) AISI 1020 substrate, 1.91 × 10−4 mm3/N·m. The wear mechanism observed on the coating surfaces was predominantly abrasive and by fracture originated from preexisting cracks. In addition to abrasive wear, the occurrence of oxidative wear was also observed on the worn surface of the substrate. The protective coatings produced by L-PBF proved to be an interesting approach to protect and to repair the surface of steel substrates from wear, besides highlighting the use of L-PBF for coating production.

Surface finishing and residual stress improvement of chemical vapour deposited tungsten carbide hard coatings by vibratory polishing

Hard coatings are widely used in several industries to improve the service life of engineering components. W/WC coatings deposited through chemical vapour deposition (CVD) have the capability of providing the required protection on parts with complex geometries, commonly used in high wear and corrosive environments. Despite the improvement in service life, a key important factor is the adherence to low roughness and tolerance specifications, necessitating the need of a post-coating finishing process. In this work the impact of vibratory polishing on W/WC coating was studied using a vibratory barrel setup and two types of ceramic-based media. An improvement in average Ra of 0.2–0.3 μm was achieved over a duration of 4 h with abrasive wear being the predominant polishing mechanism. Insignificant weight loss (<0.017 g) and hardness changes (−2 < ΔHV < 8) were confirmed while the compressive residual stresses of the coating were found to increase with process time (max Δσ = −1058.3 MPa).

Friction surfacing: A tool for surface crack repair

The present work demonstrates the feasibility of friction surfacing as a tool to repair surface cracks. An artificial crack, made on Inconel 718 plate was repaired by depositing a self-mating coating by friction surfacing. The crack was completely filled and the coating exhibited sound bonding with the substrate. For complete filling of the crack, the optimized process parameters depends on the crack dimensions. The coating microstructure was characterized by equiaxed fine grains with an average grain size of 1–3 μm and with a high fraction (>78%) of high angle grain boundaries. The microstructure in the coating evolves through dynamic recrystallization process, driven by combination of high strain rate and high temperature during friction surfacing. The method opens up a new way of repairing surface cracks and enhancing the service life of engineering components. • We demonstrate that friction surfacing can be used as a tool to repair surface cracks. • Surface crack on Inconel 718 repaired by depositing a self-mating coating • Coating microstructure was equiaxed and fine grained with >78% high angle grain boundaries. • Strong adhesion exists between the deposited coating and substrate.

Correlation of Microstructural Evolution with Mechanical and Tribological Behaviour of SS 304 Specimens Developed Through SLM Technique

This research work focuses on the development of SS 304 specimens using the selective laser melting technique and analyses the microstructural modifications. Further, it correlates the evolution of microstructure with mechanical properties like microhardness, nanoindentation and tribological behaviour. The conventionally prepared as-cast SS 304 specimens were taken for comparison of the results obtained with the SLM technique. The diffraction pattern obtained from x-rays disclosed the absence of δ phase and confirmed that refinement of grains occurred in the structural level through decrease in the intensity of α peaks. Optical micrograph witnessed that the grains were in micron and sub-micron size. SEM images depicted the presence of columnar and cellular sub-grains within a grain which were in ultrafine level. The microhardness and nanoindentation results obtained for the SLM specimen were almost multiple times higher than the conventional as-cast specimens. There was a significant improvement in the wear resistance in the SLM specimens than the conventional as-cast specimens. From the results, SLM is found to be a favourable technique to manufacture metallic components in a way to obtain a good service life of engineering components.

Effect of voltage and spray–off distance of electric-arc spray technique on surface properties of nickel–chrome (Ni–Cr) coating developed on 304L stainless steel

Nickel–chrome coatings are widely used to improve surface properties and service life of engineering components made from different ferrous and non–ferrous alloys. Herein, an attempt has been made to investigate the impact of various voltages ranging from 26–30 V and spray–off distances ranging from 100–300 mm of electric-arc spray technique on the surface properties of Ni–Cr coating developed on 304L stainless steel. Thickness, porosity, surface morphology, surface roughness, and hardness of Ni–Cr coatings were determined to study the impact of deposition parameters. Coating deposition at 26 V exhibited the lowest porosity and the highest percentage of Cr nodules among all samples. The comparison study showed that coating deposit developed at 26 V and 100 mm spray–off distance has a maximum thickness, followed by coating developed at 30 V and 100 mm spray–off distance. This indicated that coating deposit developed at 100 mm spray–off distance results in thicker coatings. Maximum hardness was achieved at 30 V and 300 mm spray–off distance. The shorter spray–off distance revealed that coatings tend to be thicker and harder resulting in longer coating life.

Multi-Objective Optimisation of Laser Deposition of Metal Matrix Composites for Surface Coating Using Principal Component Analysis

Laser deposition is an advanced manufacturing technology capable of enhancing service life of engineering components by hard-facing their functional surfaces. There are quite a number of parameters involved in the process and also desirable output characteristics. These output characteristics are often independently optimised and which may lead to poor outcome for other characteristics, hence the need for multi-objective optimisation of all the output characteristics. In this study, a laser deposition of Ti-6Al-4V wire and tungsten carbide powder was made on a Ti-6Al-4V substrate with a view to achieve a metallurgical bonded metal matrix composite on the substrate. Single clads were deposited with a desire to optimise the composite clad characteristics (height, width and reinforcement fraction) for the purpose of surface coating. Processing parameters (laser power, traverse speed, wire feed rate, powder feed rate) were varied, the experiment was planned using Taguchi method and output characteristics were analysed using principal component analysis approach. The results indicated that the parameters required for optimised clad height, width, and reinforcement fraction necessary for surface coating is laser power of 1800 W, traverse speed of 200 mm/min, wire feed rate 700 mm/min and powder feed rate of 30 g/min. The powder feed rate was found to most significantly contribute 43.99%, followed by traverse speed 39.77%, laser power 15.87% with wire feed rate having the least contribution towards the multi-objective optimisation. Confirmation results showed that clad width and reinforcement fraction were significantly improved by the optimised parameters. The multi-objective optimisation procedure is a useful tool necessary to identify the process factors required to enhance output characteristics in laser processing.

Wear and Corrosion Behavior of Tungsten Carbide Based Coating on Carbon Steel

High velocity oxy-fuel (HVOF) coating techniques are employed mainly to improve the service life of engineering components, which is exposed to wear, erosion, corrosion or combination of both; wear and corrosion. The aim of this study is to investigate the wear and corrosion behavior of WC-10Ni and WC-12Co coating deposited onto medium carbon steel (Cast steel BS 3100 GR A3) blade. The blade was used to stir the mixture of sulfuric acid (H2SO4) with ilmenite to produce titanium dioxide (TiO2) pigments. The microstructures of both coatings before and after wear and corrosion testing were evaluated using scanning electron microscope (SEM). Vickers microhardness testing was used to examine the coatings hardness. The three-body wear test with wet condition using silicon carbide (SiC) slurry was used to investigate the wear behavior for both coating. The experiment was based on weight loss of the sample and Archard’s law to determine the wear rate of the coating. In addition, the three-electrode electrochemical test was used to investigate the corrosion behavior of the coatings. The mixture of H2SO4 and ilmenite used as an electrolyte of the test. It is found that the wear rate will increase with increasing of the weight loss. This is consistent with decreases of the volume fraction loss and hardness of the coating. After corrosion test, it can be observed that the existence of the crack and porosity on the coating increasing the corrosion behavior of coating. With high volume fraction and hardness, WC-12Co shows higher wear resistance compared to WC-10Ni. However, the value of corrosion rate for both coating has a slight difference due to better corrosion resistance of Ni binder itself.

Synthesis and Mechanical Response of NiTi SMA Nanoparticle Reinforced Mg Composites Synthesized through Microwave Sintering Process

The concept of developing intelligent Self-Healing Metallic Materials that can repair its damage is always fascinating and is of great interest in order to improve the quality service life of engineering components. Due to their low density, magnesium (Mg) and its alloys offer a combination of better specific strength (σ/ρ), damping characteristics and impact resistance and can suit best for the quest of intelligent self-healing materials development. In the current study, Mg is reinforced with 2 wt.% NiTi shape memory alloy (SMA) nanoparticles and the SMA particle effect on the mechanical properties and microstructural evolution of monolithic magnesium are studied. A near dense Mg-2 wt. % NiTi nanocomposite was obtained during the study. The addition of NiTi nanoparticle resulted in a ∼29 % and ∼73% enhancement in the microhardness and grain size of pure Mg. Damping capacity and loss rate of pure Mg also had a superior enhancement of ∼119% and ∼2.6 times, respectively due to the presence of NiTi nanoparticle. The compressive strength properties also exhibited a visible enhancement due to the presence of NiTi nanoparticle without compromising on the fracture strain of the material.

Problems on the development of hard and low friction in-situ coatings on Ti-6Al-4V using laser cladding

Coatings having high hardness and low coefficient of friction are significant for long service life of engineering components subjected to sliding wear. Some useful applications of such coatings are in various engine components including aerospace industries. Laser surface engineering has promising process characteristics for changing surface properties. In this concern, using laser cladding process hard and low friction coatings were developed on Ti-6Al-4V for improving sliding behavior of its components. To carry out the experimental investigations, the pre-placed powder mixture of B4C, hBN and Ti were used on the Ti-6Al-4V substrates and subsequently laser irradiated to form the improved surface properties. The coatings were developed with a wide range of laser scan speeds. Physical and mechanical characterizations of all samples were done rigorously. For some laser-scan-speeds in the range of studies, developed coatings resulted in very high hardness about 2200 HV. The dry sliding wear tests (against WC ball at 10 N loading) indicated a very low coefficient of friction of about 0.1 to 0.16 for the coatings. The problems experienced during development of the in-situ coatings are highlighted in the paper.

Neutron diffraction and neutron imaging residual strain measurements on offshore wind monopole weldments

Residual stress measurement is of fundamental interest in order to estimate the service life of engineering components and structures subjected to various loading conditions operating in different environments. Destructive and non-destructive techniques are used for the evaluation of residual stresses. Neutron diffraction, as a non-destructive technique, is widely used to measure the elastic strain component of a specific atomic plane from which residual stresses can be calculated. Neutron imaging is an alternative technique which enables residual stresses to be measured through strain mapping of the area of interest. In this study, neutron diffraction measurements were performed in conjunction with neutron imaging to evaluate residual strains in a compact tension, C(T), specimen extracted from a welded plate made of S355 structural steel. Neutron diffraction and imaging are two complementary techniques which have been employed in this work by performing measurements on the Engin-X and newly developed IMAT instruments, respectively, at the Rutherford Appleton Laboratory. Neutron diffraction residual strain measurements in all three directions were conducted within the Heat Affected Zone (HAZ) of the weld area whereas longitudinal residual strains were measured using the neutron imaging technique. A comparison of the neutron diffraction and neutron imaging preliminary results has shown that neutron imaging can provide acceptable measure of residual strains compared to those of obtained from neutron diffraction. The results have been discussed in terms of the possible sources of error encountered in each measurement technique and the accuracy of each technique against the other.

Three-dimensional quasi-static fatigue crack growth analysis in functionally graded materials (FGMs) using coupled FE-XEFG approach

In the present technological scenario, functionally graded materials (FGMs) are being introduced by scientific community for a wide range of effective engineering applications especially in aerospace, nuclear reactor, bio-medical and military uses. Safety and long service life of engineering components made from FGMs are one of the major objectives of engineering design process. The prediction of fracture behaviour is quite essential for safe designing of such critical components. In this work, three dimensional quasi-static fatigue crack growth has been studied in FGMs. Effects of material gradient (due to FGMs nature) have been investigated in detail. Both crack growth contours and fatigue lives are studied with reference of material heterogeneity (FGMs). Detailed analyses are presented in the form of fracture toughness, crack growth contours and fatigue life cycles. Numerical results are presented for cyclic thermal and mechanical loading environments. The variation in the material properties for FGM has been modelled by exponential law. The solution methodology has been implemented in coupled finite element (FE) and extended element free Galerkin (XEFG) approach. Few planar and non-planar crack geometries are simulated to check robustness and accuracy of the proposed technique. It has been shown that employed computational approach provides accurate fracture studies and crack growth predictions for three-dimensional functionally graded materials.

Artificial neural network model for evaluation the effect of surface properties amendment on slurry erosion behavior of AISI 5117 steel

Purpose The aim of this paper is to evaluate the effect of surface treatment on slurry erosion behavior of AISI 5,117 steel using artificial neural network (ANN) technique. Design/methodology/approach The slurry erosion wear behavior of electroless nickel-phosphorus (Ni-P) coated, carburized and untreated AISI 5,117 alloy steel was investigated experimentally and theoretically using ANN technique based on error back propagation learning algorithm. Findings From the obtained results, it can be concluded that the proposed AAN model can be successfully used for evaluating slurry erosion behavior of the Ni-P coated, carburized and untreated AISI 5,117 steel for wide range of operating conditions and Ni-P coating and carburizing improve the slurry erosion resistance of AISI 5,117 steel; however, the coating is more efficient. Originality/value Slurry erosion is a serious problem for the performance, reliability and service life of engineering components used in many industrial applications. To improve the performance of these components, engineering surface technologies have been attracting a great deal of attention. The extent of slurry erosion is dependent on a wide range of variables. To account all variables that effect on erosion behavior, prediction of erosion behavior by soft computational technique is one of the most important requirements. ANN has the ability to tackle the problem of complex relationships among variables that cannot be accomplished by traditional analytical methods.

Effect of Preheating and Buttering on Cracking Susceptibility and Wear Resistance of Hardfaced HSLA Steel Deposit

Hardfacing weld techniques apply mainly to improve the service life of engineering components either by rebuilding or fabricating a composite layer, which will protect the components from wear, erosion, and corrosion. However, hardfaced deposits are susceptible to cracks compared to the base metal due to thermal cycles and different chemical composition of hardfaced consumables. In addition, this method yields only marginal improvements in wear resistance performance. This investigation was attempted to eliminate the cracks by depositing a soft buttering layer by using austenitic stainless steel consumable in the area between base metal and hardfaced layer. Preheating was also applied at the joint. The result reveals that buttering and preheating reduce crack susceptibility and increase wear performance of hardfaced HSLA steel deposit.

Optimisation of welding mechanisms using analytic hierarchy process, technique for order preference by similarity to ideal solution and graph theory and matrix approach

The selection of an optimal welding mechanism for engineering design problems from among two or more alternatives on the basis of two or more attributes is multiple attribute decision making problems. Various approaches have been proposed in the past to help address the issue of material selection. Welding techniques are mainly used to improve the service life of engineering components and to reduce their cost either by rebuilding repeatedly or by fabricating in such a way as to produce a composite wall section. Therefore, proper selection of welding mechanism for particular application is a problem in industry. This paper presents a welding mechanisms selection using analytic hierarchy process (AHP), technique for order preference by similarity to ideal solution (TOPSIS) and graph theory and matrix approach (GTMA) for a ship building industry which uses four welding mechanisms for similar applications.

Developments in Weld Cladding

Weld cladding is a process of depositing a relatively thick layer of filler material of approximately 3mm on the base metal through welding so as to develop surfaces with desired properties. Cladding is usually done to increase the corrosion resistance, wear resistance or hardness of such base metals having inferior properties. Cladding improves the service life of engineering components, and also reduces their cost. In this paper, various weld cladding technique, and effect of process parameters on clad quality including microstructure, mechanical and other cladding properties are discussed.

Selection of welding process for hardfacing on carbon steels based on quantitative and qualitative factors

Weld hardfacing techniques are employed mainly to extend or improve the service life of engineering components either by rebuilding or by fabricating in such a way as to produce a composite wall section to combat wear, erosion, corrosion, etc. In this paper, an attempt has been made to determine the best welding process to hardface boiler grade steels based on quantitative factors (by measuring percentage of dilution) and qualitative factors (using the analytic hierarchy process [AHP]). Five different welding processes including shielded metal arc welding (SMAW), gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), submerged arc welding (SAW), and plasma transferred arc welding (PTAW) have been compared. Based on the quantitative and qualitative factors, the PTAW process is found to be the best method to hardface boiler grade steels.