Ductile Iron Surface Research Articles

Repair feasibility and performance enhancement analysis of Fe-based alloy coating on ductile iron surface by high-speed laser cladding

In this paper, high-speed laser cladding technology with a scanning speed of 40 mm/s was used to clad the ductile iron surface with the Fe-based alloy coating. The coatings' microstructure, element distribution, crystallographic structure, wear resistance, and corrosion resistance were investigated by using an optical microscope, SEM, XRD, friction and wear testing machine, super depth-of-field microscope, and electrochemical workstation. The results show that the microstructure of the coating is mainly γ-Fe solid solution and carbide eutectic structure. The phases of the coating are FCC phase (γ-Fe dominated), BCC phase, and carbide. The elemental distribution of the coating cross-section elements is uniform, and no quality obvious defects such as large gas pores and cracks are found. The coating mass loss was 60.0% and 47.1% of the substrate for different friction parameters and the more significant coating oxide build-up phenomenon with increased loading force. The self-corrosion rate of the coating was 0.006 g/m2·h, and the substrate was 0.042 g/m2·h; the maximum impedance value of the coating (1.34×104 Ω·cm2) was increased 20 times based on the substrate (619.2 Ω·cm2). In summary, Fe-based coatings with these process parameters can repair failed ductile iron parts and significantly extend their service life.

Study on ductile iron surface laser cladding austenitic stainless steel coating heat treatment to enhance wear resistance

In this paper, laser cladding technology coated the ductile iron surface with austenitic stainless steel. To improve the wear resistance of the coating, consider a heat treatment way to strengthen it. The effects of temperature and time on microstructure, hardness, and wear resistance of austenitic stainless steel coating were investigated. The results show that the martensitic phase was added to the samples at different times of 950 ℃, and the carbide precipitated phase was the main change in the microstructure. At 1050 ℃, the samples also changed from austenite to martensite at different deal times, and the microstructure mainly changed between dendrites. The hardness and abrasion resistance of the 1050 °C/2 h process improved with a hardness of 40.6 HRC, an increase of 26.1%, and a maximum relative abrasion resistance improvement of 84.63%. Which strengthening mechanism was mainly coating dendrites coarse and uniform diffusion occurs, martensite uniform phase transition presented on the surface, coating austenite grain size 9.08 µm smaller, martensite recrystallization and larger grain size of 28.57 µm, the coating as a whole in the uniform phase transition and dendritic crystal strengthening synergistic effect, hardness increased, resistance to wear became stronger.

Metallographic investigation of laser-treated ductile iron surface with different laser heat inputs

Metallographic investigation of laser-treated ductile iron surface with different laser heat inputs

Simultaneous laser in-situ generation of graphene and micro-textures on ductile iron and their effects on tribological properties

In this study, a picosecond (ps) laser was employed to produce micro-textures on ductile iron in linearly processing leading to significantly higher processing efficiency. The fabrication efficiency was increased about 1331 times as compared to the more common spot-by-spot texturing method. The ps laser induced graphene (LIG) structures were simultaneously fabricated in dimples, which further enhanced the surface tribological properties. The surface micro-textures were produced by forming micro-dimples on the substrate via the laser ablation process. The dimple diameter and area density were regulated by varying the key laser processing parameters, and were experimentally correlated to the tribological properties of the ductile iron substrate. To understand deeper into the wear reduction mechanism of the micro-dimples, simulation models based on the Reynold equation were established, which analyze the flow field pressure distribution and demonstrate the hydrodynamic lubrication effect of the micro-textures. The ball-on disk friction test showed that the area density of the micro-textures had a significant influence on the friction and wear properties. The micro-texture with the area density of 20% and the average dimple diameter of 36 μm showed the highest volume wear rate reduction of 70% and the friction coefficient reduction of 20% respectively. The results indicated that the simultaneous laser in-situ generation of graphene micro-textures is an effective way of enhancing tribological properties on the ductile iron surface. It enhances the hardness of textured surfaces, thermal diffusion, debris capture ability, and fluid dynamic lubrication effect.

Cleaning of Graphite Particles Embedded in the Surface of Ductile Iron by Using a Novel Method

Ductile iron has unique mechanical property and has been widely used in many industrial applications, e.g., engine cylinder covers, crank axles, and machine tool beds and cams. The welding performance of ductile iron is normally influenced by graphite particles in the surface of ductile iron, which needs to be removed before welding. In this article, laser cleaning technique was developed to remove graphite particles implanted in the surface of ductile iron. Laser cleaning parameters and the damage threshold value of the substrate were investigated by using a pulsed Nd: YAG laser. The optimized laser cleaning parameters were obtained to achieve high-quality cleaning effect and avoid the formation of the oxide layer. Surface morphologies and elemental compositions of specimens before and after laser cleaning were characterized by scanning electron microscopy and energy-dispersive X-ray spectroscopy. Results indicated that graphite particles implanted in the surface of ductile iron were removed completely and efficiently by using the pulsed laser without the protection of inert gas atmosphere, and surface oxidation was not observed during the laser cleaning process.

Early period corrosion and scaling characteristics of ductile iron pipe for ground water supply with sodium hypochlorite disinfection

The corrosion and scaling phenomenon have crucial impact on drinking water distribution systems (DWDS), which might lead to pipe blockage or leakage, colored water and other chemical stability issues. In this study, a simulating pipe system with continuous water flow was prepared to investigate the characteristics of corrosion and scaling on ductile iron pipe transporting ground water with sodium-hypochlorite (NaOCl) disinfection. Electrochemical assays, such as polarization curves and electrochemical impedance spectra were applied to monitor the corrosion and scaling process. Results showed the morphology and components of scale were closely related with the electrochemical analysis results. The corrosion current density decreased continuously as corrosion and scaling proceeded. The process could be divided into three stages. During Stage I (0–20 days), the corrosion current intensity of low NaOCl dosage experiments (1, 2 mg/L) were higher than those of high NaOCl dosage experiments (5, 10 mg/L). The difference could be explained by different oxidation potentials, pH and CaCO3 deposition. During Stage II (20–80 days), higher proportions of Fe3O4 in scale in experiments with no or low NaOCl dosages restrained the corrosion process and presented smaller corrosion current. Subsequently, the ductile iron surface became passivated and the difference of various NaOCl dosages affecting corrosion and scaling process turned to be negligible during Stage III (80–90 days). A negative linear relationship between the proportion of stable scale component and the corrosion current density was established. Besides the direct corrosion reaction with iron substrate, NaOCl dosing was accompanied by an increase in pH and calcium carbonate precipitation potential values, which affected the early period corrosion and scaling phenomenon greatly.

Electrochemical and microstructural study on depassivation of ductile iron surface in chloride-contained simulated cement-mortar pore solution

Depassivation on the surface of ductile iron (DI) influences the service life of cement-mortar-lined ductile iron (CMLDI) pipe in water engineering. In order to investigate the depassivated behavior and chloride threshold value (CTV) of the DI surface in chloride-contained simulated cement-mortar pore (SCMP) solution, electrochemical techniques (OCP, TP and EIS) and microstructural analyses (SEM, XPS and AFM) were used in this study. Chloride solution was gradually unleashed in six SCMP solutions with variant pHs ranging from 13.6 to 10.5, until the DI surface became depassivated. Results show that, when the chloride concentration increases to a critical value (CTV), the OCP, TP and EIS have simultaneously sudden changes, and the Fe2+/Fe3+ ratio produces a significant reduction, while there occur some defects and corrosion products on the DI surface. The depassivation of DI surface is primarily related to chloride (Cl−) and hydroxyl (OH−) concentration of SCMP solution, and the CTV at DI depassivation exponentially decreases with the hydroxyl concentration of SCMP solution. Finally, by fitting on the experimental data, a CTV equation of DI surface was proposed.

Electrochemical and microscopic investigation on passive behavior of ductile iron in simulated cement-mortar pore solution

The passive behavior of ductile iron in simulated cement-mortar pore (SCMP) solution with different alkalinity was investigated by electrochemical measurements, such as open circuit potential (OCP), Tafel polarization curve (TP), electrochemical impedance spectroscopy (EIS), and microscopic tests, including scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Results show that, with increase in immersion time, the SCMP solution with the high pH value can cause the increase of OCP and capacitive loop of ductile iron surface, a morphology of growing surface film, and the high Fe2+/Fe3+ ratios in its surface Iron-oxide compounds, presenting the formation of passive film on the surface of ductile iron. But in the SCMP solution with low pH value, its OCP, TP curve and EIS show no obvious change, and also produce the corrosion morphology of rust with low Fe2+/Fe3+ ratios, indicating loss of surface protection on the ductile iron.

Reciprocating Wear Behavior of Ductile Cast Iron Modified by Pulse Plasma Technology

Wear resistance of ductile iron can be improved through di erent surface engineering techniques, each having some limitations and drawbacks. Recently, a new method called pulse plasma technology has been introduced, which through local reinforcement with inserts improves wear resistance of ductile iron without compromising other properties. This paper deals with the improvement of the wear resistance of ductile iron surface modi ed by pulse plasma technology using a tungsten electrode. The surfaces of the samples were treated by C3H8, air, and oxygen gases. The surface morphology and the phase structure in the near surface region of original and treated samples were analyzed with optic microscope, scanning electron microscope and energy-dispersive spectroscopy. The surface properties were evaluated by measuring the microhardness, wear properties and friction coe cient, as well as the elemental depth pro les and chemical composition of the modi ed layer. It was found that the microhardness of the treated samples was much higher. The tribological resistances were also signi cantly improved, as con rmed by the reduced friction coe cient and wear track width. This improvement can be attributed to the di usion of tungsten on the surface layer.

Effect of electric contact surface treatment on microstructure and wear behaviour of ductile iron

A study of electric contact surface treatment to ductile iron has been carried out. This technology was based on the application of the contact resistance heating between the electrode and workpiece. For comparison, the experiments of induction hardening to ductile iron were studied. The microstructure, microhardness, surface residual stress and wear properties were investigated using optical microscope, scanning electron microscope, X-ray diffraction, Vickers microhardness and rolling contact wear tests. Electric contact surface treatment resulted in the formation of fine ledeburite (white bright layer) and martensite in the ductile iron surface, in which the hardness in these areas was higher than that of induction hardened surface. The wear test results showed that the ductile iron surface after electric contact surface treatment had better wear resistance owing to the fine microstructure, high hardness and residual compressive stress.

Theoretical and experimental analysis of electric contact surface hardening of ductile iron

Electric contact surface hardening was based on the application of contact resistance heating between the electrode and work piece, which makes use of the rapid and cooling cycles produced on metals surface without affecting the bulk of the work piece. Surface performance can be enhanced through the phase transformations that take place during the mentioned thermal cycles. In this work, the temperature field of strengthened layer on electric contact strengthening was simulated using ANSYS software; the depth and width of strengthened layer were calculated. Moreover, the effect of main processing parameters on strengthened layer was simulated. Finally, some experiments have been carried out to harden the surface of ductile iron by self-developed electric contact surface strengthening device to verify the simulated results. It is found that the error was controlled in 15% reposefully, which represents the simulated result and experimental results to a certain degree are in good agreement.

Microstructural study and wear behavior of ductile iron surface alloyed by Inconel 617

In this research, microstructure and wear behavior of Ni-based alloy is discussed in detail. Using tungsten inert gas welding process, coating of nearly 1–2mm thickness was deposited on ductile iron. Optical and scanning electron microscopy, as well as X-ray diffraction analysis and electron probe microanalysis were used to characterize the microstructure of the surface alloyed layer. Micro-hardness and wear resistance of the alloyed layer was also studied. Results showed that the microstructure of the alloyed layer consisted of M23C6 carbides embedded in Ni-rich solid solution dendrites. The partial melted zone (PMZ) had eutectic ledeburit plus martensite microstructure, while the heat affected zone (HAZ) had only a martensite structure. It was also noticed that hardness and wear resistance of the alloyed layer was considerably higher than that of the substrate. Improvement of wear resistance is attributed to the solution strengthening effect of alloying elements and also the presence of hard carbides such as M23C6. Based on worn surface analysis, the dominant wear mechanisms of alloyed layer were found to be oxidation and delamination.

Enhancement of wear resistance of ductile iron surface alloyed by stellite 6

This paper deals with the improvement of the wear resistance of ductile iron surface alloyed by a hypoeutectic stellite 6 alloy. In this regard, the surface alloyed layer with 3mm thickness deposited on ductile iron using tungsten inert gas (TIG) surface processing. The microstructure, hardness and wear resistance of surface alloyed layer were investigated using optical microscopy, scanning electron microscope (SEM), energy dispersive spectroscopy (EDS), X-ray diffraction analysis, Vickers hardness (HV0.3) and pin-on-plate tests. The results showed that the microstructure of the surface alloyed layer consisted of carbides dispersed in a Co-based solid solution matrix with dendritic structure. This microstructure was responsible for the improvement of the hardness and wear resistance of the coating. Further investigations showed that the dominant mechanism of the wear in the coated and uncoated samples was delamination wear.

Structure and Properties of Ductile Iron Strengthened by Laser Surface Alloying

The wear resistance, corrosion resistance, high temperature resistance layers were prepared on the surface of ductile iron via laser alloying process, using the mixed ponder of sub-micron carbides power as starting materials. The microstructures of the different laser alloying layers were characterized by XRD, SEM, EDS, TEM. The microhardness and wear resisitance of the laser alloying layers were examined. The results reveal that the flat alloyed coating combines metallurgically with the substrate. the laser area was composed by alloyed zone ,heat-affected zone and matrix zone. The alloyed zone was composed mainly by ledeburite and carbide, while martensite and retained austenite were contained in the heat affected zone, there is no significant change in the Matrix zone. Under conditions that the laser power, spot diameter remain unchanged, with in 400 ~ 1000 mm/min scanning speed, the hardness of alloyed coating increases with increasing scanning speed. The weightlessness of the alloyed samples under the dry sliding friction is one-sixteenth of ductile iron. The wear resisitance of the alloyed coating has improved significantly.