•A successful laser cladding of Ni-based alloy on gray cast iron was achieved.•The impact of laser parameters and microstructure on crack formation was studied.•An empirical relation for dilution ...ratio versus energy density was proposed.
This study aimed to investigate the influence of process parameters on crack formation in laser alloying or cladding of grey cast iron. For this purpose, the effects of laser power and feeding rate of Ni-based alloying powders were examined. The microstructure and hardness of the coating and the interface of the coating with cast iron (bonding zone) were studied. The results showed that the dilution ratio is crucial in crack formation, explaining the challenges in achieving a defect-free laser alloying coating on cast iron. The higher dilution ratio of laser alloying resulted in higher dissolved carbon and bigger (Nb, Ti)C carbides formation than in laser cladding coatings. In this study, cracks appeared in the coating due to the combination of the high amount of carbide in the layer and a sharp hardness gradient at the interface with the cast iron substrate. An empirical relation was proposed for dilution ratio as a function of specific energy density, which combined the most critical process parameters on crack formation.
The present research studied the combined effects of quench-tempering and laser surface hardening treatments on wear behavior of gray cast iron, and compared results with conventional austempered ...gray cast iron. Four tempering temperatures of 316 °C (600 °F), 399 °C (750 °F), 482 °C (900 °F) or 552 °C (1025 °F) with a constant holding time of 60 min and four austempering temperatures of 232 °C (450 °F), 288 °C (550 °F), 343 °C (650 °F) or 399 °C (750 °F) with a constant holding time of 120 min were utilized in the heat treatment design. The wear tests were carried out on a universal mechanical tribometer with a reciprocating ball-on-plate sliding configuration. Also, the microstructure, micro-hardness profiles and worn tracks were examined. Through this work, it was found that three zones existed under the laser hardened surface. Zone 1 was the laser hardened zone containing ledeburite with hardness of approximately 68HRC. Zone 2 was the heat affected zone containing the martensite with hardness of approximately 66HRC. Zone 3 was the substrate with hardness ranging from 42.1 to 24.8HRC. In the sliding wear tests, the quench-tempering treatment only resulted in higher wear resistance of gray cast iron when compared with untreated specimens, but lower wear resistance than that of austempered gray cast iron under similar macro-hardness. The wear performance of the quench-tempered gray cast iron was enhanced after receiving the laser surface hardening treatment. Finally, the laser hardened and quench-tempered gray cast iron with tempering temperature of 552 °C showed similar mass loss due to wear as austempered gray cast iron with an austempering temperature of 232 °C. By observing the worn surfaces, the laser hardened regions could effectively inhibit the formation and propagation of cracks developed within the substrate regions. In addition, the substrate with low hardness in laser hardened and quench-tempered gray cast iron may provide enhanced ductility and toughness for gray cast iron engineering components. The results obtained in this research have significant value in selecting the optimum heat treatment process for laser hardened gray cast iron components.
This study employed friction and wear experiments on nitrocarburized HT250 gray cast iron, utilizing GCr15 cemented carbide balls as the friction pair, to investigate the friction behavior and wear ...mechanism of the compound layer, diffusion layer, and matrix. The findings indicate that the diffusion layer exhibits the highest wear resistance, followed by the compound layer, while the matrix shows the lowest wear resistance. At lower loads, the wear form of the compound layer is characterized by minor flaking wear, the diffusion layer exhibits minor flaking and abrasive wear, and the matrix displays minor adhesive wear accompanied by abrasive wear. With increasing loads, the wear form of the compound layer transitions to flaking and abrasive wear, the diffusion layer shows fatigue flaking wear, and the matrix demonstrates severe adhesive wear, fatigue flaking wear, and abrasive wear. Electrochemical impedance spectroscopy and potentiodynamic polarization were employed to study the corrosion behavior of the compound layer, diffusion layer, and matrix in a 3.5 wt% NaCl solution. The results indicate a 27.7 % decrease in the corrosion current density of the compound layer compared to the matrix, with the diffusion layer exhibiting a corrosion current density two orders of magnitude lower than both the matrix and compound layer. In electrochemical impedance spectroscopy, the diffusion layer shows the highest impedance modulus, largest phase angle amplitude, and circular arc radius. It shows that the corrosion resistance of HT250 gray cast iron is improved after nitrocarburizing, especially the diffusion layer.
The high-temperature interaction between molten gray cast iron and Ti + C substrates that are composed of titanium and graphite powders was investigated by the sessile drop method combined with the ...non-contact heating of an alloy/substrate couple to a test temperature of 1330 °C in an inert gas atmosphere (argon). During the high-temperature testing, the images of the couple were recorded by a high-speed high-resolution CCD camera and used for estimating the values of the contact angles over time. An analysis of the wettability kinetics of the different Ti + C substrates by molten cast iron as well as a detailed structural characterization of the solidified couples with the help of light microscopy, electron microscopy (SEM, TEM), X-ray diffraction, and energy-dispersive X-ray spectroscopy have allowed us to explain the mechanism of high-temperature interaction in the selected couples. It was evidenced that the good wetting and fast infiltration of all of the examined substrates with the selected alloy had a reactive nature due to the dissolution of the Ti and graphite in the molten alloy (dissolutive wetting) and the reactively formed wettable TiC phase. These high-temperature phenomena contributed to the formation of three metal-infiltrated zones with different amounts and distributions of TiC particles in the Fe-based matrix.
•A TiC reinforced coatings were obtained by laser cladding with Cu-Ti-Ni powder.•The matrix of the coating was alloy γ-Fe, acicular martensite, and α-Cu.•The formation and evolution of TiC are ...revealed.•Laser parameters had a significant effect on the track shape and quality.•Microhardness and wear mechanism of the coatings were better than the substrate.
To improve the wear resistance of gray cast iron and the quality of the laser cladding coating, a composite coating was designed and produced using Cu-Ti-Ni blending powder on the surface of gray cast iron by fiber laser cladding system. The phase constituents and microstructure of the composite coating were investigated using X-ray diffraction (XRD) and scanning electron micrograph (SEM). Microhardness and wear resistance of the coatings were evaluated. The experimental results indicated that TiC reinforced composite coating was produced and the matrix of the laser cladding zone composed of alloy γ-Fe, acicular martensite, and α-Cu. Microscale TiC particles were synthesized in the laser melted pool using the graphite phase of the substrate and the titanium atom of the blending powder. The surface properties of gray cast iron was improved by TiC reinforced comppsite coating. The microhardness of the laser cladding zone was approximately 2 to 3 times that of the substrate and the wear resistance of the coating was significantly improved. The wear mechanism of the coating was adhesive wear and abrasive wear because the matrix was soft alloy γ-Fe and α-Cu. The coating could significantly improve the performance of grey cast iron under severe service conditions.
Directed energy deposition (DED) based remanufacturing leverages the flexibility of additive manufacturing to add value to broken or worn components. DED offers the ability to repair cast iron, a ...material difficult to repair with traditional welding techniques. Despite this, development of appropriate DED process conditions for bimetallic cast iron structures lags low- and medium-carbon steel repair. Thermal stresses and porosity generated by high-temperature deposition on cast iron often lower mechanical properties and hinder the qualification process. In this report scanning speed, powder mass flow rate, and stepover width are studied in multiple-track structures deposited on gray cast iron. Dilution and residual stresses are found to be highly dependent on the selected process parameters. Samples with a higher volumetric energy input, e.g., slower scanning speeds and higher powder feed rates, showed improved density and lower residual stresses but suffered lower dilution into the substrate. The presented conditions further the development of additive manufacturing technologies for automotive repair.
Addition of rare metal is an interesting way of microstructural controls. Herein, this study employed niobium to tailor the microstructure of gray cast iron, and further to control the tribology ...properties. Four casting discs with various niobium contents (0~0.31wt.%) were prepared to slide against one certain resin-based friction material. Friction test was performed on a 1:5 scale brake inertia dynamometer under different conditions. Results revealed the significance of niobium concentration on the microstructure by influencing the solidification process. Consequently, a modification to the mechanical and thermal properties was achieved, which was responsible for subsequent tribology behavior. Overall, 0.20wt.% was defined as the optimized formulation of a lower sensitivity to operating conditions, higher brake efficiency, and higher wear resistance.
•Microalloying element niobium addition was used to tailor the microstructure of gray cast iron.•Role of niobium addition in tribology performance of gray cast iron matched with resin based friction material was studied.•The relationship between physical properties (mechanical and thermal properties) and tribology performance was developed.•The sensitivity to speed/load/temperature was explored.•The tribology behavior was studied by analyzing the worn surfaces of friction couples.
•The effect of austempering temperatures on the mechanical properties is studied for gray cast iron.•The fatigue strength increases and the tensile strength decreases with the increase of ...austempering temperature.•The relation between tensile and fatigue strengths is discussed and explained by mechanism of damage.
It is generally accepted that the mechanical properties of gray cast iron (GCI) can be enhanced by microstructure refinement, while this perhaps needs to be reconsidered to improve the fatigue properties treated by austempering technology. Although the maximum tensile strength can be up to 480 MPa for austempered gray iron (AGI) with finer bainite fabricated by austempering transformations, the value of fatigue strength is less than the coarse counterpart with lower tensile strength. This suggests that tensile strength can be effectively improved by microstructure refinement, while fatigue cannot. It is mainly attributed to the initial defects induced by graphite and the structural toughness increased by austenite in AGI. Therefore, the general relationship between tensile strength and fatigue strength of GCI and AGI was investigated and the roles of fitting parameters were analyzed. The inverted relation provides some new insights into the fatigue strength optimization of GCI.
This study aims to determine the effect of welding current on the mechanical properties and microstructure of graycast iron welding joints using nickel electrodes with the SMAW welding process. The ...research method used wasexperimental study, starting with preparing the workpiece, welding process, making test specimens and testing the weldspecimens. The material to be joined is gray cast iron metal with a butt joint of a 60 ° open seam V open angle. The weldingprocess used uses SMAW with a current of 80 Amperes, 85 Amperes and 90 Amperes. The added material used was anENiFe-Cl type CIN 2 electrode with a diameter of 2.6 mm. Hardness testing was carried out using the Vickers method andmicrostructure testing using an optical microscope. The results showed that the maximum hardness value of the parentmetal occurred at the welding current strength of 85 Amperes, which was 192.17 VHN, then the maximum hardness value ofthe HAZ area occurred at the welding current strength of 85 Amperes, which was 203.46 VHN, while the maximumhardness value of the weld metal was 203.46 VHN. metal) occurred at a welding current of 90 Amperes, which was 211.18VHN. The results of the microstructure observation showed that the matrix formed on the parent metal was pearlite withgraphite in the form of flakes. The micro structure formed in the HAZ area was a martensite structure. Meanwhile, themicrostructure of weld metal consists of an austenite matrix with an even distribution of graphite particles.
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