Revista de Metalurgia

Wear performance of GGG60 ductile iron rollers coated with WC-Co by electro spark deposition

Mustafa Buğday — 2023-12-30

Nodular cast irons are used in many industrial applications such as machine frames and body, rollers and engine blocks due to their higher strengths and ductility with good machinability comparable to grey cast irons. In this study, the outer surface of nodular cast irons (GGG-60) was coated with WC/Co using electro spark deposition (ESD). The aim of the study is to improve both the surface quality and wear behaviour with the coatings formed on the surface of the plastic deformation rollers, whose wear resistance decreases over the time due to high stress working conditions. Heat treatment at 950 ºC for 2 h was applied to the GGG60 specimen rollers and half of the rollers were uncoated and the other half was coated with WC-Co electrodes. The wear behaviour of the heat treated and coated surfaces was measured by ball-on-disc wear method using Al₂O₃ ball bearing with a diameter of 6 mm for a sliding distance of 250 m at a sliding rate of 6.5 m·s^-1 under a dry condition, and using a load of 40 N. WC/Co coatings were successfully applied to rollers. In the SEM/EDS images, the presence of W, Fe, C, Co and Al elements in the coated part of the rollers and Fe, C and Al elements in the uncoated region were detected. It was concluded that Coating and heat treatment increased the wear resistance by nearly 5 times and decreased the friction coefficient by 2.13 times.

Characterization of iron nugget produced from iron ore concentrate in a microwave oven using a biomass-based reductant

Mustafa Boyrazli — 2023-12-30

This study is concerned with the characterization of iron nuggets obtained from the reduction of an iron oxide concentrate in a microwave oven using a biomass-based reducing agent. In the experiments, the concentrate of iron ore consisting of hematite and magnetite minerals supplied from Elazig region and containing 67.29% Fe after enrichment, and as a reducing agent, tea plant wastes containing 94.68% C and 0.03% S after carbonization was used. Carbon required for the reduction of iron oxides to iron was stoichiometrically added to the concentrate with a grain size of -45 µm after its basicity ratio was adjusted. The composite pellets produced after the addition of reducing agent and flux (CaO) were subjected to reduction in a household microwave oven at different times. After the process, optimum (Fe₃O₄+Fe₂O₃)/C=1/4, basicity ratio (CaO+MgO)/(SiO₂+Al₂O₃) =1.2 results were obtained. It was seen that the metallic part contained 96.6% Fe, 2.4% C after being separated from the slag and that the metallic phase was separated from the slag very easily. As a result of the microstructure investigations, it was found that the product obtained had similar properties to white cast iron properties.

Characterizing the mechanical deformation response of AHSS steels: A comparative study of cyclic plasticity models under monotonic and reversal loading

Toros Arda Akşen — 2023-12-30

This study evaluates the performance of a user-defined combined hardening modeling method for advanced high-strength steels (AHSS) under monotonic and reversal loading conditions. The plastic behavior of TWIP980 and TRIP980 AHSS sheet metals is investigated using a cyclic plasticity modeling approach. The model incorporates an isotropic von Mises yield criterion and a single-term Chaboche nonlinear kinematic hardening rule. Monotonic and reversal loading stress-strain curves are predicted and compared with experimental results. The model accurately captured the Bauschinger effect for both materials, but it needs help to effectively model the permanent softening behavior observed in TWIP980 steel. Overall, the proposed modeling method agrees well with experimental results for monotonic loading and accurately represents the Bauschinger effect and transient behavior during reversal loading. However, better improvements are needed to capture the permanent softening behavior of TWIP980 steel.

Study on mechanical and micro structural properties of spin arc welding in Hastelloy C-2000

Ilavarasan Karthic Subramaniyan — 2023-12-30

Nickel-based Hastelloy C-2000 is widely used in the aerospace, chemical, and medicinal sectors. Investigating the potential efficacy of the spin arc welding process on Hastelloy C-2000 was the main focus of this study. In spin arc welding the centrifugal force has been obtained in the fusion zone, thus the weldbead quality increases. Weld current, rotating speed, and spin diameter are all separate parameters used in the welding procedure. The microstructural investigation was carried out using optical microscopy, X-Ray Diffraction (XRD), and field emission scanning electron microscopy (FESEM). The mechanical characteristics of the welded specimens were examined closely. Spin Arc Welding ultimate tensile strength (UTS), hardness value (HV), and impact experiments were compared to those of the Multi-pass Pulsed Current Gas Tungsten Arc welding method (MPCGTAW). In 27 tests, increasing the current and rotating speed resulted in greater penetration depth and weld height. The width of the weld was found to be a little high, with a spinning diameter of 2 mm. In comparison, samples 5 and 15 were found to have better hardness, tensile strength, and toughness, especially with suitable welding parameters such as current (120 I and 140 I), speed (1800 rpm), and spin diameter (2 mm and 3 mm). A microstructural study showed no grain segregation, contributing to the material’s increased hardness and tensile strength. The novel findings of the present study suggest that spin arc welding might be superior for various Hastelloy C-2000 connections that might have great applications in industries.

Investigations on microstructure, hardness and tribological behaviour of AA7075-Al2O3 composites synthesized via stir casting route

Mathusoothana Perumal Ezhilan — 2023-12-30

Aluminium matrix composite (AMC) materials play an important role in the field of automobile and aerospace industries due to their excellent properties. In this research, aluminium alloy (AA7075) was reinforced with alumina (Al₂O₃) particles to improve their hardness and tribological behaviour of the base alloy. Four composites were prepared by varying the content (4, 8 and 12 wt.%) of Al₂O₃ particles through the stir casting technique. The surface morphology of the proposed composites ensured the uniform distribution of Al₂O₃ particles into the matrix alloy. The hardness of the composite was measured using a Brinell hardness tester and the maximum value of hardness was found in the AA7075 - 8 wt.% Al₂O₃ composite. Hence, a tribological investigation was carried out on this AA7075 - 8 wt.% Al₂O₃ composite. Load (P), sliding speed (V) and sliding velocity (D) were taken as the wear parameters for conducting the experiments. A Technique for Order Preference by Similarity to Ideal Preferred Solution (TOPSIS) approach has been applied to find out the optimal conditions of parameters to obtain the lowest wear rate (WR) and the co-efficient of friction (COF). The results showed that the lowest WR and COF was obtained at ‘P’ of 15 N, ‘V’ of 1 m•s^-1 and ‘D’ of 1000 m•s^-1. ANOVA results revealed that ‘P’ is the factor with the most significant contribution (38.36%), followed by ‘D’ (28.32%). The worn surface morphology of the confirmation experiment specimen was investigated by SEM and the wear mechanism was reported.