Key Engineering Materials Vol. 856

Abstract: To facilitate the assessment of the oxide stability in H₂-H₂O or CO-CO₂ atmospheres, auxiliary axes are constructed in the Ellingham diagram. Based on A. Ghosh’s approach, the geometrical interpretation of the diagram is proposed for the reaction 2X + O₂ = 2Y, where X and Y could be originated from H₂ and H₂O or CO and CO₂. Two cases are considered when oxygen partial pressures are lower and higher than one bar. By a geometrical method, it is proved that with an appropriate set-up of values relating to the auxiliary axes, the axes representing the ratio between the equilibrium partial pressure of hydrogen and that of water vapour, as well as the ratio between the equilibrium partial pressure of carbon monoxide and that of carbon dioxide, can be constructed. The geometrical method on the construction of axes using thermodynamic derivation is explained in the paper.

Abstract: The carbon dissolution of coke pieces in hot metal mainly influences the carbon content and carbon saturation temperature in the ironmaking process. The liquid metal and slag start to drop down in the dripping zone (DZ) which is located the lower part of blast furnaces. The dissolution of carbon in liquid metal and slag droplets passing the stagnant hot gas flow in the fixed coke bed of the dripping zone were observed by a multi-droplet model based on the Computational Fluid Dynamics (CFD) method. The uniform-coke pattern was set in the model following the preferred distribution of a one-layer packed bed from a water droplet experiment. The different coke shapes relating to the shape factor from 0.75-1.0 were observed in a 40mm-coke bed. For one-time drainage, the carbon dissolution slightly increased after flow in the coke bed zone and showed a high percentage on the coke surface. The concavity and convexity of coke pieces have more effect on the interaction between liquid and coke surface. Besides, the carbon dissolution can be investigated to approach the coke consumption in one coke channel and estimate the carbon content and carbon saturation temperature of liquid metal after draining.

Abstract: Commercial F91 steel was exposed to atmospheric pressure CO₂ and laboratory air at 550 °C for exposure times up to 1000 h. In both atmospheres, a Fe-rich duplex oxide scale formed, but with different morphology, oxide phases and growth rates. In CO₂, the duplex morphology was observed at the onset of oxidation and it was found that the cooling rate affect the oxide phases formed on the outer scale. In air, the alloy initially formed a protective chromium rich oxide layer, followed by the nucleation and growth of duplex iron-rich oxide nodules at random locations, leading to breakaway oxidation. Alloy carburization was also observed in CO₂ but not in air environment.

Abstract: AISI 304 austenitic stainless steel specimens are oxidised in laboratory air at 750 °C for 48 h. They are further subjected to the reduction test in carbon at 1350 °C for 30 and 60 min. The results show that the mass gain of the oxidised AISI 304 slighter increases to be 0.08 mg cm^–2 after the reduction for 30 min and is unchanged at the longer reduction period up to 60 min. The oxide on AISI 304 is deteriorated after the reduction but its morphology tends to be unchanged when the reduction period is longer from 30 to 60 min. The results then indicate the superior performance of the AISI 304 to combat the corrosion under carbon at this high temperature.

Abstract: Aluminium matrix composites (AMCs) have emerged as the substitute for the monolithic (unreinforced) materials over the past few decades. The applications of AMCs are common in automotive, aerospace, defence and biomedical sectors due to its lower weight, high strength, high resistance against corrosion and high thermal and electrical conductivity. In this work, it is aimed fabricate a new class Al 7075 based hybrid composites reinforcing with nanoparticulates suitable for automotive application. Al7075 reinforced with fixed quantity of boron carbide (B₄C) (1.5 wt.%) and varying wt % of flyash (0.5 wt.%, 1.0 wt.%, 1.5 wt.%) is fabricated using ultrasonic-assisted stir casting technique. Physical and mechanical characterization such as density, porosity, micro hardness, tensile strength and impact strength were estimated for three different compositions. The tensile strength and percentage increase in hardness value of the nanocomposite Al7075-B4C (1.5 wt. %)-flyash (0.5 wt. %): HNC3 found maximum as 294 MPa and 32.93%. In comparison with Al7075 alloy the impact strength of HNC3 shows the highest percentage of 9.31% respectively.

Abstract: This work investigates the effect of rejuvenation heat treatment, with double-step solution treatment at the temperature from 1150 °C to 1200 °C, on the recovered microstructure of IN-738 cast superalloy. The superalloy has been long-term exposed as a turbine blade in a gas turbine prior to this study. After double solution treatment and aging at 845 °C for 12 h and 24 h, the recovered microstructures were examined by using a scanning electron microscope. Coarse γ΄ particles, that have presented in damaged microstructures, could not be observed in the samples after the rejuvenation heat treatment. In addition, the image analysis illustrates that the reprecipitated γ΄ particles in the samples with double-step solution treatments increase significantly in sizes during aging than that in the samples with the single-step solution treatment. Furthermore, the measurement of the samples hardness presents that the as-receive sample hardness is improved after rejuvenation heat treatment studied in this work.

Abstract: Machining is one of the major manufacturing processes that converts a raw work piece of arbitrary size into a finished product of definite shape of predetermined size by suitably controlling the relative motion between the tool and the work. Lately, machining process is shifting towards high speed machining (HSM) from conventional machining to improve and efficiently increase production, and towards dry machining from excessive coolant used wet machining to improve economy of production. And the tools used are mostly hardened alloys to facilitate HSM. The work piece materials are continually improving their properties by emergence and development of newer and high resistive super alloys (HRSA). In this paper an attempt has been made to validate an experimental result of cutting force obtained by performing HSM on an HRSA Inconel 718, by comparing it with the numerical result obtained by simulating the same setting using DEFORM 3D software. Based on the comparison it is found that the simulated results exhibit close proximity with the experimental results validating the experimental results and the effectiveness of the software.

Abstract: The finite element-based machining simulations for evaluation/computation of different machining responses (i.e., cutting temperature, tool wear, cutting force, and power/energy consumption) are investigated by number of researchers. In this work, finite element machining simulation was performed to obtain knowledge about cutting forces during machining of hard materials. Titanium alloy (Ti-6Al-4V) has been increasingly used in aerospace and biomedical applications due to high toughness and good corrosion resistance. The high speed machining (HSM) simulation of Ti-6Al-4V work-piece using carbide tool coated with TiCN has been conducted with different combination of cutting conditions for prediction of main cutting force (Fz). The simulated result obtained from Deform 3D software is validated with experimental result and it was found that the result found in good agreement. The parametric variation shows that depth of cut and feed are influencing parameters on cutting force.

Abstract: In this work, four fracture criteria—namely, Fracture Forming Limit Curve (FFLC), Fracture Forming Limit Stress Curve (FFLSC), Fracture Locus (FL) and Fracture Locus Embedded with Bao-Wierzbicki Ductile Damage Criterion (BW-FL)—are comparatively deployed to forecast breakage of deformed AA2024-T3 sheet aluminium-alloy. An FFLC can be experimentally formed by conducting a set of Nakajima stretch-forming based tests. To obtain an FFLSC, such an FFLC drawn in the strain space has to be entirely mapped onto the stress space. This can computationally be accomplished with the help of those well-known plasticity-relevant models like the Hill’48 anisotropic yield criterion and the Swift hardening law. Likewise, both BW-FL and FL in terms of stress triaxialities and critical plastic strains can mathematically be derived from the FFLC incorporated with the Hill’48 anisotropic yield criterion. Hole expansion and tree-point bending tests are carefully carried out both experimentally and simulatively to verify those four generated fracture limits. The more innovative FFLSC and FL demonstrate more accurate prediction on rupture of AA2024-T3 sheet aluminium-alloy than the conventional FFLC. The BW-FL however performs the worst.