In this work, alumina (Al₂O₃) ceramics were prepared using an environmentally friendly slip casting method. To this end, highly concentrated (70 wt.%) aqueous suspensions of alumina (Al₂O₃) were prepared with different amounts of the ammonium salt of a polycarboxylic acid, Dolapix CE 64, as an electrosteric dispersant. The stability of highly concentrated Al₂O₃ aqueous suspensions was monitored by viscosity measurements. Green bodies (ceramics before sintering) were obtained by pouring the stable Al₂O₃ aqueous suspensions into dry porous plaster molds. The obtained Al₂O₃ ceramic green bodies were sintered in the electric furnace. Analysis of the effect of three sintering parameters (sintering temperature, heating rate and holding time) on the density of alumina ceramics was performed using the response surface methodology (RSM), based on experimental data obtained according to Box–Behnken experimental design, using the software Design-Expert. From the statistical analysis, linear and nonlinear models with added first-order interaction were developed for prediction and optimization of density-dependent variables: sintering temperature, heating rate and holding time.

The paper investigates the effects of DC plasma nitriding on surface roughness, hardness, microstructure, micro-abrasion, and corrosion resistance of AISI 316L Austenitic Stainless (AS) steel. The nitriding has been conducted for durations ranging from 4 to 24 h at a temperature of 430 °C in a commercial vacuum furnace, Rübig PN90/70. Micro-abrasion resistance has been tested using the calotest device with a measurement diameter of craters produced on the sample surface after 10 to 60 s of wear. Corrosion resistance has been tested using the Electroimpedance Spectroscopy (EIS) method in a 3.5% NaCl water solution. The surface roughness parameters and hardness of the samples increased with longer nitriding times, attributed to the saturation of austenite and the formation of iron and chromium nitrides. Nitriding for longer than 8 h resulted in the formation of a thicker compound layer that is hard and brittle, leading to reduced wear resistance compared with shorter nitriding times. EIS measurements revealed that nitrided samples had lower corrosion resistance compared with the untreated sample. The corrosion stability was not significantly affected by nitriding time. Different nitriding times have a great influence on resistance to pitting corrosion. This study provides valuable insights into the effects of plasma nitriding on the properties of AS steel, highlighting the importance of optimizing nitriding parameters for specific applications.

The aim of a joint project between the Stiftung Institut für Werkstofftechnik, Bremen (IWT), the company Ipsen International, and the Faculty of Mechanical Engineering and Naval Architecture (FMENA), the University of Zagreb is to develop a computer program for prediction of hardness on the axial section of axially-symmetrical workpieces of any complex shape, thereupon high pressure gas quenching. The hardenability for the specimens made of tool steel grade EN-90MnCrV8 and the cooling dynamics under two gas pressures are measured using the unique facility at IWT. With developed computer simulation model, the cooling curves at different positions (J) along the end-quenched specimen are determined. Based on them, the cooling time from 800 to 500°C (t _8/5) is determined, and the curves J = f(t _8/5) are derived for different quenching conditions. This curves together with curves of hardness distributions along the end-quenched specimens can serve for the prediction of hardness distribution on the cross-sections of a batch of workpieces cooled in vacuum furnace.

A series of quenching experiments was performed according to the ISO 9950, ASTM 6200-01, and ASTM D6482-06 standards. Water based nanofluids with 0.01, 0.1, and 0.2 g/L TiO₂ were prepared using a two-step method and ultrasonic homogenization. The nanofluids were tested to see the possibility of their application as high temperature heat transfer fluids. Nanoparticles used in this series of experiments were 50 nm in diameter. All of the cooling curves were recorded and analyzed using the ivf SmartQuench system. The first set of experiments was conducted under still conditions according to the ISO 9950 standard. Pure water and nanofluids were investigated. The addition of nanoparticles showed an effect on the full film phase duration, an increase in the maximum cooling rate, and a change in transition temperature. A second series of quenching experiments was conducted according to ASTM D 6482-06. For this purpose, a quenching bath with agitation was built at the QRC. Three levels of agitation were tested: one according to the standard, 1000 rpm, one below, and one above the specified speed. Experiments with pure water and all three nanofluids were conducted and cooling curves recorded. The cooling curves were analyzed using software ivf SQintegra ver4.0. The effects of agitation and nanoparticles contents on cooling characteristics were compared.

The volume erosion rate of the slip cast monolithic and composite ceramics was studied using SiO ₂ and SiC particles as erodents, under different impact angles (30°, 60°, 90°), at room temperature. Therefore, three groups of samples were prepared: (i) monolithic alumina (Al ₂ O ₃ ); (ii) composite alumina–zirconia (Al ₂ O ₃ –ZrO ₂ ) containing 99 wt-% Al ₂ O ₃ and 1 wt-% ZrO ₂ and (iii) composite alumina–zirconia (Al ₂ O ₃ –ZrO ₂ ) containing 90 wt-% Al ₂ O ₃ and 10 wt-% ZrO ₂ . Erosion mechanisms of all prepared ceramic samples were evaluated by the volume erosion rate ([ ], mm ³ ·g ^–1 ). Obtained results were compared with the analytical Wiederhorn and Evans equations. The mechanical properties (hardness and fracture toughness) of prepared ceramic samples were compared with their [ ] under the above-mentioned conditions. It was found that the erosion of monolithic and composite ceramics increased with the increase of the impact angle. Volume erosion rate was highest at an impact angle of 90° and amounts to 115 mm ³ ·g ^–1 with SiC, and 12 mm ³ ·g ^–1 with SiO ₂ erodent particles for monolithic alumina ceramics, 77 mm ³ ·g ^–1 with SiC, and 8 mm ³ ·g ^–1 with SiO ₂ erodent particles for ceramics with the addition of 1 wt-% of ZrO ₂ , and 61 mm ³ ·g ^–1 with SiC, and 7 mm ³ ·g ^–1 with SiO ₂ erodent particles for ceramics with the addition of 10 wt-% of ZrO ₂ . Therefore, it can be concluded that the erosion resistance of monolithic Al ₂ O ₃ increases with the increasing amount of ZrO ₂ in the composite Al ₂ O ₃ -ZrO ₂ ceramics, thus erosion resistance can be improved with the addition of ZrO ₂ .

One of the main challenges in welding aluminium concerns structural integrity and a significant reduction in mechanical properties in the region adjacent to the weld. Design provisions can result in a drastic reduction, which may exceed 50% of the base metal resistance. This research aims to evaluate the accuracy of the HAZ extent values codified in Eurocode 9 for T-connections fabricated from artificially aged 6082 aluminium alloy, which is widely used in load-bearing structures. Three plate thicknesses (6, 8 and 10 mm) and two pulsed MIG welding processes (DC-MIG-P and AC-MIG-P) were used to fabricate 20 T-connection specimens (10 different configurations) in accordance with EN 1090-3. The study focuses on characterising the welding zones through hardness testing and metallographic examination. Results show that AC-MIG-P offers better control over thermal input and may reduce structural distortion, while DC-MIG-P provides more robust fusion and metallurgical continuity. Findings related to HAZ extent (12.77 mm and 15.36 mm maximum measured for AC-MIG-P and DC-MIG-P, respectively) suggest that Eurocode 9 may be overly conservative for pulsed MIG welding processes, particularly for greater plate thicknesses where a HAZ extent of 22.50 mm or more is specified. Consequently, adopting more precise, process-specific HAZ characterisations could lead to more realistic connection design and structural behaviour.