SVUM (Czechia)

Abstract This study evaluates the surface protection of a waste-to-energy boiler wall using the Eutronic Arc Spray Gun 4 HFH. The test involved coating a 3.2 m² section of the boiler membrane wall with four materials: BTW 58 (FeCr-based), METCO 8294 (NiCrMo alloy), TAFALOY 71T (Inconel 625), and Metcoloy 4 (FeCr steel). Before spraying, the surface was grit-blasted to SA 3 finish with a roughness of 75–100 μm. Coatings were applied both with and without a Metco 8450 bonding layer. Additionally, two high-temperature ceramic coatings—Fireside and Tubearmor—were tested. The wear tests were conducted on-site in the boiler's third pass. After one year of exposure, samples were evaluated for condition, wear, and scale formation. BTW 58 and TAFALOY 71T, particularly when combined with Fireside ceramic coating, provided the most effective protection.

Most power plants use the Rankine cycle, where the heat supplied to water and steam is converted into mechanical work; therefore, most components have to be made of heat-resistant steel. Sufficient mechanical properties must be ensured for welded pipes to meet stringent requirements. Therefore, laser-welded 5 mm thick heat-resistant pressure vessel steel plates were subjected to various mechanical tests, including high-cycle fatigue tests. The microstructural notches were determined using X-ray diffraction too to determine critical areas that are susceptible to crack initialization and affect the service life. Finally, a functional model of the pressure vessel subsequently verified the results and assumptions. The presented results ensure the transferability of the results to real-life applications and outline the promising application potential of laser welding for producing vessels and pipes from heat-resistant steel in the industry.

Elementary nanofibrous layers show insufficient mechanical properties, especially tensile strength and abrasion resistance.In order to overcome these disadvantages, they are combined with carrier substrates and cover materials.A critical factor of the usability of nanofibrous layers in composite structures is to ensure sufficient adhesion between the carrier medium, the nanofibrous layer and the cover material.The adhesion between the layers is fundamental for the processability of the composite structures into the final products.To ensure sufficient adhesion of the individual components, additional adhesives are commonly used, which, in addition to the ecological burden, bring additional technological steps and costs to the production.One of the possibilities for achieving sufficient adhesion without the use of adhesives is the utilization of the physical component of adhesion by means of plasma activation of surfaces prior to electrospinning.

The commercial Al–Zn–Mg–Cu-based alloys (7xxx series) are widely used in metalworking, automotive and aircraft industries as well as in aeronautical applications. The positive effect of the Sc,Zr-addition on mechanical properties of laboratory Al-based alloys is generally known. The microstructure, mechanical and thermal properties of the conventionally cast, heat-treated and cold-rolled Al–Zn–Mg–Cu (–Sc–Zr) alloys during isochronal annealing and natural ageing were studied. Microstructure observation by scanning electron microscopy and transmission electron microscopy proved the Zn,Mg,Cu-containing eutectic phase at grain boundaries. The distinct changes in microhardness curves as well as in a heat flow of the alloys studied are mainly caused by dissolution of the clusters/Guinier-Preston (GP) zones and precipitation of particles from the Al–Zn–Mg–Cu system. An easier diffusion of Zn, Mg and Cu atoms along dislocations in the cold-rolled alloys is responsible for the precipitation of the Zn,Mg,Cu-containing particles at lower temperatures compared to the cast alloys. Microhardness values of the heat-treated alloys increase immediately from the beginning of natural ageing due to the formation of the clusters/GP zones. Addition of Sc and Zr elements results in a higher hardness above ~ 270 °C due to a strengthening by coherent secondary Al3(Sc,Zr) particles with a good thermal stability. Sc,Zr-addition has probably no influence on the evolution of the solute clusters/GP zones.

Pressure vessels made of high-strength steels are usually welded by arc methods. The paper deals with the development of laser and electron thick-walled beam welding technology for the mentioned applications. The mechanical and structural properties of laser and electron beam welds of plates with a thickness of 5–20 mm are compared both with and without additional filling material. The study is completed with a detailed analysis of residual stresses and their relation not only to the used welding technology but also to the results in the weld area. Laser and electron beam welds achieve high mechanical values and sufficient fatigue life. Therefore, the technology has been verified and applied for welding the test pressure vessel.

The positive effect of Sc,Zr-addition on mechanical properties in Al-based alloys preferred for automotive manufacture to produce lightweight vehicles is generally known. Microstructure, mechanical, electrical and thermal properties of the conventionally cast and homogenized (475 °C/60 min) Al-5.4wt.%Zn-3.1wt.%Mg-1.5wt.%Cu (7075) and Al-5.2wt.%Zn-3.0wt.%Mg-1.4wt.%Cu-0.2wt.%Sc-0.1wt.%Zr (7075-ScZr) alloys during isochronal annealing were characterized. Precipitation reactions were studied by microhardness, electrical resistivity and conductivity measurements, differential scanning calorimetry and positron annihilation spectroscopy. Microstructure observation by scanning and transmission electron microscopy proved the Zn,Mg,Cu-containing eutectic phase at grain boundaries in the alloys. The melting of this eutectic phase was observed at ~ 481 °C for the both alloys. The distinct changes in microhardness and electrical resistivity isochronal curves as well as in heat flow of the alloys studied are mainly caused by dissolution of the clusters/Guinier-Preston (GP) zones and by formation of the metastable phase particles of the Al–Zn–Mg–Cu system. Clusters/GP zones were formed during the cooling and/or in the course of the storage at room temperature. These clusters/GP zones were formed predominantly by Mg and Zn alloying elements. Hardening effect after isochronal annealing at temperatures above ~ 300 °C reflects the Sc,Zr-addition in both states of the 7075-ScZr alloy. Probably precipitation of the T-phase (Al2Zn3Mg3) and S-phase (Al2CuMg) particles took place during the annealing. The Sc,Zr-addition does not significantly influence precipitation of the particles formed in the Al–Zn–Mg–Cu system.

The effect of cold-rolling on mechanical and electrical properties, microstructure and recrystallization behaviour of the AlMn, AlScZr and AlMnScZr alloys was studied. The materials were investigated during isothermal annealing at 300, 400, 500 and 550°C and during step-by-step quasilinear annealing from 200°C up to 600°C with a heating rate of 100 K/h followed by subsequent isothermal annealing at 600°C/5 h. Precipitation reactions were studied by electrical resistometry and (micro) hardness measurements. The microstructure development was investigated by electron microscopy and electron backscatter diffraction examinations. The hardening effect is due to uniformly distributed Al3Sc and/or Al3(Sc,Zr) particles. The distinct changes in resistivity of the alloys above ∼ 300°C are mainly caused by precipitation of Mn-containing particles. It has a negligible effect on hardness. Phase transformations in the AlMn and AlMnScZr alloys are highly enhanced by cold rolling. The precipitation is dependent on the deformation degree – the more deformation the more intensive precipitation of the Mn-containing particles. The combination of Mn, Sc and Zr additions to Al substantially suppresses recrystallization at 550°C. A partial recrystallization was observed in the AlScZr alloy and AlMnScZr alloy after annealing 550°C/60 min and 550°C/760 min, respectively. The decomposition sequence of the supersaturated solid solution of the AlMnScZr alloy is compatible with the decomposition sequence of the AlScZr system accompanied and/or followed by the formation of Mn-containing particles.