P. Bała

Electrophoretic deposition of organic/inorganic composite coatings containing ZnO nanoparticles exhibiting antibacterial properties

To address one of the serious problems associated with permanent implants, namely bacterial infections, novel organic/inorganic coatings containing zinc oxide nanoparticles (nZnO) are proposed. Coatings were obtained by electrophoretic deposition (EPD) on stainless steel 316L. Different deposition conditions namely: deposition times in the range 60-300s and applied voltage in the range 5-30V as well as developing a layered coating approach were studied. Antibacterial tests against gram-positive Staphylococcus aureus and gram-negative Salmonella enteric bacteria confirmed the activity of nZnO to prevent bacterial growth. Coatings composition and morphology were analyzed by thermogravimetric analysis, Fourier transform infrared spectroscopy, scanning electron microscopy and energy dispersive X-ray spectroscopy. Moreover, the corrosion resistance was analyzed by evaluation of the polarization curves in DMEM at 37°C, and it was found that coatings containing nZnO increased the corrosion resistance compared to the bare substrate. Considering all results, the newly developed coatings represent a suitable alternative for the surface modification of metallic implants.

3D reconstruction and characterization of carbides in Ni-based high carbon alloy in a FIB-SEM system

Abstract Dual beam focused ion beam scanning electron microscopes (FIB-SEMs) are well suited for characterizing micron and submicron size microstructural features in three dimensions throughout a serial-sectioning experiment. In this article, a FIB-SEM instrument was used to collect morphological, crystallographic, and chemical information for an Ni–Ta–Al–Cr alloy of high carbon content. The alloy has been designed to have excellent tribological properties at elevated temperatures. The morphology, spatial distribution, scale, and degree of interconnection of primary carbides in the Ni–Ta–Al–Cr–C alloy was assessed via serial sectioning in a casting cross-section. The 3D reconstructions showed that the primary carbides and dendrites were forming a dendrite surrounded by primary carbide network over the entire cross-section. Additionally, the morphology and spatial distribution of secondary carbides after heat treatment was determined.

The Influence of Cooling Rate During Crystallization on the Effective Partitioning Coefficient in High-Entropy Alloys from Al-Ti-Co-Ni-Fe System

An influence of two different cooling rates on the microstructure and dispersion of the components of high-entropy alloy from Al-Ti-Co-Ni-Fe system has been examined. For investigated alloys, the effective partitioning coefficient has been calculated. This factor indicates the degree of segregation of elements and allows for the specification of the differences between dendrites and interdendritic regions. The obtained results allow for the conclusion that the cooling rate substantially affect the growth of dendrites and the volume fraction of interdendritic regions as well as the partitioning of elements in the alloy. Furthermore, the obtained results made it possible to compare the influence of the cooling rate and the chemical composition on the dispersion of the alloying elements.

Fracture toughness of steels with nickel content in respect of carbide morphology

Abstract This paper is focused on the influence of Ni addition on the microstructure and fracture toughness of structural steels after tempering. Nickel is known to increase the resistance to cleavage fracture of steel and decrease a ductile–brittle transition temperature. The medium carbon, low alloy martensitic steels attain the best combination of properties in low tempered condition, with tempered martensite, retained austenite and transition carbides in the microstructure. In the present research, four model alloys of different Ni contents (from 0·35 to 4·00%) were used. All samples were in as quenched and tempered condition. Quenching was performed in oil at room temperature. After quenching, samples were tempered at 200°C for 2 h. An increase in nickel content in the investigated model structural steels causes a decrease in ε carbide volume fraction in their microstructure. Cementite nucleates independently in the boundaries of martensite laths and in the twin boundaries in the areas where the ε carbide has been dissolved. It was stated that stress intensity factor KIc significantly decreases in the case of the presence of dispersive elongated cementite precipitations at the boundaries of the prior austenite grains.

Strain-induced martensite reversion in 18Cr–8Ni steel – transmission Kikuchi diffraction study

ABSTRACT Reverse transformation of strain-induced martensite (SIM) was studied in the 18Cr–8Ni stainless steel. Microstructure analysis was performed on samples in an as-deformed state and after reversion annealing at 873 and 973 K, using the transmission Kikuchi diffraction. The primary, as well as reversed, austenite possesses the Kurdjumov–Sachs crystallographic orientation relationship, with respect to the SIM. The reverted austenite keeps one orientation within all reverted grains, regardless of the applied heating procedure, where the amount of reverted austenite depends only on the annealing temperature.

Analysis of Phase Transformations of Supercooled Austenite in Low-Alloy Steel with Boron Additives

Adiagram of transformations in low-alloy boron-containing steel B27 with high resistance to abrasive wear is plotted under continuous cooling. Chemical, metallographic and dilatometric analyses are performed, and the hardness of the steel is measured. Continuous cooling curves are obtained from the temperature of austenitization at a rate of 0.17 – 25 K/sec in the temperature range of 800 – 500°C.

T-Shape Connector Hydroforming Process Analysis

The work is focused on hydroforming of T-shape connector for high temperature applications. A seamless part for use in industrial applications was formed in a high pressure liquid extrusion process. Due to the occurrence of faults in the final products, numerical simulations were conducted to reveal the possible sources of such failures. The numerical simulation took into account precisely determined boundary conditions allowing proper selection of processing parameters. The microstructure of charge material as well as that of the final product was also examined. Numerical simulations of the investigated extrusion process showed the possibility of obtaining good quality product, however, the quality of final part is strongly influenced by properly designed heat treatment schedule.