Krzysztof Rozniatowski

Image Based Analysis of Complex Microstructures of Engineering Materials

Image Based Analysis of Complex Microstructures of Engineering Materials The paper presents various methods for quantitative description of material structures. The main focus is on direct methods of description based on image analysis. In particular, techniques for the estimation of the size, shape and spatial distribution of structural elements observed by different microscopic techniques are described. The application of these methods for the characterization of the structures of engineering materials is demonstrated on a stainless steel used in petrochemical installations. It is shown that the methods applied are useful for the assessment of service degradation of materials.

Quantitative characteristics of FeCrAl films deposited by arc and high-velocity arc spraying

Abstract FeCrAl coatings were deposited on grade 45 steel substrates by arc spraying (AS) and high-velocity arc spraying (HVAS) under the same spray conditions, and their characteristics were quantitatively compared. Observations of the surface morphology of the coatings were conducted in a scanning electron microscope (SEM). Microhardness values of the coatings and the substrates as a function of distance along the direction perpendicular to the coating–substrate interface were measured. The profile roughness coefficients of coatings and substrates were also measured and analysed in this paper. From the results obtained in the present work, it can be concluded that FeCrAl coatings deposited by HVAS have better microproperties than that deposited by AS.

Quantitative imaging of electrospun fibers by PeakForce Quantitative NanoMechanics atomic force microscopy using etched scanning probes

Electrospun polymeric submicron and nanofibers can be used as tissue engineering scaffolds in regenerative medicine. In physiological conditions fibers are subjected to stresses and strains from the surrounding biological environment. Such stresses can cause permanent deformation or even failure to their structure. Therefore, there is a growing necessity to characterize their mechanical properties, especially at the nanoscale. Atomic force microscopy is a powerful tool for the visualization and probing of selected mechanical properties of materials in biomedical sciences. Image resolution of atomic force microscopy techniques depends on the equipment quality and shape of the scanning probe. The probe radius and aspect ratio has huge impact on the quality of measurement. In the presented work the nanomechanical properties of four different polymer based electrospun fibers were tested using PeakForce Quantitative NanoMechanics atomic force microscopy, with standard and modified scanning probes. Standard, commercially available probes have been modified by etching using focused ion beam (FIB). Results have shown that modified probes can be used for mechanical properties mapping of biomaterial in the nanoscale, and generate nanomechanical information where conventional tips fail.

Effects of stress and its dependence on microstructure in Mn–Zn ferrite for power applications

Abstract The relationship between magnetoelastic properties and microstructure has been studied for a series with different bulk density of Mn 0.70 Zn 0.24 Fe 2.06 O 4 ferrite for switch mode power supplies applications. It is shown that in investigated ferrites, in spite of their small λ s value (equal 0.6×10 −6 ), the effect of stress is considerable. The course of magnetoelastic characteristics B ( σ ) H and H c ( σ ) H of investigated Mn–Zn ferrites depends significantly on its microstructure.

Effect of carbon content on the microstructure and properties of silicon carbide-based sinters

The paper presents the results of investigations of the influence of carbon activator content on the microstructure and mechanical properties of silicon carbide sinters with 1, 3, and 6 wt.% of carbon.

Imaging resolution of AFM with probes modified with FIB.

This study concerns imaging of the structure of materials using AFM tapping (TM) and phase imaging (PI) mode, using probes modified with focused ion beam (FIB). Three kinds of modifications were applied - thinning of the cantilever, sharpening of the tip and combination of these two modifications. Probes shaped in that way were used for AFM investigations with Bruker AFM Nanoscope 8. As a testing material, titanium roughness standard supplied by Bruker was used. The results show that performed modifications influence the oscillation of the probes. In particular thinning of the cantilever enables one to acquire higher self-resonant frequencies, which can be advantageous for improving the quality of imaging in PI mode. It was found that sharpening the tip improves imaging resolution in tapping mode, which is consistent with existing knowledge, but lowered the quality of high frequency topography images. In this paper the Finite Element Method (FEM) was used to explain the results obtained experimentally.

Free surface contribution to sensitization of an austenitic stainless steel

Abstract Austenitic stainless steels are widely used in corrosive environments. During plastic straining these steels exhibit environmental effect. The flow stress in air at intermediate temperatures is compared with the specimens strained in vacuum. Static annealing in air and vacuum to a different degree strengthens the material at room temperature. The data reported here was collected for AISI 316 and 316L austenitic stainless steels. The specimens have been subjected to annealing at 900°C followed by water quenching+annealing at 600°C in either air or vacuum. The results obtained show that the resistance to corrosion of the grain boundaries in austenitic stainless steel subjected to recrystallization annealing at 900°C in air is particularly low in the near-surface layer of specimens. The additional annealing at 600°C either in vacuum or air per se does not lead to formation of a measurable Cr-depletion along grain boundaries in the near-surface zone. The observation of surface sensitization proves a detrimental effect, a high temperature annealing in air on corrosion resistance of an austenitic stainless steel. The results show that the harmful consequence of a high temperature annealing in air can be reversed by a subsequent annealing in vacuum at intermediate temperatures. The results also rationalize mechanical cleaning of elements subjected to a heat-treatment in air.

The Influence of Selective Laser Melting (SLM) Process Parameters on In-Vitro Cell Response

The use of laser 3D printers is very perspective in the fabrication of solid and porous implants made of various polymers, metals, and its alloys. The Selective Laser Melting (SLM) process, in which consolidated powders are fully melted on each layer, gives the possibility of fabrication personalized implants based on the Computer Aid Design (CAD) model. During SLM fabrication on a 3D printer, depending on the system applied, there is a possibility for setting the amount of energy density (J/mm3) transferred to the consolidated powders, thus controlling its porosity, contact angle and roughness. In this study, we have controlled energy density in a range 8–45 J/mm3 delivered to titanium powder by setting various levels of laser power (25–45 W), exposure time (20–80 µs) and distance between exposure points (20–60 µm). The growing energy density within studied range increased from 63 to 90% and decreased from 31 to 13 µm samples density and Ra parameter, respectively. The surface energy 55–466 mN/m was achieved with contact angles in range 72–128° and 53–105° for water and formamide, respectively. The human mesenchymal stem cells (hMSCs) adhesion after 4 h decreased with increasing energy density delivered during processing within each parameter group. The differences in cells proliferation were clearly seen after a 7-day incubation. We have observed that proliferation was decreasing with increasing density of energy delivered to the samples. This phenomenon was explained by chemical composition of oxide layers affecting surface energy and internal stresses. We have noticed that TiO2, which is the main oxide of raw titanium powder, disintegrated during selective laser melting process and oxygen was transferred into metallic titanium. The typical for 3D printed parts post-processing methods such as chemical polishing in hydrofluoric (HF) or hydrofluoric/nitric (HF/HNO3) acid solutions and thermal treatments were used to restore surface chemistry of raw powders and improve surface.

Effect of Microstructure on Rolling Contact Fatigue of Bearings

There has been proposed an innovative thermal treatment of bearing steel 100CrMnSi6-4, where the existing standard heat treatment has been replaced by austempering. The structure of low-temperature tempered martensite has been replaced by a microstructure composed of martensite and lower bainite with midrib. The kinetics of bainitic transformation and isothermal martensitic transition at selected austempering temperatures was controlled by acoustic emission. The research on contact strength was made under the conditions of rolling-sliding friction. The microstructure was revealed with the use of a light microscope and the forms of pitting wear were displayed by a scanning electron microscope. It was found that the optimum microstructure providing the best used contact strength of the tested steel is conditioned by the formation of a lower bainite with midrib at the temperatures near MS. A plausible cause of the increased resistance to pitting is bifurcation of fatigue cracks on dispersion bainitic carbides in combination with primary carbides, in bainitic-martensitic matrix.

Description of the homogeneity of material microstructures: using computer-aided analysis

The paper presents and compares three methods for the quantitative description of particle spatial distribution, namely, the linear covariance, Radial Distribution Function (RDF) and tessellation methods. First, model structures were analysed using these methods. It was shown that the particle spatial distribution and the quantitative parameters are clearly interrelated. The presented methods were applied for a quantitative description of the structure of AlN-TiB2 composite obtained via Self-Propagation High-Temperature Synthesis (SHS). Several parameters quantitatively describing the particle spatial distribution in the studied material were determined. The influence of the structural parameters on mechanical properties was investigated. The results are discussed in terms of further optimisation of the studied material.