Mikroskopiakonferenssi Scandem 2022

publishedVersio

Wetting Behavior and Functionality Restoration of Cold-Sprayed Aluminum-Quasicrystalline Composite Coatings

Coating design is an efficient strategy to engineer wettability of surfaces and adjustment of the functionality to the necessities in industrial sectors. The current study reveals the feasibility of functional aluminum/quasicrystalline (Al-QC) composite coatings fabrication by cold spray technology. A commercially available Al-based quasicrystalline powder (Al-Cr-Fe-Cu) was combined with aluminum alloy (Al6061) feedstock materials to make coatings with various compositions. A set of cold spray process parameters was employed to deposit composite coatings with different QC-Al ratios and Al6061 coatings as counterparts. The wettability of the coating surfaces was measured by static water droplet contact angles using a droplet shape analyzer and investigation of the dynamic of water droplet impact by high-speed imaging. Through microstructural studies, the Al-QC composites revealed dense structure, well-integrated and adherent deposits, providing structural reliability and enhanced hydrophobic behavior. In the last step of this work, composite coatings were deposited over eroded cold-sprayed Al6061 and a selected composite to demonstrate the feasibility of repairing the damaged part and function restoring. The results and approach used in this work provide understanding of cold-sprayed Al-QC composite coatings manufacturing and their wetting behavior state for cross-field applications.publishedVersionPeer reviewe

Effect of abrasive properties on the high-stress three-body abrasion of steels and hard metals

Especially in tunneling, the abrasiveness of rock is an important property, which can easily be determined by several methods developed for the purpose. With this in mind, it is rather surprising that the effects of different rock types on the wear mechanisms of engineering materials have not been too widely studied. In this paper, high stress three-body abrasive tests were conducted with four different abrasives with a relatively large (2-10 mm) particle size. As test materials, three different steels and three hard metals were used. The tests clearly showed that material type has an influence on how different abrasive and material properties affect the abrasive wear mechanisms and severity. For example with hard metals, the most important property of the abrasives is their crushability, as only small abrasive particles are able to properly attack the binder phase and cause high wear rates. On the other hand, it seems that the abrasiveness of rock is not the dominating property determining the severity of wear in the current test conditions for any of the tested materials. In fact, with steels no single abrasive property could be shown to clearly govern the abrasive wear processes. In any case, when using the determined abrasiveness values in wear estimations, the contact conditions in the method used for determining the abrasiveness values should be as similar as possible with the end application

Synergistic effects of heat treatments and severe shot peening on residual stresses and microstructure in 316L stainless steel produced by laser powder bed fusion

This study investigated the post-processing of laser powder bed fusion (LPBF) built 316L stainless steel components to address quality-related issues such as dangerous residual stresses and poor surface finish. Two different heat treatments (HT) at 600 °C and 900 °C, followed by severe shot peening (SSP), were employed to mitigate these concerns. The impact on roughness, residual stresses, microhardness, and microstructure in both as-printed and post-processed states was examined. Results indicate that the 600 °C HT fails to relieve residual stresses, while the 900 °C HT significantly reduces them by 90%. Furthermore, the SSP effectively reduced surface roughness by more than half of the initial values. The initial microstructures and residual stresses of the as-printed, 600 °C HT, and 900 °C HT samples differ, leading to distinct responses to identical SSP treatments. Notably, the 900 °C HT sample exhibited the deepest grain refinement after SSP and experienced the most substantial increase in surface hardness compared to the other samples. This research addressed critical quality issues in LPBF-built components by combining specific heat treatments and SSP. The 900°HT combined with SSP stood out as an effective method for relieving residual stresses and enhancing material properties. The distinct responses of the samples to post-processing highlight the importance of tailored treatments for LPBF components. These findings have significant implications for improving the quality and performance of LPBF components, with potential applications demanding improved fatigue and stress corrosion cracking performance.Peer reviewe

Grinding burn classification with surface Barkhausen noise measurements

Industrial Barkhausen noise (BN) measurements are commonly utilized for final quality control after machining operations such as grinding to point out grinding burns. Grinding burns might compromise the final use and fatigue lifetime of the ground component. The industrial BN method itself is based on a pre-determined threshold value of the BN root-mean-square value (RMS). Elevated RMS values indicate detrimental changes in the component. Usually, the evaluation of grinding burn severity is not carried out. In this study, real ground cylindrical samples were collected that were rejected based on an industrial quality control with a BN unit. A more detailed BN analysis was carried out for 41 individual grinding burn locations followed by X-ray diffraction based residual stress (RS) surface measurements and residual stress and diffraction peak full-width-at-half-maximum (FWHM) depth profiles. K-means clustering was applied to profiles to label the data points related to grinding burns of different severity. Three classes of grinding burns were identified and verified by micrographs and hardness. A linear discriminant classification model was then identified between the surface BN measurement features and labeled data points. The classification results were reasonable with about 80 % classification accuracy at worst. They showed that the classes identified can be detected with the surface BN measurements. Thus, the approach presented in this paper shows great potential in the practical use of BN measurement where grinding burns can be detected and evaluated with a surface BN measurement.Peer reviewe

The Effect of Severe Shot Peening on Fatigue Life of Laser Powder Bed Fusion Manufactured 316L Stainless Steel

Severe shot peening (SSP) was used on additive manufactured 316L by laser powder bed fusion. The effect of the post processing on the surface features of the material was analyzed through residual stress measurements, tensile testing, hardness-depth profiles, and fatigue testing by flexural bending. The results showed that SSP can be utilized to form residual stresses up to −400 MPa 200 µm below the surface. At the same time, a clear improvement on the surface hardness was achieved from 275 HV to near 650 HV. These together resulted in a clear improvement on material strength which was recorded at 10% improvement in ultimate tensile strength. Most significantly, the fatigue limit of the material was tripled from 200 MPa to over 600 MPa and the overall fatigue strength raised similarly from a low to high cycle regime.publishedVersionPeer reviewe

Comparative study of additively manufactured and reference 316 L stainless steel samples – Effect of severe shot peening on microstructure and residual stresses

The as-built selective laser melted (SLM) austenitic stainless steel 316 L components are characterized by presence of quality related concerns such as tensile residual stresses, poor surface finish, etc. These issues may prove to be detrimental during the actual usage of components and could result in poor mechanical performance. Therefore, it is important to perform the apt post processing such as heat treatment and shot peening to tailor such problems and facilitate improved mechanical performance. In the present work, additively manufactured (AM) 316 L samples were subjected to shot peening with different parameters including the severe shot peening (SSP) procedure. The identical shot peening protocol was also applied to reference samples to evaluate the comparable response. Both the shot peened reference and AM samples were studied for residual stresses, surface topography, microhardness, and the corresponding microstructure. The results indicated, that SSP induced higher values of compressive residual stresses deeper into the samples. This was accompanied by reduced surface roughness, increased grain refinement depth, and higher microhardness near the surface. The SSP resulted in transformation of original austenite to martensite near the surface in the reference samples.publishedVersionPeer reviewe

Optimized dispersion of nanoparticles for biological in vitro and in vivo studies

Background: The aim of this study was to establish and validate a practical method to disperse nanoparticles in physiological solutions for biological in vitro and in vivo studies. Results: TiO(2) (rutile) dispersions were prepared in distilled water, PBS, or RPMI 1640 cell culture medium. Different ultrasound energies, various dispersion stabilizers (human, bovine, and mouse serum albumin, Tween 80, and mouse serum), various concentrations of stabilizers, and different sequences of preparation steps were applied. The size distribution of dispersed nanoparticles was analyzed by dynamic light scattering and zeta potential was measured using phase analysis light scattering. Nanoparticle size was also verified by transmission electron microscopy. A specific ultrasound energy of 4.2 x 10(5) kJ/m(3) was sufficient to disaggregate TiO(2) (rutile) nanoparticles, whereas higher energy input did not further improve size reduction. The optimal sequence was first to sonicate the nanoparticles in water, then to add dispersion stabilizers, and finally to add buffered salt solution to the dispersion. The formation of coarse TiO(2) (rutile) agglomerates in PBS or RPMI was prevented by addition of 1.5 mg/ml of human, bovine or mouse serum albumin, or mouse serum. The required concentration of albumin to stabilize the nanoparticle dispersion depended on the concentration of the nanoparticles in the dispersion. TiO(2) (rutile) particle dispersions at a concentration lower than 0.2 mg/ml could be stabilized by the addition of 1.5 mg/ml albumin. TiO(2) (rutile) particle dispersions prepared by this method were stable for up to at least 1 week. This method was suitable for preparing dispersions without coarse agglomerates (average diameter < 290 nm) from nanosized TiO(2) (rutile), ZnO, Ag, SiO(x), SWNT, MWNT, and diesel SRM2975 particulate matter. Conclusion: The optimized dispersion method presented here appears to be effective and practicable for preparing dispersions of nanoparticles in physiological solutions without creating coarse agglomerates

Multi-instrumental approach to domain walls and their movement in ferromagnetic steels – Origin of Barkhausen noise studied by microscopy techniques

Two steels, ferrite and ferrite-pearlite were thoroughly characterized by a multi-instrumental microscopy techniques to get detailed information about their microstructure and magnetic structure. Microstructural features act as pinning sites for the motion of magnetic domain walls (DWs) leading to changes in the magnetization of the sample. This phenomenon is the basis for industrially relevant non-destructive Barkhausen noise (BN) technique. With magnetic force microscopy (MFM), using bulk samples, and Lorentz microscopy, using thin films, we noticed that bulk and thin samples have similar domain structure still giving different BN signal amplitudes. We could explain an in-plane DW movement under out-of-plane applied magnetic field using anisotropy energetics. In-situ transmission electron microscopy (TEM) in Lorentz mode was used to visualize the motion of DWs and their interactions with different pinning sites. To help the interpretation of DW motions, alignment and denoising processes were tailored for in-situ TEM studies. Multi-instrumental and multidimensional structural analysis enabled us to visualize and verify many theoretical hypotheses related to the origin of BN signal in ferrite and ferrite-pearlite steels.Peer reviewe