Defect and Diffusion Forum Vol. 405

Abstract: Maraging steel is an iron-nickel steel alloy, which achieves very good material properties like high toughness, hardness, good weldability, high strength and dimensional stability during heat treatment. In this work, maraging steel 18Ni-300 was manufactured by selective laser melting. It is a method of additive manufacturing (AM) technology, which produces prototypes and functional parts. Sample of additively manufactured and conventional steel with the same chemical composition were tested after in three different states – heat treated (as-built/as-received), solution annealed and precipitation hardened. Resulting microstructures were analysed by light and scanning electron microscopy and mechanical properties were obtained by hardness measurement and tensile test. Cellular martensitic microstructures were observed in additively manufactured samples and conventional maraging steel consisted of lath martensitic microstructures. Very similar mechanical properties were obtained for both steels after the application of the same heat treatment. Ultimate tensile strengths reached 839 – 900 MPa for samples without heat treatment and heat treated by solution annealing, the samples after precipitation hardening had tensile strengths of 1577 – 1711 MPa.

Abstract: The composition of each grinding wheel depends on the specific application, and nowadays, there are many types of grinding wheels on the market. Bakelite bonded grinding wheels are fast becoming the standard choice for grinding and finishing processes in automotive, aerospace and other special fields of industry. Increasing requirements on higher quality and lifetime push manufacture to continuous research and development in this field. From that reason, it is necessary to characterize the structure and properties of already produced commercial grinding tools. In this contribution, two in chemical composition identical bakelite bonded grinding wheels with different properties were studied. Processing parameter like compression force is the main factor resulting in either hard grinding wheel for machining soft materials or soft grinding wheel for machining hard materials. The main components of both grinding wheels are abrasive particles of brown alumina (Al₂O₃) and two bonding agents based on synthetic rubber and bakelite. In addition, grinding wheels contain additives, e.g. vulcanization accelerators, fillers etc. to improve functional properties of grinding wheel. Fractures and metallographic samples morphology was studied by scanning electron microscopy. Porosity of grinding wheels was estimated using image analysis. Hardness of binder and abrasive brown alumina particles was measured by Rockwell hardness test.

Abstract: The microstructure and fracture surfaces were investigated for five Fe₃Al – based iron aluminides doped by different alloying elements (Nb, Zr + C, Cr) or without addition. Generally, iron aluminides are considered as brittle material at room temperature, therefore the type and distribution of secondary phases affect the fracture behaviour. The influence of present secondary phase particles on impact toughness at room temperature was evaluated in comparison to binary alloy. The type and the volume fraction of particles affect the value of impact toughness significantly – these values decrease with increasing volume fraction of precipitates. On the other hand, the solid solution strengthening improves impact toughness.

Abstract: Iron and iron-phosphorus open-cell foams were tested for their potential use as synthetic bone graft substitutes. The samples were manufactured using a replica method based on a powder metallurgical approach. Iron foams alloyed with 0.5 wt. % of phosphorus were prepared with the aim of enhancing the mechanical properties and manipulating the corrosion rate. The manufactured foams were tested for their microstructure, porosity, corrosion behaviour and mechanical properties. SEM analyses of the foams’ microstructures confirmed the presence of an open, three-dimensional interconnected macroporous network similar to that of the human bone. The corrosion behaviour was studied by a static immersion test and potentiodynamic polarisation in Hank’s solution. The results showed that the presence of phosphorus slightly decreased the corrosion rate as compared to pure iron foams. The mechanical properties studied by a compression test confirmed a positive effect of phosphorus on the mechanical properties of the manufactured foams.

Abstract: This work studies the surface welding parameters for a practical repair for pearlitic rail grades: R260 and R350HT. A filler metal containing low carbon (0.15 %), high silicon (0.5 %) and nickel (2.5 %), self-shielded flux-core welding electrode (FCAW-S) is the candidate in order to ensure the preferable carbide-free bainite. The film-like morphology of the retained austenite is reported to promote the wear resistance and is ensured by silicon and nickel. The effect of preheat temperature and dilution on the microstructure and resulting hardness can be concluded. Too high dilution, as a result of high current and travel speed, and the reheating during the welding of the second layer can result in martensite formation and too high hardness. Proper control of the dilution ensures satisfactorily hardness and avoids martensite formation.

Abstract: By the non-destructive testing of a dissimilar weld joint (DWJ) of cold collector DN 1100 (CC) on a steam generator, indications were found on inner-side cold collector’s surface at the root position of the examined weld. All the identified indications were very similar in shape and form, therefore, it was decided to cut out a part of the damaged site from this type of DWJ DN 1100 and get the obtained ring (real piece of material) for complex metallographic analysis. This paper briefly describes the results and recommendations found for the future reference during the next long‑term operation induced ageing and degradation of critical steam generator parts in NPP Bohunice Unit 4. There are summarized the results obtained from evaluation of original DWJ material.

Abstract: The paper presents the results of the research aimed at quality determination of cladding layers for renovation of the rollers during continuous casting of steel. Four newly designed additive materials in the form of filled tubular wires of diameter 2.4 mm were evaluated. Additive materials were experimentally designed for the renovation of support rollers of the hot rolling mill. The cladding layers were applied on 31CrMoV9 material (EN 10085). Method used in experimed was submarged cladding 121 - EN ISO 4063 SAW. A specially developed flux WLDC 17 was used. The structure of cladding layers, basic mechanical propertis and their chemical composition were determined. The JOEL JSM-7000F electron microscope was used for analysis. Layers were tested under tribological conditions with pin-on-disc adhesion wear. Tests were performed on a Bruker UMT 3 device. Observation and measurement of wear traces were performed on the Sensofar PLu Neox confocal microscope.

Abstract: The paper deals with the complaint between the manufacturer and the customer. The object of the dispute is a damaged stroller construction made by welding Al-Mg-Si aluminum alloy profiles with the final surface layer produced by anodic oxidation. The aim of the analysis is to identify clearly the causes of breaking the aluminum structure using fractographic and metallographic techniques.

Abstract: Additively manufactured metals have their specifics which influence their performance. Based on fractography, these specifics are depicted in this paper on the example of titanium alloy Ti6Al4V manufactured by selective laser melting (SLM). While very fine microstructure contributes to high strength during static loading, dynamic loading is impaired by rough as-built surface and internal defects. With post-processing treatment, these undesirable features can be removed or significantly reduced. To densify the material, hot isostatic pressing (HIP) closing internal voids is commonly used. Rough surface can be removed by machining or other operations, including chemical treatment. The influence of HIP and machining on fatigue failure are in the focus of this paper.

Abstract: We tested stability of 43 selective sorbents, covering the widest range of functional groups, efficiency of sorption, method of production, and which are theoretically useful for sorption of cesium, strontium, cobalt, arsenic and actinoids. We present 3 of them: A = TiO₂, B = Al₂O₃ and C = MxH(TiO)₄(SiO4)₃ . z H₂O. In first testing, sorbents were exposed to the model solution of boric acid for 168 hours, in which they were mixed in a closed container with a rotator. After the exposure, sorbent solutions were filtered and analysed by spectroscopic techniques (Infrared Spectroscopy (IR), Raman Spectroscopy (RS) and newly by Scanning Electron Microscopy (SEM), combined with Energy Dispersive Spectroscopy (EDS)). Exposed spectra were compared with spectra of new, non-exposed sorbents. In second testing, sorbents were exposed to gamma radiation for 12 days with total dose 666 ± 43 kGy, produced by cobalt bomb and analysed by same techniques. The aim of our testing was to find out how sorbents behave in model boric acid solution and what effect has the gamma radiation on sorbent spectra and to analyse sorbents by SEM with EDX.