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1764. Influence of laser beam shape and post heat-treatment on the microstructure and mechanical properties of nickel-based alloy IN718 manufactured by laser powder bed fusionMatjaž Godec, Narges Mirzabeigi, Črtomir Donik, Danijela Anica Skobir Balantič, Simon Malej, Irena Paulin, Bojan Podgornik, Jonas Grünewald, Tobias Novotny, Florian Bayer, Francisco Ruiz-Zepeda, Katrin Wudy, 2025, original scientific article Abstract: This study examines the effect of Gaussian and ring-shaped laser beam profiles on the microstructural development and mechanical properties of the PBF-LB/M processed nickel-based alloy Inconel 718 in its as-built and post-heat-treated conditions. Beam shaping was employed to achieve a faster build rate without compromising material properties. One of the objectives was to optimise heat treatment conditions for the beam-shaped profile. The post-heat-treatment process included four different solution annealing temperatures (954 °C, 984 °C, 1034 °C and 1154 °C), followed by two-step ageing, respectively. The microstructure evolution was revealed using scanning electron microscopy (SEM) equipped with energy-dispersive X-ray diffraction (EDS). The mechanical properties in all investigated conditions were evaluated based on tensile tests at room temperature. Using a Gaussian laser beam profile results in a fine-grained microstructure without a strong columnar orientation, while the ring beam profile produces a distinct columnar structure with larger nanodendritic grains and dislocation cells. Both beam profiles exhibit a similar proportion of Laves phase. After post-heat treatment, the Gaussian beam profile generally provides 3-7 % higher mechanical properties. The differences in mechanical properties between horizontal and vertical building directions are greater for ring-shaped laser beam profiles. Heat-treatment temperature above 1034 °C leads to recrystallisation, grain growth and the formation of carbonitrides which reduce mechanical properties. Based on the results, the proposed optimal heat-treatment temperature for both investigated laser beam shapes is 984 °C. At this temperature, tensile strength equalises between horizontal and vertical build directions while yield strength increases, which is beneficial for most applications.
Keywords: PBF-LB/M, beam shaping, IN718, heat treatment, mechanical properties
Published in DiRROS: 07.07.2025; Views: 497; Downloads: 253
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1767. Nevzdržna svoboda vzporednih svetovIgor Ž. Žagar, 2025, independent professional component part or a chapter in a monograph Abstract: Prispevek je nadaljevanje besedila »Vzhodno od raja« z »drugimi sredstvi«. Če se prvo besedilo ukvarja z retorično optiko nasprotnikov poziva, skuša pričujoče besedilo osvetliti ideološko podstat te optike, vključno z vzroki za rusko-ukrajinsko vojno.
Keywords: mednarodni odnosi, geopolitika, etika, vojni konflikti, ZDA, Rusija, Ukrajina
Published in DiRROS: 07.07.2025; Views: 400; Downloads: 181
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1768. Normal covers of 2-arc-transitive graphs of prime-power orderMarston D. E. Conder, Primož Potočnik, 2025, original scientific article Abstract: In a paper by Cai Heng Li in Bull. London Math. Soc. 33 (2001), it was suggested that ‘non-basic’ $2$-arc-transitive graphs of prime-power order that occur as normal covers of smaller $2$-arc-transitive graphs might be rare and difficult to construct. This note describes some of the background to Li’s suggestion, and gives some examples of small valency, and then goes on to show that in fact there are infinitely many examples of valency $d$, for every integer $d \ge 2$. It is also noted that the hypercubes $(Q_n)$ for $n \ge 4$ even, together with a $2$-arc-transitive group $G$ of index $2$ in ${\rm Aut}(Q_n)$, show that the claims of Corollary 1.2 in the above paper by Li are not quite correct.
Keywords: graphs, s-arc-transitive, normal cover
Published in DiRROS: 07.07.2025; Views: 329; Downloads: 201
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1770. An analysis of PIRLS 2021 mode effects : differences in reading achievement related to the assessment mode for PIRLS 2021 in Croatia and SloveniaEva Klemenčič Mirazchiyski, Plamen Mirazchiyski, Ines Perović, 2025, independent scientific component part or a chapter in a monograph Abstract: This chapter analyzes the differences in reading achievements related to different assessment modes (digital and paper) among students in Croatia and Slovenia using IEA’s Progress in International Reading Literacy Study (PIRLS) 2021 data. It focuses on the relationship various ICT-related variables may have with the reading achievement by the mode of administration. The findings revealed no significant differences in average reading scores between the two modes, with both education systems showing similar outcomes. Although differences in achievement between the two modes could not be detected, nuances emerged regarding the association between ICT variables and reading achievement. Notably, ownership and the sharing of digital devices like smartphones indicated contrasting impacts for each country, suggesting country-specific digital divides. Additionally, while certain ICT resources seemed to marginally benefit reading scores, the general lack of significant disparities between digital and paper assessments highlights the complex interplay of factors influencing educational outcomes. Digital self-efficacy is related to reading achievement only in Slovenia. The study outlined in this chapter calls for nuanced understanding and policy interventions considering these subtle yet crucial differences.
Keywords: education, reading literacy, PIRLS 2001, reading achievement, assessment mode, digital self-efficacy, Croatia, Slovenia
Published in DiRROS: 07.07.2025; Views: 388; Downloads: 234
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