Stvarni modul savijanja motki koje imaju sloj od staničnog materijala i uporaba tog modula za određivanje stvarnog modula elastičnosti staničnog materijala

Rectangular bar-shaped sandwich-like samples consisting of a cellular-material core between two standard material layers were prepared. The cellular materials were made of both ferrous and bronze hollow spheres. Using these specimens and testing method based on flexural vibrations, expected differences were observed in effective modulus values determined by means of vibrations parallel and perpendicular to layers. Information on distribution of material throughout the bar cross section was obtained through metallographic studies. The thickness of particular layers, measured values of “parallel” and “perpendicular” effective flexural modulus, and expressions derived for flexural rigidity of quasi-layered bars were used for evaluating the values of effective Young’s modulus of material of particular layers constituting the sample. Reasonable agreement was found among results obtained for various samples.Pripremljeni su pravokutni sendvič-uzorci motki koji se sastoje od jezgre sa staničnim materijalom između dva sloja standardnog materijala. Stanični materijali su napravljeni od željeznih i brončanih šupljih kugli. Uporabom tih uzoraka i metoda testiranja zasnovane na vibracijama savijanja, očekivane razlike su prijećene u postojećim vrijednostima modula određenih pomoću vibracija paralelnih i okomitih na slojeve. Informacija o rasporedu materijala u presjeku motke dobivena je na osnovu proučavanja metalografije. Debljina pojedinih slojeva izmjerenih vrijednosti “paralelnih” i “okomitih” stvarnog modula savijanja i izraza izvedenih iz savitljive krutosti poluslojevnih motki koje se koriste za procjenjivanje vrijednosti stvarnog efektnog Youngovog modula materijala pojedinih slojeva koji sačinjavaju uzorak. Razumno suglasje je pronađeno među rezultatima dobivenim za razne uzorke

Mikrostruktura, mehanička svojstva i greške na sinterovanom čeliku Fe-3Mn-0.7C

Mechanical properties of Fe-3Mn-0.7C sintered steel were determined in tension and in bending following laboratory and industrial sintering at the temperatures of 1120, 1180 and 1200 °C in a H2-rich atmospheres with the dew points of -33 °C and/or - 30 °C and -55 °C and/or - 60 °C. The microstructure of sintered specimens is complex and heterogeneous, formed by products of the diffusive and non-diffusive transformations. The highest strength properties of the tested alloy were recorded after sintering at 1200 °C in dry atmosphere: R0.2 = 490 MPa, Rm = 642 MPa, bend strength of 1256 MPa, apparent hardness of 207 HV10, tensile and maximum bend strains were 1.02 and 3.6 %. The reproducibility of tensile and bend strengths data was high, characterised by Weibull module, m, of 12 - 38. The large pores or their agglomerates (50 - 70 µm in size) act as the failure originating sites in the tensile and bend specimens.Mehanička svojstva čelika Fe-3Mn-0.7C, sinterovanog u laboratoriju i pogonu na temperaturi od 1120, 1180 i 1200 °C u atmosferi bogatoj vodikom (H2) s rosištima od -33, i/ili -30 i -35 i/ili -60 °C, određena su na vlak i na savijanje. Mikrostruktura uzoraka je kompleksna i heterogena, oblikovana je proizvodima difuzivnih i nedifuzivnih transformacija. Najbolja svojstva čvrstoće testirane slitine zabilježena su nakon sinterovanja na 1200 °C u suhoj atmosferi: R0.2 = 490 MPa, Rm 642 MPa, čvrstoća na savijanje od 1256 MPa, prividna čvrstoća od 207 HV 10, naprezanje na vlak i maksimalna naprezanja na savijanje su bila 1.02 i 3.6 %. Stupanj ponavljanja podataka o čvrstoći na vlak i na savijanje je bio visok i okarakteriziran Weibulovim modulom, m, od 12-38. Velike pore, ili njihovi aglomerati (dimenzije 50 - 70 µm) imaju ulogu grešaka originalnih veličina na uzorcima za ispitivanje na vlak i savijanje

The Influence of Preparation Methods on Magnetic Properties of Fe/SiO₂ Soft Magnetic Composites

An analysis of several variants of the Fe/polymer/SiO₂ composites in terms of the impact of iron powder particle shape (irregular, spherical), of the content (0.4-2.0 wt%), of the polymer type (shellac, thermoset SL450) and the method of its application as well as the effect of the preparation procedure of the composites (mixing and/or vacuum-pressure impregnation) on properties of electrical insulating layer (thickness and coherence), electrical resistivity and magnetic properties was carried out. It was found that the main governing factor of the microstructure formation is the shape, surface microgeometry of the iron particles and the insulator layer. These determine not only the uniformity of thickness and cohesion of the insulating layer of the applied polymer or its hybrid modification (polymer+SiO₂ nanoparticles), but also the most suitable method of preparation in terms of the achieved values of electrical and magnetic properties of the composites

Tribological behavior of hydrogenated W-C/a-C:H coatings deposited by three different sputtering techniques

Abstract The evolution of structure, mechanical properties and friction behavior of DC magnetron sputtered (DCMS), high power impulse magnetron sputtered (HiPIMS) and high target utilization sputtered (HiTUS) W-C:H coatings was investigated as a function of the addition of acetylene and hydrogen into Ar atmosphere. The gradual addition of reactive gases caused a transition from PVD toward hybrid PVD-PECVD and even PECVD dominant processes. The coating structure evolved from nanocrystalline toward nanocomposite and amorphous structure with the increase of acetylene addition. Deposition rates in all techniques increased linearly with the increase of acetylene flow until certain saturation limit due to the limited energy available for acetylene fragmentation during hybrid PVD-PECVD deposition. Hardness and coefficient of friction in DCMS and HiTUS W-C:H coatings deposited in this regime followed standard congruent tendencies whereas PECVD dominated deposition process produced coatings with different dependencies. In contrary, HiPIMS W-C:H coatings showed low sensitivity to the influence of acetylene and hydrogen additions. Lower coefficients of friction (<0.1) and moderate hardness (around 20 GPa) of HiPIMS W-C:H coatings over a wide range of acetylene additions seem to be a principal advantage of HiPIMS compared to DCMS and HiTUS techniques in this class of coatings