Analiza međupovršine eksplozijski zavarenih ploča iz niskougljičnog čelika i titana

On the basis of experimentally obtained data, it was established that a very thin layer of a melt is generated at the explosive welding of two metals at the bond interface within which impurities flow at the bond during melting. Rapid cooling after the collision generates an alloy of different structure and very small grains of an average thickness approximately 1 to 2 mm. The generation of such an amorphous layer in the bond area has been noticed with various metal combinations and represents a fundamental mechanism of explosive welding of metals. Using the metallographic analysis, the development of the vortices which were formed by the explosive welding of low-carbon steel and titanium plates is described in the paper.Na osnovi eksperimentalnih rezultata utvrđeno je da pri eksplozijskom zavarivanju dvaju metala na međupovršini spoja nastaje veoma tanki sloj rastaljenog metala unutar kojeg dolazi do istjecanja nečistoća tijekom taljenja. Velika brzina hlađenja nakon sudara dovodi do nastanka sitnozrnate legure drugačije strukture s proječnom veličinom od 1 do 2 mm. Zapaženo nastajanje amorfnog sloja na području spoja kod različitih kombinacija metalnih materijala predstavlja temeljni mehanizam eksplozijskog zavarivanja metala. Primjenom rezultata metalografske analize u radu je opisan razvoj vrtloga koji su nastali eksplozijskim zavarivanjem ploča iz niskougljičnog čelika i titana

Unutarnja oksidacija Cu-Se legura

The purpose of our investigation was to perform the thermodynamic calculation of all possible reactions in the Cu-Se-O system and to explain the oxidation mechanism in various conditions. For such study, a model of copper with one single inclusion and alloy with 1.65 wt. % Se were made. Depending on time, the oxidation has been taking place at two different temperatures and two oxygen partial pressures. The oxidized samples have been investigated by DTA, optical and electron microscopy (SEM).Namjena istraživanja je izraditi termodinamički proračun svih mogućih reakcija u sustavu Cu-Se-O i obrazložiti mehanizme oksidacije u različitim uvjetima. Za takovo izučavanje izrađen je model bakra sa samo jednim uključkom i legura sa 1,65 mas. % Se. U ovisnosti od vremena, oksidacija se odvijala kod različitih temperatura i kod dviju različitih djelomičnih tlakova kisika. Oksidirani uzorci su bili ispitivani metodom DTA, optičkom i elektronskom mikroskopijom (SEM)

Detection of a variable ultra-fast outflow in the Narrow Line Seyfert 1 galaxy PG 1448+273

Relativistically blueshifted absorption features of highly ionised ions, the so-called ultra-fast outflows (UFOs), have been detected in the X-ray spectra of a number of accreting supermassive black holes. If these features truly originate from accretion disc winds accelerated to more than 10 per cent of the speed of light, their energy budget is very significant and they can contribute to or even drive galaxy-scale feedback from active galactic nuclei (AGN). However, the UFO spectral features are often weak due to high ionisation of the outflowing material, and the inference of the wind physical properties can be complicated by other spectral features in AGN such as relativistic reflection. Here we study a highly accreting Narrow Line Seyfert 1 galaxy PG 1448+273. We apply an automated, systematic routine for detecting outflows in accreting systems and achieve an unambiguous detection of a UFO in this AGN. The UFO absorption is observed in both soft and hard X-ray bands with the XMM-Newton observatory. The velocity of the outflow is (26900 +- 600) km/s (~0.09c), with an ionisation parameter of log ({\xi} / erg cm s^-1)=4.03_{-0.08}^{+0.10} and a column density above 10^23 cm^-2. At the same time, we detect weak warm absorption features in the spectrum of the object. Our systematic outflow search suggests the presence of further multi-phase wind structure, but we cannot claim a significant detection considering the present data quality. The UFO is not detected in a second, shorter observation with XMM-Newton, indicating variability in time, observed also in other similar AGN.Comment: Accepted for publication in MNRAS. 14 pages, 11 figures, 1 tabl

Evidence for a Variable Ultrafast Outflow in the Newly Discovered Ultraluminous Pulsar NGC 300 ULX-1

Ultraluminous pulsars are a definite proof that persistent super-Eddington accretion occurs in nature. They support the scenario according to which most Ultraluminous X-ray Sources (ULXs) are super-Eddington accretors of stellar mass rather than sub-Eddington intermediate mass black holes. An important prediction of theories of supercritical accretion is the existence of powerful outflows of moderately ionized gas at mildly relativistic speeds. In practice, the spectral resolution of X-ray gratings such as RGS onboard XMM-Newton is required to resolve their observational signatures in ULXs. Using RGS, outflows have been discovered in the spectra of 3 ULXs (none of which are currently known to be pulsars). Most recently, the fourth ultraluminous pulsar was discovered in NGC 300. Here we report detection of an ultrafast outflow (UFO) in the X-ray spectrum of the object, with a significance of more than 3{\sigma}, during one of the two simultaneous observations of the source by XMM-Newton and NuSTAR in December 2016. The outflow has a projected velocity of 65000 km/s (0.22c) and a high ionisation factor with a log value of 3.9. This is the first direct evidence for a UFO in a neutron star ULX and also the first time that this its evidence in a ULX spectrum is seen in both soft and hard X-ray data simultaneously. We find no evidence of the UFO during the other observation of the object, which could be explained by either clumpy nature of the absorber or a slight change in our viewing angle of the accretion flow.Comment: 10 pages, 4 figures. Accepted to MNRA

Analiza međupovršine niskougljičnog čelika/tantal nakon eksplozivnog zavarivanja

The article discusses the morphology, microstructure and chemical composition of the boundary layer in explosive welding of low-carbon steel and tantalum plates. Pools of melt composed of both metals and having a heterogeneous chemical composition appear on the boundary layer. This phenomenon is the result of incomplete mixing of both: molten metals due to rapid cooling and solidification. Within the pools of alloy, a large number of non-metallic oxide inclusions, products of deoxidation of molten alloys, can be found. The non-metal inclusions are round (0.1 to 2 µm in diameter) and vary in both: size and chemical composition. The main component of the non-metal inclusions is Ta2O5, which also contains iron, manganese, and aluminium oxides. The number of non-metal inclusions is unusually high for low-carbon steel and comparable to the number of non-metal inclusions in welds. Oxygen which causes the large number of deoxidised products does not originate in the low-carbon steel, as this steel is relatively clean. The most probable source of oxygen is the oxide scale from the surface of the low-carbon steel, which was poorly cleaned prior to welding.Članak raspravlja o morfologiji, mikrostrukturi i kemijskom sastavu pograničnog sloja pri eksplozivnom zavarivanju traka niskougljičnog čelika i tantala. Područje zone taljenja sastavljeno je od oba metala i na graničnom sloju pojavljuje se heterogeni kemijski sastav. Ova pojava je posljedica nepotpunog miješanja oba rastaljena metala, zbog naglog hlađenja i očvršćivanja. Unutar područja spajanja legure može se utvrditi veliki broj nemetalnih oksidnih uključaka, produkata dezoksidacije rastaljenih legura. Nemetalni uključci su okrugli (0.1 do 2 µm) i variraju u veličini i kemijskom sastavu. Glavna komponenta nemetalnih uključaka je Ta2O5, koji također sadrži željezne, manganove i aluminijeve okside. Broj nemetalnih uključaka je neouobičajeno velik za niskougljični čelik i usporediv je s brojem nemetalnih uključaka u zavarima. Kisik koji dovodi do nastanka velikog broja produkata dezoksidacije ne potiče iz niskougljičnog čelika jer je čelik relativno čist. Najvjerojatniji izvor kisika je površinski oksidni sloj niskougljičnog čelika koji je slabo očišćen prije procesa zavarivanja

Origin of central abundances in the hot intra-cluster medium - I. Individual and average abundance ratios from XMM-Newton EPIC

The hot intra-cluster medium (ICM) is rich in metals, which are synthesized by supernovae (SNe) explosions and accumulate over time into the deep gravitational potential well of clusters of galaxies. Since most of the elements visible in X-rays are formed by type Ia (SNIa) and/or core-collapse (SNcc) supernovae, measuring their abundances gives us direct information on the nucleosynthesis products of billions of SNe since the epoch of the star formation peak (z ~ 2-3). In this study, we use the EPIC and RGS instruments onboard XMM-Newton to measure the abundances of 9 elements (O, Ne, Mg, Si, S, Ar, Ca, Fe and Ni) from a sample of 44 nearby cool-core galaxy clusters, groups, and elliptical galaxies. We find that the Fe abundance shows a large scatter (~20-40%) over the sample, within 0.2$r_{500}$ and, especially, 0.05$r_{500}$. Unlike the absolute Fe abundance, the abundance ratios (X/Fe) are quite uniform over the considered temperature range (~0.6-8 keV), and with a limited scatter. In addition to a unprecedented treatment of systematic uncertainties, we provide the most accurate abundance ratios measured so far in the ICM, including Cr/Fe and Mn/Fe that we firmly detect (>4{\sigma} with MOS and pn independently). We find that Cr/Fe, Mn/Fe and Ni/Fe, differ significantly from the proto-solar values. However, the large uncertainties in the proto-solar abundances prevent us from making a robust comparison between the local and the intra-cluster chemical enrichments. We also note that, interestingly, and despite the large net exposure time (~4.5 Ms) of our dataset, no line emission feature is seen around ~3.5 keV.Comment: 17 pages, 9 figures, accepted for publication in A&

Influence of the Deep Cryogenic Treatment on AISI 52100 and AISI D3 Steel’s Corrosion Resistance

The effect of deep cryogenic treatment (DCT) on corrosion resistance of steels AISI 52100 and AISI D3 is investigated and compared with conventional heat-treated counterparts. DCT’s influence on microstructural changes is subsequently correlated to the corrosion resistance. DCT is confirmed to reduce the formation of corrosion products on steels’ surface, retard the corrosion products development and propagation. DCT reduces surface cracking, which is considered to be related to modified residual stress state of the material. DCT’s influence on each steel results from the altered microstructure and alloying element concentration that depends on steel matrix and type. This study presents DCT as an effective method for corrosion resistance alteration of steels