Notranja oksidacija Cu-C in Ag-C kompozitov

The internal oxidation in copper-carbon and silver-carbon composites occurs when they are exposed to air or oxygen at high temperature. Solubility of carbon in copper or in silver is very low. The kinetics of oxidation at high temperature and activation energy were determined and the mechanism of internal oxidation was analysed. The kinetics of internal oxidation was determined for both cases and it is depended from the diffusion of oxygen following parabolic time dependence according to Wagner\u27s theory. The activation energy for Cu-C composite is 70.5 kJ/mol, and for Ag-C composite is 50.1 kJ/mol, what is in both cases close to the activation energy for the volume diffusion of oxygen in copper or in silver. In both cases gas products are formed during the internal oxidation of composites. In the internal oxidation zone pores, bubbles occur. The carbon oxidates directly with the oxygen from solid solution as long there is a contact, which breaks down with the presence of gas products. Then the oxidation occurs over the gas mixture of CO and CO2.Pri visokih temperaturah kompoziti bakra in srebra z ogljikom na zraku ali v kisiku reagirajo po mehanizmu notranje oksidacije. Topnost ogljika v trdnem bakru in trdnem srebru je zelo majhna. Analizirali smo kinetiko oksidacije kompozitov, določili aktivacijsko energijo in mehanizem notranje oksidacije. Kinetika oksidacije je pri obeh skupinah materialov odvisna od difuzije kisika in sledi parabolični odvisnosti od časa v skladu z Wagnerjevo teorijo. Aktivacijska energija procesa je za kompozit Cu-C enaka 70,5 kJ/mol, za kompozit Ag-C pa 50,1 kJ/mol, kar je blizu aktivacijski energiji za volumsko difuzijo kisika v trdnem bakru oziroma srebru. Pri oksidaciji kompozita nastajajo plinski produkti. Oksidacija ogljika poteka neposredno s kisikom iz trdne raztopine, ko pa se zaradi nastanka plinske faze stik prekine, pa preko plinske zmesi CO in CO2

Effect of heat treatment on Charpy impact energy of microalloyed steel

U ovom radu istraživan je niskolegirani visokočvrsti čelik Niomol 490K koji sadrži dodatak niobija (0,032 mas. %). Toplinska obrada čelika se sastojala od austenitizacije pri 1250 °C u trajanju od 5 minuta i ponovnog zagrijavanja do 750 °C u trajanju od 5 s. Nakon austenitizacije provedeno je kaljenje u vodi kod temperature od 70 °C i u olovnoj kupci do temperature od 400 °C uz naknadno hlađenje na zraku. Utvrđeno je da je Charpy energija udara viša, a prijelazna temperatura niža za transformaciju austenita u bainit nego kod transformacije austenita u martenzitnu mikrostrukturu. Eksperimentalni rezultati su pokazali različite prijelomne površine. Pokazano je da je preferentno cijepajući prijelom zapažen po ravnini rešetke (001), neovisno o mikrostrukturi.In this paper the microalloyed high-strength low-alloy (HSLA) Niomol 490K steel with an addition of niobium (0,032 wt. %) has been investigated. Heat treatment of the steel consisted of austenitisation at 1250 °C for 3 minutes and reheating up to 750 °C for 5 s. After austenitization the quenching was carried out in water with temperature of 70 °C and then in a lead bath up to 400 °C following cooling on the air. It was found that Charpy impact energy is higher and the transition temperature is lower for the transformation of austenite to bainite than to martensite microstructure. Experimental results showed that different fracture surface was observed. It is shown that preferred cleavage fracture occurred in the lattice plane (001) independently of steel microstructure

Unutarnja oksidacija legura srebra s telurom, selenom i sumporom

Silver alloys with tellurium, selenium and sulphur fulfil the conditions for the internal oxidation. Microstructure of these alloys consists of matrix (dilute solid solution) and particles of intermetallic compounds. Internal oxidation of ternary alloys is very similar to that of the binary alloys, but there are also distinctions in thermodynamics properties of alloying elements. At the direct oxidation of the particles of the intermetallic compound the phenomena of the selective oxidation was observed. Concentration of more reactive elements is increasing in the oxidized part of the particles of the intermetallic compound (Te in AgTeSe alloys). Therefore the precipitated oxides formed with diffusional internal oxidation are richer with less reactive alloying element (Se in AgTeSe alloy). In the precipitated oxide particles the concentration of selenium is more than twice higher than of tellurium.Legure srebra s telurom, selenom i sumporom ispunjavaju uvjete za unutarnju oksidaciju. Mirkostruktura ovih legura sastoji se od osnove (razrijeđena kruta otopina) i čestica intermetalnih spojeva. Unutarnja oksidacija ternarnih legura veoma je slična onoj za binarne legure, ali postoje i razlike u termodinamičkim svojstvima legirajućih elemenata. Kod izravne oksidacije čestica intermetalnog spoja zapažena je pojava selektivne oksidacije. Koncentracija reaktivnijih elemenata raste u oksidiranom dijelu čestica intermentalnog spoja (Te u AgTeSe leguri). Prema tome precipitirani oksidi nastali difuzijskom unutarnjom oksidacijom su bogati s manje reaktivnim legirajućim elementom (Se u AgTeSe leguri). U percipitiranim oksidnim česticama koncentracija selena je dvostruko veća nego telura

Mikrostrukturna in fazna analiza spominske zlitine CuAlNi po kontinuirnem litju

The results of the characterization of a CuAlNi shape-memory alloy after continuous casting technology are shown. Using this procedure a bar with a diameter of 8 mm was manufactured. After solidification of the alloy the microstructure characterization was carried out using optic microscopy (OM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) methods. Our results showed that the as-cast alloy consisted of the parent β1 and β1’ martensite phases. The martensite phase primary as the needle-like inside grains was observed. Martensite laths have different orientations inside particular grains. It was found that the average grains size is 98.78 µm. The grain diameter near to the external surface is higher than in the center. The average hardness of the alloy was 275 HV1.Prikazani so rezultati karakterizacije spominske zlitine CuAlNi po postopku kontinuirnega litja. Po navedeni proceduri so bile izdelane palice premera 8 mm. Po strjevanju zlitine je bila izvedena karakterizacija mikrostrukture z uporabo metod optične mikroskopije (OM), vrstične elektronske mikroskopije (SEM), diferencialne vrstične kalorimetrije (DSC) in rentgenske strukturne analize (XRD). Rezultati so pokazali, da lita zlitina sestoji iz izhodne faze β1 in martenzitne faze β1’. Opažena je bila martenzitna faza v obliki iglic v primarnih zrnih. Letve martenzita imajo različne orientacije v posameznih zrnih. Ugotovili smo, da je srednja velikost zrn 98,78 µm. Premer zrn v v bližini zunanje površine je večji kot v centru. Srednja trdota zlitine je bila 275 HV1

Classification of hot-rolled plates using the Mahalanobis distance of NMIs in Ti-stabilized austenitic stainless-steel produced by secondary metallurgy

Three charges of scrap-based, Ti-stabilized, Cr-Ni-Mo austenitic stainless steel in the form of hot-rolled steel plates were characterized. Based on automated metallographic analyses of representative microstructures, a quality characterization in terms of cleanliness of the hot-rolled steel plates was performed. Elevated contents of impurities, especially Pb, Bi, and oxygen, which affect the hot workability of stainless steels, were detected. The recycled FeTi-cored wire was the main source of the elevated levels of impurities detected in the hot-rolled, Ti-stabilized, stainless-steel plates. Related to this, elevated levels of nonmetallic inclusions (NMIs) and segregations were formed. The three charges were classified based on calculations of the Mahalanobis distance (MD) between the inclusions. The charge with the smallest number of nonmetallic inclusions was set as the reference class. The selection of outlier inclusions based on their MDs and their back-representation into ternary diagrams gave relevant metallurgical information about the abnormalities. The advantage of this technique is that the calculations of the MD and the threshold can be fully automated

Synthesis and characterization of hardened Cu-Fe-Ni-P alloy

In the manufacturing industry of electrical contacts, the prohibition of the use of toxic metals (Cd, Be), and desire to avoid the alloying with precious metals (Ag) has created a need for new alloys with good electrical conductivity and high mechanical properties at elevated temperatures. As a potentially useful material for this purpose, we have analyzed the continuously cast Cu-Fe-Ni-P alloy in various heat treatment conditions. Sequence of phase transformations during heat treatment was followed by 4 point D.C. electrical resistivity measuring method, and analyzed by scanning (SEM) and transmission (TEM) electron microscopy. Measurements of Vickers hardness and electrical conductivity after various heat treatment procedures indicate on high potential of Cu-Fe-Ni-P alloys as a material for electrical contacts

Energy for the future - nuclear fusion

Ocenjeno je naraščanje prebivalstva na Zemlji v naslednjih desetletjih, sočasno naraščanje potreb po primarni energiji in napisani so možni nosilci primarne energije. Razložen je princip jedrske fuzije, navedeni so robni pogoji, pri katerih je zlitje jeder sploh mogoče, in opisana je razlika med jedrsko fisijo in fuzijo. V obeh primerih se skupna masa po končani jedrski reakciji zmanjša, del mase se namreč spremeni v energijo. Prikazani so doslej vloženi napori znanstvenikov, skupaj z najnovejšim projektom ITER. Projekt naj bi končno realiziral težko pričakovano samodejno reakcijo zlitja jeder vodika v jedro helija in s tem rešil problem preskrbe človeštva s primarno energijo.Evaluation of the growth of word population for the next decades, the parallel growth of consumption of primary energy and the sources of primary energy are listed. Description the principle of nuclear fusion, of the boundary conditions for this fusion and of the difference between nuclear fusion and fission are explained. In both cases the mas is decreased in the reaction, since part of the mass is transformed to energy. The achievents of scientists in this field, the newest ITER project included, are presented. In the project the expected self supporting reaction of fusion of hydrogen nuclea to a helium nucleus will be achieved and the problem of supply of primary energy for the humanity solved

A NEW GENERATION OF ARMORED STEEL PLATES

The engineers of PROTAC d.o.o. and the biggest Slovenian steelwork ACRONI d.o.o., in cooperation with domestic and foreign institutions of science, have been designed and developed a new generation of armored steel PROTAC 500. Steel PROTAC 500 belongs to the group of high strength low alloy (HSLA) steels. It is made in steelwork ACRONI d.o.o. by the standard industrial procedures. The relevant mechanical properties of that steel are achieved by corresponding heat treatment procedure: quenching and tempering.Preliminary tests of the mechanical properties of the steel have indicated the possibility of using steel PROTAC 500 for light armored vehicles. The presented work studied the response of new generation armored steel plates PROTAC 500 to the ballistic testing with armored piercing bullets with a core of tungsten carbide, charge 7.62 mm. However, the interactions between the piercing bullets and the armored steel plate were also investigated. The most obvious and significant phenomena in penetrating of the piercing bullets Nammo AP8 in steel target PROTAC 500 are strain hardening of steels, the appearance of cracks and local failure, adiabatic shear bands (ASB) with related phase transformations, and melting as well as alloying at the interface between bullet and steel plat