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This paper describes a surface preparation on the properties of a nitrided or nitrocarburised layer. Nitrocarburation is carried out by TENIFER process (580 C/1h) on non-alloyed quality steel test specimens W.Nr. 1.0330 (EN 10130 DC01). The effect of cleaning and preparation of samples on the visual appearance, surface qualiy and corrosion resistance of the nitrocarburised layer was investigated. The surface quality was examined by determining the profile and roughness parameters. The corrosion resistance was tested by a gravimetric method with exposure of samples to a fog of 5% salt (NaCl) solution for 24 h.

radu su ispitana svojstva prevlake TiN nanesene PACVD postupkom na vertikalno postavljene ravne površine od alatnog čelika za topli rad X38CrMoV5–3. Uzorak visine 150 mm bio je postavljen direktno na katodu vakuumske peći RübigGmbH, tip PC 70/90 i prevučen prevlakom TiN. Analizirana je debljina, prionjivost i brazdanje prevlake po visini uzorka za tri orijentacije površine prema smjeru nastrujavanja prekursora TiCl4: za direktno nastrujavanu, bočnu i zaklonjenu površinu. Ispitivanjima i statističkom analizom utvrđena je ovisnost svojstsva prevlake o udaljenosti od katode peći. Također je utvrđeno da orijentacija vertikalno postavljene površine značajno ne utječe na svojstsva prevlake.

U radu su istražena mehanička svojstva tankih tvrdih prevlaka primjenom instrumentirane metode utiskivanja. Nanostrukturirani tvrdi metali prevučeni su postupkom plazmom potpomognutom prevlačenja iz parne faze, PACVD. Nanesene su višeslojne gradijentne PACVD prevlake kombinacijom slojeva titan nitrida TiN i titan karbonitrida TiCN. Ispitivanja su provedena primjenom različitih opterećenja u svrhu određivanja kritične sile loma prevlake. Na temelju nagiba krivulje sila-dubina prodiranja pri opterećenju i rasterećenju praćene tijekom ispitivanja određene su tvrdoća po Martensu, tvrdoća indentacije, modul indentacije i tvrdoća po Vickersu. Mjerenja su provedena u svrhu određivanja optimalnih parametara ispitivanja PACVD prevlaka na supstratu od tvrdog metala.

Tool wear has large impact not only on production costs but also on the quality of the final product. Therefore the intensivity of the tool wear should be reduced as much as possible. This leads to the development of new surface- engineering techniques in order to improve their wear resistance. In this paper new duplex treatment consisted of plasma nitriding and gradient multilayer PACVD coating was developed. The improvements of the treated surfaces in terms of wear and corrosion resistance have been analysed and new duplex treatment showed significantly higher wear resistance when compared to non-coated steel. Finaly, new duplex treatment was successfully applied on the moulds.

This paper investigates the tribological and corrosion properties of the direct current plasma assisted chemical vapour deposition TiN/TiCN coating applied to substrate of hardened and tempered tool steel for cold work grade X153CrMoV12. The developed coating is composed from a TiN sublayer and TiN/TiCN gradient layer with the final TiCN layer. The base coating properties have been characterized by examination of the surface roughness, chemical composition, thickness, adhesion and hardness. Wear resistance of the coating was tested by abrasion and erosion method. Corrosion resistance of the coating was determined using electrochemical polarization in aqueous 3.5% NaCl. Wear and corrosion resistance of the coating were compared with the same properties of the non-coated substrate. After laboratory tests, newly developed gradient multilayer TiCN coating was successfully applied on cold forming tools and moulds for plastic industry.

The paper compares the abrasion and erosion wear resistance obtained on test samples made from the high-speed steel Böhler S390 Microclean. The specimens were hardened and tempered, with or without application of DCT, and after that they had been coated by the thin PVD TiAlN layer. Tests of abrasive wear resistance were performed using an abrasive wear testing machine constructed according to the norm ASTM G 65-85. The weight loss was measured after 26 m, 52 m and 78 m during the abrasive wear testing. Test of erosion resistance was carried out by exposing test samples to abrasion or impact erosion of fine sand particles and determining the weight loss after 30 and 60 minutes of wear. Worn surface were analyzed by scanning electron microscopy. The significant influence of austenitization temperature on abrasion wear resistance has been observed, while the DCT has a minor effect. The DCT has significant influence on impact erosion resistance, while the austenitization temperature has a secondary influence.

The paper investigates methods for the thickness measurements of the direct current plasma assisted chemical vapor deposition TiN/TiCN coating applied to substrate of hardened and tempered tool steel for cold work grade X153CrMoV12. The developed coating is composed from a TiN sublayer and the TiCN as upper layer. The base coating properties have been characterized by examination of the surface roughness, chemical composition and thickness. The thickness of the sublayer and upper layer of the same TiN/TiCN coating was determined by the four methods: the ball grinding test (calotest ), the scanning electron microscopy (SEM), the energy dispersive spectroscopy (EDS) and by the quantitative depth profile analysis using glow discharge optical emission spectroscopy (GDOES). Results of measurements were statistically analize in aim to evaluate the accuracy and reliability of tested methods

With daily growth of the world's industry scientists are faced with rapid and continues changes, visible on product's diversity, lifetime and high quality demands. As a material for cutting tools hardmetals (WC-Co) stand out as an optimal material comparing the price and tool lifetime. Coating technology is the main way to improve the cutting tools performance. The area of application for these types of coated materials is expanding with the development and application of ultra fine powder grain sizes, as well as the advancements in technology. One method of coating hardmetals is plasma assisted chemical vapour deposition (PACVD), rarely used for coating hardmetals with ultrafine grain size. In this paper the potential of using multilayer gradient PACVD coating on the ultrafine grained WC-Co hardmetal samples is explored. The samples were consoldated by two different powder metallurgy processes ; sinter-HIP and convetional liquid phase sintering in hydrogen atmosphere. Multilayer gradient coating system consists of TiN layer, gradient layer of TiN + TiCN and layer of TiCN. Coating thickness measurements and Rockwell adhesion tests were conducted.

The paper compares the corrosion resistance of the TiN/TiCN coatings applied to samples of hardened and tempered tool steel for cold work grade K390 MC in relation to the plasma nitrided and non-coated samples. The multilayer coating of the TiN/TiCN is produced by a plasma-assisted chemical deposition from the vapor phase (PACVD) in industrial furnaces with hot wall. Plasma nitriding is performed in the same furnace in a separate cycle. Corrosion tests for determining the density of corrosion current, corrosion potential and corrosion rate were carried out using electrochemical polarization in aqueous 3.5% NaCl. Investigation of factors affecting coating’s corrosion resistance included testing of surface roughness before and after deposition, testing of chemical composition and structure of the coating. The microstructure and chemical composition of the coatings were examined by scanning electron microscopy (SEM). The results showing the increasing of the corrosion resistance of the TiN/TiCN coating three times in comparison with non-coated samples and the samples were plasma nitrided without a compound layer. The multilayer TiN/TiCN coating corrodes with a pitting corrosion, while non-coated and plasma nitrided samples corrode with local and general corrosion.

Nabavom novog uređaja za plazmatsko nitriranje i prevlačenje postupkom PACVD-a na FSB-u u Zagrebu omogućena je uporaba najmodernijih tehnologija modificiranja i prevlačenja u plazmi. Opisani su postupci sa svim potrebnim preduvjetima za osiguranje kvalitetnog modificiranja i/ili prevlačenja površina, svojstva koja se postižu i primjena. Na pokusnim uzorcima i konkretnim segmentima alata od visokolegiranih alatnih čelika za topli i hladni rad provedeni su pokusi nitriranja i/ili prevlačenja slojevima TiCN i TiBN. Prikazani su rezultati laboratorijskih i pogonskih ispitivanja. Primjenom novih slojeva TiCN i TiBN visoke tvrdoće ostvarena su značajna poboljšanja u pogledu: otpornosti na trošenje, otpornosti na koroziju te produljenje trajnosti alata. Uvođenjem ovih novih tehnologija u površinsku obradu zahtjevnijih konstrukcijskih dijelova i alata omogućuje se poboljšanje svojstava i kvalitete proizvoda te se podiže konkurentnosti proizvoda na globalnom tržištu.

Nitriding increases surface hardness and improves wear resistance of stainless steel. However, nitriding can sometimes reduce their corrosion resistance. In this paper, the influence of nitriding on the corrosion resistance of martensitic stainless steel was investigated. Plasma nitriding at 440 oC and 525 oC and salt bath nitrocarburizing were carried out on X17CrNi16-2 stainless steel. Microhardnes profiles of the obtained nitrided layers were examined. Phase composition analysis and quantitative depth profile analysis of the nitrided layers were performed by X-ray diffraction (XRD) and glow-discharge optical emission spectroscopy (GD-OES), respectively. Corrosion behaviour was evaluated by immersion test in 1% HCl, salt spray test in 5% NaCl and electrochemical corrosion tests in 3.5% NaCl aqueous solution. Results show that salt bath nitrocarburizing, as well as plasma nitriding at low temperature, increased microhardness without significantly reducing corrosion resistance. Plasma nitriding at a higher temperature increased the corrosion tendency of the X17CrNo16-2 steel.

Alatni čelici za topli rad namijenjeni su za izradu alata za oblikovanje metalnih i drugih materijala koji se u radu zagrijavaju na temperaturu iznad 200°C poput kalupa za tlačni lijev, ukovnja, alata za prešanje, ekstruziju, valjanje i duboko vučenje te kalupa u staklarskoj industriji. Navedeni alati u radu su izloženi, osim visokim toplinskim opterećenjima uslijed kontakta površine alata s obrađivanim materijalom, značajnim mehaničkim, tribološkim i kemijskim opterećenjima. Stoga, alatni čelici za topli rad moraju zadovoljiti cijelu skalu vrlo specifičnih svojstava. Za tribološku zaštitu i poboljšanje svojstava reznih alata, u cilju produljenja njihova vijeka trajanja i povećanja produktivnosti, najčešće se koriste tvrde prevlake. Prednosti primjene tvrdih prevlaka, koje su dobro poznate za rezne alate, u znatno su manjoj mjeri istražene kod alata za oblikovanje. Uzroci su složena geometrija, velika masa i niža tvrdoća osnovnog materijala ovih alata što negativno utječe na prionjivost prevlake, a time i na svojstva površinskog sloja. U okviru doktorskog rada razvijeni su novi površinski slojevi postupcima plazmatskog nitriranja i plazmom potpomognutog prevlačenja iz parne faze (PACVD) s ciljem poboljšanja svojstava alatnih čelika za topli rad i produljenja vijeka trajanja alata. U tu su svrhu razvijeni plazmatski nitrirani sloj i dvije višeslojne gradijentne prevlake TiCN i TiBN. U teorijskom dijelu rada detaljno su opisani mehanizmi dotrajavanja alata od alatnih čelika za topli rad, postavljeni su najvažniji zahtjevi vezani uz njihova svojstva te je dan pregled postupaka modificiranja i prevlačenja iz perspektive primjene na alatnim čelicima za topli rad. U eksperimentalnom dijelu rada analizirana su postignuta svojstva novorazvijenih površinskih slojeva, od karakterizacije slojeva do svojstava koje bi alatni čelici za topli rad trebali imati, s posebnim naglaskom na otpornost prema toplinskom umoru kao glavnom uzroku dotrajavanja ovih čelika. Ispitivanje površinskih slojeva i usporedba s konvencionalnom toplinskom obradom kaljenja i popuštanja koja se koristi u praksima provedena je na alatnom čeliku za topli rad X38CrMoV5-3. Detaljna karakterizacija dobivenih površinskih slojeva provedena je analizom kemijskog sastava slojeva (GDOES i EDS) i njihove mikrostrukture (svjetlosnim i skenirajućim elektronskim mikroskopom), određivanjem kristalne strukture (XRD) i hrapavosti površine, ispitivanjem prionjivosti prevlaka metodom brazdanja i metodom utiskivanja Rockwell C indentora, debljine prevlaka metodom utiskivanja kuglice i mikrotvrdoće dobivenih slojeva. U cilju kvantificiranja utjecaja novorazvijenih površinskih slojeva na svojstva i trajnost alatnog čelika za topli rad provedeno je ispitivanje otpornosti na trošenje u uvjetima abrazijskog (suhi pijesak/gumeni kotač), adhezijskog (eng. load scanning test) i erozijskog trošenja (erozija česticama), određivanje faktora trenja i kliznog trošenja (kuglica na ploči) te ispitivanje otpornosti na koroziju. Ispitivanje otpornosti na toplinski umor provedeno je na vlastito konstruiranom i izrađenom uređaju. U cilju potvrđivanja rezultata laboratorijskih ispitivanja novorazvijenih površinskih slojeva i istraživanja njihovog utjecaja na trajnost kalupa za tlačni lijev provedeno je ispitivanje u eksploatacijskim uvjetima na kalupu za tlačni lijev radijatora od aluminijske legure. Provedena analiza dobivenih rezultata ukazala je na bitno poboljšanje svojstava i produljenje vijeka trajanja alatnog čelika za topli rad primjenom novorazvijenih površinskih slojeva što je i potvrđeno ispitivanjem u eksploatacijskim uvjetima. Hot-work tool steels are intended for the fabrication of tools used for the shaping and forming of metals and other materials, such as die casting dies, drop hammer dies, tools for pressing, extrusion, rolling, deep drawing, and moulds used in glass industry. In service, these tools are heated to temperatures above 200oC because the tool surface and the material being formed are in contact. Besides being subjected to high temperatures, these tools are also subjected to mechanical loads and there are tribological issues and chemical actions involved in the process. Therefore, hot-work tool steels must have a wide range of specific properties. Hard coatings are generally used for tribological protection of cutting tools in order to improve their properties and thus to prolong their life and to increase productivity. Advantages of the application of hard coatings that are well known in the field of cutting tools have been studied less extensively in the field of tools for shaping and forming. This fact can be accounted for by a complex geometry and great weight of the tool together with a lower hardness value of the tool base material, which have a negative effect on the coating-substrate adhesion, and thus on the surface layer properties. In this doctoral thesis, new surface layers have been developed by using plasma nitriding and plasma assisted chemical vapour deposition (PACVD) with the aim of improving the properties of hot-work tool steels and of prolonging the tool life. For that purpose, a plasma nitrided layer and two gradient multilayer coatings, TiCN and TiBN, have been developed. The theoretical part of the thesis gives a detailed description of wear mechanisms in tools made of hot-work tool steels together with key requirements related to their properties. In addition, an overview of modification and coating processes is given regarding their application to the hot-work tool steels. In the experimental part of the thesis, the properties achieved in the newly-developed surface layers are analysed in terms of layer characterisation and expected properties of hotwork tool steels, with special focus on resistance to thermal fatigue as the main cause of failure in hot-work tool steels. The developed surface layers on the X38CrMoV5-3 hot-work tool steel were tested and results were compared with the results of conventional heat treatment processes of hardening and tempering commonly used in practice. Detailed characterisation of the surface layers was carried out by the analysis of their chemical composition (using Glow Discharge Optical Emission Spectrometry – GDOES and Energy Dispersive Spectrometry – EDS) and microstructure (using a light microscope and a scanning electron microscope), by determining their crystal structure (using X-Ray Diffraction – XRD) and surface roughness, by testing the adhesion of coatings (using the scratch test method and the Rockwell hardness test method - Rockwell C indenter) and the thickness of layers (using the ball indentation test) and by testing the micro hardness of nitrided layers and PACVD coatings. In order to quantify the effect of newly-developed surface layers on the properties and durability of hot-work tool steels, the following properties were tested: abrasive wear resistance (using the dry sand/rubber wheel test), adhesive wear resistance (using the load scanning test), erosive wear resistance (using the solid particle erosion test), and corrosion resistance. Resistance to thermal fatigue was tested using a device designed and manufactured by the doctoral candidate. In addition, the coefficients of friction and sliding wear were determined using the ball on flat sliding test. A die for the casting of aluminium alloy radiators was tested in real conditions in order to confirm the results of laboratory testing of the newly-developed surface layers and of their influence on the durability of the die. The analysis of results showed that the properties of the tool steel were significantly improved and the tool life prolonged by the newly developed surface layers, which was confirmed in real conditions.

Quenching of tool steels in a warm bath, i.e. martempering process, is implemented in order to reduce the residual stresses, strain and risk of rupture of steels and also to obtain a martensitic microstructure with the required properties. The implementation of this process is limited to steels with good hardenability, used for tools with a limited thickness. Acceptable steel properties were obtained by prescribing proper parameters of austenization and quenching. The paper describes the problems in the selection of optimal martempering parameters, such as optimum temperature and holding time in the warm bath, and in achieving them depending on the hardened steel, the weight and size of the tool. The characteristics of the cooling in a specially designed salt bath are described. Special features of its design include the workpiece cooling rate control by adding a small amount of water (up to 2%) to the salt AS140, by the regulation of temperature and by the agitation of molten salt. Such regulated and intense quenching allows the application of martempering process on tools with large cross-sectional area that are made of steel with medium to low hardenability. This was confirmed on the tool steel EN 90MnCrV8.

Advantages of applying deep cryogenic treatment (DCT) after the quenching of high speed steels are well documented in references. But still there are no fully established methods for testing wear resistance that would clearly distinguish the impact of DCT from the impact of other stages in the heat treatment process on the steel tribological properties. In search of solutions to this problem, the own abrasive and erosive wear tests were carried out on the samples made from PM S390 MC high speed steel quenched with three different austenitizing temperatures, with and without DCT prior to tempering. Erosive wear testing was conducted with jets directed to the tested surface at angles of entry of 90 or 30 degrees, which generated cases of impact erosion or abrasion erosion. Test results have shown an increased resistance to impact erosion on deep cryogenically treated samples, as opposed to the conventionally heat treated samples which have showed an increased resistance to abrasion erosion and pure abrasion, with a significant influence of austenitizing temperature.

Application of deep-cryogenic treatment (DCT) in heat treatment of high speed steels are well documented in an number of references. But using DCT is not universal solution for all requirements in high speed steel tools usage. This paper compares the improvements of mechanical and tribological properties achieved by heat treatment with or without application of DCT on test samples made of the HS10-2-5-8 high speed steel. The deep-cryogenic process or three high temperature tempering process has been applied after gas quenching from an austenization temperature selected between 1130 °C, 1180 °C or 1230 °C. The influence of these heat treat parameters to the improvement of the following properties has been compared: dimensional stability, secondary hardening and fracture toughness and erosive wear resistance.

Stainless steels are widely used due to their corrosion resistance, but low wear resistance limits their industrial application. Nitriding increases surface hardness and improves wear resistance. However, nitriding can sometimes reduce the corrosion resistance of stainless steels due to CrN precipitation. In this paper, the influence of nitriding on the corrosion resistance of martensitic stainless steel was investigated. Plasma nitriding at 440°C and 525°C and salt bath nitrocarburizing were carried out on the martensitic X17CrNi16-2 stainless steel. Microhardness profiles of the obtained nitrided layers were examined. Corrosion behaviour of samples was evaluated by immersion test in 1 % HCl and by electrochemical corrosion tests performed in 3.5 % NaCl. Results show that salt bath nitrocarburizing, as well as plasma nitriding at low temperature, increased microhardness without reducing corrosion resistance. On the other hand, plasma nitriding at a higher temperature reduced the passivity of the martensitic steel and increased the corrosion tendency.

In this paper, the effect of the heating rate on the process of tempering and the obtained hardness of the EN 100 V1 carbon tool steel has been investigated and determined. Steel specimens in two initial states were investigated: after quenching and after quenching and deep-cryogenic cooling. The specimens were submitted to tempering in a dilatometer, varying the heating rates, temperature of tempering between 200 °C and 690 °C and duration of keeping the specimens at that temperature. A common effect of these factors on the temperature of the start of particular stages in tempering and the obtained properties was determined using dilatometry. Differential dilatation analysis was carried out, together with hardness tests and XRD (X-ray diffraction) analysis.

The effect of tempering time and tempering temperature on the properties of hardened (and tempered) steel is usually presented by the Hollomon-Jaffe parameter expressed as P = T (C + logt). The expression does not take into account the heating rate at which a given tempering temperature is reached. A need to investigate how the heating rate at which a tempering temperature is reached affects both the tempering process and the properties has arisen from the fact that the tempering of an workpiece made of hardened steel is carried out at a finite heating rate at which a tempering temperature is reached. The heating rate as an additional factor in the process should not be neglected, particularly in a tempering process involving high heating rates (with or without keeping the workpiece at a tempering temperature). The paper deals with the effect of the heating rate at which a tempering temperature is reached on the development of the tempering process and on the obtained hardness in the hardened and tempered condition of non-alloyed tool steel grade EN 100 V1 (W.No. 1.2833). Two starting conditions of steel were investigated: the standard quenched condition and the quenched and deep cryogenically treated condition. The joint effect of the prior state and the heating rate on the temperature at the beginning of a particular stage in tempering and on the obtained properties was investigated by a dilatometric method (differential dilatation analysis), hardness tests, and XRD analysis. The test samples were tempered in a dilatometer at varying heating rates, tempering times and tempering temperatures between 200 and 690 ° C. It was found that the heating rate at which a tempering temperature is reached has a marked effect on the beginnings of microstructural transformations which are typical of tempering. If higher heating rates are involved, tempering processes start at higher temperatures. The joint effect of the heating rate, tempering temperature and tempering time at a given tempering temperature is given by the effective tempering parameter P* = T*(C + log t*). The results of conducted tests were analysed by means of a regression analysis to formulate equations expressing the dependence of microhardness and dimensional changes (dilatation) of test samples on the effective tempering parameter P*. The practical application of the obtained equations can be found in the preparation of tempering processes for hardened non-alloyed and low-alloyed tool steels as well as for structural steels which offer the possibility of reducing the duration of tempering.

U cilju poboljšanja otpornosti na trošenje i korozijske postojanosti skupine čelika EN C45, površina čelika podvrgnuta je postupku nitrokarburiranja u solnoj kupki, sa ili bez naknadne oksidacije. Značajno poboljšanje u svojstvima čelika osobito je vidljivo nakon nitrokarburiranja te još značajnije tijekom naknadne obrade u oksidacijskoj kupki. Za evaluaciju utjecaja parametara naknadne oksidacije na površinsku tvrdoću i otpornost na koroziju i trošenje, ispitni uzorci podvrgnuti su ispitivanju otpornosti na elektrokemijsku koroziju i ispitivanje otpornosti na adhezijsko trošenje. Dobiveni rezultati potvrđuju povoljan učinak naknadne oksidacije nitrkokarburiranog sloja na otpornost prema adhezijskom trošenju i otpronost prema elektrokemijskoj koroziji. Isti učinak nije zabilježen u slučaju bez naknadne oksidacije.

Senzorom momenta i sile moguće je mjeriti tri komponente momenta koje se javljaju na završnom članku robota, odnosno hvataljci. Korištenjem ovih informacija moguće je programirati adaptivno ponašanje robota u uvjetima kada zbog grešaka u pozicioniranju dolazi do prostorne kolizije. U sklopu rada su proučeni principi rada konkretnog senzora sile i momenta. Također, senzor je implementiran u robotskoj aplikaciji na primjeru umetanja osovinice u rupu (eng. „peg – in – hole).

U radu se obrađuju propisi, mjere i aktivnosti koje se primjenjuju u gradnji spremnika naftnih derivata. Posebno se analiziraju moguće opasnosti po okoliš u slučajevima nepoštivanja propisa i kontrole u eksploataciji.

Razvijena je i implementirana aplikacija temeljena na segmentaciji koja koristi kod prepoznavanja uzoraka strojnim vidom.

Poslovni kompleks na parceli tvornice Jadran u Zagrebu

Determining the strain flow and stress distribution in metallic materials during their deformation represents a significant challenge for researchers. The foil strain gage gave the possibility to test the actual stress in the deformation zone. Their application at higher deformations has proven to be limited, and does not give information on the entire deformation zone. With the development of digital technology, methods of digital image correlation (DIC) and thermography were developed. Their applications in researches today are more frequent, and are commonly being used for studying deformation of metals. The aim of this study was to determine the possibility of applying DIC method parallel with thermography to monitor the stresses distribution in deformation zone during the static tensile testing. The possibility of measuring with both methods on the same side of the sample, and the impact of markers required for DIC on the thermographic measurements, were tested. It has been proven that it is possible to use both methods on the same side of the sample without affecting one on the other. It was also found that by application of these two methods it is possible to observe the stresses distribution in the deformation zone.

U radu su uspoređene promjene hrapavosti i mikrostrukture površinskog sloja, otpornost na adhezijsko trošenje te otpornost na koroziju Ti6Al4V legure nakon postupaka toplinske oksidacije, anodne oksidacije i PACVD postupka prevlačenja. Otpornost na elektrokemijsku koroziju ispitana je metodom impendancijske spektroskopije. Otpornost na adhezijsko trošenje ispitana je metodom „Block on Ring“. Površina uzoraka je analizirana primjenom skenirajuće elektronske mikroskopije (SEM). Ispitivanja su pokazala značajni utjecaj stanja površine (morfologije, hrapavosti i mikrostrukturnog stanja) na tribološka i korozijska svojstva legure Ti6Al4V

Contemporary requirements pose ever more stringent requirements to the product development process. With demands for product quality enhancement and flexibility of product development and production there is a demand for cost reduction and shortening the time of product development. The trend that is increasingly noticeable in certain market segments is the abandonment of mass production in favor of small series, very often individualized (personalized) production. In order to meet such market demands additive manufacturing(AM) are being developed and applied.The main feature of these procedures is adding the material layer by layer to create wanted part. Such a production principle makes it possible to produce very complicated geometries. The biggest disadvantage of AM is the choice of materials that are limited to classical polymer materials. In the process of fused deposition modeling - FDM, the possibilities of applying new composite materials, i.e. materials, which, by combining two types of different materials, contribute to some of the better properties. The application of the composite increases the applicability of products made with AM. This paper analyzes the mechanical properties of three different test specimens. In the first case the test specimens have no reinforcement. The second and the third test specimens have 15% of the mass from glass fibers which are embeddedconcentrically and at an angle of 45 and 135. It can be concluded from the study that fiberglass reinforced products have better mechanical properties and that the mechanical properties depend on the direction of fiber placement.

U skladu sa zahtjevom IMO MSC.215 (82) Performance Standard for Protective Coatings priprema oštrog brida definirana je sa 3 prolaza brušenjem ili radijusom od 2 mm, aplikacijom dva dodatna ručna premaza te uklanjanje brušenjem utisnuća od valjaka i tvorničke oznake u skladu s normom ISO 8501-3. U ovom radu prikazati će se aplikacija premaza na različito pripremljenim bridovima i odnos debljine suhog filma na ravnom dijelu i na bridu te utjecaj debljine suhog filma na pripremljenim površinama oštrog ruba. Iz ekonomskih i praktičnih razloga nameče se pitanje opravdanosti zahtijeva navedene norme.

U radu je provedeno mjerenje gustoće i određivanje stupnja poroziteta nanostrukturiranih tvrdih metala. Uzorci nanostrukturiranih tvrdih metala konsolidirani su sinter-HIP postupkom koji se ubraja u postupke kojima se postižu teoretske gustoće. Za polazni prah odabran je novorazvijeni nanoprah volfram karbida, WC, dok je za materijal matrice odabran prah kobalta, Co. Tri mješavine s različitim udjelom veziva ; 5, 10 i 15 wt. %Co konsolidirane su za potrebe istraživanja. Mjerenje gustoće provedeno je nakon postupka konsolidacije vaganjem uzoraka na zraku i u tekućini sukladno normi HRN EN ISO 3369. Analiza polirane površine provedena je radi određivanja poroziteta i nevezanog ugljika. Analiza se sastojala od pregledavanja polirane površine ispitnih uzoraka pri raznim povećanjima. Stupanj poroziteta i nevezanog ugljika određen je usporedbom polirane površine uzoraka s fotomikrografima navedenim u normi ISO 4505:1978. Na temelju provedenih mjerenja doneseni su zaključci o svojstvima nanostrukturiranih tvrdih metala.

The paper describes mechanical testing on specimens made from 13CrMo4-5 boiler steel and numerical analysis based on conducted experiment. During magnetic particle testing (MT) examination of weld on the bottom header of a front wall of boiler large amount of indications (cracks) were noticed. In the experimental part of paper tension test was conducted in order to determine basic mechanical properties of specimens. After that, bend testing was conducted to determine an angle on which cracks occur, and ultimately fracture. In order to compare obtained results with results obtained experimentally, 3D model of specimens was created, and numerical analysis by finite element method (FEM)was carried out. Analysis of results has given guidance for further examinations, assuming that they will ultimately give an answer on type an incurred cracks.

Zona zapljuskivanja najugroženije je strukturno područje odobalnih objekata koje je podložno koroziji. Praćenje stanja zaštitnog premaza u zoni zapljuskivanja, važno je zbog pravovremenog održavanja, produljenja radnog vijeka i pouzdanosti objekata. Istraživanje je provedeno s ciljem karakterizacije elektrokemijskog terenskog senzora, koji će omogućiti brzo i jednostavno otkrivanje stanja sustava premaza na zaštićenoj površini objekta. Istraživanje smo provodili na dvije terenske lokacije, uzorcima postavljenim u obalnom području kruga Terminala Janafa u Omišlju i na različitim pozicijama u zoni zapljuskivanja samopodizne platforme Labin u Puli. Inicijalna mjerenja provedena su u laboratoriju u Zagrebu. Uzorci su izrađeni većinom od ABS AH 36 čelika, debljine 8, 12 i 20 mm, s pripremom površine do stupnja čistoće Sa 2 1/2 i St3, te su na njih naneseni zaštitni sustavi premaza različitog broja i debljina slojeva, upotrebom zračnog štrcanja pod tlakom ili valjka, ovisno o specifikaciji. Mjerenja su provedena na ukupno 50 različitih uzoraka i više lokacija na platformi, metodom elektrokemijske impedancijske spektroskopije pri f=0.1 Hz, i ponovljena nakon četiri i sedam mjeseci izloženosti morskom okolišu. Na svakom uzorku provedeno je više mjerenja impedancije i kapaciteta premaza, koja su pokazala konzistentnost uz prihvatljiva odstupanja i dovoljnu razlučivost za njihovu pouzdanu primjenu u svrhu ocjene stanja premaza.

Sve veći zahtjevi tržišta kao što su povećanje kvalitete proizvoda, fleksibilnost pri razvoju i proizvodnji, sniženje troškova, skraćenje vremena izrade, personalizirana proizvodnja, izrada komponenata složene geometrije i slično rezultirali su razvitkom i uvođenjem u primjenu postupka aditivne proizvodnje električnim lukom i žicom (engl. Wire and Arc Additive Manufacturing – WAAM). Pri WAAM postupku, zbog svoje velike produktivnosti, često se koristi MIG/MAG postupak. Ipak, konvencionalni MIG/MAG postupak ima brojna ograničenja u odabiru optimalnog područja parametara, pa se stoga konvencionalni MIG/MAG postupak često zamjenjuje modificiranim inačicama. U radu je opisana primjena MAG CBT postupka za aditivnu proizvodnju električnim lukom i žicom. Određeno je optimalno područje parametara što je rezultiralo stabilnim procesom i zadovoljavajućom produktivnošću. Makroanalizom, mjerenjem tvrdoće i čvrstoće ispitan je utjecaj unosa topline na geometriju zida i mehanička svojstva.

U radu je istražena primjenjivost instrumentirane metode utiskivanja za karakterizaciju mehaničkih svojstva nanostrukturiranih tvrdih metala. Istraživanja su provedena na uzorcima nanostrukturiranih tvrdih metala konsolidiranih iz polaznih prahova WC veličine zrna od 95 i specifične površine 4, 0 m2/g jedinstvene kombinacije visoke tvrdoće i žilavosti te homogene mikrostrukture. Tijekom ispitivanja kontinuirano su praćene sila i dubina prodiranja na temelju kojih su konstruirane krivulje sila-pomak. Na temelju nagiba krivulje sila-pomak pri opterećenju i rasterećenju određene su tvrdoća po Martensu, tvrdoća indentacije, modul indentacije i tvrdoća po Vickersu. Doneseni su zaključci o primjenjivosti instrumentirane metode utiskivanja za karakterizaciju nanostrukturiranih tvrdih metala.

U radu su istražene mjeriteljske karakteristike referentne pločice tvrdoće po Vickersu izrađene od bakrene legure. Jedan od nedostataka bakrenih legura jest promjena tvrdoće tijekom vremena kao posljedica starenja materijala i zaostala naprezanja pa je valjanost takvih pločica gotovo dvostruko niža od onih izrađenih od čelika. Ispitivanja su provedena na referentnom etalonu Vickers tvrdoće, a za potrebe istraživanja korištena je komercijalno dostupna, umjerena referentna pločica Vickers tvrdoće vrijednosti tvrdoće 191, 3±3, 93 HV5. Ispitana je jednolikost tvrdoće na temelju dvadeset otisaka raspoređenih jednoliko preko cijele referentne površine. Referentni otisci izmjereni su na referentnom etalonu tvrdoće u svrhu usporedbe referentnih vrijednosti dijagonala otisaka sa izmjerenim vrijednostima dijagonala nastalih prilikom ispitivanja jednolikosti tvroće. Na temelju provedenih mjerenja doneseni su zaključci o mjeriteljskim karakteristikama referentnih pločica tvrdoće od bakrene legure.

U cilju dugotrajne zaštite nosivih čeličnih konstrukcija provodi se dodatna zaštita pocinčanih čeličnih elemenata sustavom premaza. Pri tome je dostignuta debljina premaza jedan od elemenata kvalitete antikorozivne zaštite. Nedestruktivne metode mjerenja zasnivaju se na fizikalnim principima koje ovise o svojstvima kako samog premaza tako i same podloge, tj. osnovnog materijala kao kombinacije cinka na čeliku. U radu su prikazani rezultati istraživanja mjerenja debljine prevlake za dvije različite metode u odnosu na referentne standarde na način usporedbe uz izraženu mjernu nesigurnost.

Napredak civilizacije od samih njezinih početaka usko je povezan s otkrivanjem, dobivanjem, preradom i oblikovanjem materijala u uporabive tvorevine. Termin „metali antičkog doba“ odnose se na sedam metala koje je čovječanstvo otkrilo i koristilo u prapovijesti. Tih sedam metala (zlato, bakar, srebro, olovo, kositar, željezo i živa) su metali na kojima je ustanovljena moderna civilizacija. Prvi pronađeni željezni artefakti datiraju iz 4. tisućljeća pr. Kr. i izrađeni su od meteoritskog željeza. Ipak, kao početak željeznog doba uzima se vrijeme kada se željezo počelo proizvoditi iz rude (oko 1500. godine pr. Kr.). Razvojem načina proizvodnje i toplinske obrade, materijali na bazi željeza dobivaju sve bolja svojstva i ubrzo postaju najkorišteniji tehnički materijal, što su i danas, 6000 godina nakon prve primjene.

In the manufacturing industry, it’s trivial to use steels tools. Those alloys, called tool steels, are special alloys designed for working on other materials. Typical applications are hot-work forging and extrusion dies, helicopter rotor blades, etc. The tooling industry is increasingly demanding improvement in the tools’ quality, i.e., longer lifetime and lower costs of the tools. For longer life and higher design accuracy, properties of this type of tool steel can be improved by various types of heat treatment. The mechanical and metallurgical tools’ properties are directly related to which heat treatment they were submitted. Thus, excellence in heat treatment is sought. The vacuum furnace with pressurized gas cooling is a widespread technology in heat treating for the tooling industry. Despite having advantages over the traditional process, it remains an expensive and less versatile process. It was developed in Croatia an innovative furnace with an inert helium gas atmosphere and space attach a tank filled with any liquid quenchant. It is expected that this furnace can reduce costs and achieve better properties of tools. The interest of this study is to perform heat treatments in some H series tool steels in the two furnaces mentioned above. This way, comparing mechanical through impact tests, thermal fatigue, hardness, and thus analyze the advantages and disadvantages of this innovative proposal to the tooling industry.

Današnjom UV Inkjet tehnologijom tiska omogućena je alternativa otiskivanja limenih proizvoda. U ovom radu pokazati će se kolika je mehanička čvrstoća otisaka na metalnim čepovima otisnutih tehnikom Inkjeta sa tri različita stroja. Sukladno tome, otisci će se prvenstveno podvrgnuti denzitometrijskim mjerenjima, a nakon toga i mehaničkom oštećenju. Denzitometrijska kontrola provedena je kako bi se utvrdila kvaliteta otisnutih tonova, te su izrađene krivulje reprodukcije. Iz dobivenih krivulja vidljivo je kako je reprodukcija na Rolandu nešto tamnija, dok su otisci dobiveni Durst strojem najumjereniji. Kako bi se odredila razlika između Inkjet UV sušećih bojila izvršena je međusobna komparacijska kolorimetrijska analiza. Iz promatranja njihovih različitosti, utvrđeno je da nema pravilnosti između otisaka, te se svaki ponaša zasebno. Svi otisci su podvrgnuti mehaničkom oštećenju, tj. provedeno je ispitivanje Cross Cut testa. Ispitivanje je pokazalo kako su otisci izuzetno stabilni na metalnoj podlozi, te su njihova oštećenja nakon ispitivanja minimalna. Slikovnom analizom uzoraka potvrđeni su vizualni rezultati i oni daju veću preciznost pri određivanju oštećenja površine.

U radu je prikazan utjecaj tretiranja površine piezokeramike plazmom argona na adheziju dvokomponentne silikonske mase pri različitim parametrima, provođenjem destruktivnih testova. U preliminarnom nizu eksperimenata ispitan je utjecaj tretiranja površine uzoraka piezokeramike plazmom argona prema parametrima u preporuci proizvođača. Destruktivan test se provodio na uzorcima tretiranim i netretiranim plazmom. Kako bi se skratilo vrijeme potrebno za tretiranje površine piezokeramike, u drugom nizu eksperimenata uzorci su tretirani plazmom argona uz promjenu sljedećih parametara: snaga generatora, tlak plina te vrijeme tretiranja površine. Na površine tretirane plazmom nanesen je sloj dvokomponentne silikonske mase. Iz dobivenih rezultata određeni su optimalni parametri tretiranja površine uzoraka piezokeramike plazmom argona – oni pri kojima je postignuta najbolja adhezija silikona. U usporedbi s preporukom proizvođača uređaja, proces tretiranja skraćen je na pola.

Nowadays, more and more attention is given to cemented carbides with small grain size, which stand out with their enhanced mechanical properties and exploitation characteristics. The advantages of small grained cemented carbides can only be utilized if that grain size can be preserved after the sintering. For that reason grain growth inhibitors GGIs are added into the starting powder mixture of WC-Co before sintering. The experiments were carried out on three different samples sintered from diferent mixtures of WC powder with the cobalt content of 5, 10 and 15 wt.% with the constant content grain growth inhibitors (0.41% VC, 0.80% Cr3C2). The grain size after sintering has been determined by conducting coercive force measurements. On the samples of cemented carbides, Vickers hardness measurements (HV30) have been carried out. By analysing the obtained results a significant correlation between the Vickers hardness and WC grain size influenced by the Co content in the stating mixture has been determined.

The basic requirement which is placed in front of modern thermal power plants is higher degree of utilization rates. As one of possible way of fulfilling the requirement is to increase steam parameters, which is conditioned by application of materials suitable for work on default temperatures and pressures. Materials used in steam boiler production must fulfill quality requirements, which are defined according to terms of exploitation which will be exposed during his lifespan, but also should be appropriate for the manufacturing process. At the same time, with the development of of boiler power plants, development of materials to be installed in boilers has run also. As one of significant representative of materials in boiler power production is also heat resistant low alloy steel 13CrMo4 - 5. Aim of this paper was to present and analyze main causes which led to the occurence and propagation of crack on bottom header front wall of crack. After conducted experiments type of cracks is determined, and after detailed analysis causes of cracks.

U radu su prezentirani rezultati istraživanja utjecaja vrste plinske mješavine na geometriju i korozijsku postojanost zavarenog spoja. Eksperiment je urađen na limovima debljine 2 mm od duplex čelika W.Nr.1.4462. Zavarivan je sučeljeni spoj pomoću Nd:YAG lasera. Korišteni su zaštitni plinovi i to argon, dušik, helij i njihove mješavine. Provedena je statistička obrada rezultata mjerenja i matematičko modeliranje metodom odzivnih površina. Dobiven je značajan utjecaj zaštitnih plinskih mješavina i unosa topline na geometriju zavarenog spoja dok rezultati uglavnom nisu pokazali značajan utjecaj zaštitnih plinskih mješavina i unosa topline na otpornost na rupičastu koroziju.

Vrijednosti tvrdoće izmjerene Vickersovom metodom ne ovise o primijenjenom opterećenju. Ova tvrdnja ne vrijedi za vrlo male iznose opterećenja tj. kod mjerenja mikrotvrdoće. Kod nekih materijala izmjerena tvrdoća se smanjuje s porastom opterećenja, što se karakterizira kao normalan utjecaj opterećenja na tvrdoću, dok se kod drugih materijala izmjerena tvrdoća povećava s opterećenjem, što je obrnut utjecaj opterećenja na tvrdoću. U radu je izmjerena tvrdoća osovine promjera 35 mm od čelika za poboljšavanje oznake 39NiCrMo3. Tvrdoća je mjerena pri opterećenjima od 0, 4903 N, 0, 9807 N, 1, 961 N i 4, 903 N, od ruba presjeka prema sredini. Osovina je toplinski obrađena poboljšavanjem. Dobiveni podaci su analizirani i statistički obrađeni s tri matematička modela: Meyerov zakon, model otpornosti razmjeran svojstvima uzorka (PSR) i modificirani model otpornosti razmjeran svojstvima uzorka (MPSR), a dobiveni rezultati ukazuju na postojanje ovisnosti između opterećenja i tvrdoće. Najviše vrijednosti tvrdoće dobivene su pri opterećenju 0, 4905 N, a najniže kod opterećenja 4, 905 N.