Effect of high-pressure torsion on microstructure, mechanical properties and corrosion resistance of cast pure Mg

© 2018, The Author(s). High-pressure torsion (HPT) processing was applied to cast pure magnesium, and the effects of the deformation on the microstructure, hardness, tensile properties and corrosion resistance were evaluated. The microstructures of the processed samples were examined by electron backscatter diffraction, and the mechanical properties were determined by Vickers hardness and tensile testing. The corrosion resistance was studied using electrochemical impedance spectroscopy in a 3.5% NaCl solution. The results show that HPT processing effectively refines the grain size of Mg from millimeters in the cast structure to a few micrometers after processing and also creates a basal texture on the surface. It was found that one or five turns of HPT produced no significant difference in the grain size of the processed Mg and the hardness was a maximum after one turn due to recovery in some grains. Measurements showed that the yield strength of the cast Mg increased by about seven times whereas the corrosion resistance was not significantly affected by the HPT processing

Microstructures, mechanical stability and strength of low-temperature reversion-treated AISI 301LN stainless steel under monotonic and dynamic loading

Abstract Refining grain size is known to enhance mechanical properties also in austenitic stainless steels. To better understand the background of these properties, various reversion-treated structures were created in AISI 301LN (18Cr-7Ni-0.15N) steel and the microstructural features affecting flow behaviour and strength under monotonic and cyclic straining were investigated. Fully and partially reversed microstructures were produced using prior cold rolling thickness reductions in the range of 32–63% and both resistant and induction heating. Some selected reversed structures were also strengthening rolled to 20% reduction. The resultant microstructures were characterised using different research equipment and methods and their mechanical properties determined by microhardness, tensile and fatigue tests. The main interest was focused on the microstructural features of low-temperature reversed structures and the stability of austenite in them. Effective grain refinement was achieved after 56–63% rolling reduction. Depending on the reduction and annealing conditions, the reversed structures consisted of various amounts of submicron- and medium-sized austenite grains and retained phases. All the reversed structures showed non-homogenous, often bimodal grain size distribution. It was demonstrated that the stability of austenite was much reduced after annealing at temperatures ≤ 850 °C, which was attributed to precipitation occurring at these low temperatures. Fine grain size itself promoted higher stability, but the coarsest retained austenite was stable due to its special orientation. Therefore, medium-sized grains of 3–10 μm, formed mainly from slightly deformed strain-induced martensite, appeared to be most unstable, the fraction being highest after the lowest reduction. The yield and fatigue strengths of the low-temperature reversion-treated structures were significantly higher than those of commercial 301LN. Fatigue strength corresponded to that of a 20% cold-rolled sheet. Strength was highly enhanced even after the lowest cold rolling reduction of 32%, for the lower strength of the coarser reversed grain structure was balanced by the higher fractions of strong retained austenite and martensite phases.Tiivistelmä Austeniitin raekoon hienontamisen tiedetään parantavan merkittävästi ruostumattomien terästen mekaanisia ominaisuuksia. Hienorakeisten reversiorakenteiden muokkauslujittumiseen ja lujuuteen vaikuttavien tekijöiden yksityiskohtaista tutkimista varten tuotettiin AISI 301LN (18Cr-7Ni-0.15N) teräkseen 32–63% kylmävalssausreduktiota ja sen jälkeistä vastus- tai induktiokuumennusta käyttäen täysin sekä osittain reversoituneita mikrorakenteita. Lisäksi osa reversiorakenteista vielä lujitusvalssattiin 10–20% reduktioon saakka. Mikrorakenteiden karakterisointiin käytettiin monipuolisesti eri tutkimuslaitteita ja menetelmiä sekä mekaanisten ominaisuuksien määrittämiseen mikrokovuus-, veto- ja väsytyskokeita. Ensisijaisena tarkoituksena oli tutkia yksityiskohtaisesti matalassa reversiolämpötilassa muodostuneita mikrorakenteita sekä hienorakeisen austeniitin stabiilisuutta monotonisessa ja syklisessä kuormituksessa. Reversiokäsitellyissä rakenteissa esiintyi vaihteleva määrä hienoja (raekoko alle 1 μm) ja keskisuuria (raekoko 3–10 μm) austeniittirakeita mahdollisien karkeiden jäännösfaasien lisäksi kylmämuokkaustilasta ja lämpökäsittely-parametreista riippuen. Suuri muokkausaste edesauttoi selvästi raerakenteen hienontumista, mutta kaikki rakenteet olivat raekokojakaumaltaan epähomogeenisia. Työssä demonstroitiin kuinka alle 900 °C:ssa hehkutetut reversiorakenteet ovat huomattavasti epästabiilimpia kuin korkeammassa syntyneet verrokkirakenteet, minkä osoitettiin johtuvan krominitridien erkautumisesta. Raekoon hienontuminen itsessään suosii suurempaa stabiilisuutta, mutta karkeimmat muokkautuneet jäännösausteniittirakeet olivat stabiileja niiden orientaation takia. Täten keskisuuret rakeet olivat epästabiileimpia. Keskisuurien rakeiden osoitettiin syntyvän pääasiassa vähän muokkaantuneesta martensiitista, ja niitä esiintyi eniten 32% reduktiolla valssatuissa rakenteissa. Matalassa lämpötilassa syntyneiden reversiorakenteiden lujuus oli merkittävästi korkeampi kuin kaupallisen teräksen. Väsymislujuus vastasi noin 20% lujitettuvalssattua tuotetta. Hehkutusta edeltänyt kylmämuokkausaste vaikutti vain vähän reversiorakenteiden lujuuteen, sillä vaikka pienin muokkausaste johti karkeimpaan keskimääräiseen raekokoon, siinä lujuutta lisäsivät kovat jäännösfaasit

Overall equipment efficiency measurement system based on Raspberry Pi

Abstract A complete system with the associated hardware, software and graphical user interface for Overall Equipment Efficiency measurement was developed in this work and then thoroughly tested on a factory environment for a period of over three years. The system was designed to be easily utilized on a typical production line, where the products can be identified with a simple sensor, which could also be deployed without interfering the line itself and the related electronics. This work shows that an extremely cost-effective solution based on popular Raspberry Pi architecture can be effectively utilized for all the required tasks needed for a functioning independent system. Data collection electronics with the related database for storing the data and a web server for the graphical user interface and reporting, were all integrated on a single enclosure. In addition, an analysis software was developed to get the benefit from the collected data, and the software was further developed along with the graphical user interface based on the feedback from the collaborating factory. During the test period, over three million products were correctly detected, and all the stoppages were recorded. The developed system revealed important bottle necks on the production line

Ultimate theoretical span lengths for snow and ice arches and vaults

Abstract The article discusses the theoretical basis for the design of arch and vault structures. In the design of arches and vaults, it is essential to realize that the optimal shape of the arch is determined by the loading. This article clarifies the use of parabolic shapes in snow structures. If parabolic shape is used, it is required that, the vertical load is constant along the arch. This means that the snow thickness in the arch changes so that the thickness is smallest at the base. Catenary, the shape of a hanging chain, is another well-known shape. We show analytical and numerical calculations yielding the optimal parameters for the catenary arch. It is demonstrated that the compression stress in a catenary arch is minimized when the span-to-height ratio of the catenary arch is 2,96. Snow vaults should be compressed structures. This means that the arch thrust line should lie within the middle third of the arch cross section. The compression line is a familiar concept historically as a stone and concrete vault design principle. In snow and ice structures, the compression line should be designed to travel along the axis of the arch, resulting in a uniformly distributed compression stress in the cross section. The general design principle is to retrieve the moment-less shape of the structure, that is, to design the shape so that the thrust line is centric. The extreme theoretical spans can be achieved when the moment-less arch is designed such that its compressive stress is uniform across the arch. The article illustrates the dimensions of a constant stress arch, a catenary arch, and a parabolic arch when the design is based on the same compressive stress level. The theoretic ultimate span and the shape of the constant stress snow arch is found when the span-to-height ratio is close to unity. Guidelines for designing snow arches and vaults have been published. It should be noted that theoretically the correct form is the shape of the centreline of gravity of the arch. Because the snow structures have rather thick cross-sections, the shape of the inner surface of the vault may be different from the optimal shape of the centreline. The article presents calculations that illustrate this

Tehokkuutta monimenetelmävalmistuksesta

Abstract Efficient applications using multi-method production project sought to find ways to promote low-carbon production through metal 3D printing. This technology enables the design and manufacturing of innovative products in a new way. The method makes it possible to achieve low product costs with a low ecological footprint, leading to the opening of new products and new markets for local industry. Additive manufacturing can also provide significant advantages over traditional manufacturing methods and can be utilized alongside traditional manufacturing methods. There was little to none research available on the post-processing of metal 3D prin- ted products at the beginning of the project. However, they can significantly improve the product’s properties in terms of strength, fatigue and corrosion resistance as well as appearance. In addition, multi-method production allows the best aspects of different methods to be combined when reliable methods are found to connect parts made in different ways. The project extensively studied the post-processing of printed metal parts: welding, coating, surface quality improvement, heat treatments and hybrid product manufacturing, as well as basic research related to the removal of support materials. The more detailed research results of the project revealed the suitability and effect of many coatings, such as anodizing, silver and gold coating, on the properties of parts such as corrosion resistance, as well as the general suitability of powder coatings, cerakote, PVD and mechanical treatments on the printed surface. The research results showed that laser welding can be used to produce highly reliable joints between prints. Based on the results, for example, sheet metal can be joined to printed parts with 316L material both by laser welding and by printing directly on the plate. Good results were also obtained from the mixed pair joints of 316L and Inconel 718 materials and the hybrid products thus prepared.Tiivistelmä Tehokkuutta monimenetelmävalmistuksesta -hankkeessa pyrittiin löytämään keinoja tuotannon vähähiilisyyden edistämiseksi metallin 3D-tulostuksen avulla. Kyseinen tekniikka mahdollistaa uudella tavalla innovatiivisen tuotteen suunnittelun ja valmistuksen. Menetelmällä on mahdollista saavuttaa alhaiset tuotekustannukset vähäisellä ekologisella jalanjäljellä, mikä johtaa uusien tuotteiden ja uusien markkinoiden avautumiseen paikalliselle teollisuudelle. Ainetta lisäävällä valmistusmenetelmällä voidaan myös saavuttaa merkittäviä etuja perinteisiin valmistusmenetelmiin verrattuna ja sitä on mahdollista hyödyntää perinteisten valmistusmenetelmien rinnalla. Metallista 3D-tulostettujen tuotteiden jälkikäsittelyihin liittyen oli hankkeen alkaessa menetelmästä riippuen hyvin vähän tai ollenkaan tutkittua tietoa. Niiden avulla voidaan kuitenkin tuotteen ominaisuuksia parantaa merkittävästikin niin lujuuden, väsymis- ja korroosiokeston kuin ulkonäönkin kannalta. Lisäksi monimenetelmävalmistuksella voidaan eri menetelmien parhaat puolet yhdistää, kun löydetään luotettavat menetelmät liittää eri tavoin valmistetut osat toisiinsa kokonaisuuksiksi. Hankkeessa tutkittiin laajasti metallitulosteiden liitettävyyttä, pinnoittamista, pinnanlaadun parannusta, lämpökäsittelyitä sekä hybridituotteiden valmistusta sekä tehtiin perustutkimus tukimateriaalien poistoon liittyen. Hankkeen tarkemmista tutkimustuloksista selvisi monien pinnoitteiden, kuten anodisoinnin, hopea- ja kultapinnoitteen soveltuvuus ja vaikutus kappaleiden ominaisuuksiin kuten korroosiokestoon, sekä yleinen jauhemaalien, cerakoten, PVD:n sekä mekaanisten käsittelyjen soveltuvuus tulostetulle pinnalle. Laserliitosten tutkimustulosten perusteella sillä voidaan tuottaa erittäin luotettavia liitoksia tulosteiden välille. Tulosten perusteella esim. levymateriaali-tuloste -liitokset onnistuvat 316L-materiaalilla sekä laserhitsaamalla että suoraan levyn päälle tulostamalla. Hyviä tuloksia saatiin myös 316L- ja Inconel 718 -materiaalien sekapariliitoksista ja näin valmistetuista hybridituotteista

Static properties of laser welded ultra-high-strength stainless steel tube

Abstract This paper investigates static properties of laser welded ultra-high-strength (UHS) stainless steel tube. The material of the tube was cold-hardened ultra-high-strength austenitic stainless steel (AISI 301 2H) with a tensile strength of 1.55 GPa. The AISI 301 steel tubes were manufactured by laser welding from two U-shaped parts. For comparison, low strength stainless steel (AISI 304) tubes were also examined in the experiments. The microstructure of the welded joints was studied by optical microscopy. The hardness of the laser weld joint was determined. The strength of the tubes was studied by three-point bending and compression tests. It was observed that the hardness at the HAZ of the AISI 301 joint was 51% lower than that of the base material. HAZ showed new fine grains of austenite phase structure due to the reversion transformation from martensite to austenite. Result showed that the AISI 304 weld had the same hardness as the base material. Three-point bending experiments revealed that the bending strength of the UHS (AISI 301) steel tube was approximately 60% higher than that of low strength AISI 304 steel tube. The location of the weld relative to the direction of the compressive force had a significant effect on the compressive strength of the UHS (AISI 301) steel tube

Contactless online characterization of large-area conductive thin films by thermography and induction

Abstract Testing and characterization techniques intended for traditional electronics production are rarely compatible with modern large-area, thin film electronics manufacturing processes such as roll-to-roll fabrication. Online quality monitoring of conductive thin films is necessary for upscaling and maintaining high-yield production. Thermography has already shown its usefulness in these kinds of applications, but has suffered from the lack of proper non-contact electrical heating. Now a fully contactless quality inspection technique based on thermal imaging and induction heating is implemented and evaluated. This approach is capable of discovering defected areas and estimating conductivity degradation online with full coverage over conductive thin films

Reversed microstructures and tensile properties after various cold rolling reductions in AISI 301LN steel

Abstract Heavy cold rolling is generally required for efficient grain size refinement in the martensitic reversion process, which is, however, not desirable in practical processing. In the present work, the influence of cold rolling reductions of 32%, 45% and 63% on the microstructure evolution and mechanical properties of a metastable austenitic AISI 301LN type steel were investigated in detail adopting scanning electron microscopy with the electron backscatter diffraction method and mechanical testing. A completely austenitic microstructure and a partially reversed counterpart were created. It was found that the fraction of grains with a size of 3 µm or larger, called medium-sized grains, increased with decreasing the prior cold rolling reduction. These grains are formed mainly from the shear-reversed austenite, transformed from slightly-deformed martensite, by gradual evolution of subgrains to grains. However, in spite of significant amounts of medium-sized grains, the tensile properties after the 32% or 45% cold rolling reductions were practically equal to those after the 63% reduction. The austenite stability against the formation of deformation-induced martensite in subsequent straining was reduced by lowering the cold rolling reduction, due to the larger grain size of medium-sized grains and the shift of their orientation towards {211} <uvw>

Enhancement of grain structure and mechanical properties of a high-Mn twinning-induced plasticity steel bearing Al–Si by fast-heating annealing

Abstract In this study, a cold-rolled Fe-0.01C-21.3Mn–3Al–3Si (wt.%) TWIP steel was undergone a fast-heating (FH) annealing at high temperatures of 1000–1200 °C and 2 s soaking time for grain refinement and controlling the phase structure and thereby to enhance the mechanical properties. For comparison, recrystallization annealing was conducted at lower temperatures of 650 and 700 °C for 180 s. The microstructural evolution of the FH annealed steel was surveyed using electron backscatter diffraction. The strain hardening behavior of the FH structures was studied by tensile tests. The tensile flow curves were also predicted by a phenomenological model based on the evolution of dislocation density during deformation. Fine mainly austenitic structure was promoted by FH annealing at 1000 and 1100 °C. At the lower temperatures of 650 and 700 °C, bands of finer grains, indicative of some inhomogeneity, were evident in the mostly austenitic recrystallized microstructure. However, at 1200 °C, the structure consisted of coarse austenite and ferrite with almost equal fractions. The FH annealed structures exhibited a remarkable improvement in the mechanical properties (a better combination of yield and tensile strength and ductility) compared to conventional long annealing cycles

Processing and properties of reversion‐treated austenitic stainless steels

Abstract Strength properties of annealed austenitic stainless steels are relatively low and therefore improvements are desired for constructional applications. The reversion of deformation induced martensite to fine-grained austenite has been found to be an efficient method to increase significantly the yield strength of metastable austenitic stainless steels without impairing much their ductility. Research has been conducted during thirty years in many research groups so that the features of the reversion process and enhanced properties are reported in numerous papers. This review covers the main variables and phenomena during the reversion processing and lists the static and dynamic mechanical properties obtained in laboratory experiments, highlighting them to exceed those of temper rolled sheets. Moreover, formability, weldability and corrosion resistant aspects are discussed and finally the advantage of refined grain structure for medical applications is stated. The reversion process has been utilized industrially in a very limited extent, but apparently, it could provide a feasible processing route for strengthened austenitic stainless steels