High entropy alloys (HEAs) are a new class of alloys that contains five or more principal elements in equiatomic or near-equiatomic proportional ratio. The configuration entropy in the HEAs tends to stabilize the solid solution formation, such as body-centered-cubic (BCC), face-centered-cubic (FCC) and/or hexagonal-closed-pack (HCP) solid solution. The high number of principal elements present in HEAs results in severe lattice distortion, which in return gives superior mechanical properties compared to the conventional alloys. HEAs are considered as a paradigm shift for the next generation high temperature alloys in extreme environments, such as aerospace, cutting tools, and bearings applications. The project is based on the development of refractory high entropy alloy and film. The first part of the project involves designing high entropy alloy of CuMoTaWV using spark plasma sintering (SPS) at 1400 oC. The sintered alloy showed the formation of a composite of BCC solid solution (HEA) and V rich zones with a microhardness of 600 HV and 900 HV, respectively. High temperature ball-on-disc tribological studies were carried out from room temperature (RT) to 600 oC against Si3N4 counter ball. Sliding wear characterization of the high entropy alloy composite showed increasing coefficient of friction (COF) of 0.45-0.67 from RT to 400 oC and then it decreased to 0.54 at 600 oC. The wear rates were found to be low at RT (4 × 10⁠−3 mm⁠3/Nm) and 400 oC (5 × 10⁠−3 mm⁠3/Nm) and slightly high at 200 oC (2.3 × 10⁠−2 mm⁠3/Nm) and 600 oC (4.5 × 10⁠−2 mm⁠3/Nm). The tribology tests showed adaptive behavior with lower wear rate and COF at 400 oC and 600 oC, respectively. The adaptive wear behavior at 400 oC was due to the formation of CuO that protected against wear, and at 600 oC, the V-rich zones converted to elongated magneli phases of V2O5 and helped in reducing the friction coefficient. The second part of the project consists of sintering of novel CuMoTaWV target material using SPS and depositing CuMoTaWV refractory high entropy films (RHEF) using DC-magnetron sputtering on silicon and 304 stainless steel substrate. The deposited films showed the formation of nanocrystalline BCC solid solution. The X-ray diffraction (XRD) studies showed a strong (110) preferred orientation with a lattice constant and grain size of 3.18 Å and 18 nm, respectively. The lattice parameter were found to be in good agreement with the one from the DFT optimized SQS (3.16 Å). The nanoindentation hardness measurement at 3 mN load revealed an average hardness of 19 ± 2.3 GPa and an average Young’s modulus of 259.3 ± 19.2 GPa. The Rutherford backscattered (RBS) measurement showed a gradient composition in the cross-section of the film with W, Ta and Mo rich at the surface, while V and Cu were found to be rich at the substrate-film interface. AFM measurements showed an average surface roughness (Sa) of 3 nm. Nano-pillars of 440 nm diameter from CuMoTaWV RHEFs were prepared by ion-milling in a focused-ion-beam (FIB) instrument, followed by its compression. The compressional yield strength and Young’s modulus was calculated to be 10.7 ± 0.8 GPa and 196 ± 10 GPa, respectively. Room temperature ball-on-disc tribological test on the CuMoTaWV RHEF, after annealing at 300 oC, against E52100 alloy steel (Grade 25, 700-880 HV) showed a steady state COF of 0.25 and a low average wear rate of 6.4 x 10-6 mm3/Nm.

Iron- and steel production is a material- and energy intensive industrial activity. The production of one tonne of steel commonly results in some 400 kilograms of residual materials such as metallurgical slags, dusts, sludge and scales generated in the processes. Much work is continuously devoted to finding possible ways of using residual materials and minimising landfilled volumes. As these materials often contain considerable amounts of valuable elements such as iron, coal, manganese and calcium, it may be profitable to use them to replace virgin raw materials or to sell them as products that may be useful in other industries and/or processes.    The thesis is based on case studies that exemplify how the use of process integration, through system analysis, can assist in assessing effects and opportunities for different concepts for increased material efficiency in Nordic ore-based steelmaking systems. The process integration approach taken for this research work was the simulation of a specific iron- and steel production system and the use of an optimisation tool for the evaluation of an extended system including the symbiosis between four steel plants.   Three different cases were studied including: system effects of increased magnesium oxide content in the lime raw material, investigation of the prospects for vanadium enrichment and slag reduction concept and a study of the logistics perspective for a joint residual material upgrading and recycling venture between four steel plants. The analysed cases present possibilities to improve the material efficiency by: •      Enhanced recovery of residual materials; •      Upgrading of residual materials to products; •      Specific elements recovery; •      Decreased use of virgin raw material; •      Improved quality of residual materials; •      Decreased amounts of materials placed in long-term storage or landfills.   From the results of the cases studied, the best scenarios and potential gains by enhanced material efficiency is presented. In the case of system effects of increased magnesium oxide content in the lime raw material, the issue was mainly to obtain maximum usage of metallurgical slags without compromising the quality of the main product. The calculated possibility of increased slag recirculation enabled further a decreased consumption of iron ore pellet and limestone. Regarding the investigation of the vanadium enrichment and slag reduction concept, the best scenario markedly increased the internal slag recirculation in order to enrich the vanadium content in the slag for ferrovanadium production. By the vanadium enrichment and recovery concept, considerable amounts of vanadium would be made useful instead of ending up in long-term storage. The study of a shared Nordic concept for residual materials upgrading and use demonstrated the potential for upgrading the materials to a direct reduced iron product for recovery in blast furnace. The concept showed high potential for significantly reducing the amount of material being long-term stored or deposited to landfill and thus a potential step towards achieving the zero-waste philosophy target.   None of the concepts for enhanced material efficiency studied in this thesis work has been implemented; however, they are still of relevance for the Nordic steel industry.

Layer by layer manufacturing (additive manufacturing, AM) of metals is emerging as an alternative to conventional subtractive manufacturing with the goal of enabling near net-shape production of complex part geometries with reduced material waste and shorter lead times. Recently this field has experienced rapid growth through industrial adaptation but has simultaneously encountered challenges. One such challenge is the ability of AM metal to withstand loading conditions ranging from static loads to complex multiaxial thermo-mechanical fatigue loads. This makes fatigue performance of AM materials a key consideration for the implementation of AM in production. This is especially true for AM in the aerospace industry where safety standards are strict. Defects in metal AM materials include rough surfaces, pores and lack-of-fusion (LOF) between build layers. These defects are detrimental to fatigue as they act as local stress concentrators that can give rise to cracks in the material.  Some defects can be avoided by careful build process optimization and/or post-processing but fully eliminating all defects is not possible. Because of this, a need arises for the capability to estimate the fatigue performance of AM produced critical components containing defects. The aim of the thesis is to increase understanding regarding the connection between defect characteristics and the fatigue behaviour in AM produced Ti-6Al-4V. Defect distributions are statistically analysed for use in a simple fracture mechanical model for fatigue life prediction. Other study areas include the impact of post-production treatments such as chemical surface treatments and hot isostatic pressing (HIP) on defects and fatigue behaviour. The thesis constitutes three scientific papers. The AM technique studied in these papers is Electron Beam Melting (EBM) in which an electron beam selectively melts pre-alloyed metal powder. In paper 1, defects were studied using X-ray computed tomography (XCT) and fatigue crack initiation was related to the observed defect distribution. In paper 2, XCT data was used to relate the surface morphology and roughness of post-production treated EBM material to the surface near defect distribution. The connection between this distribution and manufacturing parameter has also been explored. Paper 3 builds on and extends the work presented in paper 1 by including further fatigue testing as well as a method for predicting fatigue life using statistical analysis of the observed defect distribution. The impact of a defect on the fatigue behaviour of the material was found to largely depend on its characteristics and position relative to the surface. Production and post-processing of the material was found to play a role in the severity of this impact. Finally, it was found that a probabilistic statistical analysis can be used to accurately predict the life of the studied material at the tested conditions. / SUDDEN

The development of a process chain for Inconel 718 production utilizing Binder Jetting has been investigated. Different powder sources were compared by the effect they had on machine compatibility, powder bed packing, recyclability, green density, sintering parameters, final density, porosity, and mechanical properties. The three powder lots investigated originated from two different production sites. One of the three powder lots has a finer powder size distribution, due it being produced simultaneously with another powder lot with a coarser powder size distribution fraction. This synergy production results in a higher yield of the atomization process and thus is economically and environmentally beneficial. The compatibility between powder lots and Binder Jetting machine was investigated using new powder and recycled powder. By using recycled powder in the process an increase in green density by 5% could be achieved. Several temperature and hold time relations were tested to develop a sintering program with an acceptable final density above 94% of theoretical density. 1270◦C with a hold time of 4h generated the best results. Sintered samples did not reach acceptable strength properties. The elongation value was twice as high as required for one of the powder lots using recycled powder. Post heat treatment generated samples with an acceptable yield strength but highly reduced elongation properties.

No description available.

The mechanical properties of three austenitic stainless steel alloys, namely 21-6-9, 316L and a modifed 316, fabricated via laser powder bed fusion, have been studied. From the results previously obtained through tensile tests at room and cryogenic temperatures, their strength and ductility were compared against similar conventionally processed materials. The three alloys exhibited a higher or similar strength than their conventional counterparts at both temperatures. In the case of ductility, the additive manufactured 316L was the only alloy that outperformed a conventional 316L at room temperature. At cryogenic temperature, the ductility of the three alloys was either similar or lower. Also, their plastic behavior throughout di˙erent stages of deformation was characterized from their microstructure evolution. At room temperature, a two stage, monotonically descending strain hardening rate was observed, similar to FCC medium stacking fault energy materials. At cryogenic temperatures, four stages of strain hardening rates were observed, caused by a martensite transformation induced by plastic deformation, as it happens in TRIP steels.

Data mining, and in particular topological data analysis (TDA), had proven to be successful inabstracting insights from big arrays of data. This thesis utilizes the TDA software AyasdiTM inorder to improve the accuracy of the energy model of an Electric Arc Furnace (EAF), pinpointingthe causes of a wrong calculation of the steel temperature. Almost 50% of the charges analyzedpresented an underestimation of temperature, while under 30% an overestimation.First a dataset was created by filtering the data obtained by the company. After an initialscreening, around 700 charges built the dataset, each one characterized by 104 parameters. Thedataset was subsequently used to create a topological network through the TDA software. Bycomparing the distribution of each parameter with the distribution of the wrong temperatureestimation, it was possible to identify which parameters provided a biased trend. In particular, itwas found that an overestimation of temperature was caused by an underestimation of themelting energy of materials not having through a melting test. It was also found a possible biasedtrend in some distribution of parameters like %O in steel and slag weight, which it is believedare all connected together. Despite not finding a global solution for the reasons behind theunderestimation of temperature, it is believed that a different settings more focused around thematerials used as scrap mix can highlight more on that subject. In conclusion TDA proved itselfefficient as a problem solving technique in the steel industry.

Today, fastening articles such as screws and nails are treated with different surface coatings to withstand corrosion. The Swedish distributor ESSVE® Produkter AB uses a nano coating called CorrSeal™ for high corrosion protection of their screws. Thermal diffusion galvanization (TDG) is a more environmentally friendly method that the company seeks to use as replacement for the current treatment. This process of zinc diffusion is carried out at around 400 °C for several hours. The aim of the project is to investigate the possibility to surface treat a wood screw using TDG. The elevated temperature is suspected to decrease the hardness of the hardened screw. Therefore, a hardened and tempered screw without surface treatment is sent to a TDG facility. Industrial furnaces are used for similar heat treatments of screws with different hardenings. Both processes are analyzed by evaluating the results of hardness, bending, and microscopy. No immediate correlation between the TDG process and heat treatment in the industrial furnaces is found. Results show that the tested screws softened to a higher degree in the TDG process compared to treatment in the industrial furnaces. The mechanical properties of the tested screws, after the TDG process, are not acceptable. The zinc layer thickness on the screws is uneven yet believed to meet the required demands on corrosion resistance. Results also show that incorporating the TDG process in the tempering step is essential to meet the demands on hardness. Additionally, changing the composition of the material can lead to higher resistance against softening at the elevated temperatures. Further research is however needed to present a screw with sufficient corrosion resistance from the TDG process that will meet the demandson hardness and bending.

Electron Beam Powder Bed Fusion manufacturing of components is an additive manufacturing process that is complex and has widespread advantages for aerospace and many industrial processes. It reduces costs and has a larger powder particle size requirement. This gives the benefit of a higher mass deposition rate and thus faster production time compared to Laser-Powder Bed Fusion process. Powder bed manufacturing processes often lead to columnar grain structure formation along the build direction, resulting in components that have anisotropic physical and mechanical properties. This is a major problem that limits the applications of this technique. In order to promote equiaxed grains, as well as refine the columnar morphology and eliminate anisotropic properties, the roles of process conditions and presence of inoculants or heterogeneous nucleating sites are considered. In this study, the addition of titanium nitride inoculants is used to promote columnar to equiaxed grain transition in ferritic stainless steel with the use of melting strategies and variable process parameters. It has been found that the thermal gradient (G) to solidification rate (R) ratio (G/R ratio) controls grain morphology and texture: a low G/R ratio has been shown to promote the formation of equiaxed grains. The process conditions for this transition were investigated. The samples were analyzed after printing single line tracks in the Freemelt One machine, and thereafter studied with the aid of optical microscopy to ascertain the combination of machine parameters that results in a successful transition from columnar grains to equiaxed. The study concluded that there was an increase in the fraction of equiaxed grains under these conditions; a low thermal gradient, high scanning velocity and low area energy. Ultimately, further investigation will be needed to establish the exact process parameters that will promote the transition from columnar to equiaxed grains in ferritic stainless steel. The findings from this study can be used by future researchers to create solidification maps for this steel grade and assist industry to tailor specific textures in ferritic stainless steel to achieved desired microstructures and mechanical properties. / Electron  Beam  Powder  Bed  Fusion  (E-PBF)  tillverkning  av  komponenter  är en  additiv tillverkningsprocess  som  är  komplex  och  har  omfattande fördelar  för  flyg  och  många industriella processer. Det minskar kostnaderna och har ett större krav på pulverpartikelstorlek. Detta ger fördelen av en högre massavsättningshastighet och därmed snabbare produktionstid jämfört med Laser-Powder Bed Fusion-processen. Tillverkningsprocesser för pulverbädd leder ofta  till  att en kolumnformig  kornstruktur  bildas  längs  byggriktningen, vilket resulterar  i komponenter  som  har  anisotropa  fysikaliska  och mekaniska egenskaper.  Detta  är  ett  stort problem som begränsar tillämpningarna av denna teknik. För att främja likaxliga korn, samt förfina den kolumnära morfologin och eliminera anisotropa egenskaper, övervägs rollerna för processbetingelser och närvaron av ympmedel eller heterogena kärnbildningsställen. I denna studie  används  tillsatsen  av  inokulanter  av  titannitrid  för  att  främja  kolumnär  till  likaxlig kornövergång  i  ferritiskt rostfritt  stål  med  användning  av  smältstrategier  och  variabla processparametrar.  Det  har  visat  sig  att  förhållandet  mellan  termisk gradient  (G)  och stelningshastighet   (R)   (G/R-förhållande)   styr   kornmorfologi   och   textur:   ett   lågt   G/R- förhållande har visat sig främja bildningen av likaxliga korn. Processförhållandena för denna övergång undersöktes. Proverna analyserades efter att ha skrivit ut spår med en rad i Freemelt One-maskinen  och  studerades  därefter  med  hjälp  av  optisk mikroskopi  för  att  fastställa kombinationen   av   maskinparametrar   som   resulterar   i   en   framgångsrik   övergång   från kolumnära  korn till  likaxliga.  Studien  drog  slutsatsen  att  det  fanns  en  ökning  av andelen likaxliga korn under dessa förhållanden; en låg termisk gradient, hög avsökningshastighet och låg areaenergi. I slutändan kommer ytterligare undersökningar att behövas för att fastställa de exakta processparametrarna som kommer att främja övergången från kolumnära till likaxliga korn i ferritiskt rostfritt stål. Resultaten från denna studie kan användas av framtida forskare för att skapa stelningskartor för denna stålkvalitet och hjälpa industrin att skräddarsy specifika texturer i ferritiskt rostfritt stål för att uppnå önskade mikrostrukturer och mekaniska egenskaper.

Additive  manufacturing  technologies  are  widely  used  in  aerospace,  space,  and  turbine industries. Parts can be manufactured directly by selectively adding materials layer-by-layer. A key aspect that is critical to the quality of the final component being manufactured is the powder characteristics. The prevailing powder characterisation techniques help in predicting the flowability of powders but do not relate to the spreading nature of the powder. To create high-quality thin layers of metal powder, it is essential to understand powder spreadability in powder bed-based additive manufacturing processes. The objective of this study was to create spreadability metrics using image analysis, mass analysis, and density analysis. A lab-scale experimental setup was constructed to replicate the powder bed-based additive manufacturing process. The impact of spreading speed and layer thickness on five different steel powders were studied using the suggested metrics. The metrics obtained powder rheometry and revolution powder analysis. The flowability parameters were compared to the spreadability analysis. Image analysis was shown to be efficient to predict the spreading nature of the powder when the processing parameters are varied. One metric, the convex hull ratio, was found to be high for  free-flowing  powders.  The  spread  area  of  free-flowing  powders  was  higher  than  the powders with poor flow properties. A mass-based analysis procedure shows that the ratio of mass deposited to the theoretical mass fluctuated in a systematic manner as a function of testing parameters  and  for  different  powders,  suggesting  that  the  mass  analysis  might  be  another potential   metric   to   assess   spreadability.   The   density-based   analysis   was   effective   in differentiating the layer density of different powders under various experimental conditions. It   is   expected   that   the   proposed   metrics   will   be   a   beginning   for  developing   further characterisation techniques. For example, the layer thickness could be studied by creating a homogenous  layer.  We  anticipate  these  metrics  to  be  used  to  develop  standardisation techniques for defining and quantifying powder spreadability, and thereby improve quality ofadditive manufacturing processes. / Additiv  tillverkning  är  teknologier  som  har  stor  uträckning  inom  flyg-,  rymd  och  turbin industrier. Delar kan bli tillverkade direkt genom att lagervis addera material på varandra. En nyckelaspekt som är kritisk till kvalitén av den slutgiltiga komponenten är egenskaperna hos pulvret. De allmänna teknikerna för pulverkarakterisering hjälper till att förutspå flytförmågan hos pulver men relaterar ej till dess spridningsförmåga. För att kunna skapa högkvalitativa skikt av  metallpulver  är  det  nödvändigt  att  förstå  pulvrets  spridningsförmåga  inom  pulverbädds baserade additiva tillverkningsprocesser. Målet  med denna studie var  att skapa ett mått för spridningsförmågan  genom  bild-  och  massanalys.  Ett  experimentellt  upplägg  i  labbskala konstruerades för att efterlikna en pulverbädds baserad additiv tillverkningsprocess. Effekten av bladets hastighet och lagrets tjocklek på fem olika pulver studerades genom användandet av de  föreslagna  mätetalen.  De  framtagna  mätetalen  jämfördes  sedan  med  existerande  pulver karakteriseringsmetoder  såsom  FT-4  Rheometer  och  pulver  analys  med  hjälp  av  roterande trumma. Slutligen så jämförs flytbarhets parametrarna med spridbarhets mätetalen. Det visar sig att bildanalysen är tillräckligt bra på att förutspå spridningsförmågan hos pulvret när  processparametrarna  låtes  vara  varierande.  Mer  specifikt  så  var  förhållandet  mellan pulvrets yta och det konvexa höljet stort för pulver som visar bra spridning. De framtagna procent  värden  från  massanalysdiagrammen  fluktuerar  vid  olika  processparametrar  hos  de olika  pulvren,  vilket  kan  betyda  att  massanalys  kan  vara  ett  potentiellt  sätt  för  att  mätta spridningsförmågan hos pulver. Det är förväntat att dessa föreslagna mätetal kommer vara början för utveckling av ytterligare karakteriseringstekniker. Till exempel, för att studera densiteten och tjockleken hos ett lager skulle man kunna skapa homogena lager. Vi förutser att dessa mätetal kommer att bli använda för att skapa standardiseringstekniker för att definiera och kvantifiera spridningsförmågan hos ett pulver och genom detta förbättra kvaliteten av den additiva tillverkningsprocessen.