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Quantum mechanics basis of quality control in hard metals
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap, Tillämpad materialfysik.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.ORCID-id: 0000-0002-6794-6744
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.
KTH, Skolan för industriell teknik och management (ITM), Materialvetenskap.ORCID-id: 0000-0003-4825-7430
Vise andre og tillknytning
2019 (engelsk)Inngår i: Acta Materialia, ISSN 1359-6454, E-ISSN 1873-2453, Vol. 169, s. 1-8Artikkel i tidsskrift (Fagfellevurdert) Published
Abstract [en]

Non-destructive and reliable quality control methods are a key aspect to designing, developing and manufacturing new materials for industrial applications and new technologies. The measurement of the magnetic saturation is one of such methods and it is conventionally employed in the cemented carbides industry. We present a general quantum mechanics based relation between the magnetic saturation and the components of the binder phase of cemented carbides, which can be directly employed as a quality control. To illustrate our results, we calculate the magnetic saturation of a binder phase, 85Ni15Fe binary alloy, using ab-initio methods and compare the theoretical predictions to the magnetic saturation measurements. We also analyse interface and segregation effects on the magnetic saturation by studying the electronic structure of the binder phase. The excellent agreement between calculations and measurements demonstrates the applicability of our method to any binder phase. Since the magnetic saturation is employed to ensure the quality of cemented carbides, the present method allows us to explore new materials for alternative binder phases efficiently.

sted, utgiver, år, opplag, sider
Acta Materialia Inc , 2019. Vol. 169, s. 1-8
Emneord [en]
Ab-initio calculations, Binder phase, Hard metal, Magnetic saturation
HSV kategori
Identifikatorer
URN: urn:nbn:se:kth:diva-246425DOI: 10.1016/j.actamat.2019.02.036ISI: 000465365300001Scopus ID: 2-s2.0-85062451846OAI: oai:DiVA.org:kth-246425DiVA, id: diva2:1300957
Merknad

QC 20190401

Tilgjengelig fra: 2019-04-01 Laget: 2019-04-01 Sist oppdatert: 2020-05-12bibliografisk kontrollert
Inngår i avhandling
1. Defects in Austenitic Steels and Hard Metals - A DFT-based Study
Åpne denne publikasjonen i ny fane eller vindu >>Defects in Austenitic Steels and Hard Metals - A DFT-based Study
2020 (engelsk)Doktoravhandling, med artikler (Annet vitenskapelig)
Abstract [en]

Materials are never 100% pure due to the limitation of purification method or manufacturing process. Nor are they perfect, especially under deformation. The present work aims to explore different roles played by the defects in austenitic steels and hard metals.

The first focus is iron-manganese (Fe-Mn) based twinning induced plasticity(TWIP) steels which are a category of austenitic materials showing a good combination of high strength and ductility. The planar fault is fundamental for the TWIP mechanism. First, the γ-surface of pure γ-Fe (fcc-Fe) is calculated for different magnetic states. Next, the effects of alloying elements, including Mn,interstitial carbon (C) and nitrogen (N), are addressed. The γ-surface includes several prominent stacking fault energies that are fundamental for, e.g, predicting critical twinning stress and twinnability. The present work compares the γ-surface obtained at different magnetic states, including nonmagnetic (NM), paramagnetic(PM), antiferromagnetic single-layer (AFMI) and double-layer (AFMD) states. The local magnetism significantly influences the γ-surface. In addition, the existing antiferromagnetic (AFM) order results in two different deformation paths inγ-Fe, leading to the generations of superlattice intrinsic stacking fault (SISF) and complex stacking fault (CSF), respectively. The intrinsic stacking fault energy corresponding to SISF is relatively low while its corresponding unstable stacking fault energy is relatively high. The magnetic structures are investigated in the unstable stacking fault and the intrinsic stacking fault configurations via Monte Carlo (MC) simulations. The MC results show that only SISF configuration is favourable, and the two distinctive unstable stacking fault configurations may coexist.

The Mn effect on the γ-surface of γ-Fe is studied at AFMI state and the crystal tetragonality is considered. The comparison with experimentally measured stacking fault energy (SFE) dependence on Mn composition shows that the AFMI results reproduce better the experimental trend in high-Mn Fe-Mn alloys than the PM results. Further, the interstitial alloying effects of C and N on the γ-surface of γ-Fe are investigated and no remarkable difference is observed betweenthe C and N impacts. The interaction between dislocation and interstitial atoms, which is fundamental to understand the phenomenon like dynamic strain ageing (DSA), is studied using the generalized stacking fault as an approximation of the partial dislocation core. The minimum migration energy path (MEP) and migration energy surface (MES) of C in the dislocation core of AFMD γ-Fe are calculated. In contrast to the common assumption that the interstitial atoms are stationary during the passage of fast-moving dislocations, the present work suggests that a pair of dislocation partials are capable of moving C atoms forward on the slip plane by one full Burgers vector. Moreover, at the stacking fault ribbon and especially near the dislocation core, the in-plane diffusion energy barriers of C are significantly reduced compared to that in the bulk, rendering a fast diffusion channel for C. The proposed mechanisms for C transport and diffusion are not decided by local magnetic order and can be used to explain the strain rate dependent formation kinetics of twinning or hexagonal close-packed (hcp) martensite in C-alloyed TWIP steels or high entropy alloys. Similarly, the ab initio results show that the diffusion energy barrier of N in the dislocation core is approximately 14.9% of that in the bulk. According to experimental observations, carbon promotes while N suppresses the DSA. However, the different C and N effects on the DSA cannot be understood from current thermodynamic investigations.

The defects in the binder phase of hard metals (cemented carbides) are another important topic in this thesis. The interstitial tungsten (W) and C defects in hard metals come from the sintering process during industrial manufacturing. The cemented carbides are composite materials made of tungsten carbide (WC) grains glued together by a binder phase. Typically, the binder phase consists of ductile cobalt (Co) and some amount of dissolved W and C. The measurement ofthe magnetic saturation is one method employed for quality control of cemented carbides. Despite the great success of Co, a substitute of Co is needed due to its rising price and health threats. The substitution of a material in production processes can be complex. Ideally, manufacturing processes and quality controls should be used as usual or at least new ones have to be devised in a simpleway. The present work selects 85Ni-15Fe (85 at.% of Ni and 15 at.% of Fe) to demonstrate the relation between the magnetic saturation and the components of the binder phase of cemented carbides using ab initio method, which providesa non-destructive quality control method in cemented carbides.

Abstract [sv]

Järn-Mangan (Fe-Mn)-baserade twinning induced plasticity (TWIP) stål är en kategori av austenitiska material som har en kombination av hög hållfasthet och god duktilitet. För att få en mer tydlig bild av olika roller som spelas av defekter i Fe-Mn-baserade legeringar med ytcentrerad kubisk struktur (fcc), specifikt deras effekter på mekaniska egenskaper och magnetiska strukturer, beräknas först γ- ytan för rent γ-Fe vid olika magnetiska tillstånd. Därefter behandlas effekterna av legeringsämnet mangan och de interstitiella legeringsämnena kol (C) och kväve (N).

γ-ytan innehåller flera framstående staplingsfelenergier som är grundläggande för att, till exempel, förutsäga kritisk spänning för tvilllingbildning och twinnability . Vi jämför γ-ytan som erhålls vid olika magnetiska tillstånd, inklusive ickemagnetisk (NM), paramagnetisk (PM), antiferromagnetiskt enkelskikt (AFMI) och dubbelskikt (AFMD). Det har visat sig att det lokala magnetiska momentet väsentligt påverkar γ-ytan. Dessutom resulterar den befintliga antiferromagnetiaka (AFM) ordningen i två olika deformationsvägar i γ-Fe. De två olika deformationsvägarna leder till generering av intrinsiska supergitterstaplingsfel (SISF) respektive komplexa staplingsfel (CSF), där den intrinsiska staplingsfelenergin motsvarande SISF är relativt lägre medan den motsvarande instabila staplingsfelenergin är relativt högre. Vi undersöker sedan de magnetiska strukturerna nära det instabila staplingsfelet och det intrinsiska staplingsfelet med Monte Carlo (MC) simuleringar. Vi fann att närvaron av stapelfel ändrar fördelningen av magnetiska moment för på bulkmaterial. Och i verkligheten är det bara SISF som är gynnsamma med avseende på CSF, men de två distinkta instabila stapelfelkonfigurationerna kan samexistera.

Effekten av Mn på γ-ytan för γ-Fe studeras vidare i AFMI-tillståndet och kristall-tetragonaliteten beaktas. Jämförelsen med experimentellt uppmätt staplingsfelsenergi (SFE) beroende av Mn-innehållet visar att AFMI-resultaten reproducerar den trend som observeras experimentellt i hög-Mn Fe-Mn-legeringar bättre än PM-resultaten. Vidare undersöks effekterna av de interstitiella legeringsämnena C och N på γ-ytan för γ-Fe och ingen märkbar skillnad observeras mellan C och N-tillsats. Vi beräknar lägsta migrationsenergiban (MEP) och migrationsenergi yta (MES) för C i dislokationskärnan i AFMD γ-Fe. Vi föreslår att ett par partiella förflyttningar kan flytta C-atomer framåt på glidplanet med en hel Burgers-vektor. Vid staplingsfelsbandet och speciellt nära den partiella dislokationskärnan minskas dessutom energibarriärerna för C-diffusion betydligt jämfört med den i bulk, vilket ger en snabbdiffusionskanal för C. På liknande sätt visar inte N-diffusionsbeteendet någon signifikant skillnad jämfört med C, vilket indikerar att orsaken till att N undertrycker dynamic strain aging (DSA) medan C främjar DSA inte kan förstås fullständigt från nuvarande termodynamisk forskning.

Slutligen presenterar vi också en teoretisk studie där vi använder de beräknade effekterna av inlöst C och volfram (W) på det totala magnetiska momentet för en FeNi-bindefas i hårdmetall för att framgångsrikt beräkna W-koncentration i bindefasen vilket möjliggör icke-förstörande kvalitetskontroll.

sted, utgiver, år, opplag, sider
Stockholm: KTH Royal Institute of Technology, 2020. s. 83
Serie
TRITA-ITM-AVL ; 2020:15
Emneord
defects, austenitic steels, cemented carbides, ab-initio
HSV kategori
Forskningsprogram
Teknisk materialvetenskap
Identifikatorer
urn:nbn:se:kth:diva-273258 (URN)978-91-7873-497-9 (ISBN)
Disputas
2020-06-05, Publikt via ZOOM, Stockholm, 10:00 (engelsk)
Opponent
Veileder
Forskningsfinansiär
Swedish National Infrastructure for Computing (SNIC)Vinnova
Tilgjengelig fra: 2020-05-12 Laget: 2020-05-12 Sist oppdatert: 2020-05-13bibliografisk kontrollert

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