0.2 Vznik nove faze H DA LDA Glass HDL tm iir^ SuPer" \ Stable \\ cooled \ |iquic| N O c/5 temp. Figure 1: Solubility curve and the nitfastable zorni SUPER SATURATION (skla) Pozice hranie se mění s teplotou Solubility Curve U N DER SATURATION Složka A gent Extrémní nukl. batiéra H DA LDA Glass HDL Ur*\ Super" *• Stable LDL cooled \ |iqujd , x\ liquid * "No man's - - TfiA Viz pěstování monokrystalů např. CuS04 100 200 273 http://pubs.rsc.org/en/content/articlehtml/2012/cp/c2cp40703e Gibbs energy of nucleation (overview) / AGmrJ~lP AG" Alloys - saturation lines Fe-4Mo-Cr-C @ 1100°C Rychlost růstu a rychlost nukleace "i Konst. Teplota ^ Crystal Size on E i- E Stupeň přesycení S=c/c* G = Kontrolováno difúzí ^- *^ ^5 (Dn) nebo růstem rozhraní (Rn) B = kbAC Kontrolováno exponencielně (distribuce lokální energie). G = = Growth Rate kg = = growth constant g = growth order B = Nucleation Rate K = = nucleation constant b = nucleation order > 1 AC = supersaturation (Teplota má vliv na G a B, tím i na velikost krystalů) http: //www. scielo.br/scielo .php ?script=sci_artte xt&pid=SO 104-66322001000400007 Nukleace a růst (j) contracting geometry REACTAMT^s^v^ (ii) rvucleation & growth instant nucleatton & gro win Kontrolováno difúzí (Dn) nebo růstem rozhraní (Rn) PRODUCT Kontrolováno nukleací, difúzí a růstem (An) random nucteation & growth Figure 1 Schematic representation of the contracting geometry and nucleation- growth models Cesta A: např. oxidace povrchových vrstev, cesta B např. vznik hydridů v Zr slitinách n Kinetika vzniku tuhé fáze (krystalů) z přesyceného roztoku ■jí o LL c i*- 3 ° £r o Ě 2 H Monodisperse Colloid Growth J Role difúze Role povrchové energie o F c o O ation Threshold Ostwaíd Ripening Staturation J_I_I_I_l_t_I_i_J_I_J_ J_t_I_L J_[_L J_I_I_L_J_L 400 600 , I Time j * (Seconds) 800 1000 Příprava nasyceného roztoku při vyšší teplotě. Rychlé ochlazení Počátek a konec homogenní nukleace. Růst až do dosažení hranice rozpustnosti. Hrubnutí a sintrace Rychlost transformace rychlost difúze + rychlost nukleace Ni kTeäcnT bajiéra ^ rychlost difúze Rychlost fázové transformace jpýchlost nukleace Nehomogenní +homogenní Let us consider eutectoid reaction as ail example a .1: I fiOO 700 600 X + FeaC a + y / 727°C [/ Nukleační zona eutectoid reaction: y(0.76 wt% C) a (0.022 wt% C) + Fe3C 0 LO Composition (vrt% C) The S-shaped curves are shifted to longer times at higher T showing that the transformation is dominated by nucleation enucleation rate increases with supercooling) and not by diffusion (which occurs faster at higher T). Perlit (eutektoidní ocel) Rate of Phase Transformation |"x] CeMH-ac He yflaeTca OTo6pasnTb pucyHOK Fixed Nucleätion All out Df material - "done!" maximum rate reached - now amount unconverted decreases so rate slows rate increases a$ surface area increases & nuclei grow Growth Log Time Adapted from Fig. 10.10, CaHister7e - Modeled by the Avrami Rate Equation Rate of transformation can be defined as reciprocal of time for trans formation to proceed halfway to completion: 1= i/tM Rate incr eases with temp era toe accordmg to Arrhemiu equation. characteristic for thermally activated processes: r = A exp ( Q4/kT) = A exp (Qm/ RT) t' t Per atom Per mole ■6 1? LOO 80 60 40 20 LO* Time [rnin) ÍLogarithmiĽ style! Percent recrystallization of pure copper at different T Temperature Ti Rozsah fázové transformace ^ 100 0 I I I c TO i i 99% Transformation 1% Transformation / I i i\y 61 i l l Eutectoid -H 1^00 temperature o Q. E .c 1 dav 500 — 1200 Austenite -> pearl ite transformation Denotes that a transformation is occurring — 1000 10 10* 10' 10" soo 105 Time (s) TTT Diagrams > The family of S-shaped curves at different T are used to construct the TTT diagrams. > The TTT diagrams are for the isothermal (constant T) transformations (material is cooled quickly to a given temperature before the transfonnation occurs, and then keep it at that temperature). > At low temperatures, the trans formation occurs sooner (it is controlled by the rate of uucleation) and grain growth (that is con tolled by diffusion) is reduced. > Slow diffusion at low temperatures leads to fine-grained micro structure with thin-layered structure of pearlite (fine pearlite). > At higher temperatures, high diffusion rates allow for larger gram growth and formation of thick layered structure of pearlite (coarse pearlite). > At compositions other than eutectoid, a proeutectoid phase (ferrite or cementite) coexist with pearhte. Additional curves for proeutectoid transforniation must be included on TTT diagrams. Formation of Baiiiite Microstnicture (I) hoc 700 GOOr— g 400 300 h- 200 I T T Eutecloid temperature 60% 100 lo-i I 10 10* Time (s) 103 104 If transformation temperature is low enough (<540CC) baiiiite rather than fine pearlite f onus. Bainit: cementite and dislocation-rich ferrite IB Upper baiuite ; Martenzitická transformace (při kalení) Introduction to Materia h Science. Chapter 10. Pliage Tríir^foiniatioiii in Merali [O01]y f [001]« ó— [10% Each atom displaces a small (sub-atomic) distance to transform FCC y-Fe (austemte) to martensite which ha* a Body Centered Tetragonal (BCT) unit cell (like BCC but one unit cell axis is longer than the other two). The ma Hens it ic trans formation involves the sudden reorientation of C and Fe atoms from the FCC solid solution of y-Fe (austenite) to a body-centered tetragonal (BCT) solid solution (martensite). [100]« (a) O O (bj TTT Diagram including Martensite £00 i-1-1-1-1-1— Eutectoid temperature 200 — 100 — M 4 A A: Austenite P: Pearlite B: Bainite M: M a it e us it e o 10 -i 10 10J 10J 10' 10: Time (i) Ideal TTT-curve for 0,65% carbon steel depicting time interval required for beginning, 50% and 100% transformation of austenite at a constant temperature A= Austenite F= Ferrite P = Pearlite B = Bainite TraitaFapm&tion Time. (LofrScBfe) Martenzit: teragonah Drodlouzena BCC) presycena uhllkem Role reálné rychlosti ochlazení mim© L he J"J"J' diagram for a cutectoid ťe-C alloy *M0 2000 D09A 1* ) 3000 Obr. 4 Průběh ochlazování tlustých plechů z oceli 0,5 Cr-0,5 Mo-0,3 V na vzduchu a ve vodě 4Q00 727, y (stable) Eutecloid temperature o » ra r. í Ochlazováni rozdílných průměrů rotoru z oceli 17133 v oleji a ve vodě 8 - 700 600 \B 400 ■ 200 — 100 — :2 -: Eutectoid temperature A/(start) h: (c) ía) 100% 50% Pearl ite 100% Martensite b0% Bainite Bamile 10 ioz i:y Time (s) RYCHLOST OCHLAZOVÁNÍ »1,2 malá rychlost ochlazení, vznik perlitu » 3 vyšší rychlost ochlazení, vznik bainitu následně martenzitu » 4 přichází přímo k bainitické přeměně, výsledkem je bainit + —čas Vliv rychlosti ochlazování na rozpad austenitu Transformation start Water quench 10' 10' 0.1 1 10 100 10* 10* 10f Time (seconds) Mechanical properties of Fe-C alloys Ceinentite is harder and more brittle than feiiite -increasing cementite fraction therefore makes harder, less ductile material. — -± ■0 ■l 1200 — 1100 — 1000 — 900 — »00 — 700 — 600 — 500 — 4O0 — 300 — 16Ü — 140 — 120 — lüü — 30 — ■j-j — 40 — Percent Fe^C 6 9 Mechanical Behavior of Fe-C Alloys (EE) Pearlite + te-rite The strength and hardness of the different tmcrostructures is inversely related to the size of the microstructures (fine structures have more phase boundaries inhibiting dislocation motion). Mechanical properties of bainite. pearhte. spheroidite Considering micro structure we can predict that > Spheroidite is the softest > Fine pearlite is harder and stronger than coarse pearhte > Baimte is harder and stronger than pearlite i Yield suength I _L 0.2 0.4 0.6 O.S Composition (wt% C) Mechanical properties of rnartensite Of the various microstructures in steel alloys > Martensite is the hardest, strongest and the most brittle The strength of rnartensite is not related to rnicrestructure. Rather, it is related to the interstitial C atoms hindering ! q dislocation motion (solid solution hardening. Chapter 7) and to the small number of slip systems. Í2C 200 - 1» ft" T T Fins pear lile T ......... ).2 O.-- ů.ů 0 S CcrmKsitim tvtft Cl Brinell hardness number = Brinellovo číslo tvrdosti W.' rj.4 "M L I 20 Martenzit Martensite is so brittle that it needs to be modified for practical applications. This is done by heating it to 250-650 °C for some time (tempering) which produces tempered martensite. an extremely fine-grained and well dispersed cementite grains in a ferrite matrix. > Tempered martensite is less hard/strong as compared to regular martensite but lias enhanced ductility (fenite phase is ductile). > Mechanical properties depend upon cenientite particle size: fewer, larger panicles means less boundary area and softer, more ductile material -eventual limit is spheroidite. > Panicle size increases with higher tempering temperature and/or longer time (more C diffusion) - therefore softer, more ductile material. Temperovaný (popuštěný) martenzit Tempered Marten site (II) 1 min ~r Higher temperature & 351— time: splieroirtite (soft) 10 I J 10J 10s rim#(* 10< Electron micrograph of tempered martensite Summary of austenite transformations Austenite Rapid quench Moderate cooling Pear lite (ex + Fe3C) + a proeutectoid phase Bainite (ct + Fe3C) Martensite (BCT phase) Reheat \ Tempered martensite (ct + Fe3C) Solid lines are diffusions 1 transformations, dashed is diffusionless martensitie transformation 1. Spinodální rozpad -fázová přeměna bez nukleace v C OJ 2IHI ISO 1 m % 141) 5 I 12« J 104 "3 ? HO i.í) ■W Spinodální rozpad (fázová přeměna) Náhodná fluktuace c c *-equl *-spl Composition .......v* (.2 um v. ~" ~......■ - *j ; - mm 390 400 Temperature <°Q espontální oblast (nukleace je nutná) Koncentrační profil při spinodálním rozpadu: Není nutné nukleační stádium Schematic phase diagram for the NM-EG mixture, showing the different quench pathways employed in this study. (I) Proposed pathway for the formation of bridged bijels through combined spinodal decomposition and nucleation and growth. (II) Off-critical quench in a NM-rich mixture. (Ill) Off-critical quench in an EG-rich sample. primary riudeation rate, m s' U) TD i. fii s^otiaccJ- povodci iJ-Ánihcy (kc^^aA/ac^ htS-U&i&f] *) 2, leploU\ - m&t%/ dívčin/ hrtfrcien/js *j gvlfunu/t tyctás^ i /po* A. dolet: K 2Ln<> fandit het fa t 2^ Magnetická levitace Diskuse Kovová skla 1100 L------T--------------------------- S "55 1000 H 900 A 800 n liq Zr4i,2T'i3.3Cu125Ni1O0Be,25 supercooled liquid 4 log time (s) Metalurgická magie The Legend of Damascus Steel 10* 5X 10s http://io9xom/5831683/a-brief-histo 43 Gibbs energy of nucleation AG Undercooling can be removed by addition of grain seeds or decreased Tims, [il 9/ChapterlOc.pdf J ^ **"" (TrontFornitjľ iú n tala) Ä' {jwc Uarlcň rar*) I■ 1 1 ■ I ■ 1 1 ■I 1 11 1 I 1 I I ' A Eash ft üptregraw (derived) ■ Fric* »I aJ (dHtvtd) 1000 900 5 700 ■ LĽ- i soo - 500 - 400 * 300 • -200 ■ 100 - .....»■—.......1 ........1............I O Oa^ a ů B. + inb-Tagr-anular-Ylpcy » L12 ■ DiecaitiiůUĚV iDty + Spoiodi D No Iransf-ŕTríiMi Oram boundary ■+ inU5igranuiar vťDO^i Di&conliniJDus 7 {DC ; ■Ěpinodal ■ - j J 'J u_■ ■ ■ ■ 10° 101 102 103 10' Time, s I o5 Phase transformations. Kinetic 5 liase transformations (change of the niic restructure) can e divided into three categories: > Diffusion-dependent with no change in phase composition or number of phases present (e.g. melting, solidification of pure metal, allotropic transformations, recrystallization. etc.) > Diffusion-dependent with changes in phase compositions and/or number of phases (e.g. eutectoid transformations) > Diffusion less phase transformation - produces a metastable phase by cooperative small displacements of all atoms m structure (e.g. martensitic transformation discussed in later in this chapter) Materiály s tvarovou pamětí SMA:Shape memory alloy.. Mnrtonsilo Ti Ni Martensite Austenite https ://www .wikiskripta.eu/w/Materi%C3 % A1 ly_s_tvarov ou_pam%C4%9Bt%C3%AD Tvarová paměť byla poprvé sledována u mosazi v roce 1939, od 60. let zájem o tuto oblast stoupá. V roce 1962 byla zkoumána ekviatomární slitina Ni a Ti, u níž byla objevená mimořádně výrazná tvarová paměť. K tomuto objevu dospěl z Naval Ordnance Laboratory ve White Oak v Marylandu, USA. Podle složení a místa vzniku se tato slitina nazývá NITINOL. Mezi další materiály s tvarovou pamětí patří keramické materiály jako je oxid zirkoničitý (Zr02), oxid horečnatý (MgO), oxid ceričitý (Ce02), dále také a některé kovové slitiny jako například měď-hliník-nikl, měď-zinek-hliník, železo-mangan-křemík. Deformace materiálu s tvarovou pamětí VIDEO' https://smartwires.eu/index.php?id_product=9&controller=product&id_lang=7 Cíl O a t auslenil ohřev +*-*-*-*^4+ i , + f pfl • h f** ŕ t t * o í p r b. ■» ■ ■ Qhr 1 Pleteny sten! deformace ->■ * # t ■ * c ŕ * < https ://www.engineering. sk/st rojarstvo-extra/2742-kovove-materialy- s-tvarovou-pameti martenzit martenzit Qbr i* Schéma martenľHicke Iransfoi mace SMÄ malerialĽ 3 Cu . Al, 3 Cu . Zn (běžná mosaz, tvarová paměť se objevuje až v nízkých teplotách), Cu-AI-Ni, Cu-AI-Mn, Ni-Ti-Cu, Ni-Ti-Hf a mnoho dalších. Existuje celá řada dalších kovů, u kterých se tento jev vyskytuje, ale ty nejsou moc využívány, protože mají jen slabý efekt nebo jsou nestabilní. Všechny tyto slitiny patří do skupiny intermetalik, Navštiv stránky http://people.virginia.edu/-lz2 n/mse209/Chapter1 Oc.pdf