MJRSandim EEL-USP.

Apresentação em tema: "MJRSandim EEL-USP."— Transcrição da apresentação:

1 MJRSandim EEL-USP

2 Eivani et al. AA7020 Aluminum alloy ● isothermal homogenization treatments were performed at temperatures of 390oC to 550oC , for 2 to 48 hours at each temperature ● the samples were water quenched ● electrical resistivity measurements were performed using the eddy current technique, at room temperature MJRSandim EEL-USP

3 homogenization treatment before hot deformation
Eivani et al. homogenization treatment before hot deformation Creates small dispersoids that later act as recrystallization inhibitors during deformation and annealing treatments MJRSandim EEL-USP

4 Background

5 Temperature-dependent electrical resistivity of the pure base metal
Eivani et al. Background Matthiessen’s law: Temperature-dependent electrical resistivity of the pure base metal Specific electrical resistivity of the ith solute Relative concentration of the ith solute MJRSandim EEL-USP

6 coherent interfaces increases the electrical resistivity
Eivani et al. Background ● ...the presence of elements in the solid solution and small particles possessing coherent interfaces increases the electrical resistivity ● ..the size and distribution of small particles affect the electrical resistivity of the alloy” a) Regardless of the interface of the dispersoid formed, if the precipitate spacing is greater than the mean free path of the electron (100nm in aluminum alloys), the effect of particles is negligible b) In the intermediate range of precipitate and dispersoid particle spacings the contribution of precipitates to electrical resistivity is less clear..... MJRSandim EEL-USP

7 Homogenization treatment
Eivani et al. Background Decrease in the electrical resistivity, due to the depletion of the elements in the matrix and the formation of the dispersoids Homogenization treatment However, depending on the temperature: Formation of dispersoids and the dissolution of constituint particles Homogenization treatment How this affects the electrical resistivity? MJRSandim EEL-USP

8 Background (outras fontes)

9 Endurecimento por precipitação Sistema Cu-Al
Callister Endurecimento por precipitação Sistema Cu-Al Representação esquemática de vários estágios do processo de formação da fase precipitada () de equilíbrio Distorção da rede cristalina (a) Solução sólida  super-saturada ( interfaces coerentes) Fonte: Callister (b) Fase precipitada ” (de transição) MJRS EEL-USP (c) Fase  de equilíbrio, dentro da matriz 

10 Os movimentos das discordâncias são dificultados como consequência
Endurecimento por precipitação Sistema Cu-Al Distorção da rede cristalina dentro e em torno do precipitado Os movimentos das discordâncias são dificultados como consequência dessas distorções Liga mais dura e resistente MJRS EEL-USP Callister

11 Endurecimento por precipitação Sistema Cu-Al
● A resistência máxima coincide com a formação da fase ” Pode ser preservada com o resfriamento da liga até a temperatura ambiente ● superenvelhecimento Continuidade do crescimento das partículas (fases ’ e ) MJRS EEL-USP Callister

12 Precipitados também interferem na resistividade elétrica do material
Outras referências

13 átomos de soluto tendem a aumentar a resistividade elétrica de um metal ou liga metálica
é esperado que fenômenos de precipitação, os quais causam uma diminuição de átomos de soluto na matriz, levem a uma diminuição da resistividade elétrica do metal isso é geralmente observado, mas, em alguns casos, o início da precipitação é acompanhado por um aumento anômalo na resistividade elétrica da liga (KELLY,1966; HERMAN,1963; JUNG , 2011). Esse comportamento anômalo de aumento de resistividade elétrica relacionado à precipitação pode ser verificado, por exemplo, em ligas dos sistemas Al-Cu e Al-Zn (KELLY, 1966) M. J. R. Sandim EEL-USP

14 Deformação da rede cristalina ao redor do precipitado
esse comportamento anômalo de aumento de resistividade elétrica pode ser atribuído à presença de campos de deformação elástica na rede ao redor das partículas de segunda fase (tensões elásticas de coerência), especialmente nas de pequenas dimensões (zonas de Guinier-Preston, por exemplo) (HERMAN, 1963). À medida que as partículas de segunda fase sofrem engrossamento, a deformação elástica da rede ao redor das partículas diminui (perda de coerência) e a resistividade elétrica do metal cai Deformação da rede cristalina ao redor do precipitado Fonte: Shackelford M. J. R. Sandim EEL-USP

15 Referências JUNG, J. G.; PARK, J. S.; KIM, J.; LEE, Y. K. Carbide precipitation kinetics in austenite of a Nb-Ti-V microalloyed steel. Materials Science and Engineering A, v. 528, p , 2011. KELLY, A.; NICHOLSON, R. B. Progress in Materials Science. 2nd ed. Oxford: Pergamon Press, 1966. HERMAN, H.; COHEN, J. B.; FINE, M. E. Formation and reversion of Guinier-Preston zones in Al-5.3at%Zn. Acta Metallurgica, v. 11, p , 1963. M. J. R. Sandim EEL-USP

16 ....Back to the paper Experimental data Eivani et al. MJRSandim
EEL-USP

17 Eivani et al. As cast samples

18 Homogenization treatment
Eivani et al. Homogenization treatment

19 MJRSandim EEL-USP Eivani et al.

20 Eivani et al. As-cast 390oC (2 h) 510oC 550oC (2 h) (2 h) MJRSandim
EEL-USP

21 dissolution of Al17(Fe3.2Mn0.8)Si2 particles Eivani et al.
Increase in the volume fraction of particles Mg2Si + MgZn2 and other particles As-cast 390oC 510oC 550oC dissolution of Al17(Fe3.2Mn0.8)Si2 particles Eivani et al. MJRSandim EEL-USP and formation of new precipitates

22 ● Formation of small particles or dispersoids from Zr, Cr, Fe, and Mn
Homogenization treatment – Eivani et al. ● Formation of small particles or dispersoids from Zr, Cr, Fe, and Mn ● Dissolution of constituint particles and formation of new ones, depending on the homogenization temperature and holding time ● in the present work the dispersoid interspacings is larger than 150 nm, regardless of the homogenization treatment employed In this regard there is no increase in the electrical resistivity expected due to the formation of dispersoids. Notice that for aluminum, the mean free path of the electron is 100 nm ● in this case: Formation of dispersoids Decrease of the electrical resistivity ...consistent with the depletion of the corresponding alloying elements from the structure MJRSandim EEL-USP

23 In this material ....It is possible to identify at least four different types of dispersoids
Zr- (type 1), Cr-(type 2), and Mn-containing (type 3) dispersoids, and those that have a combination of various elements (type 4) The Mn-containing dispersoids (type 3) are only observable after homogenization at 510oC....for a holding time of at least 4 hours

24 ...This indicates that Fe and Mn are the primary controlling elements of the measured
electrical resistivity among all the elements present in the alloy

25 Homogenization treatment – Eivani et al.
● low-temperature homogenization (390oC) - The dissolution of the large particles does not occur and precipitation occurs depletion of Zr and Cr in the matrix by forming dispersoids and depletion of Mg, Si, and Zn forming precipitates electrical resistivity shows a continuous decrease up to 48 h of homogenization MJRSandim EEL-USP

26 Homogenization treatment – Eivani et al.
● high-temperature homogenization (510 – 550oC) dissolution of Al17(Fe3.2Mn0.8)Si2 Higher Fe and Mn concentrations in the solid solution They are also present in the third type of dispersoid, which precipitates out during homogenization Mn-containing dispersoids after homogenization at 510oC or 550oC for more than 2 h

27 Homogenization treatment – Eivani et al.
● high-temperature homogenization (510 – 550oC) About the decrease of electrical resistivity ... ...

28 Homogenization treatment – Eivani et al.
● high-temperature homogenization (510 – 550oC) dissolution of Al17(Fe3.2Mn0.8)Si2 Higher Fe and Mn concentrations in the solid solution Mn-containing dispersoids after homogenization at 510oC or 550oC for more than 2 h Formação de precipitados Diminuição da resistividade elétrica Dissolução de partículas Aumento da resistividade elétrica Numa situação de equilíbrio entre esses efeitos competitivos A resistividade elétrica se mantém aproximadamente inalterada When the electrical resistivity levels off....

29 Quando a resistividade elétrica não se altera.....
...When the rate of the increase in the electrical resistivity due to the dissolution of constitutive particles ….becomes equal to the rate of the decrease in the electrical resistivity due to the formation of Zr- and Cr-containing dispersoids, a peak or plateau is observed in the electrical resistivity curve…. Para reflexão: 1) peak ??? 2) Faltou mencionar os precipitados relativos ao Mn Formação de precipitados Diminuição da resistividade elétrica Dissolução de partículas Aumento da resistividade elétrica Numa situação de equilíbrio entre esses efeitos competitivos A resistividade elétrica se mantém aproximadamente inalterada Quando a resistividade elétrica não se altera.....

30 homogenization treatment before hot deformation
About recrystallization.... Homogenization treatment Hot compression until a strain of 0.6 Annealing at 575oC for 10 minutes All the specimens are recrystallized Remember.... homogenization treatment before hot deformation Creates small dispersoids that later act as recrystallization inhibitors during deformation and annealing treatments

31 Homogenized for 24 h at: 390oC 470oC 510oC 550oC smallest grain size

32 ●… One of the primary objectives of homogenization is to form small Mn-, Zr-, and Cr-containing dispersoids.[1] ●… The lowest electrical resistivity of the sample homogenized at 550 C for 24 hours is consistent with the formation of a large volume fraction of dispersoids, leading to the depletion of solutes in the matrix. ●… Therefore, based on the findings of this investigation, the homogenization treatment at 550 C has resulted in the largest volume fraction of dispersoids, with a noticeably higher number density. Therefore, this temperature is considered as an optimum one for the homogenization of this alloy. ●...Therefore, the smallest grain size of the samples homogenized at 550 C for 24 hours (127 ± 15 lm) is due to the strongest recrystallization inhibition as a result of the presence of the dispersoids. ●…The lowest electrical resistivity of the samples homogenized at 550 C is a proof of the largest volume fraction of dispersoids. This, together with the smallest dispersoid interspacing for samples homogenized at 550 C, provides the highest Zener drag pressure for these samples