Mechanizmy odkształcenia materiałów nanostrukturalnych

• Autorzy: Krella A.

Warianty tytułu

EN

The deformation mechanisms of nanostructured materials

• Języki publikacji: PL

Abstrakty

PL

Nanomateriały stanowią obecnie ważną grupę materiałów znajdujących zastosowanie prawie we wszystkich dziedzinach przemysłu. W badaniach nanomateriałów stwierdzono, że zależność Halla-Petcha nie jest spełniona dla całego zakresu 1÷100 nm. W przypadku nanomateriałów o wielkości ziaren poniżej pewnej wartości krytycznej zaobserwowano efekt zmniejszenia twardości wraz ze zmniejszeniem się wielkości ziarna. Z tego względu wiele badań poświęcono poznaniu ich budowy i mechanizmów odkształcania. Badania prowadzone za pomocą transmisyjnego mikroskopu elektronowego wykazały, że nanokrystaliczne materiały są zbudowane z małych krystalitów o zróżnicowanej orientacji krystalograficznej, oddzielonych od siebie szerokokątowymi granicami ziaren, w których są obserwowane pustki (rys. 1). Pustki te były wyraźnie większe w miejscach styku trzech ziaren, tzw. triple junction. Ze względu na istotny wzrost udziału granic ziaren (rys. 2) wraz ze zmniejszaniem się wielkości ziaren oraz mniejszą gęstość atomową w porównaniu z ziarnami, najczęstszym modelem struktury nanomateriałów jest model dwufazowy składający się fazy wewnętrznej ziarna i fazy granicy ziarna (rys. 3). Jednym z wyjaśnień zjawiska zmniejszenia twardości nanomateriałów jest zwiększenie w budowie nanomateriału udziału granic ziaren (rys. 2), których gęstość jest znacznie mniejsza niż gęstość ziaren oraz odmienne mechanizmy odkształcania. Badania doświadczalne, symulacje dynamiki molekularnej oraz modele odkształcenia nanokrystalicznych materiałów wykazały, że odkształcanie nanomateriałów przebiega na skutek poślizgu wzdłuż granic ziaren, dyfuzji po granicy ziaren, dyfuzji w ziarnach, rotacji ziaren, powstania pasm ścinania, generowania dyslokacji przez granice ziaren, mechanicznego bliźniakowania, a także w wyniku ruchu dyslokacji wewnątrz ziaren, z tym, że ten ostatni mechanizm zanika wraz ze zmniejszaniem się wielkości krystalitów.

EN

Nanomaterials are nowadays very important group of materials which are used in most branches of industry. The investigations of the strength of nanomaterials showed that the Hall-Petch law is not valid in the same form for the whole range from 1 to 100 nm. When the grain size falls below the critical size the effect of decrease of strength (softening) is observed. Therefore, many studies were performed to learn their structure and deformation mechanisms. Investigation performed by means of high resolution transmission electron microscopy (HRTEM) showed that nanocrystalline materials consist of small crystallites of different crystallographic orientations separated by the grain boundaries of large angle type, which consists of pores (Fig. 1). These pores have bigger size at triple junctions. Due to low atomic density of grain boundary and an increase of grain boundary fraction with decrease of grain size (Fig. 2), the most frequent model of nanomaterials structure is two-phase model which consists of the grain interior phase and the grain boundary phase (Fig. 3). One of the explanation of the softening effect of the nanostructured materials is the increase of fraction of grain boundary (Fig. 2), whose density and strength is lower than those of grains. Another explanation says that the softening effect is due to deformation mechanisms that are different from those present in their coarse-grained counterparts. Experimental investigations, molecular dynamic simulation and many models showed that deformation of nanocrystalline materials develops via grain boundary sliding, grain boundary diffusion, shear-band formation, mechanical twinning, dislocation climb, rotation at triple junctions, grain-boundary dislocation creation and annihilation and also via dislocation motion inside grain.

Słowa kluczowe

PL

materiały nanostrukturalne; mechanizmy deformacji

EN

nanostructured materials; deformation machanisms

• Wydawca: Wydawnictwo SIGMA-NOT
• Czasopismo: Inżynieria Materiałowa
• Rocznik: 2011
• Tom: Vol. 32, nr 5
• Strony: 844--850
• Opis fizyczny: Bibliogr. 65 poz., rys.

Twórcy

autor

Krella A.

• Instytut Maszyn Przepływowych im. R. Szewalskiego, PAN, Gdańsk,

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