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Microstructure inhomogeneity of Fe-31%Ni alloy and stabilization of austenite.

Dzevin IM - Nanoscale Res Lett (2015)

Bottom Line: Сrystal structure and mechanism of crystallization of Fe-Ni alloys were studied by methods of X-ray diffraction and metallography.It has been found that macro- and microstructure of austenitic alloy was essentially heterogeneous at the contact and free surfaces and in the volume of a ribbon.The indentified peculiarities of the austenitic phase in different areas of the ribbon are attributed to different cooling rates and the melt crystallization conditions.

View Article: PubMed Central - PubMed

Affiliation: G.V.Kurdyumov Institute of Metal Physics NAS of Ukraine, Vernadsky blvd. 36, Kiev, 03680 Ukraine.

ABSTRACT
Сrystal structure and mechanism of crystallization of Fe-Ni alloys were studied by methods of X-ray diffraction and metallography. It has been found that macro- and microstructure of austenitic alloy was essentially heterogeneous at the contact and free surfaces and in the volume of a ribbon. The indentified peculiarities of the austenitic phase in different areas of the ribbon are attributed to different cooling rates and the melt crystallization conditions.

No MeSH data available.


Related in: MedlinePlus

Martensitic volume part vs the number of γ-α-γ cycles. Change of the martensitic volume part vs the number of γ-α-γ cycles for the contact (1), free (2) surfaces of a spinning ribbon, and bulk (3) Fe-30.6 wt.% Ni-0.05 wt.% C alloy. Reduction of the size of austenitic grain in melt-spun ribbons results in more considerable stabilization of reverted austenite as compared to the bulk alloy of the same chemical composition. It was found that after 30 γ-α-γ cycles of reverse diffussionless transformations in the ribbon, the amount of martensite on a free side dropped by 61%, on a contact side by 43%, while in a bulk alloy, only by 8%. Investigations indicated that the size effect of martensitic transformation yielded a higher degree of stabilization of reverted austenite on a free side of the ribbon as compared to a contact side. Quenching in liquid nitrogen caused essential difference of grain structure on both the sides of the ribbon as well as the gradient distribution of the amount of martensitic phase inside it. Austenitic grains on a contact surface was smaller than on a free surface. As a result of the size effect of the transformation, amounts of martensitic phase on a contact and free surfaces were different - 59% and 82%, respectively.
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Fig2: Martensitic volume part vs the number of γ-α-γ cycles. Change of the martensitic volume part vs the number of γ-α-γ cycles for the contact (1), free (2) surfaces of a spinning ribbon, and bulk (3) Fe-30.6 wt.% Ni-0.05 wt.% C alloy. Reduction of the size of austenitic grain in melt-spun ribbons results in more considerable stabilization of reverted austenite as compared to the bulk alloy of the same chemical composition. It was found that after 30 γ-α-γ cycles of reverse diffussionless transformations in the ribbon, the amount of martensite on a free side dropped by 61%, on a contact side by 43%, while in a bulk alloy, only by 8%. Investigations indicated that the size effect of martensitic transformation yielded a higher degree of stabilization of reverted austenite on a free side of the ribbon as compared to a contact side. Quenching in liquid nitrogen caused essential difference of grain structure on both the sides of the ribbon as well as the gradient distribution of the amount of martensitic phase inside it. Austenitic grains on a contact surface was smaller than on a free surface. As a result of the size effect of the transformation, amounts of martensitic phase on a contact and free surfaces were different - 59% and 82%, respectively.

Mentions: Reverse transformation that occurred on heating of quenched alloy in the temperature interval of α-γ transformation at a speed higher than critical one has a diffusionless character. Under this character of atomic redistribution, the degree of stabilization of the austenite reverted by γ-α-γ transformations appeared considerably lower than in the case of the diffusive character of reverse transformation. It happened since diffusionless reverse transformation did not change the size of initial austenitic grain but the boundaries of grain become unclear and distorted (Figure 1B). Certain substructure shows up in a volume of grain. After tens of diffusionless α-γ transformations, the fragments of different orientation of reverted austenite reached nanoscale size [4]. Low-angle sub-boundaries of these fragments were less effective barrier for the martensitic crystals to grow as compared to high-angle boundaries of grains. However, as accumulation of misorientated fragments occurs during repetitive γ-α-γ cycles (Figure 1), completeness of the direct transformation decreases. Reduction of the size of austenitic grain in melt-spun ribbons results in more considerable stabilization of reverted austenite as compared to the bulk alloy of the same chemical composition. It was found that after 30 γ-α-γ cycles of reverse diffussionless transformations in the ribbon, the amount of martensite on a free side dropped by 61%, on a contact side by 43%, while in a bulk alloy, only by 8% (Figure 2). Investigations indicated that the size effect of martensitic transformation yielded a higher degree of stabilization of reverted austenite on a free side of the ribbon as compared to a contact side.Figure 1


Microstructure inhomogeneity of Fe-31%Ni alloy and stabilization of austenite.

Dzevin IM - Nanoscale Res Lett (2015)

Martensitic volume part vs the number of γ-α-γ cycles. Change of the martensitic volume part vs the number of γ-α-γ cycles for the contact (1), free (2) surfaces of a spinning ribbon, and bulk (3) Fe-30.6 wt.% Ni-0.05 wt.% C alloy. Reduction of the size of austenitic grain in melt-spun ribbons results in more considerable stabilization of reverted austenite as compared to the bulk alloy of the same chemical composition. It was found that after 30 γ-α-γ cycles of reverse diffussionless transformations in the ribbon, the amount of martensite on a free side dropped by 61%, on a contact side by 43%, while in a bulk alloy, only by 8%. Investigations indicated that the size effect of martensitic transformation yielded a higher degree of stabilization of reverted austenite on a free side of the ribbon as compared to a contact side. Quenching in liquid nitrogen caused essential difference of grain structure on both the sides of the ribbon as well as the gradient distribution of the amount of martensitic phase inside it. Austenitic grains on a contact surface was smaller than on a free surface. As a result of the size effect of the transformation, amounts of martensitic phase on a contact and free surfaces were different - 59% and 82%, respectively.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4385281&req=5

Fig2: Martensitic volume part vs the number of γ-α-γ cycles. Change of the martensitic volume part vs the number of γ-α-γ cycles for the contact (1), free (2) surfaces of a spinning ribbon, and bulk (3) Fe-30.6 wt.% Ni-0.05 wt.% C alloy. Reduction of the size of austenitic grain in melt-spun ribbons results in more considerable stabilization of reverted austenite as compared to the bulk alloy of the same chemical composition. It was found that after 30 γ-α-γ cycles of reverse diffussionless transformations in the ribbon, the amount of martensite on a free side dropped by 61%, on a contact side by 43%, while in a bulk alloy, only by 8%. Investigations indicated that the size effect of martensitic transformation yielded a higher degree of stabilization of reverted austenite on a free side of the ribbon as compared to a contact side. Quenching in liquid nitrogen caused essential difference of grain structure on both the sides of the ribbon as well as the gradient distribution of the amount of martensitic phase inside it. Austenitic grains on a contact surface was smaller than on a free surface. As a result of the size effect of the transformation, amounts of martensitic phase on a contact and free surfaces were different - 59% and 82%, respectively.
Mentions: Reverse transformation that occurred on heating of quenched alloy in the temperature interval of α-γ transformation at a speed higher than critical one has a diffusionless character. Under this character of atomic redistribution, the degree of stabilization of the austenite reverted by γ-α-γ transformations appeared considerably lower than in the case of the diffusive character of reverse transformation. It happened since diffusionless reverse transformation did not change the size of initial austenitic grain but the boundaries of grain become unclear and distorted (Figure 1B). Certain substructure shows up in a volume of grain. After tens of diffusionless α-γ transformations, the fragments of different orientation of reverted austenite reached nanoscale size [4]. Low-angle sub-boundaries of these fragments were less effective barrier for the martensitic crystals to grow as compared to high-angle boundaries of grains. However, as accumulation of misorientated fragments occurs during repetitive γ-α-γ cycles (Figure 1), completeness of the direct transformation decreases. Reduction of the size of austenitic grain in melt-spun ribbons results in more considerable stabilization of reverted austenite as compared to the bulk alloy of the same chemical composition. It was found that after 30 γ-α-γ cycles of reverse diffussionless transformations in the ribbon, the amount of martensite on a free side dropped by 61%, on a contact side by 43%, while in a bulk alloy, only by 8% (Figure 2). Investigations indicated that the size effect of martensitic transformation yielded a higher degree of stabilization of reverted austenite on a free side of the ribbon as compared to a contact side.Figure 1

Bottom Line: Сrystal structure and mechanism of crystallization of Fe-Ni alloys were studied by methods of X-ray diffraction and metallography.It has been found that macro- and microstructure of austenitic alloy was essentially heterogeneous at the contact and free surfaces and in the volume of a ribbon.The indentified peculiarities of the austenitic phase in different areas of the ribbon are attributed to different cooling rates and the melt crystallization conditions.

View Article: PubMed Central - PubMed

Affiliation: G.V.Kurdyumov Institute of Metal Physics NAS of Ukraine, Vernadsky blvd. 36, Kiev, 03680 Ukraine.

ABSTRACT
Сrystal structure and mechanism of crystallization of Fe-Ni alloys were studied by methods of X-ray diffraction and metallography. It has been found that macro- and microstructure of austenitic alloy was essentially heterogeneous at the contact and free surfaces and in the volume of a ribbon. The indentified peculiarities of the austenitic phase in different areas of the ribbon are attributed to different cooling rates and the melt crystallization conditions.

No MeSH data available.


Related in: MedlinePlus