KnE Engineering | XIX International scientific-technical conference “The Ural school-seminar of metal scientists-young researchers” | pages: 281–287

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1. Results and Discussion

Research of structural and textural states in FCC-metals with a low and average value of the energy of a packaging defects are of great interest until the present time [1–5]. Special attention is paid to the formation of mesostructures such as twins and shear bands (SBs) during the deformation and recrystallization of such elements of the mesostructure. Crystallographic orientations, which are contained in these elements of the mesostructure, have a dominant influence on the formation of a texture state during recrystallization annealing, and, as a result, determine both technological and functional orientation-dependent properties of products from FCC-metals [1,2].

The aim of the work was to establish the structural and textural state of the alloy with an FCC-lattice after cold rolling deformation, which is characterized by a low energy value of the packaging defect.

The material for the research was a corrosion-resistant superalloy of the Ni–Cr–Mo system, wares from this alloy are used in aggressive media at high temperatures. The starting material had a recrystallized (annealed) state before deformation. Under laboratory conditions, the process of flat cold rolling of a sheet was modeled (the diameter of the rolls is much larger than the cross-section of the product). The degree of deformation was 0.7. Texture analysis was performed by the method of electron backscatter diffraction (EBSD) on a two-beam electron-ion microscope (system) ZEISS CrossBeam AURIGA.

During the deformation, the structural state was obtained, shown in Fig. 1. Grains strongly elongated along the rolling direction (RD) had dimensions in cross section from 10 to 40 microns. Also structural analysis showed the presence of a large number of bands representing deformation twins (TWs) and / or shear bands (SBs). The amount and width of the bands differed in different grains. In some grains there were intersecting bands forming the "fishbone" mesostructure. The range of tilt angles of the all mesostructure elements to the RD was 10 to 35 . From these works [4,6–8], the tilt angles of the SBs to the direction of deformation can lie in the range from 10 to 45 .

fig-1.jpg
Figure 1
Structural state of the alloy after deformation.

A texture analysis of the sheet was carried out over the entire cross section of the samples after cold rolling to assess the deformation state. The integral texture is a set of orientations, including the strong components {110}<112> and the weaker components {110}<001> , {110}<111> (Fig. 2). All orientations are typical for rolling texture (RT) of FCC-metals. As a rule, shear texture is formed in the surface zone of the sheet during rolling, different from RT [9,10]. In this case, only the components of the RT are present over the entire section of the sheet. Apparently, this is due to the conditions of the experiment: rolling was carried out without tension, with a large diameter of the rolls.

fig-2.jpg
Figure 2
Pole figures of integral texture after deformation with decoding of texture components.

Also in this paper, questions of the relationship between the orientations of the matrix and crystallites within the bands constituting the mesostructure are considered. Due to the increased density of dislocations, the internal structure of most bands did not give in to identification. In this connection, only the orientations of individual elements within the bands and the matrix in which they were formed were determined (Fig. 3).

Texture analysis showed that the crystal lattice inside the bands arising in the grains of the main matrix orientation {110}<112> , regardless of their width and angle of inclination to RD, has an orientation close to {110}<001> (Fig. 3). All pole figures (Fig. 3,b–d), corresponding to the orientation map (Fig. 3,a), show that the orientations of the objects of the mesostructure are strongly scattered. The orientation of the matrix {110}<112> is also not absolutely stable, somewhat dissipates in the process of deformation. The formation of the {110}<001> texture component inside SBs has been discussed in a number of papers [4,6,11–13]. Moreover, the shear orientation inside SBs was associated with the orientation of the matrix by rotating around TD, as in the present work. In this case, the orientation of the matrix and the elements of the mesostructure are connected to each other by turning an angle of 70 around the axis <110> parallel to TD (or turning the angle of 60 around the axis <111> slightly deviated from ND). That is, the orientation of the band relative to the matrix is close to the special misorientation Σ3 (60 , axis <111> ) from the from the coincidence site lattice (CSL), which is also a twin disorientation.

fig-3.jpg
Figure 3
Microstructure and texture of the sheet area after cold rolling: a - orientation map with RD; b–d – pole figures {100} , {110} , {110} , corresponding to microregions 1–3, divided into “a” by rectangles, respectively

The histogram of the distribution of the CSL boundaries also indicates the presence of the dominant special disorientation of the CSL Σ3 in the deformed state (Fig. 4).

fig-4.jpg
Figure 4
Distribution of the CSL boundaries in the deformed state, obtained by extrapolation of the initial points (data) to their intersection.

In FCC-metals with an average and low energy of a packing defect, the deformation is carried out also by the mechanism of deformation twinning [14]. Thus, the presence of Σ3 CSL in the deformed state in the FCC-metal can be explained by the preservation in the deformation process of the twin boundaries arising during twinning at the beginning of the deformation. That is, during deformation, the crystallites are reoriented with retaining the Σ3 boundary, as an energetically favorable state of the arrangement of atoms in accordance with the results of [15–17].

It is worth noting that the CSL 25b is in the deformed state in the material.

2. Conclusion

  • It has been established that a multicomponent rolling texture is formed during cold rolling of Ni–Cr–Mo nickel-based alloy, including: a strongly pronounced component { 110 }< 112 > and weaker components { 110 }< 001 > , { 110 }< 111 > .

  • The textural component { 110 }< 001 > is located in bands representing deformation twins and shear bands formed at different stages of deformation in the matrix grains { 110 }< 112 > . The formation of orientation in the bands can be represented as a rotation around TD (close to the crystallographic direction < 110 > ) at an angle of 70 . Such a misorientation corresponds to the twinning misorientation of the CSL Σ3 (60 , axis < 111 > ).

  • The special disorientation (special boundary Σ3) formed at the beginning of the process of deformation a is preserved in the deformation process as an energetically stable object.

Acknowledgments

This study was supported by the Russian Science Foundation (grant 18-79-00126)

The work was carried out using the laboratory equipment ”Structural methods of analysis and properties of materials and nanomaterials” of the Center of Ural Federal University.

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