Tverdokhlebova S.V.
Dniepropetrovsk National University. Dniepropetrovsk.
Ukraine
PHASE TRANSFORMATIONS IN CONDITIONS OF THERMAL LOADING OF THE BORON-CONTAINING ALLOYS
The modern mashine-building has been required in the creation of fundamentally new materials respondent to extremal conditions of the exploitation. A numbers of scientists [1] considers that the decision of this problem can be realized with the idea of the heterophase materials as about the «intellectual» structural system promoting to the protect from the failure at the thermal electrical stress. The present work has been devoted to the investigation of the structural changes of boron-containing alloys in conditions of the thermal electrical stress in the key-note of the above mention idea. Boron-containing alloys were employed by the objects of the present investigation. The high-voltage condensed spark discharge (HCS) from the IVS-23 generator carried out the function of thermal action. The pulse duration of HCS was approximately 7,56 mks. The phase transformations were fixed by X-ray method. X-ray diffraction analysis was made with using of DRON–3 in copper-radiation. The dispersion analysis was led by the schemes stated in the mathematical statistics. The mass portion of elements was determined with the optical atomic emission spectroscopy method [2]. Electron-vibration spectra were recorded by the spectrophotometer of Specord 75 IR in the range of wave numbers such as 400-5000 cm-1 with using of known technique of the KBr – disk We are showing that the thermal loading from the concentrated sources of the energy causes the self-organization of the structures. The self-organization is developed with the concentration effect, the change of the electron structure and as consequence the phase transformations. The spectral analysis shows that the mass portion of elements in the nanocrystalline layer on the ground part of crater of the sparking spot is distinguished from the concentration of elements in the surface layers ( The Table 1). In addition the changes of concentration is estimated with t- distribution. It varies from the 72,1 till 87,7 at the tn equaled to 3,18. Side by side with this the electron overbuilding of phases takes in place [3].
Table 1
The mass portion of elements of boron-containing layers of sparking spot
|
The name of
layer |
The mass
portion of elements, % |
||||
|
B |
C |
Mn |
Cr |
Si |
|
|
The initial
surface |
3,10 |
1,30 |
1,46 |
4,30 |
1,73 |
|
The ground part
of the crater |
5,70 |
1,95 |
2,37 |
6,60 |
2,78 |
They are fixed with X-ray method. Moreover X-ray diffraction analysis is made in the nanocrystalline layer of ground part of crater of the sparking spot. The experimental and the tabulated values of grating period, d, of the phases and the identification of phases are situated in the Table 2.
Table 2
Data of X - ray analysis of boron-containing alloys
|
The
experimental dHKL |
The tabulated dHKL
|
The
identification of X-ray lines |
|
1 |
2 |
3 |
|
2,841 |
2,865 |
The solid
solution of chromium in iron |
|
1,993 |
2,01 |
The solid
solution of chromium and boron in iron with the martensite grating |
|
1,162 |
1,166 |
The solid
solution of chromium and boron in iron with the martensite grating |
|
1,425 |
1,428 |
The solid
solution of chromium and boron in a-iron (the remanent austenite) |
|
2,004 |
2,01 |
Fe2(B,C) |
|
1,21 |
1,202 |
Fe2(B,C) |
|
2,187 |
2,19 |
Fe(B,C) |
|
2,277 |
2,28 |
Fe(B,C) |
|
1,999 |
2,01 |
Fe(B,C) |
|
1,895 |
1,90 |
Fe(B,C) |
|
1,24 |
1,239 |
Fe(B,C) |
|
2,028 |
2,035 |
Fe3(C,B) |
|
1,855 |
1,85 |
Fe3(C,B) |
|
2,042 |
2,04 |
(Cr,Fe)7C3 |
|
2,124 |
2,12 |
(Cr,Fe)7C3 |
|
1,817 |
1,81 |
(Cr,Fe)7C3 |
|
1 |
2 |
3 |
|
1,739 |
1,74 |
(Cr,Fe)7C3 |
|
2,295 |
2,30 |
(Cr,Fe)7C3 |
|
2,033 |
2,037 |
Fe23
(C,B)6 |
|
2,346 |
2,367 |
Fe23
(C,B)6 |
|
2,167 |
2,161 |
Fe23
(C,B)6 |
|
1,797 |
1,792 |
Fe23
(C,B)6 |
At the same time the diffusivity of
X-ray line of the remanent austenite with HKL equaled to 200 testifies about
the high dispersitivity of the sparked structure.The reflexes from phases such
as the solid solution of boron and chromium in
a-iron, Fe3(C, B) and Fe2(B,
C) are discovered in initial samples. The obtained results of X-ray analysis of
the initial and the sparked samples have testified that the thermal forced stress
has caused the protected reaction from the failure of the phases of
boron-containing alloys. It is developed in the sight of surface
transformations as the austenite in the martensite as the formation of
nanocrystalline structures of iron and chromium carbides and carboborides of
the type (Cr,Fe)7C3, Fe23(C,B)6.
New structures have ensured the reduce of the entropy in the heterosystem [3].
At the same time the view [4] exists in the literature that the surface
transformations under the act of concentrated sources of the energy occur due
to processes of the oxidation and the nitrogenization. The surface
transformations are developed with the spectral method through the growth of
concentration of the elements. Two-factors dispersion analysis of contribution
of A factor of the oxidation, the nitrogenization and the B factor of
self-organization of the structural constituents of boron-containing alloys in
the forming of phase transformations through the elements mass portion
parameter is carried out. The obtained results of two-factors dispersion
analysis are listed in the Table 3. The 
, 
, 
are the selective
dispersions connected with the chance and the A and B factors. F0,95
is the quintile at the level of the significance equaled to 0,05. The 
, 
are the dispersions
of contribution of the A and B factors in the forming of phase transformations
through elements mass portion parameter. As shown in the Table 3 the B factor
that is the self-organization of the structural constituents of
boron-containing alloys has made the significant contribution in the forming of
the phase transformations as 
. Moreover, the B factor
Table 3
Results of two-factors dispersion analysis
|
The dispersions |
||||||
|
|
|
|
|
|
|
|
|
0,08 |
0,16 |
3,0 |
2,0|18,5 |
37,5|19,2 |
0,04 |
0,97 |
|
|
`contribution such as 0,97 in the forming of elements mass portion has exceed two orders as large as much the A factor contribution such as 0,04. Thus, the dominant of contribution of self-organization of the structural constituents of boron-containing alloys in the forming of phase transformations is established. At last, the mechanical tests are shown the growth of the relative wear resistance of the sparked surface in 1,5-2,5 times as compare with the initial samples.
Thus, it is established the presence of phase transformations as the austenite in the martensite as the formation of nanocrystalline structures of iron and chromium carbides and iron and chromium carboborides of the type (Cr, Fe)7C3 and Fe23(C, B)6 ensuring the reduce of the entropy in the heterosystem. These structural formations testify about the protected reaction from the thermal stress.
LITERATURE
1. Чеховой А.Н. Перспективы интеллектуальной методологии новых российских нанотехнологий // Наукоемкие технологии. №5.-2001.-С.15.
2. Tverdoklebova S.V. Atomic emission spectroscopy method in composites structure characterization || Proceeding of 10 th International Metallurgical Conference. Czech Republic. 2001. Ostrava. CD-ROM. Symposium C.
3.
Tverdokhlebova S.V. Peculiarities of
boron-containing alloys hardening in conditions of the electrical spark
treatment. || Nauka i studia. №4(9).-2008.-P. 66-72
4.
Буравлев Ю.М.
Атомно-эмиссионная спектрометрия металлов и сплавов. Донецк.:
ДонГУ.-2000.-374с..