Structure and properties of Fe-B-C powders alloyed with Cr, V, Mo or Nb for plasma-sprayed coatings
In the present study, the microstructure development and properties of the starting Fe-B-C powders for plasma spraying fabricated by dispersing a consumable rotating rod were investigated as functions of alloying elements additions. These powders were prepared in the following compositional ranges:...
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irk-123456789-1944172023-11-24T15:11:07Z Structure and properties of Fe-B-C powders alloyed with Cr, V, Mo or Nb for plasma-sprayed coatings Sukhova, O.V. Physics of radiation and ion-plasma technologies In the present study, the microstructure development and properties of the starting Fe-B-C powders for plasma spraying fabricated by dispersing a consumable rotating rod were investigated as functions of alloying elements additions. These powders were prepared in the following compositional ranges: B (10…14 wt.%), C (0.01…0.5 wt.%), Me (0…5.0 wt.%), where Me – Cr, V, Mo or Nb, balance Fe. Structural properties were characterized by metallography, X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Mechanical properties of the powders were measured by a Vickers indenter. Compression strength, oxidation resistance, and melting temperature were also determined. Chromium or vanadium were found to dissolve completely in Fe₂(B, C) and Fe(B, C) constituent phases of the Fe-B-C powders replacing iron and forming substitutional solid solutions. By entering into the iron borides structure, these alloying elements improve ductility and oxidation resistance but lower melting temperature and hardness of the powders. Molybdenum or niobium were mainly found in secondary phases such as Mo₂B, Mo₂(B, C) or NbB₂ at the Fe₂(B, C) boundaries. As a result, these alloying elements enhance hardness, oxidation resistance and melting temperature of the powders. Досліджували вплив легуючих елементів на процеси формування структури та властивостей порошків для плазмового напилення, виготовлених методом розпилення обертового стрижня. Склад порошків знаходився в наступному концентраційному діапазоні: B (10…14 ваг.%), C (0,01…0,5 ваг.%), Me (0…5,0 ваг.%), де Me – Cr, V, Mo або Nb, Fe – залишок. Структуру порошків вивчали методами металографії, рентгеноструктурного аналізу, сканувальної електронної мікроскопії, рентгеноспектрального мікроаналізу. Механічні властивості порошків вимірювали на мікротвердомірі Віккерса. Також визначали міцність на стиск, окалиностійкість, температуру плавлення. Хром та ванадій повністю розчиняються в структурних складових Fe₂(B, C) і Fe(B, C) порошків Fe-B-C, заміщуючи залізо в кристалічних ґратках фаз і формуючи тверді розчини заміщення. Проникаючи в структуру боридів заліза, ці елементи підвищують їх пластичність і опір окисленню, але знижують температуру плавлення і твердість порошків. Молібден та ніобій в основному присутні в структурі у вигляді вторинних фаз, таких як Mo₂B, Mo₂(B, C) або NbB₂, що виділяються по межах кристалів Fe₂(B, C). Як наслідок, ці легуючі елементи підвищують твердість, опір окисленню і температуру плавлення порошків. Исследовали влияние легирующих элементов на процессы формирования структуры и свойств порошков для плазменного напыления, изготовленных методом распыления вращающегося стержня. Состав порошков находился в следующем концентрационном диапазоне: B (10…14 вес.%), C (0,01…0,5 вес.%), Me (0…5,0 вес.%), где Me – Cr, V, Mo или Nb, Fe – остаток. Структуру порошков изучали методами металлографии, рентгеноструктурного анализа, сканирующей электронной микроскопии, рентгеноспектрального микроанализа. Механические свойства порошков измеряли на микротвердомере Виккерса. Также определяли прочность на сжатие, окалиностойкость, температуру плавления. Хром и ванадий полностью растворяются в структурных составляющих Fe₂(B, C) и Fe(B, C) порошков Fe-B-C, замещая железо в кристаллических решетках фаз и формируя твердые растворы замещения. Присутствуя в структуре боридов железа, эти элементы повышают их пластичность и сопротивление окислению, но снижают температуру плавления и твердость порошков. Молибден и ниобий в основном присутствуют в структуре в виде вторичных фаз, таких как Mo₂B, Mo₂(B, C) или NbB₂, выделяющихся по границам кристаллов Fe₂(B, C). Как следствие, эти легирующие элементы повышают твердость, сопротивление окислению и температуру плавления порошков. 2020 Article Structure and properties of Fe-B-C powders alloyed with Cr, V, Mo or Nb for plasma-sprayed coatings / O.V. Sukhova // Problems of atomic science and tecnology. — 2020. — № 4. — С. 77-83. — Бібліогр.: 30 назв. — англ. 1562-6016 PACS: 81.10.Fq, 81.30t, 61.50 Ks, 52 .50 Dg, 52. 77. Dq, 61.66.Dk, 64.70.Kb http://dspace.nbuv.gov.ua/handle/123456789/194417 en Вопросы атомной науки и техники Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
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Physics of radiation and ion-plasma technologies Physics of radiation and ion-plasma technologies Sukhova, O.V. Structure and properties of Fe-B-C powders alloyed with Cr, V, Mo or Nb for plasma-sprayed coatings Вопросы атомной науки и техники |
| description |
In the present study, the microstructure development and properties of the starting Fe-B-C powders for plasma spraying fabricated by dispersing a consumable rotating rod were investigated as functions of alloying elements additions. These powders were prepared in the following compositional ranges: B (10…14 wt.%), C (0.01…0.5 wt.%), Me (0…5.0 wt.%), where Me – Cr, V, Mo or Nb, balance Fe. Structural properties were characterized by metallography, X-ray diffraction, scanning electron microscopy, and energy dispersive spectroscopy. Mechanical properties of the powders were measured by a Vickers indenter. Compression strength, oxidation resistance, and melting temperature were also determined. Chromium or vanadium were found to dissolve completely in Fe₂(B, C) and Fe(B, C) constituent phases of the Fe-B-C powders replacing iron and forming substitutional solid solutions. By entering into the iron borides structure, these alloying elements improve ductility and oxidation resistance but lower melting temperature and hardness of the powders. Molybdenum or niobium were mainly found in secondary phases such as Mo₂B, Mo₂(B, C) or NbB₂ at the Fe₂(B, C) boundaries. As a result, these alloying elements enhance hardness, oxidation resistance and melting temperature of the powders. |
| format |
Article |
| author |
Sukhova, O.V. |
| author_facet |
Sukhova, O.V. |
| author_sort |
Sukhova, O.V. |
| title |
Structure and properties of Fe-B-C powders alloyed with Cr, V, Mo or Nb for plasma-sprayed coatings |
| title_short |
Structure and properties of Fe-B-C powders alloyed with Cr, V, Mo or Nb for plasma-sprayed coatings |
| title_full |
Structure and properties of Fe-B-C powders alloyed with Cr, V, Mo or Nb for plasma-sprayed coatings |
| title_fullStr |
Structure and properties of Fe-B-C powders alloyed with Cr, V, Mo or Nb for plasma-sprayed coatings |
| title_full_unstemmed |
Structure and properties of Fe-B-C powders alloyed with Cr, V, Mo or Nb for plasma-sprayed coatings |
| title_sort |
structure and properties of fe-b-c powders alloyed with cr, v, mo or nb for plasma-sprayed coatings |
| publisher |
Національний науковий центр «Харківський фізико-технічний інститут» НАН України |
| publishDate |
2020 |
| topic_facet |
Physics of radiation and ion-plasma technologies |
| url |
http://dspace.nbuv.gov.ua/handle/123456789/194417 |
| citation_txt |
Structure and properties of Fe-B-C powders alloyed with Cr, V, Mo or Nb for plasma-sprayed coatings / O.V. Sukhova // Problems of atomic science and tecnology. — 2020. — № 4. — С. 77-83. — Бібліогр.: 30 назв. — англ. |
| series |
Вопросы атомной науки и техники |
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AT sukhovaov structureandpropertiesoffebcpowdersalloyedwithcrvmoornbforplasmasprayedcoatings |
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2025-07-16T21:41:44Z |
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2025-07-16T21:41:44Z |
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1837841362623397888 |
| fulltext |
ISSN 1562-6016. PASТ. 2020. №4(128), p. 77-83.
STRUCTURE AND PROPERTIES OF Fe-B-C POWDERS ALLOYED
WITH Cr, V, Mo OR Nb FOR PLASMA-SPRAYED COATINGS
O.V. Sukhova
The Oles’ Honchar Dnipro National University,
Dnipro, Ukraine
E-mail: sukhovaya@ukr.net
In the present study, the microstructure development and properties of the starting Fe-B-C powders for plasma
spraying fabricated by dispersing a consumable rotating rod were investigated as functions of alloying elements
additions. These powders were prepared in the following compositional ranges: B (10…14 wt.%),
C (0.01…0.5 wt.%), Me (0…5.0 wt.%), where Me – Cr, V, Mo or Nb, balance Fe. Structural properties were
characterized by metallography, X-ray diffraction, scanning electron microscopy, and energy dispersive
spectroscopy. Mechanical properties of the powders were measured by a Vickers indenter. Compression strength,
oxidation resistance, and melting temperature were also determined. Chromium or vanadium were found to dissolve
completely in Fe2(B, C) and Fe(B, C) constituent phases of the Fe-B-C powders replacing iron and forming
substitutional solid solutions. By entering into the iron borides structure, these alloying elements improve ductility
and oxidation resistance but lower melting temperature and hardness of the powders. Molybdenum or niobium were
mainly found in secondary phases such as Mo2B, Mo2(B, C) or NbB2 at the Fe2(B, C) boundaries. As a result, these
alloying elements enhance hardness, oxidation resistance and melting temperature of the powders.
PACS: 81.10.Fq, 81.30t, 61.50 Ks, 52 .50 Dg, 52. 77. Dq, 61.66.Dk, 64.70.Kb
INTRODUCTION
Boron-rich Fe-B-C alloys with boron content in the
range of 10…14 wt.% are nowadays well-established
materials due to their high hardness, relatively low
coefficient of friction, and good oxidation and corrosion
resistance [1–4]. As such these alloys have attracted
significant attention both in basic as well as in applied
research areas, resulting in several studies on phase
stability, mechanical and performance properties of the
ternary Fe-B-C system [5–7]. These properties are
attributed to the formation of Fe2B and FeB borides in
the structure which are major constituents of boron-rich
Fe-B alloys. Meanwhile, carbon may be considered as
natural addition to Fe-В alloys since these alloys are
very reactive with respect to carbon. This element is
found to dissolve in the iron borides forming Fe(B, C)
and Fe2(B, C) solid solutions and add strength at
elevated temperatures [8]. At that, with cooling rate of
Fe-B-C alloys increasing, carbon solubility increases
which enhances solid-solution strength, as well as
hardness.
In view of the increasing importance of boron-rich
Fe-B-C alloys in practical applications, it is surprising
how little is known about the influence of alloying
elements on their structure and properties. The studies
mainly concern the effects of alloying on boron-
containing steels [9–14]. Very important elements for
alloy steels are chromium, vanadium, molybdenum, and
niobium. Probably one of the most well-known effects
of chromium on steel is the tendency to resist staining
and corrosion. Chromium can also increase the
toughness of steel, as well as the wear resistance. The
metal also improves hardenability, strength, response to
heat treatment. Vanadium can produce stable carbides
that increase strength at high temperatures. By
inhibiting grain growth during heat treatment, it helps
enhance the toughness and strength of the steel.
Molybdenum tends to minimize temper brittleness and
protects against pitting corrosion caused by chlorides
and sulfur chemicals. Found in small quantities in
stainless steels, molybdenum increases hardenability
and strength at high temperatures. Niobium like
vanadium has the benefit of stabilizing carbon by
forming hard carbides and, so, is often found in high
temperature steels. In small amounts, niobium can
significantly increase the yield strength and, to a lesser
degree, the tensile strength of steels, as well as have a
moderate precipitation strengthening effect.
Fe-B-C alloys are widely used as protective hard
coatings produced by various methods, including
plasma spray of atomized powders [15–19]. Plasma
spraying process that utilizes a high energy heat source
to melt and to accelerate fine powders onto a prepared
surface is very effective for producing thick coatings
due to their rapid cooling rates. Fe-B-C plasma-sprayed
coatings have attracted interest due to their unique
mechanical properties, high wear resistance, excellent
corrosion resistance, and low cost [20–22]. The main
advantages of using plasma spraying to form Fe-B-C
coatings include good adhesion between the coating and
substrate and reproducible results. In addition, plasma
spraying is an industrial process, enabling mass
production.
Performance properties of plasma-sprayed coatings
are strongly influenced by a structure of starting
powders [23, 24]. Alloying is a powerful method to
improve the characteristics of powders for the
manufacture of coatings. Understanding both the
positive and negative effects of alloying elements on the
structure and properties of boron-rich Fe-B-C powders
can help to identify what applications certain coatings
can be used in. The very high cooling rates of
atomization processes may also contribute to the
solubility of alloying elements in phase constituents of
the powders thus affecting their properties.
Therefore, the purpose of this work is to investigate
the influence of alloying elements (Cr, V, Mo or Nb) on
the formation of structure and properties of boron-rich
Fe-В-С powders for plasma straying.
1. MATERIALS AND METHODS
Fe-B-C-Me powders for plasma spraying containing
10.0…14.0% B, 0.01…0.5% C, 0…5.0% Me (where
Me – Cr, V, Mo or Nb), balance Fe (in wt.%) (purity
better than 98.5%) were produced by dispersing a
consumable rotating rod [25, 26]. A rotating rod
(anode), which was 28…30 mm in diameter and
200…300 mm in length, made of the alloy to be
atomized, was melted by an electric arc between the
anode and a water-cooled tungsten cathode. Liquid
powders were then projected from the anode by the
centrifugal force and solidified in the chamber filled
with argon at a pressure of 0.1…0.15 MPa. The
atomization process parameters were as follows:
380…400 A, 40 V. The lower threshold was determined
by the requirement of the highest output of the process.
But, if the strength of current was higher than 400 A,
there was not enough time for metal to spheroidize and
it solidified as shapeless powders. But the powders to be
injected into the plasma must possess good flow
properties, which is associated with their spherical
shape. The powders diameters ranged from 100 to
200 m, and average diameter defined by the
cumulative weight fraction of 50% was about 125 m.
Powders with this narrow size distribution are preferred
in order to achieve uniform heating and acceleration of
a multicomponent powder. The cooling rate of the
powders was 10
3
…10
4
K/s.
The microstructural characterization of the powders
was performed by light metallographic microscope
Neophot-32 and quantitative analyzer Epiquant. The X-
ray diffraction (XRD) measurements of lattice
parameters of the phases were carried out using
diffractometer HZG-4A with CuKα radiation. The XRD
analyses were performed with powder samples. The
microstructure was also studied with a scanning electron
microscope Jeol-2010 F (SEM) equipped with an
energy dispersive spectrometer (EDS). The melting
temperature (Tm) of the powders was measured by
differential thermal analysis at 5 K/min heating rate.
Vickers microhardness tests were carried out using
device PMT-3 at 0.05 kg load in order to observe the
crack propagation in the samples. A mean Vickers
microhardness (Hμ) was obtained by averaging over 20
indentations. Total Vickers hardness was calculated
considering additivity of this characteristic. The fracture
toughness (KIC) was evaluated from the crack length
initiated at the corners of the Vickers microindentation
using an empirical equation proposed in [27].
Compression strength () was measured at room
temperature with load applied up to fracture of the
powders. Oxidation resistance factor (Ko) was measured
with powders oxidized in air at 1273 K for 2 h.
2. RESULTS AND DISCUSSION
The effects of alloying elements in boron-rich
Fe-B-C powders are as follows. The addition to
powders of elements such as Cr or V does not basically
alter the microstructures formed. The Fe2B- and FeB-
based solid solutions are observed in the structure (Figs.
1, 2). So, the chromium or vanadium do not form
chemical compounds, and consequently the only form in
which they can be present in the powders is in solid
solutions with iron borides. Chromium and vanadium
can dissolve in either the Fe2B and FeB borides but
predominantly they dissolve into iron monoboride (see
Figs. 1, 2). These elements tend to cause distortions of
crystal lattices of Fe2(B, C) and Fe(B, C) typical for
substitutional solid solutions. Their atoms are of similar
size and behaviour [28] and so the lattice structure of
the Fe2B and FeB borides does not alter greatly as a
result of substituting Fe atoms for Cr or V (Table 1).
a
b
c
Fig. 1. SEM of polished cross-sections of Fe-12.1В-0.1С
powder alloyed with 5% of Cr:
a – second electron image;
b – elemental EDS X-ray mapping;
c – elemental profile along scanning line
Table 1
The lattice parameters of Fe(B, C) and Fe2(B, C) crystals in the Fe-12.1B-0.1C powders
alloyed with 5% of V, Cr, Mo or Nb
Alloying
element
Fe(B, C) (rhombic lattice) Fe2(B, C) (tetragonal lattice)
a, Å b, Å c, Å a, Å c, Å c/a
w/o 5.50410.0052 4.05960.0106 2.95010.0037 5.11200.0001 4.24180.0001 0.8298
Сr 5.49110.0032 4.05690.0052 2.96020.0021 5.11730.0004 4.23130.0046 0.8269
V 5.49980.0020 4.05760.0066 2.96970.0011 5.11740.0014 4.24270.0053 0.8291
Mo 5.50830.0018 4.06710.0038 2.96630.0007 5.11840.0010 4.24670.0075 0.8297
Nb 5.50550.0042 4.06880.0067 2.94910.0042 5.11310.005 4.24140.0028 0.8295
a
b
c
Fig. 2. SEM of polished cross-sections of Fe-12.1В-0.1С powder alloyed with 5% of V:
a – second electron image; b – elemental EDS X-ray mapping; c – elemental profile along scanning line
Table 2
Structural and mechanical characteristics of Fe(B, C) and Fe2(B, C) crystals in the Fe-12.1B-0.1C powders
alloyed with 5% of V, Cr, Mo or Nb
Alloying
element
Fe(B, C) Fe2(B, C)
Dendrite parameters*, m
H, GPa KIC, MPam
1/2
H, GPa KIC, MPam
1/2
d0 l0 d0/l0
w/o 4.90.1 5.30.1 0.92 20.10.1 5.00.2 17.00.1 4.50.1
Сr 4.10.1 4.30.1 0.95 18.60.2 – 15.70.3 5.20.1
V 4.40.1 4.80.1 0.92 19.10.1 – 15.80.2 –
Mo 3.10.1 3.60.1 0.86 21.00.2 4.40.1 17.80.2 4.10.1
Nb 2.40.05 2.80.1 0.86 20.20.1 4.90.1 17.10.1 4.40.2
*Where d0 – diameter of secondary dendritic arms, l0 – interdendritic distance.
In the Fe-B-C powders, the presence of chromium or
vanadium increases fracture toughness KIC while not
appreciably reducing Vickers hardness H of the
constituent phases (Table 2). Chromium or vanadium
improve significantly compression strength and
oxidation resistance factor Ko due to formation of inert
passive films on the surface which resist attack by
oxidizing reagents (Table 3). In Fe-B-C powders,
chromium appears to have a greater beneficial effect on
compression strength but vanadium – on resistance to
oxidation. These elements also provide slightly lower
melting temperature Tm.
Table 3
Performance properties of Fe-10.3B-0.7C-5.0 Me
powders (Me – Cr, V, Mo or Nb)
Alloying
element
Total Hμ,
GPa
, MPa Tm, K
Ko, relative
units
w/o 17.90.1 261010 17234 1.0
Сr 16.60.2 285020 17134 1.320.12
V 16.80.1 280020 17134 1.530.08
Mo 19.10.2 275010 17584 1.120.10
Nb 18.80.1 267520 17634 1.240.06
Small amounts of Mo added to Fe-B-C powders
completely dissolve. At some point, additional
amounts of this alloying element will not dissolve.
When that solid solubility limit is exceeded, Mo
slightly dissolves in Fe2B boride but preferentially in
FeB dendrites refining their size (Fig. 3, Table 2).
The addition of this element that dissolves in the
Fe2B and FeB lattices replacing iron atoms causes
noticeable distortions because of the difference in
atom size (see Table 1) [28]. Besides, with boron
molybdenum forms Mo2B, but in the presence of
carbon it forms Mo2(B, C) as well. Thus, at the
amount of 5% this alloying element forms mainly
special borides and borocarbides.
a
b
c
Fig. 3. SEM of polished cross-sections of Fe-12.1В-0.1С
powders alloyed with 5% of Mo: a – second electron
image; b – elemental EDS X-ray mapping;
c – elemental profile along scanning line
Since the molybdenum atoms are larger than the
surrounding atoms, they introduce compressive lattice
strains. They disrupt the regular arrangement of ions
and make it more difficult for the layers to slide over
each other. This makes the FeB and Fe2B phases harder
and less ductile than those of the master Fe-B-C
powders (see Table 2). For example, powders of 5% Mo
raise the total hardness from 17.9 to 19.1 GPa (see
Table 3). Besides, the addition of Mo to Fe-B-C
powders rises melting temperature and slightly
improves oxidation resistance.
When niobium is added to Fe-B-C powders, it does
not form solutions in iron borides and enters NbB2
secondary phase formed at Fe2(B, C) boundaries (Fig. 4).
a
b
c
Fig. 4. SEM of polished cross-sections of Fe-12.1В-0.1С
powders alloyed with 5% of Nb: a – second electron
image; b – elemental EDS X-ray mapping;
c – elemental profile along scanning line
Insolubility of niobium in iron borides is in good
agreement with XRD measurements of lattice
parameters of Fe(B, C) and Fe2(B, C) phases (see
Table 1). This implies that Nb is continually pushed out
in the melt ahead of the moving solid-liquid interface
into the interdendritic regions of growing Fe(B, C)
dendrites slowing their growth and causing noticeable
refinement (see Table 2). As a result, the secondary
crystals of NbB2 appear at the Fe2(B, C) boundaries.
Fe-B-C powders with 5% niobium are harder (see
Table 3), on account of the finer Fe(B, C) dendrites
formed and the presence of NbB2 secondary phase.
Niobium, as such, performs in the same way as that
described for molybdenum. The addition of niobium to
Fe-B-C powders has a substantial effect on the melting
temperature (see Table 3). Its presence also improves
oxidation at high temperatures.
It should be noted that the solubility of investigated
alloying elements in the constituent phases of Fe-B-C
powders increases in the order Nb, Mo, V, Cr. Taking
into account the metallic radii of individual metal
atoms [28] allows to explain why Cr and V completely
dissolve in Fe-B-C powders, but Mo and Nb have
partial or no solubility, as in this sequence the atomic
radii decrease. It is also understandable why alloying
elements are predominantly dissolved in the rhombic
lattice of Fe(B, C) than in more close-packed tetragonal
lattice of Fe2(B, C).
For a thorough understanding of mechanical
properties of alloyed Fe-B-C powders, it is important to
consider the electronic structure of the constituent
phases, including the electron distribution [29]. In
Fe2(B, C), boron forms strong covalent Fe-B bonds
[30]. According to the crystal structure, these bonds
connect B to eight neighboring Fe atoms. In the crystal
structure of Fe(B, C), B atoms forming zigzag chains
are in the interstices surrounded by Fe atoms. The
strong interactions between the atoms lead to strong
covalent B-B bonds. The combination of the covalent
Fe-B bonds and metallic Fe-Fe bonds in Fe2(B, C) or
the combination of the covalent B-B bonds and metallic
Fe-Fe bonds in Fe(B, C) contribute to the properties of
these compounds [30].
In assessing the alloying effects, the relative change
in concentration of the collectivized valence electrons
forming the Fe-B and Fe-Fe bonds, when Fe atoms are
replaced by Me atoms (where Me – Cr, V or Mo), is
responsible for the observed changes in mechanical
properties. Here, a decrease in hardness is predicted by
alloying with Cr and V, related to a decreased
concentration of collectivized electrons taking part in
the electronic exchange [29]. As a result, Me-B and Fe-
Me bonds become weaker; the hardness of the Fe-B-C
powders is found to reduce, but compression strength
improves.
According to electronic structure of Mo and Nb,
these elements rather act as electron acceptors. Their
valence electrons are localized in the stable d
5
-
configurations [29]. Any re-distribution of bonding
electrons caused by replacing Fe with Mo or Nb in the
crystal lattices of Fe(B, C) and Fe2(B, C) phases leads to
destruction of stable configurations. It results in limited
or extremely low solubility of correspondingly Mo or
Nb and formation of secondary phases. In the Fe-B-C
powders, some of the added molybdenum ions, larger
than iron ions making up the lattice, disrupt the regular
arrangement of ions and make it more difficult for the
layers to slide over each other. This makes the powders
harder and less ductile than the master powder (in which
the layers slip over each other more easily). Niobium
does not contribute to any hardness increase of Fe(B, C)
and Fe2(B, C) phases and enhances the hardness of
powders with preserving compression strength by
strengthening via the precipitation of secondary phases.
CONCLUSIONS
This study shows that the major constituents of
boron-rich Fe-B-C powders sized from 100 to 200 µm
in diameter are found to be Fe(B, C) and Fe2(B, C) solid
solutions. When adding up to 5% of Cr or V to Fe-B-C
powders, these elements have complete solubility in the
structural constituents, preferentially dissolving in
Fe(B, C) phase and forming substitutional solutions. Cr
or V introduce the smallest lattice distortions which
relates to the relatively small differences in the atomic
sizes between the iron and substituting atoms.
Molybdenum or niobium have correspondingly a
limited or extremely low solubility in Fe-B-C powders.
At that, the refinement of structure is observed by Mo or
Nb additions. When the Mo or Nb content reaches 5%,
these elements are found in powders in the form of
chemical compounds with boron and/or carbon (Mo2B,
Mo2(B, C), NbB2) precipitated at Fe2(B, C) boundaries.
All alloying elements that form solid solutions in
Fe(B, C) and Fe2(B, C) phases affect their hardness.
Chromium, similar to vanadium, decreases hardness,
while molybdenum gives the hardness increase caused
by substitutional strengthening. This is because the
different atom size of Mo interrupts the orderly
arrangement of atoms in the lattices. Besides,
molybdenum like niobium increases hardness due to
formation of secondary phases.
Chromium has the largest effect on compression
strength, followed by decreasing effects from vanadium,
molybdenum and then niobium. Although different
mechanisms are involved in compression strength, the
addition of all alloying elements produces a rise in this
characteristic.
Chromium or vanadium are most effective for
improving oxidation resistance whereas molybdenum or
niobium increases this property to a lesser degree. This
improvement of the oxidation resistance is credited to
the affinity of alloying elements for oxygen and, as a
consequence, protective films are formed on the surface
of the powders that prevent the further diffusion of
oxygen.
Alloying elements, such as Cr and V, which enter
into Fe(B, C) and Fe2(B, C) solid solutions lower the
melting temperature, with the exception of Mo and Nb
that give rise to melting temperature.
The effects of investigated alloying elements
replacing iron atoms in the Fe-B-C powders may be
explained considering a local change of the electronic
structure of alloyed Fe(B, C) and Fe2(B, C) phases
which is an indicator for stronger/weaker bonded atoms
in the crystals.
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Article received 04.03.2020
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СТРУКТУРА И СВОЙСТВА ПОРОШКОВ Fe-B-C, ЛЕГИРОВАННЫХ Cr, V, Mo
ИЛИ Nb ДЛЯ ПЛАЗМЕННОГО НАПЫЛЕНИЯ
Е.В. Суховая
Исследовали влияние легирующих элементов на процессы формирования структуры и свойств порошков
для плазменного напыления, изготовленных методом распыления вращающегося стержня. Состав порошков
находился в следующем концентрационном диапазоне: B (10…14 вес.%), C (0,01…0,5 вес.%), Me
(0…5,0 вес.%), где Me – Cr, V, Mo или Nb, Fe – остаток. Структуру порошков изучали методами
металлографии, рентгеноструктурного анализа, сканирующей электронной микроскопии,
рентгеноспектрального микроанализа. Механические свойства порошков измеряли на микротвердомере
Виккерса. Также определяли прочность на сжатие, окалиностойкость, температуру плавления. Хром и
ванадий полностью растворяются в структурных составляющих Fe2(B, C) и Fe(B, C) порошков Fe-B-C,
замещая железо в кристаллических решетках фаз и формируя твердые растворы замещения. Присутствуя в
структуре боридов железа, эти элементы повышают их пластичность и сопротивление окислению, но
снижают температуру плавления и твердость порошков. Молибден и ниобий в основном присутствуют в
структуре в виде вторичных фаз, таких как Mo2B, Mo2(B, C) или NbB2, выделяющихся по границам
кристаллов Fe2(B, C). Как следствие, эти легирующие элементы повышают твердость, сопротивление
окислению и температуру плавления порошков.
СТРУКТУРА І ВЛАСТИВОСТІ ПОРОШКІВ Fe-B-C, ЛЕГОВАНИХ Cr, V, Mo
АБО Nb ДЛЯ ПЛАЗМОВОГО НАПИЛЕННЯ
О.В. Сухова
Досліджували вплив легуючих елементів на процеси формування структури та властивостей порошків
для плазмового напилення, виготовлених методом розпилення обертового стрижня. Склад порошків
знаходився в наступному концентраційному діапазоні: B (10…14 ваг.%), C (0,01…0,5 ваг.%),
Me (0…5,0 ваг.%), де Me – Cr, V, Mo або Nb, Fe – залишок. Структуру порошків вивчали методами
металографії, рентгеноструктурного аналізу, сканувальної електронної мікроскопії, рентгеноспектрального
мікроаналізу. Механічні властивості порошків вимірювали на мікротвердомірі Віккерса. Також визначали
міцність на стиск, окалиностійкість, температуру плавлення. Хром та ванадій повністю розчиняються в
структурних складових Fe2(B, C) і Fe(B, C) порошків Fe-B-C, заміщуючи залізо в кристалічних ґратках фаз і
формуючи тверді розчини заміщення. Проникаючи в структуру боридів заліза, ці елементи підвищують їх
пластичність і опір окисленню, але знижують температуру плавлення і твердість порошків. Молібден та
ніобій в основному присутні в структурі у вигляді вторинних фаз, таких як Mo2B, Mo2(B, C) або NbB2, що
виділяються по межах кристалів Fe2(B, C). Як наслідок, ці легуючі елементи підвищують твердість, опір
окисленню і температуру плавлення порошків.
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