REV.CHIM.(Bucharest) 69No. 8 2018 http:www.revistadechimie.ro 2217Structural Metallographic Investigations of New [623831]

REV.CHIM.(Bucharest) ♦69♦No. 8 ♦2018 http://www.revistadechimie.ro 2217Structural Metallographic Investigations of New
Composite Materials, Used as Coating Layers
ILIE BUTNARIU*, NICOLAE CONSTANTIN
University Politehnica of Bucharest, 313, Splaiul Independentei 060042, Bucharest Romania
The paper presents the results of metallographic investigations on the structural properties of new composite
materials to be used as coatings for the manufacture and refurbishment of rolling stock components.
Structural investigations were carried out both on the coating layer of the composite material and on the
interface between the coating layer and the base metal material, using optical microscopy and electron
microscopy. The obtained structural results have confirmed that these new composite materials have
particular structural properties and as such can be used as coatings for the manufacture and refurbishing of
metallic parts for the rolling stock industry and the chemical and metallurgical industry, presenting both
economic and environmental advantages.
Keywords: composite materials; structure; optical microscopy; electron microscopy; properties
One of the challenges facing the rolling stock industry
is the cost associated with the manufacturing and
replacement of metal bearings and axles, as thesecomponents are more prone to wear and tear. In order to
lower the manufacturing costs for the rolling stock industry,
more durable components need to be mnufactured andexisting components need to be refurbished and reused.
The use of coating layers enables both the
manufacturing of more durable metal bearing parts andaxle parts, as well as their refurbishment and reuse, thus
providing a lower cost than that associated with the
production of new rolling stock components.
The use of composite metallographic materials as
coating layers provides better structural and mechanical
properties than the use of individual metallographicmaterials.
In order to determine appropriate materials to use as
coating layers for rolling stock industry components, thestructural and mechanical properties of the following
composite metallographic materials were studied :
1. for metal bearing parts: Steel + Al, Al + Bz, Al + Cu;2. for metal axle parts: Steel + Al
2O3, Steel + SiO2, Steel
+ ZrO2.
In this paper we will examine only the structural
properties of the following composite metallographic
materials:
1. Steel type 40Cr130 + Al 99.8%;2. Al 99.8% + Bz type CuSn6.
For each composite material couplet, 5 samples were
taken, and for each sample both optical microscopy andelectrical microscopy experiments were performed.
Experimental part
A series experiments were conducted in order to
establish the best thermal spraying technology for coating
metal bearing parts with composite metallographicmaterials. The experiments concluded that the best coating
of metal bearing parts with composite metallographic
materials is obtained using a process called metallizationwith electric arc.
Metallization with electric arc is a thermal spraying
procedure in which the input materials, represented by 2wires insulated from one another, are moved by driving
rollers towards a spray gun situated at a distanced of 80 –
150 mm from the spraying surface.
* email: [anonimizat] the 2 wires (electrodes) come close together, an
electrical current is applied, forming an electric arc between
the 2 wires and thus enabling their progressive melting.The melted particles are then pulverized using an air jet
with a speed of aprox. 250 m/s, inculcated in the arc area.
Unlike other thermal spraying procedures, metallizationwith electric arc uses continuous current in order to melt
the input materials. Because the input materials are melted
directly by the electric arc, the thermal yield of thisprocedure is considerably greater that the thermal yield of
other thermal spraying procedures.
Compared to thermical spraying using an open flame or
a plasma jet, metallization with electric arc presents
several benefits, which make it suitable for spraying a widerange of materials (polimers, glass, wood, even paper
products) [1]:
– The sprayed particles are melted before being directed
towards the substrate surface;
– Unlike other thermal spraying procedures, the sprayed
particles start cooling as soon as they leave the electricarc area;
– The heating of the sprayed substate material is much
lower in the absence of an open flame or a plasma jet, theonly heat transfer occuring due to the particles sprayed on
the surface.
The equipment used to carry out the meteallization with
electric arc was Arc Spray 4 [4].
The metal support probes were ferrite-pearlitic unalloyed
steel mark S355J2G2 (EN 10025 + Al). The metal supportprobes were prepared for coating using electro-corundum.
For the Steel + Al coating layer, a wire of Steel type
40Cr130 and a wire of Al 99.8% were used, and for the Al +Bz coating layer, a wire of Al 99.8% and a wire of Bz type
CuSn6 were used. All the wires have a diameter of 1.6mm.
The parameters used for metallization with electric arc:- current of I = 50 A and U = 30 V;
– air jet of p = 5 bar;
– distance of spraying of d = 170 mm.Quality control of the metalic probes’ surface after
spraying was done visually in accordance according to the
EN ISO 8501-3 standard, by looking for a matte, uniformsurface, completely devoid of physical impurities (such as
oxides, salts, paint, and so on) [2].
The metallographic structural investigations were
performed using [3]:

http://www.revistadechimie.ro REV.CHIM.(Bucharest) ♦69♦No. 8 ♦2018 22181. optical microscopy, carried out using a Reichert
microscope equipped with optical analysis software, video
camera image processing, interface and software for Buehlerquantitative analysis;
2. electron microscopy, carried out using an e lectronic
microscope type ESEM XL -30 FEI (Philips) .
The optical microscopy investigations performed are the
following:
– Structure of the metallic layer thickness (highlighting
inclusions and pores);
– Thickness of the composite metallic layer;
– Metallic morphology of the composite compound layer;
– Microstructure of the layer at the interface.
In order to accurately determine the thickness variation of
the composite metallographic layer, for each compositematerial we took a 8.5 mm long sample and performed 24
equally spaced thickness measurements. The resulting data
measurements were then statistically processed.
Results and discussion
a)-Metallographic Investigations
a1)-Str uctural i nvestigations of the composite metallic layer ,
using optical microscopy
Figure 1a-b present the optical micrographic structure,
both captured and processed, of the composite Steel + Al
layer, and the metallic layer thickness distribution. We
notice the presence of inclusions and small pores in thestructure of the composite layer. To accurately determine
the thickness distribution of the metalic layer, we made 24
equally spaced thickness measurements, using a 8.5 mmlong sample, as seen in figure 1a. The statistical processingof the data derived from the thickness measurements lead
to the following results:
– the average thickness of the layer is 2.026 mm;- the minimum thickness of the layer is 1.776 mm;
– the maximum thickness of the layer is 2.195 mm.
Figure1b presents the histogram of the composite layer
thickness distribution.
Figure 2a-b present the optical micrographic structure,
both captured and processed, of the composite Al + Bzlayer, and the metallic layer thickness distribution. We
notice the presence of inclusions and some relatively big
pores in the structure of the composite layer.
To accurately determine the thickness distribution of
the metalic layer, we made 24 equally spaced thickness
measurements, using a 8.5 mm long sample, as can beseen in figure .2a.
The statistical processing of the data derived from the
thickness measurements lead to the following results:
– the average thickness of the layer is 3.674 mm;
– the minimum thickness of the layer is 3.534 mm;
– the maximum thickness of the layer is 3.952 mm.Figure 2b presents the histogram of the metallic layer
thickness distribution.
a2)-Str uctural i nvestigations, using optical microscopy , of
the morphology and microstructure of the composite
metallic layer at the interface between it and the underlying
metallic substrate
Figure 3a shows the morphology of the Steel + Al
composite metallic layer. We notice that the layer structureis relatively uniform, presenting pores and possible
inclusions.
Fig.2. Optical micrographic structure of
the Al + Bz composite material layer
showing the 24 equally spaced thickness
measurements (a), and the metallic
layer thickness distribution (b)
Proof: bearing 2 Objective: 2x
Material: Al + Bz Calibration: 4.86790
[jm / Pixel]Fig.1. Optical micrographic structure of
the Steel + Al composite layer showing
24 equally spaced thickness
measurements (a), and metallic layer
thickness distribution (b)
Proof: bearing 2 Objective: 2x
Material: Al + Bz Calibration: 4.86790
[jm / Pixel]
Fig.3. Morphology of the Steel + Al composite
material (a), and morphology of the interface
layer between the Steel + Al composite
material and the base metallic material (b)

REV.CHIM.(Bucharest) ♦69♦No. 8 ♦2018 http://www.revistadechimie.ro 2219Fig. 5. The microstructural composition of the
Steel + Al composite metallic layer, consisting
of four sections. Magnification 200x.
Fig.4. Morphology of the Al + Bz composite
metallic layer (a), and morphology of the
interface layer between the Al + Bz
composite material and the base metallic
material (b)
Figure 3b presents the microstructure of the interface
between the composite metallic material and base
metallic material. We notice from figure 3 a good adhesion
between the composite metallic material and the basemetallic material.
Figure 4a shows the morphology of the Al + Bz
composite metallic layer. We notice that the layer structureis uniform, presenting only a few, sparse pores.
Figure 4b presents the microstructure of the interface
between the composite metallic material and basemetallic material. We notice from figure 4 a low adhesion
between the composite metallic material and the base
metallic material.
b)-Electronic microstructural investigations of the
composite metallic layer on bearings
Figure 5 presents the microstructural composition of
the Steel + Al composite metallic layer, consisting of foursections, at a magnification of 200x. By analysing this figure,
we notice the presence of some black and gray inclusions
in the composite metallic layer.Figure 6 shows the chemical composition of the
composite metallized layer. By analysing this figure, we
can observe the presence of some iron and chromiuminclusions.
Figure 7 presents the chemical composition of
inclusions. By analysing this figure, we can observe:
– Figure 7a presents filiform inclusions of oxides, iron
and chromium in the composite metallic layer
– Figure 7b presents gray inclusions of chromium and
iron oxides in the composite metallic layer;
– Figure 7c presents black inclusions of aluminum oxides
in the composite metallic layer;
– Figure 7d presents inclusions of iron and aluminum in
the interface between the composite metallic layer andthe base metallic layer.
Figure 8 shows the microstructural composition of the
Al + Bz composite metallic layer. By analysing this image,we found:
– the presence of some white particle inclusions in the
composite metallic layer;
Fig.6. Chemical composition of the composite
metallized layer
Fig. 7a. The chemical composition of inclusions from
the composite metallic layer: filiform inclusions (a)

http://www.revistadechimie.ro REV.CHIM.(Bucharest) ♦69♦No. 8 ♦2018 2220- the presence of some black particles at the interface
layer;
– the presence of some dark gray, gray and white particles
in the base metallic layer.
Figure 9 shows the chemical composition of white
particle inclusions from the composite metallic layer. By
analysing this figure, we found that the white particles
contain mostly copper and aluminium.
Conclusions
The experimental studies confirmed the possibility of
obtaining new composite materials using the material
couplets Steel + Al, and Al + Bz. The new composite
materials have different microstructure and physico-chemical properties than the starting materials used for
metallization. These composite materials can be used to
manufacture new components or to refurbish existing onesfor the rolling stock industry and for other industrial branches
Fig. 7b,c,d. The chemical composition of inclusions
from the composite metallic layer: gray inclusions (b)
and black inclusions (c), and from the interface
between the composite metallic layer and the base
metallic layer (d)
where components are prone to wear and tear.
The experimental results and structural observations are
presented in table 1.
By analysing and comparing the two composite
materials from a structural and an adhesion standpoint,we conclude that the Steel + Al composite material has
superior properties to the Al + Bz composite material. The
Steel + Al layer has a lower average thickness, of only 1.9-2.2 mm, compared to that of the Al + Bz layer, of 3.4-3.7
mm. The Steel + Al layer structure is more homogenous
and compact, has a lower porosity and a superior adhesion.
The investigations carried out show that, from a
structural standpoint, the Steel + Al composite material
is preferred for the refurbishment of metal bearing partsand other components for the rolling stock industry. The
refurbishment is done using thermal spraying in the form
of metallization with electric arc.
Obtaining composite materials using metallization with
electric arc has a positive impact on the environment by
reducing the amount of industrial waste by about 5%, and
Fig.8. The image composition of the Al + Bz composite
metallic layer. Magnification 25x
Fig.9. Chemical composition of white particle inclusions from the composite
metallic layer.

REV.CHIM.(Bucharest) ♦69♦No. 8 ♦2018 http://www.revistadechimie.ro 2221 Table 1
THE
EXPERIMENTAL
RESULTS AND
STRUCTURAL
OBSERVATIONS
the emission of gaseous polluants.
Future research focuses on analysing:- the structural properties of other composite
metallographic materials;
– the physico-mechanical properties of different
composite material coating layers;
– the tribological characteristics of different composite
material couplets .
References
1. BUTNARIU I., CONSTANTIN N., Research contract no.289/2006-2008,
UPB-MedN-PNCDI-Program CEEX, Bucharest, Romania, unpublished
research, 2006-2008.2. CONSTANTIN N., BUTNARIU I., Research contract no.72-210/2012,
UPB-MedN-PNCDI-Partnerships Program, Bucharest, Romania,
unpublished research, 2012.3.BUTNARIU I., CONSTANTIN N., Research contract no.1532/2013, UPB-
CEMS-ANCS, Bucharest, Romania, unpublished research, 2013.
4. DONTU, O., GANATSIOS ,S., COVRIG M., The laser welding of some
stainless steels used in process installations from the chemical
industry, Rev. Chim. (Bucharest), 56, no.3, 2005, p.322
Manuscript received: 21.02.2018