I. VOLOKITINA et al.: EFFECT OF ULTRASONIC PROCESSING ON THE PROPERTIES OF ULTRAFINE-GRAINED BRASS
301–307
EFFECT OF ULTRASONIC PROCESSING ON THE PROPERTIES
OF ULTRAFINE-GRAINED BRASS
VPLIV ULTRAZVO^NE OBDELAVE NA LASTNOSTI ULTRA
DROBNO ZRNATE MEDENINE
Irina Volokitina
1*
, Abdrakhman Naizabekov
2
, Sergey Lezhnev
2
, Evgeniy Panin
1
,
Vasily Rubanik
3
, Yury Tsarenko
3
1
Karaganda Industrial University, Republic av. 30, Temirtau, Kazakhstan
2
Rudny Industrial Institute, 50 let Oktyabrya str., Rudny, Kazakhstan
3
Institute of Technical Acoustics of the National Academy of Sciences of Belarus, ave. Ludnikova 13, Vitebsk, Belarus
Prejem rokopisa – received: 2024-01-22; sprejem za objavo – accepted for publication: 2024-03-14
doi:10.17222/mit.2024.1099
This article establishes the relationship between the parameters of an ultrasonic action on the microstructure and the complex
properties of ultrafine-grained brass. Ultrasonic action on brass after radial-shear rolling at certain amplitudes of mechanical
stresses helps to relax the nonequilibrium structure of grain boundaries and relieve internal stresses. In this case, the relaxation
effect of the structure depends on the amplitude of the ultrasound. It has been shown for the first time that ultrasonic processing
is an effective way to relax the structure of highly deformed materials, which leads to an increase in the proportion of large-an-
gle grain boundaries and triple grain joints, without leading to a significant grain growth.
Keywords: ultrasonic processing, ultrafine-grained, brass
V ~lanku avtorji opisujejo postavitev zveze med parametri delovanja ultarzvo~ne obdelave na mikrostrukturo in kompleksne
lastnosti ultra fino zrnate medenine. Delovanje ultrazvoka na medenino z dolo~eno amplitudo po radialnem stri`nem valjanju, ki
povzro~i notranje mehanske napetosti pomaga sprostiti le-te ter uravnote`i strukturo kristalnih mej. V tem primeru je u~inek
sprostitve mikrostrukture odvisen od amplitude ultrazvoka. Avtorji so prvi~ pokazali, da je ultrazvo~na obdelava u~inkovit na~in
relaksacije mikrostrukture mo~no deformiranih materialov, ki povzro~i pove~anje dele`a dele`a veliko kotnih kristalnih mej in
trojnih vezi kristalnih mej, ne da bi pri tem pri{lo do pomembne rasti kristalnih zrn.
Klju~ne besede: ultrazvo~na obdelava, ultra drobna kristalna zrna, medenina
1 INTRODUCTION
The requirements for the properties of structural ma-
terials in modern conditions are becoming higher and
more differentiated. First of all, this applies to responsi-
ble metal products operating under extreme operating
conditions in aerospace, chemical, medical and other in-
dustries. One of the methods of increasing the strength of
materials is to reduce the size of crystallites from micron
to ultrafine-grained (UFG) and nanoscale (NS) states.
The formation of an ultrafine-grained structure of
metals and alloys with severe plastic deformation meth-
ods (SPD) makes it possible to exert a significant influ-
ence on the deformation behavior and mechanical prop-
erties of metals and alloys, which makes it possible to
consider SPD a very promising method for controlling
the structure and properties of metal materials.
1–3
The
greatest interest in nanostructured materials is due not
only to their unique physical-chemical properties, but
also to very high mechanical properties: strength, ductil-
ity, wear resistance. Due to the fact that ultrafine-grained
materials have appeared relatively recently, their resis-
tance to external influences, in particular, to plastic de-
formation and heating, has not been sufficiently studied.
The processes and methods of processing such materials
have not yet been sufficiently studied.
4–6
Significant advantages of radial-shear rolling is a
complete structural processing of a metal along an entire
section and its sealing, and an increase in the physical
and mechanical properties of rolled products; due to a
significant feed angle, an increase in the technological
plasticity of workpieces by more than 300 % is achieved.
In the deformation zone created with radial-shear rolling,
a stress-strain state scheme is implemented, close to
comprehensive compression with large shear strains,
which is favorable for the formation of an UFG structure.
The main feature of radial-shear rolling is the nonmono-
tonicity and turbulence of deformation, as well as differ-
ences in the plastic flow and the structure processing in
different zones of a workpiece due to the trajectory-ve-
locity features of the process.
7,8
What is common to the UFG and NS materials ob-
tained with deformation methods of nanostructuring is
that their microstructure is nonequilibrium (metastable).
Electron microscopic studies show a diffuse diffraction
contrast of grain boundaries in UFG and NS materials,
indicating the presence of high internal stresses. The
sources of these stresses are nonequilibrium grain
Materiali in tehnologije / Materials and technology 58 (2024) 3, 301–307 301
UDK 544.57:57.012.3 ISSN 1580-2949
Original scientific article/Izvirni znanstveni ~lanek MTAEC9, 58(3)301(2024)
*Corresponding author's e-mail:
irinka.vav@mail.ru (Irina Volokitina)

boundaries formed during plastic deformation. The high
density of crystalline defects and significant stored en-
ergy lead to low thermal stability and conductivity of
nanometals, which makes their application difficult. Ma-
terials scientists propose various processing methods
such as incomplete recrystallization annealing, gradient
deformation, etc., to produce a heterogeneous micro-
structure of a metal and then optimize the strength/duc-
tility/conductivity ratio.
It has been shown that ultrasonic exposure leads to a
noticeable increase in the thermal stability of the struc-
ture of UFG nickel, associated with the relaxation of the
grain boundary structure, reduction of internal stresses
and stabilization of the material structure at the same
time.
9–11
The effect of increased plasticity in ultrasonic
processing has been established, occurring simulta-
neously with an increase in the yield strength and tensile
strength of UFG nickel obtained with equal-channel an-
gular pressing (ECAP), which may be practically impor-
tant for increasing the complexity of mechanical proper-
ties of UFG materials.
The Institute of Technical Acoustics (ITA) of the Na-
tional Academy of Sciences of Belarus has developed
designs of ultrasonic oscillatory systems and tools for
obtaining and processing extended materials with an
ultrafine-grained structure using the ECA-stretching
method. This process increases the strength properties of
materials while maintaining high plastic properties, al-
lowing the production of extended products.
12
It has been shown that ultrasonic processing reduces
the defect density of ultrafine-grained nickel samples,
11
and affects the deformation behavior and the nature of
martensitic transformations in materials.
13
2 EXPERIMENTAL PART
It is proposed to use concentrator waveguides of vari-
ous designs for processing UFG materials, depending on
the geometric dimensions of the samples.
Since the maximum amplitude of displacements of
ultrasonic transducers in the resonant mode is usually
about 10–12 μm, a booster is used to increase the ampli-
tude of vibrations of the working tool and match the
transducer with the load. Boosters are transformers of
the amplitude of longitudinal ultrasonic vibrations and
are cylindrical rods with a variable cross-section, which
are usually made of steels, titanium and aluminum al-
loys.
The most used boosters with respect to the possibility
of obtaining significant displacement amplitudes at a low
load are step boosters, whose amplitude gain is equal to
the ratio of the input and output cross-sections. An ultra-
sonic oscillatory system using a step booster has a nar-
row range of operating frequencies and, therefore, a lim-
ited possibility of frequency adjustment with load
changes. In this case, it is necessary that the ultrasonic
generator has the function of automatic frequency tuning
since a small deviation of the resonant frequency of the
oscillatory system with a step booster in the absence of
this function leads to a noticeable decrease in the effi-
ciency of the entire oscillatory system. By selecting the
transformation coefficient, it is possible to achieve the
optimal load, matching with the converter. A designed ti-
tanium-alloy booster with a gain coefficient of 2.25 for
ultrasonic processing of UFG samples is shown in Fig-
ure 1. The booster is designed for an operating fre-
quency of 17.8 kHz of the PMS15A-18 magnetic-friction
converter.
The presence of a transition section with an R10
rounding radius reduces the stress concentration in the
concentrator material and provides more favorable con-
ditions for the propagation of ultrasonic vibrations.
The calculation and manufacture of the components
of an ultrasonic oscillatory system and a tool allowing
processing samples of copper and brass in the form of
discs with a diameter of up to 20 mm were performed.
Figure 2 shows a photo of the booster, waveguide and
clamping screw manufactured according to the drawing
presented above.
The PMS15A-18 converter was powered by ultra-
sonic generators UZG2-4M with an operating frequency
of 16.8–19.2 kHz and an output power of 4.5 ± 0.5 kW,
and UZG2-1M with an operating frequency of
22 ± 1.65 kHz and an output power of 1 ± 0.2 kW.
We calculated and manufactured the components of
an ultrasonic oscillatory system and a tool allowing pro-
cessing samples of copper and brass in the disc form
with a diameter of up to 20 mm, as well as extended cy-
lindrical samples with a diameter of 15 mm of half-wave
I. VOLOKITINA et al.: EFFECT OF ULTRASONIC PROCESSING ON THE PROPERTIES OF ULTRAFINE-GRAINED BRASS
302 Materiali in tehnologije / Materials and technology 58 (2024) 3, 301–307
Figure 2: General view of the acoustic-system elements: 1 – booster,
2 – waveguide, 3 – clamping screw Figure 1: Drawing of a booster for UFG samples in the disk form

length. The studies were carried out on L63 brass sam-
ples with a thickness of 0.45–0.6 mm and in the form of
discs with a diameter of 15 mm, which were cut from cy-
lindrical samples after radial-shear rolling (Figure 3).
A sample was fixed inside the cavity of the wave-
guide in the antinode of mechanical stresses using a spe-
cial screw, providing a reliable acoustic contact between
the waveguide and the sample.
Ultrasonic processing of the samples was carried out
with an amplitude of alternating stresses in the samples
of up to 70 MPa using the scheme shown in Figure 4.
The processing was performed with the same compres-
sion force in the voltage range of the waveguide while
the tightening torque of the screw was 90 N·m.
The second part of the samples from the materials
was made in the form of a cylindrical rod with a diame-
ter of 15 mm and a length of 155 mm. It was the wave-
guide of the acoustic system.
Figure 5 shows a diagram of ultrasonic processing of
a long-length sample made of copper and brass, while
Figure 6 shows a drawing of a titanium-alloy booster
with a gain coefficient of 2.5.
The booster is designed for an operating frequency of
21.8 kHz of a magnetic-friction converter. An M12×1.25
threaded hole is made on the left end surface of the
booster for mounting it with a stud to the PMC1-1 con-
verter.
A hole with a thread for an M8 stud was made on the
end surface of the samples, with which attachment to the
booster was carried out.
During ultrasonic processing of the samples, the tem-
perature of the waveguide was controlled, which did not
exceed 45 °C at maximum values of alternating voltages.
The amplitude of ultrasonic displacements at the end of
the waveguide was measured with a non-contact vibro-
meter, whose measurement error was2%+0.1micron.
Some of the cylindrical samples were subjected to ul-
trasonic processing at low temperatures. After being
placed in a Dewar laboratory glass vessel, the studied
brass samples were pre-aged for 5 min before USP to
equalize the temperature throughout the volume. The
temperature in the processing zone of cylindrical sam-
ples was controlled by a copper-kopel thermocouple. Af-
ter USP at low temperatures, the distribution of the
microhardness over the sample surface was studied.
X-ray diffraction analysis (XRD) of the structure of
copper and brass samples after ultrasonic treatment was
carried out on X-ray diffractometers of the DRON-2 type
(CuKa radiation). X-ray images were decoded using the
Crystallographica Search-Match software. X-ray photog-
raphy was carried out with Bragg-Brentano focusing in
the scanning mode.
The obtained samples were also examined with dif-
ferential scanning calorimetry (DSC) on a DSC 214
Polyma device. The process of measuring and processing
the output information in the calorimeter was controlled
by an IBM-compatible personal computer using Proteus,
I. VOLOKITINA et al.: EFFECT OF ULTRASONIC PROCESSING ON THE PROPERTIES OF ULTRAFINE-GRAINED BRASS
Materiali in tehnologije / Materials and technology 58 (2024) 3, 301–307 303
Figure 5: Scheme of ultrasonic processing of a long sample: 1 – ultra-
sonic transducer, 2 – concentrator, 3 – booster,4–wave guide
Figure 3: General view of the samples in the disc form for ultrasonic
processing
Figure 6: Drawing of a booster for ultrasonic processing of long sam-
ples
Figure 4: Scheme of ultrasonic processing of UFG samples in the disc
form: 1 – ultrasonic transducer, 2 – concentrator, 3 – booster, 4 –
waveguide, 5 – sample, 6 – preload screw

a special software package. The samples were examined
in a temperature range of 25–500 °C with a heating rate
of 10 °C/min.
The study of the structure and determination of the
grain size were carried out using a MeF-3 light micro-
scope from Reichert (Austria) at a magnification of
100×.
The mechanical properties of copper and brass sam-
ples in the ultrasonic state before and after ultrasonic
treatment at different values of the amplitude of alternat-
ing stresses were studied by measuring the microhard-
ness on a Micromet-II microhardness meter with a load
of 50 g according to GOST 9450-76.
3 RESULTS
The diffractograms of the studied samples obtained
as a result of X-ray diffraction are shown in Figure 7.
The results of the DSC analysis are shown in Fig-
ure 8.
Figure 9 shows photographs of the microstructure of
L63 brass after radial-shear rolling without and with ul-
trasonic processing at different capacities.
The results of the microhardness measurements of
various copper samples are shown in Figure 10.
4 DISCUSSION
A decrease in the broadening of X-ray lines indicates
a decrease in the microstresses in the sample after the
X-ray diffraction analysis, as well as a slight increase in
coherent scattering regions (CSRs) (Figure 7). The size
of the CSRs is usually identified with the average size of
the crystallites; when this size is determined, it is possi-
ble to assess the nature of the change in the size of the
crystallites in the material depending on the processing
conditions. Based on the results of the X-ray diffraction
analysis, the size of the CSR samples was estimated by
broadening the reflexes on the obtained diffractograms
according to the Scherrer–Selyakov formula:
D =  Cu
/I·cos ,
I. VOLOKITINA et al.: EFFECT OF ULTRASONIC PROCESSING ON THE PROPERTIES OF ULTRAFINE-GRAINED BRASS
304 Materiali in tehnologije / Materials and technology 58 (2024) 3, 301–307
Figure 7: Diffractogram (CuKa) of the L63 brass sample after radial-shear rolling: a – without ultrasonic processing; b – ultrasonic processing at
40 MPa; c – ultrasonic processing at 70 MPa
Figure 8: DSC curves of L63 brass samples: a – without ultrasonic
processing; b – ultrasonic processing at 40 MPa; c – ultrasonic pro-
cessing at 70 MPa

where  Cu
– the radiation wavelength of the copper an-
ode (0.1540 nm), – the scattering angle, B – physical
broadening.
The size of a CSR is usually identified with the aver-
age size of the crystallites; having determined which, it
is possible to assess the nature of the change in the size
of the crystallites in the material depending on the pro-
cessing conditions. Ultrasonic processing led to an in-
crease in the CSR by 8–20 % in all the samples. It was
also established with the XRD method that brass of the
L63 brand is a mixture of two main phases according to
the equilibrium diagram of the Cu–Zn system. The main
phases are the CuZn phase ( -phase) and a solid solution
of zinc in copper ( -phase). In addition to the basic alpha
solution, there are copper and zinc form a number of
phases of the electronic types beta, gamma and epsilon.
Most often, the structure of brass consists of alpha or al-
pha + beta’ phases: the alpha phase is a solid solution of
I. VOLOKITINA et al.: EFFECT OF ULTRASONIC PROCESSING ON THE PROPERTIES OF ULTRAFINE-GRAINED BRASS
Materiali in tehnologije / Materials and technology 58 (2024) 3, 301–307 305
Figure 9: Microstructures of L63 samples at the edge of the surface (a, c, e) and in the center (b, d, f); a, b – without ultrasonic processing;
c, d – ultrasonic processing at 40 MPa; e, f – ultrasonic processing at 70 MPa
Figure 10: Distribution of microhardness: a) – over the diameter of a
L63 disc after radial-shear rolling: 1 – without ultrasonic processing;
2 – ultrasonic processing at 40 MPa; b) – along the length of an L63
half-wave cylindrical sample after radial-shear rolling and ultrasonic
processing at temperatures of: 1) 40 °C; 2) –100 °C; 3) diagram of al-
ternating stresses at ultrasonic processing along the length of the sam-
ple

zinc in copper with a crystalline lattice of copper HCC,
and the beta’ phase is an ordered solid solution based on
the Cu
5
Zn
8
electron compound with a BCC lattice.
As the DSC analysis showed, there is one exothermic
peak found for the L63 samples. The peak is caused by
the phase transition in temperature ranges of
193–269 °C (Figure 8a), 182–322 °C (Figure 8b) and
227–301 °C (Figure 8c). Also, after ultrasonic process-
ing, the peak area increases, which is associated with a
change in the level of internal stresses.
14
As can be seen from Figure 9, the microstructure of
the surface layer of the L63 brass rod (Figure 9a) after
radial-shear rolling it to a diameter of 15 mm (from the
initial workpiece diameter of 30 mm) differs signifi-
cantly from the microstructure in the central part of the
bar (Figure 9b). In the surface zone, the average grain
size is in a range of 5–10 μm, in the central zone, the
grain size is in a range of 25–40 μm, i.e., there is a gradi-
ent distribution of the microstructure over the cross-sec-
tion of the deformed rod. Subsequent processing of brass
rods subjected to radial-shear rolling by ultrasonic pro-
cessing with amplitudes of alternating stresses of
40 MPa and 70 MPa showed that USP practically does
not affect the microstructure evolution in the central zone
of a rod. Thus, with USP, with amplitudes of alternating
stresses of 40 MPa and 70 MPa in the central part of the
rod being formed, the grain size remains at the same
level, i.e., in the range of 25–40 μm (Figures 9d, f). If
neither ultrasonic processing itself nor the change in the
amplitude of alternating stresses during USP does not
significantly affect the change in the grain size in the
central part of a workpiece, then the opposite is observed
when studying the surface layers of the rods. In particu-
lar, USP leads to both the growth formed in the surface
layer during radial-shear rolling of the grain and its
alignment, i.e., a more uniform structure is obtained. At
the same time, the higher the amplitude of alternating
stresses in USP, the more the grain grows. Thus, with
USP with an amplitude of alternating stresses of 40 MPa,
the average grain size increased to 9–10 μm (Figure 9c),
while with USP with an amplitude of alternating stresses
of 70 MPa, the average grain size was in a range of
14–15 μm (Figure 9e). That is, the conducted studies in-
dicate that although USP does not significantly affect the
evolution of the microstructure in the central part of a
rod, it allows a reduction in the gradient of the structure
distribution over the cross-section of a rod deformed
with a radial shear rolling mill due to an increase in the
size of its surface zone. In addition, the higher the ampli-
tude of alternating stresses during USP, the smaller is
this gradient. USP also helps to obtain a more uniform
structure (with a smaller grain-size spread) in the surface
area of the deformed rod (Figures 9c, e).
Graphs of changes in the microhardness along the
cross-section of a bar after radial-shear rolling and USP
(Figure 10a) are generally consistent with the studies of
the microstructure evolution during these processes.
Thus, in both cases, the gradient of the microhardness
distribution over the cross-section of a bar is observed. It
is found that the gradient after radial-shear rolling and
USP is lower than that after just radial-shear rolling. The
highest values of the microhardness in the cross-section
of a bar formed on a radial-shear rolling mill are ob-
served in the intermediate zone (on average 4 mm from
the surface of the bar). This is because two gfrinding ef-
fects are observed. First, due to the implementation of
severe plastic deformation, intensive grain grinding oc-
curs in the surface layer, which should lead to an in-
crease in microhardness values. However, at the same
time, another type of grinding – more intensive than in
the intermediate and central zones – occurs in the surface
layer, specifically targeting carbides, leading to a slight
decrease in the microhardness of the surface zone (Fig-
ure 10a). Conducting a subsequent USP with an ampli-
tude of alternating stresses of 40 MPa leads to a slight
alignment of this gradient along the cross-section of the
rod. At the same time, there are a slight increase in the
microhardness (by about 25–30 MPa) in the surface
layer, a more significant increase (by 50 MPa) in the cen-
tral zone, and a slight decrease in the microhardness of
the molded brass in the intermediate zone (by 25 MPa).
In total, this leads to a decrease in the gradient of the
microhardness distribution over the cross-section of a
rod made of L63 brass alloy and formed on the ra-
dial-shear rolling mill.
A study of the microhardness distribution over the
surface of a cylindrical sample made of brass alloy L63
after RSR and USP at temperatures of 40 °C and
–100 °C (Figure 10b) showed that there is a dependence
of the microhardness distribution on the magnitude of
the alternating stresses during USP along the length of
the sample and on the USP temperature. An increase in
the intensity of ultrasonic processing leads to a decrease
in the microhardness. At the same time, at a temperature
of 40 °C, a systematic dependence of the distribution of
microhardness on the surface of a rod, along the length
of the sample, is observed in accordance with the dia-
gram of alternating stresses during USP along the length
of the sample, as opposed to USP at a temperature of
–100 °C. This indirectly indicates that the L63 brass al-
loy exhibits more stable properties after its deformation
on a radial-shear rolling mill and subsequent USP at the
temperature of 40 °C than after USP at the temperature
of –100 °C.
5 CONCLUSIONS
For ultrasonic processing of ultrafine-grained materi-
als, an ultrasonic oscillatory system was developed, con-
sisting of an ultrasonic transducer, booster and wave-
guide, providing an amplitude of oscillating stresses in
the processed samples of up to 70 MPa. Ultrasonic
equipment for processing brass samples was tested. The
relationship of the ultrasonic exposure parameters with
I. VOLOKITINA et al.: EFFECT OF ULTRASONIC PROCESSING ON THE PROPERTIES OF ULTRAFINE-GRAINED BRASS
306 Materiali in tehnologije / Materials and technology 58 (2024) 3, 301–307

the microstructure and complex properties of the UFG
copper and brass samples were established. It was shown
that an ultrasonic action carried out on the materials after
radial-shear rolling at certain amplitudes of mechanical
stresses promotes the relaxation of the nonequilibrium
structure of grain boundaries, thus relieving internal
stresses. The scientific understanding of the mechanism
and patterns of the structure formation in UFG metals
and alloys under ultrasonic exposure has been expanded.
Acknowledgment
This research was funded by the Science Committee
of the Ministry of Science and Higher Education of the
Republic of Kazakhstan (Grant – AP14869128).
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