Materials. Technologies. Design.

INFLUENCE OF THE INITIAL STATE OF CU-0.6CR-0.1ZR ALLOY ON CHANGES IN STRUCTURE AND PROPERTIES DURING HIGH-PRESSURE TORSION

2025-03-27T19:14:15+00:00

In this work, the dependence of the change in structural characteristics and physical and mechanical
properties of the Cu-0.6Cr-0.1Zr (wt.%) alloy under high-pressure torsion (HPT) on the structural
characteristics of the initial state – after quenching with a supersaturated solid solution and after
aging with an ensemble of large micron-sized particles and a low concentration of the solid
solution – was established. It is shown that in the case of a quenched state with a supersaturated
solid solution, changes in the physical and mechanical properties during the HPT process occur at
the first stages of deformation (1–2 turns) and subsequently the property values stabilize. In the case
of the initial state with an extremely low concentration of the solid solution and an ensemble of large
particles, a non-monotonic change in the physical and mechanical properties of the Cu-0.6Cr-0.1Zr
alloy is observed, which is closely related to the initial shape, size and distribution of particles in the
material matrix.

THE INFLUENCE OF HEAT TREATMENT ON THE MICROSTRUCTURE AND PROPERTIES OF AL30 ALLOY OBTAINED BY ELECTROMAGNETIC CASTING

2025-03-27T19:23:35+00:00

The article considers the heat treatment effect on the microstructure and microhardness of AL30
alloy ingots with diameters of 12 and 80 mm, obtained by casting in an electromagnetic crystallizer
(EMC). A homogeneous microstructure formed by a mixture of an aluminum solid solution
and a eutectic phase was formed in the investigated ingots. It was established that the microstructure
dispersion and the microhardness level of AL30 alloy ingots significantly depend on the
crystallization rate. Heat treatment of cast samples with diameters of 80 and 12 mm performed
according to the T6 mode makes it possible to achieve microhardness values of 147±9 HV and
156±3 HV, respectively. Evaluation of heat resistance showed that at the temperature of 300 °C
the nature of the change in samples microhardness of different diameters is identical. After holding
for 100 hours, the microhardness of AL30 alloy samples strengthened as a result of T6 heat treatment
is ~67 HV.

UNUSUAL FATIGUE BEHAVIOR OF DISSIMILAR AL/TI FRICTION-STIR LAP WELDS

2025-03-27T19:30:17+00:00

This work was undertaken in order to evaluate the fatigue performance of dissimilar AA6013/
Ti-6Al-4V friction-stir lap welds. It was shown that the avoidance of direct contact between the
welding tool and titanium part results in a narrow (~0.5 μm) intermetallic layer at a dissimilar
interface. Consequently, the fatigue failure of dissimilar welds occurred solely within the aluminium
part. In other words, the intermetallic layer was not a critical issue in the fatigue behaviour of the
welded joints. It was also found that the fatigue endurance of dissimilar welds was approximately an
order of magnitude lower than that of a monolithic aluminium alloy. This effect was attributed to a
specific geometry of the lap-welded joints. Specifically, the end section of the welded joint virtually
served as a precursor of a fatigue crack. Thus, the fatigue behaviour of the welded joints was solely
governed by a crack propagation.

POSSIBLE MECHANISM HETEROGENEOUS LAYERED STRUCTURES FORMATION DURING GROWTH OF MARTENSITE CRYSTALS

2025-03-07T14:37:52+00:00

The main features of iron-based g-a MTs are briefly described, including macroscopic morphological features and supersonic (relative to longitudinal waves) crystal growth rate. The key provisions of the dynamic theory of martensitic transformations are listed. It is noted that the idea of a quasi-equilibrium nucleus in the dynamic theory is replaced by the concept of an initial excited state arising in the elastic field of a dislocation nucleation center and generating a wave process that controls the formation of martensitic crystal growth. It is essential that the controlling wave process inherits and transfers the deformation created in the region of localization of the initial excited state. It is shown, using the example of crystals of surface martensite with habits close to {112}, that the growth of crystal faces within the framework of the dynamic theory can be interpreted as the formation of thin layers parallel to the faces, and the resulting layers can directly contact the faces of the original crystal, or be separated by layers representing distorted residual austenite or martensite, generally distinguished by the choice of the main axis of Bain deformation and, probably, orientation relationships. Thus, inhomogeneous structures can be observed in the peripheral regions of martensite crystals. Clarification of the specifics of such inhomogeneities requires separate studies.

FORMATION OF COMPOSITE COATING «NICKEL-SILICON CARBIDE»

2024-12-18T11:07:05+00:00

The influence of processed sample position relative to the equipment bottom and electrolyte mixing
speed during an electrochemical processing aluminum alloy AK7 samples surface on a formed metal
matrix composite coating «Ni+SiC» quality was considered. It has been shown that the composite
coating microstructure formed in a glass container under the horizontal sample positioned with
a minimum mixing speed and in a vertical equipment with the automatic stirring possibility has
significant differences. The quality of the «Ni+SiC» composite coating is determined by the position
of the sample being processed relative to the bath bottom and the electrolyte speed mixing. With a
horizontal sample position and minimal electrolyte mixing speeds, a composite nickel coating is being
formed with a uniform distribution of strengthening SiC particles with a volume fraction of 24%, a
rough surface and single pores. With a vertical position and high electrolyte mix speeds, a coating
is being formed with a volume strengthening particles fraction of 2% and a smooth surface without
pores. It is proposed to develop a horizontal-vertical equipment for electrodeposition, allowing stably
produce a «Ni+SiC» composite coating with a uniform strengthening particles distribution and a
minimal roughness based on the obtained results.

Anti-weld coating for the production of hollow parts by diffusion welding and superplastic forming

2024-12-18T11:56:00+00:00

The work is devoted to the development of an effective and import-independent composition of an anti-welding coating for further use in serial technological production in the manufacture of hollow parts from titanium alloy VT6 by diffusion welding and superplastic forming. It is shown that the obtained composition of the anti-diffusion coating is inert to the titanium alloy at the temperatures of the diffusion welding process. The protective coating can be used for diffusion welding of titanium blades of a gas turbine engine, ensuring the connection of only certain areas to impart the necessary strength and rigidity, while maintaining a light hollow structure.

TIN COATING THICKNESS UNIFORMITY IMPROVEMENT FROM VACUUM ARC DISCHARGE PLASMA ON A BLISK SIMULATOR

2025-03-29T13:19:10+00:00

During the deposition process of complex parts, there can be unevenness in the thickness of the
coating. This may exceed the tolerance limits specified in the design documentation. An example of
this is blisk. According to literature data, the thickness of coating on inner surfaces can be up to four
times greater than on outer surfaces. In this research, we used Monte Carlo simulation to improve
the uniformity of coating thickness on a three-blade blisk simulator. The initial coating thickness
was between 0.5 and 9 microns, while the optimized coating thickness ranged from 2 to 8.5 microns.
Measurements on samples showed a significant increase in microhardness, 30% in average, from
920–900 HV0.05 to 1300–1900. Adhesive strength and roughness remained relatively unchanged.