Instytut Podstawowych Problemów Techniki

Streszczenie:

Investigating of the material properties and physical mechanisms responsible for plastic deformation caused by complex loading is crucial for bimetallic structures. These materials are a type of functionally graded multi-material structures designed to combine diverse material properties within the same framework while optimizing manufacturing costs. In the present work, the initial yield surface and its subsequent evolution were determined for a Ti-Cu bimetal based on the definition of yield stress for 0.01% plastic offset strain. The subsequent yield surfaces were determined after introducing monotonic axial tension and axial tension-cyclic torsion pre-deformation up to 1% permanent axial strain. It was found, that the determined initial yield surface was close to the Huber-von Mises-Hencky isotropic yield locus. Furthermore, subsequent yield surfaces were determined to assess a hardening/softening effect in the loading direction applied. Interestingly, only the monotonic tension caused a significant enhancement of the tensile yield strength as the monotonic tension associated with cyclic torsion caused its reduction. On the other hand, the sizes of subsequent yield surfaces reflecting pre-deformation were reduced in the axial compression direction. Finally, microstructural studies revealed, that only shear strain magnitude affects the yielding behaviour of bimetallic structure since more slip systems were activated when the higher strain magnitude was applied. Consequently, material recrystallization and subsequent softening in the radial direction (RD) occurred. The texture evolution is primarily interface-driven and deformation-mode dependent.

Słowa kluczowe:

Yield Surface,Plastic deformation,Bimetal,Texture evolution,Thin-walled tubular specimen

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Streszczenie:

This study investigates the dynamic mechanical behavior and microstructural evolution of commercially pure titanium (CP-Ti) under high-strain-rate loading at subzero temperature. Using a Split Hopkinson Pressure Bar setup equipped with a cryogenic environmental chamber, CP-Ti specimens were dynamically compressed at − 100 °C across strain rates of 1 × 103 s−1 and 2 × 103 s−1. The results show a significant increase in flow stress at − 100 °C compared to room temperature, with peak true stresses reaching approximately 825 MPa at 2 × 103 s−1 and 730 MPa at 1 × 103 s−1 representing ~ 25–30% higher values than those observed at 22 °C. Electron backscatter diffraction analysis revealed a transition in deformation mechanisms with increasing strain rate and decreasing temperature. At room temperature, plastic deformation was predominantly accommodated by dislocation slip and deformation twinning. At low temperature, while twinning activity intensified, it was eventually superseded by shear band formation, indicating the onset of strain localization. A physically based viscoplastic constitutive model incorporating dislocation density evolution and thermally activated mechanisms was developed and calibrated against experimental data. The model accurately captured the stress–strain behavior across all tested conditions, with deviations below 5%, demonstrating its suitability for predictive simulations of low-temperature forming processes in HCP metals

Słowa kluczowe:

CP-Ti, Split Hopkinson Pressure Bar, Low temperaturę, Deformation twinning, Shear bands, Constitutive modeling

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Streszczenie:

Uniaxial testing methods to characterize materials provide only limited data that is insufficient to fully understand all aspects of their behaviour, such as initial texture or anisotropy. Therefore, this research aims to conduct complex stress loading experiments to understand the physical mechanism accountable for plastic deformation caused by monotonic tension and tension assisted by proportional cyclic torsion in the CP-Ti (Commercially Pure Titanium). The yield surface approach was applied to assess the variation of mechanical properties in the as-received and predeformed material. It was found, that such monotonic tension associated with cyclic torsion caused a significant decrease of the tensile stress. The initial yield surface obtained for the asreceived material exhibits anisotropic behaviour, whereas, the sizes of subsequent yield surface reflecting pre-deformation were reduced in all directions with exception of the tension direction.

Słowa kluczowe:

yield surface,pre-deformation,plastic anisotropy,cycle loading,tubular specimen

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The fatigue response and high-temperature corrosion resistance of Inconel 740 nickel alloy in its as-received state, and the same material with aluminized surface layer, were investigated. The aluminized layer was applied by using the chemical vapor deposition process with the participation of AlCl3 vapors under a hydrogen protective atmosphere at a temperature of 1040°C for 8 h and internal pressure of 150 hPa. The microstructure of the aluminized layer was characterized through scanning electron microscopy and x-ray energy dispersive spectroscopy analysis. It was found that Inconel 740 with an aluminized surface exhibited an improved hardness and fatigue response of 100 MPa in the whole range of stress amplitudes from 350 MPa to 650 MPa. Additionally, the application of the aluminization process enhanced service life as well as the corrosion resistance of the alloy in question and effectively protected it against high-temperature corrosion.

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In this paper, the LENS technique with optimized parameters was applied to investigate the feasibility of Inconel 625 repair process. The process was performed on the substrate material heated to 300 ◦C at laser power of 550 W. Subsequently, the specimens were subjected to microhardness and three-point bending tests to assess the effectiveness of the repair system. The results showed that the mechanical properties of the Inconel 625 specimens repaired by using the LENS system were similar or even better than those of the substrate material.

Słowa kluczowe:

LENS technology, Inconel alloys, repair process, additive manufacturing

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Streszczenie:

In this paper, the Inconel 625 laser clads characterized by microstructural homogeneity due to the application of the Laser Engineered Net Shaping (LENS, Optomec, Albuquerque, NM, USA) technology were studied in detail. The optimized LENS process parameters (laser power of 550 W, powder flow rate of 19.9 g/min, and heating of the substrate to 300 °C) enabled to deposit defect-free laser cladding. Additionally, the laser clad was applied in at least three layers on the repairing place. The deposited laser clads were characterized by slightly higher mechanical properties in comparison to the Inconel 625 substrate material. Microscopic observations and X-ray Tomography (XRT, Nikon Corporation, Tokyo, Japan) confirmed, that the substrate and cladding interface zone exhibited a defect-free structure. Mechanical properties and flexural strength of the laser cladding were examined using microhardness and three-point bending tests. It was concluded, that the LENS technology could be successfully applied for the repair since a similar strain distribution was found after Digital Image Correlation measurements during three-point bending tests.

Słowa kluczowe:

LENS technology, Inconel alloys, repair process, additive manufacturing

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Słowa kluczowe:

inconel alloys, repair process, additive manufacturing

Afiliacje autorów:

Słowa kluczowe:

inconel alloys, repair process, additive manufacturing

Afiliacje autorów:

Słowa kluczowe:

LENS, wytwarzanie przyrostowe, stopy niklu, stopy tytanu, regeneracja

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