Search

The effects of severe plastic deformation induced by ultrasonic impact treatment (UIT) and the electric discharge surface alloying (EDSA) with chromium on the stress-controlled fatigue response of low-carbon steel 20GL are studied. The surface microrelief and integrity were analyzed using light microscopy and scanning electron microscopy (SEM). The structural formations in the sub-surface layers were characterized by means of X-ray diffraction analysis and transmission electron microscopy (TEM). The steel specimens underwent UIT, and complex UIT+EDSA and UIT+EDSA+UIT processes demonstrate the fatigue strength magnitudes increased respectively by ~15, ~5 and ~30% on the base of 10 7 cycles in comparison with that for the pristine specimen. SEM analysis of fracture surfaces reveals the subsurface crack nucleation in the UIT-processed specimens instead of superficial crack initiation observed in the pristine and EDSA-processed ones. TEM studies demonstrate that a dislocation-cell structure forms in ferrite grains and partial dissolution of cementite occurs in pearlite grains both at the surface after UIT and in the layer at a depth of 15–25 µm after the UIT+EDSA+UIT process. The enhanced fatigue strength and prolonged lifetime of the low-carbon steel specimens after UIT and UIT+EDSA+UIT processes are concluded to be associated with the subsurface crack nucleation achieved by the following factors: (i) minimized surface roughness and improved integrity of the modified layer; (ii) compressive residual stresses; and (iii) surface hardening coupled with the alloying by chromium and with the formation of the dislocation-cell structure containing the cell walls impenetrable to moving dislocations at cyclic loading. [ABSTRACT FROM AUTHOR]

Abstract: In this study the method of electron beam deposition of a mixture of titanium and yttrium vapours was used to produce condensates at different ratios of elements in the substrate temperature range from 200 to 800°C. Condensates consist of grains of yttrium and titanium, the dimensions of which are reduced from the submicron to nanosize scale at lowering of substrate temperature. The temperature of composite transition into the nanosized state depends on yttrium content and can be 200–300°C higher than in the case of pure titanium. Such structural changes are accompanied by an abrupt increase of microhardness. At the change of yttrium content the microhardness of condensates deposited at the same temperature changes non-monotonically. Possible causes of non-monotonic variation of concentration dependencies in Ti–Y condensate microhardness are discussed. [Copyright &y& Elsevier]

Structure, mechanical properties, and oxidation behaviour of a Al 55 Cr 23 Ti 22 (in at%) lightweight (ρ = 3.92 g/cm3) medium-entropy intermetallic alloy were studied. The initial as-cast structure consisted of an (Al, Ti)-rich L1 2 matrix and Cr-rich C11 b lamellae with semi-coherent interfaces due to a (111) L12 || (110) C11b , [1 1 ̅ 0] L12 || [3 3 ̅ 1 ̅ ] C11b orientation relationship. The alloy demonstrated a combination of good plasticity (17–19%) and strength (600–610 MPa) both at 22 and 600 ℃; the latter gradually decreased to 155 MPa at 1000 ℃, while plastic strain exceeded 40%. Deformation at 600 and 800 ℃ led to the precipitation of (semi-) coherent C11 b _1 and Al 2 Ti particles inside the L1 2 matrix and C11 b phase, respectively, due to elemental redistributions within the initial phases and low lattice mismatch with a matrix. The alloy gained only 0.27 mg/cm2 after oxidation in the air at 1000 ℃ for 100 h thanks to an early formation of a protective Al 2 O 3 layer. Compared to the current state-of-art lightweight and Al/Cr-containing refractory high/medium-entropy alloys, the Al 55 Cr 23 Ti 22 alloy had a higher 1000 ℃-specific strength, room-temperature plastic strain, and demonstrated the best oxidation resistance. The obtained results suggest that the multicomponent L1 2 -based trialuminides can be used as structural materials for potential high-temperature applications. • An intermetallic Al 55 Cr 23 Ti 22 (at%) medium-entropy alloy (MEA) was analysed. • The alloy consisted of L1 2 matrix and C11 b lamellae with semi-coherent interfaces. • Both initial phases decomposed after compression at 600 and 800 ℃. • New phases were formed due to good lattice matching and reduced solubility. • The alloy was stronger and more oxidation-resistant than current refractory H/MEAs. [ABSTRACT FROM AUTHOR]

• Electric discharge surface alloying by chromium improves corrosion resistance of steel S355. • High-frequency mechanical impact forms ultrafine-grains and compressive residual stresses. • The optimum sequence of the combined EDSA(Cr) + HFMI process for the noblest surface, ultrafine microstructure, and detracted surface and microscopic stress risers is found. • EDSA(Cr) + HFMI enhances the corrosion fatigue life of welded sample by 12 times. The combined effects of severe plastic deformation induced by high-frequency mechanical impact (HFMI) treatment and the electric discharge surface alloying (EDSA) with chromium on the corrosion fatigue life of low-carbon S355 steel transverse non-load-carrying specimens are studied in this paper. First, for various alternations of the combined HFMI + EDSA process, the surface alloyed layer integrity and depths were analyzed using scanning electron microscopy (SEM) accompanied with energy dispersive spectroscopy (EDS) and hardness measurements. The alloying and hardening depths were respectively observed to be 10–30 μm and 0.15–0.75 mm and the surface hardness increased up to 3.6–3.9 GPa. Polarization tests demonstrated higher corrosion resistance of the EDSA-processed samples in 3% NaCl. The near-surface layers of the HFMI + EDSA(Cr) + HFMI processed sample characterized by X-ray diffraction (XRD) analysis and transmission electron microscopy (TEM) contain the dislocation-cell structure formation and partially dissolved cementite. The fatigue tests in 3% NaCl confirmed that the HFMI + EDSA(Cr) + HFMI post-weld process increased corrosion fatigue life (1.77 × 106 cycles) of the S355 steel welded joint at the stress level of 260 MPa by 2 and 12 times in comparison with the HFMI-treated (0.9 × 106) and as-welded (0.14 × 106) samples, respectively. [ABSTRACT FROM AUTHOR]

The effect of cold plastic deformation by upsetting (e = 1.13) on structure and hybridised bonds of carbon in the fcc Invar Fe-30.9%Ni-1.23% C alloy was studied by means of X-ray phase analysis and X-ray photoelectron spectroscopy. Carbon precipitates along grain boundaries and inside of grains in the alloy after annealing and plastic deformation were revealed. The presence of mainly sp2- and sp3-hybridised C-C bonds attributing to graphite and amorphous carbon as well as the carbon bonds with impurity atoms and metallic Fe and Ni atoms in austenitic phase were revealed in the annealed and deformed alloy. It was shown for the first time that plastic deformation of the alloy results in partial destruction of the graphite crystal structure, increasing the relative part of amorphous carbon, and redistribution of carbon between structural elements as well as in a solid solution of austenitic phase. [ABSTRACT FROM AUTHOR]