A new idea is proposed to reduce the SCC risk through microalloying to control the SCC mechanisms.
The combined addition of Nb and Sb significantly decreases the SCC susceptibility in a polluted ...marine atmosphere.
Nb relieves the HE susceptibility of microstructure and Sb restrains the AD effect underneath the corrosion products.
A series of high-strength steels microalloyed with Nb and Sb were prepared via vacuum melting and hot rolling, and their resistance to stress corrosion cracking (SCC) was investigated through various tests in a SO2-polluted marine atmosphere. The results indicated that the steel microalloyed with 0.06 % Nb and 0.1 % Sb exhibited the best resistance to SCC. The anodic dissolution (AD) and hydrogen embrittlement (HE) mechanisms were simultaneously inhibited under the synergistic effect of Nb and Sb. Specifically, the role of these two elements in enhancing SCC resistance was clarified from electrochemical, environmental and microstructural aspects.
Springs made of low-alloy carbon steels are often exposed to the effects of a corrosive environment, such as high humidity and concentration of road salt, rain and snow erosion, temperature ...fluctuations in combination with dynamic loading and mechanical wear. One of the possibilities to improve their resistance in a corrosive environment is their microalloying by Cr, Ni, Mo or Cu. This study tested the effect of microalloying of 54SiCr6 steel by copper on the corrosion behavior in model rainwater and saltwater. The corrosion resistance of the steel samples was tested using electrochemical tests by measuring the polarization resistance and the anodic parts of the potentiodynamic curves at three different temperatures. The surface of the steel samples was observed using SEM/EDS, surface analysis, and XRD diffraction. The measurement results showed that copper in the amount of approx. 1.5 wt % does not affect the microstructure of the spring steel 54SiCr6 after the heat treatment significantly, but improves the corrosion resistance during short-term exposure in both model rainwater and saltwater.
•Cu does not affect the structure of spring steel negatively.•Cu improves the corrosion resistance in model rainwater and saltwater.•Dual layer of corrosion products is formed in model saltwater.
The 2024 aluminum alloy has excellent mechanical and low corrosion due to the existence of the high Cu levels, which shortens its service life. In this paper, we have systematically investigated the ...mechanism of the influence of three elements (Sc, Zr, and Ag) on the microstructure and corrosion behavior of 2024 aluminum alloy after microalloying. The results showed that microalloying treatment of 2024 aluminum alloy reduced the dendritic spacing of cast aluminum alloy; decreased the sizes of Cu-rich intermetallic particles (Cu-IMPs) within the peak aging of the T6 alloy to make their distribution more uniform; and changed the grain boundary phases (GBPs) and precipitate-free zones (PFZs) width of the T6 alloy. Microalloying treatment significantly changed the corrosion resistance of the alloy. Both Zr and Ag elements significantly improved the corrosion resistance of the alloy and reduced IGC depth and electrochemical corrosion rate, however, the Sc elements deteriorated the corrosion resistance of the alloy. Moreover, the corrosion mechanism of the alloy was also discussed in detail.
•The PFZ of 2024 aluminum alloy can be narrowed by microalloying Zr and Ag elements, while the PFZ can be broadened by Sc elements.•Microalloying of Al-Cu-Mg alloy with Zr and Ag elements can reduce the corrosion susceptibility of the alloy.•The aggregate of Zr elements near the GBs forms Al3Zr particles, which prevent the formation of GBP of 2024Z alloy.
Display omitted
•Nb micro-alloying significantly improved the HIC resistance of HSLA steel.•Few-nanometer-sized NbC precipitates played a larger role than larger precipitates.•NbC precipitates did ...not initiate cracks and instead reduced intergranular cracking.•Nb increased the reversible/irreversible H trap density and hindered H aggregation.•The effect of Nb is attributed to hydrogen trapping and microstructure optimization.
Hydrogen-induced cracking (HIC) susceptibility tests, hydrogen permeation tests and the electron backscatter diffraction (EBSD) measurements were used to study the effect of Nb on the HIC resistance of the high-strength low-alloy (HSLA) steel. The Nb microalloying significantly improved the HIC resistance and decreased the proportion of intergranular cracks through the hydrogen trapping effect and microstructure optimization. Dispersed nanometer-sized NbC precipitates effectively increased the number of irreversible traps, hindered hydrogen aggregation, and enhanced the resistance to crack initiation and propagation. Moreover, Nb optimized the microstructure by increasing the proportion of the low-angle grain boundaries (LAGBs), refining the prior austenite grain size, decreasing the dislocation density, and changing the distribution of Σ3 boundaries.
We develop high-strength of Al-Zn-Mg-Cu-based alloys (7xxx series) by optimizing the amount of Mg/Cu with a trace addition of Sc. The highest mechanical properties are achieved with σUTS=672 MPa ...(σy=644 MPa) and ε=8.6%. Based on quantitative symmetry measurements, the improved mechanical strength originates from nanoscopic structural distortion caused by the excessive solutes of Mg and Cu as the amount of Mg/Cu increases. In addition, Sc microalloying induces grain refinement, thus enhancing the mechanical properties.
Display omitted
The magnetocaloric properties of as‐cast (GdTbDyHo)100−xScx (x = 0–0.5 at%) high‐entropy alloys (HEAs) have been studied via microalloying strategy. The results show that microalloying of Sc can ...effectively enhance the working temperature range and the refrigeration capacity of the base HEA—GdTbDyHo. In particular, with addition of only 0.3 at% Sc, the working temperature range can be elevated up to 108 K under an applied magnetic field of 5 T. This, in turn, results in a remarkable refrigeration capacity as high as 802 J kg−1, which is 30% larger than that of GdTbDyHo HEA. This work shows that microalloying of Sc can be used as an effective way to improve the magnetocaloric performance of rare‐earth HEAs.
Magnetocaloric properties are enhanced in (GdTbDyHo)100−xScx high‐entropy alloys via microalloying of Sc. With addition of 0.3 at% Sc, the working temperature range can be elevated up to 108 K under an applied magnetic field of 5 T, resulting in a remarkable refrigeration capacity of 802 J kg−1, which is 30% larger than that of GdTbDyHo alloy.
The equiatomic CrMnFeCoNi high-entropy alloy (HEA) exhibits outstanding toughness and excellent strength-ductility combination at cryogenic temperatures. However, its strength is relatively low at ...room temperature. In order to strengthen this HEA, microalloying additions of 0.8 at.% Nb and C were made and its properties and microstructure evaluated. It was found that the microalloying resulted in the formation of carbide precipitates and a reduction of the grain size to ∼2.6 μm. As a result, the room-temperature tensile yield strength (732 MPa) of the microalloyed HEA is roughly double that of the base HEA (with a concomitant increase in the ultimate strength) while its ductility is maintained at a relatively high level (elongation to fracture of ∼32%). The strengthening is due to precipitation hardening from the nanoscale carbide particles and grain refinement.
Display omitted
•Nanoscale NbC particles in CrMnFeCoNi were obtained by microalloying with Nb and C.•Yield stress of NbC-added CrMnFeCoNi HEA is roughly double that of the base HEA.•The ductility of NbC-added CrMnFeCoNi HEA is maintained at a high level (∼32%).•Strengthening is due to precipitation hardening and grain refinement.
Effects of adding Nb and V components on the microstructure and mechanical properties of hot-stamped steel and corresponding strengthening mechanisms were investigated by both qualitative and ...quantitative methods, which include grain refining strengthening, dislocation strengthening, solid solution strengthening and precipitation strengthening. Results revealed that adding 0.046 wt% Nb to 30MnB5 steel can significantly improve the strength and hardness in comparison with other investigated steels with the same heat treatment processes. For the studied two steels adding both Nb and V, with the V content increases, the strength and hardness show a downward trend as dispersed nanometer precipitates, which play various strengthening roles, consume a part of carbon content and then reduce dislocation density. Our study shows that the major strengthening mechanism of the investigated four steels is the dislocation strengthening, which accounts for about 60% of total yield strength.
In this paper, the role of primary stored energy and structural heterogeneity on the subsequent effects of hydrogen microalloying in glassy alloys was studied. For this purpose, two bulk metallic ...glasses with different chemical compositions and initial stored energy, i.e. Zr
60
Co
30
Al
10
and Zr
55
Co
30
Al
10
Nb
5
, were fabricated in a hydrogen-induced environment. Dynamic mechanical analysis and nanoindentation tests were carried out to evaluate relaxation behavior and mechanical properties of bulk metallic glasses, respectively. The nanoindentation results indicated declining serrations in load–displacement curves of hydrogen-affected samples. This event was related to the annihilation of localized deformation in hydrogen-affected samples under the external load. Moreover, the dynamic mechanical analysis showed that the hydrogen microalloying process improved the plasticity behavior of metallic glasses by activating fast
β
′ relaxation. Finally, the results unveiled that the higher initial structural heterogeneity and stored energy in the bulk metallic glass with the alloying composition of Zr
55
Co
30
Al
10
Nb
5
led to the improvement of microalloying effects on the corresponding properties.
The remarkable microalloying effect of nickel (Ni) on grain refinement and strengthening of selective laser melted titanium alloy is elucidated here. The addition of Ni up to ~0.4 wt.% avoided the ...formation of brittle eutectoid Ti2Ni phase and an ultrafine and ductile microstructure consisting of nano-size lath α′ was obtained in selective laser melted Ti-0.4Ni alloy. The solid solution strengthening and refinement effect of Ni led to significant increase in strength from ~745 MPa for pure Ti to ~1120 MPa for Ti-0.4Ni alloy, and good elongation of 8.8%. It is underscored that microalloying of titanium alloys with Ni can enhance the properties of titanium alloys processed by additive manufacturing.
Display omitted
PDF
