Abstract
Low-temperature decomposition of supersaturated solid solution into unfavorable intergranular precipitates is a long-standing bottleneck limiting the practical applications of nanograined ...aluminum alloys that are prepared by severe plastic deformation. Minimizing the vacancy concentration is generally regarded as an effective approach in suppressing the decomposition process. Here we report a counterintuitive strategy to stabilize supersaturated solid solution in nanograined Al-Cu alloys via high-density vacancies in combination with Sc microalloying. By generating a two orders of magnitude higher concentration of vacancies bonded in strong (Cu, Sc, vacancy)-rich atomic complexes, a high thermal stability is achieved in an Al-Cu-Sc alloy that precipitation is nearly suppressed up to ~230 °C. The solute-vacancy complexes also enable the nanograined Al-Cu alloys with higher strength, greater strain hardening capability and ductility. These findings provide perspectives towards the great potentials of solute-vacancy interaction and the development of nanograined alloys with high stability and well-performed mechanical properties.
•Minor Al, Mn, Cu, Ag and Li were added to improve mechanical properties of Zn.•New ternary Al-Mn-Zn phase was formed and β-LiZn4 was precipitated from Zn.•Alloy without Li exhibits ultrahigh ...ductility, with elongation of up to 82.2% ± 2.94%.•Alloy with 0.35%Li has tensile strength & elongation of 449 ± 7.4 MPa & 62.3% ± 4.63%.•Electrochemical and immersion tests show that Li improves corrosion resistance.
In this work, Zn microalloyed with Al, Mn, Cu, Ag and Li was cast, annealed and extruded. The results showed that addition of multiple trace elements causes significant change in the microstructures, mechanical properties and corrosion behavior of Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag (11Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag is abbreviated as ZM.ZM), Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag- 0.1Li (22Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag-0.1Li is abbreviated as ZM-0.1Li.ZM-0.1Li) and Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag-0.35Li (33Zn-0.1Al-0.1Mn-0.1Cu-0.1Ag-0.35Li is abbreviated as ZM-0.35Li.ZM-0.35Li) alloys. Two ternary phases with the approximate compositions of Al13Mn3Zn34 and Al10MnZn89 phases are formed in the casting and annealing processes of these alloys, respectively. Wavy β-LiZn4 lamellae that have not been extensively reported are precipitated from the primary Zn dendrites in the casting process of ZM-0.35Li alloy. Also, Zn laths are precipitated from the eutectic β-LiZn4 phase in the annealing process of ZM-0.35Li alloy. The above-mentioned phases are crushed or elongated in the as-extruded alloys, which play an important role in improving the strength of the alloys. All the as-extruded alloys have typical (0001) basal texture, accompanied with relatively low {0001}<112¯0> slip and high {101¯2}<101¯1¯> twinning Schmid factors, which are advantageous and disadvantageous to the strength enhancement of the alloys, respectively. All the as-cast alloys exhibit poor mechanical properties, especially low ductility. The as-extruded ZM alloy exhibits ultrahigh ductility, with an elongation of up to 82.2% ± 2.94%. The as-extruded ZM-0.35Li alloy shows the best comprehensive mechanical properties, with yield strength, ultimate tensile strength, elongation and hardness of 380 ± 1.6 MPa, 449 ± 7.4 MPa, 62.3% ± 4.63% and 98 ± 1.4 HV, respectively. Electrochemical corrosion rates of the ZM, ZM-0.1Li and ZM-0.35Li alloys are 0.241 ± 0.004, 0.206 ± 0.006 and 0.189 ± 0.008 mm/year, respectively. In vitro immersion corrosion rates (after 26 d in SBF solution) of them are 0.134 ± 0.005, 0.125 ± 0.004 and 0.121 ± 0.003 mm/year, respectively. The as-extruded ZM-0.35Li alloy exhibits the best corrosion resistance.
•The effect of Cr and Ni on mechanical response and the microstructural evolution of nanocrystalline ferrite are explored using molecular dynamics.•Cr reduces dislocation density and leads to a ...transformation in mechanical properties during tensile and scratching.•Cr and Ni enhance the atomic binding strength with Fe and form lattice distortion.•Ni suppresses grain boundary slip and migration.•The formation of more nanoscale twins and twin-dislocation interactions can enhance strain-hardening ability during tensile.
Microalloying plays a critical role in improving the mechanical properties of steel. To offer a better theoretical guide for experimental research at the atomic level, this paper investigated the synergistic mechanism of adding trace amounts of alloy Cr and Ni and the microstructure evolution of nanocrystalline ferrite during the mechanical response process. First-principles calculations were implemented to investigate electronic properties. Hybrid molecular dynamics and Monte Carlo simulations were employed to explore the deformation mechanism under uniaxial tension and scratching. Specifically, comprehensive differences between doped and pure nanocrystalline ferrites were explored regarding local stress-strain state, dislocation evolution, twin expansion, and grain boundary activity. The results show that Cr- and Ni-doped nanocrystalline ferrite has higher strength and better wear resistance. The potential mechanism is that the addition of Cr and Ni enhances the atomic bonding strength with Fe atoms, hinders the movement of dislocations caused by lattice distortion, and suppresses grain boundary slip and migration, thereby improving the resistance to plastic deformation and grain boundary stability. Theoretical calculations based on microstructure indicate that compared to solid solution strengthening, Ni-induced grain boundary strengthening plays a dominant role in improving yield strength. Under large deformation, the trend of mechanical response is reversed. The suppression of dislocation motion by Cr reduces the dislocation density and dislocation entanglement, resulting in flow stress and local scratch force being smaller than that of pure samples. However, the formation of more nanoscale twins and twin-dislocation interactions enhances strain-hardening ability during tensile. Finer nanostructured subgrains are formed under scratching. These results provide valuable insights into the understanding of the strengthening mechanism and plastic deformation mechanism of Cr-Ni system low alloy steel under dynamic loading.
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Effect of microalloying by Tb on the microstructure, phase transitions, and functional properties of the Fe-19Ga-xTb and Fe-27.4Ga-xTb (where x = 0, 0.15, 0.3, 0.4, or 0.5 at.%) alloys was ...investigated by several techniques including in-situ neutron diffraction, X-ray diffraction (XRD), SEM-EBSD, magnetic measurements, and mechanical spectroscopy (internal friction). We could establish a microstructural understanding to figure out why doping with the trace amounts of Tb leads to an enhanced magnetostriction in the Fe-27.4Ga alloy up to 242 ppm. Our results demonstrate that the microalloying of Fe-27.4Ga with Tb significantly suppresses the formation of the phases with close-packed L12 and D019 structures and stabilizes the dominant phase with D03 structure. The L12 has negative magnetostriction compared to positive magnetostriction of the D03 matrix; therefore, the lower the volume fraction of the L12 is the higher the saturation magnetostriction at room temperature is. The influence of Tb on decelerating the kinetics of the phase transitions in the Fe-27Ga alloys can be reasonably explained by considering a possible competition between precipitation of the Tb-enriched phase and the nucleation of the L12 at the grain boundaries. Both Tb-enriched and the L12 prefer D03 grain boundaries for their nucleation as demonstrated by EBSD analysis. Nevertheless, the Tb-enriched phase already precipitates during casting, and therefore, at subsequent annealing, these precipitations prevent the nucleation of the L12 on the grain boundaries of the as-cast (D03) structure.
•Microalloying of Fe-19Ga and Fe-27.4Ga alloys by Tb (0.15, 0.3, 0.4, and 0.5 at.%).•Employing in-situ neutron diffraction to study the phase transitions.•Effect of Tb on functional properties (magnetic, magnetostrictive, and internal friction).•Microalloying with the trace amounts of Tb leads to an enhanced magnetostriction.
•High-density SFs and L-C locks were formed in René 104ScY.•Microalloying resulted in the formation of nano-Al3(Sc, Y) phases and fine subgrains.•The strength–ductility was improved by the ...synergistic effect of the multiple strengthening mechanisms in René 104ScY.•René 104ScY demonstrated an excellent strength-ductility synergy (YS = 1059 ± 15 MPa, UTS = 1405 ± 10 MPa, EL = 28.8 % ± 0.6 %).
Improving the strength–ductility is crucial to the development of high-performance nickel-based superalloys fabricated via additive manufacturing (AM). In this study, Sc and Y microalloying is used to regulate the microstructure and improve the strength–ductility of René 104 supealloy (René 104ScY). The results suggest the formation of high-density stacking faults (SFs), Lomer–Cottrell locks, and nano-Al3(Sc,Y) phases in the René 104ScY matrix. The cellular/columnar structures are refined, the number of equiaxial grains increases, and the number of columnar grains and their aspect ratio decrease in René 104ScY. The synergistic effect of multiple strengthening mechanisms, including that formed by SFs, improves the strength and ductility of René 104ScY fabricated via laser powder bed fusion. The yield strength, tensile strength, and elongation of René 104ScY are 1059 ± 15 MPa, 1405 ± 10 MPa, and 28.8 % ± 0.6 %, respectively. This study provides a novel approach for developing high-performance nickel-based superalloys using AM.
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•The corrosion resistance of Al-Mg-Si alloys was enhanced through La addition.•La-rich shell formed on Mg2Si particles inhibited localized corrosion initiation.•Modified Si particles ...with La addition could suppress corrosion propagation.
The effect of micro-alloying element La on the corrosion behavior of Al-Mg-Si alloys in 3.5 wt. % NaCl solution was investigated. The results demonstrate that micro-alloying La causes the formation of a microstructure with discrete short-rod like Si particles and Mg2Si particles with a La-rich surface shell. The La-rich shell slows down the dissolution of the Mg2Si particles and mitigates the localized corrosion around the Mg2Si particles. The isolated Si particles hinder the corrosion propagation along grain boundaries. As a result, micro-alloying element La causes a significant improvement in the corrosion resistance of Al-Mg-Si alloys.
Carbon neutrality of the steel industry requires the development of high-strength steel. The mechanical properties of low-alloy steel can be considerably improved at a low cost by adding a small ...amount of titanium (Ti) element, namely Ti microalloying, whose performance is related to Ti-contained second phase particles including inclusions and precipitates. By proper controlling the precipitation behaviors of these particles during different stages of steel manufacture, fine-grained microstructure and strong precipitation strengthening effects can be obtained in low-alloy steel. Thus, Ti microalloying can be widely applied to produce high strength steel, which can replace low strength steels heavily used in various areas currently. This article reviews the characteristics of the chemical and physical metallurgies of Ti microalloying and the effects of Ti microalloying on the phase formation, microstructural evolution, precipitation behavior of low-carbon steel during the steel making process, especially the thin slab casting and continuous rolling process and the mechanical properties of final steel products. Future development of Ti microalloying is also proposed to further promote the application of Ti microalloying technology in steel to meet the requirement of low-carbon economy.
•V-microalloying synergistically enhanced strength and toughness of HNSBS.•V addition controlled interstitial partitioning, refined coarse RA and reduced TM.•V-microalloying refined precipitates and ...restrained intergranular precipitation.•More film-like RA and dislocation martensite coordinated plastic deformation of 0.2 V steel.
High-nitrogen stainless bearing steel (HNSBS) with ultra-high tensile strength (∼ 2403 MPa) and good toughness (∼80.0 J) was obtained by V-microalloying, overcoming the strength-toughness trade-off of conventional V-free HNSBS. In this work, since V-microalloying facilitated the enrichment of interstitial atoms (C and N) in precipitates, the content of interstitial atoms in the matrix was reduced accordingly (i.e., interstitial partitioning). On the one hand, V-microalloying reduced the substantial intergranular precipitates and transformed the precipitates from M23C6 + M2N into V-containing M23C6 + M2N + MN with multi-scale particle sizes, causing a coupling strengthening effect, which contributed to the toughness and additional strength increase. On the other hand, V-microalloying controlled interstitial partitioning, effectively refined coarse retained austenite (RA), increased the fraction of dislocation martensite, and reduced the fraction of twin martensite. The more film-like RA and dislocation martensite with high dislocation density coordinated plastic deformation and prevented crack propagation, thus obviously enhancing the strength and toughness of 0.2 V steel. This study provides a new route to develop high-performance HNSBS for aerospace applications.
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Thermomechanical processing has been used to control the grain size/shape of the equiatomic CrCoNi medium-entropy alloy (MEA) and obtain excellent strength and ductility. However, in the cast state, ...the alloy has coarse columnar grains with average widths and lengths of approximately 120 and 1000 μm, respectively, resulting in inferior mechanical properties. To overcome this deficiency, here we microalloyed with Ti and C and successfully changed the grain shape (from columnar to equiaxed) and refined the grain size. The degree to which the microstructure changes depends on the amount of Ti and C added, with the best results obtained at 0.4 at.% each. In the optimal alloy (CrCoNi)99.2Ti0.4C0.4, the as-cast grains were nearly equiaxed with a uniform size of ∼75 μm. Associated with this change in grain shape/size was a significant improvement of yield strength, ultimate tensile strength and elongation to fracture at both 293 and 77 K. The columnar to equiaxed transition is attributed to the strong mutual affinity of C and Ti, which leads to their build-up ahead of the solid-liquid interface and, in turn, to enhanced constitutional undercooling.
•Grain refinement of cast CrCoNi alloy is reported for the first time.•It was accomplished by microalloying with Ti and C.•Grain refinement in as-cast state enhances both tensile strength and ductility.•Mutual affinity/segregation of Ti and C induces undercooling and grain refinement.
The stress-induced martensitic transformation of Cu50Zr50 at. % shape memory alloy was tuned through microalloying and co-microalloying. The effect of microalloying elements Co or Ni individually or ...combined (i.e., co-microalloying) was investigated and compared at the macro- and nanoscale. From nanoindentation experiments, change in the slopes of (P/h)-h curves, plastic index and recovery ratio after annealing were investigated: partial replacement of Cu by 1 at. % Ni was observed to promote twinning while for 1 at. % Co the twinning propensity decreased and co-microalloying using 0.5 at. % Co and Ni had an intermediate effect. The recovery ratio of the Cu50Zr50 alloy, calculated from the volume change of a residual indent after annealing at 400 °C for 5 min after annealing at 400 °C for 5 min increased from 15.6% to 19.5% when substituting Cu by 1 at. % Ni. These results, obtained at the nanoscale, are in agreement with macroscale test observation, namely, differential scanning calorimetry and x-ray diffraction. Therefore, microalloying opens up possibilities for the development of more cost-effective CuZr alloys, with a view to develop commercial actuators that could replace costly NiTi alloys in the near future.
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•Partial replacement of Cu by 1 at. % Ni in Cu50Zr50 at. % alloy was observed to promote twinning.•The twinning propensity decreases for 1 at. % Co and it is intermediate for 0.5 at. % Co and Ni.•The results at nanoscale are in agreement with macroscale test observations.•Microalloying opens up possibilities for the development of more cost-effective CuZr alloys.
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