Alloy design based on single-principal-element systems has approached its limit for performance enhancements. A substantial increase in strength up to gigapascal levels typically causes the premature ...failure of materials with reduced ductility. Here, we report a strategy to break this trade-off by controllably introducing high-density ductile multicomponent intermetallic nanoparticles (MCINPs) in complex alloy systems. Distinct from the intermetallic-induced embrittlement under conventional wisdom, such MCINP-strengthened alloys exhibit superior strengths of 1.5 gigapascals and ductility as high as 50% in tension at ambient temperature. The plastic instability, a major concern for high-strength materials, can be completely eliminated by generating a distinctive multistage work-hardening behavior, resulting from pronounced dislocation activities and deformation-induced microbands. This MCINP strategy offers a paradigm to develop next-generation materials for structural applications.
Three stainless steel alloys, high-purity 304 (HP304), high-purity 304 with high Si (HP304
+
Si) and commercial purity 304 (CP304), were irradiated with 2
MeV protons to a dose of 5
dpa at 360
°C and ...subsequently examined using atom probe tomography (APT) and scanning transmission electron microscopy–energy dispersive X-ray spectrometry (STEM–EDS). Several novel features of radiation-induced segregation and radiation-induced precipitation were observed. There is a significant variation in the composition of enriched and depleted elements in the grain boundary plane and along the dislocation loop core. Boron segregation to the grain boundary prior to irradiation is not affected by the irradiation. Phosphorus segregation is enhanced by irradiation. Carbon depletes at the grain boundary and may be affected by co-segregation with Cr. APT and STEM–EDS measurements are in excellent agreement for almost all the elements studied. The segregation behavior of elements at dislocations mirrors that at the grain boundary, but at a lower magnitude, except for Si. Ni/Si-rich clusters formed in irradiated HP304
+
Si and CP304 are probably the precursors of
γ′ or other Si- and Ni-rich phases. Copper depletion was observed at both the grain boundary and the dislocation loops. Regions adjacent to the depleted zones were sites for Cu cluster formation, which were also spatially correlated with Ni/Si-rich clusters.
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We report on the alloy design strategies, precipitation mechanism and mechanical properties of an ultra-high strength steel hardened by co-precipitation of nanoscale NiAl and Cu ...particles. The steel, developed through a computational-aided alloy design approach, exhibits a tensile strength of ∼1.9GPa, an elongation of ∼10% and a reduction in area of ∼40%. Atom probe tomography (APT) reveals an interesting type of co-precipitation mechanism of NiAl and Cu nanoparticles, in which the NiAl particles first come out of the supersaturated solid solution and the rejection of Cu solutes leads to the heterogeneous precipitation of Cu particles adjacent to the NiAl particles. The observed precipitation sequence of “supersaturated solid solution→NiAl→NiAl+Cu” is substantially different from the one previously reported in Cu-strengthened steels, which involves the process of “supersaturated solid solution→Cu→Cu+NiAl”. The modulation of the precipitation sequence is attributed not only to the relatively high Ni/Cu and Al/Cu ratios but also the synergistic combination of Ni, Al, Mn and Cu additions in the steel. In addition, APT also reveals the precipitation of a small amount of nanoscale Fe3(Mo,W)3C- and NbC-type carbides. The combination of the strengthening effects from the nanoscale NiAl particles, Cu particles and carbides contributes significantly to the overall ultra-high strength of the steel.
Progress in understanding radiation damage in structural materials is hampered by the lack of test reactors, long irradiations and high cost. Here we show that through strict control of experimental ...parameters and accounting for He production and damage-rate differences, the microstructure of ion-irradiated ferritic–martensitic steel closely resembles that created in-reactor across the full range of microstructure features. The level of agreement establishes for the first time the capability to tailor ion irradiation to emulate in-reactor radiation damage.
In the present study, the polarization characteristics of La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) - Gd0.1Ce0.9O1.95 (GDC) composite cathodes with different volume ratios were investigated. Samples with volume ...ratios of 20:80, 30:70, 50:50, 70:30 and 100:0 vol % were tested. The electrochemical impedance spectroscopy tests and current voltage curve measurements were carried out for the current densities from 0 to 0.2 Acm−2 with an interval of 0.05 Acm−2. The results showed that a volume ratio of LSCF:GDC = 30:70 composite cathode led to the lowest overpotential, and the overpotential increased in the order of 30:70, 50:50, 70:30, 100:0, 20:80 vol %. Three dimensional microstructures of composite cathodes were reconstructed and quantified by dual beam focused ion beam-scanning electron microscope (FIB-SEM). The results showed that neither LSCF surface area nor triple phase boundary (TPB) alone could explain the dependence of polarization characteristics on volume ratios. Current and electrochemical potential distributions were simulated by the Lattice Boltzmann method, in which both surface and TPB reactions were considered. Prediction considering both surface and TPB reactions could predict qualitatively the dependence of overpotentials on LSCF - GDC cathode composition.
•LSCF-GDC composite cathode with different volume ratios of components are fabricated.•Polarization characteristics are evaluated.•Microstructures are reconstructed by FIB-SEM technique.•Cathode overpotential is correlated to the microstructural characteristics.•Performance of LSCF-GDC cannot be explained only by the surface reaction.
To simultaneously obtain superior superelasticity and biological properties, single- and multi-layer Ti–23Nb coatings were deposited on a cold-rolled NiTi substrate using laser metal deposition ...(LMD). The microstructure of the single-layer coating consisted of a cellular structure with a grid size of ∼300 μm in the eutectic layer, strip structures and prior β-(Ti, Nb) phases surrounded by the Ti2Ni(Nb) phase in the Ni diffusion zone. In contrast, the microstructure of the multi-layer coating consisted of α′, α′′, and prior β phases, which arise from the partition of Nb. Compared with the NiTi substrate, the Ni ion release concentration of the single-layer coating is reduced by 45% with similar nano-mechanical behavior, i.e. a nanohardness, H, of ∼4.0 GPa, a reduced Young's modulus, Er, of ∼65 GPa, an elastic strain to failure, H/Er, of ∼0.06, a yield stress, H3/Er2, of ∼0.016 GPa, and a superelastic strain recovery, ηsr, of ∼0.3. The reduction of Ni ion concentration for multi-layer coating after 35 days is even better at up to 62%, but at the cost of a degradation in the mechanical properties. The LMD coatings have a high dislocation density, and their creep is controlled by dislocation movement.
•The diffusion of Ni during laser melting leads to the formation of cellular and strip subgrains.•α″ martensite is critical for the properties of the TiNb binary alloys produced by LMD.•The single-layer coating can suppress the release of Ni ions while preserving the superelasticity of substrate.
Strength through disorder
Jet turbine blades and other objects with ultrahigh strength at high temperatures are made of special alloys that are often grown as costly single crystals to help avoid ...failure. Yang
et al.
discovered that adding a small amount of boron in a nickel-cobalt-iron-aluminum-titanium alloy creates an ultrahigh-strength material. Critically, the alloy has a nanoscale-disordered interface in between crystal grains that substantially improves the ductility while preventing high-temperature grain coarsening. This alloy design creates attractive high-temperature properties for various applications.
Science
, this issue p.
427
Disordered interfaces in a polycrystalline super-alloy create an ultrahigh-strength alloy with ductility.
Alloys that have high strengths at high temperatures are crucial for a variety of important industries including aerospace. Alloys with ordered superlattice structures are attractive for this purpose but generally suffer from poor ductility and rapid grain coarsening. We discovered that nanoscale disordered interfaces can effectively overcome these problems. Interfacial disordering is driven by multielement cosegregation that creates a distinctive nanolayer between adjacent micrometer-scale superlattice grains. This nanolayer acts as a sustainable ductilizing source, which prevents brittle intergranular fractures by enhancing dislocation mobilities. Our superlattice materials have ultrahigh strengths of 1.6 gigapascals with tensile ductilities of 25% at ambient temperature. Simultaneously, we achieved negligible grain coarsening with exceptional softening resistance at elevated temperatures. Designing similar nanolayers may open a pathway for further optimization of alloy properties.
Post-irradiation annealing was performed on a 304L SS that was irradiated to 5.9 dpa in the Barsebäck 1 BWR reactor. Evolution of dislocation loops, radiation-induced solute clusters and ...radiation-induced segregation at the grain boundary was investigated following thermal annealing at 500 °C and 550 °C up to 20 h. Dislocation loops, Ni-Si and Al-Cu clusters, and enrichment of Ni, Si and depletion of Cr at the grain boundary were observed in the as-irradiated condition. Dislocation loop size did not change significantly after annealing at 550 °C for 5 h but the loop number density decreased considerably and loops mostly disappeared after annealing at 550 °C for 20 h. The average size of Ni-Si and Al-Cu clusters increased while the number density decreased with annealing. The increase in cluster size was due to diffusion of solutes rather than cluster coarsening. Significant volume fractions of Ni-Si and Al-Cu clusters still remained after annealing at 550 °C for 20 h. Substantial recovery of Cr and Ni at the grain boundary was observed after annealing at 550 °C for 5 h but neither Cr nor Ni was fully recovered after 20 h. Annihilation of dislocation loops, driven by the thermal vacancy concentration gradient caused by the strain field and stacking fault associated with the loops appeared to be faster than annihilation of solute clusters and recovery of Ni and Si at the grain boundary, both of which are driven by the solute concentration gradients.
Void evolution in Fe++-irradiated ferritic-martensitic alloy HT9 was characterized in the temperature range of 400–480°C between doses of 25 and 375 displacements per atom (dpa) with pre-implanted ...helium levels of 0–100appm. A systematic study using depth profiling in cross-section samples was conducted to determine a valid region of analysis between 300 and 700nm from the surface, which excluded effects due to the injected interstitial and the surface. Pre-implanted helium was found to promote void swelling at low doses by shortening the nucleation regime and to retard void growth at doses in the transient regime by enhancement of nucleation of small voids. Swelling was found to peak at a temperature of 460°C. The primary effect of temperature was on the nucleation regime; nucleation regime was the shortest at 460°C compared to that at 440 and 480°C. The growth rate of voids was temperature-invariant. Steady state swelling was reached at 460°C between 188 and 375dpa at a rate of 0.02%/dpa.
Solution-annealed 304L stainless steel (SS) was irradiated to 130 dpa at 380 °C, and to 15 dpa at 500 °C and 600 °C, and cold-worked 316 SS (CW 316 SS) was irradiated to 130 dpa at 380 °C using 5 MeV ...Fe++/Ni++ to produce microstructures and radiation-induced segregation (RIS) for comparison with that from neutron irradiation at 320 °C to 46 dpa in the BOR60 reactor. For the 304L SS alloy, self-ion irradiation at 380 °C produced a dislocation loop microstructure that was comparable to that by neutron irradiation. No voids were observed in either the 380 °C self-ion irradiation or the neutron irradiation conditions. Irradiation at 600 °C produced the best match to radiation-induced segregation of Cr and Ni with the neutron irradiation, consistent with the prediction of a large temperature shift by Mansur's invariant relations for RIS. For the CW 316 SS alloy irradiated to 130 dpa at 380 °C, both the irradiated microstructure (dislocation loops, precipitates and voids) and RIS reasonably matched the neutron-irradiated sample. The smaller temperature shift for RIS in CW 316 SS was likely due to the high sink (dislocation) density induced by the cold work. A single self-ion irradiation condition at a dose rate ∼1000× that in reactor does not match both dislocation loops and RIS in solution-annealed 304L SS. However, a single irradiation temperature produced a reasonable match with both the dislocation/precipitate microstructure and RIS in CW 316 SS, indicating that sink density is a critical factor in determining the temperature shift for self-ion irradiations.
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