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The microstructural characterization of duplex Fe-Cr-Ni-based alloy processed through sub-rapid solidification and subsequent solid solution heat treatment was investigated, and the mechanism underlying the phase transformation and the improvement in the tensile properties of the alloy was discussed. A metastable thermodynamic balance emerged immediately during sub-rapid solidification which promoted the multiple phase transformation deviate from equilibrium transformation, e.g., suppressed dendrite δ phase, coupled structure features and constrained constituent diffusion behavior. The phase transformation in subsequent solid solution heat treatment proceeded very quickly, which resulted in decomposition of the primary δ phase and the polymorphic transformation (γ → δ). The solid solution heat treatment also led the change of grain size and shape, crystallographic orientation and constituents' distribution characterization. The application of solid solution heat treatment significantly improves the yield strength from 643.65 to 1014.09 MPa, and the ultimate tensile strength from 729.54 to 1029.31 MPa, corresponding to an increase of 57.55% and 41.09%, respectively. The results showed that the lamellar structures in sub-rapid solidified could give rise to strain concentration during loading and result in performance deterioration, which is different with the adverse effect derived from coarse dendrites in previous research. The underlying mechanism for the enhanced mechanical performance after solid solution heat treatment is discussed. It is demonstrated that the crack propagation and their interaction with individual microstructure features (dislocation, dimple or inclusions) play a vital role in final enhance performance. And the crack propagation is essentially orientation dependent. [ABSTRACT FROM AUTHOR]

G115 martensitic heat-resistant steel has been widely used in high parameter thermal power units because of its excellent mechanical properties and oxidation resistance. The microstructure and mechanical properties of single pass G115 steel welded joints fabricated by different welding currents were investigated in this study. The results show that larger welding current causes the widening of martensite laths, the coarsening of M23C6 carbides and the decrease in Vickers hardness in weld metal. However, welding current will affect evidently the microstructure and Vickers hardness of heat-affected zones only when it reaches to 120 A, which is mainly manifested by larger diameter and lower area fraction of M23C6 carbides and lower Vickers hardness. The tensile strength of welded joint firstly decreases and then increases with the increase in welding current, while the yield strength and elongation firstly increase and then decrease. The welded joint with welding current of 100 A is more recommended, due to the combination of highest yield strength and best ductility. [ABSTRACT FROM AUTHOR]

Precipitation evolution and strengthening effect of Al-15wt%Mg2Si-5wt%Cu alloy were studied by characterizing the change of morphology and tensile properties after ageing at 200 °C for various times. At the under-ageing condition (ageing for 0.5 h), metastable θ″, θ′, fine dots and σ phases are formed. After ageing for 1 h (peak-ageing condition), θ″ and θ′ are dominant phases, and the high number density of precipitates produces a significant improvement of the hardness (173 Hv) and ultimate tensile strength (356 MPa). As ageing time is prolonged (ageing for 24 h), plenty of σ phases are formed at the expense of θ"/θ′ phases and act as the main strengthening precipitates. The over-aged microstructure consequently causes a decrease in the hardness (134 Hv) and ultimate tensile strength (311 MPa) of the alloy. [ABSTRACT FROM AUTHOR]

In the present work, Tungsten (W)/oxide dispersion strengthened (ODS) steel joints were fabricated by the direct solid state diffusion bonding (SSDB) technology with a multistage cooling process, and the microstructure and tensile strength of the bonded interfaces and parent materials were experimentally investigated. The results show that W and ODS steel can be successfully bonded at the temperature ranging from 900 °C to 1050 °C, without severe macroscopic deformation or obvious microscopic defects. Reaction layers generated at the bonded interfaces are evolutive with the bonding temperature, result in different fracture locations of the bonded joints. In the joint bonded at 950 °C, a higher interfacial strength of ~ 234.2 MPa is achieved, due to the formation of nano-scale intermetallic compound FeW. Microstructure of W remains stable after all the SSDB processes, while the lath structure of ODS steel is completely broken and transformed into the equiaxed grains, which should be responsible for the deterioration of strength. When the bonding temperature is higher than 950 °C, the pinning effect of precipitates M23C6 and nano-oxide particles on the movement of dislocations is observed. [ABSTRACT FROM AUTHOR]

The effect of zirconium (Zr) addition on the microstructure and tensile properties of aluminum (Al) added ferritic ODS steel Fe-16Cr-3Al-1.5W-0.35Y 2 O 3 (16Cr3Al ODS) was investigated. Experimental analysis indicated that the addition of Zr refined oxide particles by forming finer Y-Zr-O particles instead of Y-Al-O particles encouraged grain refinement obviously from the results of TEM. The mean size of oxide particles decreased from 9.8 ± 1.7 nm to 8.0 ± 0.9 nm and the mean inter-particle distance decreased from 14.6 ± 1.5 nm to 10.5 ± 0.7 nm when Zr was added. In addition, the 16Cr3Al ODS steel containing Zr showed preferable yield strength and ultimate tensile strength compared with the ODS steel without Zr at several test temperatures, indicating the enhancement of tensile properties by the addition of Zr due to the optimization of microstructure in ODS steel by Zr addition. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened (ODS) steel is one of the most promising candidate structural materials for the high-temperature nuclear reactor application. In this study, two compositions of ODS steels (14Cr-ODS and 14Cr-Zr-ODS) were prepared to investigate the influence of Zr addition on the microstructures and mechanical properties of ODS steels. The microstructures, including dispersion morphology and crystal structures of oxide particles, particle-matrix interface coherency and particle-dislocation interactions, were characterized using TEM, HRTEM, and SEM, and the mechanical properties at room and high temperatures were measured using uniaxial tensile tests. Results show that Zr addition leads to the formation of finer precipitated particles, which was identified as rhombohedral Y 4 Zr 3 O 12 , with denser dispersion in the matrix. The calculation results reveal that the lattice misfit, δ , at the interface between particle and matrix increases as the particle size increases. In addition, the strength and elongation of ODS steels are improved with Zr addition due to the stronger interface bonding force between fine particles and matrix as well as the larger pinning effect of small particles to dislocation movements. [ABSTRACT FROM AUTHOR]

To investigate the effects of hafnium (Hf) addition on the microstructural and mechanical performance of an aluminum (Al) added 16Cr ODS steel, the microstructures of the 16Cr ODS steel with and without Hf were investigated by EBSD and TEM, and tensile tests were conducted at high temperature to evaluate the strength and ductility changes at different temperatures. The Hf addition is beneficial to the grain refinement of the 16Cr ODS steel. The average grain size decreases from 1.795 μm to 1.027 μm with Hf addition. In addition to the Y Al O nanoparticles, Y Hf O complex oxides with a finer size are also observed in the sample with the Hf addition, which reduces the mean size of oxides within the steel and increases the number density of the oxide particles. The yield strength and tensile strength of the 16Cr ODS steel are further improved by Hf addition due to its optimized microstructures with further refined grains. [ABSTRACT FROM AUTHOR]

The excellent mechanical performance of oxide dispersion strengthened (ODS) steels is attributed to the highly dispersed and extremely stable oxide particles with diameters of a few nanometers. Studies were made to determine the microstructure and tensile properties of a 14Cr ODS ferritic steel with the nominal composition of Fe–14Cr–2W–0.3Ti–0.2V–0.07Ta–0.3Y 2 O 3 produced by Hot Isostatic Pressing (HIP) in this work. Through the microstructure investigations, numerous nanoparticles with the average size of 5 nm was found to be located at the grain boundaries and inside the grains, and the average grain size was identified to be approximately 300 nm. The as-HIPed ODS steel proved to have excellent ductility at room temperature by tensile test, which is due to the bimodal structure with uniformly distributed nanoparticles and the addition of vanadium and tantalum. [ABSTRACT FROM AUTHOR]

In this work, reactive-inspired ball-milling (RBM) and spark plasma sintering (SPS) were employed to produce an ODS-316 L steel. The evolution of Y 2 O 3 particles during RBM and SPS processes was investigated, and the powder milled for different times was characterized for exploring the precipitation and coarsening behaviors of Y 2 O 3 particles. It was found that Y 2 O 3 particles with a metastable hexagonal structure precipitated in the early stage of ball-milling, and gradually transformed to a stable body centered cubic (BCC) structure during subsequent growth process. The size of Y 2 O 3 particles maintained at about 3–4 nm and no longer increased significantly in the RBM stage, but their average size increased rapidly to about 12 nm after SPS. The HRTEM results of the alloy after SPS showed that Y 2 O 3 particles inside the grains had a semi-coherent interface with the matrix. Compared with other methods, the united technology of RBM and SPS could significantly improve the tensile properties of the ODS-316 L steel. It was considered that the successful introduction of uniform and fine Y 2 O 3 particles by RBM and the small size of austenite grains due to rapid sintering of SPS were responsible for the improved tensile properties. [Display omitted] • An ODS-316 L steel was prepared by reactive-inspired ball-milling and SPS. • The size of oxides tended to be stable when it grew to 3–4 nm. • Hexagonal-to-cubic structural transformation of Y 2 O 3 precipitates occurred. • The ultimate tensile strength was 865 MPa and the elongation was 20.5%. [ABSTRACT FROM AUTHOR]

[Display omitted] Bonding of tungsten (W) with oxide dispersion strengthened (ODS) steel is an urgent challenge during the practical manufacturing process in many applications, including advanced nuclear reactor systems, military equipment, etc. To eliminate the generation of brittle intermetallic compounds Fe-W and relieve the residual thermal stresses, a novel composite interlayer Zr/Cu, for bonding W with ODS steel using the transient liquid phase (TLP) diffusion technology, was designed in this work. The bonding materials were prepared as a sandwiched structure of W/Zr-Cu/ODS steel in a vacuum diffusion bonding device. Interfacial structure and tensile strength of the bonded joints were investigated, and the processing parameters were optimized. After the bonding process, a reliable Cu/ODS steel interface could be built at all applied temperatures or holding times. Nevertheless, only as the bonding temperature was 1000 °C or even higher, the inserted Zr foil could be completely consumed and a stable W/Cu interface free from intermetallic compounds and micro-cracks was built. Additionally, the bonding ratio was gradually improved with increasing the bonding temperature or holding time. As a result, a high-strength W/Cu/ODS steel joint of ∼430.4 MPa could be fabricated at 1000 °C for a holding time of 60 min, and the bonding ratio was as high as 98 %, which provided a significant guide for the assembly of plasma facing components (PFCs). [ABSTRACT FROM AUTHOR]

In this paper, the effects of Cr and Mo microalloying on the microstructure evolution, mechanical properties, and austenite stability of 0.2C-7Mn steel were investigated at different intercritical annealing temperatures plus the same tempering treatment. Both the yield strength and ultimate tensile strength can be enhanced by nano-sized precipitates and solution hardening effect owing to Cr-Mo addition, while the ductility is well retained. The precipitates are mainly distributed on the ferrite matrix of the (Cr, Mo)-added steel, and directly produce a precipitation hardening effect. Due to the precipitation hardening and solution hardening effects of ferrite, the austenite in the (Cr, Mo)-added steel exhibits a lower mechanical stability, and more strain partitioning among the austenite and ferrite can be borne by the austenite than that in the reference steel, resulting in an accelerating transformation of austenite and a prevailed transformation-induced plasticity effect in the (Cr, Mo)-added steel. [ABSTRACT FROM AUTHOR]

Here the tensile behavior of a 9Cr-1.7W-0.1C reduced activated ferritic-martensitic steel over the temperature region from room temperature (RT) to 600 °C was studied. The variation of the dislocation distribution under the interplay mechanism of dislocations with solute atoms and lath boundaries was found to be the main reason for the decreasing of plasticity in the intermediate temperature zone. Temperature and strain rate were confirmed to affect the interaction intensity of this dynamic strain aging (DSA) phenomenon on the tensile deformation behavior through changing the extent of dislocation pile-up on the lath boundaries. The variation of average rate of crack propagation in the fibrous region was determined to be related to the DSA effect on the dislocation mobility. [ABSTRACT FROM AUTHOR]

In this work, 316L/CuCrZr functionally graded materials were prepared by laser powder bed fusion. Not only the strong bonding of 316L and CuCrZr was achieved, but more importantly, the grain-size gradients and heterogeneous microstructures were introduced into the samples. The gradient microstructure was characterized by ultrafine equiaxed grains sandwiched between micron-scale columnar grains. The dual-scale heterogeneous microstructure was composed of the BCC α-Fe and FCC ε-Cu phases. This grain size gradient and heterogeneous microstructure ensure that the samples possess high shear and tensile strength. The formation mechanisms of the grain-size gradients and heterogeneous microstructures of the samples were further discussed. The proposed strategy that functionally graded materials with grain size gradients and heterostructures can be fabricated by additive manufacturing may open up a new avenue for materials design. [Display omitted] [ABSTRACT FROM AUTHOR]

A reduced activation ferritic/martensitic (RAFM) steel with perfect creep property at elevated temperature (600 °C) was designed by implementing adding trace amount of Ta, Zr elements. In order to reveal the mechanism of creep property enhancing through adding Ta, Zr elements, the microstructural and mechanical evolution behaviors of RAFM steels, with and without containing Ta, Zr elements, were analyzed. It was found that Ta, Zr can not only refine the M 23 C 6 carbide particles, but also can increase the mean size of MX particles in RAFM steels, especially for Zr element. Furthermore, both of Ta and Zr can contribute to increasing the amount of MX particles. Through combining with experimental results and excluding the influence behavior of parent austenite grain (PAG) size on the mechanical property of RAFM steel, it is not the M 23 C 6 particles, but is the precipitation amount of MX carbide particles that promoted by adding Ta, Zr, which can have a significant effect on enhancing the strength and decreasing the creep rate of RAFM steel at 600 °C condition. In addition, the synergistic effect of Ta and Zr elements can significantly increase the creep-resistance breaking time of RAFM steel under the same conditions comparing with other RAFM steels, and then the mechanism of it was revealed in this work. • A reduced activation ferritic/martensitic (RAFM) steel with excellent creep property by changing Ta, Zr elements was developed. • Based on containing Ta element, adding Zr can slightly increase the size and amount of MX carbide particles in RAFM steel, which enhances the microstructure stability of RAFM steel at elevated temperatures. • M 23 C 6 particles have limited influences on increasing the tensile strength and creep properties of RAFM steels at 600 °C, but MX particles can do well with it. [ABSTRACT FROM AUTHOR]

The Ti 2 AlNb and Mo-modified Ti 2 AlNb alloys were fabricated by hot isostatic pressing, and then underwent annealing treatment at 800 °C for 1, 2 and 3 h respectively. To evaluate the tensile properties of the two kinds of alloys, tensile tests were conducted at ambient temperature and 650 °C in this study. For the Ti 2 AlNb alloy, the room-temperature ultimate tensile strength (UTS) was 700–900 MPa, and the highest elongation to failure (ε f) reached 6.2% after aging for 2 h at 800 °C. Since the Mo addition promoted the precipitation of the coarse B2+O colony structure near the grain boundary, the Mo-modified Ti 2 AlNb alloy exhibited decreased UTS and ε f at room temperature. As for the high-temperature performance of both the Ti 2 AlNb and Mo-modified Ti 2 AlNb alloys, the UTS reached approximately 700 MPa and the ε f exceeded 3.0%. Meanwhile, the two kinds of alloys presented the same tendency that both the high-temperature UTS and ε f increased firstly and then decreased as the aging time increased. Among them the specimens after aging at 800 °C for 2 h for both alloys acquired the highest UTS and ε f. Moreover, the Mo-modified alloy exhibited a better high-temperature ductility than that at room temperature, which is associated with the B2↔O phase transformation during the loading at 650 °C. The Mo addition effectively refined the lath of the precipitates in the grain and the grain size of the matrix, and it induced abundant dislocations. Thus, the Mo-modified Ti 2 AlNb alloy aged for 1 and 3 h exhibited superior high-temperature mechanical properties than those of the Ti 2 AlNb alloy. [ABSTRACT FROM AUTHOR]

The correlation of microstructure-properties of the Ni-based superalloy with coprecipitation of γ'/γ'' phases has been studied in details. To obtain the different γ'/γ'' microstructures, various heat treatments were attempted. The experimental results show that high amounts of the compact γ'/γ'' phases contribute to the tensile strength of Ni-based superalloy, which decreases with the coarsening of γ'/γ'' structures. The γ'/γ'' phases can restrain the motion of the dislocations. Further increasing the size of the γ' and γ'' phases, the deformation mechanism transforms from dislocation pairs shearing to Orowan bypassing, and then to dislocation shearing. Stacking faults (SFs) also appears in γ'/γ'' phases. Additionally, the moderate η/δ phases effectively pin the grain boundary, which enhances the alloy's ductility. [ABSTRACT FROM AUTHOR]

[Display omitted] • Cr influences the thermal properties of C14–Laves Fe 2 W phase. • Cr decrease the Gibbs energy and bulk modulus of C14–Laves Fe 2 W phase. • Cr increase the thermal expansion of C14–Laves Fe 2 W phase. • Cr and He can reduce the tensile strength aligning to [0001] of C14–Laves Fe 2 W phase. The influence of chromium (Cr) on the thermal properties of C14–Laves Fe 2 W phase were studied in detail based on the quasi–harmonic approximation. The effect of Cr on the helium (He) trapping behavior of the C14–Laves Fe 2 W phase was also investigated based on the defect formation energy with density functional theory (DFT). The results indicated that Cr could not only decrease the values of the Gibbs energy and bulk modulus of the C14–Laves Fe 2 W phase, but could also increase the thermal expansion coefficient of the C14–Laves Fe 2 W phase. In addition, Cr could reduce the capacity of the C14–Laves Fe 2 W phase to trap He. The coupling effect of Cr and He on the mechanical behavior of the C14–Laves Fe 2 W was studied, wherein both Cr and He could reduce the tensile strength that was aligned to the [0001] of C14–Laves Fe 2 W phase. The relation between the mechanical behavior of the C14-Laves Fe 2 W or Cr doped Fe 2 W phases and their thermal properties were also discussed. The fracture mechanisms of the C14–Laves Fe 2 W phases, with or without Cr/He–doping, along the (0001) grain plane was analyzed based on the charge density and partial densities of states (pDOS). [ABSTRACT FROM AUTHOR]

Microalloying of an Al-15%Mg 2 Si alloy (wt%) with 1%Cu produced an enhanced age-hardening response, increasing peak hardness and ultimate tensile strength due to a modified precipitation process. The solid solubility of Cu in Al-15%Mg 2 Si alloy effectively promotes the formation of the high number density of Guinier-Preston-Bagaryasky (GPB) zones combined with S precipitates. It suppresses β′ and β″ formation during ageing at 200 °C. Consequently, Al-15%Mg 2 Si-1%Cu alloy with the high density of GPB zones and S phase exhibited high peak hardness (121 HVN) and ultimate tensile strength (284 MPa), 42.4% and 49.5% higher than that of the Al-15%Mg 2 Si alloy, respectively. • The addition of 1% Cu in Al-15%Mg 2 Si alloy has a significant influence on precipitation during ageing at 200 °C. • Cu addition promotes the formation of GPB zones and S phase, instead of β′ and β″ precipitates. • The high number density of GPB zones and S phase produces an enhanced age-hardening response. [ABSTRACT FROM AUTHOR]

The evolution of η phase and its effect on the tensile properties at 700 °C in 718Plus superalloy after three solution (at 940 °C for 1 h) and single aging (at 870 °C for 25 h, 50 h and 100 h) heat treatments, were investigated. The results showed that there were several various morphologies of η phase in 718Plus samples. As aging time increased, the volume fraction of needle-like/plate-like increased continuously from 5.32%, 7.78% to 29.52%, while the volume of granular/short rod-like η phase firstly increased from 0.46% to 0.68% then decreased to 0.56%. The high temperature tensile properties were affected by η phases with various morphologies. With aging time increasing, the ultimate tensile strength was obviously improved from 797.11 MPa to 860.57 MPa, which could be attributed to a certain number of plate-like/needle-like η phases at the grain boundaries which could hinder the dislocations motion near the grain boundaries. And the elongation weakly increased firstly from 16.84% to 18.76% and then decreased to 18%, which was closely related to granular/short-rod η phases. Enhancing tensile strength and acceptable ductility could be obtained by morphology control of η phase applying SA heat treatments in the study: promoting the simultaneous precipitation of an appropriate amount of plate-like/needle-like η phases and a small amount of granular/short rod-like η phases. • The morphologies of η phases found in studied 718Plus superalloy samples are plate-like/needle-like, granular/short rod-like. • With aging time extending, the volume fraction of needle-like/plate-like increased, resulting in improving tensile strength. • By applying SA aging heat treatments, an enhancing tensile strength could be obtained by morphology control of η phase [ABSTRACT FROM AUTHOR]