The mechanical properties and high temperature oxidation behaviors of 9Cr2WVTa steels with Mn contents in the range of 0.04–0.93 wt% were investigated. There are no obvious differences in the tensile properties at room temperature and high temperature, only a slight reduction in the impact toughness when Mn content reaches 0.93 wt%. Remarkably, the high temperature oxidation resistance is significantly improved with an increase of Mn content. After 500 h of oxidation, a (Fe0.6Cr0.4)2O3 oxide scale is developed on the steel with 0.04 wt% Mn, Mn1.5Cr1.5O4 oxides are occasionally detected when Mn content reaches 0.47 wt%, while a thin compact scale with a mixture of Mn1.5Cr1.5O4 and Cr1.3Fe0.7O3 oxides is formed on the steel containing 0.93 wt% Mn. Addition of Mn promotes the formation of Mn-oxides, which lowers oxygen partial pressure and accelerates external oxidation of Cr. At last, the presence of Mn-Cr spinels and Cr-rich oxides improves the oxidation resistance.

•Surface mechanical rolling treatment was applied to 9Cr2WVTa steel.•Microstructure in the surface layer of the steel was refined into nanometer scale.•Oxidation resistance of the nanostructured sample is evidently enhanced in air.•Oxide scale on the nanostructured sample is more compact and enriched with Mn.•Oxide scale on the nanostructured sample is more protective in liquid Pb–Bi.A nanostructured surface layer was pre-formed on a 9Cr2WVTa reduced activation ferritic/martensitic steel sample by means of surface mechanical rolling treatment (SMRT). In comparison with the initial sample, oxidation experiments at 600 °C in air showed that the oxidation resistance of the SMRT sample is markedly enhanced, due to the formation of a more continuous, homogenous, and compact oxide scale enriched with Mn. Furthermore, oxidation experiments at 550 °C in oxygen-saturated liquid Pb–Bi eutectic alloy showed that the oxidation resistance is improved on the SMRT sample after pre-oxidation in air, due to depressed diffusivities in the pre-formed oxide scale.

The effect of continuous extrusion forming (CEF) process on the microstructure and mechanical properties of a CuCrZr welding joint was investigated. The experimental results showed that after the CEF process the grains were refined to submicron-scale through dynamic recrystallization, which improved the mechanical properties of the welding joint as well as the base material. Meanwhile, the micron-scale precipitates aggregated at the grain boundaries in the welding process were broken down to smaller ones and recrystallized grains of several micrometers formed around the precipitates after CEF process, which could alleviate the negative effect induced by the micron-scale precipitates during plastic deforming process. Finer grains and smaller micron-scale precipitates made contributions to improve the properties of a CuCrZr alloy with a welding joint.

Effects of the aging temperature on the hardening response, the tensile properties and the precipitate microstructure evolution of 1460 alloy were studied in this work. It was found that Al3 (Sc, Zr) and δ′ (Al3Li) phases were precipitated from the matrix at the very early aging stage, while the precipitation of T1 (Al2CuLi) and θ′ (Al2Cu) was much slower than that of the δ′ phase. When aging at higher temperature (160 and 190 °C), the δ′, T1 and θ′ phases tended to form simultaneously and grow up very quickly. Conversely, the δ′ and θ″ (Al2Cu) phases were precipitated separately and more dispersive at lower aging temperature (130 °C). Taken together, the alloy aged at 160 °C exhibited improved mechanical properties owing to the uniform dispersion of the fine T1 precipitates.

Microstructure and mechanical properties of electron beam welded alloy J75 were studied under as-welded and post-weld aging treatment (PWAT) conditions. The results showed that high-quality welds were produced by electron beam welding. Under as-welded condition, a fine dendritic structure consisting of gamma dendrite matrix and Laves phase was observed in the welds. Better mechanical properties were obtained in the weld zone than that of base metal because of the fine size of the dendritic structure. After PWAT, a discontinuous distribution of γ′ particles existed in the dendritic structure. The presence of a γ′ depletion zone in the dendrite core resulted in a significant degradation of mechanical properties of the weld.

Hydrogen-induced modification in the deformation and fracture of a precipitation-hardened Fe–Ni based austenitic alloy has been investigated in the present study by means of thermal hydrogen charging experiment, tensile tests, scanning electron microscopy (SEM) and transmission electron microscopy (TEM). It is found that the γ′ particles are subjected to the multiple shearing by dislocations during plastic deformation, which promotes the occurrence of the dislocation planar slip. Moreover, the alloy will be enhanced by hydrogen resulting in the formation of strain localization at macroscale. So, the mechanisms of deformation and fracture in the alloy have been proposed in terms of serious hydrogen-induced planar slip at microscale which can lead to macroscopic strain localization.

The effect of minor addition of Sc on microstructure, age hardening behavior, tensile properties and fracture morphology of 1460 alloy have been studied. It is found that Sc content increase from 0.11 wt% to 0.22 wt% is favorable for grain refinement in as-cast alloy but results in a coarsening of Cu-rich particles. The alloy with 0.11 wt% Sc exhibits enhanced mechanical properties and age hardening effect. Transmission electron microscopy (TEM) investigations on the alloy with 0.11 wt% Sc have suggested that a large amount of Al3(Sc, Zr) particles precipitated at the earlier aging may inhibit recrystallization effectively.

Effect of prior deformation on strain amplitude-dependent internal friction has been studied in a FeNi based austenitic alloy subjected to solution and peak-aged treatment. The internal friction initially shows increase and then decreases with pre-strain increase in solution-treated alloy. Nevertheless, it is interesting to find that the internal friction shows continued increase with prior deformation degree in peak-aged alloy. Results could be explained using the breakaway model of dislocation in both state alloys. The discrepancy of internal friction behavior, correlated to dislocation arrangement observation, is discussed in terms of slip mode transition from wavy slip to planar slip with introduction of coherent precipitation particles.Highlights► The internal friction (IF) increases initially and then decreases with prior deformation degree in solution treatment alloy. ► The IF shows continued increase with prior deformation degree in austenitic alloy containing coherent precipitation particle, an experimental phenomenon not reported before. ► The dislocation slip mode transition may be related to the discrepancy of IF behavior.

Fe–Cr–Ni–Mo high-strength steels with four different V contents (0%, 0.03%, 0.08% and 0.14%) were prepared in this paper and carbides evolution was investigated by means of three-dimensional atom probe (3DAP) and transmission electron microscopy (TEM). The results indicated that there appeared MC, M2C and M6C types of carbides after addition of V in the steels while it was M23C6 in 0.0%V steel (M is any combination of Cr, Mo, Mn, Fe or V), and the size of carbides decreased gradually with improving V content. The mechanical properties significantly depended on the content of V. The strength and elongation increased gradually with increase in the V content, meanwhile the impact toughness decreased gradually. The excellent combination of mechanical properties can be obtained in the steel with about 0.03%—V content.

The hydrogen-induced cracking behavior is investigated in two Fe–Ni based austenitic alloys with different amounts of γ′ phase. It is observed that intergranular cracking existed in both alloys, while hydrogen-induced twin boundary cracking only occurred in the alloy with higher amount of γ′ phase. The occurrence of twin boundary cracking is primarily related to the stacking fault energy (SFE) of alloys, which decreases with the increasing amounts of γ′ phase. Enhanced slip planarity and increased difficulty in cutting through twin boundary are observed in the low-SFE alloy. Therefore, twin boundary cracking is induced by cooperative effects of SFE and hydrogen in Fe–Ni based austenitic alloys.

A Cu–0.16Cr–0.12Zr alloy with an initial grain size of about 400 μm was extruded by continuous extrusion forming (CEF), where severe plastic deformation and precipitation process occurred. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) were employed to examine the microstructure and morphology of the precipitates. Experimental results show that a notable grain size reduction to sub-micron scale is obtained through continuous dynamic recrystallization and precipitates maintain a fine and disperse morphology after the CEF process. These two features are considered as the effective ways to improve the strength and ductility of the CuCrZr alloy after cold deformation and subsequent aging process without a significant decrease of electrical conductivity.

Microstructure and mechanical properties of electron beam welds after post-weld aging treatment (PWAT) in Fe–Ni based alloys with different amounts of Ti were investigated. The results show that a γ′ depletion zone in the dendrite core was induced by electron beam welding and the tensile strength of welds was degraded. However, the appropriate increase of Ti content promoted the uniform distribution of γ′ phase in the dendrite core and interdendritic region. As a result, the mechanical property of welds was improved.

Damping behavior of Ti50.1Ni49.9 shape memory alloy during reverse martensitic transformation has been investigated by dynamic mechanical analyzer in a dual-cantilever mode. With the increase of strain amplitude, internal friction (IF) of the alloy increases in martensite and austenite states while decreases in transformation region. Based on the regularity of IF attenuation in isothermal condition, IFTr and (IFPT+ IFI) are decomposed from the strain amplitude dependent IF in transformation region. For practical application of shape memory alloys as a damping material, it is significant to evaluate the damping capacity by eliminating the influence of IFTr and consider its time independent real IF (IFPT+ IFI).

The mechanism of hydrogen embrittlement (HE) in a γ′-Ni3(Al,Ti) phase strengthened Fe–Ni based austenitic alloy has been investigated in detail. Hot hydrogen charging experiment and tensile test reveal that the alloy with coherent γ′ phase exhibits a much higher decrease in reduction of area (RA) than that of the alloy in the solution-treated state. However, three-dimensional atom probe (3DAP) experiment shows that segregation of hydrogen atoms is not found at the coherent interface between the γ′ phase and the matrix, which indicates that the interface is not a strong hydrogen trap. Furthermore, high-resolution transmission electron microscopy (TEM) observation indicates that the interface coherency is maintained during the deformation, even tensile to fracture. It is found that macroscale slip band rupture and intergranular fracture are promoted by serious dislocation planar slip, which become the predominant features in the tensile-to-fracture sample after hydrogen charging. This phenomenon has been interpreted as a result of combined effects of the γ′ phase and hydrogen in the precipitation-strengthened Fe–Ni based austenitic alloy.

Tensile tests on a FeNi-base austenitic alloy were conducted at room temperature (RT) and 400 °C, when serrated flow did not and did occur, respectively. Deformation microstructures such as topographies of slip bands (SBs), morphologies of twin boundaries (TBs) and arrangements of dislocations near TBs, as well as concentrations of strain were investigated. It is shown that TBs block SBs and induce remarkable stress accumulations at 400 °C. Effect of TB-density on the serrated flow was also investigated by comparative tensile tests on specimens with different TB densities at 400 °C. Details of tensile curves reveal that more TBs induce more pronounced serrations. Therefore, interaction between TBs and SBs is proposed to induce the serrated flow of the FeNi-base alloy at 400 °C.

The damping capacity mainly comes from the motion of martensite boundaries, which is larger than that from different phase interfaces in TiNi-based shape memory alloys. The fine and disperse precipitation in the TiNi matrix will increase the damping capacity of the TiNiNbMo alloy in the martensitic state but little affect the damping capacity during the martensite transformation. The dispersed Nb-rich particles and the internal stress fields around them influence the change tendency of damping capacity with the increasing of strain amplitude.

The reverse martensitic transformation behavior of a Ni–Ti–Nb shape memory alloy pipe-joint was investigated systematically by means of differential scanning calorimetry. It was found that the reverse transformation start temperature (A′s) of the pre-deformed pipe-joint increased while the transformation temperature interval decreased when the wall thickness declined. The reverse transformation temperature interval was widened by inserting a connecting pipe into the hole of the pipe-joint, demonstrating that the connecting pipes impeded the reverse transformation of the pre-deformed pipe-joints. On the basis of the kinetics of thermoelastic martensitic transformation, the specific characteristics of the reverse martensitic transformation behavior of shape memory alloy pipe-joints were explained.