The microstructural evolution of a HfNbTaTiZr high-entropy alloy subjected to cold rolling and subsequent annealing was investigated. The dislocation activity dominates the deformation process. The microstuctural evolution of the alloy during cold rolling can be described as follows: (i) formation of dislocation tangles, (ii) formation of microbands, (iii) formation of thin laths and microshear bands containing thin laths, (iv) the transverse breakdown of the lath to elongated segment, and (v) formation of fine grains. During annealing at 800 and 1000 °C, decomposition of the metastable high-temperature body-centered cubic phase proceeded through a phase separation reaction. Annealing at 800 °C resulted in a nonrecrystallized microstructure with abundant second-phase particles distributed randomly. The second-phase particles with an average size of ∼145 nm were enriched in Ta and Nb, while the chemical composition of the matrix was close to the average composition of the alloy. Meanwhile, an unknown phase slightly enriched in Hf, Zr, and Ti was detected in the interfacial region between the second-phase particles.

In the present investigation, AA6351 aluminum alloy matrix composites reinforced with various percentages of AlN particles were fabricated by stir casting technique. The percentage of AlN was varied from 0 to 20% in a step of 4%. The prepared AA6351-AlN composites were characterized using scanning electron microscope (SEM) and x-ray diffraction (XRD). The mechanical properties such as micro-hardness, compression strength, flexural strength, and tensile strength of the proposed composite have been studied. X-ray diffraction patterns confirm the presence of AlN particles in the composites. SEM analysis reveals the homogeneous distribution of AlN particles in the AA6351 matrix. The mechanical properties of the composite were found to be noticeably higher than that of the plain matrix alloy due to augmented particle content. The produced composites exhibit superior mechanical properties when compared with unreinforced matrix alloy. Fracture surface analysis of tensile specimens show the ductile–brittle nature of failure in the composites.

A kind of nickel–aluminum bronze (Cu–10Al–4Fe–4Ni) prepared by centrifugal casting (CC) and gravity casting (GC), respectively, were investigated. The results indicate that CC alloy, which is totally different from GC alloy, consists of α, κI, κII, κIII, κIV, and β′ phases and the microstructures of CC alloy shows nonuniformities from external to internal layer mainly because the distribution of iron and nickel are influenced by centrifugal force. Besides, it is noted that comprehensive mechanical properties of CC alloy are superior to those of GC alloy. Additionally, heat treatments were performed on CC alloy. The results demonstrate the optimal heat treatment is aging at 450 °C/1 h by air cooling after solution treated at 890 °C/1 h by water quench. The ultimate tensile strength and hardness are increased by about 10% and 56%, respectively, and wear resistance is also greatly improved. However, the elongation is decreased by 53%.

In this paper many studies have been carried out to ascertain the phenomenon of strain-induced precipitation and coarsening of carbides in AISI H13 hot-work die steel during the tests at 700 °C. The microstructure of H13 with various loadings was studied to identify the effects of mechanical strain on the evolutionary behavior of carbides. SEM and TEM were used to observe the size and distribution of the carbides of each sample. It was found that the coagulation of carbides is more obvious in mechanical strained samples than that in mechanical strain-free sample which means mechanical strain promotes the precipitation and coarsening of carbides, and these processes are affected by the mechanical strain amplitude. Precipitation is increased by the strain enhanced because of more nucleation sites produced and accelerate the diffusion of solute atoms. Moreover, the results are shown that lower strain rates are more beneficial for precipitation and coarsening of carbides under the same strain because they provide a longer time to nucleate and grow into nuclei.

The deformation mechanisms responsible for the strength and ductility of nanostructured Cu and Cu–Al alloys processed by high pressure torsion have been analyzed in frames of a model of elastic–plastic medium and using the available experimental data. The income of the Peierls strength, as well as solid solution hardening, dislocation hardening, twinning hardening, taking into account possible annihilation processes has been estimated. It was shown that in the Cu–5 at.% Al alloy annihilation processes contribute to the maintenance of deformation. The material is hardened by the accumulation of dislocations at the twin boundaries, postponing the moment of reaching the ultimate strength. In the Cu–16 at.% Al alloy processes of the annihilation are limited. As a result, the possibility of further deformation is limited and the degree of homogeneous deformation decreases in comparison with the case of the Cu–5 at.% Al alloy. Significantly increased concentration of deformation vacancies contributes to the destruction of the former alloy as well.

In this research work, planetary ball mill has been used to disperse carbon nanotubes (CNTs) in Al powders. Al-CNT nanocomposite samples have been produced using double pressing double sintering (DPDS) method. The effects of CNTs weight percent and secondary pressing and sintering on the hardness, tensile, and bending strength of Al-CNTs nanocomposites were investigated. Enhancements of about 98% in hardness, 40% in tensile strength, and 20% in bending strength of Al-CNTs nanocomposites were observed as compared with pure Al samples. Using DPDS technique increments of 2.4–16.14% in density has been obtained as compared with the nanocomposites produced by conventional sintering method. The composites were studied by scanning electron microscope and differential thermal analysis. The X-ray diffraction (XRD) was used to identify various phases if present in Al-CNTs nanocomposites.

Influence of corrosion/fatigue factors on the fatigue life of 7B04-T6 aluminum alloys were studied in this paper. Different kinds of alternating corrosion-fatigue tests were carried out. Three factors influencing fatigue life were investigated: pre-corrosion time, corrosion/fatigue alternation frequency, and specimen’s size. The results show that: with the extension of pre-corrosion time, fatigue lives decreased; although the total corrosion time was the same (192 h), as the corrosion/fatigue alternation frequency increased, the total fatigue lives increased. The total fatigue lives of specimens subjected to two, four, and six corrosion/fatigue cycles (n = 2, 4, 6), in which specimens underwent pre-corrosion for 96 h per cycle (n = 2), 48 h per cycle (n = 4), and 32 h per cycle (n = 6), respectively, was measured. It was found that the fatigue lives increased by 56.4, 84.4, 136%, as the number of cycles increased, compared to tests in which no alternation took place (192 h of continuous corrosion). When exposed to the same corrosion times, different sized specimens demonstrated different fatigue lives. The fatigue lives of small specimens were shorter than the larger specimens. These results are all due to the specific properties of corrosion/fatigue factors.

The fatigue crack growth (FCG) tests were performed on a Ni–17Mo–7Cr base superalloy before and after thermal exposure to investigate the influence of microstructural variation on the alloy's FCG behavior. It was observed that the original alloy consists of Ni matrix and MoC particles. When the alloy was aged at 1350 °C for 0.5 h, the MoC melts together with circumambient Ni matrix, forming a eutectic–like structure. The microstructural analysis shows that, for original alloy, the crack basically propagates in the matrix. When it encounters the particles, the crack meanders to avoid them, creating a linear da/dN–ΔK curve. As the crack approaches the eutectic-like structures within the aged alloy, however, it cuts through them but circumvents tiny particles within the structures, producing torturous crack paths and waved da/dN–ΔK curve. The aged alloy has a higher FCG resistance in contrast to original alloy.

The effects of different Sn contents on the microstructure and tensile properties of an in situ prepared Al–15% Mg2Si composite were investigated. Adding 5 wt% Sn not only reduced the average size of Mg2Si primary particles from ∼55 µm to ∼10 µm, but also increased the ultimate tensile strength and elongation values. Mg2Sn intermetallic was identified in Al–15% Mg2Si–5% Sn composite and the lowest disregistry was also found for $\left( {001} \right)_{{\rm{Mg}}_2 {\rm{Sn}}} {\parallel} \left( {001} \right)_{{\rm{Mg}}_{\rm{2}} {\rm{Si}}}$ , indicating that Mg2Sn can be a potent heterogeneous nucleation site for Mg2Si particles. Computer-aided cooling curve analysis revealed that Sn addition changes the solidification performance of the material by increasing both solidification time and recalescence undercooling and also reducing the growth temperature to some extent. The solidification behavior of the composite was also explained in terms of the presence of oxide bifilms in the liquid Al.

Single- and double-hit hot compression tests were performed at 1030 °C and strain rate of 0.1 s−1 on Ti–13V–11Cr–3Al beta Ti alloy to investigate the flow behavior and mechanism of microstructural evolution during the interpass period. It was observed that the flow stress level and the extent of yield point phenomena (YPP) were increased by an increase in the grain size. After the first pass, the microstructure was bimodal of large deformed grains and small recrystallized grains formed by continuous dynamic recrystallization. The increase in the interpass time to 100 s, led to the decrease in the yield drop and extent of YPP. However, the further increase in the interpass time to 300 s would result in an inverse effect. A combination between static recrystallization and metadynamic recrystallization was found responsible for grain refinement in the samples subjected to the interpass times below 100 s. At longer interpass times, i.e., 300 s, grain growth increased the average grain size.

As-annealed commercial pure titanium (grade 1) was selected as a model material whose crystalline structure was hexagonal close-packed. The evolution of the microstructure and micro-orientation induced by high-speed compression was characterized to elaborate the formation mechanism of the high-speed deformation characteristic microstructure in α-titanium. Twinning played a coordinating role for dislocation slipping that was the main plastic deformation mechanism. The high-speed deformation characteristic microstructure of as-annealed commercial pure titanium was an adiabatic shear band (ASB) with an average width of 50 μm at a strain rate of 5400 s−1, whose initial grains were 0.5–1.0 μm in size. The formation and extension of ASB were attributed to the interaction between the shear stress and the adiabatic temperature rise. A formation model of ASB in α-Ti was proposed in terms of the formation mechanism of the high-speed deformation characteristic microstructure.

In this study, a mesoscale dislocation simulation method was developed to study the orthogonal cutting of titanium alloy. The evolution of surface grain structure and its effects on the surface mechanical properties were studied by using two-dimensional climb assisted dislocation dynamics technology. The motions of edge dislocations such as dislocation nucleation, junction, interaction with obstacles, and grain boundaries, and annihilation were tracked. The results indicated that the machined surface has a microstructure composed of refined grains. The fine-grains bring appreciable scale effect and a mass of dislocations are piled up in the grain boundaries and persistent slip bands. In particular, dislocation climb can induce a perfect softening effect, but this effect is significantly weakened when grain size is less than 1.65 μm. In addition, a Hall–Petch type relation was predicted according to the arrangement of grain, the range of grain sizes and the distribution of dislocations.

Simple shear deformation via hybrid cutting-extrusion is used to produce continuous electrical steel sheet from a commercial high-silicon (nominal 4 wt%) iron alloy of poor workability in a single deformation step, a fundamentally different route from the multi-step processing of rolling and annealing currently in use. The shear texture created in the sheet is found to be quite different from that produced by rolling. The magnetic properties of the shear-textured Fe–Si sheet are measured using closed-circuit permeametry and compared with those from sheet produced by rolling of the same alloy and a commercial non-grain-oriented sheet of similar composition. Properties compared include maximum relative permeability, induction, coercivity, and hysteresis loss. The results are interpreted in terms of microstructure, texture, and composition. A unit cell representation of the shear texture components is introduced that relates the expected orientation of easy magnetization directions with the sheet axes.

Hot deformation characteristics of 2304 duplex stainless steel were analyzed by hot compression tests at temperature range of 850–1150 °C and strain rates of 0.001–1 s−1. The flow curves at low temperatures and high strain rates were suggesting sluggish dynamic recovery (DRV) in ferrite and partial dynamic recrystallization (DRX) in austenite. However, at high temperatures and low strain rates, the flow curves showed implied the domination of DRV in ferrite. The hyperbolic sine equation with activation energy of 508 kJ/mol could relate the processing parameters. Microstructural observations showed that DRV in ferrite is the controlling mechanism at all deformation conditions. However, at high temperatures and strain rates partial DRX could also occur in austenite. Based on the law of mixture and Baragar’s equations a modified model was proposed to consider work hardening and dynamic softening in the constituents. The model could satisfactorily predict the flow curves at different deformation regimes.

Inhomogeneity may lead to premature failure and operationally determines the lifetime estimation of thick weld joints. Considerable novelty of this paper was the achievement of the microstructural and mechanical inhomogeneity, especially along the thickness direction, in the narrow-gap weld seam of thick gas metal arc (GMA) welded Al–Zn–Mg alloy plates. The microstructure of the weld seam was investigated by means of optical metallography, scanning electron microscopy (SEM), transmission electron microscopy (TEM), and energy dispersive spectrum (EDS), after which the phase composition was ascertained according to the x-ray diffraction (XRD) analysis and selected area diffraction analysis by TEM (TEM-SAD). The generation of intergranular short rod-shaped MgZn2 particles changed the distribution of precipitates on the grain boundary with intragranular ellipsoidal MgZn2 particles simultaneously formed as the strengthening phase, which rendered preferable mechanical performances to the bottom layer of the weld seam. The above conclusion was farther affirmed by micro fractography and EDS test results on the fractured surface of the tensile samples. In addition, the effect of following weld passes on the microstructure and micro hardness profile of the finished weld pass was investigated.

Ultrasonic impact treatment (UIT) combined with high energy electropulsing (EP) was applied to low carbon steel to introduce severe plastic deformation on the surface. The investigation indicated that a strengthened layer with a maximum hardness of approximately 330 HV on cross section was obtained, in comparison with the hardness value of 260 HV resulted from UIT solely. Alongside with high hardness, the enhanced structure layer was extended to a distinguishing depth of 2 mm. Microstructure in the cross section revealed a crack-free superficial layer by EP-UIT and pearlite colonies here experienced morphology variations by redistribution and spheroidization of cementite. A 3 μm oxide layer consisting of amorphous oxide and nitride as well as MnFe2O4 and hematite crystalline was formed on the treated surface. Thermal and athermal effect of EP was the key factor in these phenomena and it is assumed that acoustic softening, electro plasticity, and thermal softening were engaged simultaneously.

The flash allowance and upset allowance have significant effects on characteristics of flash butt welded RS590CL steel joints. The overheated zone (OZ) widths increased with flash allowance (δf) increase, and decreased as the upset allowance (δu) increased. The coarsened upper bainite was formed in interface zone (IZ) and OZ as δf increased. With increasing δu, the large plastic deformation occurred and the interface formability improved. The hardness in IZ was a little lower than that in its vicinity OZ due to some ferrite existence and dislocation amount decreased in IZ. The tensile strengths of flash butt welding (FBW) joints were in good match with base metal and the ductilities were lower. The maximum bending crack length was 0.68 mm which indicated that the bending properties of FBW joints were good. Under this experiment, relatively large δf (10–12 mm) and δu (5.5–6.5 mm) were recommended for the benefit of high quality FBW joints.

Semisolid forging is a type of semisolid metal processing with high solid fraction. However, the presence of nanosized particles has strong influences on flow behavior of the composites in the semisolid forging process. In this study, the compression deformation behavior of nanosized Al2O3 particles (Al2O3np) reinforced 7075 aluminum matrix composites with high solid fraction was investigated by conducting semisolid isothermal compression experiment. The microstructures after semisolid compression were characterized. The results showed that the true stress decreased with the increase of the deformation temperature and size of Al2O3np, the decrease of the strain rate and mass fraction of Al2O3np. After semisolid compression, deformation degree in large deformation zone was larger than that in free deformation zone. Besides, the solid grains in large deformation zone showed evidence of having undergone different degrees of plastic deformation under different deformation conditions. Simultaneously, the deformation mechanisms during the semisolid compression process were discussed.

The instability and fracture process during uniaxial tension was observed from load-stop tensile tests and finite element simulation. The results indicate that at the end of instability, the direction of the maximum principle stress near the necking groove turns to being perpendicular to the groove. This tensile stress is critical to the growth of fracture. The fracture initiates from the internal of the sheet at the center of volume where the two local necking grooves intersect. Material here is under triaxial tensile stress state and the principle stresses in all three directions are the largest. Once the initial crack occurs, it propagates along the zero-strain-rate necking groove. Moreover, the final fracture angle between the fracture plane and the tensile axis is always larger than theoretical value. An important reason is the ignorance of the triaxial stress state evolution during instability in theoretical calculation.

Microstructures of new heat-resistant steel grade T23 welded joint without PWHT and its corresponding mechanical properties including creep were investigated to clarify its premature failure mechanisms in the large water wall panel of the advanced power plant boiler. The results show that the T23 steel GTAW welded joint in a wall thickness of 6.5 mm without PWHT exhibits high tensile strength, good ductility, and sufficient impact toughness, while the hardness of the WM is higher than the maximum permitted value of 350 HV due to the large amount of un-tempered martensite formed during the cooling process of welding. This WM in as-welded condition has higher creep rupture strength but poorer rupture ductility than the tempered BM. Poor rupture ductility taken place in the WM results from inter-granular cracking during creep exposure and is not related to the second hardening because no hardness rise occurs in the fractured WM compared with as-welded condition. The paper does not specifically investigate the effect of service exposure but simulates the failure of WM by a creep test. The main point is that the WM has low creep ductility, especially at a stress concentration.