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A magnesium-based ‘supra-nanometre-sized dual-phase glass-crystal’ (SNDP-GC) coating had been fabricated on AZ31 alloy by magnetron sputtering. Surface mechanical attrition treatment (SMAT) was also introduced to form a gradient structure in order to reduce the hardness mismatch between Mg-based SNDP-GC coating and substrate. Microstructure, mechanical properties and corrosion behaviors of the as-received AZ31 (AR), AZ31 with Mg-based SNDP-GC coating (SC) and AZ31 after SMAT with Mg-based SNDP-GC coating (SSC) were investigated by optical microscope, scanning electron microscopy, transmission electron microscope, X-ray diffraction, Vickers hardness penetrator and electrochemical characterization. Results revealed the Mg-based SNDP-GC coating together with a gradient structure contributed to the improved microhardness. The decreased hardness mismatch between the coating and substrate prevented the delamination of the coating from the substrate. There is a decrease trend in Ecorr in sequence of AR, SC and SSC, while a rise in icorr in the same sequence. Corrosion uniformity was decreased in sequence of AR, SC and SSC, and corrosion cracks exhibited on corrosion products due to formation of galvanic cells and stress concentration. These results indicated the presence of gradient structure and Mg-based SNDP-GC coating led to better mechanical properties but worse corrosion resistance.

The present work investigates the change in the microstructure and the improvement in the mechanical property of ternary Mg-Al-Gd alloys induced by a static magnetic field of 1 T, applied during homogenization at 525 °C. The application of the magnetic field increases the concentration of Gd in α-Mg from 7.16 to 9.00 wt% in the alloys homogenized under the same heat treatment condition without magnetic field to 10.65–11.41 wt%. A higher solid concentration of Gd gives a higher solution strengthening. The width of the 15R-type long-period stacking ordered (LPSO) laths in the homogenized alloys is significantly reduced to 46.9 nm from 236.2 nm by the magnetic field. The ultimate compression strength is enhanced by the magnetic field from 447 MPa to 473 MPa.

Cu-W-C micron powders were long-term (≥60 h) milled and hot-pressed in order to obtain copper matrix reinforced by in-situ nanoscale tungsten carbides. Both powder and sintered composite were characterized using various techniques including X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM) and assessed for hardness and electrical conductivity to investigate the ball milling time effect on the structural evolutions and properties of Cu-WC. Longer-term ball milling found the refinement and homogenization of nano-Cu and nano-W in milled powders, which enlarged W and C contact probability and promoted WC formation accordingly. At 120 h milling, the sintered material was composed of WC micro areas and Cu-rich composite areas where the nanosized and ultrafine WC coexisted. This better microstructure increased hardness by 42% only with a small reduction in electrical properties compared to the case of 60 h milling.

The microstructure and texture evolution near the adiabatic shear band (ASB) in TC17 Titanium alloy, during hot compression, were studied by electron back-scattered diffraction (EBSD). The ASB was induced in the bulk cylindrical TC17 Titanium alloy with an initially equiaxed microstructure, by hot compression with a relatively low strain rate. When the equiaxed-microstructure TC17 Titanium alloy was compressed at 600 °C, 700 °C, and 850 °C, two kinds of ASB were observed: D-ASB, which is almost parallel to the diagonal of the longitudinal section, and H-ASB, which is almost parallel to the horizontal of the longitudinal section. Dynamic recrystallization took place in β phase grains at the ASB center, while dynamic recovery dominated at the transition region. The large angle grain boundaries (LAGBs) were mainly concentrated in β phase, while the small angle grain boundaries (SAGBs) were mainly concentrated in α phase distributed along the ASB direction. Meanwhile, both α and β phase grain sizes slightly increased with increasing hot compression temperature and deformation, except for the alloy compressed at 850 °C with 70% deformation due to the phase transformation. At the ASB center, prismatic textures existed in α phase grains except for the basal textures in the alloy deformed at 600 °C. In β phase grains, the {001} planes were always normal to CD, while the {111} planes were normal to CD in the initial microstructure of the TC17 alloy. Furthermore, in β phase grains, the cubic texture {100} 〈001〉 dominated in the TC17 alloy deformed at 600 °C, 700 °C, and 850 °C. With increasing compression temperature, the crystal plane parallel to the ASB direction in α phase grains changed from {0001} to {11 2 ¯ 0} while it was stable in β phase grains, which is not beneficial to the mechanical performance of this alloy.

Despite the increasing demands of copper matrix composites for use as thermal management, their manufacturing remains a great challenge since rigorous conditions are prerequisite, including high temperature and high pressure. Here, nearly void-free copper matrix diamond composite (Cu-diamond) with near-perfect interfaces is fabricated via electroplating. The surface and internal microstructure of Cu-diamond composites are investigated. The interfacial microstructure between copper matrix and diamond is discussed. Heat flux inside Cu-diamond composites is simulated using COMSOL software. Results indicate that the nearly void-free microstructure and near-perfect interfaces lead to the high thermal conductivity (TC) of 614.87 W m−1 K−1 and the low coefficient of thermal expansion (CTE) of 9.45 × 10−6 K−1, both of which are comparable to that prepared by the conventional high temperature method. Remarkably, the electroplating technique is fully compatible with micromachining process, suggesting its potential application in microelectronic devices.

CoCrFeNiMn high entropy alloy matrix composites with in-situ carbide and oxide particles were fabricated by thermomechanical consolidation of a mechanically milled powder at 1000 and 1150 °C respectively. The sample consolidated at 1000 °C exhibited a microstructure consisting of Cr-rich M23C6 carbide particles, spinel (Cr, Mn)3O4 oxide particles, ultrafine grains with an average size of 920 nm and a major 〈001〉 + minor 〈111〉 dual fiber texture. When the consolation temperature increased to 1150 °C, Cr-rich M23C6 carbide particles were dissolved and the spinel (Cr, Mn)3O4 oxide particles coarsened. These led to larger grains with an average size of 6.06 μm and allowed formation of only sharp 〈001〉 fiber texture. This microstructural variation with the increase of consolidation temperature led to a decrease of strength and improvement of ductility. Analysis of the strengthening mechanisms reveals that grain boundary strengthening and Orowan strengthening play a major role in strengthening for the high strength sample consolidated at 1000 °C, while these mechanisms contribute significantly less to the strength for the sample consolidated at 1150 °C. It was also found that the sample consolidated at 1150 °C was weakened by the 〈001〉 texture.

A duplex treatment of plasma nitriding (PN), followed by the deposition of a CrN/CrTiAlSiN/WCrTiAlN multilayer coating, was performed on AISI 4140 steel. Untreated, plasma-nitrided, only-coated (just the coating) and duplex-treated (PN + coating) AISI 4140 steel were microstructurally and mechanically characterized. The nitrided compound layer, consisting of mainly e-Fe2-3N and γ′-Fe4N phases, was approximately 8.0 μm thick. The total thickness of the multilayer coating, which consisted of a top W-Cr-Ti-Al-N multilayer, a periodic Cr-Ti-Al-Si-N interlayer, and a CrN bottom layer, was 2.3 μm. The CrN/CrTiAlSiN/WCrTiAlN multilayered coatings possessed a super-hardness of 47.9 GPa and the highest elastic modulus of 424.8 GPa in the all samples. The microhardness (2200 HV0.05) of the duplex-treated sample was significantly higher than that of the only-coated (740 HV0.05) and nitrided (900 HV0.05) samples. The scratch tests revealed that the adhesion strength of the duplex-treated sample increased significantly due to a gradient-hardness support of the coating-nitrided layer interface.

A new Mg-5Zn-3.5Sn-1Mn-0.5Ca-0.5Cu alloy with high strength is developed and the microstructure and mechanical properties of the alloy in the as-cast, extruded and aged states are investigated. The as-cast alloy contains α-Mg, MgZn2, Mg2Sn and MgSnCa phase. The extrusion process refines the microstructure and leads to fully dynamic recrystallized grains with a tilted basal texture, which results in moderate mechanical properties of the extruded alloy. Ca acts synergistically with Cu in promoting age hardening and the combined addition of Ca and Cu significantly enhances the peak hardness of the alloy after double aging treatment, the effect is more obvious than the alloys with single addition of Ca or Cu. Fine and densely distributed Mg–Zn and Mg2Sn precipitate after double aging treatment, which contributes to the strengthening of the alloy. The yield strength, ultimate tensile strength and elongation of the alloy after double aging treatment reach 392 MPa, 401 MPa and 7%, respectively.

In the present study, a Ti-48Al-2Cr-2Nb alloy was bonded by transient liquid phase bonding using spark plasma sintering (SPS) process with Ti/Ni/Ti filler metal. It was found that SPS could effectively promote atomic diffusion and hence inhibit the formation of brittle TiNi and TiAlNi intermetallic phases in the joint, resulting in improved joint strength. With increasing the bonding temperature from 1100 °C to 1200 °C, the joint thickness increased from 125 to 206 μm and the microstructure changed from a layered structure into a homogeneous isothermally solidified microstructure. Meanwhile increased amounts of γ lathes and α2/γ colonies were observed. When the bonding was carried out at 1200 °C, increasing holding time from 5 to 15 min resulted in an increase of epitaxial growth layer thickness from 10 to 25 μm as well as the coarsening of α2/γ colonies due to solid diffusion. The effects of bonding temperature and holding time on joint strength were studied in relation with the microstructural evolution. The fracture behavior of the joints and the underlying mechanisms were discussed.

The dislocation strengthening effect is generally considered to be controlled by dislocation density; however, in the present study the dislocation substructure is shown to play an even more important role for Cu-20Ni-20Mn alloy. The hardness and microstructural evolution during annealing in a hot-forged Cu-20Ni-20Mn alloy are investigated. Microstructure analysis of annealed samples indicated variation in the number of dislocations and dislocation substructure related to softening of the Cu-20Ni-20Mn alloy during static recovery. The tangled dislocations formed a regular array during annealing at 600 °C, leading to a high softening fraction of 95%. In addition, rapid dislocation annihilation and sub-boundary disintegration occurred during annealing owing to the dislocation climb at 650 °C. The number of mobile dislocations within the grains decreased considerably, leading to softening in the Cu-20Ni-20Mn alloy annealed at 650 °C.

During the hot-dipping process, there is always a desire to restrain the mutual diffusion between steel and alloy bath for suppressing the formation of bath dross. However, the dissolution of steel sheets is difficult to quantify by the traditional methods. In this work, in-situ X-ray diffraction was used to investigate the solid-liquid reaction between solid Fe and Al–Zn–Si liquid alloy for quantitatively analyzing the consumption of Fe and the formation of Fe–Al compounds. The results indicated that the addition of trace Ti or La could suppress the mutual diffusion. We also observed the microstructures of the Fe–Al intermetallic multilayers and the distribution of Ti or La in the multilayers. A new quaternary phase was identified. The inhibitory effects of Ti and La were also explained by calculating the diffusion barrier energies with density functional theory.

Continuous fiber-reinforced TiAl-matrix composites are a potential structural material to satisfy the service requirements in space industry. Ta fiber with outstanding plasticity and toughness is regarded as a promising reinforcement. In this work, a 10 vol% Ta fiber-reinforced TiAl composite was prepared by combining slurry casting and vacuum hot pressing under condition of 1150 °C/ 35 MPa/ 2 h. Microstructure of interfacial reaction zone of the composite was investigated; meanwhile, thermodynamic calculation and theoretical analysis were conducted to explain the formation mechanisms of the reaction products. Three types of reaction products σ-Ta2Al, B2 and α2 phases were formed between Ta fiber and TiAl matrix. σ phase was adjacent to Ta fiber with a fine grain structure, which was formed due to the lowest formation free energy. The aggregation of β stabilizers in Ti-rich region resulted in the formation of B2 phase that was close to σ phase. α2 phase relied on B2 phase to nucleate and grow based on the Burgers relationship and their structure symmetry. Three-point bending tests show the fracture toughness (KIC) of the Taf/TiAl composite was 58% higher than that of pure TiAl matrix. The main toughening mechanism of the Taf/TiAl composite was plastic deformation of the Ta fiber, meanwhile the interfacial debonding also had a contribution to toughening the TiAl alloy. The interfacial debonding location was mainly at the Ta / LI-σ interface due to the existence of thermal residual stress.

Iron–chromium–aluminum (Fe–Cr–Al) alloys have great potential application as an accident-tolerant fuel cladding material in light-water reactors. It has excellent processing ability, resistance to steam oxidation at high temperatures (HTs), and irradiation swelling-resistance. It is necessary to improve the room- and high-temperature mechanical properties and reveal the strengthening mechanism. In this study, we analyzed the effect of Zr on the microstructure and room- and high-temperature tensile properties of hot- and warm-rolled FeCrAl alloys. The results show that the Laves phase could be effectively stabilized by Zr addition, and the proportion of low-angle grain boundaries increased. Moreover, the yield strength at room and high temperatures of the samples after Zr addition were improved, owing to the precipitation and sub-grain boundary strengthening by Zr. In addition, Zr changed the grain orientation, but had no relevance to the number of easier activated slip systems. The movable dislocation cannot slip during high-temperature tensile tests because of the pinning effect of the dynamic precipitated Laves phase, which could be the reason for the decrease in elongation at high temperatures.

The effect of intermediate annealing time on the microstructure, texture and mechanical properties of Al-Mg-Si-Cu alloys was studied by mechanical properties, microstructure and texture characterization in the present study. The results show that the intermediate annealing time has some influence on the microstructure, recrystallization texture, and final mechanical properties. After the pre-aging treatment and natural aging treatment (T4P treatment), in contrast to the sheet with short intermediate annealing time, the sheet with long intermediate annealing time possesses higher plastic strain ratio r value. Strength has no positive correlation with annealing time, and when applying the annealing time of 16 h, the strength is highest. Before solution treatment, the sheet with long intermediate annealing time has more particles with a larger average size, compared with the sheet with short intermediate annealing time. After solution treatment, they possess the similar recrystallization equiaxed grain structure and recrystallization texture. The sheet with short intermediate annealing time is comprised of CubeND {001} 〈310〉, Goss {110}〈001〉 and P {011}〈122〉 orientations, while the sheet with long intermediate annealing time possesses weak texture including CubeND {001}〈310〉, Goss {110}〈001〉 and {015}〈751〉 orientations. Finally, a particle dissolution model during solution treatment is proposed to explain the variation of strength with annealing time.

The microstructure evolution during the conventional single side friction stir welding (SS-FSW) and the bobbin tool FSW (BB-FSW) of 7085-T7452 alloy thick plate was extensively studied by using the state-of-the-art materials characterization techniques. The Electron backscattering diffraction results reveal that a significant grain refinement and a larger percentage of high angle grain boundaries (HAGBs) exist in the weld nugget zone (WNZ) and the thermal-mechanical affected zone (TMAZ) compared with the base material. Meanwhile, more obviously inhomogeneous refined grains and HAGBs in WNZ along the thickness direction and a larger percentage of low angle grain boundaries (LAGBs) were observed in SS-FSW joint than that in BB-FSW joint. The change of the average grain size is the result of friction heat and strain rate of plastic deformation combined with a certain degree of recrystallization. Moreover, the recrystallization is mainly controlled by the strain rate during the FSW process. The presence of Cube and Cube ND after welding shows that the discontinuously dynamic recrystallization (DDRX) is a major factor in the final microstructural response. The research and findings help the understanding of the mechanism of microstructure homogenization and further optimizing the welding process for application.

The microstructure evolution and mechanical properties of the compressively deformed AgInCd alloy during annealing treatment have been investigated in the present study. In the deformed AgInCd alloy, many deformation markings are formed and these deformation markings are mainly composed of nanoscale deformation twins. The AgInCd alloy exhibits a significant work hardening capability because of the formation of deformation twins. The recrystallization temperature of the deformed AgInCd alloy is between 300 °C and 350 °C. In the AgInCd alloy annealed at 300 °C, the deformation twins are eliminated and a large number of dark strips consisting of stacking faults are presented in the un-recrystallized regions, indicating that the deformation twins are transformed into stacking faults by the detwinning mechanism. The annealing twins show higher thermal stability than the deformation twins. The strength and microhardness of the deformed AgInCd alloy gradually decrease with the increase of annealing temperature.

To compare the dynamic recrystallization (DRX) behavior, microstructure evolution, and texture change of a new Mg-6Zn-1Gd-1Er alloy with and without pre-aging treatment, the uniaxial hot compression tests were carried out in the range of 10−3 s−1-1 s−1 and 280 °C–380 °C. The results show that both the fraction and size of DRX grain increase with the increase of temperature, while the increase of strain rate shows the opposite trend. The microstructure mostly exists as a necklace structure, while there are a lot of twins in the microstructure at the condition of 280 °C/1 s−1. DRX grains mainly nucleate and grow through the mechanisms of continuous dynamic recrystallization (CDRX), particle stimulated nucleation (PSN), and twin-induced dynamic recrystallization (TDRX). The pre-aging treatment sample is more conducive to DRX than the solution heat-treated sample at the same deformation conditions. This is mainly because the deformation activation energy of the alloy with pre-aging treatment is lower, and the interaction of the pre-existed precipitates with dislocations promotes the DRX behavior. At the condition of 380 °C/10−3 s−1, compared with the solution heat-treated sample, the pyramidal slip was active in the deformed grains of PT of pre-aging treatment alloy, which corresponded to the PT split from CD to TD and tilt about 15°. Similarly, at the condition of 380 °C/1 s−1, the main deformed grains of PT1 and PT2 in the pre-aging treatment sample tilted the basal texture from CD to TD under the action of pyramidal slip to form a bimodal texture.

The effect of Zn on the microstructure, texture evolution and mechanical properties of Al-Mg-Si-Cu alloys with a medium number of Fe-rich phase particles was investigated using tensile testing machine, optical microscopy (OM), scanning electron microscope (SEM), transmission electron microscope (TEM) and X-ray diffractometer (XRD) in the present study. The results show that Zn addition has a significant influence on the final mechanical properties, but a slight effect on microstructure and final recrystallization texture. Zn addition is favorable to increase yield strength, ultimate tensile strength and elongation, however it is detrimental to improve r value and reduce Δr value. During the thermomechanical processing, the microstructure almost has nothing to do with Zn addition. However, Zn could prevent the secondary phase particles from precipitating during intermediate annealing. In contrast to the alloy sheet without Zn, the alloy sheet with 1.0 wt% Zn always has weaker textures before final cold rolling, but a stronger texture after experiencing final cold rolling. After solution treatment, they almost possess the same recrystallization texture. Finally, the effect of Zn addition on the recrystallization texture was discussed. Their similar recrystallization texture can be attributed to the similar microstructure, which was caused by the medium number of Fe-rich phase particles.

Mg Zn intermetallic layer on AZ31 alloy was prepared by solid–state thermal diffusion under 20 MPa pressure. The surface microstructure, microhardness and corrosion resistance of sample were investigated using X–ray diffraction (XRD), optical microscope (OM), scanning electron microscope (SEM), microhardness tester and electrochemical workstation. As a result, the diffusion rate of Zn in AZ31 alloy with pressure was 10–fold higher than that of Zn without pressure, and Mg Zn intermetallic layer of 5 mm was produced at 390 °C within 2 h. The high–efficiency fabrication of Mg Zn intermetallic layer could be attributed to the increase of effective collision between Zn and Mg atoms by the application of pressure. During the fabrication procedure, microstructure evolution of Zn diffusion layer could be described as follow: Mg + Zn → Mg7Zn3 → MgZn + MgZn2. And the surface hardness as well as corrosion resistance of the sample first increased and then decreased after Zn diffusion treatment. For the first 1 h, Mg7Zn3 phase formed on AZ31 alloy, which raised the surface hardness to 220.0 HV0.2 and decreased corrosion current of AZ31 alloy about one order of magnitude in 3.5% NaCl solution. When the diffusion time was prolonged to 2 h, more complex phases (e.g., MgZn, MgZn2 and Mg7Zn3) were produced in the sample, and the voids and difference potentials among these Mg Zn intermetallic compounds led to the deterioration of surface hardness and corrosion resistance.

In this work, the hot workability of a spray formed 7055 aluminum alloy was successfully investigated through advanced Gleeble thermo-mechanical simulation technology, and the EBSD technology was adopted to analyze the evolution of deformation microstructure comprehensively. From the results, the occurrence of the adiabatic heating phenomenon is confirmed, and an abnormal stress drop caused by which is then corrected by the extrapolation method. Moreover, it is noteworthy that with rising deformation parameters (including deformation temperature T from 350 °C to 450 °C, strain rate e from 1 s−1 to 20 s−1 and true strain e from 0.1 to 0.8), the grains become finer, and the distributions of crystal orientation tend to be more homogeneous. Besides, it is found that both the Continuous Dynamic Recrystallization (CDRX) and Discontinuous Dynamic Recrystallization (DDRX) mechanisms coexist during hot deformation. Moreover, the increase of the three deformation parameters enlarges the misorientation angle inside the grains, which facilitates the DRX progress.

Transmission electron microscopy is utilized to investigate the microstructure development of iron-containing SiC fibers as a function of their annealing temperatures. Compositional and structural gradients along the radial directions start to form within SiC fibers fabricated at temperatures above 1200 °C. The graded microstructures are associated with the outward diffusion of iron-rich particles along the radial direction. In-situ heating TEM experiments suggest that the iron-rich particles within SiC fibers are highly mobile at elevated temperatures. Therefore, we propose that the graded microstructures along the radial directions are the synergetic effects of iron catalyzation and outgassing, namely, iron-rich particles are progressively driven to the surface of SiC fibers and in the trajectory of iron-rich particles, the decomposition of the amorphous SiCxOy phase is accelerated, promoting the growth of SiC grains. The current study emphasizes the important role of the outgassing process to the microstructure evolution of SiC fibers. Our proposed mechanism can be extended to understand the microstructural evolution of SiC fibers that use metallic additives as sintering aids.

In the present paper, the short fatigue crack behavior in wire arc additive manufactured (WAAMed) Ti-6Al-4V was investigated. It was found that the crack in the colony microstructure showed the highest fluctuation range (213 μm) because the crack deflected at the colony boundary. While the crack in the duplex microstructure showed the lowest fluctuation range (48.3 μm) because the crack cut through the αp (primary α) and αs (secondary α) directly. In addition, the short crack growth behavior was determined by the highest Schmid factor (M) and the burgers orientation relationship (BOR), which indicated that the short crack tended to pass through the α/β interface along with the basal slip systems within the shortest path distance. It was suggested that the short crack behavior with colony microstructure was determined by the α/β interface while the crack growth behavior with duplex microstructure was determined by the critical resolved stress (τCRSS) and the αs/β interface.

The effect of annealing at 1180 °C from 10 to 40 h on a wrought Ni 3 Al-based alloy was investigated using EBSD, SEM and TEM. We characterized the grain boundary character distribution (GBCD) of the annealed alloy and found that the frequency of Σ3 twin boundaries (TBs) decreased with the long term exposure. Both twinning and detwinning proceeded in the post-recrystallized microstructure during the thermal hold. The 10-hour annealing resulted in the highest frequencies of Σ3 TBs and the high order TBs. Σ3 TBs evolved into twin junctions via meeting of bulging corner twins and colliding of the nonparallel twins. With prolonged annealing, detwinning prevailed, shown by the decreasing frequency of Σ3 TBs, with simultaneous increase of fraction of substructured grains and subgrain boundaries (SGBs). Detwinning occurred via disintegration of primary twins, and dissociation of secondary microtwins/nanotwins that leads to partial formation of SGBs.

Damage mechanism of Alloy 690TT mated with Type 304 stainless steel (SS) subjected to fretting wear in partial slip regime was investigated. The results indicated that material transfer occurred in stick region and micro-slip region of the worn surfaces. The formation of tribologically transformed structure (TTS) was attributed to the dynamic recovery of deformed structures with high density of dislocations. The TTS layer was characterized by roughly equiaxed grains with an average size of ~ 282 nm. The oxidation behavior only occurred in micro-slip region, which resulted in the formation of the ultrafine-grained third body layer (TBL) containing the oxides of Ni(Cr,Fe) 2 O 4 and Cr 2 O 3 . The TBL was characterized as having a multilayered structure. The external part was mainly composed of Fe-rich oxides because of the Fe-rich material transferred from 304SS and its subsequent oxidation. The inner one contained Ni-rich oxides which was derived from the oxidized substrate of Alloy 690TT.

This study investigated the effect of Sc addition on the microstructure and mechanical properties of a high-Zn-concentration Al (Al–49Zn) alloy. The addition of 0.5Sc obviously refined the Al grains and Zn phases in the Al–49Zn alloy during solidification. It also suppressed the Al grain coarsening and Zn dissolution in the Al–49Zn alloy during heat treatment because of the pinning effect of nanoscale Al3Sc precipitates and Sc atoms. Given its refined structure and high thermal stability, the Al–49Zn–0.5Sc alloy showed high hardness and mechanical stability after heating.

The effects of massive laser shock peening (LSP) treatment with different pulse energies on surface roughness and microstructural evolution in the surface layer of AISI304 stainless steel were investigated. The deformation-induced grain subdivision processes under two LSP treatment conditions of 3 and 6 J pulse energies were characterized and presented, respectively. Subsequently, EBSD characterization was conducted to analyze the peaks of misorientation angle for as-machined sample and LSPed samples with different pulse energies. Furthermore, a novel MT–MT intersection with four directions was found for the first time in the plastic deformation layer of AISI304 stainless steel, and the generation mechanism was completely presented according to the inherited crystal structure of austenite stainless steel. The formation process of the surface roughness and the formed microstructure subjected to massive LSP impact treatment with different pulse energies were compared and revealed.

Cast-rolling AZ31 Mg alloy sheets were manufactured at four rolling speed ratios of 0.8, 1.0, 1.2 and 1.3. The results show that the basal texture can be weakened by differential speed rolling (DSR). The AZ31 alloy sheet manufactured at a speed ratio of 1.2 exhibits a fine microstructure with an average grain size of 10.3 μm. The yield strength, ultimate tensile strength and elongation-to-failure at this speed ratio are 145 MPa, 240 MPa and 28.5% at room temperature, respectively. These parameters mainly benefit from the fine grains and weakened basal texture. The AZ31 alloy sheets processed by the DSR exhibit a remarkable improvement in elongation-to-failure compared with the AZ31 alloy sheets processed by equal speed rolling (ESR) primarily due to the weakened basal texture at room temperature. However, the difference in elongation-to-failure of the AZ31 alloy sheets processed by the ESR and DSR decreases at elevated temperatures, which can be attributed to the weakening of the influence of basal texture, with probable activation of non-basal slips and grain boundary sliding (GBS). The results obtained here will shed light on some DSR methods, which is critical to the development of Mg alloys with high mechanical properties.

The microstructure and texture evolution of an AZ31 magnesium rolled sheet during quasi-static compression at strain rates of 10 − 3 s − 1 has been investigated by in situ electron backscattered diffraction. The influence of the initial and pre-deformed texture on the predominant deformation mechanisms during compression has been examined. It has been found that extensive grain reorientation due to {10 − 12} tensile twinning appeared when compressed along transverse direction. Tensile twin variants were observed under this loading condition, and different variants will cause an effect to the following deformation. Several twinning modes occurred with continuative loading along rolling direction.

The flow behavior of a powder metallurgy (P/M) Ti-22Al-25Nb alloy during hot compression tests has been investigated at a strain rate of 0.01 s − 1 and a temperature range of 980–1100 °C up to various true strains from 0.1 to 0.9. The effects of deformation temperature and strain on microstructure characterization and nucleation mechanisms of dynamic recrystallization (DRX) were assessed by means of Optical microscope (OM), electron backscatter diffraction (EBSD) and transmission electron microscope (TEM) techniques, respectively. The results indicated that the process of DRX was promoted by increasing deformation temperature and strain. By regression analysis, a power exponent relationship between peak stresses and sizes of stable DRX grains was developed. In addition, it is suggested that the discontinuous dynamic recrystallization (DDRX) and continuous dynamic recrystallization (CDRX) controlled nucleation mechanisms for DRX grains operated simultaneously during the whole hot process, and which played the leading role varied with hot process parameters of temperature and strain. It was further demonstrated that the CDRX featured by progressive subgrain rotation was weakened by elevating deformation temperatures.

Precipitate redistribution and texture evolution are usually two concurrent aspects accompanying grain refinement induced by various surface treatment. However, the detailed precipitate redistribution characteristics and process, as well as crystallographic texture in the surface refined grain layer, are still far from full understanding. In this study, we focused on the microstructural and crystallographic features of the sliding friction treatment (SFT) induced surface deformation layer in a 7050 aluminum alloy. With the combination of transmission electron microscopy (TEM) and high angle angular dark field scanning TEM (HAADF-STEM) observations, a surface ultrafine grain (UFG) layer composed of both equiaxed and lamellar ultrafine grains and decorated by high density of coarse grain boundary precipitates (GBPs) were revealed. Further precession electron diffraction (PED) assisted orientation mapping unraveled that high angle grain boundaries rather than low angle grain boundaries are the most favorable nucleation sites for GBPs. The prominent precipitate redistribution can be divided into three successive and interrelated stages, i.e. the mechanically induced precipitate dissolution, solute diffusion and reprecipitation. The quantitative prediction based on pipe diffusion along dislocations and grain boundary diffusion proved the distribution feasibility of GBPs around UFGs. Based on PED and electron backscatter diffraction (EBSD) analyses, the crystallographic texture of the surface UFG layer was identified as a shear texture composed of major rotated cube texture {001} 〈110〉 and minor {111} 〈112〉, while that of the adjoining lamellar coarse grained matrix was pure brass. The SFT induced surface severe shear deformation is responsible for texture evolution.

In this study, the SiC/Al-Zn-Mg-Cu nanocomposites were fabricated using high energy ball milling combined with spark plasma sintering (SPS) and hot extrusion. The microstructure and mechanical properties were investigated by utilizing X-ray diffraction (XRD), scanning electron microscopy (SEM) and high resolution transition electron microscopy (HRTEM) analysis as well as tensile tests. The results showed that the as-extruded SiC/Al-Zn-Mg-Cu nanocomposite samples demonstrated a microstructure consisting of ultrafine α-Al grains, dispersed SiC nanoparticles and nano-scaled T phases probably formed by dynamic precipitation during extrusion. After T6 heat treatment, the coarsening of α-Al grains, dissolution of T phases and consequently the precipitation of fine η′ phases occurred, leading to a simultaneous increase of the strength and ductility. With increasing the content of SiC nanoparticles from 1 vol% to 3 vol%, the yield strength (YS) and ultimate tensile strength (UTS) increased from 456 and 528 MPa to 580 and 588 MPa (27.2% and 11.4% increase), respectively while the elongation to fracture decreased slightly from 11.8% to 10.2% (13.6% decrease). Various strengthening mechanism calculation results show that Orowan strengthening was mostly contributed to the improved strength of the T6 heat treated SiC/Al-Zn-Mg-Cu nanocomposites.

In this work, a highly wear-resistant cooper matrix composite reinforced by in situ formed nano-NbC particles was synthesized by hot pressing mechanically alloyed Cu+Nb+C powders. The composite possesses a smaller friction coefficient and displays a wear rate (2.6 × 10−5 mm3N−1 m−1) two orders of magnitude lower than the micro-NbC reinforced Cu composites (123.5 × 10−5 mm3N−1 m−1). Such property enhancement is attributed to the hardness improvement and the solid lubricating effects induced by nanoscale niobium carbides/oxides as well as iron oxides. The oxidation and pulverization of NbC during friction have played a key role in increasing the wear resistance and their mechanisms are discussed. The findings provided a strategy for developing other wear-resistant composite materials.

The microstructures and mechanical properties of Hf compressed at the strain rates of 300 s−1、1290 s−1 and 2800 s−1 were investigated. At a strain rate of 300 s−1, dislocation slip dominated the deformation. Meanwhile, a small number of the face-centered cubic (FCC) lamellas formed via hexagonal close-packed (HCP) structure to FCC structure transformation. As the strain rate increased to 1290 s−1, both the dislocation density and the number of the FCC lamellas increased significantly. When the strain rate reached 2800 s−1, dislocation slip, phase transformation, twinning, dynamic recrystallization and shear banding occurred in the material. However, the number of the FCC lamellas decreased significantly at the strain rate of 2800 s−1, indicating that the HCP to FCC phase transformation was restrained. The temperature rise inside the specimens compressed under the strain rate of 2800 s−1 promoted deformation twinning and dynamic recrystallization. The microhardness increased gently for the specimens compressed at strain rates of 300 s−1 and 1290 s−1, while when the strain rate increased to 2800 s−1, the microhardness increased substantially. The formation of various boundary structures, including microbands, twins and FCC bands, contributes to the hardness increase by acting as obstacles to dislocation motion. In addition, the formation of new grains by dynamic recrystallization also played a role in strengthening.

The ordering transformation occurring in a model Ni-Cr-W superalloy during prolonged exposure to proper temperature has been investigated systematically. It is demonstrated that nanometer-sized precipitates with a DO 22 structure can precipitate in the Ni-Cr-W alloy by means of simple aging treatment at 650–700 °C. The mechanism of transformation to DO 22 superlattice has been determined to be continuous ordering based on the results of high resolution transmission electron microscopy investigation and variation trend in Vickers microhardness. Different variants of DO 22 phase can coexist in the matrix with no signs of overaging as aging time increases, indicating it has a high thermal stability. The precipitates of DO 22 superlattice has been found to be of ellipsoidal shape which results in the greatest reduction of strain energy. The interfaces between DO 22 precipitates and matrix have been revealed to be coherent at the atomic scale, resulting in considerable coherency strain attributing to the lattice misfit between DO 22 particle and matrix. Because of the high-density nanometer-sized DO 22 phase, the microhardness of the alloy has been improved remarkably after aging treatment.

NiO porous nanosheets were synthesized by a facile hydrothermal reaction and subsequent calcination in air. Oxygen vacancies were generated by reducing treatment under H2/Ar atmosphere at an elevated temperature. The phase composition, morphology, microstructure and chemical composition of the samples were investigated by X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscope (TEM), and X-ray photoelectron spectroscopy (XPS). When used as the anode materials for lithium ion batteries, the optimized NiO electrode possessed a reversible capacity of 678.8 mAh g−1 after 30 cycles at a current density of 0.1 A g−1, while the reversible capacity of the untreated electrode was only 82.5 mAh g−1. At a higher current density of 1.0 A g−1, the reversible capacity was 152.2 mAh g−1, which is 15 times larger than that of the pristine NiO electrode. The synergistic effects of optimized oxygen vacancies and porous sheet-like morphology are responsible for the enhanced lithium storage properties.

A Mg-11.00Gd-1.77Zn-0.43Zr (wt.%) alloy named GZ112K was prepared by selective laser melting (SLM) with different processing parameters. The formability, element vaporization, microstructure and tensile properties of the SLMed samples at different scanning speed and hatch spacing were characterized. The process map at a constant laser power of 80 W for the alloy has been established. It shows that the optimum scanning speed and hatch spacing are 300–700 mm/s and 100 μm respectively. The SLMed samples have fine grains of about 2 μm and dispersed eutectic phase of β-(Mg,Zn)3Gd due to the very high cooling rate, high solid solubility of Gd and Zn elements in ɑ-Mg matrix owing to the effect of solute trapping. The SLMed GZ112K alloy with scanning speed of 300 mm/s and hatch spacing of 100 μm has yield strength (YS) of 325 MPa, ultimate tensile strength (UTS) of 332 MPa and elongation of 4.0% at room temperature. Compared with as-cast alloy, the SLMed GZ112K alloy has much higher YS (+162 MPa), UTS (+122 MPa) and comparable elongation (+0.4%).

The effect of welding heat input characterized by the cooling time taken from 800 °C to 500 °C (t8/5) on the microstructural evolution, V(C,N) precipitation and resultant mechanical properties of the simulated CGHAZ in high-N V-alloyed steel was comparatively investigated using a Gleeble-1500D thermomechanical simulator. Metallographic analysis indicated that the dominant microstructure transformed from lath bainite to granular bainite when t8/5 increased from 30 s to 90 s and then changed to intragranular ferrite at t8/5 of 180 s. The nanoscale V(C,N) precipitates were coarsened as t8/5 increased, coupled with a slightly increased number density. Furthermore, the orientation relationship [001]α// 1 1 ¯ 0 V(C,N) reduced the interfacial structural energy (MC/α) and enhanced the V(C,N) precipitation in the ferrite matrix. Moreover, the microhardness progressively decreased due to the combined effect of microconstituents, precipitates and grain boundaries. The impact toughness first decreased and then increased, and the optimal value was obtained at t8/5 of 180 s. Furthermore, the formation of intragranular ferrite, especially acicular ferrite, and the increased fraction of high angle grain boundaries could completely remedy the detrimental effect caused by the increased content of grain boundary ferrite and the coarsened effective grain size and precipitates. In addition, the high nitrogen content of 240 ppm accelerated V(C,N) precipitation in the austenite region, and the submicron V(C,N) precipitates could promote the formation of intragranular ferrite by providing heterogeneous nucleation sites, in combination with the larger prior austenite grain size caused by higher welding heat input.

In order to study the strengthening mechanisms in the multi-phase (FCC + BCC) high-entropy alloy cladding layer, FeCoCrNiAl1.0 coating was fabricated by laser cladding technology. For comparison, single phase (FCC) FeCoCrNiAl0.3 coating, pure copper, and pure iron were also considered. XRD analysis, optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscope (TEM) were used to investigate the evolution of phases and microstructures in the materials. The hardness and tensile property of the materials were investigated using micro-hardness and small punch tests. It was found that Al element could promote the formation of BCC solid solutions. The solidification pattern of coatings changed from columnar to equiaxed crystals. The FeCoCrNiAl1.0 high-entropy alloy cladding layer (FCC + BCC) exhibited the best mechanical properties. Furthermore, the strengthening mechanisms in the multi-phase high-entropy alloy cladding layer were analyzed systematically. The rapid solidification in the laser cladding process resulted in the formation of fine grains that strengthened the material. In addition, the FCC and BCC lattice structures contain different slip directions and types of dislocation. The lattice distortions of the two crystal structures were determined by calculating the interplanar spacings and the interplanar angles. Under external load, the FCC and BCC phases in the multi-phase high-entropy alloy cladding layer experienced different degrees of displacements, which also played a role in strengthening the material.

The effects of the processing parameters on the grain size and volume fraction of equiaxed α for Ti–5Al–5Mo–5V–1Cr–1Fe are quantitatively investigated using isothermal compression tests. The microstructure features, such as the morphology of equiaxed and acicular α phase, the dislocation distribution, the formation of substructure are in depth discussed with the help of transmission electron microscopy (TEM) and scanning electron microscopy (SEM) experiments so as to clarify the deformation mechanisms. The results show that few DRX α grains appear in the α + β phase region. In the β phase region, selective DRX occurs and the amount of DRX increases with increasing strain rate. DRV is main softening mechanism in the tested deformation temperature range. The elongated β grains are observed at medium deformation temperatures and lower strain rates. This phenomenon demonstrates that β phase is mainly involved in the deformation. At higher deformation temperatures and lower strain rates, acicular α is not observed for this alloy. Possible reason is that acicular α dissolves into the β matrix.

Laser-clad composite coatings on the Ti6Al4V substrate were heat-treated at 700, 800, and 900 °C for 1 h. The effects of post-heat treatment on the microstructure, microhardness, and fracture toughness of the coatings were investigated by scanning electron microscopy, X-ray diffractometry, energy dispersive spectroscopy, and optical microscopy. The wear resistance of the coatings was evaluated under dry reciprocating sliding friction at room temperature. The coatings mainly comprised some coarse gray blocky (W,Ti)C particles accompanied by the fine white WC particles, a large number of black TiC cellular/dendrites, and the matrix composed of NiTi and Ni3Ti; some unknown rich Ni- and Ti-rich particles with sizes ranging from 10 nm to 50 nm were precipitated and uniformly distributed in the Ni3Ti phase to form a thin granular layer after heat treatment at 700 °C. The granular layer spread from the edge toward the center of the Ni3Ti phase with increasing temperature. A large number of fine equiaxed Cr23C6 particles with 0.2–0.5 μm sizes were observed around the edges of the NiTi supersaturated solid solution when the temperature was further increased to 900 °C. The microhardness and fracture toughness of the coatings were improved with increased temperature due to the dispersion-strengthening effect of the precipitates. Dominant wear mechanisms for all the coatings included abrasive and delamination wear. The post-heat treatment not only reduced wear volume and friction coefficient, but also decreased cracking susceptibility during sliding friction. Comparatively speaking, the heat-treated coating at 900 °C presented the most excellent wear resistance.

x wt% (x = 0, 0.03, 0.40) Sn addition in Al-Mg-Si alloys were prepared to investigate the effect of Sn on the performance of Al-Mg-Si alloys. Optical microscope (OM), scanning (SEM) and transmission electron microscope (TEM) were applied to observe the microstructure of these alloys. X-ray diffraction (XRD) was used to investigate the phase component among different alloys. Electrochemical polarization measurements and intergranular corrosion test were used to investigate the corrosion behaviors of these alloys. The experimental data shows that 0.03 wt% Sn can slightly enhance mechanical properties and corrosion resistance of Al-Mg-Si alloys because of the smaller precipitate free zones (PFZ) area and grain boundary refinement. Higher Sn addition (0.4 wt%) may cause detrimental effect on both mechanical properties and corrosion resistance of Al-Mg-Si alloys. Excess Sn tends to replace part of Si in Mg2Si phase and forms Mg2(Si,Sn) phase which is thought to be an anodic phase compared to Al matrix. Electrochemical measurements may not comprehensively reveal the overall corrosion processes, such as de-alloying process of Mg2(Si, Sn) phase and thus enrichment of Sn which leads to much faster dissolution of Al.

In order to improve the electrochemical discharge and kinetics of CeMg12-type hydrogen storage materials, ball-milling was used and Ni was added to fabricate alloying materials with a nanocrystalline and amorphous structure. The phase composition and crystalline structure were characterized by X-ray diffraction (XRD) and high resolution transmission electron microscopy (HRTEM). The electrochemical discharge performances were characterized by determining the discharge capacity and electrochemical cycling stability. High-rate dischargeability (HRD), electrochemical impedance spectroscopy (EIS), and potentiodynamic polarization were utilized to investigate the changes in electrochemical kinetics. The results indicate that the addition of Ni significantly enhances the glass-forming ability of the alloy samples during ball milling, which significantly improves the electrochemical cycling stability of the alloy samples. The maximum discharge capacity of the ball-milled composites monotonously increases from 41.7mAh/g to 485.5 mAh/g with an increment in the Ni content from 50 wt>% to 200 wt%. An increase in the Ni content results in a considerable reduction in the enthalpy (ΔH) from −106.2 kJ/molto −43.1 kJ/mol and in the entropy (ΔS) from −350.73 kJ/mol/K to −22.49 kJ/mol/K. The addition of Ni reduces the stability of the hydride and improves the electrochemical discharge capacity. With regard to the electrochemical kinetics, the addition of Ni can diminish the activation energy of the alloy samples from74.02 kJ/mol to 33.28 kJ/mol with an increase in the Ni content from 50 wt% to 200 wt%, which speeds up the charge-transfer reaction on the surface. The addition of Ni accelerates the hydrogen diffusion rate(which is related to the limiting current density IL) inside the alloy particles. These effects improve the electrochemical kinetics.

In this study, the effect of magnesium addition on the inclusion formation in SS400 steel was investigated. The experimental specimens with and without Mg addition treatment were compared. The microstructure was observed using optical microscopy after etching with 3% nital. The morphology and chemical composition of the inclusions were analyzed via scanning electron microscopy and energy dispersive spectrometry. The lattice structure and orientation of the inclusions were identified by electron backscattering diffraction. The average size of inclusions in SS400 was between 0.67 and 0.75 μm, and between 0.65 and 0.68 μm in SS400 + Mg. The 2 ppm Mg addition resulted in the oxide formation change from Al 2 O 3 to MgO·Al 2 O 3 and in the inclusion formation change from Al 2 O 3 –MnS to MgO·Al 2 O 3 –MnS. Moreover, a simple-phase MnS with an average grain size of 1 μm to 2 μm was observed in rod-like, globular, and polyhedron forms.

Irradiation damage in P92 ferritic/martensitic steel irradiated by Ar{sup +} ion beams to 7 and 12 dpa at elevated temperatures of 290 Degree-Sign C, 390 Degree-Sign C and 550 Degree-Sign C has been investigated by transmission electron microscopy, scanning electron microscopy and atomic force microscopy. The precipitate periphery (the matrix/carbide interface) was amorphized only at 290 Degree-Sign C, while higher irradiation temperature could prevent the amorphization. The formation of the small re-precipitates occurred at 290 Degree-Sign C after irradiation to 12 dpa. With the increase of irradiation temperature and dose, the phenomenon of re-precipitation became more severe. The voids induced by irradiation were observed after irradiation to 7 dpa at 550 Degree-Sign C, showing that high irradiation temperature ({>=} 550 Degree-Sign C) was a crucial factor which promoted the irradiation swelling. Energy dispersive X-ray analysis revealed that segregation of Cr and W in the voids occurred under irradiation, which may influence mechanical properties of P92 F/M steel. - Graphical Abstract: High density of small voids, about 2.5 nm in diameter, was observed after irradiation to 12 dpa at 550 Degree-Sign C, which was shown in panel a (TEM micrograph). As shown in panel b (SEM image), a large number ofmore » nanometer-sized hillocks were formed in the surface irradiated at 550 Degree-Sign C, and the mean size was {approx} 30 nm. The formation of the nanometer-sized hillocks might be due to the voids that appeared as shown in TEM images (panel a). High irradiation temperature ({>=} 550 Degree-Sign C) was a crucial factor for the formation of void swelling. Highlights: Black-Right-Pointing-Pointer Small carbides re-precipitated in P92 matrix irradiated to 12 dpa at 290 Degree-Sign C. Black-Right-Pointing-Pointer High density of voids was observed at 550 Degree-Sign C. Black-Right-Pointing-Pointer Segregation of Cr and W in voids occurred under irradiation.« less

In this study, the microstructures and mechanical properties of Ti–10Mo and Ti–20Mo alloys (mass%) are investigated to assess the potential use in biomedical applications. The microstructures are examined by X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). The mechanical properties are determined from uniaxial tensile tests. The experimental results indicate that the microstructures and mechanical properties of Ti–Mo alloys are dependent upon the cold rolling, solution heat treatment, and Mo content. The Ti–10Mo alloy exhibits (α″ + β) and (β + ω) phases under the cold rolling (CR) and solution treatment (ST), respectively. By contrast, the Ti–20Mo alloy comprises only β phase under such conditions. The quenched Ti–20Mo alloy has the lowest elastic modulus and CR Ti–20Mo alloy has the highest tensile strength. The quenched Ti–10Mo alloy exhibits the excellent ductility and two-stage yielding from stress-strain curves due to the stress-induced martensite transformation from β to α″ during tensile deformation. These Ti–Mo alloys exhibit low yield strength and good ductility, and they are more suitable for biomedical applications than the conventional metallic biomaterials from the viewpoint of better mechanical compatibility. The quenched Ti–10Mo alloy has some advantages over the other β binary Ti–Mo alloys for biomedical applications. β type Ti–Mo–Sn alloys are expected to be promising candidates for novel metallic biomaterials.

Microstructural transformations of near-alpha titanium alloy under laser-surface -melted and post-heat treated conditions were systematically investigated. The results show that, after laser surface melting treatment, a melted zone and a heat-affected zone are formed in the titanium alloy. The melted zone consists of columnar grains, which are characterized by fine a″ phase, distributed dispersively in acicular martensite phase α′. Martensite transformation occurs at a lower temperature in post-heating process. The α phase in the laser-surface-melted zone is further refined during the recrystallization, and a fine dispersive α + β microstructure is formed when experienced post-heat treatment at an elevated temperature.