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In this paper, the evolution of precipitate phases in 9CrMoCoB (CB2) steel after tempering at 650 °C for different times has been investigated using transmission electron microscopy. As the tempering time prolonged from 0 to 100 h, four types of secondary phases consisting of M 3 C, M 2 X, M 7 C 3 and M 23 C 6 were identified in the experimental steel. It was found that the needle-like M 3 C carbides could be precipitated during both the air cooling process after austenization and the early stage of tempering. After tempering for 15 to 120 min, fine M 2 X particles were observed. The precipitation and growth of M 2 X were derived from the partially consumption of M 3 C carbides. After tempering for 50 h, M 2 X disappeared, while the rod-like M 7 C 3 carbides were observed to be precipitated independent of the early formed M 3 C precipitates. After tempering for 100 h, only M 23 C 6 carbides persisted, of which the number density and size kept increasing throughout 30 min to 100 h owing to their high thermostability. In addition, the precipitation mechanisms of the four types of precipitates were explained, and the relationship between the measured hardness values and microstructure was discussed. • Precipitates evolution in 9CrMoCoB (CB2) steel during tempering has been investigated. • M 3 C precipitated during both the air cooling process after austenization and the early stage of tempering. • The precipitation sequence can be given as follows: M 3 C → M 2 X → M 7 C 3 → M 23 C 6. • Hardness reduction rate of specimens decreased with the tempering time increasing. [ABSTRACT FROM AUTHOR]

Effect of dissolution and precipitation of Nb on the phase transformation during cooling was investigated. It is firstly recognized that either the formation of acicular ferrite or the separation of bainite ferrite could be adjusted by the preparation of the steel specimens with different amounts of solute Nb and Nb-precipitates in austenite (isothermally holding at 850°C for different durations). An increase in isothermal duration at 850°C would spawn more Nb(CN) precipitates, leading to a microstructural evolution from bainite ferrite to acicular ferrite/bainite ferrite dual phase, and eventually to acicular ferrite in the final microstructure. This could be explained by the solution of Nb in the austenite, due to the solute dragging effect of Nb, can decrease the Ar3 temperature and promote the formation of bainite ferrite, while the precipitation of NbC can increase the Ar3 temperature and promote the formation of acicular ferrite by increasing the nucleation sites of acicular ferrite. Thus, the properties of acicular ferrite/bainite ferrite dual phase steel can generally be improved by appropriately controlling the state of Nb (Nb(CN) as precipitates and Nb in solution) in the austenite before cooling, which provides a new approach to the modification of acicular ferrite/bainite ferrite ratio. [ABSTRACT FROM AUTHOR]

In this work, we creatively introduced MAX additives (Ti 2 AlC) into W alloy system to break the development bottleneck of ball milling technology: a large amount of oxygen impurities and large-sized second phase particles at grain boundaries (GBs). Unlike traditional oxides/carbides, Ti 2 AlC can undergo self-decomposition during high-temperature sintering stage (>1400 °C) on the basis of hydrogen sintering, and continue to adsorb a number of stubborn oxygen impurities to form various smaller, more dispersed, and stronger in-situ Ti x C y , TiO x , Al 2 O 3 , and Al x Ti y O z nanoparticles. Furthermore, these in-situ nanoparticles could maintain stable coherent interfaces with W, thereby more effectively refining, purifying, and strengthening matrix. Compared to traditional W-carbide/oxide alloys, MAX additives render our alloy with high hardness (521 ± 24 HV 0.2), a remarkable combination of high compressive strength (1262.9 ± 35.1 MPa) and large ductility (9.88%). This work provides a new perspective for the preparation of high-performance refractory metals and relevant engineering application. • The MAX phase (Ti 2 AlC) is innovatively added into W alloys. • The Ti 2 AlC phase decomposes at above >1400 °C and forms in-situ nanoparticles. • The Ti 2 AlC phase continues to adsorb stubborn oxygen impurities at sintering stage. • In-situ nanoparticles could maintain stable coherent interfaces with W. • The W-Ti 2 AlC alloy possess excellent mechanical properties. [ABSTRACT FROM AUTHOR]

To promote the wide application of the G115 steel in ultra-supercritical (USC) power plants, creep deformation, microstructure evolution and rupture mechanism of the G115 welded joint were systematically investigated. The fabricated G115 welded joint exhibits superior creep strength to the P92 or MARBN steels. The deformation behaviors are analyzed by the Norton's power law, proving that the deformation mechanism is closely associated with the stress levels. During short-term creep under higher stress, the weld metal (WM) and heat-affected zone (HAZ) exhibit outstanding microstructure stability, and the rupture occurs within the base metal (BM) due to the lath fracture. While, during long-term creep under lower stress, the brittle Type IV cracking occurs within the inter-critical heat-affected zone (ICHAZ) or fine-grained heat-affected zone (FGHAZ) due to the formed micro-voids along boundaries, obviously deteriorating the creep strength. The weld strength reduction factors are calculated under different stresses, and prove that synergistic action of back stress and dislocation motion can enhance the creep resistance of the G115 welded joint. Additionally, the allowable service stress of G115 weldments should be designed according to the creep strength of the welded joints under expected performance life. • The fabricated G115 welded joint displays superior creep strength to the P92 and MARBN steels, and the deformation mechanism is varied with the applied stress. • As the stress is lower than 180 MPa, brittle Type IV cracking occurs within the FGHAZ or IGHAZ in the G115 welded joint, which can be ascribed the coarsening of M 23 C 6 particles and the rapid recovery of dislocations. • Synergistic actions of the back stress and dislocation motions in equilibrium condition can reinforce the creep strength of the G115 welded joint. [ABSTRACT FROM AUTHOR]

The effect of carbonitrides on the growth of austenite grains in high-strength low-alloy (HSLA) steel was investigated through microstructure analysis and high-resolution dilatometry. The austenite grain growth at various temperatures was measured in situ using high temperature laser scanning confocal microscopy. Two kinds of precipitates with different morphologies containing large amounts of Ti and Nb were observed in the austenitized samples at different temperatures. The smaller Nb-rich spherical carbonitrides dissolved at the higher temperature, while the lager Ti-rich rectangular carbonitrides have a higher thermal stability and can pin at the austenite grain boundary. This study reveals that the dissolution of Nb in austenite causes the rapid growth of austenite grains and slows down the ferrite phase transition, which is beneficial to the formation of bainite. A kinetic model of austenite growth considering the dynamic dissolution of different types of carbonitrides is proposed. The results of the model show the same overall trend as the experimental results, and the individual differences can be explained. The proposed model can be used to predict the austenite grain size during the austenitizing process of HSLA steel and can reflect the austenite grain change throughout the process more continuously. • Two carbonitrides with different thermal stability at the high temperature were found. • The dissolution of Nb element affect the austenite grain size and also affect the phase transition in the cooling process. • Providing a new method to predict the pinning pressure and the austenite grain size with increasing time from dynamics. [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]

The little TiC was added into Mo alloys by facile ball milling and subsequent sintering. Interestingly, ultrafine Mo-TiC alloy (6.53 μm) possesses quasi-cleavage transgranular fracture morphology, which is differed from traditional intergranular fracture morphology of oxide-dispersion-strengthened molybdenum (ODS-Mo) alloy. The alloy interface with the lowest strength changes from Mo grain boundaries (GBs) to grain interior, hence the crack propagates along grain interior. For one thing, some C-deficient TiC (Ti 8 C 5) can adsorb adjacent impurity oxygen at sintering stage to generate in-situ TiO x , thereby purifying Mo matrix. For another thing, coherent interfaces between TiC/TiO x particles and Mo further strengthen Mo matrix. Moreover, a lot of TiC/TiO x particles within Mo grains could efficaciously accumulate dislocations and indirectly improve GBs strength. Compared to ball-milled Mo or ODS-Mo alloy reported in literatures, the sintered Mo-TiC alloys in present work possess a high hardness (468 HV 0.2), an excellent match of high strength (1287.3 MPa) and large ductility (18.1%). • Ultrafine Mo-TiC alloy (6.53 μm) possesses novel quasi-cleavage transgranular fracture morphology. • C-deficient TiC can adsorb impurity oxygen to generate TiO x and thereby purify matrix. • Coherent interfaces between TiC/TiO x particles and Mo further strengthen Mo matrix. • The Mo-TiC alloy possesses a high hardness of 468 HV 0.2. • The Mo-TiC alloy has both high strength (1287.3 MPa) and high ductility (18.1%). [ABSTRACT FROM AUTHOR]

Vacuum diffusion bonding at a relatively low temperature is a recognized method for restraining intermetallics and optimizing joint microstructure. The surface self-nanocrystallization (SSN) treatment by shot peening technology is applied on the surface before bonding a couple of Ni 3 Al-based superalloy and S31042 steel, which lowers the bonding temperature for achieving a sound joint by 100 °C. Moreover, the joint strength of samples bonding at 1000 °C after SSN treatment is 178 MPa higher than that of the bonded samples at 1100 °C without SSN treatment. SEM, XRD and TEM analyses indicate SSN treatment improves bonding efficiency by increasing surface micro-deformation and introducing nanocrystalline and deformed layer. The formation of disordered Ni-solution on the surface makes γ' strengthening phase re-precipitates in the joint and hard-brittle phase of AlN is restrained by diffusion bonding at 1000 °C. The good metallurgical bonding, re-precipitated γ' phase and the formation of refining grains zone near the bonding interface contribute to the good performance of 1000 °C-bonded samples after SSN treatment. • SSN technology realized the disordering in surface of Ni 3 Al-based superalloy. • The sound bonded joint was achieved at a lower temperature by SSN technology. • The low-temperature bonding restrained the formation of AlN phase. [ABSTRACT FROM AUTHOR]

Abstract Ti 2 AlNb-based alloys, spark plasma sintered from ball-milled octahedral Ti-22Al-25Nb powder, are aged for 0–3 h in this study. Ball milling tunes the morphology of primary orthorhombic (O) phase to be columnar, and improves the mechanical properties of the alloys. The evolution of the Widmanstätten O phase, which brought main precipitation strengthening effect, is then investigated during the ageing process. The hardness of the alloys is improved by an increasing content of O phase and the reduced width of the Widmanstätten O phase; in addition, the length of Widmanstätten O phase also brings positive effect on the hardness, which indicates that the hardness is strongly coupled with the interface of the Widmanstätten O precipitates and B2 matrix. By means of transmission electron microscopy observation, the precipitation of O initials with an amorphous state, followed by a coherent interface between (110) B2 and (002) O , which is destroyed to be semi-coherent and incoherent during the next ageing stage. Graphical Abstract Unlabelled Image Highlights • Ball milling tunes the morphology of primary O phase in Ti 2 AlNb alloys. • The interface of Widmanstatten B2 and O affects the hardness of the alloys. • The entire precipitation process of Widmanstatten O phase is reported. [ABSTRACT FROM AUTHOR]

Allvac 718Plus alloy is a newly-developed Ni-based superalloy with excellent thermal stability and mechanical performance at elevated temperatures up to 704 °C. The precipitation behavior of the rapidly-solidified Allvac 718Plus superalloy during aging is systematically investigated in this work. The microstructure evolutions of the strengthening γ' phase and the γ'/γ″ co-precipitates during aging are examined. During aging, the "duplet" γ'/γ″ and "triplet" γ″/γ'/γ″ occur and then disappear due to the dissolution of γ″ phase, which is promoted by the δ precipitation. On the contrary, the "triplet" γ'/γ″/γ' forms and remains after aging, resulting from the low diffusion rate of solute atoms through the spheroidal γ' precipitates. The lamellar δ-Ni 3 Nb phase occurs at grain boundaries. Its size and content increase with the prolongation of aging time. After long-term thermal exposure, the hexagonal η phase forms at the δ-γ interface due to the variations of local chemical composition, and then the tetragonal Cr-rich σ phase nucleates adjacent to the δ and η particles because of the segregation of Cr atoms rejected from the δ and η particles. • The rapidly-solidified γ-matrix of 718Plus is obtained with a supersaturated solid solution and a high density of defects. • The dissolution of ellipsoidal γ″ results in the disappearance of the "duplet" γ'/γ″ and "triplet" γ″/γ'/γ″. • The "triplet" γ'/γ″/γ' is remained due to the low diffusion rate of solute atoms through the spheroidal γ' precipitates. • The lamellar δ forms first and the η and σ phases successively nucleate at the δ-γ interface after long-time thermal exposure. [ABSTRACT FROM AUTHOR]

The roles of the alloying elements, Ti and Ta, on the γ' strengthening phase and the corresponding high temperature deformation responses of the CoNi-based superalloys have been systematically investigated. The results indicate that addition of either 4 at.% Ti (4Ti) or 2 at.% Ta (2Ta) can significantly increase the volume fraction of the γ' phase. Detailed analysis of the deformation mechanisms and Gibbs free energies of each phase in the two alloys at elevated temperatures were carried out by using the transmission electron microscopy (TEM) characterization and the thermodynamic calculation, respectively. The dislocations shearing into the γ' precipitates is the primary deformation mechanism in both alloys when deformed at 600 °C. However, when increasing the deformation temperature to 800 °C, the dislocation cross-slipping and by-passing mechanism dominants the 4Ti alloy's deformation, while the additional stacking faults (SFs) were introduced to the 2Ta alloy due to the lower barrier energy of the SFs formation. Continuing increasing the deformation temperature to 1000 °C will promote the dislocation-based mechanisms by lower the dislocation propagation resistance in both alloys. The process will also induce the mechanical twins in the 2Ta alloy which can further strengthening the alloy. The alloying induced deformation mechanism transition and the related high-temperature mechanical performance of the CoNi-based superalloys have been further discussed. • Adding Ti or Ta to the CoNi-based alloy will improve its γ' volume fraction to 60% • Ti and Ta will improve the flow strength at medium and high temperature, respectively • Ta can reduce the energy barrier for stacking fault formation at high temperature • Deformation mechanisms at elevated temperatures can be altered by the alloy elements [ABSTRACT FROM AUTHOR]

The microstructural evolution during long-term thermal exposure of Alloy 617 is investigated in detail. During processing, various precipitation phases were formed, including MC, M 23 C 6 , M 6 C and γ', in which the M 23 C 6 carbide is the primary strengthening phase and determines the hardness of Alloy 617. The M 23 C 6 carbides can either form from decomposing MC or precipitate directly from the γ matrix, but they most eventually transformed to M 6 C carbides after long-term aging. In addition to the phase transformation among various carbides, the morphology evolution of M 23 C 6 carbide is found to have a significant effect on the formation of γ' phase, which is closely related to the redistribution behavior of Al and Ti between M 23 C 6 and γ matrix. We also identified a faster evolution kinetic of the precipitates at grain boundary than those in grain interior, which is caused by the different local diffusion rates. This work elucidates the transformation sequence among different precipitates and the corresponding alloy element redistribution behavior during aging Alloy 617, which shed lights on the strengthening phase design and can in turn optimize the mechanical properties of Alloy 617. • The study reveals the variation of precipitates during long-term aging and its strong link to the element diffusion and redistribution behaviors. • The morphology evolution of M 23 C 6 carbide can promote the precipitation of γ' particles. • The evolution between different precipitated phases is much faster at grain boundary than that in grain interior. • M 23 C 6 carbide is mainly strengthening phase, which determines the hardness of Alloy 617. [ABSTRACT FROM AUTHOR]

In DELTA processing of Inconel 718 alloy, δ phase plays a vital role in final grain refinement, whose precipitation during intermediate thermal cycles is tailored by prior wrought structure. Therefore, it is necessary to renew insights into the effect of wrought structure on the morphology and quantity of δ phase. From this point, this work was conducted to investigate the δ precipitation behaviors in wrought Inconel 718 alloy. The results show that the δ precipitation behaviors are tailored by prior dynamic recrystallization (DRX) degree. Under partial DRX, δ precipitation exhibits twofold characteristics of preferential GB-precipitation accompanied by sluggish intragranular precipitation; while modified into predominant homogeneous GB-precipitation by fully DRX, in spite of the presence of few intragranular δ precipitates. After hot deformation, the equilibrium δ content is improved and inversely proportional to DRX degree. After 24 h aging at 900 °C, the volume fraction of δ phase is 38.6% and 27.9% for partial and fully DRX, respectively, compared to 15.1% for strain-free state. The GB-δ nucleation process is accelerated due to the occurrence of DRX, and firstly finished in few minutes; differently, the intragranular δ nucleation is grain-dependent, that promoted within unrecrystallized grains but inhibited within DRX grains. The “encounter” phenomena are observed during δ growth, and some particular coalescence mechanisms are proposed. [ABSTRACT FROM AUTHOR]

The microstructure and corrosion behavior of Al–10%Mg 2 Si alloy after heat treatment are investigated. For Al–10%Mg 2 Si in 3.5 wt.% NaCl solution, corrosion of α -Al phase initiates in (Al + Mg 2 Si) binary eutectic zones with electrochemical polarity change of Mg 2 Si phase, and expands along the eutectic Mg 2 Si precipitates. After heat treatment, eutectic Mg 2 Si transforms from long flakes and rods to short fibers, disks and spheroidized particles. The transformation of eutectic Mg 2 Si phase suppresses the rapid expansion of corrosion pits, which leads to enhancing the corrosion resistance of Al–10%Mg 2 Si alloy. [ABSTRACT FROM AUTHOR]

The development of a method for bonding W–Y 2 O 3 composites and CuCrZr heat sinks, which can meet the requirements of future magnetic confinement fusion devices, is a key problem that needs to be urgently solved. In this work, CuCrZr was vacuum-diffusion-bonded with W–Y 2 O 3 modified using surface nanoporosification, Cu magnetron sputtering, and annealing. Columnar Cu grains grew perpendicular to the surface nanoporous structure with a preferential Cu [111] orientation during sputtering deposition. A Cu layer was formed on the W–Y 2 O 3 nanoporous surface after Cu sputtering deposition and annealing, resulting in an interlocked and tightly bonded interface. The obtained W–Y 2 O 3 /CuCrZr joint exhibited a shear strength of 217 MPa, which was much higher than that of a joint without interface modification (147 MPa). The interface of the W–Y 2 O 3 /CuCrZr joint was composed of an interaction layer formed by nano-sized W particles and sputter-deposited Cu. Deposited Cu was embedded in the surface nanopores on W–Y 2 O 3 , forming a semi-coherent W/Cu interface, realizing mechanical metallurgical bonding between the W–Y 2 O 3 alloy and Cu, and thus enhancing the interface bonding strength. Improving the strength of W–Y 2 O 3 /CuCrZr joints by constructing a well-integrated interface facilitates the development of plasma-facing components for future China Fusion Engineering Test Reactor (CFETR). [Display omitted] • W–Y 2 O 3 /CuCrZr joint interface was modified by W–Y 2 O 3 surface nanoporosification and Cu sputtering deposition. • The modified W–Y 2 O 3 /CuCrZr joint have higher shear strength than the directly bonded joint. • Sputter-deposited Cu was embedded in the nanopores structure on the W–Y 2 O 3 surface, forming an interlocked joint interface. [ABSTRACT FROM AUTHOR]

Corrosion resistance is an important fact to be considered in practical engineering application of Al–Mg 2 Si alloys, besides the mechanical properties. So in the paper, corrosion behavior of Al–20%Mg 2 Si with/without Al–3%P master alloy in 3.5% NaCl solution was investigated. For the Al–20%Mg 2 Si alloy, Mg 2 Si acts as anode and corrosion starts from its surface at the initial stage of corrosion process. As the corrosion proceeds, electrochemical polarity converts between Mg 2 Si and α (Al), which results in the corrosion of Al matrix with the formation of pits. Moreover, after addition of Al–3%P master alloy, Mg 2 Si transforms from enormous dendrite to fine and uniformly distributing polyhedron, which inhibits the corrosion pits from propagating in Al matrix and enhances the corrosion resistance of Al–20%Mg 2 Si. [ABSTRACT FROM AUTHOR]

In this work, eutectic Si modification grade formula was established and effect of Sr element on modification level and mechanical properties of Al-9Si-0.4Mg-0.1Cu alloy was studied. Thermal analysis, SEM, EPMA and TEM were applied to analyze cooling curves, microstructure and Si twinning of the alloys. The results showed that precision and accuracy of eutectic Si modification grade formula were significantly improved and quantitative evaluation modification level of eutectic Si could be achieved. Modification level of eutectic Si increased first and then decreased with Sr content increasing. Though twin plane re-entrant edge (TPRE) mechanism and impurity induced twinning (IIT) mechanism were effective under certain conditions, they cannot fully explain the modification mechanism of eutectic Si in Al-9Si-0.4Mg-0.1Cu alloy. Sr element caused constitutional undercooling at the front of solid-liquid interface, promoted the formation of fine Al 2 Si 2 Sr phases and nano-precipitates, resulting in the changes of size and morphology of eutectic Si. With the improvement of eutectic Si modification level, the UTS and El of the alloys increased. While, adding excessive Sr led to the formation of coarse Al 2 Si 2 Sr, which was detrimental to the improvement of modification level and mechanical properties of alloy. • Modification level function suitable for quantitatively evaluate modification grade of eutectic Si was established. • Fine Al 2 Si 2 Sr phases and nano-precipitates change the size and morphology of eutectic Si. • Coarse Al 2 Si 2 Sr reduces the modification level of eutectic Si and the mechanical properties of alloy. [ABSTRACT FROM AUTHOR]

To investigate the hot deformation behaviour of Al-3%Mg 2 Si, isothermal compression tests were carried out in the temperature range of 300–500 °C and strain rate range of 0.01–5 s−1. The deformed microstructures were characterized by optical microscope, scanning electron microscope, transmission electron microscope and electron backscatter diffraction. The results show that the flow stress curves reveal a typical dynamic recovery characteristic. A modified Arrhenius-type constitutive equation was built to describe the flow behaviour of Al-3%Mg 2 Si alloy. Furthermore, based on the processing map of Al-3%Mg 2 Si alloy established under the strain of 0.8, microstructure evolution was analyzed. The high efficiency of power dissipation regions is mainly due to the softening mechanism of dynamic recovery and partial dynamic recrystallization. Mg 2 Si particles also play a positive role in dynamic recrystallization. The damage mechanism of unstable domains is the fracture and debonding of Mg 2 Si particles. • A modified constitutive model was built to describe the rheological properties of Al-3%Mg 2 Si alloy. • The softening mechanism is dominated by DRV with partial dynamic recrystallization. • Mg 2 Si particles play a positive role in dynamic recrystallization. • The damage mechanism of unstable domains is fracture and debonding of Mg 2 Si particles. [ABSTRACT FROM AUTHOR]

The precipitation of η phase during the solution treatments of Allvac 718Plus was investigated in this study. The results showed that there was free-γ′ zone appearing around η phase which was consistent with the hexagonal η-Ni 3 (Al/Ti) 0.5 Nb 0.5 after heat treatments. The granular η phase was found to be the transition of the plate-like η phase and have no pinning effect against the grain boundary, while the plate-like η phase has a pinning effect on the grain boundary and leads to the formation of serrated grain boundaries. With the solution temperature increasing, the size and fraction of η phase were observed to increase and then decrease with the morphology changing from granular to plate-like and then to granular. With the solution time prolonging, the fraction and size of η phase were increased, and the η phase formed in a cellular mode and then grow in a Widmanstätten morphology into the grain with its morphology changing from the dominant granular/plate-like to Widmanstättan structure. It was found that the increase in room temperature microhardness with the solution time changing from 6 h to 24 h was caused by the formation of Widmanstätten η phase. • The granular η phase is the transition of the plate-like η phase,having no pinning effect against the grain boundary. • The content and morphology of η phase changes with the solution temperature increasing. • The η phase forms in a cellular mode and then grow in a Widmanstätten morphology with the solution time prolonging. • The increase in microhardness with the solution time from 6 h to 24 h is closely related to the Widmanstätten η phase. [ABSTRACT FROM AUTHOR]

The isothermal oxidation behavior of micro-regions in multiphase Ni 3 Al-based superalloys (high Fe and Cr contents) was investigated at 600 °C in air. The oxide scale is mainly composed of the outer mixed oxide layer (NiO, NiFe 2 O 4 and Al 2 O 3) and the inner single Al 2 O 3 layer. In particular, Cr 2 O 3 is formed in the outer oxide scale of γ' + γ dendrite with enrichment in Cr element. The relative dense continuous Al 2 O 3 layer is formed in the interdendritic region (β phase with high Al content). In addition, γ' envelope (connecting the γ' + γ dendrite and interdendritic β phase) shows preferential oxidation featuring significant cellular bulge (NiO and NiFe 2 O 4 mixed oxides). Unlabelled Image • The micro-regions in multiphase Ni 3 Al-based superalloy present significant different oxidation behaviors at 600 °C. • The γ' envelope shows preferential oxidization featuring obvious cellular bulge (NiO and NiFe 2 O 4 mixed oxides). • Cr 2 O 3 is formed in the outer oxide layer of γ' + γ dendrite enriching in Cr element. • The dense protective alumina layer is formed on interdendritic region (β phase) with relative high Al content. [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]