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Two ingots weighing 400 g and 5 kg with nominal compositions of Fe–8Mn–4Al–2Si–0.5C–0.07V–0.05Sn were produced to investigate the effect of processing variables on microstructure development. The larger casting has a cooling rate more representative of commercial production and provides an understanding of the potential challenges arising from casting-related segregation during efforts to scale up medium Mn steels, while the smaller casting has a high cooling rate and different segregation pattern. Sections from both ingots were homogenized at 1250 $$^{\circ} $$ ∘ C for various times to study the degree of chemical homogeneity and $$\delta $$ δ -ferrite dissolution. Within 2 hours, the Mn segregation range (max–min) decreased from 8.0 to 1.7 wt pct in the 400 g ingot and from 6.2 to 1.5 wt pct in the 5 kg ingot. Some $$\delta $$ δ -ferrite also remained untransformed after 2 hours in both ingots but with the 5 kg ingot showing nearly three times more than the 400 g ingot. Micress modeling was carried out, and good agreement was seen between predicted and measured segregation levels and distribution. After thermomechanical processing, it was found that the coarse untransformed $$\delta $$ δ -ferrite in the 5 kg ingot turned into coarse $$\delta $$ δ -ferrite stringers in the finished product, resulting in a slight decrease in yield strength. Nevertheless, rolled strips from both ingots showed $$>900$$ > 900 MPa yield strength, $$>1100$$ > 1100 MPa tensile strength, and $$>40$$ > 40 pct elongation with $$ < 10 pct difference in strength and no change in ductility when compared to a fully homogenized sample.

The effects of the addition of different percentage compositions of graphene nanoplatelets (GNPs) to a nickel-based superalloy were investigated in this study. A spark plasma sintering (SPS) method was employed in the development of the nickel-based alloy/composites, and the developed bulk nickel-based alloy and its composites were from high-purity micron-size powder. Subsequently, the microstructure and mechanical properties (i.e., microhardness and tensile yield strength) were examined. The SPS-processed nickel-based alloy/composite samples exhibited high densification ranging from 97.64 to 98.87 pct. The addition of GNPs greatly influenced the microhardness results, which ranged from 384 to 459 Hv, and the tensile yield strength between 675 and 883 MPa. The results indicated that the addition of graphene nanoplatelets played a significant role in the microstructure and mechanical properties of spark plasma-sintered nickel-based composites. The addition of graphene nanoplatelets caused grain boundary strengthening, load transfer from the matrix to GNPs, and grain boundary strengthening by impeding dislocation movement. Coupled with the improvement caused by GNPs is the enhancement of the mechanical properties of the materials developed as a result of the high relative density values obtained.

A key-factor for the industrial implementation of beam-based additive manufacturing technologies is the development of novel Al alloys characterized by enhanced hot-tearing resistance. Indeed, most of the standard Al alloys are susceptible to solidification cracking and can hardly be used to produce structural parts by laser-based additive manufacturing processes. In this study, we investigate the strategies to design high-strength Al alloys for Laser Powder Bed Fusion. The addition of Zr to the chemical composition of an Al–Mg–Si alloy (EN AW 6182) was carried out by following two different routes to promote the formation of equiaxed grains which are able to suppress hot cracking and enhance processability of the material. The first route is based on mechanical mixing of ZrH2 particles and gas-atomized Al alloy powder and on the in-situ reaction of the hydride to form Al3Zr nucleants. The second route relies on the use of pre-alloyed gas-atomized powders that feature Zr among the alloy elements. The specimens produced using pre-alloyed powder showed the best mechanical performance. After direct aging from the as-built condition, the alloy showed yield strength and ultimate tensile strength of 354 and 363 MPa, respectively, and elongation at fracture of 9.0 pct. The achieved properties are comparable to those of wrought 6182 alloy processed by conventional routes.

In this study, room temperature tensile properties of type 304, a metastable austenitic stainless steel, prior rolled above Md temperature (200 °C and 300 °C) are compared with mill-annealed and material prior rolled at room temperature (25 °C). Strain-induced martensite that formed during the tensile tests, followed using in-situ using magnetic measurements, display kinetics that vary with prior deformation temperature and strain. Scanning Electron Microscopy and Electron Backscattered Diffraction studies provided direct evidence for shear band formation during prior deformation. Kinetics of strain-induced martensite is found to fit the Olson–Cohen equation modified to include the prior deformation strain and martensite formed during prior deformation. The systematic changes observed in the model parameters of the modified Olson–Cohen equation are explained. The strain hardening in the material is analyzed and correlated with changes in the rate of formation of strain-induced martensite with respect to strain.

The activation energy of creep rupture is determined based on a new tensile creep rupture model and then applied to rationalize the creep rupture data measured over a wide range of stresses and temperatures, which enabled the predictions of 100,000 hours and 200,000 hours creep rupture strengths to be made at different temperatures in the range of 650 °C to 875 °C for alloy Inconel 740/740H. The reliability of such long-term predictions is also analyzed.

The use of post-processing heat treatments is often considered a necessary approach to relax high-magnitude residual stresses (RS) formed during the layerwise additive manufacturing laser powder bed fusion (LPBF). In this work, three heat treatment strategies using temperatures of 450 °C, 800 °C, and 900 °C are applied to austenitic stainless steel 316L samples manufactured by LPBF. These temperatures encompass the suggested lower and upper bounds of heat treatment temperatures of conventionally processed 316L. The relaxation of the RS is characterized by neutron diffraction (ND), and the associated changes of the microstructure are analyzed using electron backscattered diffraction (EBSD) and scanning electron microscopy (SEM). The lower bound heat treatment variant of 450 °C for 4 hours exhibited high tensile and compressive RS. When applying subsequent heat treatments, we show that stress gradients are still observed after applying 800 °C for 1 hour but almost completely vanish when applying 900 °C for 1 hour. The observed near complete relaxation of the RS appears to be closely related to the evolution of the characteristic subgrain solidification cellular microstructure.

This work investigates the effect of increasing both martensite phase and ferrite phase strength on tensile properties and fracture behavior of dual-phase (DP) steels. The martensite phase strength is varied by changing its carbon contents and tempering process, whereas the ferrite phase strength is varied by dispersion of nano-sized vanadium carbides (VC) precipitates in the ferrite phase and also by changing its total fraction in DP samples. It is found that strengthening of the martensite phase improved the tensile strength with almost no loss of the tensile strength–uniform elongation balance. This is attributed to the enhancement of strain partitioning between the ferrite and martensite phase so that the work hardening rate increased. On the other hand, strengthening of ferrite phase effectively improved both the tensile strength and the tensile strength–post-uniform elongation balance due to suppression of strain partitioning which likely promoted homogenous deformation after necking. More importantly, a simultaneous increase in the strength of martensite phase and ferrite phase leads to a moderate phase strength difference, which is revealed as a promising strategy to achieve high strength in addition to a good balance of tensile strength, uniform elongation, and post-uniform elongation in low-carbon DP steels. Furthermore, the quantitative analysis of void formation reveals that decohesion of the interface between the ferrite phase and martensite phase is the dominant fracture mechanism, which is less likely to be affected by phase strength difference.

The microstructure and mechanical behavior of low-carbon ultrafine grain steel (UFG; 0.165 wt pct carbon) after niobium (Nb) addition were investigated. It was found that the addition of 0.028 wt pct of Nb resulted in the optimal tensile strength of 990.8 MPa with an adequate elongation of 15.5 pct. In comparison to the normal UFG steel (without Nb), the strength of Nb-UFG steel was substantially enhanced without any sacrifice of its elongation. The main increased strengthening mechanisms of Nb-UFG steel were precipitation and dislocation strengthening. The improved work hardening and adequate elongation of Nb-UFG steel could be ascribed to geometrically necessary dislocations and heterogeneous ferrite grains. Discontinuous static recrystallization occurred by a small rolling reduction on hardened martensite laths, resulting in the formation of heterogeneous ferrite grains. Ultrafine ferrite grains were surrounded by high-angle grain boundaries, and nanoscale Nb(C, N) carbonitrides providing precipitation strengthening were precipitated mainly in the α-phase.

The possibility of improving the mechanical and wear performance of steel rails with conventional compositions, near-eutectoid and without special alloying elements, using a two-step heat treatment was investigated. The heat treatment involved a first step involving quenching to a low temperature, near the Ms, maintaining at this temperature for a short time, followed by a second step at higher temperatures until complete transformation. The microstructures, tensile, and wear properties of the obtained products were characterized. The dilatation data confirmed that the remaining austenite was completely eliminated by the bainitic transformation at 400 °C for only 300 seconds, in the absence of alloying elements such as silicon without formation of carbide precipitates. The refined bainite-ferrite microstructure obtained by the two-step heat treatment significantly increased mechanical properties, as well as wear resistance measured using tensile and pin-on-disk tests. The bainitic ferrite structure exhibited approximately 20 pct higher hardness and about 53 pct less mass loss on pin-on disk test than the as-received pearlitic sample. Dilatometric and microstructural analysis using EBSD-electron backscattered diffraction techniques provided evidence that the two-step heat treatment increased the nucleation rate of the bainitic transformation and shortened the incubation time for transformation at the second step, at the same time increasing the density of crystallographic defects such as dislocations and grains boundaries. The proposed heat treatment, besides improving the mechanical properties and wear resistance, avoids the technological difficulties of using molten salt or metal for isothermal heat treatment of long products as rails.

Microstructural response and variations in strength and electrical conductivity of a Cu−20 at. pct Ni–6.7 at. pct Al alloy during isothermal aging at temperatures from 723 K to 1023 K (450 °C to 750 °C) were investigated to discuss the age-induced precipitation behavior and strengthening mechanism. At all aging temperatures, fine spherical γ′-Ni3Al particles were found to nucleate coherently with parent Cu grains by continuous precipitation and then grew gradually by Ostwald ripening. Domains with a high density of twins developed at grain boundaries during aging below 873 K (600 °C) followed by cellular components composed of fiber-shaped γ′-Ni3Al and Cu solid solution phases at the domain boundaries later. Both the domains and cellular components were suppressed at aging above 923 K (650 °C). The age-induced strengthening principally resulted from fine dispersion of γ′-Ni3Al coherent particles in the grains. The precipitation strengthening by the fine γ′-Ni3Al coherent particles exhibited a maximum at an aging temperature of 873 K (600 °C), resulting in excellent mechanical properties such as a high hardness of 340 ± 7 HV and an ultimate tensile strength of 980 ± 14 MPa, which are comparable to those of other commercial age-hardened Cu–Be, Cu–Ni–Si, and Cu–Ti alloys.

Thermo-mechanical treatments were performed to exploit the recrystallisation and deformation induced ferrite transformation (DIFT) during processing and study their effect on the microstructure and strength-ductility balance of a low-carbon, low alloy CMnSiAl TRIP-aided steel containing a small amount of Mo and Nb. A particular focus of the work was to study the influence of prior transformation of retained austenite to martensite (i.e., absence of the TRIP effect) on the strength-ductility balance of the steel by comparing the tensile properties of samples quenched in water and in liquid nitrogen. It was observed that the formation of high carbon martensite as a result of the prior transformation of retained austenite does not necessarily lead to brittle failure. The work also revealed that the TRIP effect per se may not play a major role and it is the deformation of a composite microstructure comprising hard and soft phases, which allows TRIP aided steels to offer a better combination of mechanical properties (strength, ductility and strain hardening) in comparison with conventional high strength steels (HSS) like high strength interstitial free (HS-IF) steel and high strength low alloy steel (HSLA) and other first generation advanced high strength steels (AHSS) like dual phase (DP) steels. The new insight into the TRIP effect may further be exploited in the design of alloy composition and subsequent thermo-mechanical treatments.

The effect of thermal aging on the mechanical properties of a Fe–19Cr–5.5Al oxide dispersion strengthened (ODS) hot rolled steel plate was evaluated. Tensile tests, sub-size Charpy impact tests, microhardness measurements and small punch tests were performed to analyze the embrittlement phenomenon occurring at an aging temperature of 475 °C as a consequence of a miscibility gap in the Fe–Cr system. These mechanical tests were able to confirm the age hardening and its intensity grade at different testing temperatures. Fractured impact and small punch specimens exhibited parallel delaminations promoted by a microstructure formed by elongated ferritic grains with a texture being 〈110〉 along the rolling direction. This study has revealed that small punch test represents a valuable technique for assessing the embrittlement susceptibility of high-Cr ODS alloys at different operational temperatures.

The correlation of delta-ferrite with the tensile and Charpy impact properties of austenitic Fe-23Mn-Al-C steels with different Al and C contents for cryogenic applications was investigated in this study. Microstructural analysis showed that the two steels with duplex phases had banded or layered microstructures with relatively fine-grained austenite and coarse-grained delta-ferrite which increased with Al content and decreased with C content. The geometrically necessary dislocation density increased with the fraction of the delta-ferrite phase. The steel with the highest delta-ferrite fraction of 26.6 pct had the highest yield strength of 576 MPa, while that with the delta-ferrite phase of less than 10.0 pct exhibited a mixed deformation behavior comprising deformation twins and dislocation glide which contributed to the highest tensile strength of 802 MPa and total elongation of 43.6 pct owing to an increase in the work hardening rate. In contrast, the Charpy impact test results revealed that the steels with duplex phases of austenite and delta-ferrite exhibited ductile-to-brittle transition behavior, whereas the steel with single-phase austenite had a higher absorbed energy exceeding 100 J at − 196 °C. The delta-ferrite phase had no significant effect on the absorbed energy at room temperature, but it acted as the main site for the propagation of brittle cracks at cryogenic temperatures and thus decreased the low-temperature toughness.

A warm forming process with a simultaneous retrogression heat treatment, termed retrogression forming, can achieve good formability in high-strength aluminum alloys and recover their high strength through a single reaging heat treatment after forming. Tensile data from two commercial aluminum alloy sheet materials, AA7075-T6 and AA6013-T6, are presented for conditions suitable to retrogression forming. AA7075-T6 sheet was tested at temperatures from 180 °C to 220 °C and strain rates from 3.2 × 10−3 to 10−1 s−1. AA6013-T6 sheet was tested from 230 °C to 250 °C and 3.2 × 10−3 to 10−1 s−1. Both materials exhibit nearly steady-state flow at these temperatures and produce a modest strain-rate sensitivity of m = 0.039. The activation energies for plastic flow under these conditions are 221 kJ/mol for AA7075-T6 and 253 kJ/mol for AA6013-T6. Test data are used to construct predictive models for flow stress as a function of temperature and strain rate. AA7075-T6 demonstrates an excellent potential for retrogression forming at 200 °C and strain rates up to 10−1 s−1 if time at temperature is held to under 12 minutes. AA6013-T6 exhibits a modest potential for retrogression forming at 240 °C and strain rates up to 10−1 s−1 if time at temperature is held to under 7 minutes.

Yanagihara S., Ueki K., Ueda K., et al. Development of Low-Yield Stress Co–Cr–W–Ni Alloy by Adding 6 Mass Pct Mn for Balloon-Expandable Stents. Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science, 52, 9, 4137. https://doi.org/10.1007/s11661-021-06374-7., This is the first report presenting the development of a Co–Cr–W–Ni–Mn alloy by adding 6 mass pct Mn to ASTM F90 Co–20Cr–15W–10Ni (CCWN, mass pct) alloy for use as balloon-expandable stents with an excellent balance of mechanical properties and corrosion resistance. The effects of Mn addition on the microstructures as well as the mechanical and corrosion properties were investigated after hot forging, solution treatment, swaging, and static recrystallization. The Mn-added alloy with a grain size of ~ 20 µm (recrystallization condition: 1523 K, 150 seconds) exhibited an ultimate tensile strength of 1131 MPa, 0.2 pct proof stress of 535 MPa, and plastic elongation of 66 pct. Additionally, it exhibited higher ductility and lower yield stress while maintaining high strength compared to the ASTM F90 CCWN alloy. The formation of intersecting stacking faults was suppressed by increasing the stacking fault energy (SFE) with Mn addition, resulting in a lower yield stress. The low-yield stress is effective in suppressing stent recoil. In addition, strain-induced martensitic transformation during plastic deformation was suppressed by increasing the SFE, thereby improving the ductility. The Mn-added alloys also exhibited good corrosion resistance, similar to the ASTM F90 CCWN alloy. Mn-added Co–Cr–W–Ni alloys are suitable for use as balloon-expandable stents.

The purpose of the present work is to study the mechanical behaviour of AA2219-T87 friction stir weld (FSW) joints at different temperatures (Room temperature (RT), 77 K and 20 K) and correlate them to the microstructures evolved during the joining process. For this purpose, standard full length tensile specimens as well as miniature tensile specimens extracted from different microstructural regions of the joint such as weld nugget zone (WNZ), thermo-mechanically affected zone (TMAZ) and heat-affected zone were used. Similarly, fracture toughness (FT) was evaluated by placing notches at the three microstructurally different regions. The tensile properties at 77 K and 20 K were higher compared to those at room temperature. Miniature tensile specimens extracted from WNZ and TMAZ regions showed similar strength properties; however lower hardness and ductility were observed in TMAZ. Failure of standard full length samples was always in TMAZ since it has lower hardness and ductility, as a result of strain hardening. The higher FT noticed in WNZ is attributed to the presence of very fine grains. The lower FT observed in the TMAZ is attributed to combined effect of the absence of strengthening precipitates and recrystallization. Comparison of the mechanical properties of AA2219-T87 FSW and TIG weld joints revealed superior tensile properties at room and cryogenic temperatures for FSW weld joints, thus making FSW, a better alternative for the fabrication of large sized earth storable and cryogenic propellant tanks of satellite launch vehicles.

In brazing, the choice of base metal, brazing filler metal (BFM), and braze process conditions involves complex tradeoffs among cost, mechanical strength, corrosion resistance, and others. In this work, the tradeoff between strength and corrosion resistance of 316L stainless steel joints brazed with a newer “very corrosion-resistant” Ni-Cr-P-Mo-Si BFM and a more established “corrosion-resistant” Ni-Cr-Si-B BFM is quantitatively analyzed. Corrosion tests and microstructural analyses were performed using common practices. Joint strength was evaluated by testing brazed single-lap joints (SLJs) in tension following standardized procedures. However, conventional interpretations were found to be inadequate for quantitative comparisons. Therefore, the SLJ stress state was analyzed in detail and a complete interpretation was developed. Joint strength is shown to be determined by the SLJ geometry, base metal properties, and braze microstructure. This analysis was used to explain the occurrence of different failure modes (fast fracture, peeling, and base metal failure) and to make suggestions for improved methods for conducting and analyzing brazed SLJ tensile tests. The newer BFM is shown to provide significantly better corrosion resistance for a moderate reduction in mechanical strength.

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

The effect of temperature over the range of ambient to 704 °C and strain rate from 10−4 to 10−2 s−1 on the tensile properties and fracture behavior of ATI 718Plus was investigated. The results showed that with increase in temperature at a strain rate 10−4 s−1, there is a small reduction in the yield strength, but a large drop in ductility at 704 °C. This reduction was accompanied by a change in fracture mode from ductile transgranular to brittle intergranular cracking. Detailed analysis of the microstructure and microchemistry of the areas around the crack using electron microscopy showed that the driving mechanism behind the failure at elevated temperatures and slow strain rates is oxygen-induced intergranular cracking, a dynamic embrittlement mechanism. In addition, the results suggest that the δ precipitates on the grain boundaries tend to oxidize and may facilitate the oxygen-induced intergranular cracking. Finally, an increase in strain rate at 704 °C caused a small increase in the yield strength and a huge increase in ductility. This increase in ductility was accompanied by a change in fracture mode from brittle-to-ductile failure. Possible mechanisms for the deformation, failure mechanisms, and strain rate dependence are discussed.

At present, optimization of mechanical properties in quenching and partitioning (Q&P) steels relies primarily on the tailoring of microstructural characteristics by manipulating the alloying elements and the Q&P process. However, adjusting the final microstructure by taking advantage of the inheritance effect derived from the initial microstructure has received less attention. Based on a typical Fe–C–Mn–Si system, the present investigation explores the effect of microstructural inheritance in an ultrahigh strength hot-rolled Q&P steel. The typical hot rolling process is followed by three cooling rates, including quenching, air cooling, and coil cooling, to obtain different initial microstructures of full martensite, bainite–austenite, and ferrite–pearlite, respectively. The same Q&P treatment is then performed to elucidate the inheritance mechanism, and the final Q&P products consist of different fractions of tempered martensite, retained austenite, bainite and fresh martensite. With decreasing cooling rates after hot rolling, the ultimate tensile strengths of the steels after the Q&P treatment are identical at ~ 1.5 GPa, while the total elongations increase gradually from 10.9, 12.7 to 14.5 pct. The highest elongation of the coil-cooled Q&P steel can be attributed to the effect of microstructural inheritance on the Q&P process and retained austenite, leading to larger austenite grain sizes and more equiaxed morphologies. The combination of austenite chemistry and morphology results in the optimal mechanical stability for retained austenite to provide continuous and durable strain hardening. Compared to cold-rolled products, hot-rolled Q&P steel is very attractive to the industry as it can potentially eliminate the cold rolling step and reduce the production cost. Utilizing the microstructural inheritance effect provides a simple and feasible route to control the microstructures and mechanical properties of ultrahigh strength hot-rolled Q&P steel.

T-lap joints are widely utilized in connecting various structural elements owing to their efficient application. Typically, the mechanical properties of the joints are critical in maintaining an effective connection. In this study, we examined the role of the interface morphology in failure behavior of the dissimilar friction stir welded (FSWed) T-lap joints of 7075/5083 aluminum alloys. The experimental results verified that the morphology of interface of the joints was sensitive to the number of welding passes and tool offset. Additionally, the kissing bonds (KBs) were minimized significantly when the tool offset was combined with the double-pass welding. Furthermore, both the tensile and fatigue strengths of the joints were extremely sensitive to the interface geometry. We performed a quantitative analysis using a simplified fracture mechanics model and finite element method to clarify the failure behavior of the FSWed T-lap joints that must be optimized in terms of both the size and geometry of the KBs by altering the welding conditions.

Crack healing in metallic materials has significant economic, ecological, and social benefits. However, the morphological evolution and mechanism of crack healing have no clear consensus. Therefore, in this study, isothermal heat treatment was applied to heal internal cracks at temperatures of 900 °C to 1200 °C for 15 to 120 minutes. Subsequently, microhardness and tensile tests were performed on the specimen to evaluate the reliability of the healed specimens. The results show that the morphology evolution in crack healing can be divided into three stages. Both atomic diffusion and recrystallization dominate crack healing. Atomic diffusion and recrystallization work together to heal cracks in the first stage. Atomic diffusion allows the recrystallization of materials, and recrystallization accelerates the processes of atomic diffusion. In the second and third stages, atomic diffusion controls crack healing on its own. In addition, with increasing healing time, the ultimate tensile strength and microhardness of the crack healing zone decrease due to the difference in the healing mechanism.

Friction welding or electron/laser beam welding of nickel superalloys compromises the microstructure with localized melting and heat-affected zones (HAZ). In this work, Field-Assisted Sintering Technology (FAST) is studied as an alternative method for solid-state diffusion bonding of superalloys CM247LC and Inconel 718. Bonding microstructures and room-temperature tensile strengths are evaluated. Preliminary results suggest that FAST bonding leads to an interface with a compositional gradient without producing a HAZ and without losing tensile strength.

High-temperature tensile testing and X-ray microscope (XRM) characterization were performed to assess the effects of the micro-addition of Gd and the three-dimensional (3-D) network structure on the improvement of Al-6Cu-3.5Ni-0.8Fe alloy under as-cast conditions. Gd addition contributed to the modification of the microstructure, where a new thermally stable micro-sized Al3CuGd phase was formed, and the refinement occurred in Al3CuNi and Al9FeNi. The tensile test results revealed that the alloy modified with 0.4 pct Gd exhibited optimal properties at 623 K (350 °C), with an ultimate tensile strength, yield strength, and elongation of 74.1 MPa, 61.2 MPa, and 15.5 pct, respectively. Fractographic analysis after the tensile tests indicated that at ambient temperature, brittle cleavage-type fracture of the precipitates and ductile fracture of the matrix were dominant, whereas the transformation from mixed fracture to fully ductile trans-crystalline fracture was detected at elevated temperatures. According to the CT characterization, there was no significant difference in the curvature or interconnectivity of the 3-D network structure formed by the aluminides between before and after the tensile test at 623 K (350 °C). It is believed that the 3-D continuous network structure of aluminides, equipped with excellent heat resistance, plays a pivotal role in the high-temperature performance of the studied alloys. This work provides a new and promising idea for solving the current heat resistance problems of cast Al alloys.

A Cu-Fe-Cr-Ag alloy was prepared by directional solidification (DS) and upward continuous casting (UCC) to study the effect of different casting methods on the structure and properties of Cu-Fe-Cr-Ag. The results showed that the directionally solidified Cu-Fe-Cr-Ag alloy had excellent mechanical properties and conductivity. After cold drawing and isothermal aging, the peak tensile strength (789 MPa) and peak conductivity (65.5 pct IACS) of directionally solidified Cu-Fe-Cr-Ag alloy were 21 MPa and 4.7 pct IACS higher, respectively, than those that of the upward continuously casted Cu-Fe-Cr-Ag alloy. Compared to upward continuously casted Cu-Fe-Cr-Ag alloy, the Fe dendrites in directionally solidified Cu-Fe-Cr-Ag alloy were much finer, more uniform, and arranged along the direction of the magnetic field. Cu and Ag formed a Cu-Ag eutectic structure at the edge of the directionally solidified Cu-Fe-Cr-Ag alloy rod. After multi-stage thermomechanical treatment, Ag was mainly distributed around the material and formed a structure similar to Ag-clad Cu. The directionally solidified Cu-Fe-Cr-Ag alloy had a smaller lattice constant and finer Fe fibers. The small lattice constant and Fe fibers and the special distribution of Ag lead to the excellent comprehensive performance of the directionally solidified Cu-Fe-Cr-Ag alloy.

The tensile mechanical behavior and spall response of a selective laser melted (SLM) 17-4 precipitation-hardening (PH) stainless steel were studied comprehensively through tensile test, plate impact experiment and microstructure characterization in the present study. The results reveal a steel with significant strain rate dependence on the tensile mechanical behavior and spall response. As the strain rate increases, the tensile yield stress increases, but there is no monotonic variation trend for the peak stress; grain structure remains unchanged first and then becomes fine; high-angle grain boundaries (HAGBs) increase; the martensite phase decreases at first and then increases. There is a close correlation among impact velocity, strain rate, peak stress, Hugoniot elastic limit (HEL) and spall strength. Strain rate, peak stress and HEL increase, while spall strength remains almost constant with the increase of impact velocity. As impact velocity increases, grain structure becomes fine, HAGBs increase and the martensite phase increases. The significant phase transformation is responsible for the tensile mechanical behavior and spall response, and the temperature rise was calculated to analyze its effect on phase transformation. Whether the preferred orientations are along the building direction or tensile direction is dependent on strain rate. Tensile and spallation specimens exhibit the ductile fracture mode and the damage originates from voids. It is interesting that the voids always tend to nucleate at melt pool boundaries. A spall damage evolution model is illustrated to describe the damage process.

Hot stamped boron steel parts with martensite and bainite combined microstructures are widely used in lightweight manufacturing of automotive bodies. The final products usually experience the manufacturing process, such as trimming or punching, which inevitably introduces inner stress and plastic strain. Hot stamped parts with complex microstructures and manufacturing effects exhibit some special characteristics of hydrogen embrittlement (HE) in service. In this paper, hardened boron steels with a total martensite content and different martensite-bainite combinations, called martensite or bainite dominant microstructures (MDM/BDM), are experimentally obtained by a flexible quenching tool, and the HE susceptibility considering the effects of prestrain and inner (tensile/compressive) stress is investigated based on slow strain rate tensile tests by developing hydrogen charging equipment under constant loads. SEM and EBSD analyses on hydrogen-inducted cracks (HICs) and thermal desorption analysis of hydrogen for different microstructures and strain/stress states are carried out to illustrate the HE mechanism. The HE susceptibility of the as-quenched specimen decreases with increasing volume fraction of bainite, with the fractograph exhibiting intergranular fracture in the MDM and the dimples feature in the BDM. Prestrain weakens the HE susceptibility in the MDM but raises it in the BDM due to the enhancement of hydrogen adsorption, promoting local plasticity in the evolution of the HICs. Inner stresses increase the HE susceptibility in the MDM, which lifts the hydrogen segregation at the grain boundaries to intensify the hydrogen-enhanced decohesion effect. Tensile stress intensifies the sensitivity to HE in the BDM. The promotion of hydrogen adsorption facilitates crack initiation. However, compressive stress has opposite effects on the HE susceptibility due to the improvement of the material ductility by reducing the hydrogen content in the specimen.

The structure, martensitic γ ↔ e transformation temperatures, Young’s modulus, mechanical properties, and electrochemical behavior of Fe-30Mn-5Si (wt pct) biodegradable shape memory alloy subjected to various thermomechanical treatments (TMT) comprising hot rolling or cold rolling with post-deformation annealing were characterized by optical microscopy, energy-dispersive X-ray spectroscopy, X-ray diffraction, differential scanning calorimetry, tensile testing, open circuit potential, and polarization curves measurements in Hanks’ solution, as compared to reference heat treatment. The optimum combination of mechanical properties (low Young’s modulus, high tensile strength, and appropriate ductility) for biomechanical compatibility was obtained after TMT with hot rolling at 600 and 800 °C due to the formation of favorable dynamically polygonized and recrystallized structures and decrease in the γ↔e transformation starting temperature down to the human body temperature. The TMT did not show a significant effect on the corrosion rate as compared to the appropriate corrosion rate after the reference heat treatment. It is concluded that the TMT with hot rolling at 600 or 800 °C, which provides an optimum combination of the required corrosion rate in the simulation body fluid with high biomechanical compatibility, can be considered a promising treatment of Fe-30Mn-5Si biodegradable alloy for bone implants.

The tensile fracture behavior of oxide dispersion strengthened 18Cr (ODS-18Cr) ferritic steels milled for varying times was studied along with the oxide-free 18Cr steel (NODS) at 25, 200, 400, 600, and 800 °C. At all the test temperatures, the strengths of ODS–18Cr steels increased and total elongation decreased with the duration of milling time. Oxide dispersed 18Cr steel with optimum milling exhibited enhanced yield strength of 156 pct at room temperature and 300 pct at 800 °C when compared to oxide-free 18Cr steel. The ductility values of ODS-18Cr steels are in the range 20 to 35 pct for a temperature range 25 to 800 °C, whereas NODS alloy exhibited higher ductility of 37 to 82 pct. The enhanced strength of ODS steels when compared to oxide-free steel is due to the development of ultrafine grained structure along with nanosized dispersion of complex oxide particles. While the pre-necking elongation decreased with increasing temperature and milling time, post-necking elongation showed no change with the test temperature. Fractographic examination of both ODS and NODS 18Cr steel fractured tensile samples, revealed that the failure was in ductile fracture mode with distinct neck and shear lip formation for all milling times and at all test temperatures. The fracture mechanism is in general followed the sequence; microvoid nucleation at second phase particles, void growth and coalescence. The quantified dimple sizes and numbers per unit area were found to be in linear relation with the size and number density of dispersoids. It is clearly evident that even nanosized dispersoids acted as sites for microvoid nucleation at larger strains and assisted in dimple rupture.

This work examined the effects of specimen layout on physical, microstructural, and mechanical properties of 17-4PH (AISI 630) fabricated by metal-fused deposition modeling process. Tensile specimens were 3D-printed with the different layouts using 100 pct infill. The as-printed and as-sintered specimens with the flat layout had the best appearance, green, relative sintered density, and sintered tensile properties with good repeatability, while the specimens with the vertical layout were the worst. The as-sintered tensile properties of specimens with the side layout were slightly lower than those with the flat layout but significantly higher than those with the vertical layout. Moreover, the tensile properties of specimens with the flat and side layouts met the Metal Powder Industry Federation standard 35 for metal injection molding. The tensile properties and corresponding fracture surfaces can be explained in terms of the combined effect of load-bearing and stress concentration due to the pre-existence of voids at perimeters. The fracture surfaces of specimens with the vertical layout showed large defects induced during printing and voids between perimeter walls generating high stress concentration and layer delamination. The difference between tensile properties of specimens with the side and flat layouts is mainly due to the characteristic of the printing—voids in the side layout are larger and more detrimental to the mechanical properties—which was confirmed by the evidence of cracking in the fracture surface.

A newly designed composition of non-equiatomic Fe40Cr25Ni15Al15Co5 medium-entropy alloy (MEA) was produced by induction melting (IM). The as-cast alloy was found to consist of a two-phase microstructure of BCC (2.87 ± 0.01 A) and ordered B2 (2.88 ± 0.02 A) type phases. The structures of these phases were confirmed through X-ray diffraction (XRD) and transmission electron microscopy (TEM) techniques. It was observed that the Ni-Al-enriched ordered B2 phase of cuboidal shapes (~ 100 to 200 nm) is homogeneously distributed in Fe-Cr-rich BCC matrix with a cube-on-cube orientation relationship. The formation of the columnar dendrites (width 50 to 100 μm) was identified through optical microscopy (OM). The structural and microstructural stability of the alloy was investigated by heat-treating the alloy through different schedules. Heat-treated samples at different temperatures (< 1273 K) exhibit a similar type of two-phase microstructure with columnar dendrites. However, compositional rearrangement takes place during long time exposure to develop polymorphically related phases. The alloy was observed to possess a high compressive yield strength and hardness, i.e., ~ 1047 MPa and 391 ± 9 HV, respectively, at room temperature. Heat-treated samples at 600 °C and 900 °C (873 K and 1173 K) showed an increase in yield strength and ultimate strength with a significant increase in plasticity due to the increase in volume fraction of B2 phase and softening of the BCC matrix phase. The thermal stability and high strength of this alloy may open new avenues for high-temperature applications.

The secondary explosive welding process promotes the diffusion of the carbon element and accumulation of chromium carbide, which leads to a decrease of tensile properties and toughness of the material. In this work, the average shear strength value increased from 400 to 421 MPa. The crack of the fatigue specimens started from the inclusions rich in alumina near the surface, and the harmful hard-phase inclusions were exposed because of stress concentration. The maximum load limit of 10CrNi3MoV steel undergoing secondary explosive welding was between 590 and 605 MPa.

Selective laser melting (SLM) is an additive manufacturing (AM) technique designed to use a high energy density laser to fuse metallic powders for producing three-dimensional parts. So far, most studies of SLM have been focused on using virgin metal powders. There are few comprehensive studies on the microstructure and mechanical properties of SLM-produced parts using recycled powders, especially for maraging steels. In this study, we employ recycled steel powder (reused after 113 building cycles) in the SLM process to print multiple shaped components and systematically characterize the microstructure and mechanical properties (indentation, tensile, and Charpy testing). Our results show that maraging steel produced with recycled powder exhibit the nearly identical microstructure and mechanical properties (940 MPa yield strength, 1127 MPa ultimate tensile strength, 11 pct elongation, and 47.5 J room temperature impact fracture energy) to those produced using virgin powders. This study provides a useful generic guide towards using recycled metal powders in the SLM processing, promoting an economic solution to industrial productions.

In this study, a novel severe plastic deformation technique referred to as rotational constrained bending (RCB) is introduced. A special constrained bending die, which imposes bending deformation to the billet during the first pass, was developed for repetitive processing of pre-extruded commercially pure Ti. Strain-induced microstructural changes were investigated by a special technique of automated crystal orientation mapping in TEM simultaneously with advanced X-ray line profile analysis. Plastic deformation distribution, imposed to the billets after a selected number of passes, was followed by precise microhardness mapping. Exceptional microstructure refinement was attained by the application of repetitive bending deformation. Average grain size decreased down to 400 nm, and the dislocation density increased by about 35 pct after ten passes. X-ray macrotexture measurements revealed the formation of a basal slip texture component commonly observed in HCP materials processed by equal channel angular pressing; however, exceeding four passes, a strong $$ \left\{ {11{\bar{2}}0} \right\} $$ fiber texture started to form. Mechanical testing in tension showed a significant increase in strength in the RCB-processed samples. The proof-stress and tensile strength increased by 30 and 15 pct after four passes, respectively. At a higher number of passes, the proof stress slightly decreased because of the texture softening.

The influence of 3.5 wt pct NaCl on the work-hardening response of AA 7004 is investigated through subjecting the tensile data to Kock-Mecking analysis. Due to the exposure to chloride, the decay in the work-hardening rate (−dθ/dσ) increases by ~28 pct when the alloy has GP zones and decreases by ~22 pct when η′/η precipitates are present. In contrast, no significant variation in ultimate tensile strength and elongation values are observed for the alloy, although it suffered embrittlement which results in tearing topography surfaces. Accordingly, −dθ/dσ seems to be a more reliable parameter to assess the environmentally assisted cracking (EAC) susceptibility of the less EAC susceptible AA 7004.

Microalloyed low-carbon steels are used for line pipe applications as they combine high strength and acceptable fracture toughness with good weldability. During multi-pass welding, the strength and impact toughness of the material in the heat-affected zone (HAZ) is potentially degraded, in particular the regions where the thermal fields from multi-pass welds overlap (for example: the intercritically reheated coarse grain heat-affected zone, ICCGHAZ). Using a Gleeble thermomechanical simulator, bulk microstructures were produced that are representative for the ICCGHAZ for two high-strength X80 line pipe steels. Here, the first thermal cycle produces a bainitic microstructure that is characteristic of the coarse grain heat-affected zone (CGHAZ) and the second cycle involves intercritical annealing of this region to form microstructures representative of the ICCGHAZ. The effect of the intercritical austenite fraction and the resulting martensite–austenite (M/A) constituents on the tensile properties and the ductile-brittle transition temperature (DBTT) has been quantified for two steels with different carbon contents, i.e., 0.063 and 0.028 wt. pct. Detailed fractography studies have been conducted to evaluate the fracture mechanisms with respect to the microstructural features. Upon intercritical annealing (relevant to ICCGHAZ), the ductile–brittle transition temperature was above room temperature when a nearly continuous necklace of M/A formed on the prior austenite grain boundaries (for M/A ≈ 10 pct). Finally, the role of carbon content on the yield strength and plasticity of martensite has been considered for the tensile fracture behavior and ductile–brittle transition temperature. It is proposed that as the average carbon content of the M/A decreases (both due to (i) a decrease in the bulk carbon content of the steel and (ii) an increase in the volume fraction of austenite formed during intercritical annealing), martensite plasticity was possible which reduced nucleation of voids or cracks at the M/A–bainite interface.

Effect of 1 wt pct Gd addition on the microstructural evolution, mechanical properties and bio-corrosion behavior of the biodegradable Mg-4Zn alloy was studied. The average grain size of the base alloy decreased from 14.6 to 5.7 µm after Gd addition. In contrast to the base Gd-free alloy, a fiber texture with higher intensity of basal poles and lower Schmid factor was formed during the hot extrusion in the Gd-containing alloy. This was attributed to the presence of a relatively high volume fraction of un-recrystallized grains. The respective yield stress (YS) and ultimate tensile strength (UTS) values were significantly improved from 198 MPa and 301 MPa in the Mg-4Zn alloy to 241 MPa and 336 MPa in the Mg-4Zn-1Gd alloy, due to the finer grain size, second phase particles and textural hardening. Extension twins were responsible for achieving the respective high elongations of 33.9 and 20.6 pct for the base and Gd-containing alloys, during tensile loading. Electron backscattered diffraction (EBSD) analysis of the corroded surfaces indicated high pitting susceptibility of the non-basal planes and un-recrystallized grains. Despite the higher stored energy in the Gd-containing alloy due to the lower fraction of recrystallized grains, the finer grain size and the presence of Gd in the corroded layer resulted in improved biodegradability of this alloy.

Plastic deformation and microstructure evolution are investigated at elevated temperatures in a low-impurity (ASTM B393-18 Type 1) niobium sheet material. Data from tensile tests are reported for temperatures from 1473 K to 1823 K (1200 °C to 1550 °C) at constant true-strain rates of 10−3 and 10−4 s−1. Microstructures produced by static annealing and by tensile deformation at these temperatures are characterized using backscatter electron imaging. Significant static grain growth is observed and increases with increasing temperature. Young’s elastic modulus data for niobium from the literature are reviewed to recommend modulus values from 293 K to 2300 K (20 °C to 2027 °C) for randomly textured polycrystalline niobium. Steady-state creep analysis of data above 1370 K (1097 °C), half the melting temperature, produces a stress exponent of 5.6 and an activation energy for creep of 454 kJ/mol, which is close to that of lattice self-diffusion. Dislocation substructure is observed following elevated temperature deformation. These data are compared with data from the literature to conclude that low-impurity niobium deforms by five-power creep across the conditions examined.

The fracture resistance of different advanced high-strength steel (AHSS) sheets for automotive applications is investigated through conventional tensile tests, fracture toughness measurements, and hole expansion tests. Different fracture-related parameters, such as the true fracture strain (TFS), the true thickness strain (TTS), the fracture toughness at crack initiation (w e i ), the specific essential work of fracture (w e), and the hole expansion ratio (HER), are assessed. The specific essential work of fracture (w e) is shown to be a suitable parameter to evaluate the local formability and fracture resistance of AHSS. The results reveal that fracture toughness cannot be estimated from any of the parameters derived from tensile tests and show the importance of microstructural features on crack propagation resistance. Based on the relation fracture toughness-local formability, a new AHSS classification mapping accounting for global formability and cracking resistance is proposed. Furthermore, a physically motivated fracture criterion for edge-cracking prediction, based on thickness strain measurements in fatigue pre-cracked DENT specimens, is proposed.

One concern regarding boron (B)-modified Ti alloys is that TiB formed in the alloy could cause early fatigue crack initiation, especially when its tensile strength is considerably higher than 1100 MPa. Therefore, the present study was undertaken to determine whether TiB could indeed become an origin of fatigue crack initiation in a high strength 0.1 pct B-modified β-type Ti-6.8Mo-4.5Fe-1.5Al alloy. An alloy with or without B was subjected to different types of heat treatments to produce various microstructures. The resultant tensile strengths ranged from 1217 to 1564 MPa. Both the B-free and B-modified alloys showed almost the same tensile strength when they were subjected to the same heat treatment. When the tensile strength level was below ~1200 MPa, the B-modified alloy showed higher HCF strength compared to the B-free counterpart. In these cases, the fatigue crack originated from grain boundaries. In contrast, when the tensile strength level was above 1250 MPa, the HCF strength of the B-modified alloy was inferior to the B-free counterpart. The fatigue crack initiated neither from the grain boundaries nor from the microstructural unit but rather from the interface between TiB and matrix. In sum, the HCF behavior and the origin of the fatigue crack initiation of a B-modified alloy was highly dependent on its microstructures, and, thus, on its tensile strength including the critical tensile strength level at ~1250 MPa, where deterioration of fatigue strength occurred due to the presence of TiB.

Additive manufacturing of an equimolar CoCrNi medium entropy alloy (MEA) by selective laser melting (SLM) was investigated, emphasizing its microstructure, properties, and metallurgical defects. It was found that SLM sample density exhibited a non-monotonic relation with their volume energy density (VED); the density first increased but then decreased while the input VED was gradually increasing. A maximal relative density of 98.9 pct was accessible at a VED of 83.3 J/mm3. X-ray diffraction indicated that the printed CoCrNi MEA exhibited an FCC single-crystal structure where the lattice constant decreased with the increasing VED owing to the evaporation of the Cr element in the SLM process. The average grain size gradually increased with increasing VED, irrespective of whether viewed from the top or the side of the printed part. Similarly, the residual stress increased with increasing VED, which produced more microcracks and deteriorated the tensile preformation of the printed samples, although the yield strength (630 MPa) showed no apparent difference at different VEDs. Owing to the ultrafine cell structure, the mechanical property of the SLM printed sample was twice that of cast or wrought CoCrNi MEA.

Herein, the effect of Ta addition (0 and 2 wt pct) on the tensile properties of a Ni-Co base superalloy was investigated in the temperature range of 23–900 °C. The results revealed that the addition of Ta improved the strength of the superalloy at all experimental temperatures and increased the plasticity at 760 °C. In addition, the microstructural observations indicate that Ta addition promoted the precipitation of γ′ precipitates, as well as the precipitation of (Ta, Ti)-rich MC carbides. The addition of 2 wt pct Ta promoted twinning and, thus, transformed the fracture mechanism of the alloy from an intergranular brittle fracture to a mixed ductile and brittle fracture at 760 °C. Furthermore, the tensile properties and the related microstructures, deformation mechanisms, and fracture mechanisms of the experimental alloys are discussed. Finally, we demonstrated that the combined effect of the increase in the grain boundary strength, the reduction in the critical resolved shear stress, and the promotion of twinning induced the synchronous improvement of strength and plasticity of the alloy at 760 °C.

In this study, degradation of the mechanical properties of 9Cr ferritic-martensitic P91 steel by supercritical CO2 (sCO2) power cycle environment was investigated. P91 tensile specimens of 2.54 mm and 0.5 mm thicknesses were exposed to a simulated direct-fired sCO2 power cycle environment at 650 °C for 1000 hours. The exposed specimens were tensile stressed at room temperature and the resulting deformation behaviors were studied. While the thicker P91 had ductile failure with decreased ductility, the failure of the thinner P91 was completely brittle and at a significantly lower tensile stress. These results indicate that the mechanical properties of the thinner P91 were severely degraded by the exposure. Microstructural analyses reveal that the thinner P91 became carbon saturated. This resulted in breakaway oxidation, where fast growing iron-rich oxide layers consumed a significant portion of the specimen thickness. The thicker P91 also carburized during the exposure, however it did not become carbon saturated and growth of iron-rich oxide layers consumed a much smaller portion of the thickness. Hardness tests performed on specimen cross-sections showed increased hardness for both thicknesses. However, the increase was considerable for the thinner P91, where a thick oxide layer and extensive carbide formation in the alloy caused its brittle failure.

In this study, the effect of Co addition on the microstructure and creep rupture properties of 9Cr-1.8W-xCo weld metals is investigated. Herein, stick electrodes were fabricated for producing weld metals with 0.5, 1.0, and 1.5 wt pct Co and without Co, which were then processed by post-welding heat treatment at 760 °C for 4 hours. The microstructures of weld metals, including the prior austenite grain size, tempered martensite lath size, delta ferrite content, and precipitate quantity and size, were characterized via optical microscopy, scanning and transmission electron microscopy, and electron backscattered diffraction. The precipitates were identified by X-ray diffraction after they were extracted from the matrix. The Curie temperature was determined via differential scanning calorimetry, which allowed the evaluation of diffusion rate as a function of Co content. The weld metals were mechanically characterized by creep rupture tests conducted at 675 °C under 150 MPa and by hardness and tensile tests conducted at room temperature as well as Charpy impact tests conducted at various temperatures from − 40 °C to 60 °C. The results obtained herein suggest that the addition of Co significantly increases the creep rupture time of 9Cr-1.8W steel (by approximately 20 times than that of Co-free steel), reduces the prior austenite grain size and tempered martensite lath size, hinders the formation of detrimental delta ferrite, and promotes the formation of precipitates with slightly larger size. Herein, the highest creep resistance from the viewpoint of creep rupture time was obtained for 9Cr-1.8W weld metal with 1.5 wt pct Co. Furthermore, the results suggest that a finer and more stable substructure is required for improving the creep resistance.

Microstructure and texture development in Al/AMCs sandwich composites and the connection between the tensile properties and microstructure/texture have not been fully understood. In this study, the AA 1060 aluminum alloy and spark plasma sintering (SPS) processed Al-TiC composite were prepared into the 1060/Al-TiC/1060 sandwich composites by hot-roll bonding (HRB). The influence of rolling reduction on the microstructure, texture and tensile properties was studied. An inhomogeneity of microstructure through the thickness of Al layer was observed after the HRB process. The grains at the surface Al layer were tilted to 19 deg with respect to the rolling direction after 34.8 pct reduction, and the tilted grains were developed to a deeper region with increasing rolling reduction. The degree of grain-subdivision and number of high-angle boundaries decreased as the observed area moved from the surface to the interface. The cube texture at the surface of the Al layer transformed into the rotated-cube shear texture during HRB process. The strength of the rotated-cube texture at the interface layer was lower than at the surface layer. The initial random texture in the Al-TiC layer was changed to the α-fiber and β-fiber rolling textures after the HRB process. The yield strength and ultimate tensile strength of the sandwich composites increased with increasing rolling reduction, and the sandwich composites showed a high elongation with 43.0 pct reduction.

The microstructure and properties of a Fe-2Cr-Mo-0.12C (wt pct)-tempered steel plate at different normalization temperatures after hot rolling were investigated to enhance its comprehensive mechanical properties. The microstructure of the steel was mainly composed of a ferrite-bainite-tempered martensite mixture after the normalization-tempering process. The tensile properties and the ductile-brittle transition temperature values indicated that the best comprehensive mechanical properties can be obtained by normalizing at 930 °C and tempering at 700 °C. When the normalization temperature was 880 °C to 930 °C, the yield strength increased as the bainite and tempered martensite hard phase volume fractions increased. However, when the normalization temperature surpassed 980 °C, the precipitation strength behavior compensated for the adverse influence of the effective grain size growth, and yield strength was nearly unchanged. Total elongation reached a peak value when normalized at 930 °C, due to the optimal volume fraction ratio of the soft to hard phase. The Charpy impact fracture changed from a ductile to a brittle fracture with an increase in the normalization temperature. When the normalization temperature was 930 °C, the existence of a certain volume fraction of nano-precipitates and soft ferrite in the microstructure contributed to excellent ductile properties.

As candidates for conductors used in high-field extreme conditions, Cu-Ag in-situ composites are required to possess high strength and conductivity; however, most Cu-Ag in-situ composites do not possess both characteristics. Therefore, it is important to determine the appropriate composition design of Cu-Ag composites that can enhance the mechanical properties while maintaining a relatively good electrical conductivity. This paper describes the effect of several potential alloying elements (Cr, Nb, and Zr) on the microstructures and mechanical properties of Cu-6 pctAg in-situ composites. The results reveal that the addition of both Cr and Nb refined the morphology of the Ag filaments and considerably improved the tensile strengths of the drawn Cu-Ag composites at large strains. Particularly, the ultimate tensile strengths of the Cu-6 pctAg-1 pctCr composites were improved by approximately 23 pct than that of the Cu-6 pctAg binary composites, with only a slight loss in conductivity. By contrast, the addition of 1 pctZr to the Cu-Ag composites had a negative effect on the morphology of the Ag filaments; it only improved the hardness at low drawing stains while reducing both the tensile strength and electrical conductivity.

Linear friction welding (LFW) offers a new approach to manufacture aerospace components while improving the buy-to-fly ratio. However, the fundamental knowledge associated with the LFW process, including the attendant microstructural evolution and corresponding mechanical behavior is still rather limited. In this research effort, subscale tensile coupons were prepared and tested to determine the properties of each discrete zone of the linear friction welded specimen, namely the welded zone, thermomechanically affected zone, and parent material. The results show that the yield strength of the welded zone is 20 pct higher than the parent material and the thermomechanically affected zone is 13 pct higher than the parent material. Materials characterization, including optical microscopy, scanning electron microscopy, electron backscattered diffraction-based orientation microscopy and transmission electron microscopy, was conducted to develop an understanding of the microstructure–property relationships. The highly refined nature of the microstructure makes final interpretations challenging, but the evidence suggests that the mechanical behavior is dominated by phenomenon that operate at the 1 to 50 nm length scale, including strain hardening and highly refined features that hinder slip.

We investigated the effects of hydrogen on e-martensite-related damage evolution (crack/void initiation and growth) in Fe-Mn-Si-base austenitic steel using tensile tests after gaseous hydrogen charging at 100 MPa. Specifically, we evaluated the quantitative hydrogen effects on e-martensite fraction and associated damage evolution with different strains and strain rates. Hydrogen charging increased the probability of e-martensite-related damage initiation and deteriorated micro-damage arrestability, which decreased elongation. The primary factor causing the detrimental hydrogen effects on resistance to damage evolution was the promotion of deformation-induced γ-e martensitic transformation. An increasing strain rate from 10−4 to 10−2 s−1 suppressed the γ-e martensitic transformation and correspondingly increased elongation. Interestingly, the e-martensite fraction near the fracture surface did not change with increasing strain rate, but the area fraction of the brittle-like fracture region decreased. This fact implied that the brittle-like fracture at the low strain rate, which had a longer time for damage growth, was assisted by stress-driven hydrogen diffusion near the crack/void tips.

High-strength alloys of Al-xZn-3Cu (x = 20, 30, 40 wt pct) are developed for die-casting process. The maximum tensile strength of the developed alloy is 435 MPa, with a stain to fracture of ~ 4 pct. Microstructural investigation shows that the grain size of α-Al gradually decreases and the area of the Zn-rich region increases as the amount of Zn increases. Local symmetry investigation reveals that the major phase of α-Al contains very fine nanoprecipitations of Zn phase (