Room Temperature Tensile Properties Research Articles

Effects of Cu additions on microstructure and mechanical properties of as-cast CrFeCoNiCux high-entropy alloy

The influences of Cu additions on the microstructural evolution and room-temperature tensile properties of the as-cast CrFeCoNi were investigated in detail. The results revealed that the structure of the alloy changed from a FCC single-phase to FCC1 plus FCC2 dual-phase by adding Cu element. The FCC2 phase was determined to be Cu-rich phase existing in the inter-dendrite region, and its volume fraction increased with the increase of Cu additions. The formation of Cu-rich inter-dendrite was mainly ascribed to the liquid-phase separation induced by the large positive mixing enthalpy between Cu and other metallic elements. The yield and ultimate tensile strengths against the Cu content displayed a positive correlation due to the enhancement of short-range obstacles to dislocations slip, while the more significant superposition of stress field produced by the dislocation piling-ups at grain boundaries of Cu-containing high-entropy alloys led to a small fracture strain.

Combining multiscale structure and TRIP effect to enhance room temperature tensile properties of 304 stainless steel by cryogenic cyclic plastic strengthening

In this paper, 304 austenitic stainless steel was strengthened by cryogenic cyclic plastic strengthening (CCPS) method to obtain a material that combined multiscale structure and transformation-induced plasticity (TRIP) effect. After strengthening, there were harder small α′-martensite particles limited to the dense slip bands skeleton in the austenite coarse grains, which led to dynamic strain partitioning during uniaxial tension tests at room temperature. In addition, martensitic transformation occurred steadily throughout the strain range of the tensile tests. At room temperature, the characteristics of cryogenic transformation were maintained and the saturation value of the transformation was increased. The strengthened material showed an excellent combination of high strength and ductility at room temperature.

Evaluation of the interaction between SiC, pre-oxidized FeCrAlMo with aluminized and pre-oxidized Fe-8Cr-2W in flowing PbLi

Dissimilar materials interactions are a major concern when liquid metals are used as a working fluid. To simulate a dual-coolant PbLi blanket, chemical vapor deposited (CVD) SiC, pre-oxidized FeCrAlMo (APMT) and pre-oxidized aluminized coating on Fe-8Cr-2 W (F82H) specimens were exposed to flowing commercial Pb-17at.%Li with a peak temperature of 650 °C in a pre-oxidized APMT thermal convection loop (TCL) for 1000 h. Similar to prior results in static PbLi, the coated F82H showed small mass changes and limited degradation of room-temperature tensile properties. After exposure, the α-Al2O3 on the surface coated F82H reacted with the PbLi to form LiAlO2. However, no significant Al coating loss or interdiffusion was observed. Mass transfer was observed between the APMT, TCL and the SiC specimens. Fe, Cr and Ni were dissolved into the molten flowing PbLi and transported through the TCL to react with the SiC specimens. Compared to a prior experiment with a majority of bare FeCrAl specimens that were exposed in a TCL with a peak temperature of 700 °C for 1000 h, the SiC reaction was reduced to only a few microns of carbides and silicides. Oxygen dissolved in the molten PbLi sustained the formation of an Al2O3 scale on the surface of the coating and induced the formation of a thin surface SiO2 layer on the surface of the SiC.

Influence of phase morphology, static recrystallization, and crystallographic texture on room temperature tensile properties of Ti–6Al–4V alloy: Comparison between post-tested equiaxed, bimodal, and lamellar microstructures

The influence of phase fractions, morphology, recrystallization, and crystallographic texture on the room temperature uniaxial tensile properties were investigated in a Ti–6Al–4V (Ti-64) alloy. The hot rolled and annealed Ti-64 alloy was heat treated to generate three different microstructures (equiaxed, bimodal, and lamellar) with varying volume fractions and dimensions of constituent phases (equiaxed primary α, transformed α laths, and β laths). The tested tensile specimens were characterized using techniques such as electron backscattered diffraction (EBSD), transmission electron microscopy (TEM), and X-Ray diffraction-based bulk texture analysis to determine the deformation mechanism of the alloy. Among three different microstructures, the equiaxed microstructure (α/β-900/950-FC) exhibited a superior strength-toughness combination, while the lamellar microstructure (β-1050-AC) displayed poor tensile properties. The bimodal microstructure (α/β-900/950-AC) showed intermediate tensile properties. Recrystallized α grains and their connectivity promoted an extended steady-state flow during deformation and ductile fracture. The bimodal microstructure work hardened faster as compared to the other two microstructures. TEM investigation on the post-tested microstructures showed that events such as dislocation multiplication and dislocation-dislocation interactions, formation of slip bands across the α grains, multiple slip and dislocation pile-ups contribute to hardening mechanisms during deformation. Whereas, slip transfer across α/α boundary and breaking of β laths are the events of softening mechanisms. The slip transfer across two adjacent α grains happens when the misalignment between grains is less than 10°. Equiaxed microstructures exhibited maximum slip transfer due to interconnected primary α grains. Bimodal microstructures (α/β-900/950-AC) exhibited slip transfer when a higher fraction of interconnected primary α is present in the microstructure. In contrast, the lamellar microstructure showed no evidence of slip transfer. The prism slip is the dominant active slip system in the equiaxed and bimodal microstructures. However, the lamellar microstructure with no primary α showed only the prismatic <c+a> and pyramidal <a> slip activities.

Thermal stability of dislocation structure and its effect on creep property in austenitic 316L stainless steel manufactured by directed energy deposition

The objective of this study is to investigate the thermal stability of dislocation structure and its effect on the creep behaviour of laser-directed energy deposited 316L stainless steel (L-DED-316L SS). Post-processing heat treatments at temperatures ranging from 300 to 1200 °C were performed on the as-deposited DED samples. The microstructural changes induced by the heat treatment were correlated to the corresponding variations of the room temperature tensile properties and creep behaviour at 650 °C/225 MPa. Results show that dislocations produced during DED process tend to distribute uniformly, with only a few localized fine dislocation cells (average cell size of ∼0.4 μm) being detected. At 600 °C, the remaining dislocations rearrange and organize into a coarse dislocation cell structure with an average cell size of ∼1.6 μm, leading to a slight decrease in yield strength, while the creep performance is not obviously affected. At 800 °C, the annihilation of dislocations and destruction of dislocation cell structure, as well as elemental diffusion contribute to a significant drop in yield strength and creep rupture time with a noticeable increase in steady creep rate. Further increasing heat treatment temperature above 1000 °C removes the dislocation cell structure and elemental segregation on cell walls, which results in a continuous increase in steady creep rate. The present work demonstrates that the presence of chemical micro-segregation is crucial for the stabilization of dislocation cells structure and the resulted creep performance of the heat-treated L-DED samples.

Formation of dendrites and strengthening mechanism of dual-phase Ni36Co30Fe11Cr11Al6Ti6 HEA by directional solidification

In order to reveal the effect of solidification rate on microstructure and improve room and high temperature tensile properties, Ni36Co30Fe11Cr11Al6Ti6 high entropy alloys (HEAs) were prepared by directional solidification at different solidification rates (5, 10, 20, 50 and100 μm/s). Results show that two kinds of dendrite form in the directionally solidified process. One is primary solidified dendrite, which is composed of FCC1 phase enriched in Co, Cr and Fe. Another is secondary solidified dendrite, forming between the primary solidified dendrites and consisting of the FCC2 phase enriched in Ni, Al and Ti. As the solidification rate increases, the primary solidified dendrite spacing decreases, the solute enrichment layer overlaps, and the constitutional undercooling in the inter-dendrite region decreases, increasing the difficulty of the secondary solidified dendrite formation. Tensile results show that the strength of Ni36Co30Fe11Cr11Al6Ti6 HEAs gradually increases with the increase of solidification rate. The alloy with a solidification rate of 100 µm/s exhibits excellent comprehensive room temperature properties, the yield strength, fracture strength and tensile strain are 732 MPa, 1020 MPa and 34.9 %, respectively. Furthermore, the directionally solidified Ni36Co30Fe11Cr11Al6Ti6 HEA still remains high yield strength of 533 MPa at 900 ℃. Fine grain strengthening, solid solution strengthening, second phase strengthening and hysteresis diffusion effects play an important role in enhancing the mechanical properties. By comparing the mechanical properties of other HEAs at room and high temperature, the proposed directionally solidified Ni36Co30Fe11Cr11Al6Ti6 HEAs with excellent mechanical properties show great potential in industrial applications.

Enhanced strength-ductility synergy in a wire and arc additively manufactured Mg alloy via tuning interlayer dwell time

Strength-ductility trade-off is a common issue in Mg alloys. This work proposed that a synergistic enhancement of strength and ductility could be achieved through tuning interlayer dwell time (IDT) in the wire and arc additive manufacturing (WAAM) process of Mg alloy. The thermal couples were used to monitor the thermal history during the WAAM process. Additionally, the effect of different IDTs on the microstructure characteristics and resultant mechanical properties of WAAM-processed Mg alloy thin-wall were investigated. The results showed that the stable temperature of the thin-wall component could reach 290 °C at IDT=0s, indicating that the thermal accumulation effect was remarkable. Consequently, unimodal coarse grains with an average size of 39.6 µm were generated, and the resultant room-temperature tensile property was poor. With the IDT extended to 60s, the thermal input and thermal dissipation reached a balance, and the stable temperature was only 170 °C, closing to the initial temperature of the substrate. A refined grain structure with bimodal size distribution was obtained. The remelting zone had fine grains with the size of 15.2 µm, while the arc zone owned coarse grains with the size of 24.5 µm. The alternatively distributed coarse and fine grains lead to the elimination of strength-ductility trade-off. The ultimate tensile strength and elongation of the samples at IDT=60s are increased by 20.6 and 75.0% of those samples at IDT=0s, respectively. The findings will facilitate the development of additive manufacturing processes for advanced Mg alloys.

Revealing the dynamic recrystallization mechanism, extrusion deformation mechanism, and tensile deformation behavior of Mg–6Al–1Zn–1.1Sc alloy

In this study, extruded deformed billet and extruded rod of Mg–6Al–1Zn–1.1Sc (wt. %) alloy were characterized by optical microscopy (OM) and electron backscatter diffraction (EBSD). The room temperature tensile properties and deformation behavior of extruded alloy were investigated using a universal testing machine and the visco-plastic self-consistent (VPSC) model. The results indicated that the coarse deformed grains (DGs) progressively disappeared and the degree of dynamic recrystallization (DRX) of the alloy increased as the sampling position approached the outlet of the extrusion die. In addition, the grain boundary strengthening induced by DRX increased the corresponding Vickers hardness. DRX mechanisms during extrusion included discontinuous DRX, continuous DRX, twin-induced DRX, and particle-stimulated nucleation (PSN). The EBSD-based in-grain misorientation axes (IGMA) analysis revealed that the slip modes within DGs were dominated by prismatic slip in the early stages of extrusion and by multiple slip modes in the later stages. The yield strength, ultimate tensile strength, and elongation of the extruded alloy were 172.4 MPa, 290.1 MPa, and 26.9%, respectively. The combination of grain boundary strengthening, texture strengthening, and secondary phase strengthening resulted in the high yield strength. The VPSC model well simulated the tensile deformation of the extruded alloy with (0001)//ED (extrusion direction) fiber texture. The superior plasticity of the extruded alloy was ascribed to the high Schmid factor (SF) of the non-basal slip and the activation of the non-basal slip facilitated by the reduction in the ratio of the critical resolved shear stress (CRSS) between the non-basal slip and the basal slip.

Effect of heat treatment on microstructures and mechanical properties of Inconel 718 additively manufactured using gradient laser power

To achieve high-performance nickel-based superalloys by laser powder deposition for applications in the aviation industry, post-heat treatments are always indispensable. We prepared two typical as-deposited microstructures by constant laser power deposition (CLP) and gradient laser power deposition (GLP), respectively. A systematic research on the room-temperature microstructural evolution, hardness, tensile property and fracture morphology of Inconel 718 after three kinds of heat treatments is performed. The as-deposited microstructure and segregation ratio (SR) can significantly influence the microstructure evolution. The as-deposited GLP samples with fine discrete Laves phases and a low SR can achieve a relatively uniform element distribution and γ′′ and γ′ phase precipitation after standard solution treatment plus aging (STA), while CLP samples with coarse long-chain Laves phases and high SR require a high-temperature homogenization plus STA (HSTA) heat treatment to achieve the uniform element distribution. Differences in heat treatments have a greater impact on the fracture mechanism. With the transformation of heat treatments from direct aging, STA to HSTA, the fracture mode of both CLP and GLP samples transforms from a ductile transgranular fracture mode to a mixed mode of transgranular and intergranular fractures.

Microstructure and hot tensile behavior of Hastelloy X superalloy laser powder-bed fusion-fabricated through different scanning patterns

Tailoring the microstructure of the additively manufactured metal parts through adjusting process parameters is a useful pathway to reduce the necessity of post-treatments, leading to a reduction in cost and production steps. This work deals with the effects of scanning patterns on microstructures and hot tensile behavior of the laser powder-bed-processed Hastelloy X Ni-based superalloy at the as-built condition. Two scanning patterns of meander and island were used to build fully-dense specimens. The scanning transmission electron microscopy observations revealed the generation of dislocation-cell structure within the columnar austenitic grains. Dense-dislocation tangles and some Cr- and Mo-rich precipitates decorated the cell walls. Both meander and island specimens had almost the same crystallographic texture, average local misorientation, and average geometrically necessary dislocations density. However, the specimen employing the island scanning pattern had a larger grain size and cell size than the meander one. It was due to a lower cooling rate in the island specimens than in the meander one. It was found that although the room-temperature tensile properties of both specimens were not significantly different, the island specimen had superior tensile properties at high temperatures. However, the meander and island tensile specimens both underwent intergranular brittle fractures at 760 °C and 860 °C, leading to ductility loss at elevated temperatures. The fractography observations illustrated that combined influences of the weakening of the grain boundaries with an increase in temperature and the accumulation of dislocations resulted in intergranular cracking, leading to brittle fracture and ductility loss at high temperatures.

Experimental study on tensile deformation behaviors under room and elevated temperatures induced by microstructure inhomogeneity of ZK60 Mg with a longitudinal weld

The tensile tests of the extruded ZK60 Mg containing a longitudinal weld seam were carried out at room and elevated temperatures, and the effects of induced microstructure inhomogeneity on tensile deformation behavior was clarified. The results show that the deformation mode, dynamic recrystallization (DRX), texture evolution and mechanical properties are strongly affected by the longitudinal weld seam, temperature, and loading direction. The room temperature (RT) deformation of welding zone is controlled by the dislocation slips with the association of some twins, while twinning plays significant roles in the accommodation of c-axis strain of the coarse grains on matrix zone. The deformation at RT stretched along extrusion direction (ED) and transverse direction (TD) are controlled by basal slip/twinning and basal slip/prismatic slip/twinning, respectively. During high temperature tension, the dislocation cross slip of pyramidal slip is activated, and grain boundary sliding occurred in welding zone, leading to the superplastic behavior. With the increase of tensile temperature, the predominant DRX mode is transformed from continuous DRX to discontinuous DRX. Moreover, the basal poles of the grains spread from TD towards ED with the decrease of maximum pole intensity when stretched along ED, while non-basal textures are transformed to 〈10–10〉 fiber texture when stretched along TD. The slip-dominated flow is seen during RT tension along ED, while twinning becomes predominant during RT tension along TD. The fine grain structure causes the superior RT tensile properties along ED of welding zone with ultimate tensile strength of 315 MPa and elongation to failure of 13.8%. With the increase of tensile temperature, the slipping-dominated deformation is transformed into twinning-dominated, causing the decrease of strength and increase of elongation.

The precipitation behavior effect of δ and γ" phases on mechanical properties of laser powder bed fusion Inconel 718 alloy

The mechanical properties of additively manufactured materials were mainly influenced by the precipitations in the microstructure. In this work, Inconel 718 (IN718) superalloy was fabricated by laser powder bed fusion (LPBF) and treated by solution and dual-aging treatments. The δ and γ" phases with different sizes and morphologies have been obtained by different solution temperatures. The precipitation behavior effect of δ and γ" phases on the room temperature tensile and high temperature stress rupture properties has been investigated. The results showed that the Laves phase formed in the as-fabricated sample. After solution heat treatment, the Laves phase dissolved and transformed to δ phase. As the solution temperature increased, the needle-like δ phase gradually dissolved, while only a little short rod-like δ phase remained. During aging heat treatment, the Nb element released from dissolved δ phase was beneficial to promote the precipitation of γ" phase. The content and size of nano-scale γ" phase significantly affected the yield strength of IN718 alloy. At higher solution temperature, the γ" phase with suitable size exhibited the highest yield strength of 1283 MPa. On the other hand, δ phase had a significant impact on high temperature stress rupture properties. The stress rupture life increased from 37.2 h to 52.5 h with decreasing volume fraction of δ phase. • Revealing the precipitation behavior of δ and γ" phases in different heat treatments. • The Nb released from the dissolved δ phase was beneficial to the precipitation of the γ" phase. • Quantitatively describe the effect of phase content, size and morphology on mechanical properties.

Thermodynamics, microstructure evolution and mechanical properties of Al- and C-added CoFeMnNi multi-principal element alloys

Navigating through the phase space of multi-principal element alloys (mpeas) with desired microstructures and outstanding properties is challenging due to extremely high degrees of freedom in alloy composition and processing conditions. Separate Al and C additions and the resulting precipitation of hard phases are commonly used to strengthen CoCrFeMnNi-type alloys. However, the combined alloying effect and especially the high hardening potential of C in solid solution of mpeas are rarely investigated, but the few existing investigations reveal a high potential. Therefore, the properties of the Al0−22.1C0−2.3(CoFeMnNi)100−75.6 (at.%) system were comprehensively investigated, where Cr was intentionally removed to keep C in solid solution. For theoretical and experimental screening of the system, a custom calphad database was extended, samples were manufactured by additive manufacturing (am) and annealed between temperatures of 1150 and 550 °C. Detailed microstructural and mechanical analysis on 40 different revealed the properties of the equiatomic CoFeMnNi alloy and the effect of the separate and combined additions of Al and C, including comprehensive precipitate characterization. The system was especially potent in its room temperature tensile properties in the Al- and C-added fcc-based region, where it caused the activation of twinning-induced plasticity (twip) and combined high strength and ductility increases.

The microstructure evolution and tensile properties of Ti–43Al–4Nb–1Mo-0.2B alloy during hot rolling

Ti–43Al–4Nb–1Mo-0.2B (at.%) (TNM) alloy sheets were fabricated, and the corresponding microstructure developed from lamellar to duplex structure with the rolling reduction increased from 50% to 72.5%. Interestingly, a novel Z-type lamellar structure developed at 67.5% deformation strain, and the formation process was discussed by calculating the Schmid factor. Moreover, α2+γ→βo phase transformation occurred at the kink band boundaries. Subsequently, as the reduction increased to 72.5%, the coarse βo phase decomposed and transformed to α2+γ phases due to the distortion energy stored after multi-pass rolling. Finally, the room-temperature tensile properties of the TNM sheets were tested. With the comparison of the as-forged alloy, the strength and ductility increased significantly by hot rolling, and the ultimate tensile strength reached 880 MPa at 60% total reduction. The relationship between the rolling process, microstructure evolution, and corresponding properties was established.

Improving high-temperature mechanical properties of laser powder bed-fused Inconel 738 alloy by hot isostatic pressing: Tailoring precipitates and healing defects

Microscopic defects and inferior high-temperature mechanical properties that occur during laser powder bed fusion (LPBF) of Inconel 738 alloys can severely hinder their industrial applications. Hot isostatic pressing (HIP) is a promising method to overcome these issues. In this study, the effects of HIP on the defects, grain structure, precipitated phase behavior, room- and high-temperature mechanical properties of an as-built Inconel 738 alloy were investigated. The results showed that, after HIP treatment, the defect densities in the XY and YZ planes of the as-built Inconel 738 alloy decreased from 0.537% and 0.292% to 0.251% and 0.123%, respectively. Moreover, the grain morphology of the as-built Inconel 738 alloy changed from elongated columnar grains to coarse equiaxed grains after HIP treatment, and the grain size became six times larger than that of the original sample, which was attributed to recrystallization and grain growth. Moreover, HIP treatment eliminated cellular dendritic segregation and significantly reduced dislocation densities in the as-built Inconel 738 alloy. Consequently, fewer M23C6 carbides were formed, but block-like M23C6 carbides were uniformly distributed at the grain boundaries after a combination of HIP and standard heat treatments. The HIP treatment reduced the room-temperature tensile properties of the as-built Inconel 738 alloy because of grain growth, low dislocation density, and coarser precipitates. However, the high-temperature (800 °C) tensile properties of the HIP sample with standard heat treatment (σuts = 827.8 MPa, σy = 744.3 MPa, εf = 2.2%) increased significantly compared to those of the as-built sample with standard heat treatment (σuts = 715.6 MPa, σy = 653.3 MPa, εf = 0.6%) and alleviated the embrittlement fracture owing to the formation of uniform carbides and lower defect densities. These results indicate that HIP treatment can significantly improve the high-temperature mechanical properties of LPBF-built nickel-based superalloys with high Al and Ti contents.

Avoiding cracks in additively manufactured non-weldable directionally solidified Ni-based superalloys

Additive manufacturing of directionally solidified Ni-based superalloys faces at least two critical obstacles, namely, the formation of stray equiaxed grains and the susceptibility to cracking; circumventing both of these simultaneously is considered difficult. In this study, a comparative study of a non-weldable superalloy IN738 fabricated through the laser directed energy deposition (DED) without preheating the base plate and the electron beam powder bed fusion (EB-PBF) with preheating up to the upper bound of ductility dip temperature range was performed. With appropriate process parameters, a steep and unidirectional temperature gradient, a sufficiently high cooling rate at the liquid/solid interface, and a relatively low cooling rate at the γ′ solvus are obtained simultaneously in the EB-PBF process. The prevalence of these conditions results in the growth of well-aligned columnar dendrites, mitigates the elemental segregation, reduces the built-in microscopic defects, and lowers the stored deformation energy. Consequently, cracking is successfully prevented and reasonable room temperature tensile properties are achieved in the as-printed EB-PBF product. Moreover, recrystallization is not triggered during the post-printing heat treatment, and thus the <001> fiber texture is preserved. This study provides a detailed understanding of the critical factors that need to overcome for producing directionally solidified superalloys through additive manufacturing. • Non-weldable IN738 superalloys was successfully fabricated by EB-PBF with preheating up to the upper bound of DTR. • A steep and unidirectional temperature gradient permits the directional growth of columnar dendrite. • High cooling rates during solidification suppress element segregation and low cooling rates at γ′ solvus help avoid cracks. • The as-printed EB-PBF product with a low stored deformation energy exhibits an excellent resistance to recrystallization.

Cold-rolled Ti-Al-V-Zr-Fe titanium alloy tubing with outstanding tensile properties

Increasing the operating pressure of the hydraulic lines is one of the directions to improve the comprehensive performance of the hydraulic system of an aircraft. However, the existing Ti-3Al-2.5V (limited strengths) and Ti-6Al-4V (poor cold formability) alloy tubing are not applicable to the hydraulic lines with an operating pressure over 28 MPa. In this work, a new type of Ti-Al-V-Zr-Fe titanium alloys were developed and the thin-walled seamless tubing was fabricated by cold rolling. After being annealed at 550 °C, Ti-4Al-2V-1.2Zr-0.3Fe (σb=1029 MPa, δ = 19%) and Ti-4.5Al-3V-1.5Zr-0.45Fe (σb=1102 MPa, δ = 18%) alloy tubing have outstanding room temperature tensile properties mainly due to dislocation strengthening. In addition, the strong radial textures in Ti-Al-V-Zr-Fe titanium alloy tubing, which increase the average Schmid factors under axial tensile loads, play a vital role in the strengthening contributions from dislocations and in the plastic deformation mechanisms. This work is of theoretical importance and practical value for developing aerospace hydraulic tubing with an excellent combination of mechanical properties.

Interstitial carbon content effect on the microstructure and mechanical properties of additively manufactured NiCoCr medium-entropy alloy

In this study, we manufactured the NiCoCr medium-entropy alloy (MEA) for the first time with controlled interstitial C content of 0.25 at% and 0.75 at% (0.25 C MEA and 0.75 C MEA) using a powder bed fusion-type additive manufacturing (AM) process. Moreover, we investigated the effect of interstitial C content on the microstructure, room temperature tensile properties and deformation behavior of MEA. The initial microstructure shows that both AM-built interstitial C-doped MEAs had a heterogeneous grain structure and epitaxial growth grains along the building direction. The analysis of electron channeling contrast images showed a large amount of nano-sized precipitates (in-situ precipitates) distributed at the sub-structure boundaries formed by a dislocation network, and a large number of stacking faults were simultaneously observed inside the sub-structure. The fraction of in-situ precipitates was higher in 0.75 C MEA than in 0.25 C MEA. A room temperature tensile test measured yield strengths (YS) of 747.5 MPa for 0.25 C MEA and 832.2 MPa for 0.75 C MEA, indicating the highest properties among additively manufactured MEAs reported to date. Considering the strengthening mechanisms, we compared the microstructural characteristics that affected YS, and identified that in-situ precipitates and high-dislocation density were major strengthening factors. On the other hand, deformation twin, which improves strain hardening rate and ductility was observed in both alloys. Based on the above results, we discuss the correlation of microstructure, mechanical properties, and deformation mechanism of AM-built interstitial NiCoCr MEA. • i-MEAs with different carbon contents were fabricated by additive manufacturing. • Mechanical and deformation behavior of AM-built i-MEAs were investigated. • Higher carbon addition lead to the enhanced tensile properties in AM-built i-MEA. • The predicted YS of i-MEAs corresponded well with the experimental data.

The Effect of Hot Oscillatory Pressing Temperature on Microstructure and Tensile Behavior of Powder Metallurgy Superalloy

The effect of the hot oscillatory pressing (HOPing) temperature on the microstructure and tensile behavior of the powder metallurgy superalloys was investigated and compared with those of the hot pressed (HPed) sample. The results show that as the HOPing temperature rises, the pores and residual dendrites disappear, the grain size becomes coarser and more uniform, the prior particle boundaries (PPBs) scale decreases; the yield strength decreases gradually; the ultimate tensile strength and elongation increase first and then decrease; the tensile property stability gradually increases. The highest ultimate tensile strength and elongation of 1403 MPa and 35%, respectively, are reached when the HOPing temperature is 1160 °C. The fracture mode of the sample hot oscillatory pressed (HOPed) at 1160 °C is a transgranular and intergranular mixed fracture. Compared with the HPed sample, room temperature tensile properties of the HOPed sample improve remarkably due to the reduced size and density of PPBs precipitates.

Microstructural Features, Tensile Properties, and Impact Toughness of Linear Friction Welded High-Temperature Alloy Joints for Blisk Assembly Applications

The main objective of this investigation is to analyze the microstructure, tensile properties, and impact toughness of Ti6Al4V alloy joints developed using optimized parameters of linear friction welding (LFW) for gas turbine blisk assembly applications. The 6 mm thick plates of Ti6Al4V alloy were joined using a friction time of 40 sec, a friction pressure of 20 MPa, a forging pressure of 10 MPa, a forging time of 3 sec, and an oscillating frequency of 14 Hz. The different regions of joints were analyzed using a stereo zoom microscope. Optical and scanning electron microscope (SEM) was used for analysing the microstructural features of joints. The room temperature tensile properties, hardness, and impact toughness of LFW-Ti6Al4V alloy joints were evaluated and correlated to the microstructural features of weld region. The fractured sections of tensile and impact toughness specimens of joints were analyzed using SEM and the failure of joints was correlated with the hardness survey. Results showed that the LFW-Ti6Al4V alloy joints developed using the optimized parameters exhibited a tensile strength (TS) of 1015 MPa, a yield strength (YS) of 940 MPa, and an elongation (EL) of 8%. The joints revealed 98.54%, 95.91%, and 66.67% of tensile strength, yield strength, and ductility of the parent metal. The LFW joints disclosed impact toughness (IT) of 17.2 J which is 89.77% impact toughness of the parent metal. The superior tensile properties and impact toughness of LFW-Ti6Al4V alloy joints are mainly attributed to a greater degree of refinement of α + β grains in the weld interface, which offers greater resistance to tensile deformation and crack propagation.