Phase Refinement Research Articles

Repetitive corrugation and straightening (RCS) of NiTi shape memory alloy strip product

ABSTRACT Repetitive corrugation and straightening (RCS) is a novel method of severe plastic deformation in bulk metallic materials. In this study, the effect of RCS on the properties of NiTi shape memory alloy (SMA) is investigated. Cold-rolled (CR) Ni49.8–Ti50.2 (at. %) strips with varying degrees of cold-work were subjected to RCS and evaluated for transformation, mechanical and functional properties. The study demonstrated that RCS can be used effectively to improve the strength and ductility of the CR SMA strips, while its transformation and functional properties are largely preserved. The ultimate tensile strength (UTS) and elongation to failure of the 30% CR strip post RCS increased from 950 MPa to 1130 MPa and ~19% to ~26%, respectively. The microstructural evaluation confirmed that RCS resulted in notable grain refinement and re-distribution of Ti2Ni second phase in the matrix. Consequent to its high strength, the cyclic response of the RCS strip on stress-free thermal cycling was found to be better than the CR strip.

Influence of Cooling Rate on Primary Silicon Size in Hypereutectic Al–Si Alloy Fabricated by Laser Powder Bed Fusion

Herein, the effects of cooling rate on primary silicon (Si) phases in laser powder bed fusion (PBF‐LB/M) processed hypereutectic Al–Si alloy are investigated. These alloys are particularly in demand for automotive and electronic applications, thanks to their excellent wear and thermal properties. Nevertheless, when processed by conventional methods like casting with comparatively lower cooling rates, the coarse primary Si phases are responsible for increasing brittleness and inducing crack propagation. The refinement of the primary silicon phases is aimed to be achieved through the PBF‐LB/M process, which offers a high cooling rate. The primary Si phases are observed under three different thermal substrate plate conditions—untempered, with cooling and heating, and additionally with varying volume energy density. Furthermore, the impact of primary Si size on the hardness of the fabricated samples is evaluated. The findings show that a faster cooling rate has a notable effect on refining the primary Si size. Then, hardness is directly affected by the primary Si size, with larger Si resulting in decreased hardness.

Refinement of Primary Si Phase in Hypereutectic Al–Si Alloy by Electrically Assisted Solidification with P Addition

Refinement of Primary Si Phase in Hypereutectic Al–Si Alloy by Electrically Assisted Solidification with P Addition

Effect of B4C nanoparticles addition on the refinement of Fe-rich phase in ZL108 alloy

Refining effect of B4C nanoparticles in ZL108 alloy on Fe-rich phase was studied in this work. It was observed that B4C nanoparticles apparently refines the size of the Fe-rich phases and partially transforms Fe-rich phases morphology from hollow polyhedron to petal-like shape. The DSC results show that B4C nanoparticles does not affect the initial nucleation temperature of the Fe-rich phase. However, the addition of B4C nanoparticles to ZL108 alloy inhibits the growth of Fe-rich phase. The TEM results confirm that the addition of B4C nanoparticles alters the lattice parameter of Fe-rich phase due to incorporation of C atoms, thereby suppressing the growth of the Fe-rich phase and ultimately leading to its refinement. From the perspective of fracture behavior, the addition of B4C nanoparticles remarkably reduces the stress concentration of Fe-rich phase, and the elongation of the alloy increases by 25.3%. These findings provide a new perspective for further research and development to refine Fe-rich phase.

Analysis of crystallographic phase retrieval using iterative projection algorithms.

For protein crystals in which more than two thirds of the volume is occupied by solvent, the featureless nature of the solvent region often generates a constraint that is powerful enough to allow direct phasing of X-ray diffraction data. Practical implementation relies on the use of iterative projection algorithms with good global convergence properties to solve the difficult nonconvex phase-retrieval problem. In this paper, some aspects of phase retrieval using iterative projection algorithms are systematically explored, where the diffraction data and density-value distributions in the protein and solvent regions provide thesole constraints. The analysis is based on the addition of random error to thephases of previously determined protein crystal structures, followed by evaluation of the ability to recover the correct phase set as the distance from the solution increases. The properties of the difference-map (DM), relaxed-reflect-reflect (RRR) and relaxed averaged alternating reflectors (RAAR) algorithms are compared. All of these algorithms prove to be effective for crystallographic phase retrieval, and the useful ranges of the adjustable parameter which controls their behavior are established. When these algorithms converge to the solution, the algorithm trajectory becomes stationary; however, the density function continues to fluctuate significantly around its mean position. It is shown that averaging over the algorithm trajectory in the stationary region, following convergence, improves the density estimate, with this procedure outperforming previous approaches for phase or density refinement.

Effect of pre-aging on mechanical reinforcement of the Cu–Fe–Nb composites

Pre-aging treatment was demonstrated to significantly enhance the mechanical properties of Cu–10Fe–1Nb (wt.%) composites. Specifically, after rolling and aging at 400 °C for 8 h, the microhardness, tensile strength, and elongation of the pre-aged samples reached 163 HV, 559 MPa, and 11.2%, respectively. The refinement of Fe-rich phases in pre-aged samples was primarily attributed to the increased shear strain between the Fe-rich phases and the matrix, which was driven by the precipitation-strengthening effect induced by pre-aging. Additionally, the matrix of the pre-aged samples suffered significant refinement as dynamic recovery and recrystallization of the matrix were suppressed during the rolling process, forming a high-density dislocation structure that greatly enhances the work-hardening effect. The main contribution to strength improvement in the Cu–10Fe–1Nb composites was identified as precipitation strengthening, refinement strengthening, and work hardening. Moreover, compared with the sample without pre-aging treatment, the refinement strengthening and work hardening effects of pre-aged samples exhibited substantial improvements, with increment of 49 MPa and 21 MPa, respectively.

Effect of multidirectional forging on grain structure and mechanical properties of hypereutectic Al–20%Si alloys with added refiners and modifiers

ABSTRACT The present work is focused on the multidirectional forging (MDF) of Al–20 wt-% Si alloys with the addition of refiners and modifiers. The MDF process was performed at 200°C with a cumulative strain of 0.63. Microstructural characterization and mechanical performance were evaluated on the Al–20Si, Al–20Si–4.5Cu, Al–20Si–4.5Cu–1(Al–Ti–B), Al–20Si–4.5Cu–1(Al–Ti–B)–10(Al–Sr). The microstructure analysis revealed significant changes in the eutectic and primary phase refinement. The micro-Vickers hardness confirmed that the MDF process resulted in increased hardness (125 ± 1.9 VHN) compared to the homogenized samples (96 ± 2.7 VHN). Tensile test results showed that with the accumulation of strain, ultimate tensile strength increased to 435 MPa from 302 MPa with reduction in the percentage of elongation from 7.8 to 5.6. The grains were more uniformly distributed with addition of modifiers, and refiners further reduced the nucleation number of eutectic grains. The wear study demonstrated that the wear resistance is more in the Al–Si-Cu-Sr sample due to the increased level of hardness. The combination of multidirectional forging techniques with judicious incorporation of refiners and modifiers engenders a synergistic enhancement of microstructural integrity, hardness profiles, and wear-resistant properties in hypereutectic Al-20Si alloys.

Optimization of microstructure and high-temperature mechanical properties of Ti4822/Ti2AlC composites through multiple solution-aging treatments

In this paper, a Ti-48Al-2Cr-2Nb (Ti4822, at%) based composite with uniformly distributed Ti2AlC nano-micro precipitates was prepared by powder metallurgy followed by a multiple solution-aging treatment. Multiple solution treatments eliminated the equiaxial γ grains in the sintered composites and refined the coarse-grained primary Ti2AlC phases, resulting in a fully lamellar microstructure with fine Ti2AlC precipitates embedded between the α2/γ lamellae. The high-temperature ultimate tensile strength of the heat-treated Ti4822/Ti2AlC composites reached 543 MPa at 800 ℃, and the elongation was 7.7 %, increased by 9.7 % and 0.8 % correspondingly compared to that of the sintered composite. The enhancement of the properties of Ti4822/Ti2AlC composite in the heat-treated state was due to the elimination of γ grains in the microstructure to transform the full lamellar microstructure on the one hand, and the refinement and dispersion of agglomerated Ti2AlC precipitates on the other hand. This study provided a valuable reference for the refinement and dispersion of the second phase in TiAl composites.

Ultra-High Strength in FCC+BCC High-Entropy Alloy via Different Gradual Morphology.

In this study, high-pressure torsion (HPT) processing is applied to the as-cast Al0.5CoCrFeNi high-entropy alloy (HEA) for 1, 3, and 5 turns. Microstructural observations reveal a significant refinement of the second phase after HPT processing. This refinement effect is influenced by the number of processing turns and the distance of the processing position from the center. As the number of processing turns or the distance of the processing position from the center increases, the fragmentation effect on the second phase becomes more pronounced. The hardness of the alloy is greatly enhanced after HPT processing, but there is an upper limit to this enhancement. After increasing the number of processing turns to 5, the increase in hardness at the edge becomes less significant, while the overall hardness becomes more uniform. Additionally, the strength of the processed alloy is significantly enhanced, while its ductility undergoes a noticeable decrease. With an increase in the number of processing turns, the second phase is further refined, resulting in improvement of strength and ductility.

Microstructure refinement and wear resistance enhancement of cost-effective Fe50−2xMn30Co10Cr10NixCux (x = 0, 5 at%) high-entropy alloys through cyclic closed-die forging process

Novel low-cost Fe50−2xMn30Co10Cr10NixCux (x = 0, 5 at%) high-entropy alloys (HEAs) were produced by vacuum melting and then processed by the cyclic closed-die forging (CCDF) process. It was found that both the as-homogenized and CCDF-processed specimens primarily consisted of a single face-centered cubic (FCC) structure, and the severe plastic strain through CCDF did not result in phase transformations. The microstructure of the CCDF-processed Fe50Mn30Co10Cr10 alloy after the sixth pass demonstrated a uniform structure with ultrafine grains measuring 285 nm in size, whereas for the CCDF-processed Fe40Mn30Co10Cr10Ni5Cu5 alloy, the grain size was 135 nm, with a relatively uniform distribution. The CCDF-processed Fe50Mn30Co10Cr10 and especially the Fe40Mn30Co10Cr10Ni5Cu5 alloy exhibited significantly higher microhardness compared to the as-homogenized state, with microhardness values being 2.42 and 2.72 times higher, respectively. Furthermore, the wear test results indicated that the CCDF processing effectively increased the wear resistance of the alloys, which was attributed to the changes in morphology and distribution of as-cast dendrites, along with the grain refinement of the matrix phase during CCDF. The CCDF-processed Fe40Mn30Co10Cr10Ni5Cu5 alloy exhibited the lowest wear rate, i.e., (1.2 ± 0.2) × 10–5 mm3.N−1.m−1, whereas that for the Fe50Mn30Co10Cr10 alloy was (2.4 ± 0.1) × 10–5 mm3.N−1.m−1. Analysis of wear surfaces indicated that the wear mechanisms of the as-homogenized HEAs were adhesive wear and abrasive wear with some delamination, while plastic deformation and adhesive wear were significantly reduced in the CCDF-processed specimens, especially in the Fe40Mn30Co10Cr10Ni5Cu5 alloy. These findings suggest that CCDF has the potential to achieve cost-effective nanostructured HEAs and to implement them in engineering applications.

Effects of Y2O3 Content on the Microstructure and Tribological Properties of WC-Reinforced Ti-Based Coatings on TC4 Surfaces

To extend the safety service life of aviation TC4 alloy, the composite coatings of TC4 + Ni-MoS2 + WC + xY2O3 (x = 0, 1, 2, 3, 4 wt.%) were prepared on TC4 by coaxial powder feeding laser cladding technology. The results showed that all the coatings had the same generated phases which mainly consisted of TiC, Ti2Ni, Ti2S, matrix β-Ti, and unfused residual WC. Y2O3 formed co-dependent growth relationships with TiC, Ti2S, and Ti2Ni. Meanwhile, TiC-Ti2S, TiC-Ti2Ni, and Ti2S-Ti2Ni coherent composite structure phases were effectively synthesized in all the coatings. With the increase in the Y2O3 content, the exposed area of the matrix increased and other phases refined progressively. When the Y2O3 content in the coatings were 3 and 4 wt.%, the degree of phase refinement in the coatings was consistent and the phases grew along grain boundaries, but microstructure segregated in the 4 wt.% Y2O3 coating. The microhardness of all the coatings was higher than that of TC4 and decreased with the increase in the Y2O3 content. Higher friction coefficients and lower wear rates both appeared in all the coatings than in the substrate, and they presented a trend of decreased first and then increased with the addition of Y2O3, in which the 3 wt.% Y2O3 coating had the lowest friction coefficient and optimal wear resistance. The research found that the Y2O3 could not change the types of phases in the coatings and could serve as a heterogeneous nucleation center for the refinement of the TiC-Ti2S-Ti2Ni coherent structure phase. Meanwhile, except for the matrix phase, Y2O3 could attract other phases to pinning on the grain boundaries of the coatings. The content of Y2O3 was negatively correlated with the hardness and wear resistance of the coating and it had the optimal tribological properties with the moderate amount of Y2O3. The wear mechanism of all coatings was abrasive wear.

Characterization of Sm-rich phase and properties of hypereutectic Al-Ni alloys modified by Sm

The impact of Samarium (Sm) addition on hypereutectic Al-Ni alloys was systematically investigated, focusing on microstructural changes and thermal-physical, mechanical properties. The addition of 0.1–0.5 wt% Sm resulted in the refinement of primary Al3Ni phases from coarse lath-like structures to small particles, enhancing mechanical properties and reducing thermal expansion coefficients (CTE). Thermal conductivity (TC) improved with 0.1–0.3 wt% Sm addition, but declined at the amount of 0.5 wt%. Excessive Sm addition leads to the formation of a Sm-rich phase, characterized by a two-phase mixed structure of Al11(Ni, Sm)3 surrounded by Al4Sm. Sm addition lowered the precipitation temperature of the primary Al3Ni phase, inducing significant constitutional undercooling and exhibiting a phase refinement effect. The Al-9Ni-0.3Sm alloy showed excellent performance, with a TC of 211.8 W/(m·K), CTE of 17.3×10−6/K (@25–100 °C), ultimate tensile strength of 169.5 MPa, and elongation of 10.4 %. Optimal addition of Sm improved TC, mechanical properties as well as reduced the CTE in the Al alloy at the same time and showed a good modification effect.

Refinement of Primary Si Phase in Hypereutectic Al–Si Alloy by Electrically Assisted Solidification with P Addition

The efficient processing of hypereutectic Al–Si alloys depends on controlling the microstructure of the primary Si phase during solidification. This study investigates the effects of electric current and phosphorus (P) addition on the refinement of primary Si, with the results confirming that applying electric current during solidification refines the primary Si phase; introducing P further enhances this refinement. Notably, when 10 ppm of P is added (below the identified critical amount of 20 ppm), an improved refinement effect is observed compared with the application of either electric current or P alone. Applying an electric current generates a circulating flow within the melt, resulting in an increased cooling rate, which leads to improved nucleation behavior for the primary Si phase. In addition, the circulating flow generated within the melt influences the dispersion of aluminum phosphide during nucleation. Adding P at concentrations above 40 ppm does not yield further benefits, suggesting a saturation point for its efficacy. This study demonstrates that the concurrent electric current application and minimal P addition can significantly enhance the refinement of primary Si phases, offering a potent approach for optimizing the microstructural properties of hypereutectic Al–Si alloys.

Effect of Al-Ti-B-Er on the Microstructure and Properties of Ultrahigh-Strength Aluminum Alloy

To refine the grain size and improve the mechanical properties of ultrahigh-strength aluminum alloy (Al-10Zn-1.9Mg-1.6Cu-0.12Zr), the Al-Ti-B-Er grain refiner was prepared by the melt reaction method using the aluminum melt and Al + Ti + B precursor. The results exhibit that the Al-Ti-B-Er grain refiner is mainly composed of a block TiAl3 phase, and loose agglomerated nano-sized TiB2 and Al3Er phases. The microstructure of ultrahigh-strength aluminum is significantly affected by the Al-Ti-B-Er refiner, which changes from dendrite to equiaxial grain with increasing Al-Ti-B-Er content, and the size of the eutectic phase is significantly refined. The high-efficiency refinement of Al-Ti-B-Er is due to Er promoting the uniform distribution of TiAl3 particles and the formation of loose agglomerated nano-sized TiB2 particles. The optimal addition content of Al-Ti-B-Er into ultrahigh-strength aluminum alloys is 1 wt%, whose grain size is approximately 40 µm. Additionally, the strength and ductility of ultrahigh-strength aluminum alloys are simultaneously improved by adding 1wt% Al-Ti-B-Er after the T6 treatment, reaching 756 MPa and 20%, respectively. This enhancement in strength and ductility is mainly attributed to grain refinement and the eutectic phase refinement.

Microstructural refinement and mechanical properties improvement of Mg–Al–Mn–Zn–Ca alloy processed by rotary swaging at room temperature

Mg-4.1Al-0.6Mn-0.5Zn-0.4Ca alloy with high strength was prepared through hot extrusion at 330 °C followed by room temperature rotary swaging. The changes of microstructure and mechanical behaviors of extruded and swaged alloys after undergoing different rotary waging passes were investigated. The results reveal significant microstructural refinement, fragmentation of the Al8Mn5 phases, and precipitation of the Al2Ca phases after rotary swaging. With the increase of rotary swaging passes, a noticeable rise in the fraction of LAGBs and a more uniform distribution and refinement of second phases occurred. The texture with <10–10> parallel to processing direction was formed after rotary swaging. The rotary swaging largely improves the alloy's strength, with the ultimate tensile strength and yield strength increasing from 298 MPa to 198 MPa for the as-extruded alloy to 372 MPa and 359 MPa for the as-swaged alloy after 13 passes, respectively. The improvement of mechanical properties is a result of grain boundary strengthening, dislocation strengthening, and the strengthening of second phases. This result may provide valuable insights and guidance in the design of high-strength magnesium alloys as well as their plastic processing methods.

Modification and strengthening of recycled Al-Mg-Si-based alloy upon continuous rheological extrusion (CRE) forming

With global warming and resource scarcity, it is crucial to devise a simple, energy-efficient, and low-emission recycling method for aluminum alloys. In the recycled Al-Mg-Si-based alloy, the coarse α-Al dendrites, the long plate-like β-Al5FeSi phase and bulk Mg2Si phase significantly impair the microstructure and mechanical properties of the alloys. In this works, combined the continuous rheological extrusion (CRE) technology with the addition of CRE Al-5.0Ti-1.0B (wt%) refiner, the recycled Al-Mg-Si-based alloy wires at extrusion ratios (ER) of 3, 5 and 7 were prepared. The refinement of Mg2Si and β-Al5FeSi phases and the grain refinement caused by the continuous dynamic recrystallization (CDRX) behavior in the CRE process were discussed. The strengthening mechanism of recycled Al-Mg-Si-based alloy was revealed. The results showed that, CRE technology and CRE Al-5.0Ti-1.0B (wt%) refiner can effectively refine Mg2Si and β-Al5FeSi phases, and even to the nanometer level. At the same time, the increase of ER and the addition of CRE Al-5.0Ti-1.0B (wt%) can promote the transformation of low angle grain boundaries (LAGBs) to high angle grain boundaries (HAGBs), thereby promoting the occurrence of CDRX. In addition, the increase of dislocations and nanophases caused by the increase of ER and the addition of CRE Al-5.0Ti-1.0B can effectively refine CDRX grains. When 0.2 wt% CRE Al-5.0Ti-1.0B (wt%) refiner was added at ER of 7, the ultimate tensile strength (UTS), yield strength (YS) and elongation (EL) of recycled Al-Mg-Si-based alloy were 259.40 MPa, 140.80 MPa and 18.20%, respectively. Grain boundary strengthening and dislocation strengthening were the primary mechanisms in enhancing the YS of the recycled Al-Mg-Si-based alloy.

Understanding of the correlation of structural and microwave dielectric performance of (1-x)MgTiO3 - xCaTiO3 ceramics for dielectric resonator antenna applications

In this article, the effect of CaTiO3 on the structural and microwave dielectric characteristics of MgTiO3 has been discussed. The (1-x)MgTiO3 - xCaTiO3 (abbreviated as (1-x)MT- xCT) for x = 0.025, 0.05, 0.075, 0.1 ceramics have been developed using a solid-state reaction route. The structural as well as morphological characteristics of specimens have been observed by employing X-ray diffraction and scanning electron microscope methods. The Rietveld refinement technique of X-ray diffraction data have been conducted for the refinement of structural phases. It suggests that two crystallographic phases have been present in all materials. The SEM images display dense well-identified grains of (1-x)MT - xCT (for x = 0.025–0.1) ceramics. The Raman spectroscopy method has been employed to detect the symmetry of ceramics and modes of vibration of the materials. The microwave dielectric characteristics like dielectric permittivity (εr), loss (tanδ), quality factor (Q×f), and temperature coefficient at resonant frequency (τf) of (1-x)MT - xCT (for x = 0.025–0.1) ceramics have been thoroughly investigated. The bond strength, bond valency, bond energy, and tolerance factor of (1-x)MT - xCT (for x = 0.025–0.1) materials have been evaluated and their relation with microwave dielectric characteristics has been discussed. The (1-x)MT - xCT (for x = 0.025–0.1) ceramics show excellent dielectric properties with near to zero τf. In addition, DRAs have been designed with (1-x)MT - xCT (for x = 0.025–0.1) materials as dielectric resonators and various antenna properties have been studied with the help of HFSS software. This work suggests that (1-x)MT - xCT for (x=0.05) material can be a promising candidate for DRA applications working in the C band.

Experimental and theoretical investigation on refining mechanism of Mg2Si by Y addition in the Mg-Al-Si alloys

Aiming at development of new lightweight and high-strength magnesium alloys, a combined experimental and theoretical study on refining mechanism of Mg2Si by Y addition in the Mg-Al-Si alloys was performed. Two alloys, Mg63.32Al22.83Si13.85 and Mg62.56Al22.55Si14.36Y0.52 (wt.%), were prepared and investigated by combining experimental characterization with quantum-mechanical and CALPHAD calculations. The experimental results indicated that Y can refine the Mg2Si phase in Mg-Al-Si alloys but it is rather sensitive to the preparation procedure of the alloys. It was observed that Al4MgY is surrounded by Mg2Si in the as-cast alloys with Y, but it undergoes separation after homogenization annealing. First-principles calculations revealed that the mechanism of Y refining the Mg2Si phase is direct adsorption on the Mg2Si surface rather than indirect adsorption in the form of the elements atomic substitution or entering the center interstitial sites of Mg2Si. The significant refinement of the Mg2Si phase after annealing is attributed to recrystallization within the grains, eliminating the original grain boundaries, and the surface activity is reduced with Y adsorption, resulting in the formation of new and smaller Mg2Si phases. The mechanism behind the Al4MgY phase being surrounded by Mg2Si in the as-cast state but subsequent separation after homogenization annealing is not heterogeneous nucleation, but maybe due to liquid entrapment.

Laser cladding Ni60 @ WC/ Cu encapsulated rough MoS2 self-lubricating wear resistant composite coating and ultrasound-assisted optimization

This research aims to broaden the scope of self-lubricating wear-resistant coatings for applications in diverse industries such as automotive, metallurgy, power, and aerospace. Employing laser cladding technology, we successfully fabricated high-performance self-lubricating ceramic composite coatings. A comprehensive investigation was conducted to understand the inhibitory effect of Cu on the thermal decomposition of MoS2, and the study systematically explored the relationship between powder composition, coating structure, and organizational properties. The mechanisms behind friction reduction and wear resistance were unveiled, shedding light on the formation of the MoS2 self-lubricating protective film. Research findings reveal that during the laser cladding process, Cu and Ni undergo solid solution, resulting in the formation of the Cu–Ni alloy phase and crystal refinement. The MoS2 aggregation area exhibits a fine dendritic structure, while the dispersion area showcases coarse dendritic and cellular crystals. The addition of Cu and MoS2 influences the content of the MxCy phase and the thermal decomposition of MoS2. The incorporation of Cu increases the average coating hardness, whereas MoS2 addition decreases it; nevertheless, the Cu/MoS2 coating hardness is enhanced by at least 6.4 %. Cu significantly improves the coating's wear resistance, with a relatively smaller impact on friction reduction. MoS2 functions as a friction-reducing phase during wear, effectively preventing the peeling of hard phases and reducing the friction coefficient. Cu is uniformly distributed in the coating, experiencing solid solution strengthening, reducing adhesive region areas, and minimizing wear debris generation. MoS2, although unevenly distributed, forms intermittent lubricating films on the surface. The lubricating film of the Cu/MoS2 coating remains stable, preventing mutual contact of the friction surface and concurrently reducing the friction coefficient and wear amount. While the study successfully prepared a self-lubricating ceramic coating with excellent wear resistance, some surface quality defects persist. Further optimization of the preparation method was achieved through ultrasound-assisted technology.

Tailoring the microstructure and mechanical properties of laser directed energy deposited Inconel 718 alloy via thermostatic substrate heating

The effects of different thermostatic substrate heating (TSH) temperatures on the stress state, microstructures, and mechanical properties of laser directed energy deposited (LDEDed) Inconel 718 alloy were systematically investigated. The results showed that the optimized TSH temperature (200 °C) transformed the original tensile residual stresses into compressive residual stresses, improved microstructure uniformity, and enhanced the comprehensive mechanical properties of the LDEDed Inconel 718 alloy. When the TSH temperature was 200 °C, the ultimate tensile strength (UTS) and yield strength (YS) of the specimen perpendicular to the building direction (0°) did not change significantly, while the elongation (EL) value was improved by 35.2 %. It was attributed to reduced dislocation density in conjunction with the relaxation of residual stresses. In contrast, the UTS and YS in the specimen parallel to the building direction (90°) increased by 20.4 % and 34.9 %, respectively, whereas the EL values decreased slightly. It was due to the combined effects of the massively precipitated finer and more homogeneous γ'' phase and grain refinement. Finally, the strengthening mechanism of TSH on the microstructures and mechanical properties of the LDEDed Inconel 718 alloy were systematically revealed.