Search

The mechanical and combustion properties of metal-nested composite hybrid rocket fuel grains composed of spiral aluminium (Al) frameworks fabricated using three-dimensional (3D) printing with an embedded paraffin-based fuel were investigated. The mechanical properties of the resulting grains were evaluated by compression tests. In addition, the combustion characteristics of the Al composite grains were examined in a lab-scale hybrid rocket engine with gaseous oxygen as the oxidizer at an initial mass flow rate of 17.9 g/s. Pure paraffin-based (PP) and acrylonitrile–butadiene-styrene (ABS) composite grains were also tested as baseline fuels for comparison. The Al-A composite grain exhibited superior mechanical and combustion properties, with Young modulus, yield stress, and regression rate increased by 757.1%, 381.3% and 52.5% compared with the PP grain. The Young modulus and combustion efficiency were also further improved, by 51.0% and 14.9%, respectively, by including perforations in the spiral blades. These improvements are discussed in detail herein based on experimental data together with numerical simulations. Emission spectra of the engine plumes were also acquired and used to qualitatively analyze the combustion characteristics of the Al blades. [ABSTRACT FROM AUTHOR]

The microstructure and microhardness of Ni-base superalloy IN-738LC fabricated by laser solid forming (LSF) with the preheating was investigated. The results showed that with the increase of the preheating temperature (T 0 ) (25 °C, 800 °C, 900 °C and 1050 °C), the total crack length decreased significantly, the segregation of Ti and Al worsened, and the volume fraction of equiaxed grain increased, as well as the size of blocky carbides, γ-γ′ eutectic and γ′ particles. The high-angle grain boundaries, at which the continuous liquid film can be easily formed, were found to be susceptible to cracking. Both the concentration of Ti and Al and the increase of dendrite spacing contribute to the growth of carbides and γ-γ′ eutectic in the interdendrite while the size of the γ′ phases was largely affected by preheating. It was interesting to find that γ′ phase exhibited a bimodal distribution in the bottom of the deposit with the preheating at 1050 °C. The average microhardness of the deposits without preheating and with preheating at 800 °C and 900 °C is about at the same level, while the deposit with preheating at 1050 °C has the lowest average value. The crack-free deposit can be obtained when T 0 was up to 1050 °C, and its room temperature tensile properties are superior to cast IN-738LC alloy. [ABSTRACT FROM AUTHOR]

The microstructure and mechanical properties of laser solid formed (LSFed) 300M steel with tempering treatment was investigated. The microstructure of laser solid formed 300M steel with tempering treatment mainly consisted of the tempered martensite, bainite and a small amount of retained austenite. When the tempering temperature increased from 250 °C to 350 °C, the size of martensite lath and martensite blocks changed little. There are two kinds of tempered martensite. With increase of the tempering temperature, ε-carbide in the general tempered martensite transformed to cementite. In another kind of tempered martensite, ε-carbide were found to be precipitated along specific growth directions, with at least two variants for carbide precipitation. The hardness presented an incomplete linear correlation with the tensile strength and the yield strength for LSFed 300M steel. The hardness in LSFed 300M steel had not shown a significant change with increase of the tempering temperature. The tensile strength and yield strength increased first till the tempering temperature reaches 290 ° C–310 ° C then decreased with further increasing the tempering temperature. Especially, the strength dramatically decreased when the tempering temperature was above 310 ° C. However, the elongation and percentage reduction of area changed little with increase of the tempering temperature. The tensile fracture of LSFed 300M steel with tempering treatment presented a ductile fracture pattern. [ABSTRACT FROM AUTHOR]

Microstructure and mechanical properties of laser solid formed 300M steel were investigated. The as-deposited microstructure presented the tempered martensite, the martensite with a small amount of bainite, and the mixture of martensite and bainite from the bottom to the top of the deposits. After heat treatment, the microstructure was refined and uniform, and consisted of the mixture of tempered martensite, bainite and retained austenite. The hardness only showed a little increase from the bottom to the middle–upper of the as-deposited 300M steel, there was a significant increase in the hardness at the top of as-deposited 300M steel. The hardness in the heat treated deposits tended to be uniform and higher than that in the as-deposited 300M steel. Tensile strength and yield strength of the as-deposited 300M steel were much lower than the wrought standard. Through heat treatment, the tensile properties of laser solid formed 300M steel were improved significantly and reached the forgings standard. [ABSTRACT FROM AUTHOR]

The application of laser powder bed fusion (L-PBF) in conventional high-strength wrought aluminum alloys is a significant challenge due to its high cracking sensitivity. In this study, 2024Al and 1.3-wt% Zr-modified 2024Al alloy deposits were prepared by L-PBF using pre-alloyed powder. The solidification cracking susceptibility of the 1.3-wt% Zr-modified 2024Al alloy was reduced to ∼0.4 of that of the 2024Al alloy. Compared to the complete columnar α-Al grain microstructure in the 2024Al deposit, the crack-free Zr-modified 2024Al deposit exhibited a heterogeneous grain structure having columnar α-Al grains in the inner region of the molten pool and ultrafine α-Al equiaxed grains at the fusion boundary. Based on the time-dependent nucleation theory and constitutional undercooling analysis ahead of solidification interface, the precipitation behavior of primary Al 3 Zr nanoparticles is analyzed, and it is deduced that the high intensity of effective nucleation sites by nanosized primary Al 3 Zr at the fusion boundary of molten pool leads to the formation of equiaxed grains at the beginning of the solidification of molten pool. The as-deposited Zr-modified 2024Al exhibited a yield strength (YS) of ∼376 ± 7 MPa and an ultimate tensile strength (UTS) of 441 ± 7 MPa with an elongation of 14.1 ± 1.6%. The YS and UTS increased to 402 ± 9 MPa and 483 ± 37 MPa after T6 heat treatment, respectively. Both the tensile properties of the as-deposited and T6-treated Zr-modified 2024Al were comparable to the wrought 2024-T651 alloy and higher than most of the previous L-PBFed Al–Cu–Mg alloys. [ABSTRACT FROM AUTHOR]

To date, the application of additive manufacturing techniques in fabricating SiAlON ceramics with intricate geometries has been limited. This investigation demonstrates the synthesis of SiAlON ceramics by integrating silicon nitride (Si 3 N 4) powders with variable proportions of aluminum nitride (AlN) utilizing the vat photopolymerization (VPP) approach. The effects of AlN content on the properties of SiAlON ceramic slurries, green bodies, and sintered parts were systematically investigated. Notably, the slurry's viscosity decreases progressively with an increase in AlN, aligning with VPP printing prerequisites. Additionally, the curing depth of the slurry enhanced proportionally with AlN augmentation, elevating from 21 μm to 44 μm at an energy exposure of 800 mJ/cm2, with the pivotal addition being 15 vol% AlN, where optimal properties were achieved. The zeniths of flexural strength, bulk density, relative density, and thermal conductivity were recorded at 385.66 ± 22.63 MPa, 3.34 ± 0.09 g/cm3, 96.22 ± 2.55 %, and 37.4 ± 0.31 W m−1 K−1, respectively. The fabrication of SiAlON ceramics with complex configurations was successfully realized, heralding a novel methodology for future SiAlON ceramic production. [ABSTRACT FROM AUTHOR]

Eutectic high entropy alloys (EHEAs) have attracted considerable interest because of their excellent casting fluidity and outstanding mechanical properties. In this study, a novel system of EHEAs, namely CrFeNi x V 0.64 Ta 0.36 (1.3 ≤ x ≤ 1.9) was designed and prepared. The microstructure evolution and mechanical properties of CrFeNi x V 0.64 Ta 0.36 EHEAs were investigated in as-cast state. The results showed that the alloy was composed of σ-phase, Fe 7 Ta 3 -type intermetallic compounds (IMC), and a small amount of the eutectic phase when x = 1.3. A rare bimodal eutectic microstructure [face-centered-cubic (FCC) structure /σ + Fe 7 Ta 3 -type IMC] was observed in EHEAs, even in high entropy alloys when x = 1.6, 1.7, 1.8, and 1.84. The typical hypo-eutectic microstructure was acquired when x was increased to 1.9. The fully eutectic composition, i.e., CrFeNi 1.85 V 0.64 Ta 0.36 with alternatingly lamellar FCC and Fe 7 Ta 3 -type IMC structures exhibited the best mechanical properties, with the compressive yield strength, fracture strength, and engineering strain being 1475.9 MPa, 2799 MPa, and 38.095%, respectively. [Display omitted] • A rare bimodal eutectic microstructure was observed in EHEAs, even in HEAs and conventional alloys. • The fully eutectic Ni1.85 gained best mechanical properties with σ s and ε being 1475.3 MPa and 38.095%, respectively. [ABSTRACT FROM AUTHOR]

Al-Mg-Sc-Zr is a high-performance Al alloy developed for laser additive manufacturing (LAM). The addition of Sc/Zr can stimulate both grain-boundary and precipitation strengthening, which are closely related to the precipitation behavior of the primary and secondary Al 3 (Sc,Zr) phases, respectively. For LAM, laser direct energy deposition (L-DED) and laser powder bed fusion (L-PBF) are two typical processes. However, little is known about the disparities in the microstructural evolution and strengthening behavior of Al-Mg-Sc-Zr alloys under the L-PBF and L-DED processes. In this study, a comparative analysis of the microstructure and strengthening behavior of L-DED- and L-PBF-processed Al-Mg-Sc-Zr alloys was conducted. Owing to the higher cooling rate during L-PBF, fewer primary Al 3 (Sc,Zr) phases precipitated during solidification, and more secondary Al 3 (Sc,Zr) phases formed during aging, resulting in higher precipitation strengthening. More importantly, the ultrafine grains at the submicron scale in the L-PBF sample not only enhanced grain-boundary strengthening but also provided additional strengthening owing to the lack of mobile dislocations in the microstructure. This work is helpful for further optimizing the mechanical properties of LAM-processed Al-Mg-Sc-Zr alloys. • L-DED-processed Al-Mg-Sc-Zr alloy exhibited a continuous yield behavior. • L-PBF-processed Al-Mg-Sc-Zr alloys exhibited a discontinuous yield behavior. • The lack of mobile dislocations under L-PBF endowed an additional strengthening. [ABSTRACT FROM AUTHOR]

Abstract: Crack characterization in Rene88DT superalloy prepared by laser solid forming (LSF) was investigated; the effect of hot isostatic pressing (HIP) on crack healing, microstructure and mechanical properties was also analyzed. It was found that cracks in LSFed Rene88DT mainly nucleate and propagate in the overlap zone of laser-deposited passes, and can be attributed to the liquation cracks. The size and amount of the cracks in LSFed Rene88DT are significantly affected by the overlap of as-deposited passes. Through HIP processing, crack healing occurred, which leads to a substantial improvement of the mechanical properties of LSFed Rene88DT superalloy. However, the insufficient overlap will result in very large cracks in the deposit, which makes the diffusion bonding during HIP not completely eliminate the local segregation of Ti and Nb in the crack healing region. [Copyright &y& Elsevier]

• Combined with thermodynamic calculation, the formation mechanisms of grain morphology and Laves phase are discussed in detail. • The contribution of different strengthening mechanisms to yield strength is quantitatively calculated. • The cause of anisotropy of fatigue crack growth rate in vertical and horizontal specimens is clarified. The microstructure and the anisotropy of mechanical properties for Inconel 625 superalloy prepared by directed energy deposition (DED) were investigated in this study. The microstructure of as-deposited sample was mainly composed of epitaxial columnar grains, which showed a z-shaped distribution along the deposition direction. Combined with thermodynamic calculation, the formation mechanism of Laves phase in as-deposited Inconel 625 superalloy was discussed in detail. Owing to the anisotropic microstructure of as-deposited sample, tensile properties and fatigue crack growth (FCG) behavior showed significant anisotropy. Compared to vertical sample, the grain boundary volume fraction in horizontal sample was larger, which caused that the ability of grain boundary strengthening and the resistance of fatigue crack growth were higher in horizontal sample during tensile and fatigue crack growth process. As a result, the yield strength and the ultimate tensile strength of horizontal sample were higher, while the fatigue crack growth rate was lower. However, the elongation of horizontal sample was smaller than that of vertical sample caused by the Laves phase distribution. [ABSTRACT FROM AUTHOR]

The mechanical properties of high strength structural steel (HSSS) at elevated temperatures are the basis for fire-resistant design of HSSS members and structures. Previous studies on the mechanical properties of HSSS at elevated temperatures were mainly conducted on QT (Quenched and Tempered) HSSS, while few studies were conducted on TMCP (Thermo-Mechanical Controlled Process) HSSS. In order to identify the effect of manufacturing process on the mechanical properties of HSSS at elevated temperatures, an experimental study was carried out by steady-state method on TMCP Q690 HSSS, considering nine elevated temperatures ranging from 200 to 800 °C. Results showed that the elastic modulus and strength of TMCP Q690 HSSS decreased significantly as the temperature increased over 400 °C, while the ultimate elongation increased as the temperature increased above 500 °C. Formulas for calculating the reduction factors of mechanical properties of TMCP Q690 HSSS at elevated temperatures were proposed. Comparing the results of TMCP Q690 HSSS with those of QT Q690 HSSS previously studied, it can be found that the reduction on elastic modulus and strength was more severe for TMCP Q690 HSSS than QT Q690 HSSS in most cases, which was explained in the microstructure level of HSSS. [ABSTRACT FROM AUTHOR]

Post heat treatment is necessary to optimize the microstructure of additive manufactured Ti–6Al–4V to satisfy the aeronautical criterion. However, the relationship between the unique heat treated microstructure features and corresponding mechanical properties of wire and arc additive manufactured (WAAMed) Ti–6Al–4V has not been completely understood so far. In this study, five subtransus heat treatment regimes were used to the WAAMed Ti–6Al–4V alloy, and the different heat treated microstructure and the resultant mechanical properties were investigated. The microstructure was not substantially changed after heat treatment 600 °C/4 h/air cooling (AC). The α laths were coarsened after heat treatment 850 °C/2 h/AC, and the higher annealing temperature contributed to the appearance of α s. After solution and aging treatment, there were the discontinuous α GB , coarsened α p , and fine α s. There was the small Widmanstätten structural α s sharing the uniform crystallographic orientation after heat treatment 930 °C/1 h/AC + 550 °C/4 h/AC. The α′ martensite and extremely fine dispersed granular α s were obtained after heat treatment 930 °C/1 h/water quenching (WQ) + 550 °C/4 h/AC. The heat treatment 930 °C/1 h/WQ + 800 °C/2 h/AC was found to be the best heat treatment in this study. The discontinuous α GB , dispersed α s with various crystallographic orientations were obtained, which simultaneously increased the ultimate tensile strength (UTS) and elongation (EL) to 886 ± 8 MPa and 16.6 ± 1.6%, comparing to 847 ± 12 MPa and 12.2 ± 2.8% for the as-deposited specimen. Besides, the α/β interface phase distribution in the as-deposited and heat treated specimens was concerned. Two break-up mechanisms of α p , including boundary splitting and termination migration, were observed and discussed. • The UTS and EL were simultaneously increased by heat treatment. • The strengthening mechanisms of unique heat treated microstructure were clarified. • Two mechanisms of α p break-up were identified and investigated in heat treated specimens. • The α/β interface phase in the as-deposited and heat treated specimens was observed and discussed. [ABSTRACT FROM AUTHOR]

A Ti–6Al–4V alloy wall with 80 vol.% equiaxed prior-β grains was fabricated via wire and arc additive manufacturing. However, the equiaxed prior-β grains were characterized by strong texture. Formation mechanisms of the equiaxed prior-β grains were discussed. The tensile results presented a much lower anisotropy than that in other studies. [ABSTRACT FROM AUTHOR]

The mechanical anisotropy of laser directed energy deposition (L-DED) titanium alloys using laser solid forming (LSF) is significantly deteriorated owing to the coarse prior β columnar grains and continuous grain boundary α-laths (α GB). The influence mechanisms of trace boron (up to 0.25 wt%) on the microstructure, tensile properties and anisotropy of Ti6Al4V manufactured by LSF were investigated. The sizes of β grains and α phases both decreased with increasing boron content. Compared with the Ti6Al4V deposit, when the addition of boron was 0.08 wt%, the average width of β grains was reduced by about one order of magnitude owing to the growth restricting effect caused by boron and Zener pinning by TiB. Besides, the average length and aspect ratio of α-laths were reduced by 43% and 33%, respectively, owing to the refinement of β grains and the heterogeneous nucleation of α phases on TiB particles. With an increase in boron content, the strength anisotropy gradually decreased for the disappearance of α GB , the elongation anisotropy initially increased and then significantly decreased for the poor deformation compatibility between the TiB and the matrix. A better combination of strength and elongation could be obtained with the addition of 0.08 wt% boron to Ti6Al4V. Unlabelled Image • The prior β grains are significantly refined after the addition of boron. • The α phase aspect ratios are significantly reduced with the increase of boron content. • The highly orientated TiB phases play a significant role in the anisotropy. [ABSTRACT FROM AUTHOR]

Porous Si 3 N 4 ceramics are highly regarded as ideal materials for radomes due to their unique characteristics. However, the slurry used for the preparation of porous Si 3 N 4 ceramics suffers from a low cure depth, making it challenging to fabricate ceramic components using DLP technology. In this study, porous Si 3 N 4 ceramics were prepared by combining DLP technology with pore-forming agent method. The addition of polymethyl methacrylate (PMMA) powders with lower refractive index than that of Si 3 N 4 powders can improve the penetration depth of ultraviolet light in the Si 3 N 4 slurry. A systematic study was conducted to investigate the influence of the addition of PMMA powders on the properties of Si 3 N 4 slurries and porous Si 3 N 4 ceramics. When PMMA powders were added at 10 wt%, the slurry with a lowest viscosity of 0.13 Pa s (the shear rate is 30 s−1) and cure depth of 40.0 μm (the exposure energy is 600 mJ/cm2) was obtained. With the increase of PMMA content, porous Si 3 N 4 ceramics experienced a gradual decrease in both the flexural strength and bulk density, while the porosity increased from 14.41% to 27.62%. Specifically, when 20 wt% PMMA was added, the resulting porous Si 3 N 4 ceramics had a lowest bulk density (2.41 g/cm3), a maximum porosity (27.62%), and a flexural strength (435.87 MPa). The study is of great significance in establishing an experimental foundation for fabricating porous Si 3 N 4 ceramics by using DLP technology. [ABSTRACT FROM AUTHOR]

Porous Si 3 N 4 ceramics with high strength and high transmittance have been widely used in the field of defense and military. Additive manufacturing (AM) technology is one of the effective means to fabricate porous Si 3 N 4 ceramics. Nevertheless, it is difficult to prepare porous Si 3 N 4 ceramics by using digital light processing (DLP) because of the large refractive index difference between Si 3 N 4 powders and photosensitive resin. In this study, the effects of the amount of polystyrene (PS) powders on the properties of Si 3 N 4 ceramic slurries and sintered ceramics were systematically discussed. The addition of PS reduced the overall refractive index of powders and increased the average particle size of powders, thus improving the cure depth of Si 3 N 4 ceramic slurries from 11.0 ± 2.0 μm to 55.7 ± 1.8 μm. With the increase of PS content, the shrinkage and porosity of Si 3 N 4 ceramics gradually increased, and the bulk density and flexural strength showed the opposite trend. The slurry with low viscosity (2.38 Pa٠s at a shear rate of 30 s−1) and high cure depth (51.2 ± 4.6 μm) was obtained when the content of PS was 15 wt%, which met the thickness requirements for printing. The total porosity of Si 3 N 4 ceramics reached the maximum values at 28.21 ± 2.58%. The addition of PS solved the problem of low cure depth of slurries, and PS as a pore-forming agent could help Si 3 N 4 ceramics form porous structure. This research provides valuable insights into the fabrication of non-oxide ceramics with high refractive index using DLP technology. [ABSTRACT FROM AUTHOR]

Needle‐like nanocrystalline mullite powders were prepared through the molten salt process at the temperature of 900°C using coal gangue as raw material. Then, mullite‐based composite ceramics were prepared by a conventional solid‐state reaction between in situ synthesized mullite and Al2O3 powders. Effects of Al2O3 content and sintering temperatures on phase compositions, microstructure, and mechanical properties of the mullite‐based composite ceramics were also studied. The results show that mullite content productivity increase from 72% to 95%, as the sintering temperature increased from 1480°C to 1580°C, which led to the improvement in the bulk density and flexural strength of the samples. The three‐dimensional interlocking structure for mullite‐based composite ceramics was obtained by the in situ solid‐state reaction process. The maximum bulk density, flexural strength, and fracture toughness for the sample with 15 wt% Al2O3 content are 2.48 g/cm3, 139.79 MPa, and 5.62 MPa··m1/2, respectively, as it was sintered at the temperature of 1560°C for 3 h. The improved mechanical properties of mullite‐based composite ceramics maybe ascribed to good densification and increased mullite phase content, as well as to the in situ three‐dimensional network structure. Therefore, the results would provide new ideas for high‐value utilization of coal gangue. [ABSTRACT FROM AUTHOR]

Abstract: Al2O3/Y3Al5O12/ZrO2 directionally solidified ceramic has been considered as a promising candidate for ultrahigh temperature structural materials due to its excellent performance even close to its melting point. In this work, laser floating zone (LFZ) solidification experiments were performed on Al2O3/Y3Al5O12/ZrO2 hypereutectic with the solidification rates between 2μm/s and 30μm/s. The full eutectic lamellar microstructure is obtained with hypereutectic composition. The solid/liquid interface morphology is investigated. The microstructure characteristic is discussed based on the solid/liquid interface. The variation of lamellar spacing with different compositions and solidification rates was reported and discussed by considering an irregular eutectic growth model. The maximum hardness and fracture toughness are 19.06GPa and 3.8MPam1/2, respectively. The toughening mechanism of ZrO2 is discussed based on the scenario of the crack propagation pattern. [Copyright &y& Elsevier]

Solid-liquid composite lubrication coatings provide highly reliable and long-lasting solutions to friction, wear, and lubrication problems in extremely harsh environments. Herein, a novel type of solid-liquid composite lubrication coating with a high load-bearing capacity and long service life was constructed by introducing epoxy resin containing lubricating oil into inherent defects of thermally sprayed ceramic coatings. Compared with conventional ceramic coatings, the hybrid coatings exhibited an 80.5 % reduction in the coefficient of friction to 0.15 and a decrease in the specific wear rate from 2.69 × 10−4 mm3·N−1·m−1 to 3.86 × 10−8 mm3·N−1·m−1. The low friction and wear of the composite coating were mainly attributed to the formation of a well-covered lubrication film consisting of PFPE, epoxy resin, Al 2 O 3 , and ZrO 2 during the friction of the composite coating. This paper presented a novel approach to preparing new solid-liquid composite lubricating coatings that using unavoidable defects in thermal sprayed ceramic coatings to introduce a lubricating phase. • Novel organic-ceramic self-lubricating coatings prepared. • The filling of ER and PFPE improves the density and mechanical properties of the coatings. • Composite coatings exhibit excellent tribological properties. • A lubricating film generates at the friction interface. [ABSTRACT FROM AUTHOR]

Abstract: Inconel™ 718 (IN718) has been deposited using laser rapid forming (LRF) from the gas atomized (GA) and plasma rotation electrode preparation (PREP) powders. The mechanical properties of LRF IN718 were evaluated and compared in between as-deposited and heat-treated state. The results show that the existence of the porosities in as-deposited samples, caused by the hollow particles in the GA powders, results in the low ductility and stress rupture properties for LRF GA IN718, since it will promote the occurrence of the micro-porous coalescence failure in the tensile samples. However, the ultimate tensile strength for heat-treated LRF GA IN718 is comparable to that of the wrought IN718, which is 1.5 times of that of the as-deposited samples. It is found that there exists a continuous thin film of Nb-rich MC carbides along the grain boundaries on the fracture surface of the stress rupture samples, which makes cracks initiate and propagate along this path easily, which also results in the poor stress rupture life for LRF GA IN718. The porosities and microcracks in LRF sample were successfully eliminated by using PREP powders, which leads to a substantial improvement in both tensile and stress rupture properties of LRF IN718. [Copyright &y& Elsevier]

The effects of Fe2O3 on phase evolution, density, microstructural development, and mechanical properties of mullite ceramics from kaolin and alumina were systematically studied. X‐ray diffraction results suggested that the ceramics consisted of mullite, sillimanite, and corundum, in the sintering range of 1450°C–1580°C. However, as the sintering was raised to 1580°C, mullite is the main phase with a content of 94%, and the corundum phase content is 5.9%. Simultaneously, high‐temperature sintering had a positive effect on the densification of the mullite ceramics, where both the bulk density and flexural strength could be optimized by adjusting the content of Fe2O3. It was found that 6 wt% Fe2O3 was optimal for the formation of rod‐shaped mullite after sintering at 1550°C for 3 h. The sample's maximum bulk density was 2.84 g/cm3, with a flexural strength of 112 MPa. Meanwhile, rod‐shaped mullite grains with an aspect ratio of ~9 were formed. As a result, a dense network structure was developed, thus leading to mullite ceramics with excellent mechanical properties. The effect of Fe2O3 on the properties might be attributed to the fact that Al3+ ions in the [AlO6] octahedron were replaced by Fe3+ ions, resulting in lattice distortion. [ABSTRACT FROM AUTHOR]

Chemical short-range order (CSRO) plays an instrumental role in determining the mechanical properties of high-entropy alloys (HEAs). Current methods for controlling CSRO mainly focus on cast HEAs, which can not solve the problem of grain coarsening caused by homogenization treatments. Laser Powder Bed Fusion (LPBF), which has extremely high cooling rates, can suppress compositional segregation, refine grain structures, and achieve low CSRO. This offers a promising avenue for quantitatively controlling CSRO without the need for homogenization treatments. In this study, we investigate the CSRO of HEAs fabricated via LPBF and elucidate their influence on nanoindentation behavior. The results show that, at the low cooling rate, the average size of CSRO is 0.66 nm and they occupy 2.8% of the cross-sectional area, while at high cooling rate, the corresponding values are 0.92 nm and 9.9%, respectively, both of which are significantly smaller than those of cast HEAs. By analyzing samples with different CSROs, we observe that the hardness increases and then decreases with the increase of CSRO, primarily due to the preferential formation of dislocations in regions enriched with Cr-Mn-Ni. With the improvement of CSRO, both the size and quantity of Cr-Mn-Ni rich region gradually increased; subsequently, as multiple Cr-Mn-Ni rich regions tend to merge into one during the CSRO improvement, the size of the Cr-Mn-Ni rich region continued to increase while the quantity gradually decreased; when the size of the Cr-Mn-Ni rich region is moderate and widely dispersed, the dislocation density is higher with much more uniform distributions, which favorably improves nanoindentation hardness. [Display omitted] • High energy density leads to high CSRO. • The nanohardness initially increases and then decreases with the elevation of CSRO. • Dislocations are prone to slip in the Cr-Mn-Ni-enriched region. • The size and distribution of Cr-Mn-Ni play a crucial role in determining the dislocation density and uniformity. [ABSTRACT FROM AUTHOR]

IN718Plus superalloy with hierarchical microstructure has been successfully manufactured by laser directed energy deposition (LDED). Along building direction, microstructure varies from composing of epitaxial columnar grains oriented along <001> γ direction to equiaxed grains in flower like configuration. Striped Laves phase and fine γ'/γ'' precipitates form in the columnar grains, and would transform into fine Laves phase particles and nanoscale γ' precipitates at equiaxed layer. To improve the compositional homogeneity and microstructural stability, high temperature solution treatment has been explored on the superalloy. The treatment would not affect the morphology and orientation of columnar grains, but would redissolve Laves phase precipitates. Double aging treatment has also been performed to obtain homogeneous distributed γ' precipitates, and the synergistic regulation of microstructure enhances the mechanical property significantly, as causing the room temperature yield strength and tensile strength increased from 0.88 GPa and 1.14 – 1.04 GPa and 1.28 GPa, respectively. Moreover, the excellent mechanical property would be maintained upon 704 ℃, with yield strength of 0.93 GPa, tensile strength of 1.04 GPa and high elongation of 27.3%. [Display omitted] • IN718Plus superalloy with hierarchical microstructure has been successfully manufactured by LDED. • As-deposited microstructure is composed of columnar to equiaxed grains with hierarchical Laves phase and γ'/γ'' precipitates. • Appropriate heat treatment process has been explored as 1100 ℃/1.5 h + 788 ℃/8 h + 704 ℃/8 h to ameliorate the performance. • Excellent 704 ℃ tensile properties have been obtained with tensile strength of 1.04 GPa and elongation of 27.3%. [ABSTRACT FROM AUTHOR]

35CrMnSiA is a type of ultra-high-strength steel that finds extensive application in key components characterized by geometrically regular structures and complex extensions, such as structural shells. Laser hybrid additive manufacturing (LHAM) is an advanced manufacturing technology that combines the benefits of traditional manufacturing and additive manufacturing. LHAM has the potential for rapid and cost-effective production of these components. However, the formation mechanism of the microstructure in different zones of 35CrMnSiA steel fabricated by LHAM and its impact on the overall tensile performance remain unclear, thereby tremendously restricting its application. To address this issue, this study employed wrought 35CrMnSiA steel as the base material and utilized directed energy deposition (DED) to fabricate defect-free LHAM parts. The microstructure of LHAM-fabricated 35CrMnSiA steel is location-related. The laser deposition zone comprised ferrite with internal and boundary-distributed carbides, whereas the substrate zone comprised martensite. The heat-affected zone exhibited a gradient microstructure between the two. The microstructure in the deposition zone was primarily governed by solidification behavior and thermal history during the deposition process, while the heat-affected zone was mainly influenced by recrystallization. The non-uniform characteristics of the microstructure significantly influenced its mechanical properties, resulting in a "cask effect," namely, the tensile performance of LHAM-fabricated 35CrMnSiA steel depended on the weakest laser deposition zone. The ultimate tensile strength and elongation of LHAM-fabricated 35CrMnSiA steel are 959 MP and 15.2%, respectively. This study establishes a basis for controlling the microstructure and optimizing the performance of hybrid-manufactured ultra-high-strength steel. [ABSTRACT FROM AUTHOR]

Abstract The 2024Al alloy and 3%TiB 2 reinforced 2024Al composite were fabricated using laser solid forming (LSF). Different from the LSF processed 2024Al with a large columnar grain and apparent preferential growth orientation, TiB 2 reinforced 2024Al composite presents texture-less structure, consisting of the dendrite and fine equiaxed structures. Some TiB 2 particles distribute within the Al matrix, others distribute along the grain boundaries and intertwine with the Al 2 Cu phase. The incorporation of TiB 2 gives rise to significant grain refinement, which is one of the important reasons for the improvement of mechanical properties. Moreover, the TiB 2 reinforced 2024Al sample exhibits 284 MPa high tensile strength, 163 MPa yield strength, 108.5HV microhardness, and 18.7% excellent elongation. [ABSTRACT FROM AUTHOR]

The mechanical properties of many metallic materials have been optimized by magnetic field-assisted additive manufacturing, however, there is still a gap in high-entropy alloys (HEAs) in this field, which is not conducive to the control and optimization of the microstructure and properties of HEAs. This work studied the tensile properties of laser powder bed fusion (LPBF) CoCrFeMnNi HEA. After applying a magnetic field, the relative density increased, and the grain size became larger and more uniform. Because of amperage force, crystallographic textures gradually change from< 100 > to< 110 > and< 111 > , which contributes to the improvement of tensile properties. Additionally, low-angle grain boundaries and geometrically necessary dislocations decrease, while the Schmidt factor increases. In the results of these changes, most factors contribute to improving the mechanical property, eventually optimizing the strength and ductility simultaneously. This indicates that magnetic field-assisted LPBF is promising to be an important means to optimize the mechanical properties of HEAs. • The HEA prepared by magnetic field-assisted additive manufacturing was studied for the first time. • The existence of a magnetic field changes the microstructure of CoCrFeMnNi obviously. • Magnetic field-assisted additive manufacturing can improve both strength and ductility of CoCrFeMnNi. • <101>and<111>crystallographic textures of CoCrFeMnNi have better tensile property than<001>. [ABSTRACT FROM AUTHOR]

A series of Ti-2Al- y Mo ( y = 2,5,7,9,12) alloy samples were produced from blended elemental Ti, Al and Mo powders using the laser solid forming technology. The influence of the β stabilizer Mo on the morphology of the grains, the size and the distribution of the α laths, the Vickers hardness and the tensile properties of Ti-2Al- y Mo alloys were explored under designated laser processing parameters. It was found that the microstructure in Ti-2Al-5Mo, Ti-2Al-7Mo, Ti-2Al-9Mo, and Ti-2Al-12Mo deposited layers were composed of irregular columnar grains that grow epitaxially, with some small equiaxed grains in the upper region, while that of the Ti-2Al-2Mo alloy was composed of large columnar grains. The grain size decreased, while the thickness of equiaxed grains layer increased with increasing Mo content. This indicates a tendency towards columnar-to-equiaxed transition with increasing Mo. The dominant β grains form a basketweave microstructure composed of primary α laths, secondary α laths and retained β phase. It was also observed that with increasing Mo content, both the size of primary α laths and secondary α laths decreased significantly, while the number of secondary α laths increased sharply, and the Ti-2Al-12Mo is also constituted of α phase and β phase. The Young's modulus of Ti-2Al-7Mo, Ti-2Al-9Mo, and Ti-2Al-12Mo were basically the same within experimental error. Tensile testing of the specimens showed that Ti-2Al-7Mo exhibits a good combination of strength and elongation to failure. As a result, this material can be considered suitable as a viable feedstock for laser additive manufacturing. [ABSTRACT FROM AUTHOR]

In this work, the microstructural evolution of a directed energy deposited near β titanium alloy, Ti5Al2Sn2Zr4Mo4Cr, during post-heat treatment was investigated, and its effect on the mechanical properties was evaluated. The results showed that the equilibrium volume fraction of the α phase was reached in the first 30 min over a temperature range of 720–840 °C. Fine basketweave α laths (α BW) were homogenously distributed within the prior β grains at 840 °C. Both fine α BW and α colonies developed from the grain boundary α layers (α GBW) were obtained in the sample solutions treated at 720, 760, and 800 °C. Water-quenching and air-cooling were employed to retain the β phase at room temperature. The α phase volume fraction increased significantly and reached the equilibrium volume fraction during the furnace-cooling process. In addition, the manner in which the samples were subjected to isothermal temperatures can strongly affect the evolution of the α phase. The homogenized specimen containing a single β phase exhibited the lowest strength and the highest plasticity. The strength increased and the ductility decreased after subtransus solution treatment. The difference in the mechanical properties can be attributed to the differences in the α and β phases caused by the various heat treatments. The modified rule of mixtures appropriately described the relationship between the yield strength and microstructure characteristics. • The transformation kinetics of directed energy deposited near β Ti alloy was studied. • The manner in which the sample was subjected to isothermal temperature strongly affect the α phase evolution. • The relationship between the yield strength and microstructure was described. [ABSTRACT FROM AUTHOR]

In this paper, laser additive manufacturing (LAM) technology with powder feeding has been employed to fabricate 50%LAMed specimens (i.e. the volume fraction of the laser deposited zone was set to 50%). With aid of the 3D-DIC technique, the tensile deformation behavior of 50%LAMed Ti64ELI titanium alloy was investigated. The 50%LAMed specimen exhibits a significant characteristic of strength mismatch due to the heterogeneous microstructure. The tensile fracture of 50%LAMed specimen occurs in WSZ (wrought substrate zone), but the tensile strength is slightly higher and the plastic elongation is significantly lower than that of the wrought specimen. The 3D-DIC results shows that the 50%LAMed specimen exhibits a characteristic of dramatic plastic strain heterogeneity and the maximal strain is invariably concentrated in WSZ. The ABAQUS simulation indicates that, the LDZ (laser deposited zone) can constrain the plastic deformation of the WSZ and biaxial stresses develop at the interface after yielding. [ABSTRACT FROM AUTHOR]

Titanium matrix composites (TMCs) have attracted extensive attention of researchers due to their excellent properties. However, the strength and ductility of TMCs hardly co-exist and show a trade-off between each other. To overcome the problem, in this study, with feeding the commerically pure titanium (CP–Ti) powder decorated by nano carbon, TiC reinforced Ti matrix composites were synthesized in situ by Pulsed Laser Directed Energy Deposition (PLDED). As the C content increases, the size, content and morphology of the TiC particles gradually change and the irregular block α phase transform to lath α phase in the matrix. As for Ti+0.6 wt% C, due to the strengthening effect of dispersed eutectic TiC and the evolution of morphology of α phase in the matrix, the ultimate tensile strength of TiC/Ti composites (940 MPa) is ∼84.3% and ∼108.9% higher than that of the PLDED and forged CP-Ti respectively, while retaining excellent elongation to failure (18.9%), which effectively solves the problem of strong-plastic contradiction existing in the preparation of TMCs. And at this carbon content, the friction and wear properties of the composites are effectively improved, the friction coefficient (0.26) is 55% lower than that of CP-Ti (0.58) obtained under the same process. This work shows a great potential way to significantly improve the mechanical properties of titanium alloys. [ABSTRACT FROM AUTHOR]

Selective laser melted (SLM-ed) pre-alloyed TiB 2 /Al–Si–Mg composite reports tremendous engineering application potential. However, systematic research on its heat treatment (HT) patterns is scarce. This paper utilizes direct aging (DA), annealing treatment (AT), and solution-aging treatment (SAT) to investigate porosity, microstructure, and mechanical properties. The porosities of as-deposited (AD), DA, and AT samples remained at <1.1%, while the nanopores at the molten pool boundary of AD sample expanded into the molten pool inner of DA and AT samples. For the condition SAT, the porosity exceeded 4.8% accompanied by large-sized micropores. Porosity development resulted from the entrapped hydrogen diffusion along the eutectic Si interface. The HT had little effect on the TiB 2 particles and near-equiaxed grains. The eutectic networks of AD and DA samples broke into separate particles after the AT and transformed into coarser particles in the SAT sample. The nanoscale (Si + β′′) and β′ precipitates were exhibited for the DA and SAT samples, respectively, while there are also a few composite precipitates. The evolution of eutectic and precipitates was related to the diffusion of supersaturated solutes. Due to the significant contribution of Orowan strengthening (∼213.1 MPa), a superior combination of the ultimate tensile strength (∼521.6 MPa) and yield strength (∼389.9 MPa) was realized after the DA. The excellent elongation (∼19.3%) of AT sample was attributed to the eutectic spheroidization. However, the high porosity of SAT sample severely compromised mechanical properties. This work provides essential guidance for HT selection of SLM-ed particle-reinforced Al–Si–Mg composites. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM) has unique advantages in manufacturing oxide dispersion strengthened alloys due to its high cooling rate and tiny molten pool. In this study, the microstructure and mechanical properties of Inconel 625 alloy and Y 2 O 3 strengthened Inconel 625 alloy prepared by SLM were investigated comparatively. The highest density for Y 2 O 3 /Inconel 625 specimen with a value of 99.6% was achieved when the laser volume energy density is around 145.8 J/mm3. Compared with Inconel 625 specimen, there presents a larger molten pool, finer grain structure, and weaker texture along the deposition direction in Y 2 O 3 /Inconel 625 specimen due to the active flux effect of Y 2 O 3. During the heat treatment, the grain growth and annealing twin formation are inhibited in Y 2 O 3 /Inconel 625 specimen due to the pinning effect of Y 2 O 3 particles. The yield strength of Inconel 625 specimen increases by 11.4%, 22.0%, and 12.5% at 20, 800, and 1100 °C, respectively, due to the dispersion strengthening and grain boundary strengthening induced by the addition of 0.48 wt % Y 2 O 3 particles. In addition, the elongation of Y 2 O 3 /Inconel 625 specimen at high temperature is improved because of the contribution of Y 2 O 3 to the strengthening and oxidation resistance of grain boundaries. [ABSTRACT FROM AUTHOR]

To study the effect of surfactants on the foaming behavior of phenol-urea-formaldehyde foam, silicone oil (Dow Corning DC-193) and Tween-80 surfactants were selected to study their effects on the mechanical properties, microstructure, and combustion characteristics of the foams. The results show that the surface tension of the phenol-urea-formaldehyde resins decreased with increasing surfactant concentration. Both the foaming temperature and foaming capacity of the phenol-urea-formaldehyde foam first increased and then decreased with increasing surfactant concentration. The compressive strength and oxygen index of the phenol-urea-formaldehyde foam first decreased and then increased with increasing surfactant concentration, which is probably related to the foaming capacity of the foam. The microstructure of the foams showed that the average pore diameters first increased and then decreased with increasing surfactant concentration. The combination of DC-193 and Tween-80 surfactants significantly improved the compressive strength, uniformity of the cells, and the number of closed cells in the final foam product. [ABSTRACT FROM AUTHOR]

The microstructural evolution and mechanical properties of 3 wt% TiB 2p reinforced 2024Al (TiB 2p /2024Al) composite stimulated by T6 heat treatment are reported in this work. Morphological results showed that the initial TiB 2p /2024Al composite fabricated by laser-directed energy deposition (LDED) consists of fine equiaxed grains with well dispersed TiB 2 particles, in which nanoscale Al 2 Cu(Mg) precipitates are dispersed in the Al matrix. After the T6 heat treatment, ultrafine Al 2 CuMg precipitates and few AlCuMnFe (T) dispersoids were observed in the matrix and grain boundaries. The sample which was solution treated at 495 °C temperature showed a higher compression yield strength of about 371.3 MPa and hardness of about 145HV, whilst the sample treated at 505 °C solution temperature (ST) had a relatively low compression yield strength of 289.8 MPa and hardness of about 128 HV. The reason is deduced to originate from the existence of negative factors such as the formation of microvoids. Quantitative analysis unveiled that grain refinement and Orowan strengthening should contribute to the high strength of the annealed TiB 2p /2024Al composite. • The microstructural evolution and mechanical properties of TiB 2p /2024Al stimulated by T6 heat treatment are performed. • The mechanical measurements reveal that the ST 495 °C specimen has the highest compressive yield strength. • The Al 2 CuMg nano-precipitates plays an important role in the improvement of mechanical properties for the composites. • Grain refinement and Orowan strengthening contribute to the high strength of the annealed TiB 2p /2024Al composite. [ABSTRACT FROM AUTHOR]

The aim was to evaluate the mechanical properties and porcelain bonded strength of nickel-chromium (Ni-Cr) dental alloy fabricated by laser rapid forming (LRF). The tensile properties and porcelain bonded strengths of LRF Ni-Cr dental alloy were evaluated by tensile tests (five specimens per group) and three-point bending tests (ten specimens per group). The same tests for the cast Ni-Cr dental alloy were used as for the control. The microstructure and the bonding interface of the metal substrate to porcelain were analyzed by optical microscopy (OM), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). The tensile strength of LRF Ni-Cr dental alloy (840 MPa) was superior to that of the cast Ni-Cr alloy (670 MPa), but the ductility had decreased. The porcelain bonded strength of LRF Ni-Cr dental alloy was 44.7 MPa, which was also superior to that of the cast Ni-Cr dental alloy (41.6 MPa). According to analysis by Student's t-test, the porcelain bonded strengths of the Ni-Cr dental alloy presented statistically significant differences between the groups of LRF and cast alloy (P < 0.05), but the porcelain bonded strengths were all above the acceptable value required by the International Organization for Standardization (ISO) standard 9693 (25 MPa). The coefficient of thermal expansion (CTE, mean value of five specimens) of LRF Ni-Cr dental alloy (14 x 10(-6) degrees C(-1)) was higher than that (13.7 x 10(-6) degrees C(-1)) of the cast Ni-Cr dental alloy. Both LRF and cast Ni-Cr dental alloy had positive Deltaalpha, not exceeding the maximum difference (1 x 10(-6) degrees C(-1)) in CTE. SEM and EDS results showed that all the specimens measured for porcelain bonded strength and prepared from the LRF and cast Ni-Cr alloy exhibited a mixed mode of cohesive and adhesive failure. Evaluation of the mechanical properties and porcelain bonded strengths of LRF Ni-Cr alloy revealed that both superior tensile and porcelain bonded properties can be obtained. With improvement of the technique, it is hoped that the LRF Ni-Cr dental alloy could be a good alternative to the conventional cast Ni-Cr dental alloy in the future. [ABSTRACT FROM AUTHOR]

In this study, the effect of solution temperature on the microstructure and mechanical properties of Hastelloy X fabricated by laser directed energy deposition (LDED) was investigated. As a result, the microstructure of as-deposited (AD) sample was mainly coarse columnar grains directionally growing along the deposition direction. Due to the segregation of Mo and Cr, a lot of Laves phase precipitates in the inter-dendritic. With the increase of solution temperature, the volume fraction of Laves phase gradually decreases. When the solution temperature increased to 1200 °C, the grains of the LDED Hastelloy X superalloy exhibited fully recrystallization, and then became coarse with the solution temperature of 1225 °C. With the dissolution of the Laves phase, the microhardness of the samples drops from 231 ± 5 HV to 211 ± 5 HV. The room temperature tensile results reveal that the as-deposited sample with irregular and long-striped Laves phase presents the worst tensile strength (652 ± 10 MPa) and elongation (30 ± 2%). After heat treatment, the strength and elongation of the LDED Hastelloy X superalloy gradually increased with increasing the solution temperature. When the solution temperature was 1200 °C, the tensile strength of the sample reached the maximum value of 720 ± 1 MPa. With the increase of solution temperature, the elongation increased and then reached the maximum value of 47 ± 2% with heat-treated at 1225 °C. The tensile fracture of LDED Hastelloy X superalloy with solution treatment presented a ductile fracture pattern. [ABSTRACT FROM AUTHOR]