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In this paper, partial transient liquid phase (PTLP) diffusion bonding between Si3N4 ceramics and Ht250 cast iron was carried out by using an Ti/Cu/Kovar/Cu/Ti interlayer. The effects of the heating temperature and holding time on the microstructure, formation mechanism, and mechanical properties of Si3N4/Ht250 cast iron joints were studied. The results show that the maximum shear strength of the joint is 112 MPa when the welding temperature is 1000 °C and the holding time is 1 h. In addition, the problems of Ti/Cu/Ti intermetallic compound formation and Cu/Si3N4 ceramic residual thermal stress in the joint can be effectively alleviated. [ABSTRACT FROM AUTHOR]

Multi-principal element alloys (MPEAs) have attracted rapidly growing attention from both research institutions and industry due to their unique microstructures and outstanding physical and chemical properties. However, the fabrication of MPEAs with desired microstructures and properties using conventional manufacturing techniques (e.g., casting) is still challenging. With the recent emergence of additive manufacturing (AM) techniques, the fabrication of MPEAs with locally tailorable microstructures and excellent mechanical properties has become possible. Therefore, it is of paramount importance to understand the key aspects of the AM processes that influence the microstructural features of AM fabricated MPEAs including porosity, anisotropy, and heterogeneity, as well as the corresponding impact on the properties. As such, this review will first present the state-of-the-art in existing AM techniques to process MPEAs. This is followed by a discussion of the microstructural features, mechanisms of microstructural evolution, and the mechanical properties of the AM fabricated MPEAs. Finally, the current challenges and future research directions are summarized with the aim to promote the further development and implementation of AM for processing MPEAs for future industrial applications. [ABSTRACT FROM AUTHOR]

When two 42-mm 6082Al plates were welded by friction stir welding (FSW), a discontinuously distributing groove defect is formed on the surface of the joint. Subsequently, the FSW repairing process was conducted at the defect location. The influence of the repairing process on the microstructures and mechanical properties of the joints were studied, and a description of the softening mechanism of the repaired joints is provided. The results show that TMAZ at the advance side is the weakest zone of the as-welded joints. The repairing process increases the heat input into the joints and thus promotes the coarsening and transformation of the precipitates in the joints, which further weakens the repaired joints. The average tensile strength of the joints repaired with a 24-mm pin is 205 MPa, which is 91% of that of the as-welded joint. The tensile strength generally increases when the size of the repaired pin decreases. The average tensile strength of the joints repaired with an 8-mm pin is 220 MPa, which is equivalent to the initial joints. [ABSTRACT FROM AUTHOR]

Titanium and titanium alloys used in current medical and dental applications do not possess antibacterial properties, and therefore, postoperative infection remains a significant risk. Recently, the addition of silver and copper to conventional biomaterials has been shown to produce a material with good antibacterial properties. In this article, we investigate selective laser melting as a method of producing antibacterial Ti-6Al-4V containing elemental additions of Cu or Ag. The addition of Ag had no effect on the microstructure or strength, but it did result in a 300% increase in the ductility of the alloy. In contrast, the addition of Cu resulted in an increase in strength but in a decrease in ductility, along with a change in the structure of the material. The Cu-containing alloy also showed moderate antibacterial properties and was superior to the Ag-containing alloy. [ABSTRACT FROM AUTHOR]

A commercial Ti-Zr-Ni-Cu amorphous filler foil was applied to braze the high-temperature Ti600 and Ni-25at%Si, resulting in the good joint between both of alloys. The interfacial microstructure of Ti600/Ti-Zr-Ni-Cu/Ni-25at%Si brazed joint at 1213 K for 10 min is mainly comprised of the continuous Ti 2 Ni phase. Most of Ti-rich phases such as α-Ti, β-Ti, Ti 3 Al, Ti 2 Ni, (Ti,Zr) 2 (Ni,Cu) and (Ti,Zr) 2 Si formed in the vicinity of the Ti600 substrate except that Ti 5 Si 3 precipitates near the Ni-25at%Si region, resulting in the formation of six distinct layers. The corresponding formation mechanism were clarified. The Ti 5 Si 3 and Ni 31 Si 12 were firstly formed during the initial stage followed by diffusion reactions at Ni-25at%Si side. The continuous Ti 2 Ni phase formed through the reaction of Ti (L) + Ni (L) → Ti 2 Ni. α-Ti, Ti 3 Al, (Ti,Zr) 2 (Ni,Cu) and (Ti,Zr) 2 Si in the brazing joint precipitated through a solid-solid phase transformation. [ABSTRACT FROM AUTHOR]

Directional solidification experiments have been performed on Ni-25 at% Si alloy using electron beam floating zone method. A fully regular eutectic microstructures consisting of Ni, γ-Ni 31 Si 12 and β 1 -Ni 3 Si have been obtained. The influences of the directional solidification rate on the microstructures and properties of the full lamellar structures have been studied. The results show that the relationship between the mean interphase spacing ( λ ) and withdrawal rate ( v ) meets λ =29.9 v −0.65 . The hardness increases with the increasing of growth rate ( v ) and decreasing of the interlamellar spacing ( λ ) which meets the relationship of H V =445.2 v 0.14 and H V =910 λ −0.21 . The maximum compressive strength, 2576 MPa, for DS samples is obtained by 10 mm/h. The average fracture toughness value found for 5 mm/h, 7 mm/h, 10 mm/h is 28.3 MPa m 1/2 , 29.1 MPa m 1/2 and 35.9 MPa m 1/2 , respectively. The crack bridging and crack deflection/interface debonding are the main toughening mechanism of Ni-25 at% Si with full lamellar structures. [ABSTRACT FROM AUTHOR]

Zirconium alloy (Zr-702) joints welded by electron beam welding technique were characterized by studying the microstructures and corrosion tests. X-ray diffraction and transmission electron microscope analysis showed that the joints were consisted of α-Zr and β-Zr phases. Small β-Zr blocks were distributed along the edges of lamellar α-Zr in the fusion zone. Analysis of corrosion behavior of the joints showed that the Zr 3 Fe intermetallic was presented in the base metal strongly affected the corrosion resistance. The heat-affected zone and fusion zone showed better corrosion resistance than that of the base metal. [ABSTRACT FROM AUTHOR]

Silicon carbide (SiC) ceramic has been widely used in modern industry because of its superior mechanical properties, wear, and corrosion resistance even at elevated temperature. However, the manufacture of SiC ceramic is not an efficient process by conventional machining methods. This paper employs a steel-toothed wheel as the tool electrode to machine SiC ceramic using electric discharge milling. The process is able to effectively machine a large surface area on SiC ceramic. To further improve the process performance, three kinds of emulsion are proposed as the dielectric in this paper. The effects of dielectric, tool polarity, pulse duration, pulse interval, peak voltage, and peak current on the process performance such as the material removal rate (MRR) and surface roughness (SR) have been investigated. Furthermore, the microstructure of the machined surface is examined with a scanning electron microscope (SEM), an energy-dispersive spectrometer (EDS), and X-ray diffraction (XRD). [ABSTRACT FROM AUTHOR]

Abstract: There is an exponentially growing need for well-oriented, vertical silicon nano/micro-structure arrays, particularly in high-density integrated electronic devices. Here, we demonstrate that precisely controlled vertical arrays of silicon wires and cones can be fabricated by a combined treatment strategy of electrochemical and chemical etchings. First, a periodically ordered array of silicon wires was readily fabricated at microscale by simple electrochemical etching in which the current density played a critical role in determining the wire diameter and interspacing. The microstructures fabricated by electrochemical etching were more precisely tuned by further chemical etching, thereby transforming into cone arrays with extremely sharp tips where the cone height was controlled by the etching time. This approach could have broad utility in many electronics requiring miniaturization and high-density integration such as field emitters, photovoltaic and thermoelectric devices. [Copyright &y& Elsevier]

The nucleation and grain growth that occur during solidification have been extensively examined, but insight into the influence of an external field on the formation of heterogeneous crystal nuclei above the liquidus remains unclear in the peritectic refinement mechanism. In this work, we studied the effect of cooling rate above the liquidus on the formation of primary Al3Zr and grain refinement in Al-0.2%Zr alloys with inter-cooling annular electromagnetic stirring (IC-AEMS). The results show that the size and distribution of primary Al3Zr are greatly improved, and the morphology transformed from large plate/blocky shapes without IC-AEMS to small blocks with IC-AEMS. Meanwhile, above the liquidus, the addition of an Al-Zr master alloy to pure Al alone did little to enhance the refinement, but after IC-AEMS, the grains were refined dramatically. The refinement result seems to be explained by two hypotheses of pre-nucleation and explosive nucleation. [ABSTRACT FROM AUTHOR]

• A novel TiB 2 /2024Al filler was adopted to join SiC p /2024Al composite by LBW. • The formation mechanism of TiC precipitates in WZ was revealed. • The strength of SiC p /2024Al joint with filler increased from 109.3 MPa to 268 MPa. The effect of TiB 2 /2024Al filler on the microstructure and mechanical properties of SiC p /2024Al joint was investigated in this paper. The results indicated that needle-like Al 4 C 3 phase with a content of 18.9% was the dominant precipitate in the weld zone (WZ) of direct welded (DWed) joint, which weakened the tensile strength (109.3 MPa) of DWed joint. The introduction of TiB 2 /2024Al filler changed the microstructure of WZ. In the molten pool, TiC precipitate was precipitated preferentially due to the higher chemical affinity of Ti and C atoms and lower Gibbs free energy of TiC formation. The dispersed TiC blocks presented strong fine grain strengthening and precipitation strengthening effects. Compared with DWed joint, the strength of SiC p /2024Al joint with TiB 2 /2024Al filler increased to 268 MPa, approximately 72.9% of that of base metal (BM). [ABSTRACT FROM AUTHOR]

Massive efforts have been focused on effective electromagnetic absorbing materials, which have promising applications in suppressing or eliminating the electromagnetic radiation. In this study, Fe 3 O 4 @SiO 2 @PPy composites were prepared via a facile one-pot polyreaction. The results demonstrate that the composites loaded with 30 wt% possess an excellent electromagnetic absorbing property. Specifically, the minimum reflection loss value is −56.90 dB at 10.41 GHz at an absorber thickness of 3.7 mm. The broadest effective frequency bandwidth (reflection loss less than −10 dB) is 6.38 GHz at an absorber thickness of 3 mm. The outstanding performance implies that the Fe 3 O 4 @SiO 2 @PPy composites have a huge potential for application as advanced electromagnetic absorber with the advantages of strong absorption, wide bandwidth and low density. [ABSTRACT FROM AUTHOR]

Exploratory experiments of Electron beam welding-brazing (EBW-brazing) of 304 stainless steel (304 SS) to commercial pure aluminum (CP-Al) with an Al5Si filler wire under different beam currents were carried out. The microstructural characteristics of the joints were analyzed by SEM and XRD methods. Tensile strengths and nanoindentation were performed to evaluate the mechanical properties of the joints. The results indicated that beam current affected the thickness of the IMC layer and weld appearances, then further affected the tensile strengths of joints. The major intermetallic compound (IMC) formed at the connection layer was determined to be Al 8 Fe 2 Si with a Young's modulus of 223.2 GPa and nanohardness of 9.5 GPa. The highest tensile strength of the joints was 93 MPa under an optimum welding parameter, which was approximately equal to 83% of that of CP-Al. [ABSTRACT FROM AUTHOR]

In this study, a machine-learning approach based on Gaussian process regression was developed to identify the optimized processing window for laser powder bed fusion (LPBF). Using this method, we found a new and much larger optimized LPBF processing window than was known before for manufacturing fully dense AlSi10Mg samples (i.e., relative density ≥ 99%). The newly determined optimized processing parameters (e.g., laser power and scan speed) made it possible to achieve previously unattainable combinations of high strength and ductility. The results showed that although the AlSi10Mg specimens exhibited similar Al-Si eutectic microstructures (e.g., cell structures in fine and coarse grains), they displayed large difference in their mechanical properties including hardness (118 - 137 HV 10), ultimate tensile strength (297 - 389 MPa), elongation to failure (6.3 - 10.3%), and fracture toughness (9.9 - 12.7 kJ/m2). The underlying reason was attributed to the subtle microstructural differences that were further revealed using two newly defined morphology indices (i.e., dimensional-scale index I d and shape index I s) based on several key microstructural features obtained from scanning electron microscopy images. It was found that in addition to grain structure, the sub-grain cell size and cell boundary morphology of the LPBF fabricated AlSi10Mg also strongly affected the mechanical properties of the material. The method established in this study can be readily applied to the LPBF process optimization and mechanical properties manipulation of other widely used metals and alloys or newly designed materials. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Wrought aluminium alloys popular for automotive and aerospace applications are susceptible to solidification cracking when fabricated via laser powder bed fusion (LPBF). Another long-standing and common issue for these alloys is microstructure coarsening and corresponding strength loss caused by elevated temperature exposure. To tackle these challenges, this study designs and develops a class of 1–4 wt% Ce modified Al6061 alloys. The best alloy, with 3 wt% Ce, achieves crack-free fabrication via LPBF due to a reduction in the solidification temperature range and a new solidification pathway that achieved 0.9 solid mass fraction at just 14 °C below the solidification onset. Furthermore, a fine microstructure consisting of coarsening-resistant τ 1 -CeAlSi eutectic forms, and after hot isostatic pressing, the tensile strength and elongation of the 3 wt% Ce alloy can reach 153 ± 6 MPa and 18.3% at room temperature and 89 ± 6 MPa and 32.5% at 200 °C, respectively. The observed ductility is attributed to nanoscale dispersion of discrete, coarsening resistant τ 1 -CeAlSi particles within grains and to the presence of large columnar α-Al grains. Meanwhile, solidification cracking was inhibited by continuous grain boundary τ 1 -CeAlSi eutectic accumulation, which converted to discrete nanoscale τ 1 -CeAlSi after hot isostatic pressing. This research uncovers a simple and effective approach of designing Al-alloys for LPBF with great potential for both room temperature and high temperature applications in automotive and aerospace industries. [Display omitted] [ABSTRACT FROM AUTHOR]

A polycrystalline Ni 3 Al-based intermetallic alloy was successfully prepared via vacuum induction melting processing. Next, the microstructural evolution and mechanical properties of the intermetallic alloy were investigated by solution treatments at temperatures ranging from 1230 to 1290 °C. The results showed that the as-cast polycrystalline Ni 3 Al-based intermetallic alloy consisted of dendrite γ+γ′ with interdendritic distribution, matrix γ′ phase, and eutectic γ–γ′, and the total volume fraction of γ′ phase was ∼83.2%. After solution treatment at 1270 °C, the size and morphology of the γ′ phase changed and the secondary γ′ phase precipitated in the γ channel. The maximum room temperature yield strength, tensile strength and elongation reached 488 MPa, 686 MPa, and 5.2%, respectively. At 1100 °C, the high-temperature tensile strength of sample subjected to solution treatment at 1250 °C reached 203 MPa. It was found that solution treatment did not eliminate the incipient γ′ m , resulting in the weaker interdendritic boundary area in the alloy. Moreover, noteworthy, α-Cr particles were found in the γ′ m of the polycrystalline Ni 3 Al-based intermetallic alloy, revealing an orientation relationship such as [123] α-Cr ∥[123] γ' and (1–21) α-Cr ∥(11–1) γ'. The α-Cr particles have the strengthening effect of second-phase particles through pinning dislocations, which can improve the high-temperature creep performance of the alloy. • A vacuum induction melting polycrystalline Ni 3 Al-based intermetallic alloy was investigated for its room temperature and 1100 °C high temperature mechanical properties, and microstructure. • Nano-sized α-Cr particles formed in the γ′ phase on the Al-rich and Ni-poor side, the orientation relationship of [123] α-Cr ∥[123] γ' and (1–21) α-Cr ∥(11–1) γ' between the precipitates α-Cr and γ′-matrix. • The inter-dendrite boundary is the weakest point of the alloy. [ABSTRACT FROM AUTHOR]

High Nb containing TiAl alloys showed susceptibility to cold cracking when welding was performed without preheating and post-heating; however, crack-free welds could be made with pre- and post-heating. The room-temperature strength of the crack-free welds was 480 MPa, and failure occurred in the base metal. The fusion zone obtained at a beam current of 7 mA mainly comprised coarse β/B2-phase grains, with acicular α 2 and γ phases distributed at the grain boundaries. The fusion zone obtained at 13 mA mainly contained fine γ- and α 2 -phase grains. The fusion zone obtained with pre- and post-heating was dominated by the acicular α phase, reticular β/B2 phase, and blocky γ phase. The heat-affected zone could be divided into two characteristic regions according to the morphologies of the α 2 and γ phases. Changes in microhardness were analyzed with respect to the phase composition and microstructural morphology. [ABSTRACT FROM AUTHOR]

Metal additive manufacturing (AM) offers exceptional design freedom, but its high thermal gradients often generate non-equilibrium microstructures with chemical and interfacial instabilities. Steels that solidify as δ-ferrite often experience a further solid-state phase transformation to austenite during AM. The detailed nature of this phase transformation during AM is yet to be fully understood. Duplex stainless steel, which is known for its unique combination of high corrosion resistance and mechanical properties, is a suitable alloy to further study this phase transformation. The current study aims to gain novel insights into solid-state phase transformations and mechanical properties of duplex stainless steels during laser powder-bed fusion (LPBF). As-printed microstructures exhibit significant deviations when compared to conventionally manufactured counterparts in terms of phase balance and morphology, elemental partitioning, and interface character distribution. During LPBF, only a small fraction of austenite forms, mostly at the ferrite-ferrite grain boundaries, via a phase transformation accompanied by diffusion of interstitials. Austenite/ferrite boundaries are shown to terminate on {100} F //{111} A planes. This is due to the character of parent ferrite-ferrite boundaries which is dictated by the sharp <100> texture and geometry of austenite grains induced by directional solidification and epitaxial growth of ferrite. Benchmarking mechanical properties against a wrought counterpart demonstrates that AM offers high strength but relatively low ductility and impact toughness. A short heat treatment reverts the microstructure back to its equilibrium state resulting in balanced tensile and toughness properties, comparable to or even better than those of wrought counterparts. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM)-processed AlMgScZr alloy has aroused widespread interest in the aerospace industry due to its outstanding comprehensive performance and excellent heat resistant properties. The fine grain morphology and diffusely distributed thermally stable precipitates of this alloy are believed to play a critical role in its high-temperature performance. By modifying the alloy with Sc and Zr, nano-sized Al 3 (Sc, Zr) phases can act as heterogeneous nucleating particles to effectively promote grain refining and precipitate strengthening. In this paper, a Sc and Zr-modified Al–Mg alloy was printed by SLM, and the long-term aging treatments in the temperature range of 275–350 °C with a constant holding time of 144 h were performed to investigate the heat-resistant properties of this alloy. Under as-fabricated condition, the AlMgScZr alloy exhibited high tensile strengths of 487.7 MPa and 393.9 MPa at temperatures of 25 °C and 200 °C, respectively. When the alloy was aged at 300 °C for 144 h, its grain morphology was almost unchanged, but its tensile strength and elongation at room temperature reached 501.3 MPa and 31.3%, respectively. • The microstructure and tensile properties of SLM-processed AlMgScZr alloy was investigated. • The thermal stability of AlMgScZr alloy was significantly improved by Al 3 (Sc, Zr) precipitate. • The strength and heat resistant mechanisms of AlMgScZr alloy were systematically discussed. [ABSTRACT FROM AUTHOR]

This short communication presents 2–4 μm sized TiCN reinforced AlSi10Mg composites (TiCN/AlSi10Mg) fabricated by laser powder bed fusion (LPBF) with refined Al-Si eutectic microstructure consisting of equiaxed bi-modal α-Al grains and enhanced elevated temperature tensile strength. The formation mechanism of reported bi-modal structure is related to the modified temperature gradients and induced heterogeneous nucleation in LPBF. The enhancement in elevated temperature tensile strength is mainly attributed to refined bi-modal Al-Si microstructure and thermal stability of TiCN particles. [ABSTRACT FROM AUTHOR]