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Understanding the effects of powder storage condition is helpful to improve the mechanical properties of powder metallurgy (PM) and additive manufacturing (AM) superalloys. In this work, nickel-based FGH96 superalloy powders were stored under ambient air (relatively dry) and humid (25 °C/95%RH and 90 °C/95%RH) atmospheres and then consolidated by hot isostatic pressing (HIP). The powders and corresponding bulk alloys were characterized by XPS, OM, FESEM, EPMA, EBSD, and TEM. The results indicate that the humid atmosphere mainly affects the gas content, chemical state, and oxide/hydroxide layer thickness of powders, leading to highest values of oxygen content (∼450 ppm), hydrogen content (∼25 ppm), and NiO/Ni(OH) 2 thickness (∼13.9 nm) for 90 °C/95%RH powders, and further forms much severe prior particle boundaries (PPBs) defects in HIPed alloy. The detrimental PPBs are composed of large-sized γ', MC carbides-(Ti, Nb)C, Al 2 O 3 and ZrO 2 oxides. In comparison with ambient air powders compact, the strength of 90 °C/95%RH powders compact is unexpectedly increased, which is due to the internal grains pinned inside the original particle boundaries by higher severity degree of PPBs, and leads to the increase of grain boundary strength. Meanwhile, the ductility is significantly decreased, because the fracture mode transited from ductile transgranular fracture to brittle inter-particle debonding. The study reveals the relationship between humid atmosphere and properties of both powders and bulk alloys, and intends to obtain good combination of strength and ductility for PM Ni-based superalloys. • The characteristics of Ni-based superalloy powders under ambient air and humid atmospheres were comparatively investigated. • Higher humid atmosphere results in higher oxygen content and much severe PPBs defects. • PPBs are composed of large-sized γ', (Ti, Nb)C, Al 2 O 3 , and ZrO 2. • Higher severity degree of PPBs obviously decreases the ductility but slightly increases the strength of FGH96 superalloy. • The increase of grain boundary strength contributes to the increase of yield strength. [ABSTRACT FROM AUTHOR]

Abstract: During the manufacturing process of a cast Ni-base superalloy K403 turbine blade, the blades from some mold assembly broke down into small pieces at the thin section trailing edge in the shell removal process. The fractured blade was sampled and its fracture characterization and microstructure were investigated by chemical analysis, optical metallography (OM), scanning electron microscopy (SEM) and energy dispersive spectrometer (EDS), X-ray diffraction (XRD) and microhardness measurement in order to explore the major cause of failure. The results indicated that the fracture of K403 blade was cause by the abnormal large amount of primary β-NiAl phase formation. The primary β phase possesses a Vickers microhardness of 5.78GPa, which is a brittle phase. The primary β phase cracked extensively in turbine blades at low impact load during the shell removal process. A “river pattern” structure is obvious in β-NiAl phase on the fracture surface, which is the main feature of the cleavage fracture. The formation of the primary β phase was caused by the heavy macrosegregation of the Al and Ti elements in the master alloy ingot. [Copyright &y& Elsevier]

Abstract: A high Cr content cast Ni-base superalloy, K4648, which contains 32–35wt.% chromium, was prepared by vacuum induction melting, and poured into testing bars or heavy section specimens. The as-cast, heat treated and fractured specimens were investigated by optical metallography, quantitative metallography, X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The isothermal solidification followed quenching (ISQ) technique and differential scanning calorimeter (DSC) experiments were also carried out. The result indicated that the primary α phase precipitated from the residual liquid in interdendritic region at 1190°C near the solidus temperature. This phase can be represented as α-(Cr,Ni) in K4648 alloy because it solid solutionized by about 30at.% of element Ni. The Vickers microhardness value of primary α phase is 6.3GPa relative to 1.9GPa of the γ matrix at the load of 0.2N. This phase is brittle and tends to crack due to stress concentration during the solidification process. The primary α phase solutionized or transformed into M23C6 carbides during solid solution treatment in the range of 1180–1220°C. However, small amounts of α phase remained even at the obvious incipient melting temperature of 1200–1220°C. Therefore, primary α phase must be controlled during solidification process. The faster cooling during solidification process can decrease the amount of primary α phase in both as-cast and heat-treated K4648 alloys. Specimens cut from slow cooling heavy section castings with large amount of primary α phase possessed an impact ductility of 13.9J/cm2, which is much lower than 35.4J/cm2 of samples from faster cooling thin section testing bars. The extensive cracked α phase or transformed M23C6 carbides can be observed at the fracture surfaces and longitudinal sections of impact specimens. Large blocky primary α phase with a network-like distribution, forming as a result of slow cooling, has detrimental effects on the impact ductility of K4648 alloy and it is difficult to completely remove by heat treatment. Proper parameter to obtain faster cooling in the solidification of the alloy must be considered to avoid the detrimental primary α phase precipitation. [Copyright &y& Elsevier]

Abstract: Microstructures and tensile mechanical properties of Mg–10Gd–6Y–2Zn–0.6Zr alloy were systematically studied. Four phases were found in the as-cast specimen: α-Mg, Mg3(GdYZn), Mg12(GdY)Zn and Mg24(GdYZn)5. The long-period stacking order (LPSO) structure is found, which is the phase of Mg12(GdY)Zn. The LPSO structure has two existing forms: lamellar structure in the inner grains and block-like structure at grain boundaries. 6H-type LPSO structure with a stacking sequence of ABCBCB′ is defined in homogenized specimen, where A and B′ layers are significantly enriched by Gd, Y and Zn. The ageing hardening behavior of as-extruded specimens at 200°C has been investigated. The ultimate tensile strengths of the as-extruded and peak-aged alloys are 360MPa and 432MPa, and the elongations are 18% and 5% respectively. The effective strengthening models have been considered to predict the strength. The results suggested that the sub-micron metastable β′ phase was the main strengthening factor of the peak-aged alloy. [Copyright &y& Elsevier]

Abstract: The microstructures of as-cast and heat treated specimens and stress rupture properties for Ta-bearing high W content cast Ni-base superalloys were investigated. The results indicate that Ta promotes the formation of eutectic (γ′+α) in late solidification. The α phase is unstable during heating above 1260°C and long term exposure at 1100°C, and can transform to M6C carbides. To avoid the α phase formation, it is necessary to modify the compositions of alloys by following the principle of substitution of Ta for Al at equal atomic ratio. [Copyright &y& Elsevier]

Abstract In this work, yttrium iron garnet films were prepared on a Ga 3 Gd 5 O 12 substrate by pulsed laser deposition. The dependence of target grain size on the morphology, crystallinity, and magnetism of films was investigated. Firstly, X-ray diffraction revealed that the fine grain size of the target was beneficial for increasing the crystallinity of films. Secondly, scanning electron microscopy and roughness measurements displayed the film prepared by the small grain size of the target has better morphology and lower roughness. Lastly, magnetic hysteresis loops and ferromagnetic resonance measurements further shown that a good microstructure and fine grain size of target facilitated the growth of film with greater magnetic properties. Consequently, YIG film deposited by 1.0 μm-target has magnetic properties with a high saturation magnetization of 155 emu/cm3, a low saturation magnetic field of 1077 Oe, and low ferromagnetic resonance linewidth of 42 Oe. [ABSTRACT FROM AUTHOR]

In this work, Na0.5Bi4.5Ti4O15-Na0.5Bi0.5TiO3 and Cr2O3-modified Na0.5Bi4.5Ti4O15-Na0.5Bi0.5TiO3 composite ceramics were fabricated and investigated as potential candidates for high-temperature piezoelectric applications. The microstructure, phase structure, and resulting piezoelectric properties of the ceramics were studied in detail. The coexistence of bismuth layer-structured ((Bi2O2)2+(Am−1BmO3m+1)2−) and perovskite structured (ABO3) phases was confirmed by X-ray diffraction analysis. The volume fraction ratio of pristine Na0.5Bi4.5Ti4O15-Na0.5Bi0.5TiO3 was determined to be 84.3:15.7, while that of the Cr2O3-modified one was 85.9:14.1, which agreed well with the theoretical value. Following doping, a small amount of Cr3+ ions was diffused into the crystal lattices of both phases, promoting the grain growth and resulting in a slight increase of the Curie temperature TC from 656 to 658 °C. Moreover, optimized piezoelectric properties with a significant piezoelectric constant d33 of 25 pC/N and a stable thermal annealing behavior were achieved in this ceramic. In addition, compared with the pure composite ceramic, the Cr2O3-modified composite ceramic exhibited a higher resistivity of 0.04 MΩ·cm at 600 °C. These results demonstrated the potential of the Cr2O3-modified Na0.5Bi4.5Ti4O15-Na0.5Bi0.5TiO3 composite ceramic in high-temperature piezoelectric applications. [ABSTRACT FROM AUTHOR]

W Cu alloy and high temperature co-fired ceramic (HTCC) were metallized through electroless nickel plating, then one series of W-Cu/Ni/AgCu/Ni/HTCC joints were successfully brazed with AgCu filler. The microstructure, mechanical properties, and hermeticity of W-Cu/HTCC joints were systematically investigated, and the fracture paths of the joints were summarized. The results revealed that the interface microstructure of the joints consisted of Ni(Cu)-W, Ni 3 P, Cu Ni, Cu(s,s), and Ag(s,s) phases. As the brazing temperature increased, Ni atoms gradually diffused from the Ni P layer into the filler layer and substrate. At 900 °C, the Ni P layer dissolved, and Cu atoms from the W Cu alloy diffused into the solder layer, leading to a sharp growth in joint thickness. The shear tests indicated that the promotion of Cu content in the filler layer effectively alleviated the residual stress in the joints, resulting in higher joint strength. The maximum shear strength of 73.57 MPa was reached when the joints brazed at 840 °C. The hermeticity measurement results showed that the joints brazed at 900 °C for 10 min exhibited exceptional hermeticity, with a helium leakage rate of 2.51 × 10−11 Pa·m3/s. This work provided a reference for the connection of metal packaging materials with high temperature co-fired ceramics. • Maximum shear strength of 73.57 MPa was reached when the W-Cu/AgCu/HTCC brazed at 840°C for 10 min. • At 900°C, Cu atoms from the W-Cu alloy diffused into the solder, causing a sharp growth in joint thickness. • The joint brazed at 900°C for 10 min exhibited excellent hermeticity, with a helium leakage rate of 2.51×10-11 Pa·m3/s. [ABSTRACT FROM AUTHOR]

In this study, yttrium iron garnet co‐doped with Zn and Zr atoms with a chemical formula Y3ZnxZrxFe(5−2x)O12 (x = 0.0‐0.3) has been successfully prepared by the solid‐state reaction method. The effects of doping concentration on the microstructure, crystal structure, magnetic properties, and dielectric properties of Y3ZnxZrxFe(5−2x)O12 were investigated. The microstructure analysis indicates that co‐doping of YIG with Zn and Zr can effectively reduce the grain size of the ceramic. The crystal structure results reveal that the doping concentration of Zn–Zr has substantial influence on the lattice parameters of YIG, such as, increases the lattice constant, crystal cell size, and interplanar spacing. However, the second phase of ZrO2 appears once x ≥ 0.15. Additionally, the dielectric properties of YIG ferrite can be regulated using this Zn–Zr co‐doping method. Zn–Zr co‐doping can improve the dielectric stability and reduce the dielectric loss at high temperature. The magnetization measurement shows that the saturation magnetization is stabilized at x < 0.15, and the magnetic loss is decreased with the increase in the doping concentration. Overall, the findings show that the ceramic with x = 0.1 exhibits better properties included high saturation magnetization (24.607 emu/g), low magnetic loss (0.0025 @ 1 MHz), and relatively low dielectric loss (496 @ 400°C). [ABSTRACT FROM AUTHOR]

YIG film with thickness of 203 nm was deposited on Si (1 0 0) substrates by the magnetron sputtering. A two-step annealing process was employed to fabricate YIG films, which involving two holding process at different temperature. The influences of two-step annealing conditions on crystallinity, microstructure and magnetic properties of YIG films have been investigated. It was found that high-quality crack-free YIG films with excellent magnetic properties could be successfully achieved on Si Substrates by adjusting the annealing conditions. The YIG film prepared by the two-step annealing process with the first-step annealing temperature of T 1  = 750 °C and holding time of t 1  = 3 h, the second-step annealing temperature of T 2  = 500 °C and holding time of t 2  = 3 h, exhibited a crack-free microstructure and presented excellent comprehensive performances with a saturation magnetization of 127 emu/cm 3 , coercive field of 37 Oe and FMR linewidth of 67 Oe. [ABSTRACT FROM AUTHOR]

The grain-size effects of the direct piezoelectric coefficient (d 33 ) and the converse piezoelectric coefficient (d 33 *) of BaTiO 3 ceramics with different Ba/Ti ratios were systematically explored. It was found that both d 33 and d 33 * exhibited strong grain size (g) dependences for BaTiO 3 ceramics with various Ba/Ti ratios. Although d 33 showed similar grain-size dependence for all the Ba/Ti ratios except a subtle shift of the critical grain size from 1 μm to 3 μm, two entirely different grain-size dependence of d 33 * were observed. By carefully examining the microstructure and ferroelectric properties of the ceramics, the variations of domain configurations and maximum polarization of BaTiO 3 ceramics with different Ba/Ti ratios were considered to be responsible for the different grain-size dependence of d 33 and d 33 *, respectively. [ABSTRACT FROM AUTHOR]

In this paper, oriented of micron-thick yttrium-iron-garnet ferrite films were deposited on Gd 3 Ga 5 O 12 substrate by magnetron sputtering based on layer-by-layer growth method. The effect of layer by layer growth method on films morphology, crystal structure and magnetic properties were investigated. X-ray diffraction θ-2θ reveals the maximum thickness of oriented film was increased by layer-by-layer growth method. In addition, scanning electron microscopy displays excellent morphology with uniform size of grain for the film prepared under 2.4 μm@800 nm condition. Magnetic hysteresis loops and FMR spectrum represent this layer-by-layer growth method can effective increase film saturation magnetization and decrease FMR linewidth. Specifically, oriented micron-thick (2.4 μm) YIG film with only 12 Oe of FMR linewidth has been obtained by this layer-by-layer growth method. [ABSTRACT FROM AUTHOR]

The influence of Ti–Mg and Ti on the impact toughness of the heat affected zone in steel has been studied comparatively. The changes of microstructure and grain size in the heat affected zone are analyzed. It has been found that the content of acicular ferrite in the steel treated by Ti–Mg is more than that in the steel treated by Ti. The size of the primary austenite grain in Ti–Mg treated steel is smaller than that in the steel treated by Ti. During the welding thermal cycle, the second phase particles in steel can be re‐dissolved and coarsened. After welding, the second phase particles in Ti–Mg treated steel are smaller than those in Ti treated steel, and the number of the second phase particles in Ti–Mg treated steel is more than that in Ti treated steel. The pinning effect of the second phase particles in Ti–Mg treated steel is obvious stronger than that in Ti treated steel. The impact toughness of the heat affected zone has a significant improvement after the addition of Ti–Mg. [ABSTRACT FROM AUTHOR]

Abstract: Porous silicon templates have been prepared by the metal-assisted chemical etching approach with optimized (HF/H2O2) solutions and Cu nanoparticles as the catalyst agents. The effects of metallization time and the concentration of Cu ions on the surface density of Cu nanoparticles on silicon templates have been studied. Besides, the effects of illumination and the composition of etching solution on the morphologies of the obtained nanopores have been investigated. It is found that uniform, isolated and nearly spherical Cu nanoparticles on the silicon surface can be obtained with the metallization processes containing 0.15mM copper nitrate and 25ml HF at room temperature for 15s. Subsequently, the porous silicon templates containing uniform pores with a mean diameter of 1.8μm have been successfully fabricated under an optimized etching process. The porous silicon templates are believed to be potentially employed for fabrication nanowires (nanotubes) devices compatible with semiconducting industries. [Copyright &y& Elsevier]

• Three new amorphous filler metals were designed for brazing Ni-based alloys. • Cr-Mo rich borides in diffusion zone increased with the increase of Cr content. • More Nb 6 Ni 16 Si 7 phase formed in brazed seam with more Cr in filler material. • Joint shear strength decreased by increasing the Cr content in filler material. Three nickel-based amorphous filler materials with composition of [B-Ni 9-x Cr x ]BSiNi (x = 0,1,2) were designed to braze K4169 superalloy according to cluster-plus-glue-atom model. The microstructure of K4169 nickel- based alloy brazed joints was examined, and the shear strength of the joint was also measured via pressure-shear tests. The brazed seam consists of γ-Ni solid solution, Nb 6 Ni 16 Si 7 and CrB phases of joint brazed with [B-Ni 7 Cr 2 ]BSiNi filler. More Nb 6 Ni 16 Si 7 phase formed in the brazed seam with more Cr addition in filler material, because Cr promoted the diffusion of Nb atoms from base material to brazed seam. Diffusion zone was composed of needle-like Cr-Mo rich borides and blocky MC carbides (NbC, TiC). The amount of Cr-Mo rich borides went up with the enhancement of Cr content in filler material. The shear strength of joint reached 689 MPa when brazed with [B-Ni 9 ]BSiNi filler, followed by 562 MPa with [B-Ni 8 Cr 1 ]BSiNi filler and 450 MPa with [B-Ni 7 Cr 2 ]BSiNi filler. In addition, Cr-Mo rich borides and continuous precipitation (Nb 6 Ni 16 Si 7 and CrB) exhibited low resistance to crack, resulting in the degradation of joint strength. [ABSTRACT FROM AUTHOR]

• High out-of-plane orientation of BaM film with remanence ratio of 0.53 was successfully deposited by PLD method. • It was confirmed that the crystal structure, morphology and magnetism of the film was dependent on the substrate temperature. • XRD and TEM results displayed high degree of orientation of the film deposited at high temperature. In this paper, a hexagonal M-type barium ferrite (BaM) film with a high remanence ratio was deposited on a sapphire substrate by the pulsed laser deposition (PLD) method. The characterization results showed that the film growth at a high substrate temperature (950 °C) has a high out-of-plane orientation, good crystallinity, and smooth surface. Additionally, the hysteresis loops indicated that the film deposited at a high substrate temperature has a high remanence ratio of 0.53, which is higher than that of the other reported BaM films prepared by the PLD method. [ABSTRACT FROM AUTHOR]