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In this study, the diffusion bonding among YG18 cemented carbide, 30Cr2Ni2Mo alloy steel, and M4 high-speed steel was successfully realized by hot isostatic pressing. The microstructure and element diffusion of 30Cr2Ni2Mo/M4, YG18/M4, and Y18/30Cr2Ni2Mo joints were studied by electron-probe microanalysis and field emission scanning electron microscope. The mechanical properties of the three joints were evaluated by a uniaxial testing machine. The results showed that significant element diffusion occurred at the three connection interfaces. Although Kirkendall voids appeared at the 30Cr2Ni2Mo/M4 interface due to the unbalanced interdiffusion of elements, the negative effect of the Kirkendall void on the interfacial bonding strength was negligible. The η phase with a thickness of ⁓1.5 μm was formed at the YG18/M4 and Y18/30Cr2Ni2Mo interfaces. A diffusion distance of ⁓20 μm was generated at these two interfaces, where Co diffused from YG18 to M4 or 30Cr2Ni2Mo, and Fe diffused from M4 or 30Cr2Ni2Mo to YG18. The ultimate tensile strength of the 30Cr2Ni2Mo/M4, YG18/30Cr2Ni2Mo, and YG18/M4 joints was 1300.4 MPa, 736.2 MPa, and 631.2 MPa, respectively and the corresponding shear strength was 879.9 MPa, 810.0 MPa, and 360.2 MPa. The tensile and shear strength of the 30Cr2Ni2Mo/M4, Y18/30Cr2Ni2Mo, and YG18/M4 joints reached 80% of that of YG18. The tensile specimens of the 30Cr2Ni2Mo/M4 and YG18/30Cr2Ni2Mo joints failed at the M4 or YG18 side rather than at the interface, indicating that the two interfaces achieved good metallurgical bonding. The tensile specimens of the YG18/M4 joint fractured at the interface due to the existence of cracks at the YG18/M4 interface. The hot isostatic pressing enabled reliable connection among YG18, M4, and 30Cr2Ni2Mo. This study provides valuable exploitation for the reliable connection of YG18 cemented carbide and steels by hot isostatic pressing. • Effective diffusion bonding among YG18 hard alloy, 30Cr2Ni2Mo steel, and M4 steel was successfully realized by HIP. • The microstructure observation and mechanical evaluation of interfaces were investigated in depth. • The tensile and shear strength of the interfaces were much higher than the values reported in previous publications. • This study proved the engineering reliability of HIP diffusion bonding for WC-Co cemented carbides and steels. [ABSTRACT FROM AUTHOR]

Abstract Ti-6Al-2Zr-1Mo-1V (TA15) with ultrafine crystallites and numerous nano-scale twins were successfully prepared by selective laser melting (SLM). The room-temperature and high-temperature (500 °C) tensile properties of SLM-fabricated samples were visibly higher than those of TA15 fabricated by conventional techniques, other near α titanium alloys and even comparable to TA15-based composites. [ABSTRACT FROM AUTHOR]

In this study, titanium borides reinforced Ti-6Al-4V composites have been successfully prepared by hot isostatic pressing (HIPing). The microstructure of the as-fabricated samples was investigated using X-ray diffraction technique, secondary electron microscopy and electron backscatter diffraction and the mechanical properties evaluated through micro-hardness and wear resistance measurements together with nano-indentation. It was found that during HIPing the additive particles TiB 2 have transformed into TiB needles which tend to decorate at prior particle boundaries of the consolidated powder particles to form a network structure. Under the same HIPing condition, the needles became increasingly coarser and agglomerated with increased addition of TiB 2 . The micro-hardness of the synthesized materials increased with increased volume fraction of TiB. Nano-indentation measurement demonstrates that the TiB network structure shows much higher nanohardness than the surrounding matrix regions. The friction coefficient of the synthesized composites decreased continuously with increased volume fraction of TiB, indicating improved wear resistance. High resolution transmission electron microscopy analysis on wear debris revealed the formation of a series of oxides suggesting that chemical reaction between alloy elements and oxygen in air may have happened. It is thus believed that the wearing of the current samples is a result of both friction and chemical reaction. [ABSTRACT FROM AUTHOR]

α-Al2O3 four-channel hollow fiber (4CHF) membrane owns high permeability as well as great mechanical strength. In this work, three typical microstructures of 4CHF membranes with sponge-like layer located in centric (S1), inner (S2) and outer (S3) regions were demonstrated by changing polyethersulfone content of spinning suspension, ethanol contents of internal and external coagulants, respectively. The 4CHF-S1 membrane could be prepared by using water as both internal and external coagulants. The central sponge-like region expanded towards both surface sides with the polyethersulfone content. The 4CHF-S2 membrane was obtained by using ethanol as internal coagulant while water as external coagulant. And the 4CHF-S3 membrane was achieved by using ethanol as internal coagulant while water as external coagulant. The typical 4CHF-S1, 4CHF-S2 and 4CHF-S3 membranes exhibited pure water fluxes of 3.38, 3.34 and 3.74 m3 · m−2 · h−1 and fracture loads of 20.86, 20.08 and 18.12 N, respectively. © 2016 Curtin University of Technology and John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

This work presents a comprehensive study of the densification behavior, phase and microstructure development, high temperature tensile performance of a novel near-α high-temperature titanium alloy fabricated by hot isostatic pressing (HIP) at representative temperatures. The results indicated that numerous rod-like S 2 silicides ((TiZr 0.3 ) 6 Si 3 ) and α 2 phase (Ti 3 Al) precipitated from α matrix. The microstructural characteristics of HIP-fabricated parts experienced a successive change on increasing the HIP temperature: lathlike structure + little equiaxed grains → equiaxed grains + little lathlike structure → fully equiaxed grains. In addition, the grain size of samples unceasingly growed up with the increase of HIP temperatures. Over the entire tensile tests temperature range, the equiaxed grains plus little lath-like structure (HIP-B) exhibited the highest tensile strength. As to the ductility, the elongation of specimens increased successively with the increase of HIP temperatures, which is mainly due to the type of microstructure and the diffusion-metallurgical bond. [ABSTRACT FROM AUTHOR]

The coating manufacture on the complex-shaped parts still has many technical difficulties in the real industry. In this study, the Ti–Ni coating was in-situ manufactured during hot isostatic pressing of Ti6Al4V parts. The prepared coating was characterized in terms of microstructure, element distribution, phase composition as well as the mechanical properties, including microhardness and wear resistance. The present work preliminarily verified that hot isostatic pressing could be considered as a candidate for integrated manufacturing complex-shaped Ti6Al4V components with a wear-resistant coating. [ABSTRACT FROM AUTHOR]

In this study, CoCrFeNiTi 0.3 high-entropy alloy (HEA) was designed and prepared via the in-situ laser powder bed fusion (LPBF) of CoCrFeNi and Ti powders to improve the undesirable tensile strength of CoCrFeNi HEA. With the introduction of Ti, semi-elliptic melt pool characteristics became blurred with the concentration of Ti at melt pool boundaries, which was correlated with a Marangoni-convection-driven chaotic flow and insufficient diffusion of Ti during the rapid melting/solidification process of LPBF. During the solidification process, Ti acted as nucleation sites and triggered a columnar-to-equiaxed transition of grains in the printed CoCrFeNiTi 0.3 HEA. Partial diffused Ti combined with Ni to form nanoscale Ni 3 Ti precipitates because Ti and Ni had the most negative mixing enthalpy compared with Co, Cr, and Fe. The nanoscale Ni 3 Ti precipitates were located at the sub-grains and showed a network structure. This was associated with the sub-grain boundary segregation driven by severe lattice distortion. The yield strength of the Ti-modified CoCrFeNi was enhanced from 509 MPa to 796 MPa, which suggested a 56.4% increase obtained by adding a small amount of Ti. The theoretical calculation was deduced to validate the strengthening mechanism mainly stemming from dislocation hardening and precipitation hardening. This study is anticipated to provide insights into the enhancement in the mechanical performance of HEA through composition modification via the in-situ alloying during LPBF. [ABSTRACT FROM AUTHOR]

Abstract A newly-developed γ′-hardenable powder metallurgy (P/M) nickel based surperalloy FGH4097 developed by China was fabricated by hot isostatic pressing (HIP) with different processing temperatures. The microstructure evolution, tensile properties and fracture mechanism of the FGH4097 superalloy were systematically studied. Grains size, strengthening γ′ phase, prior particle boundaries and carbide precipitations, were characterized by optical microscopy (OM), scanning electron microscopy (SEM) and transmission electron microscopy (TEM), meanwhile the mechanical properties were assessed by hardness measurements and tensile tests at room temperature (RT) and 650 °C. A dendrite structure inherited from the pre-alloy powder was partially reserved in the as-sintered alloy processed at 1100 °C. It transformed into a cellular structure when the HIP temperature was increased to 1200 °C. With increasing the HIP temperature, the contents of γ′ phase forming element decreased, accompanied by the decrease of γ′ lattice parameters and volume fraction. Due to a promoted atomic diffusion at higher temperatures, MC carbide and two types of HfO 2 precipitations formed in the γ matrix that were not present in the pre-alloy powder. Besides, the grain size increased with increasing HIP temperatures, and the average grain sizes of the sintered samples were 5.8 µm (1100 °C), 17.8 µm (1200 °C) and 74.7 µm (1300 °C), respectively. Compared with two other processing temperatures, samples fabricated with at 1200 °C had the highest ultimate tensile strengths (1410 MPa at room temperature and 1236 MPa at 650 °C), along with a superior elongation (33.0 at room temperature and 31.4 at 650 °C), which was attributed to an appropriate microstructure and mediate volume fraction of γ′ phase. Owing to the incomplete recrystallization and prior particle boundaries, the yield strength and ultimate tensile strength at 1100 °C exhibited a bit less than that of at 1200 °C, but showed obvious difference in elongation. However, the tensile strengths decreased significantly at 1300 °C as a result of coarse grains. With increasing the HIP temperature, the fracture appearances indicated that the fracture changed from dimple ductile mode to brittle mode, because of the formation of coarsening MC carbide at grain boundaries. [ABSTRACT FROM AUTHOR]

Abstract This work for the first time investigated the effect of laser scan line spacing on the microstructure, phase evolution and nanohardness of Ti-48Al-2Cr-2Nb/RGO (reduced graphene oxide) metal matrix composites (MMCs) fabricated by selective laser melting (SLM). The results show that with increasing the laser scan line spacing from 80 to 140 μm, the average grain size generally decreases from 10.13 to 8.12 μm. The SLM-processed Ti-48Al-2Cr-2Nb/RGO parts are dominated by high-angle (>15°) grain boundaries (HAGBs) and α 2 (Ti 3 Al) phase. With the increase in laser scan line spacing, the contents of HAGBs and α 2 phase both decrease. Due to instantaneous high temperature during the SLM process, some RGO sheets transform to amorphous carbon. The nanohardness of SLM-processed Ti-48Al-2Cr-2Nb/RGO parts increase from 8.13 ± 0.39 GPa to 9.85 ± 0.46 GPa when increasing the laser scan line spacing from 80 to 140 μm, which is much higher than that of the traditional casting TiAl counterparts (4.98 ± 0.10 GPa). Graphical Abstract Unlabelled Image Highlights • The average grain size generally refines with increasing the laser scan line spacing. • The phase transformation mechanism during SLM is determined by HRTEM. • Some RGO sheets transform into amorphous carbon during SLM process. • The nanohardness is much higher than those casting counterparts. [ABSTRACT FROM AUTHOR]

Superior thermal quenching and degradation of phosphors are required for long lifetime lighting devices, such as light-emitting diodes, which can be realized through composition modification. Here, Al-N bonds in AlON: Eu 2+ phosphors are substituted by higher bond order of Si-C. Photoluminescence (PL) results show thermal quenching (at 150 °C) and thermal degradation (after 600 °C treatment in air) are improved by 5% and 8% with a small decrease of PL intensity in 5% SiC doped AlON: Eu 2+ phosphor. To explain these observations, first-principles computational study was performed to understand the Si and C configuration in AlON:Eu 2+ . The calculations reveal that Si and C elements are not randomly distributed in AlON lattice. It was found that Si prefers occupying tetrahedral sites (Td-Si) and the insertion of C in Td-Si is always energetically favorable, which results in the formation of SiC 4 and SiNC 3 clusters. Thus, the Al-N substitution by Si-C induces a stronger local structure, which accounts for the emission redshift and better thermal stability. [ABSTRACT FROM AUTHOR]

[Display omitted] • Ti-6Al-4V samples were fabricated through hybrid in situ point-mode forging and laser additive manufacturing techniques. • Effects of press down volume (PDV) on microstructure evolution and mechanical properties were investigated. • The equiaxed grain sizes were decreased with the increase in the PDV. • The microstructure with fine equiaxed grains and a bimodal morphology was achieved via the PDV of 0.25 mm. The intrinsic high cooling rates and high thermal gradients of laser additive manufacturing leaded to a tendency towards columnar grains. Hybrid in situ point-mode forged and laser additive manufacturing (HFAM) was a newly-developed printing technique with the capability of full transition from columnar grains to fine equiaxed grains in the HFAM-processed samples. Press down volume (PDV) of point-mode forging, an important parameter in the HFAM technique, affected the microstructure of the HFAM-processed samples. The effects of PDVs on the microstructure and mechanical properties of the HFAM-processed Ti-6Al-4V were investigated. The HFAM-processed samples showed equiaxed grains. The grain sizes were decreased with the increase in the PDV. The higher PDV contributed to the generation of the equiaxed primary α-Ti phase. The microstructure with fine grains and a bimodal morphology was achieved via the PDV of 0.25 mm, providing excellent comprehensive mechanical properties. The tensile strength and elongation at break of 0.25 mm PDV sample were ∼20.6% and ∼115.1% higher than that of un-forged one. [ABSTRACT FROM AUTHOR]

A third-generation powder metallurgy nickel-based superalloy (WZ-A3) was prepared by hot isostatic pressing (HIP) at 1100 °C, 1150 °C, 1200 °C, and 1250 °C, respectively. The characteristics of grains, precipitates, and elemental distribution revealed its microstructural development. The samples prepared at a sub-solvus temperature (1100 °C) consisted of fine recrystallized grains and dendritic structures. However, the microstructure became a completely recrystallized structure when the HIP temperature reached or exceeded 1150 °C. The average grain size increased from 4.0 µm (1100 °C) to 53.1 µm (1250 °C) due to the promoted recrystallization and atom diffusion rate. Prior particle boundaries (PPBs) with continuously distributed precipitates were identified as a mixture of (Nb, Ti)C carbides and Hf 0.5 Zr 0.5 O 2 oxides. By increasing the HIP temperature from 1100 °C to 1200 °C, the PPBs were reduced but not eliminated. As a result, samples prepared at 1200 °C experienced interparticle debonding with relatively high strengths, and the ultimate tensile strength values were 1388.7 MPa and 1228.3 MPa at room temperature (RT) and 700 °C, respectively. When the HIP temperature was 1250 °C, the presence of coarse grains, large carbides, as well as eutectic structures formed at the junction of grain boundaries caused dramatic drops of tensile strengths and brittle fractures. These results emphasized the importance of parameter optimization for controlling the microstructure and mechanical properties during the HIPing process. • A newly-developed powder metallurgy nickel-based superalloy was prepared by HIP. • Microstructural evolution under different HIP temperature was revealed. • The PPB precipitates were identified a mixture of (Nb, Ti)C and Hf 0.5 Zr 0.5 O 2. • Relationships between processing parameter and tensile properties were revealed. [ABSTRACT FROM AUTHOR]

A novel P/M nickel-based superalloy is developed with an excellent combination of strength and ductility for use in turbine disks. This superalloy is prepared through hot isostatic pressing (HIP) and subsequent hot extrusion (HEX) with different extrusion ratios (λ). The effects of λ on the evolution and mechanism of γ′ precipitation behavior, grain refinement, microtexture, and mechanical properties are systematically studied. As λ increases, the primary γ′ phase fraction decreases from 17.22% to 8.47%, and the precipitation morphology changes from an irregular to a spherical shape. Increasing λ is beneficial to dynamic recrystallization. Fully recrystallized fine grains with a diameter of 4.47 μm are obtained at an optimal λ = 5.0, a decrease of 76% compared with the HIPed alloy. Abnormal grain coarsening was observed at a higher λ with 8.5 owing to the lack of γ′ pinning and a stronger driving force for grain boundary migration induced by deformation heat. The yield strength (YS) and ductility of the HEXed alloy are over 30% higher than those of the HIPed alloy, thanks to refined grains and the γ′ phase. The alloy extruded with λ of 5.0 exhibits a high YS of 1376 MPa with a ductility of 22.6% at room temperature and a YS of 1208 MPa with a ductility of 18.3% at 700 °C, which are better than those of other superalloys. A multi-mechanistic strengthening model is constructed by correlating the chemical composition, size and fraction of γ′, grain size, and YS. The calculations suggest that precipitation strengthening contributes more than 60% of the YS. Extrusion can dramatically enhance the YS of the superalloy owing to the increment of grain boundary strengthening and precipitation strengthening. This work provides a practical route and theoretical support for optimizing microstructure and enhancing the mechanical properties of a HIPed P/M nickel-based superalloy. • A novel P/M nickel-based superalloy with high strength (1376 MPa) and ductility (22.6%) was prepared. • Role of extrusion ratio on microstructure evolution mechanism of the superalloy was revealed for the first time. • Abnormal property deterioration was observed at the highest extrusion ratio (8.5). • Dissolution of primary γ′ results in the abnormal grain coarsening at the highest extrusion ratio. • Enhanced mechanical properties were quantitively elucidated by a multi-mechanistic strengthening model. [ABSTRACT FROM AUTHOR]