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Hot isostatic pressing (HIP) of nickel-based superalloys still suffer from some detrimental carbides precipitated along the prior particle boundaries (PPBs), resulting in the degradation of mechanical properties of superalloy parts. In this study, a novel asynchronous loading HIP strategy, elevating temperature to the highest value first and then raising pressure, was proposed for FGH4097 to overcome this industrial challenge. The results manifest this novel strategy paves the way for fabricating nickel-based superalloys with both significantly enhanced strength and ductility by in-situ eliminating carbides precipitated along PPBs during HIP process, further boosting HIP process as a potential technology for the near-net manufacturing of key components in aerospace field. [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, fully dense Ti-6Al-4V alloy parts were successfully fabricated by an in-situ tooling (skin or shell) via a novel hybrid process of selective laser melting (SLM)/hot isostatic pressing (HIP). In this hybrid process, the in-situ tooling of Ti-6Al-4V parts was prepared via selective laser melting, then filled with Ti-6Al-4V powder, and finally consolidated by hot isostatic pressing to build fully dense complex parts without the need of removal of anything. The interface between tooling and consolidated powder was investigated in detail using scanning electron microscope (SEM) and electron backscattered diffraction (EBSD), and the bond strength was evaluated by tensile and fatigue testing. It was found that there was no obvious element diffusion around the interface, but the pronounced difference in microstructure type and gain size could be seen. Regardless of HIP temperatures, the tensile and fatigue samples preferentially failed on the tooling side due to the coarser Widmanstatten microstructure. Compared with the as-SLMed parts, the samples prepared by this hybrid SLM/HIP process exhibited higher mechanical properties such as superior strength and outstanding ductility, and became more competitive, even than wrought Ti-6Al-4V parts. [ABSTRACT FROM AUTHOR]

Hot isostatic pressing (HIP) shows distinct advantages in the manufacture of difficult-to-process materials into components with geometric complexity and high mechanical performance. In this work, a near-α titanium alloy Ti–6Al–2Zr–1Mo–1V (TA15) designed for service temperatures of ~500 °C in the aerospace industry was processed by HIP at three representative temperatures. A systematic study on the phase constitutions, microstructural evolution, and tensile properties measured at 20, 500, 600, and 700 °C was carried out for the assessment of HIP TA15 specimens. The relationships among HIP temperature, crystallographic characteristic, and mechanical performance of HIP TA15 were elucidated in detail. Spark plasma sintering (SPS) was selected to compare with the HIP technique regarding the fabrication of TA15 alloy. The tensile strength and ductility of the HIP specimens at 500 °C were 14.8% and 52.8% higher than those of the SPS counterparts. Furthermore, the high-temperature tensile properties of HIP TA15 specimens were comparable to those of the forged IMI 685 and even better than those of sintered Ti60 parts. These findings can serve as a guideline for the HIP process of TA15 alloy and the HIP parameter optimization for other near-α Ti alloys applied in harsh environments. [ABSTRACT FROM AUTHOR]

Recently, the AlCoCrFeNi 2.1 eutectic high-entropy alloy (EHEA) prepared by laser powder bed fusion (LPBF) could reach a good balance of strength and ductility. The strengthening effect was only qualitatively clarified, however, quantitative analysis remained unclear. In this study, the quantitative analysis of strengthening mechanisms and the relationship between microstructural characteristics and tensile properties were revealed in depth. The AlCoCrFeNi 2.1 EHEA with FCC and BCC dual-phase nanolamellar structures (interlamellar spacings of 200–300 nm) fabricated by LPBF achieved an excellent combination of high yield strength (1116 MPa) and fracture elongation (20.3 %). Compared with as-cast EHEA samples, the FCC/BCC nanolamellar interfaces in the LPBF-printed AlCoCrFeNi 2.1 EHEA were still semi-coherent but with a higher degree of coherency, and the Al concentration in the FCC phase increased. Post-deformation analysis showed that there were high-density dislocation pile-up and slip, stacking faults (SFs), and Lomer-Cottrell (L-C) locks in the FCC phase, and there were deformation nano-twins and SFs in the BCC phase. The back stress generated in FCC/BCC phases during tensile deformation could maintain the plastic co-deformation of the two phases. The theoretical calculation revealed that the strengthening mechanisms mainly stemmed from the nanolamellar structures, dislocation strengthening, and the solution strengthening induced by the increased Al concentration in the FCC phase. The calculated result (1096.3 MPa) was consistent with the experimental value, and the nanolamellar structures strengthening (∼720.7 MPa) was the main contributor. This work provides a theoretical quantitative understanding of the strengthening mechanism of the AlCoCrFeNi 2.1 EHEA fabricated by LPBF and references for the strengthening mechanism of additively manufactured EHEAs. [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]

A copper-based shape memory alloy Cu-11.85Al-3.2Mn-0.1Ti with desirable superelasticity and shape memory effect was printed by laser powder bed fusion (LPBF), which demonstrated the feasibility of engineering applications through the deformation and recovery of complex corrugated structural components. The microstructure of LPBF-printed Cu-11.85Al-3.2Mn-0.1Ti was composed of full β 1 ' martensite with a high density of stacking faults and twin crystals. The abnormal phase constitution of full martensite in the printed Cu-11.85Al-3.2Mn-0.1Ti is correlated to substrate preheating and thermal cycling during LPBF. The start and finish transformation temperatures of martensite (M s and M f) and austenite (A s and A f) were 172.5 °C, 144.4 °C, 180.2 °C and 209.2 °C, respectively. The printed samples exhibited compressive strength of 1319 MPa with a compressive fracture strain of 16.1%. The printed alloy displayed remarkable superelasticity and shape memory effect. The superelastic recovery rate reached a maximum value of 87% at 6% pre-strain, corresponding to a superelastic recovery strain of 5.22%. The mechanism of superelasticity is attributed to the rubber-like deformation behavior. Moreover, the pre-strained samples demonstrated a desirable shape memory effect under the temperature stimulation, where the shape memory recovery rate of up to 100% at a pre-strain of 6%, corresponding to a shape memory recovery strain of 0.78%. The reasons for the favorable shape memory effect were: (i) the thermoelastic inversion of martensitic transformation and (ii) the precipitation of γ 2 (Cu 9 Al 4) phase along the grain boundaries. As a result, these findings suggest that the LPBF technique can produce Cu-Al-Mn-Ti parts with superelasticity and good shape memory properties, which provided valuable references for printed copper-based shape memory alloys with full martensitic structures. • The Cu-11.85Al-3.2Mn-0.1Ti with full β 1 ' martensite was printed by by laser powder bed fusion. The range of austenitic phase transformation temperatures was 180.2–209.2 °C. • The alloy displayed remarkable superelasticity due to the rubber-like deformation behavior. • The pre-strained samples demonstrated a desirable shape memory effect because of the thermoelastic inversion of martensitic transformation and the precipitation of γ 2 (Cu 9 Al 4) phase. [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]

This paper presents a study on the formation, microstructure and mechanical property of Cr 3 C 2 /Fe nanocomposites using selective laser melting (SLM). Scanning electron microscope (SEM), transmission electron microscope (TEM) and tensile tests were conducted to investigate the influence of Cr 3 C 2 particulates on the microstructure and mechanical properties. It was found that the porosity decreased when volumetric energy density increased from 27 to 37 J/mm 3 , then rose to 55 J/mm 3 . The results showed that the Cr 3 C 2 particulates decomposed completely during SLM process and interacted with Fe matrix to form (α-Fe, Cr) solid solution and M(Fe, Cr) 23 C 6 carbides. In addition, due to the characteristic of rapid solidification, very fine grains were obtained throughout the composites. The tensile tests showed that the ultimate tensile strength could reach up to 1158 MPa. [ABSTRACT FROM AUTHOR]

Sn macro-segregation and coarse grains easily occur in the conventional casting process of the Cu–15Ni–8Sn alloy with a high Sn content. Here, hot isostatic pressing (HIP), an advanced powder metallurgy technique, was introduced to explore feasibility in alleviating or eliminating such defects. The gas–atomized powder with high homogeneity of composition was used, which was solidified rapidly. The microstructural evolution, mechanical properties, deformation mechanisms and strengthening mechanisms were deeply and systematically revealed and discussed. Nearly fully dense samples were fabricated by HIP with no Sn macro-segregation, and simultaneous strength-plasticity enhancement was obtained. The content of harmful discontinuous precipitation colonies was controlled to only ∼3.11 vol%. This was attributed to the fine grain size of the powder and the preferential complete recrystallization process during the HIP. That is, the γ nucleation sites were occupied by numerous grain boundaries provided by fine grains, and the driving force of γ growth was consumed by recrystallization. Furthermore, enhanced mechanical properties were related to the Sn macro-segregation suppression, grain refinement (∼11.0 μm), dislocation density continuous increase, and dispersion distribution of γ precipitates, etc. These encouraging findings validate the advantages and potential of HIP in the fabrication of Cu–15Ni–8Sn alloy with enhanced mechanical properties for structural applications. [Display omitted] • The Cu–15Ni–8Sn with suppressed Sn macro-segregation was fabricated by hot isostatic pressing. • The discontinuous precipitates were greatly reduced because the driving force has been consumed by recrystallization. • The ultimate compressive strength and plasticity were enhanced simultaneously compared to other copper alloys. [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]