Search

Failure of nickel-based powder metallurgy (PM) components usually originates from prior particle boundaries (PPBs), which act as cracking initiators and provide accessible channels for cracking propagation. In this study, the effect of the PPBs number and size on the microstructure and mechanical properties of the nickel-based superalloy FGH4096M was investigated. Fine (HIP-F) and coarse (HIP-C) FGH4096M powder with average particle sizes of 38.1 μm and 114.1 μm, respectively were selected to conduct HIP (hot isostatic pressing) experiments. The results revealed that the tensile strength and ductility of HIP-F are 14.1% and 88.7%, respectively, higher than those of HIP-C. This is supposed to be because refined particles make the crack expansion paths more tortuous, and result in more work hardening of HIP-F, since the cracking deflections in HIP-F are ~ 3 times those in HIP-C. Furthermore, the primary reason is that the denser PPBs of HIP-F caused higher volume fractions of carbides (~ 1.9%) in the PPBs than those of HIP-C (~ 0.8%), which leads to an average grain size of HIP-C being about 2 times that of HIP-F. Therefore, refining the size of PPBs may be a strategy to reduce their impact on the mechanical properties of PM superalloys. [ABSTRACT FROM AUTHOR]

For near‐net shape hot isostatic pressing (HIP) process, the interaction between capsules and consolidating powders at a high pressure and temperature leads to a strong interfacial element diffusion, which is harmful to the surface microstructure and mechanical properties of components. The effects of iron and carbon, in SS400 steel capsules, on the surface microstructure and mechanical properties of the FGH4096M superalloy during HIP are investigated. Results show that the interfacial difussion between the SS400 steel and FGH4096M is divided into three zones: ferrite‐martensite‐austenite mixture zone (≈32.3 µm), Fe‐rich Ni‐Fe‐based superalloy zone (≈27.5 µm), and Ni‐rich Ni‐Fe‐based superalloy zone (≈34.8 µm). The γ′ phase starts to be formed when the mass fraction of iron is below ≈27.2%. The γ′ morphology changes from fine sphere to cuboidal and butterfly‐like shapes as the mass fraction of iron is decreased successively. There is no obvious carbon diffusion around the interface due to a low carbon concentration in the capsule. The Vickers microhardness profile shows an increase, then a decrease, and eventually becomes stable at 425HV. Based on the above conclusions, an understanding of the Fe and C diffusion mechanism at the interface and its extension toward the FGH4096M side is achieved. [ABSTRACT FROM AUTHOR]

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]

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 In-situ synthesized titanium borides reinforced Ti-6Al-4V composites with a tailored reinforcement architecture were successfully prepared by hot isostatic pressing (HIP) starting from a TiB 2 /Ti-6Al-4V powder system. The microstructure of the composite samples was investigated using X-ray diffraction (XRD) technique and scanning electron microscopy (SEM), and the mechanical properties were evaluated through room and high temperature tensile testing. It is found that during HIP the additive particles TiB 2 have totally transformed into TiB needles, which tend to decorate at prior particle boundaries of the consolidated powder particles to form a network structure. With increasing TiB 2 addition from 3 wt.% to 8 wt.%, the microstructural feature of the TiB network structure experiences the variations of discontinuous TiB reinforcement → quasi-continuous TiB reinforcement → continuous TiB reinforcement. The room temperature tensile properties of the composites are improved with increasing addition of TiB 2 from 3 wt.% to 5 wt.%, but the tensile strength of the sample with 8 wt.% TiB 2 drastically decreases. As to the high temperature properties, the titanium boride reinforced Ti-6Al-4V alloy composites can be an increased maximum service temperature by over 200 °C while retaining the same tensile strength accompanied with a suitable elongation. The strengthening mechanism is mainly attributed to the load-bearing transformation, grain refinement and dispersion strengthening. [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]

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]

For the net-shape hot isostatic pressing (HIP) process, control of the internal surface roughness of as-HIPped parts remains a challenge for practical engineering. To reveal the evolution mechanism of the internal surface of the parts during the HIP process, the effect of different tooling materials (H13, T8, Cr12 steel, and graphite) as internal cores on the interfacial diffusion and surface roughness was systematically studied. [ABSTRACT FROM AUTHOR]

Hot isostatic pressing of metal powders involves a complex thermal and mechanical coupling process. A constitutive model based on Perzyna's elastic-viscoplasticity equation was proposed, and a Lagrangian finite element method was applied to analyze the large deformation, nonlinear friction, powder flow, and densification behavior during hot isostatic pressing. The mechanical behavior of the powders was analyzed in terms of stress distribution. For comparison to the simulation results, the density, shape deformation, and residual stress of the specimens were evaluated using Archimedes' principle, 3D measuring technology, and Empyrean X-ray diffractometer. [ABSTRACT FROM AUTHOR]

The effects of two different procedures (SL: simultaneous loading, AL: asynchronous loading) on the surface qualities, microstructure and mechanical properties of Ti6Al4V alloy part during hot isostatic pressing (HIP) were investigated. It was found that, in AL process, the surface qualities significantly improved. Both of microstructure were composed of equiaxed grains and lamellar structure, as well as the prior particle boundaries (PPBs) were clearly observed in SL process. Moreover, tensile strength of samples fabricated by the two different procedures was exactly similar. However, the fatigue limit of parts fabricated from AL process was higher than that of parts produced from SL process. [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]

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]

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]

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 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]