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The purpose of this research was to investigate the effect of solidification cooling rate on the microstructural characteristics of IN939 superalloy. Microstructure of castings was investigated using X-ray diffraction, optical microscopy and field emission SEM microscopes, and the most important phases in the microstructure, their morphology and micro-mechanisms of formation of these phases were evaluated. In addition, thermodynamic simulation was carried out using JMatPro software to predict the type and amount of phases in different microstructural regions, the chemical compositions of γ and γ′ phases, as well as the γ/γ′ lattice misfits. The results showed that with increasing the cooling rate, MC carbides became more regular and more polygonal, while with decreasing cooling rates, carbides morphologies changed to Chinese script form. At cooling rates around 0.13 °C/s, the γ′ particles in dendrite cores were formed into coarse and cubic patterns, whereas in interdendritic regions, γ′ particles were observed as very coarse and flower-like structures. At cooling rates around 1.1 °C/s, the morphology of γ′ precipitates in the dendrite cores was mainly spherical, and in the interdendritic areas, γ′ precipitates were a mixture of spherical and cubic particles. It was shown that the major factors controlling the morphology of γ′ particles in different regions of the microstructure are the size of these particles combined with the γ/γ′ lattice misfit. Finally, the results showed that the following equation relates the secondary dendrite arm spacing (SDAS) to the solidification cooling rate (SCR) for IN939 superalloy: SDAS = 43.177 (SCR)−0.305. [ABSTRACT FROM AUTHOR]

The harsh service environment of aeroengine hot-end components requires superalloys possessing excellent antioxidant properties. This study investigated the effect of pre-strain on the oxidation behavior of polycrystalline Ni3Al-based superalloys. The growth behaviors of oxidation products were analyzed by scanning electron microscope, transmission electron microscope, X-ray Photoelectron Spectroscopy and Raman spectroscopy. The results indicated that the 5% pre-strained alloys exhibited lower mass gain, shallower oxidation depth and more compact oxide film structures compared to the original alloy. This is mainly attributed to the formation of rapid diffusion paths for Al atoms diffusing to the surface under 5% pre-strain, which promotes the faster formation of protective Al2O3 film while continuing to increase the pre-strain to 25% results in less protective transient oxidation behavior being aggravated due to the increase in dislocation density within the alloy, which prevents the timely formation of the protective Al2O3 film, resulting in uneven oxidation behavior on the alloy. [ABSTRACT FROM AUTHOR]

Purpose: This paper aims to identify the optimal forming angle for the selective laser melting (SLM) process and evaluate the mechanical properties of the SLM-formed GH3536 alloy in the aero-engine field. Design/methodology/approach: Forming the samples with optimized parameters and analyzing the microstructure and properties of the block samples in different forming angles with scanning electron microscope, XRD, etc. so as to analyze and reveal the laws and mechanism of the block samples in different forming angles by SLM. Findings: There are few cracks on the construction surface of SLM formed samples, and the microstructure shows columnar subgrains and cellular subgrains. The segregation of metal elements was not observed in the microstructure. The pattern shows strong texture strength on the (111) crystal plane. In the sample, the tensile strength of 60° sample is the highest, the plasticity of 90° forming sample is the best, the comprehensive property of 45° sample is the best and the fracture mode is plastic fracture. The comprehensive performance of the part is the best under the forming angle of 45°. To ensure the part size, performance and support structure processing, additional dimensions are added to the part structure. Originality/value: In this paper, how to make samples with different forming angles is described. Combined with the standard of forged GH3536 alloy, the microstructure and properties of the samples are analyzed, and the optimal forming angle is obtained. [ABSTRACT FROM AUTHOR]

BACKGROUND: We compared the raw Ti–Al–V super alloy transpedicular implant screws with boronized and surface-hardened transpedicular implant screws. OBJECTIVE: To improve patients' postoperative prognosis with the production of harder and less fragile screws. METHODS: Surface hardening was achieved by applying green-body encapsulation of the specimen with elemental boron paste which is sintered at elevated temperatures to ensure the boron-metal diffusion. Boron transported into the Ti–Al–V super alloy matrix gradually while suppressing aluminum and a homogeneously boronized surface with a thickness of ∼15 microns was obtained. The uniform external shell was enriched with TiB2, which is one of the hardest ceramics. The Ti-Al-V core material, where boron penetration diminishes, shows cohesive transition and ensures intact core-surface structure. RESULTS: Scanning electron microscope images confirmed a complete homogeneous, uniform and non-laminating surface formation. Energy-dispersive X-ray monitored the elemental structural mapping and proved the replacement of the aluminum sites on the surface with boron ending up the TiB2. The procedure was 8.6 fold improved the hardness and the mechanical resistance of the tools. CONCLUSIONS: Surface-hardened, boronized pedicular screws can positively affect the prognosis. In vivo studies are needed to prove the safety of use. [ABSTRACT FROM AUTHOR]

In the current study, the effect of the weight percentage of filler and additive powder on the microstructural and mechanical properties of the wide gap activated diffusion brazing process was studied. IN738LC base metal powder and AMDRY BRB filler were used as filler metal for IN738LC superalloy brazing. Subsequently, diffusional heat treatment and aging cycle were used to modify the microstructure and mechanical properties in the restoration structure. Optical microscope and scanning electron microscope were used to identify the phases in the braze area and four-point bending tests were performed to evaluate the mechanical properties of the wide gap. For the sample brazed at 1180 °C for 30 min, heat treated at 1120 °C for 4 h, and aged at 850 °C for 24 h, the porosity and eutectic phases in the brazed area and the diffusion-affected zone maintained as low as possible. Thus, it can be referred to as the optimized sample. The samples containing 40 wt% filler had the optimum mechanical properties at ambient temperature and high temperature. Fractography showed that the place of crack initiation was mainly in the filler metal. [ABSTRACT FROM AUTHOR]

In order to clarify the strengthening mechanism of an electron-beam welded (EBW) Ni-Co based superalloy, the local deformation behavior in different regions across the weld joint was investigated by the in-situ micro-tensile test in the scanning electron microscope and analyzed by the micro digital image correlation (μDIC). The microstructures across the weld joint were systematically investigated on multiscale levels. The micro-hardness profiles were also determined across the weld joint. Significant changes in the grain size, γ' phase, MC carbides and dislocation configurations were observed within 2.0 mm from the weld line as a result of the steep temperature gradient and the resultant Marangoni flow occurring during EBW process. Furthermore, the micro-hardness profiles and microstructure-dependent mechanical properties were influenced by the variation of grain size, γ' particle size and the dislocation density in the weld joint. The cracks preferred to initiate and propagate on the blocky MC carbides, rather than the ultrafine MC carbides and the liquefaction cracks. This study proposes a method for high throughput measurement of microstructure-dependent mechanical properties, and shows a certain guiding significance for optimization of microstructure and improvement of mechanical properties of electron-beam welded Ni-Co based superalloys. • Indicates the ability of SEM-μDIC technique on the measurement of microstructure-dependent mechanical properties. • Microstructure gradient across the weld joint was systematically investigated on multiscale levels. • The microstructure-dependent deformation behavior across the weld joint were analyzed by in-situ SEM tensile testing module. • The effects of microstructure gradient on microstructure-dependent mechanical properties were analyzed. [ABSTRACT FROM AUTHOR]