Papers by Keyword: Ni-Based Alloy

Abstract: Ni-based alloy welding material has been widely used in the welding and post-welding repair of high-temperature materials. The effect of temperature on the cyclic stress amplitude of ENiCrFe-1 Ni-base alloy electrode was studied under the same strain condition. The results showed that when the temperature was lower than 400 °C, it presented the characteristics of cyclic hardening and then cyclic softening. When the temperature was higher than 500 °C, it presented the characteristics of cyclic hardening and then cyclic stability. The main reason is that with the temperature increase, the dislocation structure changed more and more stable. The results not only enrich the internal mechanism of fatigue behavior of nickel-based alloy welding materials, but also have important reference value for improving the structural safety of welded joints.

Abstract: Due to high content of carbon and poor weldability, the ultrasonic frequency induction cladding technique was utilized to fabricate Ni-based alloy coating on the substrate of gray cast irons. In order to investigate the microstructure and properties of Ni-based alloy coating, the techniques of optical microscopy (OM), backscattered electron image (BEI), X-ray diffraction (XRD) and Vickers microhardness tester were employed. And then the immersion test and potentiodynamic polarization measurement were performed to evaluate the corrosion behavior of Ni-based alloy coating. The experimental results reveal that the coating bonds metallurgically with the substrate. Due to the elemental interdiffusion between the coating and the substrate, a solid solution zone of coating is formed. The phases of γ-Ni, Ni3B, NiSi, chromium borides and carbides can be distinguished in the coating. Chromium borides and carbides are benefit for the improvement of hardness and NiSi provides good corrosion resistance.

Abstract: Glassy overspray powders of Ni₅₉Nb₃₅Sn₆ (at%) bulk metallic glass (BMG) obtained by spray forming were used in order to produce coatings on AISI 1020 mild steel substrate by laser cladding of the pre-placed powders. Different laser parameters, resulting in a variation of the power density, PD (J/mm2), were tested with a Yb fiber laser (up to 500 W). Gas atomized powders, suction cast sample trough copper mold casting and the laser clad tracks were characterized by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry (DSC) and coatings were subjected to measurements of Vickers microhardness. Atomized powder obtained showed no crystalline phases formation up to 425 μm, indicating good glass forming ability (GFA) of Ni₅₉Nb₃₅Sn₆ (at%) alloy. Microstructure characterization confirmed maximum glassy dimension of t_c =1mm for the Ni₅₉Nb₃₅Sn₆ (at%). Laser cladding track showed nanocrystalline phases embedded in a glassy matrix with Vickers microhardness ranging from 336 to 1184 HV.

Abstract: To provide insight into the mechanical behavior and microstructural evolution of bulk nanograined (NG) Ni-based alloys during annealing, the Ni-based alloy sheets with grain size about 50 nm was produced through severe cold-rolling at room temperature, and then the cold rolled (CRed) Ni-based alloys were annealed at different states. The evolution of the nanostructure of the CRed Ni-based alloy during annealing and corresponding change in mechanical properties was investigated. The results showed that the CRed Ni-based alloy exhibited prominent enhancement in the yield strength (YS), ultimate tensile strength (UTS), which increased respectively from 253 MPa to 1455 MPa, 684 MPa to 1557 MPa. Further increase of the YS and UTS were obtained in the annealed-CRed Ni-based alloy with dual-phase. The YS and UTS of the NG dual-phase Ni-based alloy was respectively 2013 MPa and 2061MPa, which was annealed at 700 °C for 1h. In terms of the microstructural evolution, lower density of defects on the grain boundary were observed and the nanograins can be maintained about 100 nm even when annealed for 30 h at 700 °C, which suggests high thermal stability at this temperature. Both the high thermal stability and strength are due to the formation of the γ′ precipitates and slight grain growth of the NG matrix.

Abstract: In this article the technology “high-speed direct laser deposition” is performed. Influence of process parameters on product properties and material structure was defined for Ni-based alloy Inconel 625. Developed technology provided the mechanic properties of products on the bottom level of rolled metal and allows avoid heat treatment and HIP in production process. Economic efficiency of this technology is demonstrated for main areas of industry.

Abstract: Dynamic recrystallization processes in heat-resistant Ni-based alloy was investigated depending on temperature, strain rate and deformation ratio. Recrystallization intensity is determined by the temperature and deformation conditions. The factors that increase the degree of dynamic recrystallization include temperature and amount of strain increasing, as well as decreasing of strain rate. Increasing the volume fraction of recrystallized structure causes a uniform fine-grained structure.

Abstract: The purpose of this study is to evaluate the effectiveness in the contribution of the interpass welding in the microstructures and properties of the dissimilar fusion zones produced with an alloy 625 and API 5L X65 steel pipes. Three multipass welded joints with v-groove, were made under the same welding parameters, therefore, changing only the interpass temperatures at: 150°C, 250°C and 450°C. The microstructural characterization was performed using the light microscopy and the scanning electron microscopy (SEM). The hardness test, charpy-V impact test and the transverse tensile test were conducted according to specific standards. The results have shown that all ruptures in the tensile tests occurred in the base metal. Both yield strengths and ultimate tensile strengths, have dropped to the 450°C interpass temperature. It was also observed a slight drop in the hardness with increasing interpass temperature. The Charpy-V impact test results showed no significant differences among the interpass temperatures. These said results indicated that the maximum interpass temperature for the alloy 625/X65 steel dissimilar welding is limited by the steel properties.

Abstract: Due to its high creep strength and oxidation resistance, C-263 is a promising Ni-based alloy for applications in superheater tubes in coal fired thermal power plants. The creep strength is mostly based on finely distributed gamma-prime precipitates. In this work, the microstructural evolution of this material during heat treatment and thermal ageing has been investigated. The investigations were carried out by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Diffraction Pattern (SADP) and Energy Dispersive Spectroscopy (EDS). Besides, equilibrium and Scheil calculations were carried out using the thermodynamic software MatCalc to analyze the stable phases and the solidification process, respectively. Precipitation calculations during solution annealing and subsequent ageing at 700°C and 750°C up to 10.000h ageing time were performed to predict the phase fraction and precipitates radius. SEM and TEM investigations of aged specimens revealed three different precipitates: M₂₃C₆, γ’ and MX. MatCalc also predicted these precipitates. The calculated phase fraction and mean radius show good agreement with experimental data.

Abstract: To develop proper Ni-based alloys for high-temperature vitriol pump which is submitted the corrosion of vitriol and rush of liquid with solid particles, the equilibrium phase diagrams of some Ni-Cr-Fe-C-Mo-Si-Cu alloys were calculated by software Thermo-Calc. Based on the simulation results and the mechanism of sigma phase precipitation strengthening, the chemical composition of a new Ni-based alloy was proposed. The alloy was casted and treated by solid solution at 1373K+2h, followed cooling to 1323K and quenching in water at room temperature, then strengthened by ageing respectively at 973K, 1023K, 1073K, 1123K for 4h. It was investigated the phases by XRD, the microstructures by OM and SEM. The proposed alloy consists of g, s and M23C6 from 1073K to 1273K. The most amount of s phase is up to 12.45 % (mass) at 1023K, it decreases with the augment of equilibrium temperature. s phase disappears above 1323K. The amount of s phase is enough in alloy to supply good precipitation hardening at a large temperature range. Experimental results were compared with the results of phase diagram simulation by Thermo-Calc. The alloy can be effectively strengthened by sigma phase precipitation at the temperature from 1023K to 1073K. Experimental results verified the validity of phase diagram simulation.

Abstract: plasma arc sufacing； magnetic field style ；Ni-based alloy；microstructure and properties Abstract. The Ni60 alloy was overlaid on low carbon steel by plasma arc surfacing with Longitudinal magnetic field or transverse magnetic field. The magnetic field current and surfacing current could been changed during surfacing. After plasma arc surfacing with magnetic field, the XRD, wear loss tes, micro-hardness test were used to analyze the effect of magnetic field style on properties of overlay deposit. The acting mechanism of magnetic field style and parameters on properties and microstructure of overlay deposit was researched. The results indicate that longitudinal magnetic field and transverse magnetic field all can improve the properties of overlay deposit, but give little effectives intervention to the process parameters. The active effect of transverse magnetic field is better than longitudinal magnetic field because of transverse magnetic field can make the microstructure finer, component more uniform.