Papers by Keyword: Nickel-Based Alloy

Abstract: In this study, the feasibility of predicting surface integrity and residual stresses by using elasto-viscoplastic finite element simulations and temperature-dependent flow softening constitutive material modeling is investigated. A friction determination method is proposed to identify friction coefficients in presence of tool flank wear. Serrated and cyclical chip formation has been simulated for using tools with and without flank wear. The predicted residual stresses and surface integrity is compared against experimental results from literature. Effect of friction on the residual stress profiles is also investigated. These results are highly essential in predicting machining induced microstructure alterations that are detrimental to fatigue life of nickel and titanium alloy components.

Abstract: A model of stress and temperature field is established on nickel-based alloy cutting by finite element modeling and dynamic numerical simulating, and then combining high-speed machining test and orthogonality analysis method, the influence law of cutting parameters on the cutting force and tool wear has been researched, and the tool life and cutting force prediction model based on cutting parameters has been obtained. Finally, by genetic algorithm method cutting parameters are selected reasonably and optimized. The result shows that the bonding wear is main tool wear, and the influence of cutting speed on cutting force is smaller than feed per tooth and axial depth of cut.

Abstract: The method of machining deep hole on Ni-base alloy which can tolerant high temperature by pulse electrochemical machining has been proposed in this paper. Five technical parameters are discussed on the effect of mass removal rate of machining process. Establish a dynamic math model, and analyze the effect of process parameters on the mass material removal rate of deep small holes. Machining accuracy of deep small holes was analyzed.

Abstract: Today’s global exploration of oil and gas leads to a range of highly corrosive environment that, in turn, require corrosion resistant high nickel content alloys for Oil Country Tubular Goods. Aimed at the problem of oil tube corrosion in environment with high content of H2S and CO2, the corrosion behavior of two nickel based alloys in 15%NaCl solution containing H2S/CO2 in high temperature and high pressure environments were researched. The pitting corrosion behavior of Ni-based alloys were investigated in FeCl3 solution by polarization curve and immersion test. The scanning electron microscopy(SEM), energy disperse spectroscopy(EDS) were applied to analyse the microstructure and corrosion performance of the samples. The results showed that the pitting-resistant of G3 was superior to Incoloy825.With the experimental temperature increasing, the corrosion rates increased and some slight corrosion pits appeared on the surface of Incoloy 825, Its maximum corrosion rate was 0.018mm/a. XRD showed that the corrosion films formed on nickel base alloys were consist of NiS, FeS and the oxides of Ni and Cr. The polarization curves showed that there were different corrosion behavior of two alloys, the anodic curve of G3 has an obvious passivation region, and there has higher pitting potential .

Abstract: TiAlN/TiN multilayer PVD coated carbide is one of the dominant tool materials for the turning applications of Inconel 718 due to its high hardness, high wear resistance, and high thermal stability. The results of a thorough investigation on TiAlN/TiN multilayer PVD coated carbide inserts were presented for turning Inconel 718. The tool wear of the PVD coated carbide inserts were tested and analyzed at different cutting speeds from 50m/min to 90m/min and different feed rates from 0.1mm/r to 0.4mm/r. The wear patterns and wear mechanisms of PVD coated carbide were analyzed. Results show that the dominant wear patterns are rake face wear, flank wear, micro-chipping, coating delamination, notch wear, built-up edge and breakage. The main wear mechanisms are adhesion, diffusion, abrasive and oxidation.

Abstract: A phase-field simulation is performed to examine the effect of elastic inhomogeneity between the  and ’ phases on coarsening of the ’ phase in Ni-based superalloys. In the calculation of elastic strain energy, the mechanical equilibrium equation in elastically inhomogeneous system is solved by an iterative-perturbation scheme. On the basis of the elastic constants of a practical Ni-based superalloy, a series of simulations is performed in which both elastic anisotropy and shear modulus are varied independently. The variation of elastic anisotropy gives significant effect on both morphology and size distribution function of the ’ particles, whereas the variation of shear modulus gives little effect on them. Furthermore, it is found that the coarsening rate constant of the cubic growth raw changes and increases with increasing the standard deviation of the ’ size distribution.

Abstract: Incoloy 903 overlays have been used to provide hydrogen environment embrittlement (HEE) resistance to welds in nickel alloy 718 structures. This is problematic because application of the required overlays has a history of high rejection and rework due to interpass microfissuring. Kovar has been identified as a potential hydrogen resistant replacement for Incoloy 903. A weldability study was initiated to compare the hot crack (microfissure) resistance of the two alloys to determine if substitution of Kovar for Incoloy 903 has the potential to improve the fabricability of HEE overlays. Varestraint testing indicates that Kovar has much higher crack initiation strains for both HAZ and weld metal cracking. Crack initiation strains were approximately 2% for Kovar while Incoloy 903 crack initiation strains were only 0.25% . Maximum crack lengths (MCL) observed on Kovar Varestraint tests were 0.12mm and 0.58mm for base and weld metal respectively, while 903 MCLs were 0.56mm and 2.3mm. Gleeble hot ductility testing indicates that Kovar has a nil ductility range of 7 degrees C while Incoloy 903 has a range of approximately 45 degrees C. The larger range observed for 903 is an indication of its greater crack susceptibility. Fabricability was correlated to material microstructure using optical microscopy, scanning electron microscopy and microprobe analysis.

Abstract: A new method for the oxidation protection of Ni-base superalloys with relatively low Al-content is proposed. By using the halogen effect the Al activity on the surface can be increased. Thus, the formation of a pure protective alumina scale becomes possible. The alloys IN738 and IN939 are considered in the present paper. Thermodynamic calculations for fluorine and chlorine predict the existence of the halogen effect for both alloys at temperatures between 900°C and 1200°C. The results also predict a change of the oxidation mechanism from internal alumina formation to external oxidation.

Abstract: The rate controlling mechanism for creep deformation of the single crystal Ni-based superalloy, CMSX-4, at 1073-1273K and 250-700MPa was investigated. Constant load tensile creep tests and creep interrupted tests up to the minimum creep stage, were conducted in air. And TEM observations carried out on creep interrupted specimens. Stacking faults in the ’ were observed on creep interrupted specimens at the temperature lower than 1223K and the stress higher than 500MPa. The number of stacking faults increases monotonously with a decrease in temperature, and remarkably with an increase in stress. The stacking fault formation depends on creep temperature and stress conditions. The stress exponent of minimum creep rate, n value, and the activation energy for creep, Qc, were constant for all creep test condition range. From these results, the stacking fault formation has no influence on creep resistance and the rate controlling mechanism for creep deformation at the low temperature and high stress condition was not thought to be shearing the ’, but movement of the mobile dislocations in the  channel as well as at the high temperature and low stress condition.

Abstract: A new method for processing large flat compositionally graded metal-ceramic parts with connected interpenetrating metal and ceramic network is described. Based on powder metallurgical methods, a metal foam is obtained by slip casting of metal powder slurries on a polyurethane foam, and used as preform to achieve a metallic interpenetration within the composite. The porous metallic preform is infiltrated with a ceramic slip and co-sintered. The metallic part is made from Ni-Cr-alloy, or the P/M superalloy Saratherm 2 and Nimonic 90, the ceramic consists of pure 8Y-ZrO2 or zirconia mixed with ZrSiO4. Composites of nominal same composition sintered without the metal foam preform show no metallic interpenetration.