Creep rupture properties of bare and coated polycrystalline nickel-based superalloy Rene®80

Creep deformation is one of the life time limiting reasons for gas turbine parts that are subjected to stresses at elevated temperatures. In this study, creep rupture behavior of uncoated and platinum-aluminide coated Rene?80 has been determined at 760?C/657 MPa, 871?C/343 MPa and 982?C/190 Mpa in air. For this purpose, an initial layer of platinum with a thickness of 6?m was applied on the creep specimens. Subsequently, the aluminizing were formed in the conventional pack cementation method via the Low Temperature-High Activity (LTHA) and High Temperature-Low Activity (HTLA) processes. Results of creep-rupture tests showed a decrease in resistance to creep rupture of coated specimen, compared to the uncoated ones. The reductions in rupture lives in LTHA and HTLA methods at 760?C/657 MPa, 871?C/343 MPa and 982?C/190 MPa were almost (26% and 41.8%), (27.6% and 38.5%) and (22.4% and 40.3%), respectively as compared to the uncoated ones. However, the HTLA aluminizing method showed an intense reduction in creep life. Results of fractographic studies on coated and uncoated specimens indicated a combination of ductile and brittle failure mechanisms for all samples. Although, the base failure mode in substrate was grain boundary voids, cracks initiated from coating at 760?C/657MPa and 871?C/343. No cracking in the coating was observed at 982?C/190MPa.

Simulation and analysis of the solidification characteristics of a Si-Mo ductile iron

High silicon and molybdenum ductile cast irons (Si-Mo alloys) are commonly used as exhaust manifold materials suffering from high temperature-oxidation and thermal-mechanical fatigue. The structural integrity of cast Si-Mo alloys under these service conditions is attributed to their microstructure consisting of spheroidal graphite and Mo-rich carbide embedded in a ferritic matrix. However, the cast structure includes also pearlite structure having a detrimental effect on the mechanical properties, therefore the cast matrix needs to be heat treated. In this study, the solidification of a Si-Mo ductile iron was investigated using (i) thermodynamic and kinetic calculations by Thermo-Calc and DICTRA software and (ii) thermal analysis in order to reveal out the sequence of phase formation and the phase transformations during solidification and (iii) microanalysis by energy dispersive spectrometer in order to determine elemental segregation and compare with the calculated values. The solidified structure was also characterized and all microstructural features were specified.

Nodule count effect on microstructure and mechanical properties of hypo-eutectic ADI alloyed with nickel

Samples of ductile iron alloyed with 0.88 % Ni with a nodule count of 606, 523, and 290 nod/mm2 were obtained from sand cast plates of different thickness in the range from 8.46 to 25.4 mm. The effect of the nodule count was evaluated during the austempering process held at 285?C and austempering times of 15, 30, 45, 60, 70, and 90 min. The volume fraction of high carbon austenite increased when the nodule count increased, however, the carbon content of the high carbon austenite kept almost constant. The process window was narrow, requiring a lower austempering time when the nodule count increased. The combination of a higher nodule count and low austempering temperature allowed obtaining a fine ausferritic microstructure which led to higher Brinell hardness and tensile strength. The process window was determined by XRD measurements and it was in good agreement with the microstructural and hardness evolution as the austempering time increased.

Liquid-vapor equilibrium and evaporation rate of Cd-Zn liquid alloy

In this study, LVE (liquid-vapor equilibrium) data of cadmium-zinc system were determined at pressure of 7.5 Pa. We compare the use of the Redlich-Kister polynomials with the Wilson equation in fitting activities. The LVE for Cd-Zn system in vacuum distillation was modeled using the two models. The results of the two models are reliable, the Redlich-Kister polynomialsis better than the Wilson equation. The LVE phase diagram is reliable for predicting the process of vacuum distillation for Cd-Zn system. Evaporation rates of elements in Cd-Zn alloy were experimental measured and calculated by the Langmuir equation. Experimental data on the evaporation of pure metals Cd and Zn are included. The evaporation coefficients of zinc and cadmium under vacuum conditions were calculated. The deviations were discussed. Comparing calculations with experimental results, it can be found that the trend is consistent. The activation energies of Cd and Zn in the Cd-Zn alloy under experimental conditions were also calculated.

Effect of partially reduced highly fluxed DRI pellets on impurities removal during steelmaking using a laboratory scale EAF

The present work represents a comparative study on the impurities removal from pig iron melt by addition of partially reduced highly fluxed direct reduced iron (DRI) to make steel in a 2 kg capacity electric arc furnace (EAF). Three types of fluxed DRI (30, 50, 80% Reduction (%R) with similar basicity-8) were used to maintain different level of oxidizing potential on the bath for studying the kinetic behaviour of impurities removal from melt. Results showed that the rate of removal of impurities (i.e. C, Si, Mn, P, S etc.) was increased initially up to 5 minutes of reaction time then decreased afterwards. Phosphorus (~64%), sulfur (~16%) and carbon (~94%) were removed simultaneously up to 25 minutes of reaction time using 30%R fluxed DRI. Similarly, phosphorus (~33%), sulfur (~50%) and carbon (~62%) were removed simultaneously using 50%R fluxed DRI while highly reduced (80%R) flux DRI removed sulfur (~58%), carbon (~56%) with a small fraction of phosphorus (~18%) from pig iron. It was observed in all the cases that silicon (>99%) and manganese (>80%) were removed. From the present study, it can be concluded that ~30%R DRI is favorable for effective phosphorus removal whereas ~80%R is favorable for sulfur removal. The significant removal of impurities could be achieved by charging ~50%R fluxed DRI in the pig iron melt.

Effects of plasma surface Ta alloying on the tribology behavior of γ-TiAl

To improve the wear resistance of ?-TiAl alloy, Ta alloy layer was prepared on surface by double glow plasma surface alloying technique. The tribology behavior of Ta alloy layer against Si3N4 at 25?, 350? and 500? were comparatively studied. The results showed that Ta alloy layer comprised a deposition layer and a diffusion layer. The deposition layer played a role in protection as a soft film. With the increase of temperature, the wear mechanism of ?-TiAl changed from abrasive wear to coexistence of abrasive wear and oxidation wear. Ta alloy layer?s wear mechanism changed from adhesive wear to coexistence of adhesive wear and oxidation wear. Surface Ta alloying process significantly reduced the wear volume, the specific wear rate and the friction coefficient of ?-TiAl and improved the wear resistance properties of ?-TiAl.

The effect of calcium fluoride on extracting magnesium from magnesite and calcium carbonate by silicothermal reduction in flowing argon

At present, the production of magnesium is mainly carried out semi-continuously with ferrosilicon as reducing agent under high temperature and high vacuum. In order to continuously produce magnesium, anew method of extracting magnesium from low-grade magnesite and calcium carbonate by silicothermal method in flowing inert gas was proposed. The effects of calcium fluoride(CaF2)on decomposition rate, decomposition kinetics, reduction rate of magnesia and crystal type of dicalcium silicate in reduction slag were investigated in the paper. The experimental results showed that calcium fluoride could accelerate the decomposition of carbonate, and had no side effect on the calcined products. In addition, the analysis results of DTA curves showed that calcium fluoridecould reduce the decomposition reaction activation energy and the reaction temperature of carbonatein the prefabricated pellets. The results of reduction experiments showed that proper calcium fluoridecould promote the reduction rate of magnesia, and in the temperature range of 1250? ~ 1350?, with same timeframe, the corresponding calcium fluoride contents were5%, 3% and 1% respectively when the reduction rate reached the maximum. Excessive calcium fluoride could reduce the reduction rate of magnesia, but it couldpromote the transformation of dicalcium silicate to ? phase in the reduction slag.

Thermodynamic modelling of the binary indium-lithium system, a promising li-ion battery material

The binary In - Li system is a promising Li-ion battery anode material as well as a part of the important ternary Ge - In - Li system. The thermodynamic descriptions of metallic systems are widely used to retrieve information necessary for alloy applications. In this work, a thermodynamic model of a binary indium - lithium system prepared by the Calphad approach is proposed. The liquid phase was described by an associate model, and the solid phases determined by the ab-initio calculation were included in thermodynamic modeling. The obtained set of self-consistent thermodynamic parameters well reproduces the available experimental data and enables further calculations of multi-component systems. A good agreement between the calculations and the available experimental data was found. The proposed model can be used for further descriptions of ternary systems.

Primary microstructure characterization of Co-20Ni-9Al-7W-3Re-2ti superalloy

The characterization of the primary microstructure of the new Co-based superalloy of Co-20Ni-9Al-7W-3Re-2Ti type was shown in this article. The investigated alloy was manufactured by induction melting process from pure feedstock materials. The fundamental technological problem related to Co-Al-W-X multicomponent alloys' casting process is a strong susceptibility to interdendritic segregation of alloying elements, especially tungsten and rhenium. The performed analysis revealed that the observed effect of alloying elements segregation is detectable and much stronger than for Co-9Al-9W and Co-20Ni-7Al-7W alloys, related to titanium, nickel and aluminium migration to inter-dendritic spaces. Consequently, the tungsten concentration gradient between dendritic and interdendritic zones is higher than for Co-9Al-9W and Co-20Ni-7Al-7W alloys. The same situation is in the case of rhenium and cobalt, but Co's concentration in the interdendritic zone is only slightly lower.

Application of two-step diffusion couple technique in high-throughput screening of optimal composition and aging temperatures for alloys design: A demonstration in binary Ni-Al system

In this paper, four binary Ni-13.4at.% Al/Ni-17.7at.% Al diffusion couples were first prepared and subjected to homogenization at 1573 K for 10800s, from which a continuous concentration profile forms. The three diffusion couples were then cooled down for aging at respective temperatures, i.e., 1173, 1123 and 1073 K, for 14400s. The effect of composition and aging temperature on the aging microstructure was studied in detail by means of different experimental techniques and statistical analysis. The volume fraction, grain size and shape factor of ?? precipitates in the three diffusion couples were plotted as a function of alloy composition and annealing temperatures. Together with the previously proposed evaluation function in which the phase fraction, grain size and shape factor of ?? precipitates were chosen as the evaluation indicators, the optimal alloy composition and aging temperature for binary Ni-Al alloys with the best mechanical properties were evaluated, and finaly validated by the measured hardness values. The successful demonstration of alloy design in the present binary Ni-Al alloys indicates that the two-step diffusion couple together with the evaluation function for mechanic properties should be of generality for high-throughput screening of optimal alloy composition and heat treatment process in different alloys.