Sharif Digital Repository

Low cycle fatigue is one of the most important phenomena affecting the lifetime of jet engine blades. In this paper, the effect of aluminide diffusion coating (CODEP-B) on low cycle fatigue properties of René 80 has been studied at temperature of 871 °C, R = 0 and strain rate of about 2 × 10-3 s-1. Experimental results show that the applied cyclic strain is lower than 0.8%, the presence of aforesaid coating increases the fatigue lifetime. In coated specimens, while the total cyclic strain is lower than 0.8%, the nucleation of the cracks occurs merely in substrate, but in cyclic strain more than 1%, as a result of simultaneous nucleation of cracks in the coating surface, diffusion layer and... 

In the present study, the surface chemical and depth profile composition of the electrodeposited Ni-Fe base alloy layers on the Cu substrates were investigated with compositions of the Ni80-Fe20 (binary) and Ni77-Fe20.7-Cr1.7-Mo0.6 (quaternary) deposits. Auger electron spectroscopy (AES) and X-ray photoelectron spectroscopy (XPS) results showed the surface accumulation of copper on the surface layers of binary alloy films in the form of Cu 2O. In the quaternary films, addition of Cr and Mo reduced the amount of the Cu accumulation at the surface, while Cu accumulation was enhanced under air-exposed condition for both alloy films. Depth profiles using the secondary ion mass spectroscopy... 

Ni-Fe and the Ni-Fe-Cr-Mo alloy films were electrodeposited from a chloride solution containing complexing compounds on ITO/glass substrates. AFM studies revealed a spherical structure for the alloy films with roughnesses from 10 up to 50 nm. The Ni-Fe-Cr-Mo alloy films were found to have a fine-grain structure. The quaternary alloy compounds containing up to 4% Cr and 2% Mo showed higher resistivity and little decrease in magnetoresistance (MR) relative to the Ni80Fe20 alloy compound. The MR of the quaternary alloy compounds was decreased for higher Cr and Mo contents. Moreover, the anisotropy (AMR) was also decreased by the addition of Cr and Mo to Permalloy films. Auger studies indicated... 

In order to provide sufficient heat without overheating healthy tissue in magnetic fluid hyperthermia (MFH), a careful design of the magnetic properties of nanoparticles is essential. We perform a systematic calculation of magnetic properties of Ni-alloy nanoparticles. Stoner-Wohlfarth model based theories (SWMBTs) are considered and the linear response theory (LRT) is used to extract the hysteresis loop of nickel alloy nanoparticles in alternating magnetic fields. It is demonstrated that in the safe range of magnetic field intensity and frequency the LRT cannot be used for the calculation of the area in the hysteresis for magnetic fields relevant for hyperthermia. The best composition and... 

Transient liquid phase (TLP) bonding was used to join a nickel-based superalloy GTD-111 using a Ni-Si-B amorphous interlayer, MBF30. Bonding was carried out at 1100 °C with different holding time under vacuum. Joint region microstructure was studied by optical and scanning electron microscopy. Microstructural studies showed that before completion of isothermal solidification, bond region consists of four distinct zones: centerline eutectic structure due to athermal solidification, solid solution phase due to isothermal solidification, diffusion-induced boride precipitates and base metal. Complete isothermal solidification, which prevents formation of centerline eutectic constituent, occurred... 

Serrated flow was investigated in superalloy IN738LC, a nickel-base γ′ age-hardened alloy. In this material serrated flow appeared between 350 and 450 °C and strain rate of (8.77 × 10-5 to 8.77 × 10-3) s-1. Activation energy for this process was calculated to be 0.69-0.86 eV which is in good agreement with the values reported for similar alloys. Results show that the diffusion rate of substitutional solute atoms at this temperature range is too low to cause this effect. This suggests that the interaction of solute atoms and moving dislocation is responsible for the observed serrated flow in this alloy. © 2007 Elsevier B.V. All rights reserved  

The age-hardening behavior and microstructure of selected samples of a Ni-Co alloy were studied using hardness testing, optical microscopy, and scanning and transmission electron microscopy. The final microstructure of the material was found to be sensitive to the temperature of the solution treatment. This approach may be used to optimize the microstructure of the alloy for different applications. © 2007 Acta Materialia Inc  

Fixtured sintering of up to 5 hours at 1223 to 1323 K is successfully used to diminish the dimensional change of NiTi memory alloys produced from mixtures of elemental Ni and Ti powders packed and pressed at room temperature under 400, 500, and 600 MPa pressure. The improvements obtained can help near-net-shape technology via powder metallurgy that overcomes the traditional casting problems such as oxygen, nitrogen, hydrogen, and carbon absorption and intermetallic compound precipitation, which lower the workability and the homogeneity of the final alloy. The effects of compaction pressure, sintering time, and sintering temperature on dimensional change, porosity, hardness, and morphology of... 

The electro-catalytic oxidation of methanol on a Ni-Cu alloy (NCA) with atomic ratio of 60/40 having previously undergone 50 potential sweep cycles in the range 0-600 mV vs. (Ag/AgCl) in 1 m NaOH was studied by cyclic voltammetry (CV), chronoamperometry (CA) and impedance spectroscopy (EIS). The electro-oxidation was observed as large anodic peaks both in the anodic and early stages of the cathodic direction of potential sweep around 420 mV vs. (Ag/AgCl). The electro-catalytic surface was at least an order of magnitude superior to a pure nickel electrode for methanol oxidation. The diffusion coefficient and apparent rate constant of methanol oxidation were found to be 2.16 × 10-4 cm2 s-1 and... 

Results of an investigation on the evolution of microstructure during simple compression testing of two face-centered-cubic (fcc) polycrystals, IN625 superalloy and 316L stainless steel, are reported and a review on the existing data related to the uniaxial deformation of fcc polycrystals is presented. It is found that while a number of fcc polycrystals show linear hardening behavior, the evolution of the underlying microstructure may be quite different. It is argued that, in contrast to the current belief, deformation twinning may not be the sole cause of linear hardening in low stacking fault energy (SFE) fcc polycrystals. It is suggested that, due to the requirement of slip system change... 

Ni-base superalloy René 80 is widely used in manufacturing aircraft turbine blades. The service temperature of this alloy is in the range of 760-982 °C. Although this alloy possesses suitable mechanical, oxidation and hot corrosion properties, it is coated in order to increase its wear, oxidation, erosion and hot corrosion properties against harmful environmental service conditions. In this paper the influence of applying diffusion coating (CODEP-B) on the tensile properties of René 80 has been studied in the temperature range of 22-982 °C. Experimental results show that the tensile properties of the coated specimens are relatively lower than that of uncoated ones in the same conditions. But... 

The Cu surface segregation is investigated in the electrodeposited Ni-Fe layers using X-ray photoelectron spectroscopy (XPS), Auger electron spectroscopy (AES), secondary ion mass spectroscopy (SIMS) and atomic force microscopy (AFM). The results indicate that Cu segregation and accumulation take place in areated and deareated baths and the amount of segregated copper increases after air exposure. This phenomenon is explained by lower interfacial tension of the Cu in comparison with Ni and Fe. Our results reveal more surface segregation in the electrodeposit than vacuum reported results. This should be due to interface charging and higher surface diffusion in applied potential. The effect of... 

A nickel base superalloy Rene 80 was bonded in the as received cast condition using transient liquid phase diffusion bonding with a Ni-base interlayer. The bonding process was carried out at 1100 °C under argon and vacuum atmospheres for various hold times. The bonds then homogenized at 1206 °C for 1 and 2 h. Microstructures of bonds were studied with optical and scanning electron microscopy. Microstructure studies showed intermetallic compounds within the joint region. However, these intermetallic compounds were removed by a post-bond heat treatment at 1206 °C for 2 h. Shear and hardness tests were undertaken to determine the mechanical properties of bonded samples. Results showed that the... 

The electrodeposition of cobalt, nickel and Ni-Co alloys was studied by electrochemical techniques. Cyclic voltammetry and current transient measurements were used to characterize the Co-Ni system in other to obtain the nucleation and growth mechanism. The cyclic voltammetry results clearly showed that electrodeposition of cobalt, nickel and Co-Ni alloy is diffusion-controlled process with a typical nucleation mechanism. The redox potentials of the Co and Ni are shifted to more cathodic potentials in the Co-Ni alloy system. In addition, the current transients revealed that nucleation mechanism is instantaneous with a typical three-dimensional (3D) nucleation and growth process. The number of... 

Results of recent studies on the effect of heat treatment after cold rolling on mechanical properties and transformation temperatures of the cast 52Ni48Ti alloys are described. It is seen that stress-induced martensite is formed when both the as-rolled and the low-temperature (≤400 °C) heat-treated samples are strained. Martensite reorientation due to the stress action occurs in samples heat treated at 500 °C and higher. Optimum recovery occurs below 600 °C resulting in hardness reduction. Recrystallization starts at 600 °C resulting in parent phase yield stress enhancement. Yield stress starts to decrease when grain growth and order-disorder transformation both occur above 700 °C. © 2006... 

The evolution of primary and secondary γ′ precipitates in the high γ′ volume fraction Rene 80 Ni based superalloy has been examined during aging at elevated temperatures for periods up to 1750 h. While the increase in average dimension of particles followed the cube rate Lifshitz, Slypzof and Wagner (LSW) law, rt-3-r0 -3=kt, there were significant discrepancies between the experimental and theoretical particle size distributions (PSDs) and inconsistency with the kinetic constants associated with the two populations of particles. These differences are attributed to the influence of elastic coherency strains which have not been considered in conventional capillarity driven coarsening models.... 

Production of NiTi alloy from elemental powders was conducted by mechanical alloying (MA) and sintering of the raw materials. Effects of milling time and milling speed (RPM) on crystallite size, lattice strain, and XRD peak intensities were investigated by X-ray analysis of the alloy. Powder compaction and sintering time and temperature effects on pore percentage of the as-mixed and the mechanically alloyed samples were empirically evaluated. The crystallite size of the mechanically alloyed Ni50Ti50 samples decreased with MA duration and with the milling speed. Depending on the crystal structure of the raw materials, the lattice strain increases with the milling duration. Metallographic... 

This work presents the effect of co-sintering on the densification and microstructural evolution in the two-layer stepwise graded composite of INCONEL 718 and INCONEL 625 superalloys. A pressureless co-sintering method in conjunction with a powder layering technique was used. The sintering was carried out in solid state and liquid phase in temperature ranging from 1260 °C through 1300 °C for 60 minutes in a low pressure of an argon atmosphere. Nonisothermal sintering behavior was also examined by dilatometric analysis. Similarly, the sintering response of the individual layers was characterized. The results reveal an enhanced densification rate during co-sintering of the composite layers.... 

Rene-80, as an alloy for production of the jet turbine blades, shows high mechanical properties as well as microstructure stability during the high temperature engine operation. In this study we tried to have a deep insight on the microstructure of the cast Rene-80 and the evolution of microstructure during the different stages of the relatively complex GE class-A heat treatment. Although the solution heat treatment homogenized the chemical alloy segregation resulted from the casting to some extent, it did not cause all the casting γ′ particles to dissolve completely in the matrix. Primary aging caused growth in the residue particles as well as growth of the new precipitated particles, which... 

Austempered ductile iron (ADI) is one of the most widely used types of ductile iron produced by austempering heat treatment. ADI heavy section parts are employed in different industries owing to their unique mechanical properties. Cooling rate in thick parts is significantly low, so heavy section ductile iron parts should have an adequate austemperability for preventing pearlite formation in the middle of the casting. In order to achieve the proper austemperability and fully ausferritic structure, alloying elements like nickel are added to the melt. The objective of this work is to study the role of austempering parameters on nickel alloyed ADI specimens fabricated from 75-mm-thick Y-block....