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AD730™ Ni-based superalloy specimens in solution-treated conditions were linear friction welded. Then, post-weld heat treatment (PWHT), consisting of γ′ sub-solvus solution treatments followed by aging, was conducted on the linear friction welded samples. High temperature creep tests were performed on the as-welded and PWHTed joints at two different temperatures: 700 °C under 600 and 750 MPa stress levels, and 850 °C under 100 and 200 MPa stresses. The creep resistance of the PWHTed joints was higher than that of the as-welded samples. The PWHTed joints exhibited better ductility than that of the base material at 850 °C, while they showed slightly lower creep life at 700 °C in comparison to the base metal. Microstructure examination showed that cracks initiated at the interface of oxidized particles at 700 °C. The decrease in creep resistance of the AD730™ Ni-based superalloy at 850 °C was related to a combination of the formation of precipitate-free zones (PFZ) in the vicinity of the grain boundaries (GBs) and microcracking assisted by oxidation. The Larson-Miller Parameter (LMP) was used to correlate the creep strength, temperature and time to failure for the as-welded and PWHTed samples. LMP values varied between 21.5 × 10 3 and 24.5 × 10 3 . It was found that in the investigated temperature range, the PWHTed AD730™ has similar creep characteristics as Udimet™720 Li and Inconel 738LC at low values of LMP and better creep properties than those of the Inconel 617 alloy at higher LMP values. [ABSTRACT FROM AUTHOR]

The kinetics of γ′ size and volume fraction changes during solution treatment of the advanced Ni-based superalloy, AD730™ are determined and the underlying mechanisms are investigated. High resolution Differential Thermal Analysis (DTA) and thermodynamic modeling were used to design and perform solution heat treatment experiments. Semi-analytical models are developed to describe the dissolution and coarsening processes. The results from the proposed models, supported by electron microscopy observations, indicate that coarsening occurs before complete dissolution takes place. Agglomeration is shown to be the governing coarsening mechanism for this alloy after calculation of the coefficients for both the Ostwald ripening and agglomeration mechanisms. Electron microscopy observations revealed that the early stages of agglomeration occur by neck formation between two neighboring particles. The splitting of γ′ particles was identified as one of the main dissolution mechanisms. Based on the obtained results, a dissolution kinetics model is proposed to quantify the volume fraction of dissolved γ′ particles and estimate the activation energy of this process for AD730™. A coarsening model based on the time-temperature dependence of the γ′ coarsening rate coefficient is also proposed taking the concentration of elements, γ′ volume fraction and the temperature into consideration. Based on this model, a method is developed to predict γ′ size evolution during aging heat treatment process and an optimum heat treatment to reach the desired γ′ distribution is proposed. The validity and accuracy of the proposed models were verified by carrying out different heat treatment experiments. [ABSTRACT FROM AUTHOR]

An experimental study of wear characteristics of electroless Ni-10% P coating sliding against hard AISI 52100 steel pin is investigated. Experiments are carried out at room and 550°C temperatures. Heat treatment effects on tribological behavior of this coating are studied. The wear surface and the microstructure of the coatings are analyzed using optical microscopy, scanning electron microscopy, energy dispersion analysis X-ray, and microhardness testing equipment. It is observed that the forming of continuous oxide film on contacting surfaces of pin and disk improves wear resistance and decreases friction coefficient of the Ni-10% P coating. The results indicate that the wear resistance of electroless Ni-10% P coating has improved with heat treatment at room temperature wear test, but it reverses in the wear test at 550°C. In addition, specimens without heat treatment have the highest wear resistance and the lowest friction for wear tests at elevated temperatures. [ABSTRACT FROM AUTHOR]

The Sar Cheshmeh porphyry copper deposit is located in the Central Iranian Volcanic-Sedimentary Belt (CIVSB). The hydrothermal alteration zones are well developed within and around the porphyry stock. Given the poor soil and vegetation cover in this area, we evaluated the usefulness of multispectral remote sensing data derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) and Enhanced Thematic Mapper Plus (ETM+) images and airborne magnetic-radiometric data for hydrothermal alteration mapping at a local scale. Principal component analysis (PCA), band ratios and the spectral angle mapper (SAM) technique were applied to the multispectral data sets to map hydrothermally altered rocks. PCA and band ratios were also applied to the airborne geophysical data. The overall results showed that the multispectral remote sensing data sets resulted in more accurate hydrothermal alteration mapping and lithological discrimination in the study area as compared with the airborne geophysical data. The radiometric data are also useful in enhancing areas with potassic alteration. [ABSTRACT FROM AUTHOR]

In this paper, a new entropy-based approach is developed for assessing the location of salinity monitoring stations in the Tehran Aquifer, Tehran, Iran. To find the optimal distance among stations, the measure of Transinformation in the Entropy Theory is used. Then a Transinformation-Distance (T-D) curve is developed and used in a multi-objective GA-based optimization model, which provides the best locations for monitoring stations. Because of the large area of the Tehran aquifer and significant spatial variations of the Electrical Conductivity (EC) of the groundwater in the study area, the C-means clustering method is used to classify the study area to some homogenous zones. The optimization model is applied to each zone to find the optimal location of monitoring stations. The results show the applicability and the efficiency of the model in assessing the groundwater monitoring systems. [ABSTRACT FROM AUTHOR]

Linear friction welding (LFW) is a near net shape solid state joining technology for aerospace applications. In this study LFW of a recently introduced Ni-based superalloy, AD730™, with superior properties for use in the hot section of gas turbines was studied. In order to minimize the number of experiments for achieving sound welds, an analytical method was developed that allowed to determine the optimum process parameters with a limited number of experiments. The predictions of the method were validated by LFW experiments, and sound samples without defects were produced. Microstructure evolution of the as-welded samples from the weld center to the base metal was investigated using laser confocal and field emission scanning electron microscopy (SEM) including electron back scatter diffraction (EBSD), energy dispersive spectrometer (EDS) and backscattered imaging (BSE). Post-weld heat treatment (PWHT), consisting of a γ′ sub-solvus solutionizing followed by aging, was conducted on LFWed blocks. Then, microstructure evolution and mechanical testing were conducted on PWHTed samples and compared with the as welded blocks. The obtained results were correlated with microhardness as well as tensile testing at room temperature and 650 °C, and interpreted in terms of fundamental metallurgical processes. Macroscopic examination of the PWHTed joints revealed that the samples failed out of the weld zone, further demonstrating the appropriate selection of LFW processing parameters using the proposed analytical method. PWHTed samples exhibited better room and high temperature tensile properties compared to those of the as-welded samples. Microscopic examination of the fracture zones of the samples showed that the higher levels of reprecipitation of γ′ particles in the thermomechanically-affected zone (TMAZ) of the PWHT samples were associated to their higher tensile properties compared to the as welded ones. Unlabelled Image • Analytical method is proposed to obtain LFW process parameters of AD730TM alloy and have a sound weld with minimum trials. • Microstructure evolution and mechanical properties as a function of LFW parameters are studied to confirm the approach. • The fracture mechanisms of the as-welded and suggested post-weld heat treated samples during tensile tests are analyzed. [ABSTRACT FROM AUTHOR]