Metallurgical investigations of Indo-Sasanian Copper-Silver alloy coins of Gurjara-Pratiharas dynasty

Five Indo-Sasanian copper-silver alloy coins were examined to determine the chemical composition and fabrication route. Based on iconography, the investigated coins were dated in the range 8th to 9th century CE. The chemical composition of the coins confirmed that the coins were made of copper-silver alloy. The percentage of silver was found to be in the range from 14 wt.% to 16 wt.%, and other elements iron and lead were present as impurities. There was no significant difference in the chemical composition from the surface to the center. Chlorine was detected in the localized green corrosion, which confirms the presence of active corrosion, and coins must be conserved by giving proper conservation treatment. The formation of unusual active corrosion compounds i.e. paratacamite was identified by the XRD, and this may be formed due to the exposure of coins to river water and soil. Optical microscopy revealed the dendritic and dual-phase structure, and the presence of dendrite showed that the coins were manufactured by the casting. It was confirmed from the optical microscopy that coins were not subjected to heat treatment and deformation. The microstructure consists of dual phases, in which the white phase is silver-rich, and the black phase is rich in copper. The morphology and chemical composition of the corrosion compound formed on the surface of the coins mainly indicated the formation of copper oxide with different morphology.

Rare Earth Metal-Based Intermetallics Formation in Al–Cu–Mg and Al–Si–Cu–Mg Alloys: A Metallographic Study

This study was conducted on Al–Cu–Mg and Al–Si–Cu–Mg alloys containing either 5%La or 5%Ce. Two levels of Ti addition were examined, i.e., 0.05% and 0.15%. Thermal analysis was the only technique used to obtain castings, from which samples were then sectioned for metallographic examination. Based on the results obtained, the following points may be highlighted. Addition of a fairly large amount of RE metals (La or Ce) leads to the appearance of several peaks in the solidification curve between the precipitation of the primary α-Al phase and the (Al–Al2Cu) eutectic reaction. Although a significant drop in the eutectic temperature is caused by the addition of 5%La or Ce, the corresponding modification of the eutectic Si is marginal. Two main types of intermetallics were documented: a gray phase in the form of sludge with a fixed composition and a white phase in the shape of thin platelets. Due to the high affinity of RE to react with Si, Fe, and Cu, several compositions were obtained explaining the observed multiple peaks in the solidification curve. Judging by the morphology of the gray phase, it is assumed that this phase is precipitated in the liquid state and acts as a nucleation site for the white phase. Lanthanum and Ce can substitute each other.

Effect of Rare Earth Metals, Sr, and Ti Addition on the Microstructural Characterization of A413.1 Alloy

The present work was performed on A413.1 alloy containing 0.2–1.5 wt% rare earth metals (lanthanum or cerium), 0.05–0.15% Ti, and 0–0.02 wt% Sr. These elements were either added individually or combined. Thermal analysis, image analysis, and electron probe microanalysis were the main techniques employed in the present study. The results show that the use of the depression in the eutectic temperature as a function of alloy modification cannot be applied in the case when the alloy is treated with rare earth metals. Increasing the concentration of RE increases the solidification zone especially in Sr-modified alloys leading to poor feeding ability. This observation is more prominent in the case of Ce addition. Depending upon the amount of added Ti, two RE based intermetallics can be formed: (i) a white phase, mainly platelet-like (approximately 2.5 μm thick), that is rich in RE, Si, Cu, and Al and (ii) a second phase made up of mainly grey sludge particles (star-like) branching in different directions. The grey phase is rich in Ti with some RE (almost 20% of that in the white phase) with traces of Si and Cu. There is a strong interaction between RE and Sr leading to a reduction in the efficiency of Sr as a eutectic Si modifier causing particle demodification.

Microstructure and High Temperature Mechanical Property of Directionally Solidified NiAl-Cr(Mo)-W/Nb Alloy

The microstructure, high temperature tensile behavior of the DS NiAl-Cr(Mo)-W/Nb alloy have been investigated. The transverse microstructure of the alloy consists typically of eutectic colonies of NiAl and Cr(Mo) phase with white phases segregating at the cell boundaries. The white phase is possibly Cr(Mo) phase containing large amount of Nb and W elements. The longtitudinal microstructure of the alloy is lamellar with the direction basically parallel to the directional solidification direction. The tensile yield strength and ultimate strength of the DS NiAl-Cr(Mo)-W/Nb alloy are much higher than that of the general cast NiAl-Cr(Mo)-W/Nb alloy, and the elongation of the alloy is also higher than that of the general cast alloy. The fracture is debonding along phase boundary and cleavage.

APPLICATION OF A LATTICE GAS MODEL FOR SUBPIXEL PROCESSING OF LOW-RESOLUTION IMAGES OF BINARY STRUCTURES

In the study an algorithm based on a lattice gas model is proposed as a tool for enhancing quality of lowresolution images of binary structures. Analyzed low-resolution gray-level images are replaced with binary images, in which pixel size is decreased. The intensity in the pixels of these new images is determined by corresponding gray-level intensities in the original low-resolution images. Then the white phase pixels in the binary images are assumed to be particles interacting with one another, interacting with properly defined external field and allowed to diffuse. The evolution is driven towards a state with maximal energy by Metropolis algorithm. This state is used to estimate the imaged object. The performance of the proposed algorithm and local and global thresholding methods are compared.