Materials Science Forum Vols. 638-642

Abstract: An austenitic Ni-30%Fe model alloy was employed to investigate the texture and substructure development within the deformed matrix and dynamically recrystallized (DRX) grains during hot torsion deformation. Both the deformed matrix and DRX grains predominantly displayed the crystallographic texture components expected for simple shear deformation. The characteristics of the deformed matrix texture evolution during deformation largely resulted from the preferred consumption of high Taylor factor components by new recrystallized grains. Likewise, the comparatively weaker crystallographic texture of DRX grains became increasingly dominated by low Taylor factor components as a result of their easier nucleation and lower consumption rate during DRX. There was a significant difference in the substructure formation mechanism between the deformed matrix and DRX grains for a given texture component. The deformed matrix substructure was largely characterized by “organized”, banded subgrain arrangements with alternating misorientations, while the substructure of DRX grains was more “random” in character and displayed complex, more equiaxed subgrain/cell arrangements characterized by a local accumulation of misorientations. Substructure characteristics of individual orientation components were principally consistent with the corresponding Taylor factor values.

Abstract: For interconnect materials in the microelectronic technology copper has replaced aluminum due to its lower resistivity, higher thermal conductivity and better electromigration resistance. Recently, it was found that nanotwinned copper exhibits ultra high yield strength, ductility and electrical conductivity. Therefore, in this study the effect of plating current density and frequency were investigated on the crystallographic texture of Cu electrodeposited to understand the twin character. Electron backscatter diffraction (EBSD) was used for characterizing the preferred orientation, grain size distribution, and grain boundary character distribution. Three kinds of <110>, <111> and <112> textures were found to be related with the electrodeposited parameters of current density and frequency. Here we will discuss the relationship between the preferred orientation and the electrodeposited parameters.

Abstract: Quantitative prediction of transformation textures in steel becomes possible if a variant selection rule is taken into account, in which ferrite nucleating on austenite grain boundaries prefers to have orientation relationship with two neighboring austenite grains at the same time. The mathematical model of the variant selection rule is described and some examples of simulation in transformation textures in hot-rolled steel sheets are presented using the textures of retrained austenite and the misorientation distribution function method. An excellent agreement is attained between the predicted and experimental ferrite textures.

Abstract: The knowledge of the structure/property relationship in polycrystalline materials is the basis for successful application of Grain Boundary Engineering. We demonstrate this relationship in the reverse way: from the selective corrosion attack observed in unique sample – loops from excavated necklace dated to the 10th century and manufactured from a Ag–1%Cu alloy – we can deduce the method of manufacturing the objects. Individual grain boundaries in this object were identified by electron back-scattering diffraction. Crystallographic maps of the grain boundaries are confronted with the level of the long-termed selective corrosion attack in the soil electrolyte under conditions of decomposing human body. It is shown that general grain boundaries, which are highly segregated by copper, are preferably attacked by corrosion. The segregated layers represent a less-noble material comparing to the surrounding bulk in this environment. In contrast, the twin and other special grain boundaries are significantly more resistant against this attack.

Abstract: The structural materials phase transformations and failure mechanisms have been under scrutiny for many years. However, the advent of new and more powerful techniques is always making possible to address unsolved problems. Nowadays, the implementation of sophisticated in-situ electron microscopy tests is providing new insights in several fields of chemistry, physics, and materials science by allowing direct observation of a wide variety of phenomena at submicron and even atomic scale. These experiments may involve controlled temperature and atmospheres, mechanical loading, magnetic and/or electric field among other conditions that are imposed to the sample while its response or evolution is studied. An in-situ high temperature deformation experiment was developed and adapted within the vacuum chamber of a scanning electron microscope (SEM). This setup was used to study the grain boundary sliding (GBS) mechanism and its effect on the high temperature cracking phenomenon known as ductility-dip cracking (DDC). The Ni-base filler metals AWS A5.14, ERNiCrFe-7 and ERNiCr-3, which correspond to alloys 690 and 600, respectively, were studied within the temperature range between 700 and 1000 °C. Analysis of the recorded digital videos that registered the high temperature deformation made possible differentiating and quantifying, with submicron resolution, two different components of GBS. The designated pure-GBS and deformation-GBS components were described and quantified. In addition, the GBS relationship with the material high temperature ductility and the DDC failure mechanism was established.

Abstract: Five samples of Pb-Ca-Sn-Al alloy with different initial microstructures were processed in the same way including cold rolling with thickness reduction of 30% at the temperature of liquid nitrogen and then annealing at 270oC (0.9Tm) for 1 to 10 minutes. Electron back-scatter diffraction (EBSD) analyses indicated the initial microstructure which is at the end of primary recrystallization with a averaged grain size around 10 microns, a fair quantity of annealing twins and a random orientation can definitely result in a final grain boundary character distribution (GBCD) mainly composed of special boundaries (SBs) of which its fraction is higher than 75%, and the averaged SB cluster size exceeds 200 microns, implying the GBCD is optimized in satisfaction. However, the initial microstructures of partial recrystallization or full recrystallization but with coarser grain size are not good at producing high fraction SBs, whereas the initial microstructure of deformation with very strong textures is harmful to the formation of SBs in the processing of rolling followed by annealing. High resolution EBSD measurements revealed that the interactions between mobile incoherent ∑3 boundaries which were probably introduced by the continuous recrystallization from the distorted coherent ∑3 ones could be the formation mechanisms of the GBCD containing high fraction SBs.

Abstract: The proportion of low ΣCSL boundaries of single phase brass, Ni based Alloy 690, 304 stainless steel and Pb alloy were enhanced to about 70% (according to Palumbo–Aust criterion) which mainly were Σ3n (n = 1, 2, 3…) types by small amount of deformation and recrystallization annealing. All the resulting microstructures were constituted of large size grain-cluster, in which all the orientation relationships between any two grains (no matter adjacent or not) could be described by Σ3n misorientations according to twin chain analyzing. Twin relationships up to 8th generation (Σ38) were found in one of such clusters. The outer boundaries of grain-clusters were crystallographically random with the adjacent clusters. In the case of high proportion of low ΣCSL boundaries, the connectivity of random boundary network was not fragmented obviously when the Palumbo–Aust criterion was used, whereas substantially interrupted when the Brandon criterion was applied.

Abstract: To improve intergranular corrosion resistance of 304 stainless steel, a novel method, laser surface remelting combined with annealing treatment was adopted, which resulted in a high population of low  CSL boundaries, especially, twin boundaries (3) on the surface of the processed specimens. The grain boundary character distribution and effect of laser processing parameters on it were investigated. The experimental results showed that the maximum frequency of the low  CSL boundaries could attain 88.6% under the optimal processing conditions. The high fraction of the low  CSL boundaries led to a high corrosion resistance to intergranular corrosion.

Abstract: In this work, two heats of 9Cr ferritic/martensitic heat resistant steels with different carbon and nitrogen contents were prepared. The steels were designed to have much lower carbon content than conventional 9-12Cr heat resistant steels for obtaining dense nano-sized MX precipitates. Microstructure of the two steels in different heat treatment states was analyzed by electron backscatter diffraction (EBSD) method. The results show that grain boundary character is greatly affected by carbon and nitrogen contents. Martensite in the steel with 0.02wt.% carbon and ultra low nitrogen is easier to recrystallize than that in the steel with ultra low carbon and 0.03wt.% nitrogen during tempering treatment. The effect of grain boundary character on stress rupture properties is also discussed.

Abstract: Ga doped ZnO (GZO) films were prepared by radio frequency (rf) magnetron sputtering on glass or silicon substrates. Electrical, optical, and structural properties of these films were analyzed in order to investigate their dependence on thermal annealing temperature. GZO films with a minimum resistivity of 5.2×10-3 Ω-cm annealed at 400°C and a transparency above 80% in visible region were observed. The temperature-dependent conductivity affected the carrier transport and was related to the localization of carriers. The results of transmission spectra were consistent with the results of atomic force microscopy (AFM) scan. X-ray diffraction analysis and electron spectroscopy for chemical analysis were also used to investigate the properties of GZO films.