Heat Treatment Effects on Pristine and Cold-Worked Thin-Walled Inconel 625

Thin-walled Inconel 625 sheet metal was sectioned into tensile specimens, plastically strained, and then heat treated. Specimens were pulled to a targeted strain, unloaded, and then subjected to one of two heat treatments with the goal of restoring the full ductility and total plastic strain capability of the material. Post-heat treatment tensile testing was performed at room temperature to evaluate the heat treatment efficacy and then followed by hardness and microstructural analysis. The results showed the amount of material recovery was affected by the initial amount of plastic strain imparted to the tensile specimen before heat treatment. Although recrystallization was not observed, grains did elongate in the load direction, and the Kernel average misorientation (KAM) increased with heat treatment. Furthermore, specimens prestrained to 40% and heat treated at 980 °C successfully recovered 88% of pre-heat treatment strain capability prior to fracturing.

Study on Laser Surface Hardening Behavior of 42CrMo Press Brake Die

Laser surface hardening is a promising surface technology to enhance the properties of surfaces. This technology was used on the 42CrMo press brake die. Its hardening behavior was investigated by using scanning electron microscopy and electron backscattering diffraction. The results indicated that the martensite in the hardening zone was significantly finer than that in the substrate. There were many low-angle grain boundaries in the martensite of the hardening zone, and the kernel average misorientation and grain orientation spread in the hardening zone grains were obviously greater, which further improved the hardness of the hardening zone, especially near the substrate. The microstructure and the properties of the blade maintained excellent uniformity with treatment by single-pass laser surface hardening with a spot size of 2 mm, scanning speed of 1800 mm/min, and power of 2200 W. The hardness of the hardening zone was 1.6 times higher than that of the base material, and the thickness of the hardening zone reached 1.05 mm.

Methodology for the Identification of Nucleation Sites in Aluminum Alloy by Use of Misorientatation Mapping

The fabrication of semi-finished hot and cold rolled sheets includes a complex evolution of both microstructure and texture to meet the demanded mechanical properties and suitable formability characteristics. The desired mechanical properties along with the optimum grain size can be obtained through the control of both recovery and recrystallization processes. This work examines the effect of recovery and recrystallization on the resulting crystallographic texture and on the local plastic deformation. A processing approach for EBSD-KAM (Electron Back Scatter Diffraction—Kernel average misorientation) evaluation is suggested with the purpose of effectively evaluating all the possible misorientation angles in-between the grains and of observing the recovery phenomenon from a different point of view. The results showed that although texture components did not alternate significantly during recovery, the fraction of sub-grain boundaries was increased indicating the completion of recovery at the selected temperature exhibited a maximum value of 90%. The initiation of recrystallization was illustrated by a different aspect, underlying newly formed grains and points which exhibited high misorientation angle, critical for the evolution of the recrystallization process and texture evolution.

Evolution of Microstructure, Texture, and Mechanical Properties of As-Extruded ND/ZK60 Composite during Hot Compression Deformation

The effects of temperature, strain rate, and strain on the microstructure, texture, and mechanical properties of as-extruded nanodiamond reinforced ZK60 composite during hot compression was systematically studied. The results revealed that the precipitating MgZn2 and the nanodiamond (ND) particles distributed in the grain interiors hindered the motion of dislocations. The ND particles act as nucleation points and promote the dynamic recrystallization (DRX) of the composites during the hot compression deformation, the flow stress of ND/ZK60 increases with strain rate increases and temperature decreases. {101¯2} extension twins are nucleated and grown in the coarse grains as the compressive strain increasing. Meanwhile, the fine grains of DRX generate and present first an increasing then a decreasing trend. The result of Schmid factor and kernel average misorientation indicates that high-density dislocation caused by dislocation climbing and cross slip aggregated in composites with increasing strain. Therefore, the work hardening trend of the composite is strengthened.

A New Experimental Method for Determining the Thickness of Thin Surface Layers of Intensive Plastic Deformation Using Electron Backscatter Diffraction Data

It is, in general, essential to investigate correlations between the microstructure and properties of materials. Plastic deformation often localizes within thin layers. As a result, many material properties within such layers are very different from the properties in bulk. The present paper proposes a new method for determining the thickness of a thin surface layer of intensive plastic deformation in metallic materials. For various types of materials, such layers are often generated near frictional interfaces. The method is based on data obtained by Electron Backscatter Diffraction. The results obtained are compared with those obtained by an alternative method based on microhardness measurements. The new method allows for determining the layer thickness of several microns in specimens after grinding. In contrast, the measurement of microhardness does not reveal the presence of this layer. The grain-based and kernel-based types of algorithms are also adopted for determining the thickness of the layer. Data processed by the strain contouring and kernel average misorientation algorithms are given to illustrate this method. It is shown that these algorithms do not clearly detect the boundary between the layer of intensive plastic deformation and the bulk. As a result, these algorithms are unable to determine the thickness of the layer with high accuracy.

In-situ EBSD characterization of deformation behavior of primary alpha phase in Ti-6Al-4V

Uniaxial tension experiments and electron back-scatter diffraction were performed on a bimodal Ti-6Al-4V alloy to study the deformation behavior of primary hcp-Ti (αp). It was found that the obtained tensile strength and elongation of the studied Ti-6Al-4V from the in-situ tensile test are higher than of which derived from the regular tensile test. The strain could be accommodated by the activation of slip systems and by grain rotations during the deformation. The prismatic slip is the primary slip mode of αp. According to kernel average misorientation analysis, we found that the dislocations mainly distributed near grain boundaries and subgrain boundaries, and partially located around slip lines. Calculated rotation angles and average rotation rates show that the rotation heterogeneity occurred among grains and subgrains.

Denoising of crystal orientation maps

This paper compares several well known sliding-window methods for denoising crystal orientation data with variational methods adapted from mathematical image analysis. The variational methods turn out to be much more powerful in terms of preserving low-angle grain boundaries and filling holes of non-indexed orientations. The effect of denoising on the determination of the kernel average misorientation and the geometrically necessary dislocation density is also discussed. Synthetic as well as experimental data are considered for this comparison. The examples demonstrate that variational denoising techniques are capable of significantly improving the accuracy of properties derived from electron backscatter diffraction maps.

Effect of Annealing on Microstructure and Tensile Behavior of CoCrNi Medium Entropy Alloy Processed by High-Pressure Torsion

Annealing of severely plastic deformed materials is expected to produce a good combination of strength and ductility, which has been widely demonstrated in conventional materials. In the present study, high-pressure torsion processed CoCrNi medium entropy alloy consisting of a single face-centered cubic (FCC) phase with a grain size of ~50 nm was subjected to different annealing conditions, and its effect on microstructure and mechanical behavior was investigated. The annealing of high-pressure torsion processed CoCrNi alloy exhibits partial recrystallization and near full recrystallization based on the annealing temperature and time. The samples annealed at 700 °C for 2 min exhibit very fine grain size, a high fraction of low angle grain boundaries, and high kernel average misorientation value, indicating partially recrystallized microstructure. The samples annealed for a longer duration (>2 min) exhibit relatively larger grain size, a low fraction of low angle grain boundaries, and low kernel average misorientation value, indicating nearly full recrystallized microstructure. The annealed samples with different microstructures significantly influence the uniform elongation, tensile strength, and work hardening rate. The sample annealed at 700 °C for 15 min exhibits a remarkable combination of tensile strength (~1090 MPa) and strain to failure (~41%).

Annealing Behavior and Kinetics of Primary Recrystallization of Copper

The microstructure evolution during the annealing treatment of a recycled copper after cold rolling to total strain of 2.6 was investigated. The cold deformation resulted in the elongation of initial grains along rolling direction and the strain-induced formation of subboundaries. Annealing recovery occurred in the temperature range 100-250 °C. The recrystallized microstructures were observed after annealing at 300-400 °C. The hardness of partially recrystallized copper samples was interpreted in terms of dislocation strengthening. The recrystallization kinetics was estimated according to a Johnson–Mehl–Avrami–Kolmogorov equation using different methods for recrystallized fraction determination, i.e., the fractional softening, the grain orientation spread, and the Kernel average misorientation.

An Examination of the Composition and Microstructure of Coarse Intermetallic Particles in AA2099-T8, Including Li Detection

Electron and proton microprobes, along with electron backscatter diffraction (EBSD) analysis were used to study the microstructure of the contemporary Al–Cu–Li alloy AA2099-T8. In electron probe microanalysis, wavelength and energy dispersive X-ray spectrometry were used in parallel with soft X-ray emission spectroscopy (SXES) to characterize the microstructure of AA2099-T8. The electron microprobe was able to identify five unique compositions for constituent intermetallic (IM) particles containing combinations of Al, Cu, Fe, Mn, and Zn. A sixth IM type was found to be rich in Ti and B (suggesting TiB2), and a seventh IM type contained Si. EBSD patterns for the five constituent IM particles containing Al, Cu, Fe, Mn, and Zn indicated that they were isomorphous with four phases in the 2xxx series aluminium alloys including Al6(Fe, Mn), Al13(Fe, Mn)4 (two slightly different compositions), Al37Cu2Fe12 and Al7Cu2Fe. SXES revealed that Li was present in some constituent IM particles. Al SXES mapping revealed an Al-enriched (i.e., Cu, Li-depleted) zone in the grain boundary network. From the EBSD analysis, the kernel average misorientation map showed higher levels of localized misorientation in this region, suggesting greater deformation or stored energy. Proton-induced X-ray emission revealed banding of the TiB2 IM particles and Cu inter-band enrichment.