Nano-grained (NG) commercially pure (CP, grade 2) Ti with average grain size of 80 nm was produced by the combination of asymmetric and symmetric rolling at room temperature. The effects of annealing on mechanical properties and microstructure of this NG Ti were investigated systematically. Examination using transmission electron microscopy (TEM) revealed that the annealed Ti samples possessed ultrafine-grained (UFG) structure in which grain size was below 200 nm even though annealed at 400 °C for 30 min, which suggested considerable thermal stability of the microstructure. X-ray diffraction (XRD) results showed that the preferred orientations along the (0 0 0 2) and (1 0  1 ¯  3) crystal plane were formed in the NG Ti and both the two preferred orientation were slightly decreased with the increase of annealing temperature. It was found that annealing of this NG Ti with appropriate temperature and time resulted in the abnormal effect that the microhardness, strength and ductility were simultaneously enhanced as compared to the as-processed state. Further increasing of the annealing temperature and time leads to the decrease of microhardness and strength. Strain rate jump tests revealed that the strain-rate sensitivity (SRS) parameter m of the NG Ti was slightly enhanced with the increase of annealing temperature. The mechanisms of variations in mechanical properties were analyzed based on microstructure evolution of the annealed NG Ti.

Effects of annealing on microstructure and mechanical properties of nano-grained titanium produced by combination of asymmetric and symmetric rolling

Identifying cost-effective parking for an autonomous vehicle, including: identifying, by a vehicle parking module, a plurality of available parking spots for parking the autonomous vehicle; determining, by the vehicle parking module, a total cost associated with each of the plurality of available parking spots for parking the autonomous vehicle; and selecting, by the vehicle parking module, a target parking spot in dependence upon the total cost associated with each of the plurality of available parking spots for parking the autonomous vehicle.

Identifying cost-effective parking for an autonomous vehicle

Combined strengthening from nanotwins and nanoprecipitates in an iron-based superalloy

Nanocrystallization and enhanced surface mechanical properties of commercial pure titanium by electropulsing-assisted ultrasonic surface rolling

The technology of high-density electropulsing has been applied to increase the performance of metallic materials since the 1990s and has shown significant advantages over traditional heat treatment in many aspects. However, the microstructure changes in electropulsing treatment (EPT) metals and alloys have not been fully explored, and the effects vary significantly on different material. When high-density electrical pulses are applied to metals and alloys, the input of electric energy and thermal energy generally leads to structural rearrangements, such as dynamic recrystallization, dislocation movements and grain refinement. The enhanced mechanical properties of the metals and alloys after high-density electropulsing treatment are reflected by the significant improvement of elongation. As a result, this technology holds great promise in improving the deformation limit and repairing cracks and defects in the plastic processing of metals. This review summarizes the effect of high-density electropulsing treatment on microstructural properties and, thus, the enhancement in mechanical strength, hardness and corrosion performance of metallic materials. It is noteworthy that the change of some properties can be related to the structure state before EPT (quenched, annealed, deformed or others). The mechanisms for the microstructural evolution, grain refinement and formation of oriented microstructures of different metals and alloys are presented. Future research trends of high-density electrical pulse technology for specific metals and alloys are highlighted.

Application of High-Density Electropulsing to Improve the Performance of Metallic Materials: Mechanisms, Microstructure and Properties.

Given the infinite diversity of microstructural inhomogeneity, the variation in spatial distribution of local strain could be infinite. However, this study finds that the statistical distribution of local strain universally follows a lognormal distribution irrespective of phase content and deformation mechanism. Moreover, this universal law is proved conditional upon the macroscopic homogeneity of deformation on the statistical window scale, equivalent to the equality between the macrostrain calculated from the displacements at the window corners and the average of the local strain. The discovery of a lognormal distribution law suggests the existence of a minimum statistical representative window (MSRW) size that is characteristic for each material. Explorations on the dependence of MSRW size on the microstructure, deformation mechanism, and strain magnitude are expected to add new dimensions to understanding of the relationship between microstructure and mechanical properties.

Lognormal Distribution of Local Strain: A Universal Law of Plastic Deformation in Material.

Two magnesium alloys AZ31 and ZEK100 were subjected to cold rolling followed by electropulse treatment (EPT) for different durations in order to investigate the microstructure and texture evolution during EPT. AZ31 started to recrystallize once the electropulse current was applied. ZEK100, in contrast, exhibited two-stage recrystallization before which an evident recovery process occurred. Texture modification was achieved in both alloys after recrystallization, with AZ31 exhibiting a weak RD-split texture and ZEK100 a TD-spread one. The results were discussed with particular emphasis on the distinct impact of electropulse current on the recrystallization texture formation. It is proposed that the promotion of the nucleation of non-basal-oriented grains, the change of the relative mobility of grain boundaries, and the non-basal dislocation activity in the continuous recrystallization are responsible for the texture modification.

Microstructure and Texture Evolution of Magnesium Alloys During Electropulse Treatment

Rapid hardening induced by electric pulse annealing in nanostructured pure aluminum

An energy absorber according to various embodiments can include a structure having a predetermined cross-sectional profile. A hollow profile is formed within the structure. The pre-determined cross-sectional profile of the structure is configured based on a deceleration-time profile that includes a first period and a second period. The first period is defined by a substantially sharp and linear increase in magnitude of the deceleration of an impact until a maximum deceleration value is achieved. The second period is defined by a rapid decrease in the magnitude of the deceleration.

Jeff Wang

Papers

Lognormal Distribution of Local Strain: A Universal Law of Plastic Deformation in Material.

Microstructure and Texture Evolution of Magnesium Alloys During Electropulse Treatment

Rapid hardening induced by electric pulse annealing in nanostructured pure aluminum

Tunable Energy Absorbers

Effect of Prior Austenite Grain Size on Impact Toughness of Press Hardened Steel