Influence of impact energy on work hardening ability of austenitic manganese steel and its mechanism

To further understand the hardening mechanism of austenitic manganese steel under actual working conditions, the work hardening ability was studied and the microstructures of austenitic manganese steel were observed under different impact energies. The work hardening mechanism was also analyzed. The results show that the best strain hardening effect could be received only when the impact energy reaches or exceeds the critical impact energy. The microstructural observations reveal that dislocations, stacking faults and twins increase with raising impact energy of the tested specimens. The hardening mechanism changes at different hardening degrees. It is mainly dislocation and slip hardening below the critical impact energy, but it changes to the twinning hardening mechanism when the impact energy is above the critical impact energy

Functions and mechanism of modification elements in eutectic solidification of Al-Si alloys: A brief review

Being used more and more widely in engineering, Al-Si alloys comprise about 80% of all kinds of aluminum alloys, which are the most widely utilized nonferrous alloys. Although most Al-Si alloys consist of multiple components, the eutectics in the structure accounts for 50%-90% of the sum volume of such alloys. Therefore, understanding the modification mechanism and function rules of the Al-Si eutectic solidification is the technical key in controlling the structures and properties of such casting alloys. The present paper chiefly reviews recent investigation developments and important conclusions along the lines of the functions of modification elements and their modification mechanism in the eutectic solidification of Al-Si alloys

The Tribological Behaviors in Zr-Based Bulk Metallic Glass with High Heterogeneous Microstructure

Microstructural inhomogeneity of bulk metallic glasses (BMGs) plays a significant role in their mechanical properties. However, there is hardly ant research concerning the influence of heterogeneous microstructures on tribological behaviors. Hence, in this research, the tribological behaviors of different microstructural-heterogeneity BMGs sliding in-air were systematically investigated, and the corresponding wear mechanisms were disclosed via analyzing the chemical composition and morphology of the wear track. Higher microstructural-heterogeneity BMGs can possess a better wear resistance both under dry sliding and a 3.5% NaCl solution. The results suggest that microstructural heterogeneity enhancement is a valid strategy to improve the tribological performance of BMGs

On Glass Forming Ability of Bulk Metallic Glasses by Relating the Internal Friction Peak Value

The internal friction (IF) behaviors of a series of LaCe-, Zr-, and La-based bulk metallic glasses (BMGs) were studied by a computer-controlled, conventional inverted torsion pendulum. The results indicate that with an increasing temperature, the IF also increases gradually in the supercooled liquid region, followed by a decrease caused by crystallization. BMGs with a good glass forming ability (GFA) usually possess a high IF peak value for an alloy system with the same constituent elements. Furthermore, the magnitude of the IF value (Qi−1) of the inflection point is an efficient criterion of GFA. The Qi−1 value is a valid criterion under the conditions of identical constituent elements and different element contents. However, Qi−1 and GFA have no relationship among different alloy systems

Enhancing thermoelectric performance of Cu-modified Bi0.5Sb1.5Te3 by electroless plating and annealing

With the capacity of energy conversion from heat to electricity directly, thermoelectric materials have been considered as an alternative solution to global energy crisis. In this work, Cu modified BiSbTe (BST) composites are prepared by a facile electroless plating Cu method, spark plasma sintering, and annealing. The annealed 0.22wt.%Cu/BST has an enhanced peak Figure of Merit (zT) of ~ 0.71 at 573 K with high average zT of 0.65 in the wide temperature range between 300 and 573 K. Due to the significant increase of electrical conductivity and low lattice thermal conductivity, the annealed 0.22wt.%Cu/BST shifts peak zT to high temperature, and shows 492% enhancement than that of pristine BST with zT of 0.12 at 573 K. Through detailed structural characterization of the annealed 0.22wt.%Cu/BST, we found that Cu can dope into BST matrix and further form CuTe nanoprecipitates, dislocations, and massive grain boundaries, leading to a low lattice thermal conductivity of 0.30 Wm K in the annealed 0.22wt.%Cu/BST. Such enhanced peak zT in high-temperature and high average zT in the wide temperature range shows that the electroless plating Cu method and annealing can improve the thermoelectric performance of commercial BST and expand the applicability of BiTe thermoelectric materials in the power generations

Ag-Segregation to Dislocations in PbTe-Based Thermoelectric Materials

Dislocations have been considered to be an efficient source for scattering midfrequency phonons, contributing to the enhancement of thermoelectric performance. The structure of dislocations can be resolved by electron microscopy whereas their chemical composition and decoration state are scarcely known. Here, we correlate transmission Kikuchi diffraction and (scanning) transmission electron microscopy in conjunction with atom probe tomography to investigate the local structure and chemical composition of dislocations in a thermoelectric Ag-doped PbTe compound. Our investigations indicate that Ag atoms segregate to dislocations with a 10-fold excess of Ag compared with its average concentration in the matrix. Yet the Ag concentration along the dislocation line is not constant but fluctuates from ∼0.8 to ∼10 atom % with a period of about 5 nm. Thermal conductivity is evaluated applying laser flash analysis, and is correlated with theoretical calculations based on the Debye–Callaway model, demonstrating that these Ag-decorated dislocations yield stronger phonon scatterings. These findings reduce the knowledge gap regarding the composition of dislocations needed for theoretical calculations of phonon scattering and pave the way for extending the concept of defect engineering to thermoelectric materials