Fracture behaviors of commercially pure titanium under biaxial tension:Experiment and modeling

The fracture behaviors and associated mechanisms of metallic materials under biaxial stress are vital for their manufacturability and service performance.In this work,the fracture behaviors of commercially pure titanium(CP-Ti)under quasi-uniaxial and equi-biaxial tension were investigated by using the digital image correlation technique and finite element modeling.The fracture behaviors under quasi-uniaxial tension were characterized by a general normal fracture.In contrast,normal fracture firstly occurred per-pendicular to the rolling direction(RD)under equi-biaxial tension,followed by secondary shear fracture along the 45°direction relative to the RD.The normal fracture was attributed to the lower strain hard-ening ability in RD compared to the transverse direction(TD)induced by the TD-split type basal texture.The different hardening abilities introduced large shear stress in the 45°direction,which contributed sig-nificantly to the secondary shear fracture.An anisotropy parameter K(△S_(s)/σ_(s)),defined as the ratio of the equivalent effective traction stress to the yield strength,was proposed for the first time,to predict the fracture path with the impact of crystallographic preferred orientation.

Enhancement of strength and electrical conductivity for a dilute Al-Sc-Zr alloy via heat treatments and cold drawing

Developing heat-resistant conductors with high strength and high electrical conductivity is a key issue in the electrical conductor industries, as the ever-increasing power transmission poses higher requirement on the thermal stability of electrical conductor wires. Dilute Al-Sc-Zr alloys are considered as promising candidates due to the excellent heat resistance and high electrical conductivity, but the low strength always limits their application on electrical wires. Yet, few efforts on process design have been made in dilute Al-Sc-Zr alloys to enhance the strength. Here, various kinds of processing paths via combination of cold drawing, ageing and/or annealing were conducted to improve the strength and electrical conductivity of a dilute Al-Sc-Zr alloy. Results show that enhanced strength and electrical conductivity were obtained after cold drawing + ageing or pre-ageing + cold drawing + annealing treatments processes.Optimal properties(194 MPa in ultimate tensile strength and 61% IACS in electrical conductivity) were obtained through cold drawing followed by ageing. Microstructure evolution which affects strength and electrical conductivity was systematically investigated using TEM and 3 DAP. The enhanced strength was mainly attributed to the suitable interactions between strain strengthening and precipitation strengthening. The enhancement in electrical conductivity was caused by precipitation of solute atoms and recovery of defects. These results provide foundations for the processing design of Al-Sc-Zr conducting wires with good properties and push forward their potential application in heat resistant conductor industries.

Correlation between precipitates evolution and mechanical properties of Al-Sc-Zr alloy with Er additions

Correlation between precipitates evolution and mechanical properties of Al-Sc-Zr alloy with Er additions during isothermal ageing were investigated by microhardness measurements,transmission electron microscopy,atom probe tomography and density functional theory-based simulations.The results demonstrate that the Er additions significantly improve the hardness during elevated temperature ageing,especially at 400℃.This is mainly because Er additions increase the nucleation rate of the Al_(3)(Er,Sc,Zr)precipitates,resulting in a higher density of fine and uniform dispersion of L1_(2)structured nanoparticles.First-principles calculations demonstrate that the second nearest neighboring solute-solute interactions for the species Sc,Zr and Er are energetically favored–a key feature to rationalize the observed precipitate structure and the underlying formation mechanism.The sequential formation of the core/shell precipitates in the Er-free alloy and core/double-shell precipitates in the Er-containing alloy arises due to the different solute-solute and solute-vacancy interaction energies,and the relative diffusivities of the Er,Sc and Zr species in Al.These results shed light on the beneficial effects of Er additions on the agehardening behavior of Al-Sc-Zr alloy and provide guidance for designing the ageing treatments for the Al-Sc-Zr(-Er)alloys.