By realizing in thin films a tensile stress state, superconductivity of 13 K was introduced into FeTe, a nonsuperconducting parent compound of the iron pnictides and chalcogenides, with a transition temperature higher than that of its superconducting isostructural counterpart FeSe. For these tensile stressed films, superconductivity is accompanied by a softening of the first-order magnetic and structural phase transition, and also, the in-plane extension and out-of-plane contraction are universal in all FeTe films independent of the sign of the lattice mismatch, either positive or negative. Moreover, the correlations were found to exist between the transition temperatures and the tetrahedra bond angles in these thin films.

No abstract

Friction stir spot welding (FSSW) is a very useful variant of the conventional friction stir welding (FSW), which shows great potential to be a replacement of single-point joining processes like resistance spot welding and riveting. There have been many reports and some industrial applications about FSSW. Based on the open literatures, the process features and variants, macro- and microstructural characteristics, and mechanical properties of the resultant joints and numerical simulations of the FSSW process were summarized. In addition, some applications of FSSW in aerospace, aviation, and automobile industries were also reviewed. Finally, the current problems and issues that existed in FSSW were indicated.

No abstract

Effect of tool rotational speed on the microstructure and mechanical properties of bobbin tool friction stir welding of Al-Li alloy, (2015), AbstractA third-generation Al-Li alloy AA2198 has been successfully welded by bobbin tool friction stir welding. The stirred zone, displaying an hourglass shape, consists of recrystallized Al grains and precipitates remaining in solution. Joint line remnants have been found in all etched welds. Symmetrical hardness profiles have been obtained in the thickness direction, which indicates that the joints have homogenous through-thickness mechanical properties. As the rotational speed increases, the grain size of the stirred zone increases, whereas the density of strengthening particles decreases; the joint line remnants become compressed remarkably in the shoulder-dominated zone while less changes occur in the probe-dominated zone; the softest region shrinks and shifts outward, the average hardness of the stirred zone increases and the hardness profile along the cross section of the joint changes from the U-shaped to W-shaped. The tensile strength of the joint initially increases with rotational speed and then decreases with the maximal strength efficiency reaching 80%; three fracture modes have been observed and cracking initiates at the joint line remnant propagating towards the heat-affected zone, and finally to the border between the thermal-mechanically affected zone and stirred zone.