Hydrogen pick-up leading to hydride formation is often observed in commercially pure Ti (CP-Ti) and Ti-based alloys prepared for microscopic observation by conventional methods, such as electro-polishing and room temperature focused ion beam (FIB) milling. Here, we demonstrate that cryogenic FIB milling can effectively prevent undesired hydrogen pick-up. Specimens of CP-Ti and a Ti dual-phase alloy (Ti-6Al-2Sn-4Zr-6Mo, Ti6246, in wt.%) were prepared using a xenon-plasma FIB microscope equipped with a cryogenic stage reaching −135 °C. Transmission electron microscopy (TEM), selected area electron diffraction, and scanning TEM indicated no hydride formation in cryo-milled CP-Ti lamellae. Atom probe tomography further demonstrated that cryo-FIB significantly reduces hydrogen levels within the Ti6246 matrix compared with conventional methods. Supported by molecular dynamics simulations, we show that significantly lowering the thermal activation for H diffusion inhibits undesired environmental hydrogen pick-up during preparation and prevents pre-charged hydrogen from diffusing out of the sample, allowing for hydrogen embrittlement mechanisms of Ti-based alloys to be investigated at the nanoscale.
Sn and Sn solder alloys in microelectronics are the most susceptible to suffer from electrochemical migration (ECM) which significantly compromises the reliability of electronics. This topic has attracted more and more attention from researchers since the miniaturization of electronics and the explosive increase in their usage have largely increased the risk of ECM. This article first presents an introductory overview of the ECM basic processes including electrolyte layer formation, dissolution of metal, ion transport and deposition of metal ions. Then, the article provides the major development in the field of ECM of Sn and Sn solder alloys in recent decades, including the recent advances and discoveries, current debates and significant gaps. The reactions at the anode and cathode, the mechanisms of precipitates formation and dendrites growth are summarized. The influencing factors including alloy elements (Pb, Ag, Cu, Zn, etc.), contaminants (chlorides, sulfates, flux residues, etc.) and electric field (bias voltage and spacing) on the ECM of Sn and Sn alloys are highlighted. In addition, the possible strategies such as alloy elements, inhibitor and pulsed or AC voltage for the inhibition of the ECM of Sn and Sn solder alloys have also been reviewed.
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