Selective growth of tin whiskers from its alloys on Ti_(2)SnC

The spontaneous growth of metal whiskers has been investigated for more than 70 years.However,there is still no agreement on its growth mechanism,and moreover,new characteristics of this whiskering phenomenon continue to emerge.In this study,Ti_(2)SnC is found to be capable of extracting Sn out of its alloys(Sn Bi,Sn Ag)by selectively growing Sn whiskers,and the Sn whiskers share the features of the traditional whiskers on platings and solders.Replacing the Ti_(2)SnC substrate with Ti C or Si C,under the same conditions,however,the selective growth of Sn whisker does not happen,which means Ti_(2)SnC plays a critical role in it.Based on the unique crystal structure of Ti_(2)SnC,active Sn atoms diffusing through the basal planes of Ti_(2)SnC is proposed to explain the selectivity.The driving force is suggested to be the high interfacial energy between Ti_(2)SnC and tin.This study is of importance to further understand the growth mechanism of metallic whiskers,and it may be also possible to be harnessed to develop paradigm-shifting technologies of metal purification and metallic whisker/nanowire preparation.

Tin whiskers prefer to grow from the [001] grains in a tin coating on aluminum substrate

This work aims at understanding the features of the Sn grains from which whiskers prefe rentially grow.The growth behavior of Sn whiskers on a 50 μm thick hypereutectic Sn-Al alloy coating was observed in situ by mapping the grain orientations before and after aging using the electron backscatter diffraction(EBSD) technique.Sn whiskers were found to grow preferentially from the(001) or near-(001) grains surrounded by the grains having perpendicular orientations,such as(100),(110) and(210).The compre s sive stress in the coating was heterogeneous,and the(001) grains exhibited the higher compressive stress close to the grain boundaries.The orientation relationship between α-Al phase and β-Sn phase was confirmed as(200)_(α-A)||(200)_(β-Sn,[011]_(α-A)||[001]_(β-Sn).The plane matching resulted in approximately0.7 % misfit strain in β-Sn,which had little impact on the growth of whiskers.Dislocations pile-ups were found in the(001) grains and repulsed by the Sn oxide layer,giving the probability of cracking the oxide.Grain boundaries were found between the whisker and underneath grain.The dominant diffusion mode for early whisker growth was grain boundary diffusion aided by pipe diffusion.

Tin whisker growth from titanium-tin intermetallic and the mechanism

Spontaneous growth of metal whiskers, represented by tin whiskers, has haunted tin-based platings and solder joints for decades and caused huge losses to the electronics industry. Despite numerous efforts, the underlying growth mechanism has been resisting interpretation, and the whiskering phenomenon even continues to expand its territory. Here, we report the growth of tin whiskers from a Ti6Sn5intermetallic.These tin whiskers share similar characteristics with those found on the platings or solder joints, but grow more and faster, with finer diameters. After tin whisker growth, Ti6Sn5retains its crystal structure,implying a dealloying process. Combining experimental and first-principles calculation results, we analyzed the growth mechanism of tin whiskers in detail, and proposed a diffusion-based growth model.The strain energy stored in Ti6Sn5during deformation provides a driving force for whisker growth, and the short-circuit diffusion paths generated by such deformation accelerate whisker growth. These findings identify the critical role of intermetallic substrate in the whiskering phenomenon, shedding new light for comprehensively understanding the whisker growth mechanisms. Furthermore, the plenty and rapid growth of tin whiskers also means a new method for the preparation of one-dimensional metallic materials.