Grain growth would occur at a high temperature in polycrystalline materials. The GB of polycrystals is in a high-energy state, and the temperature gradient could cause an energy imbalance between the grains, which is the driving force for GB migration [
15,
16]. Small grains would merge into large grains at high temperature gradient to reduce the total area of high-energy GBs [
17]. Xu et al
. [
18] reported the growth of meter-scale two-dimensional single-crystal Cu (111) by slowly passing the industrial polycrystalline Cu through a hot zone (1303 K). In selective laser melting, a directional heat flow gradient is formed in the laser molten pool, which makes the liquid alloy in the molten pool prone to directional solidification and formation of epitaxially grown coarse columnar crystals, such as titanium alloy β-columnar crystals [
19], nickel-based alloy columnar crystals [
20], and iron-based alloy columnar crystals [
21]. These epitaxial columnar crystals can reach the centimeter level. Li et al
. [
22] used electron beam selective melting (EBSM) to produce nickel-based superalloy single crystals. Helmer et al. [
23] proposed that the large single crystals in EBSM may be controllable by a suitable temperature gradient [
24]. These studies showed that small grains could be recrystallized into larger grains by employing high temperature gradient, and the selection of appropriate temperature gradient is the key to realizing grain amplification. However, the devices used in the above process are complex and expensive for a quick large-area high-thermal-gradient treatment of polycrystalline tin surface in the atmosphere. Compared with the above process, inductively coupled plasma (ICP) has a simple structure, low environmental requirements, and stable large-area treatment, making it an ideal large-thermal-gradient source [
25]. Moreover, compared with the carbon dioxide laser and oxyhydrogen flame heating methods widely used at present, ICP require neither surface pretreatment to increase laser absorption nor combustible gas combustion. Argon (Ar) for excitation is cheap and safe [
26,
27]. Therefore, ICP is expected to serve as an effective medium for increasing the grain size of polycrystalline tin.