The structure and nanomechanical properties of amorphous welds made at reduced temperature

Abstract

Presently, elements made of Fe-based amorphous materials are characterised by small dimensions. The use of the laser welding process will make it possible to increase diameters of parts along with the enhanced applicability of modern materials. To obtain exceptional post-weld properties of a given material, its structure in the heat affected zone (HAZ), the fusion zone (FZ) and in the parent material (PM) should be controlled.An important issue accompanying the welding of bulk metallic glasses (BMGs) is chemical composition of the amorphous phase. The crystallisation process is the most common phenomenon occurring in the HAZ during the welding of iron-based amorphous materials. The essence of the solution to the crystallisation issue consists in the use of laser welding as well as in the application of a cooling system enabling the reduction of temperature. The article presents the crystallisation process and a new solution to the problem.The primary objective of this research work involved the laser welding of specimens at a reduced (sub-zero) temperature and the presentation of the structure and nanomechanical properties of amorphous welds.Because of the metastable nature of welded BMGs and due to the small dimensions of the FZ, a high-resolution transmission electron microscope and a triboindenter equipped with a microscopic attachment were used in structural and properties-related tests. A decrease in temperature of the material subjected to welding was obtained using a specifically designed cooling system based on Peltier modules.The examination of the weld nanostructure revealed that the laser welding of the amorphous material cooled to a temperature of −17 °C enabled the joining of elements without the occurrence of crystalline precipitation. Detailed research revealed the presence of the amorphous phase in the PM, FZ and HAZ.