Journal Article

The influence of boron microalloying on the microstructural and mechanical properties of Ni-Mn-Sn-Gd shape memory alloy

Xu, Yangrui, Chu, Zhenhua, Feng, Yan, Gao, Li, Xin, Xiangyang, Guo, Xin, Hu, Shaohui

2024

Overview

This study systematically investigates the microstructure, martensitic phase transformation, crystal structure, and mechanical properties of (Ni 43 Mn 47 Sn 9 Gd 1 ) 100−x B x (x = 0, 0.8, 1.5 and 3 at%) shape memory alloys. Experimental results reveal that these alloys consist of a matrix phase and precipitated phases. The introduction of Gd elements leads to the formation of milky-white particles dispersed along grain boundaries, with the composition identified as GdNiSn. When the B element content reaches 1.5 at%, bright-white particles form and are uniformly distributed within the matrix. Their concentration increases with higher levels of B doping, and they are characterized as Mn 2 B. Simultaneously, the initially present Gd-rich milky-white particles distributed along grain boundaries, exhibit a diminishing trend with increasing B doping. B doping elevates the alloy’s phase transition temperature, and the compressive strength of the alloy approximately follows a linear trend with increasing B content. At a B doping level of 3%, the annealed alloy demonstrates a compressive strength of up to 1313 MPa with a compressive fracture strain of 11.6%, marking a 110% improvement. For the as-cast alloy, a compressive strength of 1652 MPa is achieved, accompanied by a compressive fracture strain of 12.3%, representing a 130% enhancement. Transmission electron microscopy reveals pronounced twinning features on the alloy surface, resulting in the formation of numerous fine lines in the as-cast state, that are magnified into voids after heat treatment. This phenomenon is detrimental to the alloy’s mechanical performance; hence, the as-cast compressive strength is favored over the annealed state.

• Publisher: Springer Berlin Heidelberg,Springer Nature B.V
• Subject: Alloys / Casting alloys / Characterization and Evaluation of Materials / Compressive properties / Compressive strength / Condensed Matter Physics / Crystal structure / Doping / Gadolinium / Grain boundaries / Heat treatment / Machines / Manufacturing / Martensitic transformations / Mechanical properties / Microstructure / Nanotechnology / Nickel / Optical and Electronic Materials / Phase transitions / Physics / Physics and Astronomy / Processes / Shape memory alloys / Surfaces and Interfaces / Temperature / Thin Films / Transition temperature