Decrement trend in mechanical performances and characteristic behavior of calcium saturated Bi-2212 Ceramics

Abstract

This study focuses on the precise changes in basic mechanical design performance parameters (Vickers microindentation hardness, elastic modulus mechanical yield strength, fracture toughness, brittleness index, ductility, and elastic hardness coefficients) and mechanical characteristic features (typical indentation size effect or unconventional reverse indentation size effect). The investigation is carried out on Bi2.1Sr2.0Ca1.1Cu2.0Oy (Bi-2212) ceramic compounds with varying calcium impurity additions in the range of 0 ≤ x ≤ 0.1. The materials are prepared through standard solid-state reaction methods. Experimental measurements are conducted using Vickers microindentation hardness testing with load intervals ranging from 0.245 N to 2.940 N. The results recorded show that the calcium impurity adversely affects the basic mechanical design performance parameters due to the increase in the permanent crystal defects and unrecoverable stress regions. Namely, the calcium ions lead to the reduction of the resistance against crack propagation, mechanical strength/durability, hardness, critic stress points, hardness, and resistivity towards to the applied force. Therefore, the increase in the calcium addition amount promotes rapid propagation of cracks and related defects, reaching terminal velocity for critical crack size at relatively lower test loads. As a result, the pure ceramic exhibits the highest mechanical performance features due to its least response and sensitivity to the applied test load while the Bi-2212 material produced with the maximum calcium oxide impurity level demonstrates the lowest performance characteristics under applied test forces. Additionally, all the ceramic materials produced exhibit standard indentation size effect (ISE) behavior due to the predominant character of recovery mechanisms over the compounds. However, the increase in Ca impurity amount disrupts the typical ISE property of the Bi-2212 ceramic system.