The Impact of Cooling Rate on the Tensile and Cyclic Stress-Strain Characteristics of Different Solder Alloys at Nanoscale

TL;DR

This study investigates how different cooling rates affect the mechanical and cyclic stress-strain properties of various lead-free solder alloys at the nanoscale using molecular dynamics simulations.

Contribution

It extends previous work by comparing multiple solder alloys and cooling scenarios, revealing how cooling rate influences their nanoscale mechanical behavior.

Findings

Slower cooling rates lead to higher ultimate strength and Young's modulus.

Higher cooling rates increase the modulus of toughness, indicating better impact resistance.

Energy dissipation stabilizes after several cyclic loading cycles.

Abstract

In recent years, lead-free solder alloys based on tin, silver, or copper have gained popularity over lead-based solder alloys due to their improved mechanical and electrical properties and their non-toxic nature. In our previous studies, we examined the stress-strain behavior of SAC305 under varying cooling rates. This study extends our investigation to various lead-free solder materials, including Sn, Sn-Ag, and SAC305, to compare their relative mechanical and cyclic properties. We employed molecular dynamics to model the atomistic behavior. Initially, the models were melted at a constant rate and then cooled at various rates, including 2.5 K/ps, 10 K/ps, 50 K/ps, and 100 K/ps. Additionally, exponential cooling was used to replicate real-world cooling scenarios.. We utilized a set of modified embedded atomic model (MEAM) interatomic potentials for the tensile test and cyclic loading. The tensile test has been conducted until fracture occurs at a constant strain rate. Furthermore, we investigated the cyclic loading behavior within a strain range of -10% to 10% for 10 cycles. The results indicated that cooling rates significantly influenced mechanical properties, with slower rates (2.5 K/ps and 10 K/ps) showing substantial differences, while the differences between higher rates (50 K/ps and 100 K/ps) were less pronounced. The ultimate strength, Young's modulus, modulus of resilience, and coefficient of thermal expansion exhibited a negative correlation with increasing cooling rates, while the modulus of toughness increased, indicating improved impact resistance. To assess energy dissipation during cyclic loading, we examined the hysteresis loop area and stress amplitude. After a certain number of cycles, the energy lost during each cycle reached a stable level.