Molecular Dynamics Simulation of Heat Transfer at Contact Interface of Hot Forming Die

Baoshan Lu,Xiang Ma,Leigang Wang

doi:10.1088/1757-899x/627/1/012024

Abstract

During metal hot forming process, the billet and the die interact by contact under high temperature, high pressure and severe sliding. In this paper, an atomistic approach is utilized to study the behaviour of heat transfer at the contact interface of hot forming die and the material. Based on non-equilibrium molecular dynamics and phonon scattering theory, the phonon heat transfer process at the billet/die rough interface at nano-scale is analysed. The effects of interfacial lattice defect concentration and average interfacial temperature on the phonon heat transfer coefficient are examined. It is found that when the lattice defect concentration increases the phonon mismatch at the interface deteriorates and the interfacial thermal resistance increases, which leads to a sharp decrease in phonon heat transfer coefficient. A higher temperature of the contact body and a higher average interface temperature lead to a higher probability of inelastic scattering of phonons at the interface. Moreover, the high frequency phonons at high temperature might be decomposed into two or more low frequency phonons during the energy transmission, which increases the propagation of phonon at the interface; thus the phonon heat transfer coefficient increases accordingly.

Highlights

The influence of incompletely contacted interface on heat transfer is an important topic in the field of micro-scale heat transfer
It is found that when the lattice defect concentration increases the phonon mismatch at the interface deteriorates and the interfacial thermal resistance increases, which leads to a sharp decrease in phonon heat transfer coefficient
There are two main reasons for this: (1) there is a lack of potential functions to precisely describe the atomic interactions of alloyed materials or dissimilar interfaces; (2) the Molecular dynamics (MD) method mainly studies the heat conduction problem caused by phonons, while the heat conduction in solid metal is dominated by free electrons where the phonon heat conduction only accounts for a small proportion of the global thermal conductivity [1]

Summary

Introduction

The influence of incompletely contacted interface on heat transfer is an important topic in the field of micro-scale heat transfer. It is generally believed that this small proportion of phonon thermal conductivity do not reflect the overall characteristics of solid metal interfacial heat transfer. These have become the bottleneck restricting the application of MD to the study of solid metal interfacial heat transfer. These non-metallic inclusions greatly inhibit the free electron conduction, while the phonon heat conduction is significantly enhanced and rapidly becomes the dominant factor in heat transfer. This paper will use a non-equilibrium Molecular Dynamics method (NEMD, [3]) to examine the phonon heat transfer behaviour in an asymmetric billet/die interfacial model. The effects of the interfacial lattice defect and the average interfacial temperature will be studied

F-S potential function and the NEMD model

MD simulation results and discussions

Findings

Conclusions