The Ideal Quenching Medium? – Characterisation of Ionic Liquids for Heat Treatment of Metallic Components

Abstract

Quenching as a part of heat treatment is an important process in the manufacturing chain of metallic components. One of the most common processes is immersion quenching in vaporising liquids. Unfortunately, this process is affected by the Leidenfrost-phenomenon. This effect can generate inhomogeneous quenching and thus asymmetrical residual stresses and avoidable distortion. In this work, ionic liquids have been investigated as new quenching media, which can be used as baths near room temperature. Aluminium cylinders have been quenched in baths of different ionic liquids with varying water contents and bath temperatures. The time-temperature curves have been recorded and the heat transfer coefficients were determined and compared to quenching in water. Addition of a few percents water to the ionic liquids increases the cooling rate significantly. Even at higher water contents, bubble boiling and convection are predominant and almost no Leidenfrost-effect occurs. This offers a huge potential to accelerate and homogenise immersion quenching.

Vapor pressure of ionic liquids at low temperatures from AC-chip-calorimetry

“…The boiling point of the quenching medium must be avoided because of the unfavorable Leidenfrost phenomenon. [40][41][42][43] Because of our reliable estimation of the boiling point for [EMIm][NTf 2 ], which exceeds twice the commonly acknowledged range of T b for typical ILs, the search for high temperature applications for common ILs can be extended significantly.…”

Stability studies of ionic liquid [EMIm][NTf2] under short-term thermal exposure

“…11 Thus, its application in a number of applications is investigated accompanied by fundamental research as well to understand its behaviour. 14 The heat treatment processes oen contain a quenching step yielding in a short term thermal stress for the liquid used. 12 Hydrogen production in aromatic and aliphatic ionic liquids was researched by Dhiman and LaVerne.…”

Room temperature ionic liquids in a heat treatment process for metals

“…It should be noted that 3.5% w/w of water was added to the IL in order to increase the cooling rate. 9 The rapid drop of the temperature within the rst seconds indicates a very good heat transfer. For water there is only a slight decrease of the temperature for almost ten seconds, which is due to lm boiling.…”

“…However, we have recently demonstrated that ILs come quite close to these specications. 9 Due to low melting points, in many cases below room temperature, and their extremely low vapor pressure, as well as high stability towards short-term temperature stress, ILs can be considered as promising candidates for quenching media. In contrast to immersion baths containing salt or metal melts, ionic liquids can be employed at room temperature.…”

“…First results on the use of ILs containing up to 10% w/w for quenching of an aluminum alloy have shown remarkable properties of the cooling medium such as high quenching power at elevated temperatures and homogenous cooling. 9 Herein we present an expansion of the previously reported method to the quenching of steel at temperatures up to 850 C, and the use of other volatile additives to increase the quenching process. We report on the inuence of the quenching process on the properties and the chemical composition of the ionic liquids.…”