Significance of temperature increase in processing by high-pressure torsion

Abstract

Experiments and finite element simulations were conducted to measure the temperature increase in processing disc samples by high-pressure torsion. Aluminum, copper, iron and molybdenum were selected as model materials. The temperature increases at the early stages of straining but saturates to steady-state levels at large strains. The increase of temperature is proportional to the hardness and rotation speed and is higher at higher imposed pressures and is somewhat higher at larger distances from the disc center.

Hardening of pure metals by high-pressure torsion: A physically based model employing volume-averaged defect evolutions

“…For Fe processed at 1 turn per minute, it has been shown [44,45] that T is 25C. Using that data we can determine C 4 .…”

“…In the model we will further consider that the sample temperature during HPT deformation can increase due to the work by deformation being converted into heat [44,45]. The temperature increase, T, is directly influenced by the ratio of mechanical deformation energy imposed on the sample divided by the heat capacity, and can be approximated as:…”

“…Finite element (FE) model predicting the temperature rise in Al, Cu and Fe during HPT processing is presented in [44,45]. We will show below that the effect of temperature increase during HPT on the hardness after HPT is relatively small, and we will here use an approximation to provide an analytical model.…”

“…One issue that can be identified is that some data on G derives from measurements on single crystals. The shear modulus of polycrystalline materials can be derived from elastic constants of the single crystal, but the relation between elastic constants and shear modulus is not unique [44]. Two widely used averaging methods are the Voigt-Reuss-Hill [ 87 , 88 , 89 ] and Hershey-KronerEshelby method [90,91].…”

Evolution of microstructure in AZ91 alloy processed by high-pressure torsion

“…This value of temperature rise has been calculated using the equation stated in [30], and is similar to the experimental value (290 K) measured directly from the thermocouple located in the upper anvil. The low value of temperature rise can be attributed to (1) the heat loss from relatively small samples in contact with the much larger HPT anvils and (2) due to the low strain rates of deformation in HPT processing [31]. A further factor, making the heat generated low, is the lower friction expected between the relatively lower strength magnesium alloy and the high strength (high speed tool steel) anvils [15,31].…”