03.04.2023 by Martin Rosenschon
Dynamic Mechanical Analysis for High-Temperature Materials
Material Characterization above 500°C by means of DMA
Dynamic Mechanical Analysis (short: DMA) is a method for determining the viscoelastic properties of materials as a function of temperature, time and frequency. The main application of DMA is the determination of glass transitions or Phase TransitionsThe term phase transition (or phase change) is most commonly used to describe transitions between the solid, liquid and gaseous states.phase transitions of polymers and polymer composites. In addition to the polymer industry, it is also used in food technology and biomedicine or in materials research in general. Usually, the viscoelastic behavior of materials at moderate temperatures up to a maximum of 500°C is characterized in these areas.
However, viscoelastic characteristics such as storage modulus E' and Viscous modulusThe complex modulus (viscous component), loss modulus, or G’’, is the “imaginary” part of the samples the overall complex modulus. This viscous component indicates the liquid like, or out of phase, response of the sample being measurement. loss modulus E" also play an important role in the high-temperature range. For example, the blades of a gas turbine often made from alloy systems such as steel, titanium or nickel alloys must be specially designed for their load - the forces and frequencies that act - and the resulting temperatures.
Temperatures of more than 2,000°C can be reached in the combustion chamber of a gas turbine . Depending on the cooling technology used and the position, maximum temperatures between 500°C and 1000°C occur at the turbine blades .
Figure 1 shows a DMA measurement of an Inconel 625 alloy up to 1000°C in 3-point bending using the DMA Eplexor® high-temperature series with up to 500 N dynamic force. Depending on the furnace installed, the system allows measurements from room temperature up to 1000°C or up to 1500°C.
Inconel 625 is a nickel-based super alloy with the main alloying elements chromium, molybdenum and niobium. This is a registered trademark of Special Metals Corp. It has a high resistance to corrosion and OxidationOxidation can describe different processes in the context of thermal analysis.oxidation. The alloy is often used in environments where high temperatures and corrosive conditions prevail, such as in turbines and other aircraft engine parts, furnace applications and piping.
Starting at around 210 GPa at 100°C, the storage modulus E' (black curve) decreases with increasing temperature and the material loses stiffness. At 400°C it is just under 200 GPa and at 800°C it is around 160 GPa. These values could be used, for example, to calculate the deformation of a turbine blade depending on the operating temperature.
In the course of the tan δ (blue curve), two effects can be identified at 713°C and 808°C (peak temperature). Nickel-based alloys such as Inconel 625 are strengthened by means of a defined heat treatment and the associated formation of intermetallic precipitates. Typical precipitation phases in nickel-based alloys, which increase strength, are the metastable face-centered cubic γ' phase Ni3 (Al, Ti) and the body-centered cubic γ” Ni3(Nb) phase . The formation and dissolution of both phases could explain the effect at 713°C in tan δ. More precise conclusions cannot be made due to a lack of information about the heat treatment condition of the starting material. Petrzak et al.  also reports for Inconel 625 the formation of the incoherent equilibrium phase δ Ni3(Nb, Ti) from 750°C, which correlates with the second peak in tan δ at around 800°C.
In addition to identifying characteristic values for a static and dynamic design of components, DMA can also be used to gain insights into the morphological development - in this case the formation of precipitations.
NETZSCH Analyzing & Testing provides the right DMA for your individual area of application, regardless of whether you want to characterize materials in the low-temperature range from -170°C to 500°C or determine the viscoelastic properties of high-temperature materials up to 1500°C.
 Boyce, M. P. (2011). Gas turbine engineering handbook. Elsevier.
 Andersson, J. (2011). Weldability of precipitation hardening superalloys: influence of microstructure. Chalmers Tekniska Hogskola (Sweden).
 Petrzak, P., Kowalski, K. & Blicharski, M. (2016). Analysis of phase transformations in Inconel 625 alloy during annealing. Acta Physica Polonica A, 130(4), 1041-1044.