Table of contents
Why thermomechanical analysis in the metal industry?
In the steel and metal industry companies are faced with constantly increasing demands: Components must withstand high thermal loads, process windows must be precisely adhered to and targeted structural changes are often the key to improved material properties. Whether it is the evaluation of welding structures, the development of innovative alloys or the validation of individual batches – the reliable characterization of metallic materials forms the foundation for sustainable quality assurance and targeted material development.
Steel and other metals undergo demanding manufacturing and processing procedures in which the individual thermal and mechanical behavior is decisive in determining how efficiently heat treatments, welding processes, casting processes or rolling processes can be designed. Precise knowledge of these properties makes it possible to optimize production processes and avoid costly rejects.
What does thermomechanical analysis (TMA) do?
Thermomechanical analysis is an established method of materials testing that measures the dimensional changes of a specimen as a function of temperature and applied force. Key parameters such as the linear
Typical measured variables include the change in length, the CTE, the deformation during relaxation, creep and recovery tests as well as the detection of transformation points, for example the martensite start in steel. Modern TMA systems such as those from Linseis guarantee an exact force resolution in the µN range. The ability to select different tip geometries and test modes significantly increases application flexibility. For sensitive material systems, measurements can also be carried out in a controlled inert gas atmosphere to avoid oxidation or undesirable reactions.
Why TMA is the right choice for steel and metals
The strengths of TMA compared to other characterization methods lie in particular in its high sensitivity and the ability to observe thermal and mechanical effects both separately and simultaneously. The precise measurement of thermal expansion is essential for the development of new alloys and the assessment of components such as weld seams. TMA is also ideal for detecting and quantifying phase transitions such as martensitic transformation. Long-term deformation and time-dependent relaxation processes can also be reliably measured using this method.
A recent study describes the high relevance of TMA measurements for the characterization of steels with regard to their phase transitions and expansion behavior (Bhattacharya et al., 2023). For high-performance materials in particular, they emphasize that TMA is one of the few methods that can simultaneously and comparably record the interaction between temperature, mechanical load and volume change. Another paper shows that the combination of TMA with targeted atmospheric control is also advantageous for the batch-related quality assurance of alloys (Lee et al., 2022). The authors emphasize the importance for process control in foundries and the prevention of faulty batches through early detection of inhomogeneities.
What is important for meaningful measurements
Several factors are crucial for reproducible and reliable results. Sample preparation plays a central role: clean surfaces and defined geometries minimize interference factors and ensure reproducible measurements. The choice of atmosphere is also relevant – inert gases or vacuum-adjustable systems are useful to prevent oxidation or undesirable reaction processes.
The selection of the appropriate force and tip geometries directly influences the measurement signals. Depending on the application, penetrating, compression or Flexur tips are used. Modern software tools also support the automated detection of transitions and the documentation of quality parameters, which considerably simplifies and accelerates evaluation.
Selection criteria for TMA systems
Several aspects should be considered when evaluating a TMA system. The temperature range is particularly important for steel alloys, as measurements up to the high temperature range of over 1000 °C are often required here. The force resolution must be fine enough to detect even the smallest deformations for high-precision applications.
Reproducibility is another important criterion: documented long-term stability and consistency of measured values ensure the comparability of batch analyses over longer periods of time. Last but not least, integration capability plays an important role – the simple connection to existing laboratory environments, both in terms of software and organization, is a key advantage for ongoing operation.
Added value for laboratory and production
The advantages of TMA measurement technology in a metallurgical context are manifold and have a direct impact on the value chain. The precise analysis of thermomechanical limits enables the accurate control of industrial processes and thus secures process windows. Continuous quality assurance with TMA avoids costly faulty batches, which is directly reflected in reduced reject rates.
Direct measurement data for relaxation and transformation accelerate the upscaling and optimization of new alloys, which makes material development significantly more efficient. In addition, verifiable and digital measurement protocols are often a prerequisite for certifications and proof of delivery, which means that TMA also contributes to the fulfillment of regulatory requirements.
Practical example: Determining the modulus of elasticity of nickel
The lens ice cream TMA L72 enables sinusoidal force programs to be applied to a wide variety of specimens. This allows the determination of the flexural and elastic modulus of almost all materials. Originally designed mainly for polymer applications, the system has recently been optimized for the measurement of harder materials such as metal alloys and pure metals. By extending the force ranges up to 20 N and increasing the sample dimensions, even demanding metallic materials can now be precisely characterized.
In a typical 3-point bending test, a nickel sample with a length of 8.4 mm, a diameter of 5.12 mm and a thickness of 0.2 mm was examined. The measurement was carried out at 50 °C using a static force of 500 mN and a superimposed sinusoidal force of an additional 1 N. The resulting change in length of the sample and the resulting calculated modulus of elasticity show excellent agreement with literature data. It is particularly advantageous that such measurements can be carried out over the entire temperature range of the instrument, enabling comprehensive screening of the mechanical properties.
Literature
Bhattacharya, S. et al. (2023) ‘Thermal expansion and phase transition analysis of advanced steel grades using TMA’, Journal of Thermal Analysis and Calorimetry.
Lee, H.W. et al. (2022) ‘Using thermomechanical analysis for alloy batch validation in metal production’, Metallurgical and Materials Transactions A.
Meier, P. et al. (2021) ‘Process optimization in foundries based on high-temperature TMA measurements’, International Journal of Materials Research.
