The manufacture of most engineering materials involves heating a part to high temperatures, within a furnace, under controlling heating rates and atmospheres. Controlled cooling from these high temperatures is also very important. The purpose of these heat treatments is to develop a microstructure, after manufacturing, that imparts a combination of mechanical and physical properties, tailored to an industrial application.
During these heat treatments, many changes can occur in the sample, all of which are important in determining the final properties of the part. These include dimensional changes, thermal property changes (e.g. specific heat, thermal diffusivity, thermal conductivity) and weight gain or loss. In many cases, the sample also undergoes a phase change which causes heat to flow in or out of the sample. The samples can also react with the furnace atmosphere or evolve gas.
In a normal industrial environment, the furnace and all that goes on inside, is essentially a black box. Measuring characteristics of the sample before and after processing is the only way to investigate what happened in-situ. This can severally limit an understanding of a process and make it difficult to develop new manufacturing methods or optimize existing ones.
The HTTAL facilities is equipped with specialized equipment and expertise that can simulate a furnace manufacturing operation while making in-situ measurements at high temperatures (up to 1500 °C). A Netzsch 404C Differential scanning calorimeter (DSC) can measure phase transformations (i.e. heat flow) and specific heat as a function of heating and cooling at specific rates. A Netzsch 402 C Dilatometer can measure the dimensional changes in a sample, allowing the measurement of density at elevated temperatures and the coefficient of thermal expansion (CTE) of materials. A Netzsch STA 447 is capable of simultaneously measuring heat flow (DSC), weight change (TG) and evolved gas composition via a coupled Gas Chromatograph (GC)-Mass Spectrometer (MS). A Netzsch 427 Laser Flash Apparatus can measure the thermal diffusivity of a material as a function of temperature. The specific heat, density and thermal diffusivity measurements can be combined to calculate the thermal conductivity of a sample as a function of temperature.
MICROSTRUCTURAL CHARACTERISATION
To take full advantage of the above thermal analysis measurements, they must be related to the microstructural changes that occur in the sample. After a sample is measured in the DSC, DIL, LFA or STA-GC-MS we examine its microstructure using Optical microscopy and image analysis, Field Emission SEM with EDS and EBSD, and XRD.