In chem lab we did an experiment with two rods, one that was martensite (one that made a thud sound) and the other austenite (one that made a ping sound). We put both of the rods in N2 and another time we put it in boiling water. Each time the rod would make an opposite sound of what it is at room temperature (the martensite sounds like PING after heated and cooled & austenite sounds like THUD when heated....but when their temperatures go back to room temp, martensite goes back to sounding like thud, and austenite goes back to sounding like ping)...why is that?
...hope this makes sense
It sounds like you are observing an interesting phenomenon related to the sound produced by martensite and austenite rods in different temperature conditions. The change in sound you are observing can be explained by the structural changes that occur in the materials due to thermal expansion and contraction.
Martensite and austenite are different crystal structures of steel that can form depending on the cooling rate during the steel's heat treatment. Martensite is a hard, brittle structure that forms when steel is rapidly cooled (quenched) from high temperatures, while austenite is a more ductile and stable structure that forms when steel is slow-cooled.
When you heated the rods in boiling water, both the martensite and austenite structures started to change. As the temperature increased, the steel expanded due to thermal expansion, causing the structure to undergo a phase change. Martensite changed into austenite, and austenite changed into a different, less stable crystal structure known as "tempered martensite."
The change in crystal structure caused by heating leads to a change in the mechanical properties of the steel, including its sound-producing characteristics. The different crystal structures have different densities and elastic moduli, which affect the way they vibrate and produce sound. This is why you observed a change in the sound produced by the rods when heated.
When you removed the rods from the heated environment and allowed them to cool back to room temperature, the reverse happened. The tempered martensite transformed back into either martensite or austenite, depending on the rod, as the structure returned to its original state. This is why the sound produced by the rods reverted back to their original sounds at room temperature.
In summary, the change in sound you observed when heating and cooling the rods can be attributed to the structural changes and resulting differences in mechanical properties of the steel at different temperatures.