Microstructure and Strength of Titanium After Heat Treatment at Different Temperatures in the Range of 680-1000°C

The main purpose of this research is to determine the effect of brazing treatment on mechanical properties of both titanium Grade 2 and titanium Grade 5 alloys. The research group obtained Grade 2 and Grade 5 titanium alloys and brazing- treated them at temperatures of 680, 800, 850, 900, 920, 950, and 1000°C. Afterward, each sample was tensile tested, mounted, hardness tested, and observed by optical microscope to investigate corresponding microstructures. Based on the result sheets, it was revealed that the yield strength and tensile strength and ultimate strength of Ti Grade 2 alloys showed drastic fall after heating to 680°C, then no change up to 850°C, fall again up to 950°C, and remained unchanged strength to 1000°C However, the Ti Grade 5 samples showed completely different behavior. The yield strength was unchanged after heating to different temperatures. When heating to 680°C. It didn’t affect the strength at all, then after heating to 800°C, the strength decreased about 100MPa. But after this, higher temperatures didn’t change strength anymore. The Ultimate strength however showed a different trend as it continuously went down at elevated temperature. Meanwhile, the hardness of both alloys decreased constantly when temperature increased. Regarding Ti Grade 2 alloys, the initial drop in strength was due to annealing. Around 800°C, alpha laths started to form and that caused strength to increase. When the temperature reached at 850°C, the basketweave alpha laths were formed. Over that temperature, the grain sizes were significantly large which caused the strength to decrease. However, there was not much of change in alpha/beta ratio for Ti Grade 5 alloys. EBSD could be a helpful method since the alpha grain size can be determined from that.