Effect of Heat Treatment on Directionally Solidified Nb Containing Tialalloys.pdf

1、This paper talks about the effect of heat treatmant (HT) on the cast and direction solidified (DS) Ti-46Al-6Nb and Ti-46Al-6.3Nb-0.1B compositions. These materials were prodused by cold crucible electromagnetic process.

2、Samples were heat treated with six different conditions with the Muffle Atmosphere Furnace XY-1600A. HT1:temperature at 1270°C for 2h + air cooling. HT2: temperature at 1330°C for 2h + air cooling. HT3: temperature at 13

3、30°C for 2h + 900°C for 30 min + air cooling. HT4:temperature at 1330°C for 2h+air cooling, and then was repeat heating at 1330°C for 10min. HT5:temperature at 1330°C for 10min+air cooling, and then was repeated the same

4、 HT process. HT6: temperature at 1330°C for 10min +air cooling, and then was repeated the same HT process four times. After HT process all samples were polished, etched and prepared for further analysis. Firstly samples

5、were taken pictures by a digital camera. Analysis of microstructure was performed by the optical microscope (OM) and the scanning electron microscope (SEM). After microstructure analysis all samples were cut into several

6、 small cylinders for compressive stress (CS) tests. CS test were tested by Inston 5960 Dual Column Tabletop Universal Testing Systems. Analysis of fracture mechanism before and after heat treatment was done by SEM.
　　

7、HT1 decreased of average grain size of cast alloy from 1.4 mm to 0.3 mm, but didn’t change the grain morphology of DS samples. Also HT1increased of the lamellar spacing from 2.46 μm to 4.38 μm. The compressive stress dec

8、reased after HT1. HT2-HT4 had insignificant influence on changing average grain size macrostructure of cast materials, but cardinally changed morphology and microstructure of DS materials. HT2-HT4 and HT6 caused eliminat

9、ion of all segregations. HT2-HT6 decreased the lamellar spacing. The best result of compressive stress property had showed HT5. Also HT5 caused the smallest lamellar spacing. HT1 and HT2 changed fracture mechanisms a lit