Friction stir welding of high temperature alloys

<p>"Friction stir welding (FSW) of Ti-6Al-4V alloy, nickel-based and iron-based oxide dispersion strengthened (ODS) alloys (MA754 and MA956) has been studied. The main aspects covered include tool evaluation, microstructural evolution, mechanical properties, and correlation between processing, microstructure and mechanical properties. Tool performance study was carried out for Ti-6Al-4V alloy with refractory tools made of W-1.1%La₂O₃ and two different grades of WC-Co based materials. The results showed that tool degradation can be attributed to mechanical and chemical interaction with processed material. The nature of tool-workpiece interaction was tool material dependent and influenced the resultant microstructure and weld quality in the stirred zone.</p> <p>FSW resulted in refined grain structure in ODS alloys by dynamic recrystallization mechanism. A critical finding was 'strain induced dispersoid agglomeration'. For Ti-6Al-4V alloy, transformed ß microstructure formed composed of fine acicular α phase (~500 nm in thickness). The fine grain structure facilitated globularization during tensile deformation at 625 ºC.</p> <p>Mechanical properties were correlated with microstructure in FSW materials. Improved mechanical properties were observed for ODS alloys due to grain refinement. An effort was made to predict room temperature yield strength for MA956 alloy with strengthening contribution analysis. On the other hand, at high temperature, degradation of creep properties was observed in MA754 alloy. Analysis of MA754 alloy with three grain structures (as-received, FSW and post-weld annealed conditions) revealed that the loss in creep strength of FSW MA754 was attributed to refined grain size and agglomerated dispersoid size"--Abstract, page iv.</p>

Name thesis:degree_name

Ph. D. in Metallurgical Engineering

Grantor

Missouri University of Science and Technology

Year dc:date.available

2016

Author dc:creator

• Wang, Jiye

• Metallurgy

Repository record dc:identifier

https://scholarsmine.mst.edu/doctoral_dissertations/37

OAI identifier oai:identifier

oai:scholarsmine.mst.edu:doctoral_dissertations-1039