Sintering and compensation effect of donor- and acceptor-codoped 3mol% Y 2 O 3 -ZrO 2

Addition of ∼0.15–0.5 mol% acceptor oxide, Al 2 O 3 , to 3 mol% Y 2 O 3 -ZrO 2 results in enhanced densification at 1350 °C. The enhancement is accounted for by a liquid phase sintering mechanism. The addition of donor oxide, Ta 2 O 5 , of 0.15–2.5 mol % at 1300–1600 °C results in the destabilization of tetragonal (t-) phase and the decrease of final density in 3 mol% Y 2 O 3 -TZP (tetragonal ZrO 2 polycrystals). X-ray diffractometry (XRD) reveals that the Ta 2 O 5 -added 3 mol% Y 2 O 3 -ZrO 2 contains monoclinic (m-) ZrO 2 and a second phase of Ta 2 Zr 6 O 17 . The decreasing in final density is attributed to the increase of m-ZrO 2 content. Complete destabilization of t-ZrO 2 to m-ZrO 2 in samples added with 2.5 mol% Ta 2 O 5 is interpreted by the compensation effect based on donor- and acceptor-codoping defect chemistry.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/44714/1/10853_2005_Article_BF01166021.pd

Effect of Post Weld Heat Treatment on Microstructures and Mechanical Properties of AZ31B Friction Welded Joint

AZ31 magnesium alloy was welded by friction welding and the effect of post weld heat treatment on microstructures and mechanical properties were investigated. Fine grained microstructure whose minimum grain size is approximately 1 mm was formed at the weld interface by dynamic recrystallization due to hot-heavy working. Although abnormal grain growth which is often found in stir zone in friction stir welding occurred near weld interface where the material was work hardened, the area was limited and did not affect the mechanical properties of weld interface. The tensile and fatigue strength of as weld joints were equal to those of base metal and did not decrease until grain size increased to approximately 15mm. The decrease in the Hall-Petch slope was found when the grain size decreased less than 3 mm in grain size in terms of yield stress. [doi:10.2320/matertrans.48.44