The hot compressive deformation behavior of cast Mg-Gd-Y-Zn-Zr alloys with and without LPSO phase in their initial microstructures

Samples of Mg-8.2Gd-3.8Y-1.1Zn-0.4Zr alloy with and without an intragranular lamellae-shaped long period stacking ordered(LPSO)phase were prepared through heat treatment and a series of hot compression tests on these materials were conducted to examine and evaluate the influence of LPSO on the hot compressive deformation behavior and deformation mechanisms at a given alloy composition.The values of activation energy for plastic flow(Qc)of the solution treated(without LPSO phase)and annealed alloys(with intragranular LPSO phase)were larger than that for pure Mg,indicating that the presence of a high amount of rare earth(RE)elements and LPSO in the Mg matrix significantly increases Qc.The Qcvalue of the annealed alloy was larger than that of the solution treated alloy at all the strain levels(223.3 vs.195.5 k J/mol in average)and the largest difference in Qcbetween the two alloys was recorded at the smallest strain of 0.1 where precipitation of LPSO during deformation was limited in the solution treated alloy.These observations imply that the formation of LPSO phase out of the RE-rich solid solution matrix during deformation increases Qc,but the increment is not so large.Analysis of the hot compressive data of the alloys with LPSO phase and the alloys with RE-rich solid solution matrix in literatures indicates the similarity of the effect of the LPSO and RE-rich solid solution matrix phases on Qcand high-temperature strength.

Melting and Annealing Peak Temperatures of Poly(butylene succinate) on the Same Hoffman-Weeks Plot Parallel to Tm=Tc Line

The crystallization and melting behavior of polymers is of theoretical importance.In this work,poly(butylene succinate)(PBS)was selected as an example to study such behavior at low supercooling via introduction of the extended-chain crystal(ECC)of the same polymer as nucleating agent.The crystallization of PBS with its ECC as nucleating agent in a wide temperature range(90–127°C)and the following melting behavior were studied.It is revealed that the melting point(Tm',for Tc≥113°C)and the annealing peak temperature(Ta',for Tc=90–100°C)show similar asymptotic behavior.Both Tm and Ta approach to a value of ca.3.3°C higher than the corresponding Tc when the crystallization time tc approaches the starting point.That is to say,the Hoffman-Weeks plot is parallel to Tm=Tc line.The crystallization line became parallel to the melting line when PBS was crystallized at Tc higher than 102°C.Based on these results,we propose that the parallel relationship and the intrinsic similarity between the Ta and the Tm observed at the two ends of the Tc range could be attributed to the metastable crystals formed at the beginning of crystallization.