Effect of aging treatment on the precipitation transformation and age hardening of Mg-Gd-Y-Zn-Zr alloy

In this study, the precipitation transformation and age hardening of solution-treated Mg-9Gd-4Y-2Zn-0.5Zr(wt.%) alloy were investigated at different aging treatment parameters. The precipitation sequences of the alloy aged at 200℃, 250℃ and 300℃ are β’’(DO19) → β’(BCO) → β(FCC), β’’(DO19) → β’(BCO) → β_(1)(FCC) → β(FCC) and β(FCC), respectively. The streaks sequences of the alloy aged at 200℃, 250℃ and 300℃ are SF, SF → 14H-LPSO and SF → 14H-LPSO, respectively. For the alloy aged at 200℃ and 250℃, the increase in hardness with increasing aging time is contributed from the increase in precipitate volume fraction and the transformation from β’’ to β’ phase with basal → prismatic and spherical → spindle-like precipitate changes. The decrease in hardness after the peak-aging stage is attributed to the appearance of micro-sized β precipitates. Because of the smaller size of precipitates and the triangular arrangement of β’ precipitate, the hardness of the alloy aged at 200℃ is higher than that aged at 250℃. For the alloy aged at 300℃, the appearance of only micro-sized β precipitate and its coarsening with increasing aging time leads to the lowest hardness and an overall decrease in hardness with the aging time.

Quantitative Research on the Role of Large Precipitates in V–Ti Micro-Alloyed Steel during Dynamic Transformation

To research the effect of large precipitates（size 〉 0.2 μm） on strain-induced dynamic transformation, the variation of V contents in large precipitates has been investigated quantitatively in two V–Ti micro-alloyed steels. The results showed that high N content promoted V precipitation on the surface of Ti large precipitates rapidly. Subsequently,large precipitates containing V induced the formation of intragranular ferrite, which accelerated the dynamic transformation process remarkably, promoted the occurrence of continuous dynamic recrystallization of ferrite and improved the refinement effect.

Formation mechanism and luminescence properties of nanostructured sodium yttrium fluoride corn sticks synthesized by precipitation transformation method

Monodisperse sodium yttrium fluoride com sticks with hexagonal nanostructure were successfully prepared by a facile and repeatable precipitation transformation method. The phase and morphology of the products were characterized with X-ray diffraction （XRD） and scanning electron microscopy （SEM）. The growth mechanism was studied, indicating that the initial generated Y（OH）3 gradually translated into YF3 and then transformed into com stick-like H-NaYF4 nanoparticles owing to the crucial role of fluorine ions in the solution. The up-conversion （UC） luminescence properties of H-NaYF4：20%Yb3＋,2%Er3＋ nanocrystals were discussed. The intensive green emission in the range of 510-570 nm was attributed to the （2Hll/2, 4S3/2）----4It5/2 transition and the weaker red emission between 640 and 680 nm was originating from the 4F9/2----4115/2 transition.

Shape Memory Behavior of [111]-Oriented NiTi Single Crystals After Stress-Assisted Aging

The shape memory behavior of [111]-oriented Ni_（51）Ti_（49） （at.%） single crystals was investigated after stressassisted aging at 500 °C for 1.5 h under a compressive stress of-150 MPa.It was found that a single family of Ni_4Ti_3 precipitates with two crystallographically equivalent variants was formed after aging under compressive stress.Stressassisted aging resulted in tensile two-way shape memory effect strain of 1.56% under-5 MPa.Thermal cycling under-600 MPa resulted in a transformation strain of-2.15%,while the subsequent thermal cycling under-5 MPa resulted in a tensile two-way shape memory effect strain of 2.2%.