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The current study concentrates on Al 2 O 3 nanoparticles (NPs) synthesis using tragacanth gel as a biotemplate source by the means of sol–gel method at different calcination temperatures. The synthesized catalysts were characterized by XRD, FTIR, FESEM, and EDX. The XRD analysis indicated that the catalyst calcined at 500 °C has amorphous and the one calcined at 900 °C has gamma phase. The comparison of photocatalytic activity of both amorphous and gamma Al 2 O 3 NPs was investigated under visible light irradiation, considering their effects on the degradation of organic dyes, for instance direct black 122 (DB122) and reactive yellow 145 (RY145). The studied effects include initial dye concentration, photocatalyst dosage, and visible light irradiation on dye degradation. Comparison of photocatalytic activity of mentioned photocatalysts exhibited better degradation of a-Al 2 O 3 than that of γ-Al 2 O 3 . The results stated that a-Al 2 O 3 catalyst could remove 97% of the direct black 122, whereas with γ-Al 2 O 3 , only 30% dye was removed. Regarding RY145, 95 and 26% degradation was observed, respectively.

In this paper, we observe for the first time that a metastable beta-Zr in the body-centered cubic (BCC) structure can form via a new phase transformation route. The as-received alpha-Zr in the hexagonal closed-packed (HCP) structure transforms partially to the gamma-Zr in the face-centered cubic (FCC) structure via Shockley partial dislocations during deformation, while the gamma-Zr can continuously transform to the beta-Zr by a uniform shear along the 112FCC direction on the 111FCC plane during subsequent hot deformation. The beta phase is in a Pitsch–Schrader relationship ((110)BCC||(0001)HCP,[11¯0]BCC||[101¯0]HCP) with the matrix alpha phase and in a Nishiyama–Wassermann relationship ((110)BCC||(11¯1¯)FCC,[11¯0]BCC||[121¯]FCC), with the gamma phase, both of which have not been reported in Zr previously. Combined with corresponding molecular dynamics simulations, the phase transition mechanism and stability of the beta phase are studied. The results show that the beta-Zr phase can be retained in the gamma phase when the cooling is fast enough.Graphic abstract

Distinctive thermal-induced prismatic-type face-centered cubic zirconium phases (named γ phase) were firstly reported in pure zirconium. Atomic insight was provided into the α/γ interface and structure of interfacial misfit dislocations. Furthermore, we proposed the formation mechanism of this γ phase. Our results revealed that the semi-coherent interface contributes to periodic extra half-plane on the γ side and the volume expansion is 19.8% due to the α → γ phase transformation. More importantly, the α → γ phase transformation involved expansion and shuffle displacement.

The solidification characteristics and segregation behavior of Cu-15Ni-8Sn alloy were systematically investigated in the present study. The solidification characteristics were revealed with the assistance of a solidification quenching experiment, DTA analysis and Scheil simulation. The solidification microstructure of Cu-15Ni-8Sn alloy was characterized by SEM, and the results indicated that the as-cast microstructure of Cu-15Ni-8Sn alloy mainly consists of Sn-depleted α-Cu(Ni,Sn) matrix, Sn-rich γ phase and lamellar (α + γ) structure. It has been demonstrated that the solidification process begins with the nucleation and growth of primary Sn-depleted α1 phase (L→α1 at 1114 °C) and terminates with the divorced eutectic reaction (L2→α2+γ at 868 °C). During the subsequent cooling process, the discontinuous precipitation (α2→α1+γ) takes place in the temperature range from about 700 °C to 600 °C. In addition, the macrosegregation behavior of Sn in Cu-15Ni-8Sn alloy was investigated by adopting vertical unidirectional solidification and measuring the cooling curves at different positions. The results indicated that an inverse macrosegregation of Sn solute exists in the as-prepared ingot, which mainly segregates at the chill surface of the alloy ingot. Namely, the Sn content is higher than 8 wt pct at the chill surface and about 8 wt pct inside the ingot for Cu-15Ni-8Sn alloy.

The formation of shear bands during hot deformation of a two-phase (α2 + γ) titanium aluminide and its consequences on dynamics softening has been investigated. The starting material consists of a colony of lamellar grains along with the segregated vanadium and niobium which was subjected to hot deformation in the temperature range 1000–1175 °C at the strain rate 10 s−1. Microstructures of the deformed samples indicate that, with increase in the deformation temperature, the orientation of shear bands changes. Moreover, the extent of dynamic recrystallization also increases with deformation temperature. The softening behaviour and crystallographic orientation change within lamellae during hot deformation have been explored. The nucleation of newly recrystallized grains has been observed at twin–parent grain boundary and within the twined γ phase. Lamellae of the γ and α2 phase have been also observed to be twisted and tilted, leading to the band formations under the load, whose mechanisms have also been explored in the present study.

The effect of different Zn content on the microstructure, thermal and mechanical properties of In-Sn-xZn alloys was investigated. The microstructure of the alloys was analyzed by optical microscopy, x-ray diffraction, transmission electron microscopy, scanning electron microscopy and energy dispersive spectroscopy. The results indicated that the alloys consisted of β, γ and Zn phases. The γ phase was generated from the decomposed supersaturation β phase in the peritectic structure, with less than 2.0 wt.% Zn content, characterized by a 120°C phase transition temperature. And a close mutual lattice relation was maintained between β and γ phases. The alloys, with Zn content from 3.0 wt.% to 6.0 wt.% and a melting point at 108°C, had an eutectic structure. Studies indicated that the morphology and distribution of the Zn phases were significantly affected by the β phase. The primary Zn tended to grow along the vertical crystal orientations and to form a cube-shaped block in the β phase. Other Zn existed in the form of a precipitate particle phase in the β phase. Most of Zn was excluded from the γ phase region, which had an effect on the phase boundary of β/γ. And the phase relationship between γ and β in In-Sn-4Zn is [01\\[ \\bar{1} \\]]γ//[\\[ \\bar{1} \\]21]β,(111)γ//(210)β. The performance of the material was significantly enhanced by Zn. When Zn content was 6.0 wt.%, microhardness and elongation of the material were increased by about 160% and 100% respectively, compared with those of In-49Sn-1Zn. Under coupling of the melting interval and the hard phase, the wetting performance of the alloy decreased as the Zn content increased. And the increase of Zn content in the solder made the diffusion distance of Cu longer, which promoted the growth of intermetallic compound (IMC).

The lattice parameters and misfit of the γ and γ′ phases in a series of model quaternary Ni-based superalloys with and without Mo additions have been determined using neutron diffraction between room temperature and 700 °C. Despite the fact that Mo is typically expected to partition almost exclusively to the γ phase and thereby increase the lattice parameter of that phase alone, the lattice parameters of both the γ and γ′ phases were observed to increase with Mo addition. Nevertheless, the effect on the γ lattice parameter was more pronounced, leading to an overall decrease in the lattice misfit with increasing Mo content. Alloys with the lowest Mo content were found to be positively misfitting, whilst additions of 5 at.% Mo produced a negative lattice misfit. A general decrease in the lattice misfit with increasing temperature was also observed.

Herein, the convenient interplay between Eu incorporation and morphology to form the perovskite (PSK) γ‐phase of CsPbI3 at 80 °C (low temperature [LT] γ‐phase) is unveiled. In contrast, CsPbI3 without Eu exists in a mixture of γ‐phase and non‐PSK δ‐phase at 65 °C or in a fully δ‐phase at 80 °C. Based on experimental and theoretical findings, an argument about a double beneficial role of Eu is presented. On one hand, it assists in the formation of the γ‐phase either by substituting Pb or by occupying interstitial positions in the CsPbI3 lattice. On the other hand, it indirectly promotes the formation of a fine‐grained layer at LT wherein the high surface‐to‐volume ratio makes the establishment of the δ‐phase unfavorable. Strain accommodation in the fine‐grained matrix and the formation of a gluing intergrain‐self‐material during the kinetics of reaction (snowplow effect) cooperate in extending the lifetime of the LT γ‐phase to ≈40 h at 65 °C compared to only ≈10–15 min in the sample without Eu for the complete phase transformation. The disclosed phenomena draw a method for the stabilization of PSK‐CsPbI3 layers based on a self‐generated thin frame of exceeding material filling the gaps between small‐sized grains that can be used hereinafter to further extend the PSK lifetime. The addition of Eu in the mother solution and the use of low formation temperature cooperate in reducing the grain size and in increasing the barrier for mass exchange that finally extends the stability window of the γ‐phase at room temperature.

Vaporization and its associated surface defect formation have become one of the most important challenges in manufacturing single-crystal components. During the kinetic-influenced casting and solution heat treatment of Ni-base superalloys, elements undergo processes of vaporization and deposition causing unpredictable defects. To quantitatively examine the vaporization phenomenon, partial vapor pressures of Ni, Al and Cr in Ni-base alloys were measured in the γ phase over the temperature range of 1473 K to 1650 K using Knudsen effusion mass spectrometry. Experimental results showed that the partial pressure of Al is about two orders of magnitude lower than that of Ni and five times lower than that of Cr, revealing that the vaporization of Al is almost negligible compared with those of Ni and Cr at solution heat treatment temperatures. Variation of partial pressures during homogenization of the as-cast Ni-base alloys was measured in long-term isothermal experiments at 1573 K. It was found that Cr vapor pressure decreases by a factor of two in the first 20 hours whereas the Ni and Al remain nearly constant.

Misch metal (Mm), consisting of Ce and La, was added to Ti–45Al–3Mo–2Nb alloys in order to investigate phase transformation and microstructural changes. The pseudo-binary phase diagram was estimated via PANDAT software™. The addition of Mm caused a decrease in both the fractions of α 2 /γ lamella and the β 0 phase, and served as an important factor for a collapse of lamellar structures. In addition, Mm significantly decreased the colony size of the alloy, resulting in an increase in high-temperature tensile yield strength of ~ 40% for the alloys with 0.3 at% Mm at 800 °C. It appears that the addition of Mm affects the phase stability and increase the proportion of the γ phase. The microstructural changes, with respect to Mm additions, were discussed in terms of structural observations during isothermal heat treatments.