Genome-Wide Tissue-Specific Occupancy of the Hox Protein Ultrabithorax and Hox Cofactor Homothorax in Drosophila

The Hox genes are responsible for generating morphological diversity along the anterior-posterior axis during animal development. The Drosophila Hox gene Ultrabithorax (Ubx), for example, is required for specifying the identity of the third thoracic (T3) segment of the adult, which includes the dorsal haltere, an appendage required for flight, and the ventral T3 leg. Ubx mutants show homeotic transformations of the T3 leg towards the identity of the T2 leg and the haltere towards the wing. All Hox genes, including Ubx, encode homeodomain containing transcription factors, raising the question of what target genes Ubx regulates to generate these adult structures. To address this question, we carried out whole genome ChIP-chip studies to identify all of the Ubx bound regions in the haltere and T3 leg imaginal discs, which are the precursors to these adult structures. In addition, we used ChIP-chip to identify the sites bound by the Hox cofactor, Homothorax (Hth). In contrast to previous ChIP-chip studies carried out in Drosophila embryos, these binding studies reveal that there is a remarkable amount of tissue- and transcription factor-specific binding. Analyses of the putative target genes bound and regulated by these factors suggest that Ubx regulates many downstream transcription factors and developmental pathways in the haltere and T3 leg. Finally, we discovered additional DNA sequence motifs that in some cases are specific for individual data sets, arguing that Ubx and/or Hth work together with many regionally expressed transcription factors to execute their functions. Together, these data provide the first whole-genome analysis of the binding sites and target genes regulated by Ubx to specify the morphologies of the adult T3 segment of the fly

Evolution of Secondary α Phase during Aging Treatment in Novel near β Ti-6Mo-5V-3Al-2Fe Alloy

Evolution of secondary α phase during aging treatment of a novel near β titanium alloy Ti-6Mo-5V-3Al-2Fe(wt.%) was studied by OM, SEM, and TEM. Results indicated that size and distribution of secondary α phase were strongly affected by aging temperature and time. Athermal ω phase formed after super-transus solution treatment followed by water quenching, and promoted nucleation of needle-like intragranular α in subsequent aging process. When aged at 480 °C, fine scaled intragranular α with small inter-particle spacing precipitated within β grains and high ultimate tensile strength above 1500 MPa was achieved. When the aging temperature increased, the size and inter-particle spacing of intragranular α increased and made the strength reduce, but the ductility got improved. When aging temperature reached as high as 600 °C, ω phase disappeared and intragranular α coarsened obviously, resulting in serious decrease of strength. While mutually parallel Widmanstätten α laths formed at the vicinity of β grain boundaries and grew into the internal area of β grains, and significant improvement of ductility was achieved. As the aging time increased from 4 h to 16 h at 600 °C, the intragranular α grew slightly and brought about minor change of mechanical properties

Effect of aging treatment on microstructure and tensile properties of Ti–4Al–6Mo–2V–5Cr–2Zr

Microstructure of novel high-strength metastable β titanium alloy, Ti–4Al–6Mo–2V–5Cr–2Zr, is extremely sensitive to both aging temperature and time length, which directly regulates their mechanical properties. Therefore, it is particularly important to clarify the roles of aging treatment in both microstructure and mechanical properties of Ti–4Al–6Mo–2V–5Cr–2Zr. Through varying the aging temperature from 520 to 640 °C and time from 2 h to 8 h, effects of aging technological parameters on the microstructure and tensile properties of Ti–4Al–6Mo–2V–5Cr–2Zr was systematically investigated. It is noted that the secondary α phase (αs) inside the β matrix coarsens as a function of the aging temperature and time length, and the shape of αs phase changes from fine needle to short rod. Moreover, lower aging temperature and longer aging time result in a higher volume fraction of αs phase. Combined with tensile test results, it is evident that volume fraction of αs phase leads to high strength. The volume fraction of αs phase in the alloy after aging at 520 °C for 6 h reaches 61.9% along with the highest ultimate tensile strength of 1367 MPa. In addition, the strengthening mechanism of reinforced phase αs was clarified with both SEM and TEM observations. Results show that the αs with the internal lattice distortion and HCP structure effectively prevent the dislocation slip. And the αs phase arranged in a triangular shape has a profound strengthening effect

Physical models for vacuum-induced multistage atomization of high-entropy FeCoCrNiMo alloy powder for 3D printing

The atomization process of high-entropy FeCoCrNiMo alloy was tested using electrode induction gas atomization (EIGA) at different powers, pressures and rotary speeds. The modelization about the physical essence in the metal drop atomization was studied. A surface tension model, a specific surface energy model, a cooling rate model, and a solidification kinetic model of the alloy drop atomization process were built. Based on these models, the quantitative relationships between the powder particle size and process parameters during the alloy atomization were determined. Together with the results of particle size and scanning electron microscopy-based morphology of the powder obtained from EIGA under different process systems, the accuracy of the above physical models was validated

Low-Temperature Superplasticity and Deformation Mechanism of Ti-6Al-4V Alloy

The low-temperature superplastic tensile behavior and the deformation mechanisms of Ti-6Al-4V alloy are investigated in this paper. Through the experiments carried out, elongation to failure (δ) is calculated and a set of values are derived that subsequently includes the strain rate sensitivity exponent (m), deformation activation energy (Q) at low-temperature superplastic deformation, and the variation of δ, m and Q at different strain rates and temperatures. Microstructures are observed before and after superplastic deformation. The deformation mechanism maps incorporating the density of dislocations inside grains at temperatures of 973 and 1123 K are drawn respectively. By applying the elevated temperature deformation mechanism maps based on Burgers vector compensated grain size and modulus compensated stress, the dislocation quantities and low-temperature superplastic deformation mechanisms of Ti-6Al-4V alloy at different temperatures within appropriate processing regime are elucidated

Thermal Deformation Behavior of Ti-6Mo-5V-3Al-2Fe Alloy

The Gleeble-3800 thermal simulation machine was used to perform hot compression experiments on a new type of β alloy, Ti-6Mo-5V-3Al-2Fe (wt.%), at temperatures of 700–900 °C, strain rates of 5 × 10−1 to 5 × 10−4 s−1, and total strain of 0.7. Transmission and EBSD techniques were used to observe the microstructure. The results show that the deformation activation energy of the alloy was 356.719 KJ/mol, and dynamic recrystallization occurred during the hot deformation. The higher the deformation temperature was, the more obvious the dislocations that occurred and the more sufficient the dynamic recrystallization that occurred, but the effect of strain rate was the opposite. When the deformation temperature was higher than the phase transition point, the recrystallized grains clearly grew up. The calculated strain rate sensitivity index of the alloy was 0.14–0.29. The constitutive equation of hot deformation of Ti-6Mo-5V-3Al-2Fe alloy was established by using the Arrhenius hyperbolic sine equation. The dynamic DMM hot working diagram with the strain of 0.7 was constructed. The relatively good hot working area of the alloy was determined to be the deformation temperature of 700–720 °C and 0.0041–0.0005 s−1

Research on the Hot Deformation Behavior of the Casting NiTi Alloy

The hot deformation behavior and processing maps of the casting NiTi alloy were studied at the deformation temperature of 650–1050 °C and the strain rate of 5 × 10−3–1 s−1 by Gleeble-3800 thermal simulating tester. The variation of the strain rate sensitivity exponent m and the activation energy Q under different deformation conditions (T = 650–1050 °C, ε˙ = 0.005–1 s−1) were obtained. The formability of the NiTi alloy was the best from 800 °C to 950 °C. The constitutive equation of the casting NiTi alloy was constructed by the Arrhenius model. The processing map of the casting NiTi alloy was plotted according to the dynamic material model (DMM) based on the Prasad instability criterion. The optimal processing areas were at 800–950 °C and 0.005–0.05 s−1. The microstructure of the casting NiTi alloy was analyzed by TEM, SEM and EBSD. The softening mechanisms of the casting NiTi alloy were mainly dynamic recrystallization of the Ti2Ni phase and the nucleation and growth of fine martensite

Superplastic Deformation Behaviors and Power Dissipation Rate for Fine-Grained Ti-6Al-4V Titanium Alloy Processed by Direct Rolling

Fine-grained Ti-6Al-4V titanium alloy plates were manufactured using a direct rolling approach, and a series of superplastic tensile tests were conducted at varying temperatures and strain rates. The maximum tensile elongation of 816% was obtained at 810 °C and 5 × 10−4 s−1, and the superplastic flow behavior was dominated by a strain-induced grain boundary slip. In addition, the superplastic behaviors of the alloy were investigated, and the α-and β-phase Gibbs free energy was calculated. The vital role of phase β in the transformation was discussed from a thermodynamical perspective. A power dissipation rate model of Ti-6Al-4V during the superplastic deformation was built and used to predict the energy changing laws in the dynamic recrystallization and grain boundary sliding during the superplastic deformation

Microstructure and Texture Evolution of a Dynamic Compressed Medium-Entropy CoCr_0.4NiSi_0.3 Alloy

Focal research has been conducted on medium-entropy alloys (MEAs) that exhibit a balanced combination of strength and plasticity. In this study, the microstructure, dynamic mechanical properties, and texture evolution of an as-cast medium-entropy CoCr0.4NiSi0.3 alloy were investigated through dynamic compression tests at strain rates ranging from 2100 to 5100 s−1 using the Split Hopkinson Pressure Bar in order to elucidate the underlying dynamic deformation mechanism. The results revealed a significant strain rate effect with dynamic compressive yield strengths of 811 MPa at 2100 s−1, 849 MPa at 3000 s−1, 919 MPa at 3900 s−1, and 942 MPa at 5100 s−1. Grains were dynamically refined from 19.73 to 3.35 μm with increasing strain rates. The correlation between adiabatic temperature rise induced by dynamic compression and dynamic recrystallization was examined, revealing that the latter is not associated with adiabatic heating but rather with phase transition triggered by the dynamic stress during compression. The proportion of Σ3n (1 ≤ n ≤ 3) grain boundaries in deformation specimens increases with increasing strain rates during dynamic compression. The formation of specific three-node structures enhances both strength and plasticity by impeding crack propagation and resisting higher mechanical stress. In the as-cast state, significant anisotropy was observed in the MEA. As strain rates increased, it transited into a stable {111} F texture. The exceptional dynamic properties of strength and plasticity observed in the as-cast state of the MEA can be attributed to a deformation mechanism involving a transition from dislocation slip to the formation of intricate arrangements, accompanied by interactions encompassing deformation nanotwins, stacking faults, Lomer–Cottrell locks, stair-rods, and displacive phase transformations at elevated strain rates