Microstructure evolution under the space-time variational solidification conditions in a melt pool: A multi-scale simulation study

The properties of welded components are dominated by the microstructure evolution in the pool, where the solidification conditions are space-time variational. To represent the variational solidification conditions in the pool, the multi-scale simulation is carried out in this paper, combining microscopic Phase-Field (PF) equations with macroscopic thermal processes. First, two different models, the GR model and TF model, are employed to simulate the single crystal solidification at a local region of pool. Results suggest the TF model is more suitable to reflect the variational conditions than the GR model. Then the single-crystal solidification and poly-crystal solidification at the whole region of pool are carried out through the TF model. The results indicate the space-time variabilities of solidification conditions across the pool. Meanwhile, the variational solidification conditions influence the microstructure evolution significantly, including the onset of initial instability at the epitaxial growth stage and the directional evolutions of the converging grain boundaries (GBs) and diverging GBs at the competitive growth stage. Moreover, the formation of axial grain structures is observed, which can be regarded as the competition between the grains along the axial direction and radial direction. This study indicates the necessity of considering variational conditions in a pool. Meanwhile, the PF model can simulate microstructure evolution under variational conditions accurately, which has a great potential for investigating solidification dynamics in a melt pool.Comment: 30pages, 14 figure

p70S6K1 (S6K1)-Mediated Phosphorylation Regulates Phosphatidylinositol 4-Phosphate 5-Kinase Type I \u3cem\u3eγ\u3c/em\u3e Degradation and Cell Invasion

Phosphatidylinositol 4-phosphate 5-kinase type I γ (PIPKIγ90) ubiquitination and subsequent degradation regulate focal adhesion assembly, cell migration, and invasion. However, it is unknown how upstream signals control PIPKIγ90 ubiquitination or degradation. Here we show that p70S6K1 (S6K1), a downstream target of mechanistic target of rapamycin (mTOR), phosphorylates PIPKIγ90 at Thr-553 and Ser-555 and that S6K1-mediated PIPKIγ90 phosphorylation is essential for cell migration and invasion. Moreover, PIPKIγ90 phosphorylation is required for the development of focal adhesions and invadopodia, key machineries for cell migration and invasion. Surprisingly, substitution of Thr-553 and Ser-555 with Ala promoted PIPKIγ90 ubiquitination but enhanced the stability of PIPKIγ90, and depletion of S6K1 also enhanced the stability of PIPKIγ90, indicating that PIPKIγ90 ubiquitination alone is insufficient for its degradation. These data suggest that S6K1-mediated PIPKIγ90 phosphorylation regulates cell migration and invasion by controlling PIPKIγ90 degradation

Microstructure evolution, solidification characteristic and magnetocaloric properties of MnFeP_0·5Si_0.5 particles by droplet melting

Mn–Fe–P–Si compounds are promising magnetocaloric materials for magnetic refrigeration. However, the microstructure evolution and solidification characteristics are rarely discussed in the literature. Here, we investigate the solidification characteristics and microstructure evolution of MnFeP0·5Si0.5 alloys under different undercooling and cooling rates based on droplet melting method. Results show that the alloy solidifies in the sequence of Fe2P phases, (Fe2P+(Mn,Fe)5Si3) eutectics and (Fe2P+(Mn,Fe)3Si eutectics. With the increase in undercooling and cooling rate, the (Fe2P+(Mn,Fe)5Si3) and (Fe2P+(Mn,Fe)3Si) eutectic growth is divorced, and the Fe2P phase experiences from coarse strips to fine dendrites, then fragmented dendrites, and finally to equiaxed dendrites. Besides, the volume fraction of the Fe2P phase increases, and its atomic ratio approaches the nominal composition. As the droplet diameters decrease, we find a drop in Curie temperatures (228-210 K) and an increase in hysteresis (4–11 K). The magnetisation of the 500 μm droplet is also up to 51 Am2/kg. These results indicate that the magnetocaloric properties of the alloys strongly depend on the phase-type, morphology and composition evolution. Additionally, the operating temperature range and the refrigerant capacity of the 500 μm droplet are as high as 41 K and 112 J/kg, respectively, which will benefit the practical application of Mn–Fe–P–Si alloys

Martensite transformation, mechanical properties and shape memory effects of Ni-Mn-In-Mg shape memory alloys

The martensite transformation (MT), mechanical properties and shape memory effect (SME) of (Ni50Mn35In15)(1−x)Mgx (x = 0%, 0.08%, 0.3%, 0.6% at%) alloys were comprehensively investigated. The results showed that due to Mg doping the MT temperature shifted to higher temperatures and a worm-like second-phase precipitated at grain boundaries and inside the grains. With increasing Mg content, the amount of precipitates gradually increased, the thermal hysteresis was almost invariant, and the SME was not obviously affected at 3% pre-strain, even when the volume of the second phase reached up to 28.75%. Compressive stress and strain experiments showed that both the strain and strength of the Ni-Mn-In-Mg alloys were improved substantially (by 46.9% and 53.4%, respectively, at x = 0.6%) compared with those of the pure Ni50Mn35In15 alloy; this effect is nearly the same as that achieved by the directional solidification method. Because Mg is nonmagnetic, the magnetization difference of the alloy with Mg doping is much lower than that of the alloy without Mg doping. Overall, the results confirm that adding a small amount of Mg is a potentially viable method for improving the mechanical properties of Ni-Mn-In alloys without adversely damaging their functional properties. Keywords: Precipitates, Martensite transformation, Shape memory alloys, Mechanical propertie

Microstructure and magnetic property of LaFe11.6Si1.4 magnetocaloric alloys by a novel short time heat treatment

Microstructure and magnetic property of LaFe11.6Si1.4 magnetocaloric alloys by a novel short time heat treatmen

Internal friction behaviors of Ni-Mn-In magnetic shape memory alloy with two-step structural transformation

The internal friction (IF) behaviors of dual-phase Ni52Mn32In16 alloy with two-step structural transformation were investigated by dynamic mechanical analyzer. The IF peak for the martensite transformation (MT) is an asymmetric shoulder rather than those sharp peaks for other shape memory alloys. The intermartensitic transformation (IMT) peak has the maximum IF value. As the heating rate increases, the height of the IMT peak increases and its position is shifted to higher temperatures. In comparison with the IMT peak, the MT peak is independent on the heating rate. The starting temperatures of the IMT peak are strongly dependent on frequency, while the MT peak is weakly dependent. Meanwhile, the heights of both the MT and IMT peak rapidly decrease with increasing the frequency. This work also throws new light on their structural transformation mechanisms

Anisotropic tensile creep behavior in laser powder bed fusion manufactured Al–Mn–Mg–Sc–Zr alloy

The recently emerged Al–Mn–Mg–Sc–Zr alloys were regarded as high-strength Al alloys suitable for high-temperature applications. However, the influence of laser powder bed fusion (LPBF) fabricated anisotropic microstructure on tensile creep performance has not been explored. In this work, we reported an anisotropic tensile creep behavior, which is superior in the vertical specimens than the horizontal counterparts. The tensile creep anisotropy was attributed to the bi-modal microstructure of columnar grains within melt pool and equiaxed grains at melt pool boundary, the “fish-scale” melt pool morphology and the resulted tortuous crack path in the vertical orientation

GSPE Inhibits HMGB1 Release, Attenuating Renal IR-Induced Acute Renal Injury and Chronic Renal Fibrosis

Grape seed proanthocyanindin extract (GSPE) is a polyphenolic bioflavonoid derived from grape seeds and has been widely studied for its potent antioxidant, anti-inflammatory and antitumor activities. HMGB1 is a newly discovered danger-associated molecular pattern (DAMP) that has potent proinflammatory effects once released by necrotic cells. However, the effect of GSPE on the HMGB1, and the relationship of those two with acute kidney injury and chronic kidney fibrosis are unknown. This study aimed to investigate the impact of GSPE on acute kidney injury and chronic fibrosis. C57bl/6 mice were subjected to bilateral ischemia/reperfusion (I/R) and unilateral I/R with or without GSPE administration. After bilateral I/R, mice administered GSPE had a marked improvement in renal function (BUN and Cr), decreased pathological damage and reduced inflammation. In unilateral I/R, mice subjected GSPE showed reduced tubulointerstitial fibrosis and decreased inflammatory reaction. The renoprotection of GSPE on both models was associated with the inhibition of HMGB1 nucleocytoplasmic shuttling and release, which can amplify the inflammation through binding to its downstream receptor TLR4 and facilitated P65 transcription. Thus, we have reason to believe that GSPE could be a good alternative therapy for the prevention and treatment of IR-induced renal injury and fibrosis in clinical practice