Synergetic effect of Si addition on mechanical properties in face-centered-cubic high entropy alloys: A first-principles study

High-entropy alloys (HEA) have been receiving increased attention for their excellent mechanical properties. Our recent study revealed that Si-doped face-centered cubic (FCC) HEAs have great potential to improve both strength and ductility. Here, we carried out first-principles calculations in cooperation with Monte Carlo simulation and structural factor analysis to explore the effect of Si addition on the macroscopic mechanical properties. As a result, Si addition increased the local lattice distortion and the stacking fault energy. Furthermore, the short-range order formation in Si-doped alloy caused highly fluctuated stacking fault energy. Thus, the heterogeneous solid solution states in which low and high stacking fault regions are distributed into the matrix were nucleated. This unique feature in Si-doped FCC-HEA induces ultrafine twin formation in Si-doped alloys, which can be a dominant factor in improving both strength and ductility.

Assessment of the Effects of Si Addition to a New TiMoZrTa System

Ti-based alloys are widely used in medical applications. When implant devices are used to reconstruct disordered bone, prevent bone resorption and enhance good bone remodeling, the Young’s modulus of implants should be close to that of the bone. To satisfy this requirement, many titanium alloys with different biocompatible elements (Zr, Ta, Mo, Si etc.) interact well with adjacent bone tissues, promoting an adequate osseointegration. Four new different alloys were obtained and investigated regarding their microstructure, mechanical, chemical and biological behavior (in vitro and in vivo evaluation), as follows: Ti20Mo7Zr15Ta, Ti20Mo7Zr15Ta0.5Si, Ti20Mo7Zr15Ta0.75Si and Ti20Mo7Zr15TaSi. 60 days after implantation, both in control and experimental rabbits, at the level of implantation gap and into the periimplant area were found the mesenchymal stem cells which differentiate into osteoblasts, then osteocytes and osteoclasts which are involved in the new bone synthesis and remodeling, the periimplant fibrous capsule being continued by newly spongy bone tissue, showing a good osseointegration of alloys. A 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay confirmed the in vitro cytocompatibility of the prepared alloys.

Nutritional and Structural Role of Silicon in Attenuating Aluminum Toxicity in Sugarcane Plants

Purpose: We investigated the interactive role of Si-mediated attenuation to aluminum (Al) toxicity in two sugarcane cultivars (‘CTC9002’ and ‘CTC9003’) grown in hydroponic conditions. Methods: Two pot experiments were distributed in randomized blocks in a factorial design (4 × 2) with four replications. The treatments consisted of 0, 10, 15, and 20 mg L−1 Al (as aluminum sulfate [Al2 (SO4)3·18H2O)], which were combined with the absence and presence of Si [(2.0 mmol L−1 as potassium silicate (K2SiO3)]. Results: Both sugarcane cultivars (‘CTC9002’ and ‘CTC9003’) were affected by Al toxicity (above 10 mg L−1), resulting in nutritional disorders and decreasing plant growth, which were drastically reversed by Si addition in the growth medium. Si supplementation decrease Al concentration and translocation to the shoots of both cultivars when Al and Si were simultaneously supplied in the growth medium. We demonstrated that in shoots of both sugarcane seedlings, Si concentration are positively related to the lignin concentrations (ranging from 12.0% to 41% in cv. ‘CTC9002’ and 12% to 47% in cv. ‘CTC9003’). In addition, Si fertilization enhanced mineral nutrition and use efficiency of macros- and micronutrients, irrespective of the cultivar. Therefore, the use of cultivar ‘CTC9003’ under Si fertilization is more recommended to cope with the adverse effect caused by Al stress. Conclusions: The findings of this study suggest that Si fertilization in sugarcane seedlings is an economic and viable strategy strongly recommended to cope with the adverse effect caused by Al toxicity at concentrations less than 20 mg L−1, which lead to increase the shoot biomass production.

The effect of titanium and silicon addition on phase equilibrium and mechanical properties of CoCrFeMnNi-based high entropy alloy

The effects of Ti and Si addition on the phase equilibrium and mechanical properties of the equiatomic CoCrFeMnNi high entropy alloy (Cantor alloy) were investigated. The phase equilibrium at 1000 °C was determined from the result of X-ray diffraction and electron probe micro-analysis. Ti addition stabilizes the $$\sigma$$ σ phase, A12 phase and C14-Laves phase, while Si addition stabilizes the A13 phase. The phase relationships were represented by projection onto (Co, Fe, Mn, Ni)–Cr–X(Ti or Si) isothermal ternary cross-section at 1000 °C in Co–Cr–Fe–Mn–Ni–X senary system. Tensile tests were conducted on Cantor-based fcc single solid solution alloys with Ti or Si dissolution at room temperature. The 0.2% yield strength and ultimate tensile strength increased with either element addition. The Ti-added alloy showed higher strength than the Si-added alloy. The difference in ductility in the alloys is related to their strain hardening behavior in the higher strain range. Graphic abstract