Polysilazane‐Type Coatings on Mo–Si–B Alloys: A Thermodynamic Assessment of the Phase Composition

Thermodynamic analysis is conducted to identify the most probable phase composition of a polysilazane‐type coating system on Mo–Mo₃Si(A15)–Mo₅SiB₂(T2) alloy. The Free Gibbs Energy of chemical reactions between these constituents and resulting phases are calculated. Silicon nitrides, silicon oxynitrides, and molybdenum silicides have been found in the phase equilibrium between the gas phase and condensed species of the proposed coating system. Silicon oxynitride and silica as components in the coating system are potential candidates for Mo–Si–B alloy oxidation protection in air at high temperatures.

     

High‐Entropy Alloys: Potential Candidates for High‐Temperature Applications – An Overview

Multi‐principal elemental alloys, commonly referred to as high‐entropy alloys (HEAs), are a new class of emerging advanced materials with novel alloy design concept. Unlike the design of conventional alloys, which is based on one or at most two principal elements, the design of HEA is based on multi‐principal elements in equal or near‐equal atomic ratio. The advent of HEA has revived the alloy design perception and paved the way to produce an ample number of compositions with different combinations of promising properties for a variety of structural applications. Among the properties possessed by HEAs, sluggish diffusion and strength retention at elevated temperature have caught wide attention. The need to develop new materials for high‐temperature applications with superior high‐temperature properties over superalloys has been one of the prime concerns of the high‐temperature materials research community. The current article shows that HEAs have the potential to replace Ni‐base superalloys as the next generation high‐temperature materials. This review focuses on the phase stability, microstructural stability, and high‐temperature mechanical properties of HEAs. This article will be highly beneficial for materials engineering and science community whose interest is in the development and understanding of HEAs for high‐temperature applications.     

Porous TiNi Biomaterial by Self‐Propagating High‐Temperature Synthesis

Porous TiNi shape‐memory alloy (TiNi SMA) bodies with controlled pore structure were produced from the (Ti+Ni) powder mixture by self‐propagating high‐temperature synthesis (SHS) method. The effect of processing variables such as the kind of starting powders, ignition temperature and preheating schedule on the behavior of combustion wave propagation, the formation of phases and pore structure was investigated. The relationship between pore structure and mechanical properties was also investigated. An in vivo test was performed to evaluate bone tissue response and histocompatibility of porous TiNi SMA using 15 New Zealand white rabbits. No apparent adverse reactions such as inflammation and foreign body reaction were noted on or around all implanted porous TiNi SMA blocks. Bone ingrowth was found in the pore space of all implanted blocks.     

Droplet Transport on a Nano‐ and Microstructured Surface with a Wettability Gradient in Low‐Temperature or High‐Humidity Environments

Directional driving of a droplet can be achieved on a gradient‐exhibiting, nanostructured microhump (GNMH) surface at low temperature and high humidity. The GNMH surface is fabricated using a commercial carbon fiber plate with an array of microscale hump structures; nanotechniques are used to form varying nanostructures on the microhump array, producing the micro‐ and nanostructured surface. The different nanostructures result in a wettability gradient along the surface, enabling droplet transport with the help of vibration—even at low temperature or high humidity. In contrast, simply nanostructured surfaces or microstructured surfaces that also have a wettable gradient do not enable droplet transport at low temperature or high humidty. In a range of subzero temperatures or in a range of high‐humidity conditions, the GNMH surface retains its superhydrophobicity and ability for directional droplet transport along its wettability gradient. These results may assist in the design of surfaces required for cold environments, such as microreactors, chemical analytic devices, and sensors.     

轻质高温结构材料--γ-TiAl基合金的研究动向

γ-TiAl基合金被认为是非常有前途的新型轻质高温结构材料,在航空航天、汽车等领域具有广阔的应用前景.简要介绍了γ-TiAl基合金的研究概况,并从高铌合金化、复合化、纳米化等方面着重阐述了其今后的发展趋势.     

镁合金的生物医用研究

镁是可被人体吸收的常量元素,且具有较高的比强度和比刚度,在医用植入材料领域具有广阔的应用前景.综述了镁及镁合金作为医用植入材料的研究现状,并对医用镁及镁合金的表面改性技术进行了简单叙述.     

Semi‐Solid Processing of Tailored Aluminium‐Lithium Alloys for Automotive Applications

This paper describes the development and evaluation of thixoformable Al‐Li‐Mg‐based alloys performed at the collaborative research center SFB 289, RWTH Aachen. Scandium and zirconium were added to AlLi2.1Mg5.5 (A1420) with the aid of DoE (Design of Experiments), and precursor billets were manufactured by pressure induction melting (PIM). To evaluate the thixoformability of the synthesized alloys semi‐solid processed connecting rods were manufactured by the rheo container process (RCP). Subsequent heat treatment raised the mechanical properties to maximum values of tensile strength, 430 MPa, yield strength of 250 MPa, and an elongation to fracture of 13 %. The RCP process was designed for the special requirements of highly reactive alloys. The paper presents the remarkable property and process benefits of the semi‐solid processing of Al‐Li alloys.     

Robust Expandable Carbon Nanotube Scaffold for Ultrahigh‐Capacity Lithium‐Metal Anodes

There has been a renewed interest in using lithium (Li) metal as an anode material for rechargeable batteries owing to its high theoretical capacity of 3860 mA h g^?1. Despite extensive research, modifications to effectively inhibit Li dendrite growth still result in decreased Li loading and Li utilization. As a result, real capacities are often lower than values expected, if the total mass of the electrode is taken into consideration. Herein, a lightweight yet mechanically robust carbon nanotube (CNT) paper is demonstrated as a freestanding framework to accommodate Li metal with a Li mass fraction of 80.7 wt%. The highly conductive network made of sp2‐hybridized carbon effectively inhibits formation of Li dendrites and affords a favorable coulombic efficiency of >97.5%. Moreover, the Li/CNT electrode retains practical areal and gravimetric capacities of 10 mA h cm^?2 and 2830 mA h g^?1 (vs the mass of electrode), respectively, with 90.9% Li utilization for 1000 cycles at a current density of 10 mA cm^?2. It is demonstrated that the robust and expandable nature is a distinguishing feature of the CNT paper as compared to other 3D scaffolds, and is a key factor that leads to the improved electrochemical performance of the Li/CNT anodes.     

Microstructural Design for Enhanced Elevated Temperature Properties in Sand‐castable Magnesium Alloys

The low pressure and gravity casting processing techniques offer the component designer an opportunity to produce pieces with increased complexity over those able to be fabricated via the high pressure die casting route. The design of appropriate microstructures for the enhancement of elevated temperature properties is dependent on the chosen processing route, with the low pressure and gravity techniques allowing for post‐cast manipulation of the microstructure through heat treatment. There are competing microstructural requirements for strength and creep resistance in casting alloys, and the optimised microstructure must, of necessity, be a compromise. The contributions from solid solution strengthening, grain boundaries and precipitation processes are described, with particular reference to elevated temperature magnesium alloys.