On the Microstructure and Properties of Nb-Ti-Cr-Al-B-Si-X (X = Hf, Sn, Ta) Refractory Complex Concentrated Alloys

We studied the effect of the addition of Hf, Sn, or Ta on the density, macrosegregation, microstructure, hardness and oxidation of three refractory metal intermetallic composites based on Nb (RM(Nb)ICs) that were also complex concentrated alloys (i.e., RM(Nb)ICs/RCCAs), namely, the alloys TT5, TT6, and TT7, which had the nominal compositions (at.%) Nb-24Ti-18Si-5Al-5B-5Cr-6Ta, Nb-24Ti-18Si-4Al-6B-5Cr-4Sn and Nb-24Ti-17Si-5Al-6B-5Cr-5Hf, respectively. The alloys were compared with B containing and B free RM(Nb)ICs. The macrosegregation of B, Ti, and Si was reduced with the addition, respectively of Hf, Sn or Ta, Sn or Ta, and Hf or Sn. All three alloys had densities less than 7 g/cm3. The alloy TT6 had the highest specific strength in the as cast and heat-treated conditions, which was also higher than that of RCCAs and refractory metal high entropy alloys (RHEAs). The bcc solid solution Nbss and the tetragonal T2 and hexagonal D88 silicides were stable in the alloys TT5 and TT7, whereas in TT6 the stable phases were the A15-Nb3Sn and the T2 and D88 silicides. All three alloys did not pest at 800 °C, where only the scale that was formed on TT5 spalled off. At 1200 °C, the scale of TT5 spalled off, but not the scales of TT6 and TT7. Compared with the B free alloys, the synergy of B with Ta was the least effective regarding oxidation at 800 and 1200 °C. Macrosegregation of solutes, the chemical composition of phases, the hardness of the Nbss and the alloys, and the oxidation of the alloys at 800 and 1200 °C were considered from the perspective of the Niobium Intermetallic Composite Elaboration (NICE) alloy design methodology. Relationships between properties and the parameters VEC, δ, and Δχ of alloy or phase and between parameters were discussed. The trends of parameters and the location of alloys and phases in parameter maps were in agreement with NICE.

On the Microstructure and Properties of the Nb-23Ti-5Si-5Al-5Hf-5V-2Cr-2Sn (at.%) Silicide-Based Alloy—RM(Nb)IC

The microstructure, isothermal oxidation, and hardness of the Nb-23Ti-5Si-5Al-5Hf-5V-2Cr-2Sn alloy and the hardness and Young’s moduli of elasticity of its Nbss and Nb5Si3 were studied. The alloy was selected using the niobium intermetallic composite elaboration (NICE) alloy design methodology. There was macrosegregation of Ti and Si in the cast alloy. The Nbss, aNb5Si3, gNb5Si3, and HfO2 phases were present in the as-cast or heat-treated alloy plus TiN in the near-the-surface areas of the latter. The vol.% of Nbss was about 80%. There were Ti- and Ti-and-Hf-rich areas in the solid solution and the 5-3 silicide, respectively, and there was a lamellar microstructure of these two phases. The V partitioned to the Nbss, where the solubilities of Al, Cr, Hf, and V increased with increasing Ti concentration. At 700, 800, and 900 °C, the alloy did not suffer from catastrophic pest oxidation; it followed parabolic oxidation kinetics in the former two temperatures and linear oxidation kinetics in the latter, where its mass change was the lowest compared with other Sn-containing alloys. An Sn-rich layer formed in the interface between the scale and the substrate, which consisted of the Nb3Sn and Nb6Sn5 compounds at 900 °C. The latter compound was not contaminated with oxygen. Both the Nbss and Nb5Si3 were contaminated with oxygen, with the former contaminated more severely than the latter. The bulk of the alloy was also contaminated with oxygen. The alloying of the Nbss with Sn increased its elastic modulus compared with Sn-free solid solutions. The hardness of the alloy, its Nbss, and its specific room temperature strength compared favourably with many refractory metal-complex-concentrated alloys (RCCAs). The agreement of the predictions of NICE with the experimental results was satisfactory.

Research of Heat Resistance and Thermophysical Properties of the Diffusion Zone Formed by Annealing by Contact Melting Mode of the Layered Metal-Intermetallic Composite of the Cu-Al System

The results of studying the effect of isothermal annealing on structural, phase transformations, and thermal diffusivity in the diffusion zone of a Cu-Al layered metal-intermetallic composite (LMIC), obtained using technology including explosion welding, pressure treatment and heat treatment, are presented. It was found that, at 530 °C (the highest temperature, excluding the formation of a liquid phase in this system) with a holding time of up to 1000 h, there are no structural phase transformations in the Al (Cu)/CuAl2 metal-intermetallic composition, and a slight increase in its mass is associated with the formation of a thin dense protective oxide film on the surface. The thermal diffusivity of Cu-Al LMIC, obtained after removal of copper residues from the surface of the diffusion zone, is 50–60 W/m×K, which is significantly lower than that of copper (410 W/m×K) and aluminum (220 W/m×K).

Refractory Metal (Nb) Intermetallic Composites, High Entropy Alloys, Complex Concentrated Alloys and the Alloy Design Methodology NICE—Mise-en-scène † Patterns of Thought and Progress

The paper reflects on the usefulness of the alloy design methodology NICE (Niobium Intermetallic Composite Elaboration) for the development of new Nb-containing metallic ultra-high-temperature materials (UHTMs), namely refractory metal (Nb) intermetallic composites (RM(Nb)ICs), refractory high entropy alloys (RHEAs) and refractory complex concentrated alloys (RCCAs), in which the same phases can be present, specifically bcc solid solution(s), M5Si3 silicide(s) and Laves phases. The reasons why a new alloy design methodology was sought and the foundations on which NICE was built are discussed. It is shown that the alloying behavior of RM(Nb)ICs, RHEAs and RCCAs can be described by the same parameters. The practicality of parameter maps inspired by NICE for describing/understanding the alloying behavior and properties of alloys and their phases is demonstrated. It is described how NICE helps the alloy developer to understand better the alloys s/he develops and what s/he can do and predict (calculate) with NICE. The paper expands on RM(Nb)ICs, RHEAs and RCCAs with B, Ge or Sn, the addition of which and the presence of A15 compounds is recommended in RHEAs and RCCAs to achieve a balance of properties.

PHASE FORMATION IN CONTACT LAYERS DURING CONTACT MELTING OF COPPER AND ALUMINUM

В настоящей работе предпринимается попытка выявить особенности структуры контактных прослоек при контактном плавлении меди с алюминием марки АМГ-2 (состав мас. %: Mg - 1,8-2,8, Mn - 0,2-0,6, Cu - 0,1, Zn - 0,2, Fe - 0,4, Si - 0,4, остальное - алюминий) и алюминий-литиевым сплавом ( Al - 0,4 ат. % Li ). Изучение контактного плавления в системе Cu / Al важно для разработки технологии контактно-реактивной пайки, получения слоистых интерметаллических композиционных материалов, создания теплоотводов полупроводниковых приборов, моделирование дендритообразования. Установлено, что в контактных прослойках образуются интерметаллиды, влияющие на хрупкость соединений меди с алюминием и эвтектические структуры. In this work, an attempt is made to identify the features of the structure of contact layers during the contact melting of copper with aluminum brand AMG-2 (mass composition, %: Mg - 1,8 - 2,8, Mn - 0,2 - 0,6, Cu - 0,1, Zn - 0,2, Fe - 0,4, Si - 0,4, rest - aluminum) and aluminum-lithium alloy (Al - 0,4 wt.% Li). The study of contact melting in the system is important for development of contact-reactive soldering technology, obtaining layered intermetallic composite materials, creating heat sinks for semiconductor devices, modeling dendrite formation. It was established that intermetallic compounds are formed in the contact layers, which affect the brittleness of copper-aluminum compounds and eutectic structures.

RESEARCH OF THE CORROSION RESISTANCE OF BIMETALLIC TRANSITION ADLEMENTS AD1 + ST3

The corrosion resistance of AD1 + St3 bimetal and a layered intermetallic composite of the same system was studied. It has been established that under the influence of an aggressive environment simulating the effect of a moist marine atmosphere, the presence of intermetallic inclusions and interlayers at the junction boundary helps to slow down corrosion processes.

FORMATION OF A MULTI-LAYERED TITANO-STEEL INTERMETALLIC COMPOSITE

The work presents the results of studies on the formation of intermetallic layers in a five-layer explosion-welded composite titanium VT-20+steel 08Cr18Ni10Ti after heat treatment at temperatures of 800, 850 and 900 °C and holding times of 4 and 10 hours. The structure, microhardness, chemical composition of the diffusion zones of the composite were studied using optic, electron microscopy and X-ray spectral analysis.

A Study of the Effect of 5 at.% Sn on the Micro-Structure and Isothermal Oxidation at 800 and 1200 °C of Nb-24Ti-18Si Based Alloys with Al and/or Cr Additions

This paper presents the results of a systematic study of Nb-24Ti-18Si based alloys with 5 at.% Sn addition. Three alloys of nominal compositions (at.%), namely Nb-24Ti-18Si-5Cr-5Sn (ZX4), Nb-24Ti-18Si-5Al-5Sn (ZX6), and Nb-24Ti-18Si-5Al-5Cr-5Sn (ZX8), were studied to understand how the increased Sn concentration improved oxidation resistance. In all three alloys there was macrosegregation, which was most severe in ZX8 and the primary βNb5Si3 transformed completely to αNb5Si3 after heat treatment. The Nbss was not stable in ZX6, the Nb3Sn was stable in all three alloys, and the Nbss and C14-NbCr2 Laves phase were stable in ZX4 and ZX8. The 5 at.% Sn addition suppressed pest oxidation at 800 °C but not scale spallation at 1200 °C. At both temperatures, a Sn-rich area with Nb3Sn, Nb5Sn2Si, and NbSn2 compounds developed below the scale. This area was thicker and continuous after oxidation at 1200 °C and was contaminated by oxygen at both temperatures. The contamination of the Nbss by oxygen was most severe in the bulk of all three alloys. Nb-rich, Ti-rich and Nb and Si-rich oxides formed in the scales. The adhesion of the latter on ZX6 at 1200 °C was better, compared with the alloys ZX4 and ZX8. At both temperatures, the improved oxidation was accompanied by a decrease and increase respectively of the alloy parameters VEC (Valence Electron Concentration) and δ, in agreement with the alloy design methodology NICE (Niobium Intermetallic Composite Elaboration). Comparison with similar alloys with 2 at.% Sn addition showed (a) that a higher Sn concentration is essential for the suppression of pest oxidation of Nb-24Ti-18Si based alloys with Cr and no Al additions, but not for alloys where Al and Cr are in synergy with Sn, (b) that the stability of Nb3Sn in the alloy is “assured” with 5 at.% Sn addition, which improves oxidation with/out the presence of the Laves phase and (c) that the synergy of Sn with Al presents the “best” oxidation behaviour with improved scale adhesion at high temperature.