Microstructure and Oxidation Behavior of Nb-Si-Based Alloys for Ultrahigh Temperature Applications: A Comprehensive Review

Nb-Si-based superalloys are considered as the most promising high-temperature structural material to replace the Ni-based superalloys. Unfortunately, the poor oxidation resistance is still a major obstacle to the application of Nb-Si-based alloys. Alloying is a promising method to overcome this problem. In this work, the effects of Hf, Cr, Zr, B, and V on the oxidation resistance of Nb-Si-based superalloys were discussed. Furthermore, the microstructure, phase composition, and oxidation characteristics of Nb-Si series alloys were analyzed. The oxidation reaction and failure mechanism of Nb-Si-based alloys were summarized. The significance of this work is to provide some references for further research on high-temperature niobium alloys.

Microstructure and Oxidation Behavior of Metal-Modified Mo-Si-B Alloys: A Review

With the rapid development of the nuclear industry and the aerospace field, it is urgent to develop structural materials that can work in ultra-high temperature environments to replace nickel-based alloys. Mo-Si-B alloys are considered to have the most potential for new ultra-high temperature structural material and are favored by researchers. However, the medium-low temperature oxidizability of Mo-Si-B alloys limits their further application. Therefore, this study carried out extensive research and pointed out that alloying is an effective way to solve this problem. This work provided a comprehensive review for the microstructure and oxidation resistance of low silicon and high silicon Mo-Si-B alloys. Moreover, the influence of metallic elements on the microstructure, phase compositions, oxidation kinetics and behavior of Mo-Si-B alloys were also studied systematically. Finally, the modification mechanism of metallic elements was summarized in order to obtain Mo-Si-B alloys with superior oxidation performance.

Rare Earth Elements Enhanced the Oxidation Resistance of Mo-Si-Based Alloys for High Temperature Application: A Review

Traditional refractory materials such as nickel-based superalloys have been gradually unable to meet the performance requirements of advanced materials. The Mo-Si-based alloy, as a new type of high temperature structural material, has entered the vision of researchers due to its charming high temperature performance characteristics. However, its easy oxidation and even "pesting oxidation" at medium temperatures limit its further applications. In order to solve this problem, researchers have conducted large numbers of experiments and made breakthrough achievements. Based on these research results, the effects of rare earth elements like La, Hf, Ce and Y on the microstructure and oxidation behavior of Mo-Si-based alloys were systematically reviewed in the current work. Meanwhile, this paper also provided an analysis about the strengthening mechanism of rare earth elements on the oxidation behavior for Mo-Si-based alloys after discussing the oxidation process. Furthermore, the research focus about the oxidation protection of Mo-Si-based alloys in the future was prospected to expand the application field.

Laser based manufacturing of titanium aluminides

Lightweight titanium aluminides (TiAl, ρ = 3.9 – 4.1 g/cm3) gain in importance as high temperature structural material. The known properties like high strength and creep resistance combined with high corrosion and wear are of continuous interest for turbomachinery applications like low pressure turbine blades. Additive manufacturing (AM) provides the possibility for near-net-shape production of functional complex parts and can contribute to reduce consumption and costs of material, tooling and finishing. The typical high brittleness and oxygen affinity of TiAl cause special requirements for processing this material with AM. In this work, recent progress in Additive Manufacturing of the TiAl alloys of the nominal compositions Ti-43.5Al-4Nb-1Mo-0.1B (at.-percent, TNM™-B1), Ti-48Al-2Cr-2Nb (at.-percent, GE4822) and Ti-45Al-2Nb-2Mn-0.8B (at.-percent, 4522XDTM) is presented. Microstructures resulting from both Laser Powder Bed Fusion (LPBF) and Direct Laser Deposition (DED) are compared with respect to the characteristics of the manufacturing processes. Hardness measurements according to Vickers are performed, and pressure strength tests are performed on selected samples. The crack-free additive manufacturing of complex geometries made of TiAl is demonstrated as well as an approach for manufacturing hybrid parts combining DED and LPBF.

Hypereutectic Al2O3/YAG/ZrO2 In Situ Composite Prepared by Horizontal Laser Zone Melting

Al2O3/YAG/ZrO2 eutectic in situ composite has now been considered as the new generation of high-temperature structural material due to its excellent performance even close to its melting point. In this work, hypereutectic Al2O3/YAG/ZrO2 in situ composite is manufactured by the horizontal laser zone melting technique. The relationship between the solidification microstructure and the solidification parameters is studied. The minimum lamellar spacing is as finer as 0.20 μm when the laser scanning rate is 800 μm/s. Compared with eutectic Al2O3/YAG/ZrO2, hypereutectic exhibits more regular and finer microstructure at the similar conditions. Meanwhile, it is found that the lamellar spacing remains almost as constant at a certain high solidification velocity. The maximum hardness and fracture toughness are 15.9 GPa and 4.2 MPa · m1/2, respectively.

Interface Migration with Segregation in MoSi2-Based Lamellar Alloy Simulated by Phase-Field Method

MoSi2–based alloys are attracting attention as ultra-high temperature structural material for super-high efficiency gas turbine power generation systems. In this study, the effects of Cr-and Zr-addition on interface migration in MoSi2/NbSi2 lamellar silicide were examined by phase field simulations employing the segregation energies evaluated by the first principles calculation in addition to thermodynamic free energy in order to take into account the chemically-driven interfacial segregation. The simulation results indicate that both Cr and Zr can segregate at the lamellar interface to suppress its migration, and the Zr-addition is more effective to lower the interface migration rate than the Cr-addition owing to its higher segregation energy.

Fatigue Crack Thresholds Significantly Affected by Thermo-Mechanical Loading Histories in an Austenitic and a Ferritic Low Alloy Steel

High cycle thermal fatigue failure of pipes induced by fluid temperature change is one of interdisciplinary issues to be concerned for long term structural reliability of high temperature structural material and components in energy systems. In order to get basic understanding on this article. the fatigue crack propagation tests were carried out in a low alloy steel and an austenitic stainless steel those were subjected to typical kinds of thermo-mechanical loading histories those included a simulated weld repair process. It was shown experimentally that the thermo-mechanical histories left their individual effects along the prior fatigue crack wake, resulting in significant change in the fatigue crack threshold. Some proposes are presented to predict those history effects.

Effect of Hot Processing Parameters on the Deformation Behavior of Superalloy GH4169

Superalloy GH4169 as one of high temperature structural material is widely used in aviation industry. Isothermal compression of superalloy GH4169 has been conducted on Gleebe-1500D hot simulation at the deformation temperatures ranging from 950°C to 1100°C,the strain rates ranging from 0.01s-1to 10s-1, and the height reduction of 50%. Effect of processing parameters ,i.e. deformation temperature, strain rate and strain, on the hot deformation behaviors of superalloy GH4169 was studied. The research shows that the fine dynamic recystallization grains could be obtained at the condition of high deformation temperature and low strain rate. Constitutive equation of superalloy GH4169 was established by experimental data. Error analysis showed that calculated stress values by the established constitutive equation were coincident with experimental data well, and it provided the theory basis to optimize forging processing of superalloy GH4169.

Research on Manufacturing Process of Carbon-Carbon Composites as Ablation Resistance Materials

C/C composites are being used as high-temperature structural material due to the superior characteristics of low density, high specific strength, high thermal conductivity, low thermal expansion coefficient and excellent anti-ablation. The state of research into the manufacturing processes of Carbon-Carbon composites is critically reviewed with emphasis in this paper. The processes include several kinds of methods, for example, CVD, CVI, Liquid Impregnation and etc. And the usages of some corresponding methods in manufacturing Carbon-Carbon materials as ablation resistant materials are shown in this paper too. It will provide the references for the further development of weaponry materials in the coming years.