TiAl alloys possess excellent properties, such as low density, high specific strength, high elastic modulus, and high-temperature creep resistance, which allows their use to replace Ni-based superalloys in some high-temperature applications. In this work, the traditional TiAl alloy Ti-48Al-2Nb-2Cr (Ti4822) was alloyed with additional Nb and fabricated using laser metal deposition (LMD), and the impacts of this additional Nb on the microstructure and mechanical and tribological properties of the as-fabricated alloys were investigated. The resulting alloys mainly consisted of the γ phase, trace β₀ and α₂ phases. Nb was well distributed throughout the alloys, while Cr segregation resulted in the residual β₀ phase. Increasing the amount of Nb content increased the amount of the γ phase and reduced the amount of the β₀ phase. The alloy Ti4822-2Nb exhibited a room-temperature (RT) fracture strength under a tensile of 568 ± 7.8 MPa, which was nearly 100 MPa higher than that of the Ti4822-1Nb alloy. A further increase in Nb to an additional 4 at.% Nb had little effect on the fracture strength. Both the friction coefficient and the wear rate increased with the increasing Nb content. The wear mechanisms for all samples were abrasive wear with local plastic deformation and oxidative wear, resulting in the formation of metal oxide particles.

High chromium cast iron (HCCI) is widely used in the manufacturing of equipment parts in the fields of mining, cement, electric power, metallurgy, the chemical industry, and paper-making because of its excellent wear and corrosion resistance. Although the microstructure and properties of HCCI can be modified by controlling the casting and heat treatment process, alloying is still the most basic and important method to improve the properties of HCCI. There are about 14 common alloying elements in HCCI, among which nickel, copper, and manganese are typical austenite stabilizing elements, which can increase austenite content and matrix electrode potential. The addition of elements such as silicon, nitrogen, boron, and rare earth (RE) is often small, but it has a significant effect on tailoring the microstructure, thereby improving wear resistance and impact toughness. It was thought that after years of development, the research on the role of the above elements in HCCI was relatively complete, but in the past 5 to 10 years, there has been a lot of new research progress. Moreover, the current development situation of HCCI is still relatively extensive, and there are still many problems regarding the alloying of HCCI to be further studied and solved. In this paper, the research results of austenitic stabilizing elements and modifying elements in HCCI are reviewed. The existing forms, distribution law of these elements in HCCI, and their effects on the microstructure, hardness, wear resistance, and corrosion resistance of HCCI are summarized. Combined with the current research situation, the future research and development direction of HCCI alloying is prospected.

This study facilitates the data-driven design of novel cast TiAl alloys by systematically investigating the critical elements and their interactions affecting room-temperature (RT) tensile properties by the machine learning method based on SHAP analysis. Comparative analysis of three algorithms within the training dataset proved the random forest regression (RFR) as the optimal modeling approach. To evaluate model performance and prevent overfitting, leave-one-out cross-validation (LOOCV) was simultaneously implemented during training. All the three well-trained models demonstrated robust predictive capabilities for ultimate tensile strength (UTS), elongation (EL), and yield strength (YS). Detailed investigation on both the magnitude and directionality of feature importance and interaction disclosed distinct elemental influences: B, C, and Nb predominantly improved UTS and YS, while Cr, Mn, and Al positively affected EL. The highly probable direction of feature interaction between two different elements on the RT tensile properties of cast TiAl alloys was basically revealed. Notably, Al–B interactions enhance UTS at Al < 45.5 at%; Cr–Mn synergistically improves EL when Cr > 1 at%; both Al–B and Al–C interactions boost YS within 44–46 at% Al. Despite a slight distinction in casting technology, this research established a qualitative relationship between the chemical elements and the RT tensile properties of TiAl alloys, providing design recommendations for cast TiAl alloys with excellent RT tensile properties.

As an advanced high-temperature structural material, TiAl alloy, is often used in the manufacturing of hot-end components of aviation and aerospace engines. However, it is difficult to increase the strength at high temperature, which limits its wider application. Adopting composite material technology is one of the effective ways to improve the comprehensive mechanical properties of TiAl alloy. In this work, by adding 3 wt.% SiC micro-particles to Ti-47.5Al-7Nb-0.4W-0.1B (at.%) pre-alloyed powder, a core-shell structure dual-MAX-phase high-temperature strengthened TiAl matrix composite (also known as TiAl-SiC composite) was prepared by combining powder metallurgy and hot forging. The microstructure and high-temperature compressive properties of the prepared TiAl-SiC composites were studied and compared with TiAl alloy prepared by the same process, and the microstructural characteristics of the TiAl-SiC composite and its microstructure evolution during processing were revealed. The results show that the matrix of as-sintered TiAl-SiC composites was mainly composed of γ phase and a small amount of Ti₂AlC particles, while the reinforcement phase was a dual-MAX-phase core-shell structure, which was mainly composed of core Ti₂AlC phase, shell Ti₃SiC₂ phase, and small Ti₂AlC particles distributed in the outer layer. After hot forging, the microstructure of TiAl-SiC composite became more compact, finer, and more uniform; the phase composition was almost not changed, but the content of Ti₂AlC, Ti₃SiC₂, and TiB₂ phases increased significantly; the content of C in each constituent phase decreased obviously, and a granular Si-rich phase was generated in the core of the reinforcement phase. The yield strength of the as-forged TiAl-SiC composite was significantly higher than that of the as-forged TiAl alloy at temperature higher than 859 °C. This is because the core-shell structure dual MAX phases can effectively reduce the softening rate of TiAl alloy in the range of 800–900 °C, thus playing a strengthening role and increasing the service temperature of TiAl alloy.