AlCrFeNiTi_0.5Mo_x (x = 0, 0.1, 0.2, 0.3 and 0.4) high-entropy alloys (HEAs) were prepared by arc melting and investigated in terms of microstructure, mechanical properties, and wear resistance. All the as-cast HEAs are composed of one disordered BCC phase (BCC) and one ordered BCC (B2) phase. The added Mo acted as a solid solute in the BCC phase. When Mo molar ratio was more than 0.3, a new type or modified BCC phase formed at the grain boundary, which was enriched with both Mo and Ti. Strength, hardness, and ductility of AlCrFeNiTi_0.5 were markedly increased with the Mo addition. The increase in hardness was caused by Mo-solute strengthened disordered BCC phase and precipitation-strengthening by precipitation of hard (Mo, Ti)-rich BCC phase at grain boundaries. The improved ductility was largely attributed to reduced interfacial lattice mismatch between the BCC and B2 phase. The Mo-free AlCrFeNiTi_0.5 showed the highest wear loss, about 2.5 times as large as that of AlCrFeNiTi_0.5Mo_0.4 alloy, which possessed the highest hardness, yield strength, maximum strength, and ductility.

Precipitation strengthening of body-center cubic (A2) alloys via ordered B2 nanoprecipitates is expected to achieve a desirable combination of strength and ductility. In this work, the A2/B2 configuration is manipulated by adjusting Fe content in medium-entropy AlCrFe_xNi (x = 0, 0.5, 1.0, 1.5, 2.0, 2.5 and 3.0) alloys fabricated via arc-melting for improved mechanical properties and wear resistance. As Fe content increases, the fraction of A2 phase increases, and A2 nanoprecipitates in the B2 matrix change to a weave-like A2/B2 structure. Continuously increasing Fe content leads to a mixture of BMAP (B2 matrix with A2 precipitates) and AMBP (A2 matrix with B2 precipitates), and finally to a complete AMBP structure. The yield strength decreases and fracture strain increases with increasing Fe content except x = 0. The alloy of x = 0 displays slightly higher hardness because of its relatively brittle B2 matrix. Cracks tend to propagate along A2/B2 interfaces. AMBP structure exhibits greater toughness than the BMAP structure. The alloy of x = 0 displays the second-greatest wear volume loss due to its relatively brittle B2 matrix. When Fe is added, the wear volume loss decreases considerably but shows a trend of an upward parabola with respect to the Fe content. After achieving the highest volume loss at x = 1.5 with a mixture of AMBP and BMAP, the volume loss decreases again. A completely uniform AMBP structure at x = 3.0 shows the least volume loss.

Microstructure, mechanical properties, wear resistance, corrosion and corrosive wear resistance of AlCrFeNiW_x (x = 0, 0.1, 0.2, 0.3 and 0.4) medium-entropy alloys (MEAs) prepared by vacuum arc melting process were investigated. Results of the study show that the microstructure of as-cast AlCrFeNiW_x alloys is composed of one disordered Fe-Cr rich BCC phase (A2) and one ordered NiAl-rich (B2) phase when x = 0 and 0.1; W particles appear when x ≥ 0.2. Hardness and strength of AlCrFeNi alloy are markedly increased by the W addition. The strengthening mechanisms include solid-solution strengthening, nano-sized precipitation strengthening and second phase strengthening. The excellent ductility of AlCrFeNi is retained with minor W addition (x ≤ 0.2) but it considerably declines as more W is added, resulting from the precipitation of excessive large-sized W particles. W addition improves the pitting resistance and passivation property of AlCrFeNi HEA in 3.5 wt. % NaCl solution. It is shown that AlCrFeNiW_0.3 possesses the highest corrosion resistance, as reflected by the highest E_corr and the lowest I_corr. Tungsten notably enhances the resistance of this HEA to wear and corrosive wear. AlCrFeNiW_0.4 with the highest strength and hardness exhibits the lowest wear volume loss under both dry and corrosive wear conditions.

The addition of third elements may help transform brittle D0₂₂-structured lightweight Al₃Ti to a relatively ductile L1₂-structured (Al, M)₃Ti (where M represents the third elements), thus increasing the ductility at the expense of hardness. Such a transformation could benefit the wear resistance of the alloy due to improved toughness if a proper balance between the hardness and ductility is achieved. In this work, a D0₂₂-predominant Al₃Ti alloy (S-Al₃Ti) and an L1₂-predominant (Al, Fe)₃Ti alloy (S-Al₆₇Ti₂₅Fe₈) were fabricated by arc melting. Change in wear resistance, corresponding to a D0₂₂-to-L1₂ transformation, caused by the addition of Fe as a representative third element, was investigated and compared with the wear resistance of a commercial Al-matrix composite reinforced by 30 wt.% SiC particles (S-Al/SiC_p) as a reference material. It was observed that wear of the S-Al₃Ti resulted from abrasion involving synergistic oxidation, leading to a larger volume loss. In contrast, the softer S-Al₆₇Ti₂₅Fe₈ showed enhanced wear resistance, benefiting from improved toughness with reasonable hardness. During the wear testing, both the alloys exhibited better performance than S-Al/SiC_p, a well-known lightweight composite. This study highlights that D0₂₂-to-L1₂ transformation enhances wear resistance due to increased toughness which can be adjusted using the addition of a third element.

316L steel is widely used in various industries and is also one of the metallic materials used for biomedical applications because of its excellent mechanical properties, corrosion resistance, and biocompatibility. This article reports a comprehensive study on the effects of equal channel angular pressing (ECAP) and subsequent recovery treatment on the microstructure and the mechanical, tribological, and corrosion properties of 316L. The process includes an initial annealing at 1050 °C for 2 h to obtain a homogenous microstructure, ECAP at room temperature with a 120° inner angle, and subsequent recovery treatment at 340 °C for 1 h. The microstructure was investigated with an optical microscope and a transmission electron microscope. The mechanical properties were evaluated with hardness and compression tests. The corrosion behavior was analyzed with dynamic polarization tests. The wear test was performed using a scratching tester, and the volume loss was measured with a profilometer. The results of the study demonstrate that the ECAP–recovery sample exhibits improved properties compared to both the annealed sample and the ECAP sample. The corrosion tests show that the ECAP sample has a corrosion resistance higher than that of the annealed sample but lower than that of the ECAP–recovery sample. The ECAP–recovery sample shows the highest wear resistance and corrosive wear resistance among the three samples.