Effect of Cryogenic-Thermal Cycling Treatment on the Tribological Properties of Fe-Based Bulk Amorphous Alloy

In many amorphous alloy systems, Fe-based amorphous alloy has been considered as a wear-resistant material due to its relatively low raw material cost, outstanding high hardness, and unique wear resistance and anti-corrosion, showing broad development prospects. However, intrinsic brittleness restricts its potential structural engineering application. Recently, a new process called deep cryogenic cycling treatment (DCT) has been applied as a simple method to improve the plasticity and toughness of bulk amorphous alloys. But there are few reports about the DCT of Fe-based bulk amorphous alloys. Moreover, the effect of the thermal cycling treatment on the tribological properties of amorphous alloys is not clear. Therefore, in this study, Fe-based bulk amorphous alloy Fe₄₁Co₇Cr₁₅Mo₁₄C₁₅B₆Y₂ was prepared using arc melting and copper mold injecting-casting to fabricate amorphous rods. Then the as-cast FeCoCrMoCBY amorphous alloy rod was prepared for processing by the cryogenic-thermal cycling treatment. FeCoCrMoCBY bulk amorphous alloy was cryogenic-thermal treated by 30 and 60 cycles, respectively. After comparing with the as-cast FeCoCrMoCBY amorphous alloy, the effects of cryogenic-thermal cycling treatment on the microstructure, wear resistance and wear mechanism of Fe-based bulk amorphous alloys were studied in order to further promote the tribological performance of amorphous materials and coatings. The effect of cryogenic-thermal cycling process on the friction and wear performance was investigated through the reciprocating friction and wear experiment on CFT-I seawater environment friction and wear test system. The XRD patterns showed that there was no detectable structure evolution of the Fe-based amorphous alloy after the cryogenic-thermal cycling treatment. And the cryogenic-thermal cycling treatment had little influence on the thermal stability of FeCoCrMoCBY amorphous alloy on account of nearly the same glass transition temperature (T_g) and crystallization temperature (T_x). By the nanoindentation tests, the amorphous alloy was softened obviously after cryogenic-thermal treatment with 30 cycles. The average hardness of the amorphous alloy decreased from 16.06 GPa (as-cast) to 14.06 GPa, and the elastic modulus decreased from 241 GPa (as-cast) to 216 GPa. The average friction coefficient and wear rate of the Fe-based bulk amorphous alloy decreased first and then increased with the increase of cryogenic-thermal cycles and applied load. When 30 cycles and 30 N load were applied, the average friction coefficient was reduced from 0.77 to 0.72, which was the minimum friction coefficient in all samples. And the wear rate decreased 13.3% than that of as-cast sample, which was the minimum wear rate 1.04×10⁻⁶ mm³/(m·N) in all samples. So, the cryogenic-thermal cycling treatment was beneficial to reduce friction coefficient and wear rate of amorphous alloys. The worn track observation showed that the dominant wear mechanism of the as-cast Fe-based bulk amorphous alloy was fatigue fracture together with mild abrasive wear. With the increase of cryogenic-thermal cycles, fatigue caused brittle fracture was alleviated and the wear mechanism changed to a combination of abrasive wear and fatigue fracture. Therefore, cryogenic-thermal cycling treatment was an effective method to regulate and control the tribological properties of amorphous metallic materials. Further understanding of cryogenic-thermal cycling treatment will promote the application of amorphous materials in tribology.