Microstructures and properties of CuZrAl and CuZrAlTi medium entropy alloys prepared by mechanical alloying and spark plasma sintering

Equiatomic CuZrAl and CuZrAlTi medium entropy alloys were designed and synthesized by mechanical alloying and spark plasma sintering technique. The alloying behavior, phase evolutions, microstructures and properties of samples were investigated by X-ray diffraction, differential scanning calorimetry, field emission scanning electron microscopy, microscopy/Vickers hardness testing and electrochemical polarization measurement. The results indicate that the final products of as-milled alloys consist of amorphous phases. Ti addition improves the glass forming ability of as-milled alloys. The as-sintered CuZrAl alloy contains face-centered cubic (fee) solid solution, Al1.05 Cu0.95 Zr and AlZr2 phases at different sintering temperatures. With Ti addition, the as-sintered sample is only composed of intermetallics at 690 °C, while feel, fcc2 and CuTi3 phases are formed at 1100 °C. CuZrAlTi-1100 °C alloy exhibits the highest hardness value of 1173 HV0.2 owing to the high sintering density, solid solution strengthening and homogeneous precipitation of nano-size crystalline phase. CuZrAlTi-690 °C alloy presents a similar corrosion resistance with 304L stainless steel in seawater solution and further possesses the lower corrosion rate.