Influence Of Pre-deformation On The Microstructure And Properties Of The Bulk Metallic Glasses

In this paper, we have investigated the RE65Co25Al10(RE=Ce, La, Pr, Sm, Gd) and Cu47.5Zr47.5Al5 metallic glasses, respectively. The effects of the pre-compression treatment on the microstructure, mechanical properties, and corrosion resistance in the seawater solution of the metallic glass at room temperature have been investigated by using X-ray diffraction(XRD), differential scanning calorimetry(DSC), electrochemical polarization measurement, field emission scanning electron microscope(FESEM), transmissionelectron microscope(TEM) and computer controlled electronic mechanical testing system.(1) The effects of the pre-compression treatment on the microstructure, mechanical properties and corrosion resistance of the metallic glasses at room temperature:The results indicate that the pressure treatment causes the changes of microstructure, and then results in the variation of the glass transition temperature and supercooled liquid region of the RE65Co25Al10 metallic glass. The RE65Co25Al10 metallic glass treated by pre-compression in 16 kN exhibits low self-corrosion current density and distinct passive region, indicating the higher seawater corrosion resistance. However, the corrosion resistance of the RE65Co25Al10 metallic glass becomes poor with increasing pre-compression stress to 30 kN. The discussion of the corrosion mechanism has been made based upon the structural relaxation and bonding force of the matrix elements and oxygen during the electrochemical corrosion process. The results of the RE65Co25Al10 bulk metallic glasses(BMGs) indicate that the pre-compression treatment induces the microstructure changes or partial crystallization, which can improve the thermal stability and significantly enhance the mechanical properties of the RE65Co25Al10 BMGs. The BMG-based composite with nanocrystals under the pre-compression stress of 450 MPa shows the exciting mechanical properties with the compressive fracture strength of 832 MPa and microhardness of 261 HV. The BMG treated by the lower pre-compression stress of 250 MPa exhibits the inspiring corrosion resistance in the seawater solution, as indicated by the low corrosion current density and high corrosion potential, combined with microstructural observation. However, the corrosion resistance of the RE65Co25Al10 BMG composite becomes poor under the pre-compression stress of 450 MPa. The discussions have been made based upon the short-range order, free-volume content and nanocrystal precipitation under the pre-compression treatment. And the observed results of the Cu47.5Zr47.5Al5 BMGs indicate that the microstructure changes or partial CuZr nanocrystallization can be induced by the pre-compression treatment, which can improve the thermal stability and significantly enhance the mechanical properties of the Cu47.5Zr47.5Al5 BMGs. The 850 MPa as-pressed Cu47.5Zr47.5Al5 BMG shows the highest thermal stability and the BMG-based composite with nanocrystals under the pre-compression stress of 1415 MPa shows the enhanced mechanical properties with the compressive fracture strength of 1620 MPa and microhardness of 715 HV. In addition, the 250 MPa as-pressed specimen exhibits the superior corrosion resistance in the seawater solution. And the corrosion resistance of the as-pressed samples shows the increased trend with increasing the pre-compression. The corrosion resistance of the as-cast Cu47.5Zr47.5Al5 BMG composite becomes excellent. The reasons can be explained by the least free-volume content, homogeneous CuZr-nanocrystal precipitation and surface element content changes induced by the pre-compression treatment. The proper pre-compression design can be beneficial for improving the practical application of metallic glasses.(2) The correlation analysis about the effect of annealing treatment and pre-compression on the microstructure and properties of Cu47.5Zr47.5Al5 BMGs:The effect of annealing treatment on the microstructure and properties of the Cu47.5Zr47.5Al5 BMGs is similar with the pre-compression treatment. The 673 K annealing treatment does not change the amorphous structure of the Cu47.5Zr47.5Al5 BMG, but the microstructure changes under the certain temperature. While the annealed Cu47.5Zr47.5Al5 specimens at 723 K and 753 K lose the typical amorphous structure and the samples almost crystallized completely, the crystallization products are Cu10Zr7 and CuZr2 phases.The annealing treatment decreases the GFA and the thermal stability of the Cu47.5Zr47.5Al5 BMGs, and the 673 K annealed sample shows the excellent mechanical properties, which is similar to the results of the pre-compression treatment. And there is a huge difference in improving the mechanical properties of the Cu47.5Zr47.5Al5 BMGs between the crystallization products of the annealing treatment and pre-compression treatment. The mechanical performance of the crystallization products after annealing treatment is very poor.The annealing and pre-compression treatment can both improve the seawater corrosion resistance of the Cu47.5Zr47.5Al5 BMGs significantly and the influence of the annealing treatment on improving the corrosion resistance is superior to the pre-compression treatment.