Pressure Sensitive Characteristic And Its Influence Factors In Zr-based Bulk Metallic Glasses

Bulk metallic glasses (BMGs) have high strength, wear resistance and corrosionresistance and other excellent performance, which have a great potential application as akind of new structural materials. However, the lack of any significant plastic deformationat room temperature of BMGs is one of the most main obstacles to their practicalapplication. It was found that BMGs was a kind of pressure sensitive material, and thepressure sensitivity index has an important influence on the plastic deformation andfracture characteritics. Deep investigation on the physical nature and influence factor ofpressure sensitivity index is benefitial to understand the deformation mechanism. In thisthesis, by using indentation methods, pressure sensitivity index of Zr-based BMGs wasmeasured. The effects of the structural relaxation and the testing temperature on thepressure sensitivity of BMGs were investigated. Moreover, the effect of external load andstructural relaxation on deformation of BMGs was investigated. The relationship betweenhardness and shear band patterns around the indentation and pressure sensitivity index wasalso analyzed. The main conclusions are as follows:(1) The two kinds of studied Zr-based BMGs were prepared by water-cooled coppermould sucking method. The two kinds of Zr-based BMG were annealedat the temperaturesranging from523to633K, and the BMGs with the different relaxation degrees wereobtained. The DSC tests reveal that structural relaxation degree of the BMGs increaseswith the annealing temperature increasing.(2) The effects of applying load and structural relaxation on pressure sensitivitycharacteristic of BMGs were investigated. It is found that the pressure sensitivity indexincresses with the the increase of the structural relaxation degree for the BMG. Under thesame structural relaxation degree, the friction and the hardness of the BMGs increase withthe increase of the applying load. As the fricion force reaches the critical value, hardnessalso tends to be a constant value. The free volume of BMGs decreased with the relaxationdegree increasing, leading to the increase of hardness. As a result, with the increase of therelaxation degree, the number of shear bands around indentation and the contrast of shearband decrease, but the average of shear-band spacing increases.(3) The effect of the testing temperature (273-373K) on pressure sensitivitycharacteristic of BMGs was investigated. It is found that the testing temperature has a littleinfluence on the pressure sensitivity index of the BMGs. However, the internal heat activation results in the decrease of the hardness and the average of shear-band spacingand the increase of the number of shear bands around indentation as the testingtemperature increases.