Research Of Glass-forming Ability And The Nanoindentation Creep Behavior Of Amorphous Alloy

Amorphous alloy is of current interest and significance in materials science and engineering because of its unique features and outstanding mechanical, applicable physical and chemical properties. Amorphous alloy materials have broad application prospects in defense, aerospace, sports, electric undertaking and other fields. The study on the glass transition of amorphous alloy and nanoindentation creep behavior are both popular direction in materials science recently. While a amount of amorphous alloy system were successfully prepared and some of thoses system have been practical applicated, low glass forming ability ( GFA ) and lacking knowledge of rheological behavior at room temperature limit the application of the amorphous alloy.The researchs of amorphous alloy material of glass forming ability and its nanoindentation creep behavior are of great significance for better exploring the performance of amorphous alloy and improving its application prospect. The main works and results of this thesis are summarized as follows:1. Brief introduction about research history, performance and application prospect of amorphous alloy has been made, the formation mechanism of amorphous alloy and the indentation creep behavior are introduced. It is summarized that the parameters which is now commonly used to evaluate the glass formation ability of amorphous material are critical cooling rate, Rc, and the maximum diameter,Dmax ,based on the literatures. The critical cooling rate is comparatively accurate for evaluating glass formation ability of amorphous alloy materials, but the current measuring steps of R. are trival and requires precise and costly instrument. Using maximum diameter to measure the glass forming ability of amorphous alloy material is simpler, but deviation on measuring the largest diameter is larger influenced by the process. At present, the value of the critical cooling rate and maximum diameter which could be mainly judged by the criterion that contains glass transition temperature, crystallization temperature and the liquids temperature of the amorphous alloy material reflects the amorphous alloy material.2. A new criteria X has been got based on thermodynamics and kinetics and the way analyzing the different criterion △Tx, Trg ,γ,△Trg,α,β1,δ,γm, φ,ξ, β2, ω1, ω3, θ, ω2, γc, β’, ω4, Gp . It is concluded that the correlation of the new criteria χ is strongest based on comparation about relationship of different criteria with the critical cooling rate, which can better determine the value of the order and better reflect the amorphous materials.3. Through analyzing correlation of criterion with critical cooling rate and maximum diameter, it is concluded that various criterion in judging the accuracy of the critical cooling rate and maximum diameter exist differences. In order to get a better criterion to judge the maximum diameter size, a new criterion χ’ has been found based on the nucleation rate and thermal stability analysis. The statistical data analysis shows that the correlation between the new criterion χ’ and the largest diameter is strongest. Consequently the new criterion can better determine the size of the largest diameter and reflect the glass forming ability of amorphous alloy.4. The equation relating the creep displacement and time in various model was derived in the insurance carrier stage based on the fractional Maxwell, Kevin and Zener model, and then the nanoindentation creep behavior of amorphous materials under different loading rate has been analysised through these relationships. The fractional order, a and flow unit effect factor, p increases with increasing loading rate under the same maximum load and the amorphous materials shows more viscous.