Microstructure And Corrosion Properties Of The Ti-base And Ni-base Multi-phase Alloys

In this work, Ti-, Ni-based Bulk Metallic Glass(BMG) alloys with crystalline phases were prepared by using copper mold casting technique. The microstructure of the as-cast Ti-base BMG with dendritic crystalline phase and its development during isothermal heat treatment at the different temperatures were investigated. In the meanwhile, the effects of the compositions on the glass forming ability and the microstructure of Ni-base BMG were discussed. On the basis of the results, the corrosion behavior of Ni-base BMG with crystalline phases were investigated in different corrosion solutions by using the weight-lose and the electrochemical methods. The crossion mechanisms of these alloys were analysed and discussed. The main results are as follows:1. As the Ti60Cu14Ni12Sn4Nb10 alloy was annealed at the temperature of 450℃,ω-Ti and Ti phase with fcc structure were formed in the alloy. As the temperature was up to 550℃,ω-Ti disappeared, and TiNi precipitated in the matrix. As the temperature was over 715℃, the TiNi phase transformed into Ti2Ni. The phase transformation ofβ-Ti→α-Ti occurred at 795℃. When the alloy was annealed at 900℃for 10min,β-Ti transformed intoα-Ti completely. Thus, the annealing temperature should be chosen over 550℃to avoid the formation ofωphase.2. The glass forming ability of Ni-based alloys with five different compositions were very different from each other. There are more volume fraction of amorphous in Ni55Nb30Sn5Ti5Zr5,Ni59.5Nb33.5Sn7,Ni55Nb30Sn5Zr10 and their glass forming ability were much higher than Ni50Cu30Zr15Sn5 and Ni60Zr20Cu15Sn5. As a result, Cu addition may decrease the glass forming ability of the Ni-base BMG.3. Several crystalline phases formed in-situ in the five alloys during solidification. The main precipitated phases were Cu10Zr7, Ni10Zr7, Ni3Nb, Ni10Zr7, NiSn etc..4. Pit corrosion occurred in Ni55Nb30Sn5Ti5Zr5,Ni59.5Nb33.5Sn7 and Ni55Nb30Sn5Zr10 alloys which contained more amorphous. As for Ni50Cu30Zr15Sn5 and Ni60Zr20Cu15Sn5, on the surface of the two alloys, a few of CuCl2 flocculent particles were formed.5. The compositions of the alloys are very important to the corrosion resistance. The corrosion resistance of the alloys containing Cu was much lower than that of the alloys without Cu. The corrosion resistance of the alloys was improved when the alloy...