Study On Glass-forming Ability, Effects Of Alloying Addition And Properties Of Cu-Ti-Based Bulk Amorphous Alloy

In the research of this dissertation, Cu47Ti34Zr11Ni8 series bulk amorphous alloys wereprepared by arc melting and suction casting method, the glass forming ability of the alloy,the influence upon the glass forming ability and thermal stability of alloying elements, themechanical properties, and the tribological properties were studied by experiments andcorrelation methods: The main works of this paper are as follows:1. Cu47Ti34Zr11Ni8 bulk amorphous alloys were prepared by arc melting and suctioncasting method, the glass-forming ability and Gibbs free energy difference betweenthe crystalline and undercooled liquid phases were studied, and the effective depth ofpair potential was studied by thermal expansion method. The Fermi surface of theCu47Ti34Zr11Ni8 bulk amorphous alloys is in contact with the pseudo Brillouin zone,which is satisfied with Hume-Rothery rules (2k_f≈k_p). In the larger undercoolingrange, Thompson-Spaepen and Lad2 expressions give a good account of the Gibbsflee energy difference between the crystalline and undercooled liquid phases ofmetallic glass-forming alloys. The onset structural relaxation Tr temperature and theeffective depth of the pair potential u₀ of bulk amorphous alloys are in the directproportion, but the relation between the glass transition temperature T_g and theeffective depth of the pair potential u₀ depends on the nature of glass transition.2. (Cu47Ti34Zr11Ni8) (100-x) Mx (M=Al, Be, Si, Nb, Fe, Co; x=1,2,4) samples werefabricated, and the effects of minor alloying addition on the glass-forming ability andthermal stability were studied. (Cu47Ti34Zr11Ni8)99M(M=Al, Be, Si, Nb, Fe, Co)bulk amorphous alloys with cross section of 5mm×0.5mm could be fabricated bysuction casting methods. With the addition of Si, the supercooled liquid regionΔT_x,reduced glass transition temperature T_rg, parameterγand stability parameter K_H areimproved, which means the glass-forming ability of the alloy is increased. With theaddition of Al, Be, Co, Fe and Nb,ΔT_x, T_rg,γand K_H are declined, which means theglass-forming ability of alloys are descended. The glass-forming ability of the(Cu47Ti34Zr11Ni8)99M alloys and the formation enthalpy of amorphous phases arein the direct proportion, while the crystallization activation energy and the atom sizeparameterδare in the inverse proportion.3. The three point-bending and compression tests of Cu47Ti34Zr11Ni8 series bulkamorphous alloys were performed on the AGS-10KN tester, the fracture surfaces and microstructure were analyzed. The Cu47Ti34Zr11Ni8 bulk amorphous alloy exhibitshigh strength, the three point-bending flexural strength and compression strength is2350MPa and 1731MPa, respectively. The typical feature of the fracture surfaces is avein-like structure, and the mechanical properties of the alloy decline with amicron-size quenched-in crystallizes appear. Because of the addition of Si or Al,nanocrystalline glassy structure appears, and which causes the mechanical propertiesenhanced. The three point-bending flexural strength of the bulk glasses are increasedfrom 2350MPa to 3260MPa and 2970MPa, respectively. The compression strength ofthe bulk glasses are increased from 1731MPa to 1894MPa and 1862MPa, respectively.With the addition of Nb, a little nanocrystalline dispersions in a glass matrix, thecompression strength of the bulk glasses are declined from 1731MPa to 1608MPabecause the distribution of nanocrystals in these samples is spatially localized.4. The tribological properties of Cu-based and Zr-based bulk amorphous alloys weretested, and the wear mechanism was studied by flash temperature. Under theexperimental conditions, the wear resistances of the bulk amorphous alloys areimproved when the contactface changes from SUS304 to Si3N4, and the steady statefriction coefficients and the wear rate are increased with the load added. Otherwise,the Cu-based metallic glasses exhibits higher wear resistance than Zr-based under theconditions of dry sliding and lubrication of fresh plasma, distilled water, andphysiological distilled water. Wear rates of BMGs indicate significant difference thatthe Cu-based metallic glasses exhibits higher wear resistance than that of Zr-basedglasses. The surface tracks indicate the existence of abrasive, viscous flow and thematerial transfer occurred from BMG rod to the ceramic disc. Since tribologicalproperties are not intrinsic properties, the wear resistance of the bulk amorphousalloys depends on its hardness, heat transfer ability, glass transformation temperatureand crystallization temperature, and the difference of wear rates under differentlubrication conditions may be attributed to the abilities of lubricants transporting thefriction heat away and reducing the local temperature.