Z. G. Liu

Mechanical milling of fullerene with carbide forming elements

Mechanical alloying of Ti, V, Cr, Mo and W with fullerene (C60(C70)) and graphite reveals that fullerene is more reactive than graphite. The formation heat of carbide is the driving force for reaction in the mechanical alloying process. Higher heat of formation results in the direct formation of carbide in Ti-C systems, and the formation of carbide in V-C systems during the subsequent heating of milled powder. In the systemsc with lower carbide heat of formation, a mixture of metal with carbon is obtained by ball milling. No carbide was obtained even after heating the milled powders up to 973 K. Small amount of fullerene remained when milled with Mo and W for 10 hours.

Relationship between hardness and tensile properties in various single structured steels

Abstract An attempt has been made to establish a relationship between hardness and tensile properties for various single structured steels: ferrite, pearlite, bainite, and martensite. It is found that the proportionality constant A Y of hardness to yield strength changes from 5.79 to 3.17 and is highest for the ferrite steel and lowest for the tempered martensitic steels. A less pronounced change was found in the proportionality constant A T of hardness to tensile strength (from 3.97 to 2.72). A dependence on microstructure of the proportionality constant at 8% strain A 0.08 was found as well. This difference in A was found to be attributable mostly to the effect of different work hardening behaviours owing to different microstructures. Regression analysis shows that hardness can be expressed as a function of accessible material parameters such as composition, grain size, and transformation temperatures for various single structured steels within a certain degree of accuracy.

Mechanically driven phase transition of fullerene

Abstract Structural evolution that takes place during mechanical milling of fullerene (C 60 (C 70 )) was investigated. Mechanical milling did not destroy the molecular structure of C 60 (C 70 ), but the fcc crystalline structure with long-range periodicity. Longer milling time results in the formation of C 60 (C 70 ) polymer, including C 60 dimer. Thermal analysis revealed a depolymerization enthalpy close to the theoretical calculation of the (2+2) cycloaddition bonding energy of polymerization. Mechanical milling may be one effective means to produce C 60 (C 70 ) polymer.

Deformation and dissolution of spheroidal cementite in eutectoid steel by heavy cold rolling

Abstract The microstructural evolution of a spheroidised Fe-0.85C wt- steel during heavy cold rolling and post-aging was studied, with the emphasis on cementite. A new morphology of cementite, wavy thin bands nearly parallel to the rolling plane, was found in the specimens subjected to rolling reductions >90. Slip on 001theta planes was observed in the deformed cementite particles. By X-ray diffraction, it was found that the initial spheroidal cementite particles dissolve partially in a solid solution of ferrite by deformation, in a manner similar to that of the lamellar cementite of pearlite. Greater strain age hardening was observed for the spheroidised steel than for a similarly treated pearlitic Fe-0.85C steel. The strain age hardening peak was observed at 573 K for the spheroidite structure, which is 150 K higher than was observed for the pearlite structure. The activation energy for age hardening was estimated to be 122 kJ mol1, which is attributed to carbon atom diffusion from cementite to dislocations in ferrite.