Showing papers by "Xianting Zeng published in 2001"

Bond contraction and lone pair interaction at nitride surfaces

Abstract: It is shown that bond contraction and nonbonding lone-pair interaction dominate at nitride surfaces. The maximum elastic recovery of a nitride surface was found to be 100% under a relatively lower nanoindentation load (<1.0 mN) and the hardness of the surface was found to be 100% higher than the bulk value. It is interpreted that the spontaneous bond contraction, estimated at 12%–14%, strengthens the binding energy and hence the hardness and Young’s modulus at the surface. The lone-pair weak interaction claims the responsibility for (i) the high elastic recovery, (ii) the lower Raman frequencies of vibration, and (iii) the existence of critical loads for slide friction or lone-pair broken.

Multilayered (Ti, Al) ceramic coating for high-speed machining applications

Abstract: A multilayered (Ti, Al) ceramic hard coating was deposited on tunsten-carbide ball-nose end mills for high-speed machining using an unbalanced magnetron-sputtering system. The process parameter dependence of the coating properties was studied. X-ray diffractometry, x-ray photoelectron spectroscopy, nanoindentation, and scratch tests were used to characterize the structural, compositional, and mechanical properties of the coatings. High hardness, up to 40 GPa; good adhesion strength, up to 100 N in scratch critical load; and high-oxidation resistance were achieved, leading to excellent performance in high-speed milling on hardened tool steel at a speed of 260 m min−1. The results show that the tool life with this coating is improved by a factor of 4 or better under the testing conditions used compared to the uncoated tools. The surface finish of the machined steel achieved with this coating is also significantly better.