Papers by Author: Jun Gong

Abstract: Fatigue tests of nanometer-thick Cu films as deposited and annealed in vacuum were conducted under constant load ranges at room temperature. Fatigue strengths of the Cu films, which is defined as the critical load range being able to cause crack initiation within 106 cycles, are determined. The experimental results show that fatigue strength increases with decreasing film thickness. Fatigue cracking behaviors were characterized by electron microscope. It is also found that fatigue cracking resistance is dependent on film thickness and increases with decreasing film thickness. Size effects on fatigue properties of the nanometer-thick Cu films are discussed.

Abstract: A WC-Co coating with self-lubricating property was deposited by detonation gun (D-gun) process, using a WC-Co powder doped with a MoS2-Ni powder, under a proper spray condition. It is proved that the MoS2 composition was kept in the resulting coating by SEM, XRD and EPMA. Evaluation on sliding wear property indicates that the MoS2 composition plays an important role in lowering both coefficient of friction and wear rate for the resulting coating, which is confirmed by observations on wear track. It suggests that the deposition of WC-Co coating with self-lubricating property by D-gun spray is feasible by controlling lubricant powder and spray conditions, which can exhibit higher sliding wear resistance.

Abstract: Thermal barrier coatings (TBCs) with the ceramic coats of hollow spherical ZrO2-8%Y2O3 powder (HSP-YSZ) were obtained on Ni-base superalloy by detonation gun (D-gun) spraying. Thermal shock cyclic tests were performed by holding samples at 1100°C for 10 min and then water quenching to room temperature repeatedly. The D-gun sprayed TBCs didn’t fail up to 300 cycles and exhibited excellent resistance to thermal shock. Failure mechanism of D-gun sprayed TBCs subjected to thermal shock cycling was discussed.